EGU General Assembly 2023  

Fossils in the mountains: Understanding the relationship between biodiversity and geography during the Early Palaeozoic

The eminent Alpine geologist, Rudolf Trümpy once stated, ‘One bad fossil is worth a good working hypothesis’. Although characterized by poor preservation, fossils have for many decades provided age and geographic constraints on the evolution of the World’s mountain belts. Palaeontological data helped expose horizontal and lateral crustal movements and signalled the importance of continental drift as a planetary-scale process. In Europe and North America the bioregionality of many fossil groups has provided key data for the definition of continents, microcontinents and volcanic arcs and their movements during the Early Palaeozoic. Moreover, identification of species pumps and refugia in the island terranes of the Iapetus and related oceans, now exposed along the length of the Caledonian-Appalachian orogenic belt, has enhanced our knowledge of the Great Ordovician Biodiversification Event and the Late Ordovician Mass Extinction. Mechanisms for the diversification and extinction of taxa can be hypothesized and many terranes hold key evidence on the early evolution and phylogeny of marine animal groups. The movement of most crustal units towards lower latitudes and their carbonate environments during the later Ordovician is correlated with the highest species richness of the period terminated by the intense, short-lived Hirnantian ice age.

How to cite: Harper, D.: Fossils in the mountains: Understanding the relationship between biodiversity and geography during the Early Palaeozoic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4207, https://doi.org/10.5194/egusphere-egu23-4207, 2023.

Paleoclimate archives, such as marine and terrestrial sediment cores, provide a valuable record of past climate conditions and can serve as "sentinels" for predicting future climate change. By using methods of sedimentology, stratigraphy, and paleontology, it is possible to reconstruct the physical and biological conditions of the past and gain a deeper understanding of how ecosystem stability has responded to changes in the environment. One excellent example of this is the UNESCO world heritage Messel fossil pit in central Europe, which dates back to the Eocene epoch and provides a glimpse into the potential future climate that may be experienced in 2150. Examining the annually laminated Messel sediments and building upon more than 60 years of paleontological excavations allows for insights into the sensitivity of terrestrial and aquatic ecosystems to environmental change under high greenhouse gas concentrations across orbital to interannual time scales. This can provide new and important constraints on aquatic ecosystem stability and potential teleconnections to the surrounding terrestrial realm in an ever-warming world. Understanding these complex interactions between terrestrial and aquatic ecosystems can inform decision-making and policy development related to climate change mitigation and adaptation.

How to cite: Kaboth-Bahr, S.: Paleoclimate archives as sentinels of future climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11406, https://doi.org/10.5194/egusphere-egu23-11406, 2023.

Cangdong sag is an important oil-rich sag in Bohai Bay Basin, eastern China. Organic-rich fine-grained sedimentary rocks with a thickness of 400m are developed in the second member of Paleogene Kongdian Formation, which have good shale oil resource potential. However, there are few studies on diagenesis of fine-grained sedimentary rocks in Kong-2 member of Cangdong sag, especially the study on pore-increasing and pore-reducing mechanism based on diagenesis is insufficient, which restricts the fine evaluation of shale oil reservoir performance in different lithofacies and stratigraphic units.

Based on the qualitative analysis of core observation description, rock thin section analysis and scanning electron microscopy of Well G108-8 , Well GD12, and Well GX12X1 in Cangdong sag, combined with quantitative characterization techniques such as XRD whole rock analysis, XRD clay mineral analysis and energy spectrum analysis, it is clear that the diagenesis of fine-grained sedimentary rocks in the second member of Kong in Cangdong sag includes compaction, cementation, dissolution, metasomatism, clay mineral transformation and thermal evolution of organic matter. Because of the widespread development of cristobalite in Cangdong sag, a large number of cristobalite cements are filled in cracks or intergranular pores. The thermal evolution of organic matter is mainly characterized by internal hydrocarbon generation pores and marginal contraction joints. Under the scanning electron microscope, it is observed that the organic matter in the second member of Kong Formation in Cangdong sag is easy to combine with clay minerals to form 'organic matter-clay aggregate'. The conversion process of clay minerals can catalyze the hydrocarbon generation of organic matter, thus promoting the development of organic pores in the aggregate. Corrosion is common in the second member of Kong in Cangdong sag, mainly developed feldspar and carbonate rock corrosion. Under the influence of organic acids released from hydrocarbon generation of organic matter, corrosion pores formed by dissolution are more likely to be seen in unstable minerals in carbonate or clastic lamina adjacent to organic matter.

According to the data of porosity and permeability, pressure porosity and permeability, gas adsorption, high pressure mercury injection and nuclear magnetic resonance, the reservoir characteristics of Kong 2 member in Cangdong sag are analyzed. The results show that the porosity of the fine-grained sedimentary rock reservoir in Kong-2 member of Cangdong sag is between 0.24% and 9.35%, with an average of 2.95%. The permeability is between (0.01-25.3) × 10-3μm2, with an average of 0.613 × 10-3μm2, and the overall reservoir is ‘ultra-low porosity and ultra-low permeability’. Pores include inorganic pores, organic pores and micro cracks. The pore size is small, mainly micro-nano pores.

The influence of diagenesis on the reservoir of the second member of Kong Formation in Cangdong sag is complex, including the mechanism of increasing porosity and reducing porosity. The pore-increasing mechanism includes thermal evolution of organic matter, dissolution and clay mineral transformation;compaction and cementation are the main factors affecting the porosity and permeability of the reservoir, which belong to porosity reduction for the reservoir of Kong 2 member in Cangdong sag.

How to cite: Feng, G.: Diagenesis Types of Fine-grained Sedimentary Rocks in the Ek2 of Cangdong sag and Their Influence on Reservoirs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-256, https://doi.org/10.5194/egusphere-egu23-256, 2023.

Flow near the confluence of two channels is complex and need investigation. The ratio of momentum of flow in the channels and confluent angle are important parameters affecting the flow structures and development of the mixing layers downstream of the confluence. Numerical modelling constitutes an essential tool for studying these complex flow phenomena. The main objective of this study is to investigate flow structure for different momentum in the channels. To achieve this, a Computational Fluid Dynamics model of the parallel open channel confluence was simulated with the help of ANSYS FLUENT and validated with an experimental study. 3D velocities were measured in the confluence region using Acoustic Doppler Velocimetry (ADV). These velocities were compared with the velocities obtained numerically and found to be in good agreement. Transverse development of the turbulent mixing layers in the post confluence region was affected by transverse distribution of the streamwise velocity.

How to cite: Ansari, M. F. and Ahmad, Z.: Experimental and Numerical Study at Parallel Open Channels Confluence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-889, https://doi.org/10.5194/egusphere-egu23-889, 2023.

Area A is located in the east of Yangjiang Sag in Zhusan Depression, Pearl River Mouth Basin. The Neogene Hanjiang Formation in this area has deposited a large number of sand, silt and mud mixed clastic sediments, with different particle sizes and complex composition. Predecessors have done some research on lithology, sedimentation and reservoir of this Formation, but the understanding of genesis and distribution of high argillaceous sandstone is not clear. In this paper, the genesis and vertical distribution of high argillaceous sandstone in Hanjiang Formation are analyzed by core, logging and analytical test data. Combined with high resolution seismic data, the density and seismic elastic parameters inversion method are used to clarify the plane distribution characteristics. The results show that high argillaceous sandstone is mainly distributed in deltaic front underwater distributary channel, interdistributary bay and distal bar. Sediment deposition rate of deltaic front underwater distributary channel is fast, low energy hydrodynamic can not be fully scoured sediment screening, resulting in high mud content. The hydrodynamic conditions of deltaic front interdistributary bay and distal bar are weak, and fine-grained and argillaceous sediments are deposited in large quantities, so the argillaceous content of sandstone is high.

How to cite: Liu, X.: Sedimentary Genesis and Distribution of High Argillaceous Sandstone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-979, https://doi.org/10.5194/egusphere-egu23-979, 2023.

The Zhujiang Formation in A oilfield of Yangjiang Sag, Pearl River Mouth Basin has superior reservoir-cap assemblage and good oil accumulation conditions. However, due to the frequent drilling of high-calcareous and low-permeability sandstone, and the unclear understanding of the formation of high-calcareous and low-permeability sandstone and the distribution of sand bodies, the oil and gas exploration progress is restricted. In this paper, the formation and vertical distribution of high calcareous and low permeability sandstone are studied by using core, logging and analysis data combined with the sedimentary background in this area, and seismic inversion of reservoir is carried out by using seismic data combined with permeability, so as to realize the plane distribution prediction of high calcareous and low permeability sandstone. The results show that the Zhujiang Formation in the study area is mainly characterized by underwater river-bay microfacies, which provides abundant carbonate provenance conditions for high calcium content of sand bodies. And the sand bodies in the underwater distributary channel microfacies are closely interlaced with the calcare-rich mudstone at the top-bottom interface, moreover the migration of carbonate from mudstone to sandstone and related chemical reactions occur at the junction, which further increases the calcium content of sand bodies. Combined with the study of permeability inversion model, it is considered that the high-calcareous and low-permeability sandstones are mainly distributed in the underwater distributary channel near the provenance in the northern part of the study area.

How to cite: Zheng, W.: Genesis and Distribution Prediction of High Calcareous and Low Permeability Sandstone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-999, https://doi.org/10.5194/egusphere-egu23-999, 2023.

The Cambrian Series 2 is challenging for biostratigraphy and correlation. In current Europe (mostly West Gondwana), this Series sequences are hard to identify due to the scarcity of its fossil record. An exception is the Ossa-Morena Zone (OMZ), southwestern Iberia, where lower Cambrian fossils are fairly abundant. The OMZ belongs to the southern branch of the Variscan Orogen of the Iberian Peninsula, comprising rocks dating from the latest Proterozoic to the Carboniferous. Its Cambrian sequences are preserved in distinct ‘blocks’, showing a significant change of facies and thicknesses, most likely related to downthrow and tilting along an active growth fault during sedimentation.  Four regional stages were proposed for the Cambrian Series 2: Ovetian, Marianian, Bilbilian and Leonian (lower part). Among these, the Marianian Stage has suffered significant conceptual modifications since its original erection. At the moment, its correlation through the Iberian Peninsula is still a subject of debate.

The OMZ record of trilobite fossils and, therefore, their biostratigraphy, has been hindered due to the limited continuity of trilobite facies in many sections, the poor preservation of the specimens, and tectonic distortion. Based on work carried out in recent years, we present the updated trilobite distribution and contribution for the biostratigraphical subdivision of the Marianian Stage in the OMZ, to improve and refine intra- and inter-regional correlation. The base of the Marianian Stage is characterized by the FAD of Strenuella; being the lower Marianian substage characterized by the co-occurrence of Delgadella souzai, Mimacca? and Saukianda andalusiae. The boundary with the middle Marianian is defined by the FAD of Strenuaeva sampelayoi, and this substage is characterized by D. souzai, S. andalusiae, Alanisia guillermoi, Perrector perrectus, Eops eo, Gigantopygus cf. bondoni, Andalusiana cornuta, Triangulaspis fusca, Callavia choffati, Rinconia schneideri, Calodiscus ibericus, Atops calanus, Hicksia elvensis and Termierella sevillana. Finally, the base and top of the upper Marianian are marked, respectively, by the FAD and LAD of Serrodiscus bellimarginatus, being this substage characterized by the presence of T. fusca, Chelediscus garzoni, Protaldonaia morenica, and Pseudatops reticulatus. The new biostratigraphical data strengthens the correlation with Cambrian Series 2 sequences along the western Gondwana margin (e.g. Banian Stage from Morocco and the Charlottenhof Fm from Germany), western and eastern Avalonia (upper Callavia and lower Strenuella sabulosa Biozones), Baltica (lowermost Holmia kjerulfi to lowermost Ellipsostrenua spinosa Biozones) and Siberia (Botoman and lowermost Toyonian Stages). In addition, biostratigraphical correlation with the Dyeran Stage of Laurentia, Elliptocephala asaphoides Biozone from the Taconic Allochthon and Pararaia janeae Biozone from Australia have been improved.

How to cite: Collantes, L., Pereira, S., Liñán, E., Mayoral, E., and Gozalo, R.: The regional Marianian Stage (Cambrian Series 2) of the Ossa-Morena Zone, SW Iberia: trilobite biostratigraphy and international correlation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2891, https://doi.org/10.5194/egusphere-egu23-2891, 2023.

There is relatively little information on the taxonomy of foraminifera found in Saudi Arabia's Cenozoic formations compared with those from the Mesozoic formations. Four outcrops in the Al Lidam area, eastern province of Saudi Arabia have been studied to document the Miocene foraminiferal assemblages. Acetic acid was used to extract foraminifera from lithified carbonate rocks from 80 samples representing seven lithofacies. Results of disaggregation using acetic acid are promising. In total, 46 species of benthic foraminifera have been identified. The foraminifera are dominated by calcareous porcelaneous Miliolina (Coscinospira, Sigmoilinita, Peneroplis, Quinqueloculina, Triloculina), followed by hyaline genera (Ammonia, Cibicides, Discorbinella, Elphidium), a few agglutinated forms (Textularina), but planktonic foraminifera are absent. Borelis melo melo indicates that the studied formation is dated to Burdigalian to Langhian age. Based on the identified species, the studied formation is interpreted as having been deposited in an arid subtropical environment in hypersaline waters that were present on a restricted and very shallow carbonate platform (inner ramp). The foraminiferal faunas of the present-day Arabian Gulf show similarity with the Miocene faunas. Thus, the present-day Arabian Gulf provides a highly suitable modern analog for earlier Cenozoic conditions in the region.

How to cite: Chan, S., Kaminski, M., and Humphrey, J.: Micropaleontological study of the Miocene Dam Formation, Eastern Province of Saudi Arabia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4059, https://doi.org/10.5194/egusphere-egu23-4059, 2023.

The development, dissemination, and communication of research findings is a critical element of the journey to completing a graduate degree.

Traditionally, in-person presentations of research at conferences, meetings, and workshops – in the form of posters, oral presentations and, interactive displays (such as PICOS), provides early career scientists with an invaluable opportunity to promote their research, ‘road-test’ hypotheses and solicit feedback in a friendly collegial atmosphere. Meeting attendance exposes early career researchers to the latest research advances, affording an opportunity to network and build collaborations with other researchers. Presentations allow students to develop their proficiency in oral and written communication – critical skills for post graduate employment.

The above may seem obvious yet, for many of us, the significance, importance, and necessity of these ‘traditional’ modes of communication were, perhaps, vastly underappreciated until they were precipitously withdrawn with the global lockdown during the COVID-19 pandemic. For many, the loss of easy access to meetings led to the realization that countless researchers have, in fact, never had the luxury of this interaction – all be it for reasons of geographical, cultural, political, health, mobility or financial isolation from the global scientific community.

The necessity to maintain communications during the pandemic resulted in an explosion in the development of on-line meetings. Among the leaders in this field was Seds Online, an initiative developed in March 2020 aiming to aid, promote, maintain and enhance communication within the global sedimentology community. At inception, Seds Online offered a series of global daily meetings (Coffee Breaks) and weekly Webinars. As the initiative developed, further formats were tried, including Sedimentology Debates and Student Webinars.

Seds Online Student Webinars provide a venue for students, regardless of location, to present their sedimentology-focused research, to the global geoscience community. A theme is selected for each webinar, and submissions are invited from the global sedimentology student community. Applicants provide a brief description of the project purpose, methods, and results, and how these relate to the webinar theme. This approach requires students to synthesize their research, communicate it succinctly, and determine its applicability in a broader geoscience context. To ensure equability, applications are anonymised, before being reviewed and ranked by a committee.

Invited presenters are provided with advice on presentation design followed by post presentation feedback. The format is similar to a ‘normal’ in-person meeting, each presentation is followed by a few questions with an additional 15 minutes at the end of the meeting for open discussion on the topic in hand. The webinar is recorded and uploaded to SedsOnline.com for wider audience viewing. The continued availability of the recorded presentation allows the presentation to be viewed beyond the time constraints of the ‘live’ event, and also serves as an artifact for students to share on their personal webpage, or link to their CV, job applications or grant proposals.

The Seds Online Student Webinar presentation format is low-risk and high-reward for students, enabling presentation of research and building confidence – we hope this format serves as inspiration for student webinars in other realms of geoscience.

How to cite: Lokier, S. and Giles, S.: Seds Online Student Webinars – Creating impactful opportunities for students to share their geoscience research, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4121, https://doi.org/10.5194/egusphere-egu23-4121, 2023.

Fan delta is an important reservoir for hydrocarbon accumulation.The channel sand bodies of fan-delta front facies are narrow , and the lithologic assemblage changes quickly in space and is sensitive to water depth changes. It is a key and challenging task to accurately identify and characterize the channel with seismic data under the condition of few Wells. In this study, we selected the fan delta deposits of the Shahejie Formation in the Gangzhong area of the Bohai Bay Basin, China as an example to explore the method to accurately characterize the channel in the fan delta system by using seismic multi-attribute fusion technology.Six types of thirty-eight seismic attributes reflecting different geological information are extracted for river channel identification in the target area, and the most sensitive attributes to geological conditions are selected in each class of attributes. The physical meaning of various attributes is analyzed to identify the differences between different river structures. The multi-attribute clustering analysis based on FCM algorithm is used to reduce data dimension and reduce redundancy. Three seismic attributes that reflect the boundaries of geological bodies and lithological characteristics are selected for RGB fusion to highlight the overall characteristics of river distribution in this area, and enhance the characterization of the boundaries of channel sand body. It provides practical value for the next favorable target prediction of channel sand body.

How to cite: Zhou, D.: Application of Multi-attribute fusion Technology in Channel Sand Body Recognition and Boundary Characterization : A Case Study of the Gangzhong Oil Field in Bohai Bay Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4211, https://doi.org/10.5194/egusphere-egu23-4211, 2023.

The Badenian/Sarmatian boundary in the Central Paratethys has been traditionally identified by the faunal turnover recording an important environmental change possibly controlled by the change from marine to brackish conditions. The strata below the Badenian/Sarmatian boundary in the northern Carpathian Foredeep in Poland are included into the Pecten beds, and those above it into the Syndesmya beds. Foraminiferal study of the Babczyn 2 borehole which is one of the crucial sections in the northern Carpathian Foredeep, well-known for the depositional age of rhyolite tuff within the Pecten beds dated by Śliwiński et al. (2012) at 13.06 ±0.11 Ma, indicated that in fact the boundary occurs within the Syndesmya beds. This conclusion is based upon the rapid change from a stenohaline foraminiferal fauna to a euryhaline one.

Benthic foraminifera and palynofacies from the Upper Badenian  Neobulimina longa, Hanzawaia crassiseptata and lower Sarmatian Elphidium angulatum and Anomalinoides dividens zones have been studied (Peryt et al., 2021).  Benthic assemblages are moderately to highly diversified. The benthic foraminiferal successions in the studied interval suggest normal marine salinity, middle shelf depth basin, with relatively small oxygenation and productivity changes during the late Badenian. The rapid change in the taxonomic composition between the H. crassiseptata and E. angulatum zones reflected by extinction/disappearance of stenohaline taxa from the foraminiferal assemblages and replace them by euryhaline forms resulted from shallowing and decrease in salinity of the Polish Carpathian Foredeep Basin.

Palynofacies is dominated by terrestrial elements represented by palynodebris (black and dark brown phytoclasts and cuticles) and pollen grains. The proportion of marine elements (dinoflagellate cysts, prasinophytes, acritarchs, and rare zooclasts) rarely exceeds 10%. Taxonomic diversity of the dinoflagellate cyst assemblages is low. Majority of samples yielded assemblages dominated by 3–4 species with remaining taxa represented by rare or even single specimens. Qualitative and quantitative analysis of aquatic palynomorphs show that the borehole interval studied accumulated during variable, unstable sedimentary conditions. A short interval that occurs just above the last occurrence of stenohaline foraminifers is characterized by lack of dinoflagellate cysts and flowering of Leiosphaeridiaceae. Lack of dinoflagellate cysts points to conditions disastrous for dinoflagellate cysts. But the most likely reason was salinity increase above the level tolerable even for hypersaline forms (e.g., Polysphaeridium) but still favourable for Leiosphaeridia. These possibly hypersaline conditions were associated with stagnant, possibly stratified waters that led to anoxic conditions in the bottom waters manifested by amorphous organic matter. A cease of these conditions was caused by a possible sea level rise and a gradual return of a less saline water regime. The latter interpretation can be supported by high frequency of Polysphaeridium (a genus known from hypersaline environments).

The study was financed by the National Science Centre, Poland, grant No. UMO-2017/27/B/ST10/01129.

Peryt, D., Garecka, M., Peryt, T.M., 2021: Geological Quarterly, 65: 18, doi: 10.7306/gq.1584; Śliwiński, M., Bąbel, M., Nejbert, K., Olszewska-Nejbert, D., Gąsiewicz, A., Schreiber, B.C., Be-Nowitz, J.A., Layer P., 2012: Palaeogeography Palaeoclimatology Palaeoecology, 326–328: 12–29.

How to cite: Peryt, D., Gedl, P., Worobiec, E., Worobiec, G., and Peryt, T.: Palaeoenvironmental changes during the late Badenian - earliest Sarmatian (Middle Miocene) in Central Paratethys inferred from foraminiferal and palynological data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4531, https://doi.org/10.5194/egusphere-egu23-4531, 2023.

Active methane venting in the upper continental slope off western Svalbard results from methane hydrate dissociation caused by bottom water warming. Lithological heterogeneity in the glaciomarine sediments influences fluid migration, accumulation, and methane venting. However, seismic imaging with an airgun source could not resolve glaciomarine stratal architecture in the top 50 m below the seafloor (mbsf). We address this limitation by collecting several deep-towed high-frequency (220–1050 Hz) SYSIF seismic data (vertical and horizontal resolutions 1 and 3 m, respectively). Based on seismic interpretation, we improve the seismic stratigraphic framework and infer the depositional processes controlling the distribution of glaciomarine sediments in the interfan region between the Kongsfjorden and Isfjorden Trough Mouth Fans. We identify six seismic reflectors that separate five seismic units, 1 (youngest)–5 (oldest), characterize the seismic facies, and map the facies distribution in different units. We assign ages to the reflectors based on the results from the drill core GS10-164-09PC collected at 846 m water depth. Basal unit 5 consists of low amplitude, chaotic reflections indicating poorly sorted glacial debris materials above a basal erosional surface. The upper part of this unit is characterized by isolated, parallel, high to moderate-amplitude reflections embedded within low-amplitude chaotic reflections. The overlying unit 4 shows parallel, well-stratified, continuous reflections pinching out upslope. Unit 3 consists of chaotic facies that occur as isolated lenses. Unit 2 consists of moderate amplitude, parallel, well-stratified, continuous reflections. The topmost unit 1 shows low amplitude, parallel, continuous reflection.

The erosional base of unit 5 is a result of incision by strong hyperpycnal flow during the onset of early mid-Weichselian glaciation. The chaotic facies within unit 5 (74–54 ka) is attributed to glacial debris flow (GDF). Glacial advancement to the shelf break led to the formation of a till delta and debris flow as the delta front steepened and failed. On the uppermost slope, eastward dipping toe thrusts within the GDFs formed due to frontal obstruction caused by pre-existing debris mound. The well-stratified layers embedded within the GDFs suggest sediment deposition from turbidity currents that emerge as a result of the mixing of debris flow with water. The well-stratified reflections within uniformly thick unit 4 covering the GDFs are primarily a result of the deposition of hemipelagic materials by contour currents between 54 and 38 ka. The isolated chaotic lens in unit 3 represents debris flow lobes detached from the parent debris unit. Their deposition occurred during the last glacial maxima (38–24 ka) when the ice sheet re-advanced to the shelf break. The well-stratified reflections in unit 2 represent plumite deposition since the last deglaciation (24–15 ka). The low-amplitude reflections in unit 1 indicate finer winnowed sediments (15 ka–Present). The well-stratified contourites and turbidites in units 4 and 5 are suitable reservoirs that can store and transmit fluid more efficiently than the GDFs. The clustering of methane seeps above these shallowest reservoirs indicates flow focusing in those sediments after the methane hydrates have completely melted.

How to cite: Trivedi, A., Sarkar, S., Ker, S., and Minshull, T. A.: An improved Weichselian seismic stratigraphic framework of the Kongsfjorden-Isfjorden Interfan region off western Svalbard from high-frequency deep-towed seismic data and its implication on fluid migration and methane venting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4906, https://doi.org/10.5194/egusphere-egu23-4906, 2023.

Ephemeral fluvial systems dominated by seasonal discharge fluctuations and episodic events of rapid flood flows are typical for arid to semi-arid climatic conditions. Dryland fluvial systems have been described from many ancient and modern, predominantly tectonically-controlled sedimentary basins across the globe. The author shows the results of detailed sedimentological analysis and palaeoenvironmental interpretation of the Early Permian (Rotliegend) Krajanów Formation exposed within a continental, fault-bounded Intra-Sudetic Basin (ISB), NE Bohemian Massif. This basin started its development in the middle Viséan (Turnau et al., 2002), as an narrow, intramontane trough and underwent complex evolution from Early Carboniferous to Late Cretaceous. The maximum stratigraphic thickness of the basin infill reaches about 11 000 metres (Nemec et al., 1982). During the Early Permian the ISB constituted a semi-enclosed, south-western outlier of the Polish Rotliegend Basin (Southern Permian Basin of Central Europe). The Permian sedimentary-volanogenic succession of the ISB exhibits distinct, large-scale cyclic structure and comprises successive, fining-upwards continental megacyclothems (megasequences) up to 600 metres thick (Awdankiewicz et al., 2003). Such megacyclic structure is thought to have originated from tectonic activity and is attributed to relatively rapid, fault-controlled subsidence of the basin floor (Nemec et al., 1982; Wojewoda and Mastalerz, 1989).

The Krajanów Formation is composed of fluvial, playa-like and lacustrine deposits which form one of such fining-upwards cyclothems and attain up to 300 m in thickness. Sediments of the lowermost part of the Formation are represented by coarse-grained fluvial red-bed assemblage. Early investigations described these sediments as fluvial in origin. The upper part of the Formation distinguished as the Upper Anthracosia Shale, is characterized by the mudstone-dominated siliciclastics interbedded with fine-grained calcareous deposits which acummulated in a floodplain-to-ephemeral („terminal”) lacustrine setting.

High-resolution sedimentological logging and facies analysis indicate that the Early Permian fluvial system in the study area was dominated by ephemeral fluvial processes influenced strongly by semi-arid to arid climate. Rapid (catastrophic?) flood events led to episodic sedimentation of poorly channelized, laterally extensive sheet-like bodies of sandstone as well as vertically and laterally amalgamated fluvial channel infills, with abundant upper-flow regime structures. The overbank deposits are poorly preserved due to the frequent lateral shifting of the channels. Soft sediment deformational structures formed due to events of river bank collapse as well as debris-flow facies point to high-energy, waning flows. It is concluded that deposition occurred on a broad, terminal-type alluvial fans, probably in their proximal- to medial sub-environments. Petrographic composition and measured paleocurrent directions show that the sediment was sourced from the framing massifs – the Sowie Mts. Block to the east and a hypothetical Southern Massif to the south/south-east.

The research was funded by the Polish National Science Centre (Grant 2017/26/M/ST10/00646).

References

Awdankiewicz, M., Kurowski, L., Mastalerz, K., Raczyński, P., 2003: Geolines 16, 165–183;

Nemec, W., Porębski, S.J., Teisseyre, A.K., 1982: Veröff. Zentralinst. Erde, Potsdam, 267–278;

Turnau, E., Żelaźniewicz, A., Franke, W., 2002: Geologia Sudetica 34, 9–16;

Wojewoda, J., Mastalerz, K., 1989: Przegląd Geologiczny 432, 173–180.

How to cite: Kowalski, A.: Development of an ephemeral fluvial system in continental fault-bounded basin – an example from the Early Permian Krajanów Formation of the Intra-Sudetic Basin (NE Bohemian Massif), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5008, https://doi.org/10.5194/egusphere-egu23-5008, 2023.

The Intrasudetic Basin represents one of the larger late- to post-Variscan intramontane troughs of Central Europe. It is situated at the northern margin of the Bohemian Massif. The Basin represents a fault-bounded synclinorial structure and was formed in the late Visean as a depression framed by tectonically active margins. During the Permian, the basin was filled with dominantly fine-grained alluvial to lacustrine deposits, accompanied by volcanic rocks. Volcanic activity evolved with time and comprised emplacement of subvolcanic intrusions, effusion of lava flows as well as deposition of widespread ignimbrites (Awdankiewicz, 1999). These volcano-sedimentary units are known as the Słupiec Formation in the Polish part and the Broumov Formation in the Czech part of the Intrasudetic Basin, respectively. So far, based on generally imprecise biostratigraphic evidence and regional correlations, the Słupiec Formation sedimentary rocks together with the intercalated volcanic rocks were (usually) assigned to the Sakmarian. However, preliminary results of U-Pb SHRIMP zircon dating of the Góry Suche Rhyolitic Tuffs and the Łomnica Rhyolites – a widespread ignimbrite sheet and associated rhyolitic laccoliths intercalated in the Słupiec/Broumov Formation - suggest that these volcanic rocks can be older than supposed by 5-10 My. Such age estimate would assign these ignimbrites and rhyolites to the Asselian, not Sakmarian.

In this contribution the biostratigraphic evidence on the position of the Słupiec/Broumov Formation is re-assessed. The fluvio-lacustrine sedimentary members of these formations accumulated probably in semi-arid palaeoclimatic conditions with seasonally-controlled watertable.Numerous footprints of reptiles and amphibians, aquatic vertebrates: chondrichthyans, actinopterygians and amphibians, also palaeobotanical remains were preserved (e. g.  Jerzykiewicz, 1987; Zajíc, 2000; Stamberg & Zajíc, 2008; Voigt et al., 2012; Opluštil et al., 2016). Unfortunately, they appear only fairly suitable for detailed biostratigraphy as their successions may be environmentally-controlled, and most of them indicate a latest Carboniferous to early Permian age. At this level of knowledge, they are not suitable for detailed biostratigraphy, and thus comprehensive and comparative studies of the Late Carboniferous and Early Permian Central European volcanic-sedimentary basins are necessary to better constrain the stratigraphic position of the Słupiec/Broumov Formation of the Intrasudetic Basin.

This research is funded by the Polish National Science Centre (Grant 017/26/M/ST10/00646).

Awdankiewicz, M. (1999): Geologia Sudetica, 32 (1): 13-47; Jerzykiewicz, J. (1987): Palynology 11: 117-131; Opluštil, S., Schmitz, M., Kachlík, V. & Štamberg, S. (2016): Bulletin of Geosciences, 91: 399–432; Štamberg, S. & Zajíc, J. (2008): Carboniferous and Permian faunas and their occurrence in the limnic basins of the Czech Republic. Museum of Eastern Bohemia; Voigt, S., Niedźwiedzki, G., Raczyński, P., Mastalerz, K. & Ptaszyński, P. (2012): Palaeoclimatology, Palaeoecology, 313-314: 173-180; Zajíc, J. (2000): Courier-Forschungsinstitut Senckenberg, 223: 563-575.

How to cite: Ploch, I., Awdankiewicz, M., Pawlak, W., Peryt, T., Raczyński, P., Voigt, S., and Pańczyk, M.: Problematic age and stratigraphic position of the volcano-sedimentary Słupiec/Broumov formation in the Permian of the Intrasudetic Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5168, https://doi.org/10.5194/egusphere-egu23-5168, 2023.

The geology of the Intrasudetic Basin (Poland and Czech Republic) in the past was studied separately in both countries. Our project combined data from both parts of the basin to study the development of the limnic basin during the seasonally extreme climate in the Early Permian. The Lower Rotliegend Słupiec Formation (Broumov Formation in the Czech part) red bed deposits appear the most promising for palaeoenvironmental and palaeoclimatic studies. Fine-grained weathering products  (black shales), tuff admixtures and autochthonous components (limestones) in lakes contain many remains of plants, and traces of activity of invertebrates and vertebrates including extraordinarily numerous traces fossils of tetrapods (reptiles and amphibians) (e.g., Voigt et al. 2012) and fish remains (e.g., Stamberg & Zajíc, 2008). The Słupiec Formation is interpreted as a successively finning-upwards megacyclothem consisting, from base to top, of alluvial fan, fluvial and lacustrine deposits (Wojewoda and Mastalerz, 1989; Kurowski, 2004). However, the cyclicity is also clearly marked by successive transitions from lacustrine sediments with preserved fish remains to terrestrial sediments with numerous tracks of terrestrial reptiles and amphibians. This seasonal climate with dominant monsoonal rainy summer and winter seasons with low precipitation is clearly recorded in deposits of alluvial-fluvial plains and lakes. Extreme weather conditions, such as possible night frosts, were also recorded in the sediments, although the basin was located relatively close to the equator.

This research was funded by the Polish National Science Centre (Grant 017/26/M/ST10/00646).

Kurowski, L. (2004); Geologia Sudetica, 36: 21–38; Štamberg, S. & Zajíc, J. (2008): Carboniferous and Permian faunas and their occurrence in the limnic basins of the Czech Republic. Museum of Eastern Bohemia; Voigt, S., Niedźwiedzki, G., Raczyński, P., Mastalerz, K. & Ptaszyński, P. (2012): Palaeogeography, Palaeoclimatology, Palaeoecology, 313-314: 173-180; Wojewoda, J. & Mastalerz, K. (1989): Przegląd Geologiczny, 37: 173–180.

How to cite: Peryt, T., Ploch, I., Raczyński, P., Voigt, S., Kiersnowski, H., and Pawlak, W.: Lower Permian sediments of the Intrasudetic Basin: a record of cyclic, climatically-controlled transitions from lacustrine to terrestrial conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5495, https://doi.org/10.5194/egusphere-egu23-5495, 2023.

The Onagraceae or evening-primrose family has a fossil record composed mainly of dispersed pollen that has been discovered in Late Cretaceous to Holocene sediments around the globe. The pollen record suggests the family reached a cosmopolitan distribution during the Eocene. Currently, there is no reliable Onagraceae leaf record, and the meagre mesofossil record is composed of only a few fruits/seeds of Circaea and Ludwigia from the Oligocene to Pliocene of Eurasia. There is also a unique fossil Fuchsia flower that was described from the early Miocene of New Zealand, but other than that, there are no fossil Onagraceae flowers known to date. In addition, Onagraceae pollen has never been found adhering to fossil insects, and as such, there is no direct evidence of which insects visited Onagraceae flowers prior to modern times. Here we present an exceptional finding, an Onagraceae flower bud of Eocene age, from Eckfeld in Germany. Due to the flower’s bud stage the stamens were still packed with pollen. Nevertheless, the in situ pollen enabled us to assign the flower to the genus Ludwigia, based on a combination of unique morphological and ultrastructural traits observed with combined LM, SEM, and TEM, making it one of the earliest records of this genus. More importantly, we also discovered the same Ludwigia-type pollen adhering to the exterior of two different fossil beetles, a Buprestidae and Scarabaeidae, from the same locality. These provide the first-ever direct evidence for paleo-flower-insect visitation in Ludwigia and Onagraceae. Interestingly, we did not discover any Ludwigia-type pollen on the several Hymenoptera fossils investigated during this study, but Hymenoptera are the main flower visitors and pollinators of Ludwigia at present. These findings might suggest that beetles were the main flower visitors and potential pollinators of European Ludwigia during the Eocene and that there has been a shift in primary pollinators through the geological record.

How to cite: Geier, C., Bouchal, J. M., Ulrich, S., Wappler, T., and Grímsson, F.: Fossil Onagraceae flower and insects with in situ or adhered pollen from the Eocene of Eckfeld, Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6116, https://doi.org/10.5194/egusphere-egu23-6116, 2023.

The early to middle Eocene maar lake of Messel is a world-renowned fossil locality. Its oil shale deposits are well-known for their exceptional preservation of vertebrates (e.g., crocodiles, early horses) and invertebrates, especially insects. The makro- and microfossil remains of plants also contributed to providing a more holistic snapshot of this Eocene ecosystem. So far, the palynoflora has mostly been investigated using only conventional LM, and the classic taxonomic qualitative/illustrative work on the palynoflora dates back to the late 1980ies. Here we report on the first results from an ongoing study using combined LM and SEM, and in some cases even TEM, to re-investigate the Messel palynoflora qualitatively. The main goals of our study are to conclude (I) if some of the spores/pollen can be systematically placed with more certainty, (II) if additional spore/pollen types can be discovered, (III) to compare our combined method of investigation with the classic LM-based counting method, and finally (IV) to conclude about the composition and species richness of the palynoflora and how it correlates with the macro- and mesofloras. To accomplish this, we first processed a single sedimentary rock sample without fine-mesh sieving and then extracted and investigated every pollen type encountered using the single-grain method. So far, this sample has produced 30 spore types, 5 gymnosperm pollen types, and about 185 different angiosperm pollen types. The previous LM-based qualitative work identified 173 palynomorphs in an accumulative account from numerous rock samples up-trough the oil shale section. Our study, on a single sample from the lowest part of the oil shale revealed every single pollen type (except for Milfordia (Restionaceae) and Pityosporites microalatus (Cathaya, Pinaceae)) discovered in the accumulative approach using the classic LM counting method. Also, in addition to the c. 140 angiosperm pollen types previously recorded, we can now add at least 45 new pollen types for this locality. Our study shows that when taxonomic resolution and diversity are key, a combined LM and SEM investigation produces higher diversity than relying only on the conventional LM counting method when single samples are compared. In addition, a well-preserved single sample extensively studied using the combined approach is likely to provide the same or even higher number of taxa when compared to conventional LM counting methods analyzing an entire stratigraphic section. The qualitative combined approach will provide a more reliable presence/absence of taxa in the accumulation site hinterland. For quantitative analysis and subtle changes in the surrounding environments conventional counting methods are more appropriate because of the universal availability of light microscopes and difficulties with SEM-counting.

How to cite: Bouchal, J. M., Geier, C., Ulrich, S., Wilde, V., Lenz, O. K., Zetter, R., and Grímsson, F.: Revisiting the Messel palynoflora using a combined LM and SEM approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6499, https://doi.org/10.5194/egusphere-egu23-6499, 2023.

The early Miocene Mush flora has the potential to provide exceptional insight into the paleoecology and floral biogeography of East Africa, which is otherwise deprived of fossil plant assemblages from that time. However, at present only three genera within two families, Englerodendron (Fabaceae: Detarioideae), Newtonia (Fabaceae: Mimoseae), and Tacca (Dioscoreaceae), have been described from the plant macrofossil record. The remaining c. 50 leaf morphotypes have been classified on the basis of their morphological features and require additional cuticle analyses and comparative study. Previous work on the palynoflora was based on light microscopy (LM) only and comprised 32 palynomorphs, representing 24 families – ferns (single family) and angiosperms. To assist in the identification of the macrofossils and to establish a more complete picture of the paleovegetation, we are investigating pollen and spores from three (out of six) of the same stratigraphic levels from which leaf macrofossil censuses have been conducted. The primary results from this combined LM and SEM study follows. The palynoflora is composed entirely of fern spores and angiosperm pollen with a notable absence of gymnosperm pollen. So far we have discovered 15 different types of fern spores, and an amazing number of different angiosperm pollen types. Interestingly, monocots are not diverse, and so far we have only identified two types, pollen of Sclerosperma (Arecaceae) and that of Pontederiaceae. The former a typical swamp element in tropical Central West Africa and the latter aquatic plants with a pan-(sub)tropical distribution. The dicot component is the most diverse with 85 different pollen types discovered so far. The highest diversity occurs in the Fabaceae (8 spp.) and the Sapotaceae (7 spp.). Other families, represented by a number of taxa, include Apocynaceae, Araliaceae, Euphorbiaceae, Malvaceae sensu lato, Moraceae, and Vitaceae. This rich angiosperm palynoflora reflects a diverse and complex forest vegetation surrounding the ancient lake. The forest was composed of various trees, shrubs, and woody climbers, thriving under a hot and humid climate. The high terrestrial diversity together with striking wetland and aquatic components hint at vegetation under tropical rainforest-like conditions. Future work will complete the SEM study from the censused levels and provide a reliable illustrated taxonomic list that will be used for pollen/spores counts within the Mush section. This will provide a final quantitative analysis based on the qualitative SEM work now in progress.

How to cite: Hoffmann, J., Jacobs, B. F., Currano, E. D., Pan, A. D., and Grímsson, F.: High taxonomic resolution SEM study of pollen and spores from the 21.73 Ma Mush flora, Ethiopia, Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6860, https://doi.org/10.5194/egusphere-egu23-6860, 2023.

The surface of some planet’s present abundant periodic topographic forms at different scales (mm- km) and in different environments. They are called bedforms and develop at the interface between a moving fluid and a deformable and/or erodible material. Sand dunes are major bedforms in aeolian systems and play an important role in understanding how aeolian environments evolve. Generally grouped in dune fields, their morphological characteristics (e.g. shape, size, patterns of spatial organization) play a critical role understanding how aeolian environments evolve and interact with global changes. Detailed maps of these morphologies are produced by GIS manual digitizing from high-resolution satellite imagery and digital terrain models but this approach remains time-consuming. One way to override these locks is to use Artificial Intelligence (AI) to increase the computational speed, accuracy and reproducibility of mapping.

We here present a GIS automated mapping protocol of aeolian bedforms contours and crestlines based on AI. First, we extract the Residual Relief in order to delete the regional topographic trend and map the different dune generations. Secondly, an unsupervised pixel-based classificator (Deep Learning, U-Net CNN) trained with Residual Relief samples of different dune forms is used to detect and map dunes independently of the bedrock. Thirdly, the dune crests are skeletonized from the identification of high inflection point of the dunes from a Volumetric Obscurance approach. The protocol is repeated for each dune order of magnitude to extract the different superimposed generations of dunes and their relationships.

To illustrate its performance, the protocol was applied on a part of the Rub’Al Khali (220,000 km²) and Namib deserts (115,000 km²) to map the various dune forms and a first morphometric analysis is realized at the scale of the two sand seas. We produced a detailed map of the aeolian morphologies for each desert at two orders of magnitude (kilometer-scale and hectometer-scale dunes). For the Rub’Al Khali desert, more than 78,000 dunes (58,000 km²) and crestlines were mapped in 6 hours of processing and more than 17,000 dunes (12,000 km²) and crestlines for the Namib desert in the same processing time. The first morphometric parameters calculated from the previous results show a spatial variability of the length, width, height and crests orientation for Rub’Al Khali and Namib dunes. Thus, the protocol contributes to provide a digital atlas of the different dune generations (kilometer-scale and hectometer-scale dunes). All of these results allow to visualize the morphological dunes diversity and contribute to understand the relationships between forms and processes at a dune field scale.

How to cite: Daynac, J., Bessin, P., Pochat, S., and Mourgues, R.: Automatically dunes mapping and morphometric analysis using Artificial Intelligence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7223, https://doi.org/10.5194/egusphere-egu23-7223, 2023.

Pyroclastic density currents (PDCs) are density-driven flows of gas, ash and rock generated during explosive volcanic eruptions, or by the collapse of volcanic lava domes. They can reach temperatures of >500 °C and are highly mobile, with the ability to travel at speeds of >200 m/s and to scale obstacles hundreds of metres high. PDCs are a devastating volcanic hazard and have killed >90 000 people since 1600 AD¹; understanding their behaviour is an important aspect of volcanic disaster risk reduction. Because of their extreme nature, PDCs are difficult to observe and quantify in real time. Volcanologists therefore use field studies and modelling techniques to investigate their dynamics.

As PDCs travel they progressively deposit ignimbrite, a poorly sorted volcanic rock typically rich in pumice and ash. Ignimbrites commonly display a variety of bedforms and stratigraphic architecture; such architecture can be interpreted to unpick the behaviour of the original PDC, and of the evolution of the eruption that created it. However, there is considerable uncertainty involved in ignimbrite bedform interpretation, due to the potential for complexity (such as cryptic bypass, erosion, and hybrid processes) and also due to fundamental gaps in our knowledge of the physical properties of PDCs.

Our work uses analogue modelling of gas-fluidised, dense, granular currents in a laboratory flume together with examples from the field to explore what the dynamics of experimental PDCs (and their resultant bedforms) can tell us about our interpretations of real-world volcanic stratigraphy. The examples presented examine a range of bedforms and processes, including the impact of fluidisation and grainsize on PDC mobility and bedform morphology, the influence of moisture on cohesivity and bedform preservation, and the implications of grading in volcanic stratigraphy. The significant challenges in quantifying the sedimentation of ignimbrites are discussed. This work seeks to improve field interpretations of volcanic bedforms and contribute to the development of volcano risk models.

1: Auker et al. (2013) J Appl. Volcanol. https://doi.org/10.1186/2191-5040-2-2

How to cite: Dowey, N., Rowley, P., Williams, R., Walding, N., Smith, G., Johnson, M., and Johnston, T.: From flume to field: using analogue modelling to delve into uncertainty in our interpretations of volcanic bedforms and what they tell us about deadly hazards, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9849, https://doi.org/10.5194/egusphere-egu23-9849, 2023.

Ripple marks formed in different sub-environments of a tidal flat are considered helpful in distinguishing such sub-environments from one another owing to the predominance of specific agencies that generate and stabilize these ripples. For example, ripple stabilized in tidal channels are dominated by tidal currents and those in estuarine settings are both wave and current dominated. In order to evaluate the possibility of using ripple morphology in distinguishing between such sub-environments, data on ripple index (RI) from an estuary and tidal channels were analyzed. These data were collected from the east coast of India that provides examples of open-coast tidal flats at Chandipur and 50 km north-east at Digha. It was found that they have overlapping morphological patterns as delineated from RI vs. the percentage fraction for each case of estuarine and tidal channels. So, while RI can broadly define environments, e.g., aeolian and water borne ripples, when it comes to separating wave from current ripples, a fair overlap is seen in tidal flat regions. On the other hand, grain-size study alone is insufficient for the purpose of delineating differences between such sub-environments. This is because it is seen in our analyses that while most estuarine sediments are finer than 3 on the Φ-scale and tidal channel sediments are coarser, much better sorted as well as mostly positively skewed, these values overlap such that a clear distinction cannot be achieved. Therefore, in order to distinguish between such sub-environments, we took into account both grain-size parameters associated with ripple marks and the corresponding RI values. A relative “distance” was calculated between pairs of samples based on RI, mean, sorting, skewness and kurtosis. In other words, this “distance” is a way to determine how similar two samples are in terms of their respective RI and grain-size parameters. A dissimilarity matrix was constructed which, in turn, was translated into a configuration of points in the Euclidean Space via Multidimensional Scaling (MDS). Four different “types” of measure of this “distance” were considered: Euclidean, Standard Euclidean, City Block and Minkowski (P=3). It was observed that the MDS plot based on City Block distance generated two distinct clusters of points for samples collected from estuary and tidal channels. A way forward is to employ Random Forest Analysis and test whether RI in conjunction with grain-size parameters may be used for classifying modern sediments or even rock samples representing paleo-environments as belonging to either estuarine or tidal channel setting.

How to cite: Roy, A., Mukerji, T., and Chakrabarti, A.: Identifying Sub-environments in a Tidal Flat: An MDS Approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11049, https://doi.org/10.5194/egusphere-egu23-11049, 2023.

In the context of warming climate and rising sea level, records from the early-to-mid Holocene provide important analogues to investigate how the environment responds to such changes. The Sunda shelf provides favourable conditions to reconstruct past environmental change as the presence of numerous large paleo-valley systems and high sedimentation rates allow transgressive deposits from the early-mid Holocene sea-level rise to accumulate continuously in topographic depressions.  To this end, we analysed the sedimentological, geochemical and micropaleontological characteristics of a sediment core (GRBH03) to investigate early-to-mid Holocene environmental changes in southern Singapore. We constrained the chronology with ten radiocarbon dates that were placed in Bchron age-depth model. Using a multi-proxy approach (e.g., grain size distribution, loss on ignition and XRF core-scanning), supported by benthic foraminifera, three sedimentary units were identified in GRBH03. Sedimentary unit I was found at the base of the core. This unit was characterised by a dark grey sandy silt unit deposited from about 9.0 to 8.9 cal ka BP. Few or no foraminifera were found in this unit, likely due to degradation of organic material. Sedimentary unit II was a blue-grey marine mud that was deposited between 8.8 and 5.8 cal ka BP. Within the marine mud unit, foraminiferal assemblages show a transition to shallow marine environment from about 8.8 to 6.4 cal ka BP as open marine species (e.g., Murrayinella murrayi and Bulimina sp. cf. B. marginata) become more abundant up-core. Subsequently, brackish species such as Muyrrayinella globosa and Ammonia veneta started to dominate mud unit assemblages, reflecting a transition from shallow marine to brackish environments, likely associated with decelerating sea level rise. The marine unit is then overlain by the sedimentary unit III, which is a shelly-silt unit deposited after 5.9 cal ka BP. This unit was mostly barren of foraminifera, which may be attributed to a high-energy marginal marine environment where conditions were unfavourable for foraminiferal preservation. Our study show that changes in sedimentary units and foraminiferal assemblages present in GRBH03 are linked to varying rate of relative sea-level rise during the early-to-mid Holocene. 

How to cite: Yan, Y. T., Switzer, A. D., Fontainer, C., Culver, S. J., Chua, S., Morgan, K., Dixit, Y., and Horton, B. P.: A sedimentary and foraminiferal record of early to mid-Holocene environmental change from Singapore, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11157, https://doi.org/10.5194/egusphere-egu23-11157, 2023.

The Miocene sequence in the Roer Valley Rift System consists of alternating shallow marine, coastal and fluvio-deltaic deposits. In this study seismostratigraphy and biostratigraphy are used to determine major unconformities and sediment dispersal patterns. This research is important for future studies related to the geothermal energy potential, and for the improvement of cross-border correlations with the German and Belgian stratigraphic framework. Results show that a depocenter developed in the south-eastern part of the Roer Valley Graben above the Early Miocene Unconformity (EMU) during the Early- and Middle Miocene. Clinoforms are present in a limited area here, but show sediment dispersal from the south-east towards the north-west during periods of progradation. From the late Middle Miocene onwards, larger displacement rates occurred along the major bounding fault zones, i.e. the Peel Boundary Fault Zone, the Feldbiss Fault Zone and the Veldhoven Fault. As a result, the depocenter narrowed and shifted to the central part of the Roer Valley Graben, where accumulation rates increased and larger-scale clinoforms start prograding both towards the west-north-west. This phase coincides with the development of a regional hiatus on the structural highs and forced regression in the south-eastern Roer Valley Graben, caused by a major sea-level fall related to the Middle Miocene Climatic Transition. The effects of tectonics, eustacy and climate resulted in the formation of the Mid-Miocene Unconformity (MMU), which represents a series of events related both to tectonics and sea-level fluctuations, and is therefore expressed differently throughout the Roer Valley Rift System. Sedimentation continued through this period in the deeper parts of the Roer Valley Graben and on the Venlo Block, while an erosional hiatus is evident on the Campine Block and Peel Block. During the latest Miocene, the depocenter migrated to the south-western rim of the Roer Valley Graben, where the youngest Miocene sediments are deposited during a latest Tortonian-Messinian sea level fall that led to the formation of the Late Miocene Unconformity (LMU).

How to cite: Siebels, A., Ten Veen, J., Munsterman, D., Deckers, J., Kasse, C., and Van Balen, R.: Miocene Depocenters and  Sediment Supply in the Roer Valley Rift System: Impacts of Tectonics, Eustacy and Climate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13111, https://doi.org/10.5194/egusphere-egu23-13111, 2023.

Palynology is widely used in both academic and industrial research for correlation and interpretation of subsurface geology on both local and regional scales. While most data gathering tools for the subsurface have undergone major technological developments during the last decades, palynological research has, apart from the use of more advanced microscopes, remained virtually unchanged and can be quite time consuming when large data sets are required. With increasing demand for faster, more high resolution and more detailed palynological analyses from the continuously developing technological industry as well as the academic science community, palynology is at risk of being left behind.

The answer could lie in adopting strategies of digitalisation and Artificial Intelligence (AI) originally developed for medical research. The technology of scanning microscope slides into a digital high-resolution image has already been developed, and AI software specifically developed for palynology can be utilised to examine the digital images and detect, identify and quantify the fossil content.

In this project we have designed and developed an AI software for clustering and classification of microfossils based on deep-learning based algorithms for detection of palynomorphs and algorithms based on autoencoders for extracting features predictive of different fossil types. The AI is trained to recognize and identify fossils from different angles, preservation levels and fragmentation stages, as well as partially obscured or folded specimens. The AI can then analyse specimens for morphological parameters such as texture, shape and/or RGB/HSV values and use these parameters to categorize the specimen into clusters. The clustering has many applications, e.g., identifying morphological variations within taxa and recognizing variations in colour and preservation related to reworking or caving during the drilling process. The project also explores the advantages and disadvantages of working with digitally scanned palynological slides and the use of AI software recognition. The project will establish if the digital scans of the palynological samples have the resolution needed to be used for quantitative analyses and develop a preparation process to reliably produce the best digital samples possible.

How to cite: Stefanowicz, S., Ask, M., Julian, C., and Lindström, S.: Detection, identification and clustering of palynomorphs using AI and machine learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14198, https://doi.org/10.5194/egusphere-egu23-14198, 2023.

Some fifteen years ago, the pioneering Arctic IODP Expedition 302 (ACEX) drilled, and partly recovered Cenozoic sedimentary successions at the Lomonosov Ridge (LR) close to the North Pole. Of the few intervals recovered, one was regarded to likely encompass the Paleogene-Neogene (P/N) transition. On board and follow up marine palynological (mainly dinoflagellate cyst) studies indicate that within this P/N section, a hiatus lasting ~ 25 Myr likely separates the top of the recovered Paleogene (dated ~44 Ma, mid Eocene) from the locally recovered base of the Neogene (likely dated ~18 Ma, mid Early Miocene).

The hiatus is represented by the boundary between local lithological subunits 1/6 and 1/5. Unit 1/5 is informally often referred to as the “Zebra unit”, owing to its characteristic (cross bedded) black/white colored alternations of silty clays. Palynological and elemental and organic geochemical studies of subunits 1/6 and 1/5 supported the inference of a major hiatus, as the proxies show a sharp change at the subunit boundary, although the reconstructed paleoenvironments of both subunits indicate marginal marine, restricted conditions. This aspect on its own already represents a challenge for geophysical models, which placed the LR at deeper waters at the P/N boundary. A key finding in the “Zebra unit” is a massive occurrence of representatives of a – back then - unknown dinoflagellate cyst genus, later formally described as Arcticacysta. Because of its morphology, akin to typical Neogene dinocyst taxa, it was postulated that the Zebra interval was early Neogene in age, confirming the existence of a major hiatus. However, successive Rhenium‐Osmium (Re‐Os) isochron ages and complementary Os‐isotope measurements from subunits 1/6 and 1/5 led to postulate that the P/N transition was in essence complete, albeit extremely condensed. This data hence challenged the presence of a major hiatus and depicted a very different geological evolution of the LR.

Here we introduce new findings from the lower to mid-Miocene sediments retrieved from the Pennell Basin during IODP Expedition 374 (Ross Sea, Antarctica) in 2018. These now constitute the second known record containing specimens of Arcticacysta. Importantly, these findings now confirm the initial age assignment of the Arctic “Zebra Unit” to the early Miocene and provide decisive evidence for a large hiatus characterizing the P/N transition on the central Lomonosov Ridge. An important corollary is that the central Lomonosov Ridge was likely subaerial or ultra-shallow marine by the end of Oligocene, leading to a totally new perspective of its Cenozoic history.

How to cite: Brinkhuis, H., Sangiorgi, F., Wubben, E., and O'Regan, M.: IODP 302: Dating 'Zebra'; was the Lomonosov Ridge a central Arctic Ocean Island in the Oligocene?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1375, https://doi.org/10.5194/egusphere-egu23-1375, 2023.

The Collisional Orogeny in the Scandinavian Caledonides (COSC) multi-disciplinary scientific drilling project characterises the structure and orogenic processes involved in a major collisional mountain belt. Located in western central Sweden, the project drilled its second fully cored borehole, COSC-2, during spring and summer 2020. It extends the COSC composite geological section, which above is composed of outcrops at Åreskutan mountain and the COSC-1 scientific borehole (drilled 2014), through the nappes of the Caledonian Lower Allochthon, the main décollement and the upper kilometre of basement rocks. In summary, the retrieved geological section differs partially from the expected geological section with respect to the depth to the main décollement and the expected rock types. COSC-2 targets include the characterisation of orogen-scale detachments, the impact of orogenesis on the basement below the detachment, and the Early to Lower Ordovician(?) palaeoenvironment on the outer margin of palaeocontinent Baltica. This is complemented by research on heat flow, groundwater flow, gas compositions and characterisation of the microbial community in the present hard rock environment of the relict mountain belt.

COSC-2 successfully, and within budget, recovered a continuous drill core to 2276 m depth. On-site scientific investigations on the drill core by experts were impeded by travel restrictions due to the Covid-19 pandemic. Thus, the core was first completely described in late 2021 at the BGR Core Repository for Scientific Drilling (Berlin Spandau, Germany). After further delay, the sampling party was held in mid-2022.

The entire operations, technical and scientific, were conducted on a 1600 m² drill site. COSC-2 was drilled by the Swedish national research infrastructure for scientific drilling, Riksriggen, with a core recovery close to 100 %. Drilling was performed with water as drilling fluid. Biodegradable polymers were added for drilling in greater depth to reduce friction. Down to 1576 m, HQ triple tube drilling was used (96 mm hole diameter, 61 mm core diameter), followed by NQ triple and double tube drilling to total depth (76 mm hole diameter, 45/48 mm core diameter). Drilling was directly followed by extensive downhole surveying. In autumn 2021, a major surface and borehole seismic survey was conducted, covering approximately an area of 20 km² around the borehole. In 2022, fluid-conducting zones were investigated and fluids sampled with different methods for geochemical (gas and fluid) and microbiological analysis.

The drill site was restored in 2022, leaving a 35 m long and 4 m wide access road to the borehole. This is sufficient for COSC-2 long-term downhole investigations. The borehole is also available for research that is not part of the original COSC project. However, observations during recent downhole investigations suggest that sedimentation with a rate of several tens of meters per year successively is limiting access to the deepest part of the borehole. Scientific results from the COSC project are presented in session TS6.4 "The Caledonian Orogen of the North Atlantic region: insights from geological and geophysical studies".

How to cite: Lorenz, H., Rosberg, J.-E., and Juhlin, C. and the COSC-2 operations team: The COSC-2 scientific drilling project: summary of science, operations, management and legacy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1869, https://doi.org/10.5194/egusphere-egu23-1869, 2023.

Coral reef records related to past higher and/or rising sea levels provide an important baseline for developing projections regarding the response of modern coastal systems to future sea-level rise. Sea-level rise at the end of the current century is expected to range between 5.5 and 10 mm. yr^-1 on average, depending on the various scenarios of  global warming [IPCC, 2019]. The Last Deglaciation (23 to 6 kyr B.P.) is seen as a potential recent analogue of the environmental changes that the Earth may face in the near future as a consequence of ocean thermal expansion and the melting of polar ice sheets. The last deglacial record from Barbados suggests a non-monotonous sea-level rise averaging 10 mm.yr^-1 and punctuated by two ‘meltwater pulses’ (MWP) characterized by several centuries of extremely rapid sea-level rise related to catastrophic ice-sheet collapse [Fairbanks, 1989, Nature, 342, 637; Bard et al., 1990, Nature, 346, 456; Peltier & Fairbanks, 2006, Quat. Sci. Rev., 25, 3322].

IODP Expedition 310 ‘Tahiti Sea Level’ and land drilling on the modern barrier reef of Papeete have provided unparalleled coral reef records encompassing the period covered by the two MWP identified previously in Barbados. Reefs accreted continuously between 16 and 10 kyr B.P. in Tahiti, mostly through aggradational processes, at growth rates averaging 10 mm yr^–1. Changes in the composition of coralgal assemblages coincide with abrupt variations in reef growth rates and characterize the response of the upward-growing reef pile to non-monotonous sea-level rise and coeval environmental changes [Camoin et al., 2012; Geology, 40, 643; Camoin & Webster, 2015; Sedimentology, 62, 401].

While the MWP-1B at approximately 11.3 kyr B.P. in Barbados is absent or very small in Tahiti [Bard et al. 1996; Nature, 382, 241; Bard et al., 2010; Science, 327, 1235; Bard et al., 2016; Paleoceanography, 31], the Tahiti offshore record has provided the opportunity to document the MWP-1A at several drill sites. A sea-level rise of 16±2 m in amplitude has been evidenced between 14.65 and 14.3 kyr B.P., coeval with the Bølling warming [Deschamps et al., 2012, Nature, 483, 559]. The rate of eustatic sea-level rise ranged from 40 to 50 mm.yr^-1 during MWP-1A, implying that this episode corresponds to one of the fastest rises in sea level ever documented in Earth history.

This paper documents in unprecedented detail the reef response to extreme sea-level rise during MWP-1A in Tahiti. It is based on new accurate U-series and ¹⁴C AMS ages of corals and algae and the reappraisal of the environmental significance and paleowater depth interpretation of various coralgal assemblages. The succession in time and space of successive reef assemblages involved in reef accretion during the MWP-1A leads, for the first time, to reconstruct reef accretion patterns during this dramatic period, which is of prime importance to help forecasting coral reef response to future sea-level change.

How to cite: Camoin, G., Bard, E., Deschamps, P., Humblet, M., Braga, J. C., Guilhou, A., Hallmann, N., Weil-Accardo, J., Fagault, Y., and Hamelin, B.: CORAL REEF RESPONSE TO EXTREME SEA-LEVEL CHANGE: THE MELTWATER PULSE 1A (14.65 ka and 14.3 ka BP). IODP EXPEDITION #310 ‘TAHITI SEA LEVEL’, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2139, https://doi.org/10.5194/egusphere-egu23-2139, 2023.

The age of the ~100 km Manicouagan impact structure (Quebec, Canada) is ~215.5 Ma (1, 2), falling roughly in the middle of the Norian (228-206 Ma) of the Late Triassic, plausibly corresponding to the mid-Norian biotic crisis in the oceans (3) and Adamanian-Revueltian (4) biotic turnover on land. The latter is the largest apparent biotic disruption in the continental Triassic of North America, as documented in the Chinle Formation of the Colorado Plateau and environs in the southwestern USA. Funded by ICDP and NSF (2013-2016), CPCP-1 cored nearly the entire Norian part of the Chinle intersecting what should be the time of the giant impact and biotic transition. Analyses of detrital CA-ID-TIMS U-Pb zircon ages and magnetostratigraphy resulted in two alternative age models for the Chinle in the core (5, 6). Model A emphasized the one-to-one magnetostratigraphic match of polarity zones between the Chinle (5) and the Newark-Hartford Astrochronostratigraphic Polarity Time Scale (N-H APTS) (7) and is consisent with the youngest zircon ages, whereas Model B emphasized the mean of the youngest coherent cluster of ages at a specific level (6). Although both age models agree for the upper stratigraphic core section of the Chinle, they differ dramatically lower down with Model B having three additional accumulation rate segments, one of which is so low as to suggest a hiatus at the Adamanian-Revueltian turnover and Manicouagan impact, similar to a  previous CA-ID-TIMS outcrop study (8). Model A predicts no discernable change in rate or hiatus at the putative event level and only one other accumulation rate segment. Timeseries analysis using Model A reveals significant ~1.8 Myr and 405 kyr cycles in both accumulation rate segments for natural gamma radiation and the elemental XRF ratios, in phase in both segments with the chaotic Mars-Earth and metronomic Venus-Jupiter cycles in the N-H APTS (9). Model B, in contrast, lacks significant cycles at these periods for the lower three accumulation rate segments. Consilience between Model A and the independent astrochronological predictions suggests it is the better model. The discrepancy with Model B is parsimoniously explained by the youngest coherent age clusters tending to be dominated by recycled zircons in the lower part of the core as suggested by LA-ICP-MS data (10). The Adamanian-Revueltian biotic turnover and Manicouagan impact therefore should have a record in the higher accumulation rate part of the Chinle and not be cut out by a hiatus or in a condensed section. Additional coring and denser CA-ID-TIMS ages will be needed to fully test the robustness of this conclusion.

1, Ramezani+ (2005) Geochim, Cosmochim. Acta 69:321. 2, Jaret+ (2018) EPSL 501:78. 3, Onoue+ (2016) Sci. Repts. 6:29609. 4, Parker & Martz (2011) EESTSE 101:231. 5, Kent+ (2019) Geochem. Geophys. Geosyst. 20:4654. 6, Rasmussen+ (2021) GSA Bull. 133:539. 7, Kent+ (2017) Earth-Sci. Rev. 166:153. 8, Ramezani+ (2014) AJS  314:981. 9, Olsen+ (2019) PNAS 116:10664. 10, Gehrels+ (2020) Geochronology 2:257.

How to cite: Olsen, P., Kent, D., Lepre, C., Kinney, S., RoyChowdhury, A., Chang, C., Tibbetts, D., and Bebo, C.: Searching for Manicouagan: astrochronological predictions and tests of alternative age models in the Late Triassic Chinle Formation [Colorado Plateau Coring Project-1 (CPCP-1), Arizona, USA] , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2476, https://doi.org/10.5194/egusphere-egu23-2476, 2023.

Sediment density flows (ρ_flow<ρ_water, overflows: flood plumes; ρ_flow>ρ_water, underflows: including turbidity currents and debris flows) are major processes for transporting sediments and organic carbon from rivers, coasts or continental shelves into deep basins. These flows can also have serious socioeconomic consequences such as breaking seabed communications cables and pipelines. Given the potential impacts of climate change, it is important to quantify how sediment density flow processes are impacted by changing environmental conditions.

Lab-simulations and/or field monitoring campaigns on the timescales of seconds to years are helpful for understanding specific triggers for sediment density flows and how their magnitude/frequency may change under different conditions. However, these methods cannot be applied to longer timescales, which are of great interest to geologists and palaeoclimatologists trying to understand the past. It is unclear whether, and if so how, long-term climate changes affect the magnitude/frequency or type of sediment density flows within a specific water body. One approach to answering this question is to analyze a comprehensive geological record that comprises deposits that can be reliably linked to modern sediment flow processes.

To address this question, we analyzed the unique ICDP Core 5017-1 from the Dead Sea (the largest and deepest hypersaline lake on Earth -- ρ_water:1240 g/L) depocenter covering MIS 7-1. Based on an understanding of modern sediment density flow processes in the lake, we link homogeneous muds in the core to overflows (surface flood plumes, ρ_flow<ρ_water), and link graded turbidites and debrites to underflows (ρ_flow>ρ_water). Our dataset reveals (1) overflows are more prominent during interglacials, while underflows are more prominent during glacials; (2) orbital-scale climate changes affected the magnitude/frequency of the flows via changing salinity and density of lake brine and lake-level (Lu et al., 2022).

The current research bridges the gap between our understanding of modern sediment density flow processes and deposits preserved in a long-term geological record in the Dead Sea, a tectonically active subaqueous environment (Lu et al., 2020). It has wider implications for turbidite paleoseismology and implies that to develop prehistoric turbidites as a reliable paleoearthquake indicator, comprehensive modern sediment flow monitoring is essential. It also has wider implications for paleoclimate research in a tectonically active subaqueous environment. A sedimentary archive is filtered to remove significant instantaneous event deposits such as turbidites and debrites could help paleoclimatologists to better reconstruct paleoclimate change.

Refs.:

Lu, Y., Wetzler, N., Waldmann, N.D., Agnon, A., Biasi, G.P., and Marco, S., 2020. A 220,000-year-long continuous large earthquake record on a slow-slipping plate boundary. Science Advances, 6 (48), doi: 10.1126/sciadv.aba4170

Lu, Y., Pope E., Moernaut, J., Bookman, R., Waldmann, N., Agnon, A., Marco, S., Strasser, M., 2022. Stratigraphic record reveals contrasting roles of overflows and underflows over glacial cycles in a hypersaline lake (Dead Sea). Earth and Planetary Science Letters, 594, 117723, doi: 10.1016/j.epsl.2022.117723

How to cite: Lu, Y., Pope, E., Moernaut, J., Bookman, R., Waldmann, N., Agnon, A., Marco, S., and Strasser, M.: How do long-term climate changes affect the magnitude/frequency of sediment density flows? Insights from the Dead Sea ICDP drilling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3744, https://doi.org/10.5194/egusphere-egu23-3744, 2023.

Shallow slow earthquakes, which last minutes to years, are important indicators of subduction megathrust slip behavior and future seismic and tsunami potential. Subducting plate roughness and seamounts have been proposed to promote slow earthquakes by inducing local geomechanical and hydrogeological anomalies. The Hyuga-Nada region offshore Kyushu, Japan is an outstanding locale for drilling and observatory experiments to investigate these effects. In this region, slow earthquakes are repeatedly observed on and near the subducting Kyushu-Palau-Ridge, KPR, chain of seamounts thus providing excellent opportunities to explore the effects of seamounts on geomechanical/hydrological/thermal properties, and ultimately seismic coupling. Long-term monitoring enabled by a planned permanent network (N-net) will allow subsurface processes during frequent (~1 year) periodical slow earthquakes and ~M7 earthquakes (~20-30 year interval) to be captured with high fidelity. Drilling, logging, and coring will provide key constraints on stress state, hydrological processes, and sediment physical properties in the region above the ridge.  We have originally proposed the drilling and monitoring plan to IODP in 2019 (Nakata et al. 2019). In this presentation, we report the updated proposal plan along with initial processing results of new site survey data acquired with JAMSTEC (Miura et al., 2021, Arai et al., 2021, Ma et al., 2021).

We propose to drill and install observatories at three primary locations in Hyuga-Nada to address two hypotheses: 1) Seamount subduction modulates stress and pore pressure, creates fracture networks and influences the thermal and hydrological state of the margin. 2) The spatiotemporal distribution of slow earthquakes is strongly influenced by seamount subduction through the processes outlined in Hypothesis 1. We will drill three primary distinct sites relative to the seamount, to (1) measure physical properties, and (2) describe deformation by LWD, APCT-3, and core analysis to characterize in-situ stress state, fracture density, heat flow, and pore fluid flow. Spatial variations in the upper plate disruption caused by seamount subduction will be revealed by comparing results from sites in the leading and lateral edges, and top of the currently subducting seamount; and these will constrain geomechanical, hydrological, and thermal models. At two of the sites, we will install a “Fiber-CORK” observatory equipped with conventional pressure and temperature sensors and cutting-edge fiber-optic sensors. One site may be connected to the N-net node for real-time data streaming. The combination will fill a gap in slip durations currently observable in this region with seismic and geodetic instrumentation. Fully characterizing slow earthquakes will reveal the degree to which they accommodate plate motion, and whether strain is accumulated for future earthquakes.

How to cite: Kinoshita, M., Nakata, R., Hashimoto, Y., Hamada, Y., Wallace, L., Sun, T., Araki, E., and Yamashita, Y.: Drilling and monitoring in Hyuga-Nada: Unveiling effects of ridge subduction on slow earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4047, https://doi.org/10.5194/egusphere-egu23-4047, 2023.

Guaymas Basin is a young marginal rift basin in the Gulf of California characterized by active seafloor spreading and rapid sediment deposition, including organic-rich sediments derived from highly productive overlying waters and terrigenous sediments from nearby continental margins. The combination of active seafloor spreading and rapid sedimentation within a narrow basin results in a dynamic environment where linked physical, chemical, and biological processes regulate the cycling of sedimentary carbon and other elements.

During IODP Expedition 385, eight sites were drilled on the flanking regions and in the northern axial graben of Guaymas Basin, recovering organic-rich sediments with sill intrusions. Those cored samples were examined for their microbial cell abundance in a highly sensitive manner by density-gradient cell separation at the super clean room of Kochi Core Center, Japan, followed by direct counting on fluorescence microscopy. Cell abundance in surficial seafloor sediment (~10⁹ cells/cm³) was roughly 1000 times higher than the bottom seawater (~10⁶ cells/cm³) and gradually decreased with increasing depth and temperature. In contrast to the cell abundance profile observed at Nankai Trough (IODP Exp. 370), the gradual decrease of cell abundance was observed up to around 75ºC, and we detected microbial cells even at hot horizons above 100ºC. The existence of smaller size of microbial cells was uniquely found in this region of subseafloor.

We will present the overview of the microbial cell distribution in the Guaymas Basin and discuss its relation to the current and past environmental conditions, e.g., temperature and sill-intrusion, etc.

How to cite: Morono, Y., Teske, A., Bojanova, D., Edgcomb, V., Meyer, N., Schubert, F., Toffin, L., and Galerne, C. and the IODP Expedition 385 Scientists: Microbial cell distribution in the Guaymas Basin subseafloor biosphere, a young marginal rift basin with rich organics and steep temperature gradient, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4098, https://doi.org/10.5194/egusphere-egu23-4098, 2023.

Limited access has hindered understanding of seismogenic zone and life at depth (e.g., ICDP Science Plan 2014-2019; 2020-2030). The 2014 M5.5 Orkney earthquake South Africa ruptured the entire vertical depth range, between 3.5 and 7 km of the West Rand Group (2.9 Ga metasedimentary formations with altered mafic/ultramafic sill/dyke complex). We could have a drilling rig at 2.9 km depth in hard-rock formations in West Rand Group at the Moab Khotsong gold mine. During 2017-2018, we accomplished NQ wireline full-core diamond drilling and downhole logging with a total length of 1.6 km (ICDP Thrill to Drill; Ogasawara et al. 2019; Nkosi et al. 2022). We could not make downhole logging at and below the intersections of the structure that hosted the Orkney main- and after-shocks. So, we exported the most critical section of the core to Center for Advanced Marine Core Research, Kochi University/Kochi Core Center (KCC) Japan to log and for further investigation. Mineral/geochemical studies (XRD, XRF, EPMA, SEM-EDS, X-ray CT, friction) at KCC, Hiroshima, Tohoku, Tokyo, and Kyoto Universities, as well as SPring8 elucidate the assemblage with talc and/or associated altered mafic minerals in greenschist facies and their mechano-chemical characteristics (e.g., Miyamoto et al. 2022; Yabe et al. 2023 GeoCongress). Our drilling also intersected the ancient hypersaline brine vein. US geomicrobiology team extensively investigated the brine (Oliver et al. 2022; Nisson et al. 2022). The outstanding outcomes include the age (>1Ga) and the salinity, the end-member in their research history since the 1990s. COVID-19 hindered, in particular, our research activity at 2.9 km depth at Moab Khotsong mine and access to the core during 2020-2021. However, we could log Holes A and B again in 2022 to compare with the previous logging data. This paper overviews the activity mentioned above, as well as prospects.

Our research is financially supported by ICDP, JSPS, JST-JICA, MEXT Japan, US NSF, German DFG, SA NRF, Ritsumeikan Univ., GFZ. Kochi Core Center, Astrobiology Center.

How to cite: Ogasawara, H. and the ICDP DSeis team: ICDP Drilling into Seismogenic zones in South African mines (DSeis; 2016 – onwards), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4104, https://doi.org/10.5194/egusphere-egu23-4104, 2023.

During a long period of its Cenozoic history, the Arctic Ocean was isolated from any global thermohaline circulation system. Thus, the opening and subsequent widening of the Fram Strait, the only deep-water connection between the Arctic and Atlantic oceans, was a fundamental tectonic process with extensive consequences for the global ocean circulation and paleoclimate evolution as well as for sedimentation processes in the adjacent ocean basins and along the continental margins.

In order to reconstruct both the development of the ocean circulation within and the glacial history of the Arctic-Atlantic gateway we interpreted sediment packages imaged in reflection seismic profiles together with updated stratigraphic information from existing Ocean Drilling Program (ODP) holes. Our new, high resolution seismic stratigraphy for the Molloy Basin (central Fram Strait) is based on a revised chronology for ODP Site 909 and on reprocessed seismic reflection data with now better resolution than in previous studies.

An improved core-log-seismic integration for ODP Site 909 and crossing seismic reflection profile AWI-20020300 was substantial in deriving the new seismic stratigraphy as well as characterizing the seismic units lithologically (Gruetzner et al., 2022). The core-seismic integration was combined with a revised magnetostratigraphy calibrated by new palynomorph bioevents which shifts previously used stratigraphies for ODP Site 909 (e.g. Myhre et al., 1995) to significantly younger ages in the time interval from c. 15 Ma to 3 Ma. The new stratigraphy implies that prominent maxima in coarse sand particles and kaolinite, often interpreted as evidence for ice rafting in the Fram Strait occur at c. 10.8 Ma, c. 3 Myr later as previously inferred. In the late Tortonian (< 7.5 Ma), sediment transport became current controlled, most probably through a western, recirculating branch of the West Spitsbergen Current. This current influence was strongly enhanced between c. 6.4 and 4.6 Ma and likely linked to the subsiding Hovgaard (Hovgård) Ridge and the widening of the AAG. Late Pliocene to Pleistocene seismic reflectors correlate with episodes of elevated ice-rafted detritus input related to major phases in Northern Hemisphere ice sheet growth such as the prominent glacial inception MIS M2 and the intensification of Northern Hemisphere glaciation starting at c. 2.7 Ma.

Tracing the most prominent reflectors in a dense net (~5800 km) of re-processed seismic profiles allowed us to extrapolate these events into the western Boreas Basin and towards the adjacent Northeast Greenland continental margin. Subsequently compilations of updated digital isochron and depth-to-horizon maps were used to map depocenter geometries of current controlled sediments and mass-transport deposits within the western part of the Arctic-Atlantic gateway.

References

Gruetzner, J., Matthiessen, J., Geissler, W.H., Gebhardt, A.C., Schreck, M. (2022). A revised core-seismic integration in the Molloy Basin (ODP Site 909): Implications for the history of ice rafting and ocean circulation in the Atlantic-Arctic gateway. Global and Planetary Change, 215, 103876.

Myhre, A. M., Thiede, J., Firth, J. V., Ahagon, N., Black, K. S., Bloemendal, J., et al. (1995). Site 909. Proceedings of the Ocean Drilling Program, Part A: Initial Reports, 151, 159-220.

How to cite: Geissler, W. H., Gruetzner, J., Matthiessen, J., Gebhardt, A. C., and Schreck, M.: The opening of the Fram Strait and its influence on sediment transport, climate and ocean circulation between the Arctic Ocean and the North Atlantic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4301, https://doi.org/10.5194/egusphere-egu23-4301, 2023.

Adaptive radiation is considered to play an important role in the diversification of life on Earth. This is especially true in isolated long-term environments where the largest adaptive radiations have been found and where the adaptive nature of diversification has been best studied. However, the environmental conditions that influence rapid diversification during adaptive radiations and potentially lead to differences in evolutionary trajectories and species richness across the tree of life are still unclear, primarily because there few, if any, fossil records for some of the most iconic examples of vertebrate radiations. Here, we use two diverse groups of diatoms (Diploneis and Afrocymbella) with different lifestyles and great fossilization potential to test the role of environment in adaptive radiation and its impact on evolutionary trajectories between different diatom clades in East African Rift lakes that are home to the world's largest radiations – that of cichlid fishes. We constructed a time-calibrated molecular phylogeny of extant and extinct species, as well as a trait matrix, and show that the two diatom groups evolved within the rift from a common ancestor over a relatively short time, with accelerated diversification leading to much higher species richness in the genus Diploneis. We then correlate the inferred diversification rates and trajectories of trait evolution with biological and environmental variables to determine the influence of the environment on the progression of adaptive radiation. This integration of genetic, morphological, and paleoenvironmental information allowed us to demonstrate the influence of the environment on a key process that has produced much of Earth's biological diversity.

How to cite: Jovanovska, E., Stone, J., Salzburger, W., and Schrenk, F.: The influence of environment on adaptive radiation of diatoms in East African Rift lakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4430, https://doi.org/10.5194/egusphere-egu23-4430, 2023.

Continuous limnic archives may record millions of years of climatic and environmental change at their locality. Typically, such archives reflect environmental conditions in the lakes’ catchments, but also the imprint of large-scale atmospheric systems e.g. related to insolation and/or global ice-sheet dynamics. These parameters may vary considerably in space and time, and our understanding on patterns across continents that relate to this forcing is still incomplete. Comparing sedimentation rates from limnic archives covering fundamental changes in the Earth’s system like the Mid-Pleistocene Transition (change from 41 kyr to 100 kyr cycle world) has potential to shed light into spatial differences in Earth’s climate response, if applied carefully.

In this context, we use age-depth models along with stratigraphic and chronological information e.g. from tephrochronology, magnetostratigraphy and tuning to assess differences in sedimentation rates of limnic geoarchives. We focus on limnic records that have been investigated during International Continental Scientific Drilling Program (ICDP) drilling projects, and specifically assess the influence of the Mid-Pleistocene Transition and the Mid-Brunhes Transition on sedimentation rates.

How to cite: Zeeden, C., Grandolas, L., Vinnepand, M., Ulfers, A., Sardar Abadi, M., Pierdominici, S., and Wonik, T.: Comparing lacustrine sedimentation rates and their response to climatic and environmental change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5598, https://doi.org/10.5194/egusphere-egu23-5598, 2023.

The Mariana forearc constitutes the southern sector of the Izu-Bonin-Mariana (IBM) trench-arc system (12° N to 35° N) in the NW Pacific Ocean. It is the only setting where active serpentinite mud volcanism is recorded.

The Mariana forearc hosts several large serpentinite mud volcanoes, among which Fantangisña seamount was cored during International Ocean Discovery Program (IODP) Expedition 366. Lithologies comprise pelagic sediments covering serpentinite mud deposits with ultramafic clasts which derive from the subducting Pacific Plate, forearc crust and mantle. In addition, nannofossil-bearing pelagic sediments and volcanic ash/tephra layers were found at the bottom of the core.

Fantangisña seamount is located in the tropical Pacific region, at low latitudes (16° N) within the latitudinal band of the North Equatorial Current (NEC). The NEC is a warm and nutrient- poor water mass, flowing westward in the tropical Pacific Ocean, driven by trade winds.

In this study, benthic and planktonic foraminifera analyses were performed at Site U1498A, located on the southern flank of Fantangisña serpentinite mud volcano. Most of our analysed interval covers the Early to Late Pleistocene as indicated by previous biostratigraphic investigation on this site. Cluster analyses on Pleistocene planktonic foraminifera resulted in two major clusters based on thermocline-dwelling species (e.g., Globorotalia spp.) to mixed-layer dwellers (e.g., G. ruber, G. rubescens, G. glutinata, Trilobatus spp.) ratio, which infer variations of the depth of the thermocline (DOT) during the Pleistocene. These changes of the DOT can be related to fluctuations in the intensity of the NEC. Our data implies a deep and stable thermocline with an intense NEC during the interval of the Early-Middle Pleistocene Transition (EMPT). In contrast, both thermocline and NEC weakened during the Middle-Late Pleistocene, following the EMPT. Variations in strength of the NEC could be associated with ENSO climate conditions (El Niño/La Niña).

Planktonic foraminifera diversity suggests that the distribution of planktonic assemblages was not affected by the serpentinite mud activity in the area. In addition, our results imply that the preservation of the planktonic tests could be enhanced by rapid burial under the serpentinite mud flows.

High diversity (99 taxa) was recorded for benthic foraminifera before and after the serpentinite mud flow volcanism indicating oligotrophic and well-oxygenated bottom-water conditions. In contrast, benthic species were severely affected by the volcanic activity due to serpentinite mud flows and gas emissions.

How to cite: Del Gaudio, A. V., Piller, W. E., Auer, G., and Kurz, W.: Planktonic and benthic foraminifera assemblages from Fantangisña serpentinite mud volcano in the NW Pacific Ocean during the Pleistocene (IODP Expedition 366), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5797, https://doi.org/10.5194/egusphere-egu23-5797, 2023.

As a contribution towards a regional environmental context of human-climate interactions, the ICDP co-funded Chew Bahir Drilling Project, a part of the HSPDP (Hominin Sites and Paleolakes Drilling Project), recovered ~280-m long cores of sedimentary strata through continental scientific drilling in southern Ethiopia. The fluvio-lacustrine coring locality in the Chew Bahir basin is situated near key archaeological and paleoanthropological sites, such as the Omo-Kibish where the Omo 1 and 2 Homo sapiens fossils were recovered.

Here we present the 620,000-year environmental record from Chew Bahir that provides an extraordinary opportunity to examine the potential influence of climate variability on hominin evolution, cultural innovation and dispersal during the Middle to Late Pleistocene. The near-continuous Chew Bahir record documents 13 environmental episodes that differ in length and character, potentially inducing habitat changes influencing hominin biological and cultural transformation. We infer that long-lasting and relatively stable humid conditions from ~620,000–275,000 years BP (Episodes 1–6) were interrupted by several abrupt and extreme hydroclimatic oscillations. This phase coincided with the appearance of high anatomical diversity in hominin groups. During Episodes 7–9 (~275,000–60,000 years BP), a pronounced pattern of climatic cyclicity was paralleled by the gradual transition from Acheulean to Middle Stone Age technologies, the emergence of H. sapiens in eastern Africa, and a key phase of human social and cultural innovation. Episodes 10–12 (~60,000–10,000 years BP), marked by high-frequency climate oscillations, is contemporaneous with the global dispersal of H. sapiens, facilitated by continued technological innovation and the alignment of humid pulses between eastern Africa and the eastern Mediterranean.

Prospectively, the Chew Bahir record represents a crucial component for the Middle and Late Pleistocene in the ongoing efforts of the scientific community (future and upcoming ICDP-funded projects) to address questions in Africa  across four topical core areas: paleoclimate, paleoenvironment, basin evolution, and modern lake systems.

How to cite: Foerster, V., Asrat, A., Bronk Ramsey, C., Brown, E. T., Deino, A., Grove, M., Hahn, A., Junginger, A., Kaboth-Bahr, S., Lane, C. S., Opitz, S., Noren, A., Roberts, H. M., Tiedemann, R., Vogelsang, R., Vidal, C. M., Cohen, A. S., Lamb, H. F., Schaebitz, F., and Trauth, M. H.: Pleistocene climatic variability in eastern Africa influenced hominin evolution: the 620,000-year climate record from Chew Bahir, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6170, https://doi.org/10.5194/egusphere-egu23-6170, 2023.

Northern Zealandia is a continent submerged for more than 90% under the water of the southwest Pacific Ocean and separated from Australia by the Tasman Sea ocean basin. Its absolute position since its drift form Australia in the Cretaceous is determined by means of global absolute plate motion models, as local paleomagnetic constraints are completely missing. We present new absolute paleolatitudes for northern Zealandia using paleomagnetic data from sediments drilled in International Ocean Discovery Program Sites U1507 and U1511 (Expedition 371^1,2). After correcting for paleomagnetic inclination shallowing, typical of sediments, we derived five paleolatitude estimates that provide a trajectory of northern Zealandia past position from the middle Eocene to early Miocene, spanning geomagnetic polarity chrons C21n to C5Er (~48–18 Ma). Generally, our results support previous works on global absolute plate motion, including a rapid 6° northward migration of northern Zealandia between the early Oligocene–early Miocene. However, paleomagnetic-determined absolute paleolatitude is systematically lower, and this difference is significant in the Bartonian and Priabonian (C18n–C13r). This discrepancy may be explained by some degree of true polar wander, a solid Earth rotation with respect to the spin axis that can be resolved only using paleomagnetic data. These new paleomagnetic dataset anchors past latitudes of Zealandia to Earth’s spin axis, with implications not only for global geodynamics, but for addressing paleoceanographic problems, which generally require precise paleolatitude placement of proxy data³.

Figure 1. Present-day map of northern and southern Zealandia, enveloped respectively by the yellow and orange dashed line. The yellow stars indicate the location of International Ocean Discovery Program Sites U1507 (26.4886°S, 166.5286°E) and U1511 (37.5611°S, 160.3156°E). Solid and dashed white lines indicate active and inactive subduction zones, respectively, with arrows lying on the overriding plate. LHR = Lord Howe Rise, NCT = New Caledonia trough, NR = Norfolk Ridge, RB = Reinga basin.

(¹) Sutherland, R. et al. Proc. Int. Ocean Discov. Progr. 371, 1–33 (2019); (²) Dallanave, E. & Chang, L. Newsletters Stratigr. 53, 365–387 (2020); (³) Dallanave, E. et al. J. Geophys. Res. Solid Earth 127, 1–19 (2022).

How to cite: Dallanave, E., Sutherland, R., Dickens, G., Chang, L., Tema, E., Alegret, L., Agnini, C., Westerhold, T., Newsam, C., Lam, A., Stratford, W., Collot, J., Etienne, S., and von Dobeneck, T.: Middle Eocene to the early Miocene northward migration of northern Zealandia determined from the sedimentary record of IODP Exp. 371 (Tasman Sea), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6477, https://doi.org/10.5194/egusphere-egu23-6477, 2023.

The European Petrophysics Consortium (EPC) is part of the ECORD Science Operator (ESO). EPC comprises the University of Leicester and Géosciences Montpellier and provides petrophysics staff scientists and petrophysicists, as well as expertise in downhole logging and core petrophysics programmes. The EPC has dedicated equipment for core logging and discrete measurements and is involved in data calibration, quality control, evaluation and interpretation of these data. The EPC is also involved in post-expedition activities, the preparation of upcoming expeditions, capability development, and training for IODP MSP expeditions and other key activities, including education and training.

Over the past pandemic years, EPC has been active within expeditions and the community. EPC recognizes the importance of scientific drilling to palaeoclimate studies amongst other key topics, which is also reflected in our new science and operations roadmap: i) hired new staff members with a paleoclimate background; ii) developed a system for knowledge exchange between petrophysics and climate scientists, for instance via the ECORD summer schools; iii) renewed focus to include the development of measurement protocols and data analysis techniques to better serve the IODP community.

EPC also has a website (http://www.le.ac.uk/epc) and will host the next ECORD Summer School Downhole Logging for IODP Science in person in Leicester in summer 2023.

*European Petrophysics Consortium Team Members:

Sarah Davies, Simon Draper, Tim van Peer, Andrew McIntyre, Marisa Rydzy (University of Leicester).

Philippe Pezard, Johanna Lofi, Erwan Le Ber, Laurent Brun (University of Montpellier).

How to cite: van Peer, T., McIntyre, A., Rydzy, M., Le Ber, E., and Team Members, E. P. C.: European Petrophysics Consortium's Contributions to IODP, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7814, https://doi.org/10.5194/egusphere-egu23-7814, 2023.

The knowledge of the global reservoir of submarine gas hydrates is of great relevance for understanding global climate dynamics, submarine geohazards, and unconventional hydrocarbon energy resources. Methane hydrate formation and preservation is favored by high pressure and low geothermal gradient and this leads the reservoir to be hosted mostly in cold passive continental margins. Several studies describe the Mediterranean basin's potential to host a Methane hydrate reservoir. However, in spite of the ample evidence of subsurface hydrocarbons, especially biogenic methane, widespread evidence of gas hydrate either from samples or seismic data is missing.  We modeled the theoretical Mediterranean distribution of methane hydrate stability field below the seafloor and in the water column using available geological information provided by 44 Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) boreholes, measured geothermal gradients, and thermohaline characteristics of the water masses from CMEMS (Copernicus Marine services). We find that the pervasive presence of high-salinity waters in sediments, coupled with the uniquely warm and salty water column, limits the thickness of the theoretical methane hydrate stability zone in the subsurface and deepens its top surface. Because of the homogeneous characteristics of water masses, the top surface in the Mediterranean sea lays uniformly from 1163 to 1391 mbsl, much deeper than the oceanic basins where it lays around 300 - 500 mbsl. The theoretical distribution of methane hydrates coincides well with the distribution of shallow, low-permeability Messinian salt deposits, further limiting the formation of pervasive gas hydrate fronts and controlling their distribution due to the prevention of upward hydrocarbon gas migration. We conclude that the Mediterranean Basin, hosting the youngest salt giant on Earth, is not prone to the widespread formation and preservation of gas hydrates in the subsurface and that the gas hydrate potential of salt-bearing rifted continental margins may be considerably decreased by the presence of subsurface brines. This study was entirely conducted using data (stratigraphy, pore water salinity, and where available downhole temperature measurements) obtained with scientific ocean drilling, thus demonstrating the importance of the legacy data as a source of quality information even decades after their acquisition.

How to cite: Corradin, C., Camerlenghi, A., Tinivella, U., Giustiniani, M., and Bertoni, C.: Legacy scientific ocean drilling data suggest that subsurface heat and salts cause exceptionally limited methane hydrate stability in the Mediterranean Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7938, https://doi.org/10.5194/egusphere-egu23-7938, 2023.

Borehole temperature measurements can be easily conducted  at the end of a drilling operation during trip out of the drill string (logging while tripping) without the need for additional operational time. After the final drilling depth was reached, an autonomous borehole logging tool including a temperature sensor is placed at the lower end of the drill string with the sensor part having passed the drill bit and sticking out in the open borehole between bottom of the borehole and drill bit. During trip out the logging tool is hooked up together with the drill string inside the borehole and measures the fluid temperature within the borehole. Stationary phases occur at regular intervals during disconnecting drill rods from the drill string. The analysis of the borehole temperatures during these stationary phases allow the investigation of changes of borehole temperatures with depth and with time. These temperature changes are a function of the geothermal gradient and the perturbation of the temperature field by the drilling action. Here we present results of a pilot study (Freudenthal et al., 2022) based on borehole temperature measurements acquired with the sea floor drill rig MARUM-MeBo200. By modeling the temperature evolution from the start of the drilling operation on, it is possible to analyze the impact of the drilling perturbation on the temperature field and to conclude on the regional heat flux.

References:

Freudenthal, T., Villinger, H., Riedel, M., and Pape, T. (2022) Heat flux estimation from borehole temperatures acquired during logging while tripping: a case study with the sea floor drill rig MARUM-MeBo. Marine Geophysical Research 43:37. doi: 10.1007/s11001-022-09500-1

How to cite: Freudenthal, T., Villinger, H., Riedel, M., and Pape, T.: Estimation of regional heat flux based on borehole temperatures acquired during logging while tripping with the sea floor drill rig MARUM-MeBo200, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7956, https://doi.org/10.5194/egusphere-egu23-7956, 2023.

Driven by the need to understand magmatic systems, to improve volcano monitoring strategy, and to develop next-generation, high-enthalpy, geothermal energy, we introduce the Krafla Magma Testbed (KMT) – located in Northeast Iceland. KMT aims to establish the first magma observatory – an international, open access, scientific platform to advance ductile zone to magma research via drilling and novel sensor systems. This frontier undertaking will enable direct, in situ sampling, instrumentation and manipulation, and monitoring of magma and its interface with solid Earth’s crust, vastly advancing models of high-temperature crustal processes. 

This initiative is enabled by past geothermal drilling at Krafla volcano that was serendipitously intersected and thus determined the exact location of magma for the first time. This unprecedented experience, including safe control of the wells, provides the basis for KMT, which stands to transform modern volcanology and geothermic disciplines. 

KMT will develop a long-term infrastructure (>25 years) for the conduct of interdisciplinary scientific, engineering, technological, and educational activities. The Krafla volcano has the advantage of a long history of geological study, volcano monitoring, and drilling as well as supporting surface facilities combining to produce the safest and most efficient base from which to explore Earth beyond the solidus.  

KMT will be the place to develop (1) our science of hot and molten Earth; (2) new ways of understanding and monitoring volcanoes; (3) our ability to extract and exploit geothermal energy sources; and (4) new technology and materials that function in the most extreme conditions in planetary systems. 

The value of potential gains in fundamental understanding of crustal processes is beyond our possibility to estimate. There is the prospect of an order of magnitude gain in geothermal energy productivity. The need to improve understanding of the source of catastrophic eruptions and to better forecast them is a compelling humanitarian one.

How to cite: Lavallée, Y., Mortensen, A., Papale, P., Eichelberger, J., Sigmundsson, F., Kennedy, B., Villeneuve, M., Jousset, P., Dingwell, D. B., Markusson, S., Eiríksdóttir, V., Pálsson, B., Tester, J., Karlsdóttir, S. N., Midgley, J., Ingolfsson, H. P., and Ludden, J.: Implementing the Krafla Magma Testbed (KMT): linking volcanology and geothermal research for future hazard and energy solutions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7958, https://doi.org/10.5194/egusphere-egu23-7958, 2023.

Earthquakes are complex natural phenomena that involve multiple spatio-temporal scales. To understand the physical/chemical processes responsible for the faulting that earthquakes occur on, a multidisciplinary approach is highly recommended. Near Fault Observatories (NFOs) aim at providing high-precision and spatio-temporally dense multidisciplinary near fault data, enabling the generation of innovative scientific products.

The Alto Tiberina Near Fault Observatory (TABOO-NFO) is a permanent monitoring infrastructure around the Alto Tiberina Fault (ATF). The ATF is a 60 km long very low-angle normal fault (mean dip 20°) located along a 3 mm/yr extending sector of the Northern Apennines (Central Italy). The presence of repeating earthquakes on the ATF, as well as a steep gradient in crustal velocities measured by GNSS stations, suggest that portions of the ATF are creeping aseismically. Both laboratory and theoretical studies indicate that any given patch of a fault can creep, nucleate slow earthquakes, and host large earthquakes, as also documented in nature for some earthquakes (e.g., Iquique, Tohoku and Parkfield earthquakes). Nonetheless, how a fault patch switches from one mode of slip to another as well as the interaction between creep, slow and regular earthquakes are still poorly documented by near field observation.

TABOO is a state-of-the-art dense network, managed by the Istituto Nazionale di Geofisica e Vulcanologia (INGV), with mean inter-distance of about 5 km between multidisciplinary sensors, deployed both at surface and within shallow boreholes (<250m). Stations record and transmit in real time via dedicated Wi-Fi technology; then data is stored in standard formats on open access thematic portals and distributed via web services (http://fridge.ingv.it). With STAR, during the Fall of 2021 and Spring of 2022, INGV in collaboration with UNAVCO, drilled six 80-160 m deep boreholes surrounding the creeping portion of the ATF, to deploy Gladwin Tensor strainmeters and short period seismometers. Each “observatory” is also equipped with surface GNSS, meteorological instruments, and additional seismic sensors. The two deepest boreholes host fibre optic cables for temperature and strain. The strainmeter array (STAR) instruments are four-gauge strainmeters, from which we can resolve the horizontal strain matrix and measure deformation on the order of nanostrain, and bridge timescales encompassed neither by GNSS nor by Seismometers. With this new suite of instruments TABOO will enable the collection and calibration of strain records with exquisitely high precision, allowing for a quantitative characterization of ATF creep (~1 mm over <1 km²), enhanced monitoring of microseismicity (below Mc 0.5), and allowing correlation between degassing (CO2, Rn) measurements and subsurface strain.

Such unique near fault data Illuminating the spatiotemporal characteristics of creep on the ATF including possible stress triggering of larger earthquakes by transient creep events, are needed to address key questions of global importance in the seismic hazards and risk assessment community about the physics that allows for both seismic and aseismic slip on a single fault patch.

After presenting the field campaigns, we give an overview of the new data, showing how they enable us to detect new dynamic and static strain features missed by the other in situ instruments.

How to cite: Chiaraluce, L., Mencin, D., Bennett, R., Barchi, M. R., and Bohnhoff, M. and the STAR team: A strainmeter array to unravel the Alto Tiberina fault slip behaviour, Central Italy - ICDP STAR Drilling Project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8462, https://doi.org/10.5194/egusphere-egu23-8462, 2023.

A founding ambition of scientific ocean drilling is to drill a MoHole that penetrates the entire ocean crust and into the upper mantle at a location representative of normal crustal accretion and evolution. This remains the only way to test many of our key ideas about how new crust forms at mid-ocean ridges, cools and ages through interactions with the oceans. The technical challenges of drilling such a deep hole limit potential locations to a small number of candidate regions, which need to be sufficiently old to be cool at Moho depths but shallow enough for riser drilling.

In December 2022 and January 2023 RRS James Cook expedition JC228 carried out the first site survey to collect complete seismic datasets in one of the candidate regions, the Guatemala Basin. We collected two grids and a long flowline profile of multichannel seismic reflection (MCS) data using a tuned airgun array of 5000 in³ together with a 6 km hydrophone streamer. Airgun shots were simultaneously recorded on 52 ocean-bottom seismometers (OBS) deployed at 84 locations. Shot spacings of 150 m and 75 m were optimised for the different recordings. The survey samples crust formed between 19 and 21 Ma, at present-day water depths of 3200-3400 m, and is approximately along a flowline from the existing ODP/IODP Site 1256, where intact ocean crust has been drilled to the gabbros. Initial processing of the MCS data on board the ship shows a normal incidence reflection Moho that is variable in amplitude over distances of ~10 km, but is present at the intersections of several MCS profiles. Wide-angle PmP reflections on the OBS are clear across the region. There is obvious anisotropy in the Pn upper mantle refraction on the OBS, with a strong and high-velocity arrival along the flowline, and weaker and slower arrivals in the isochron direction at each grid. Overall, the initial observations are extremely promising for identification of multiple viable Mohole drilling locations.

How to cite: Henstock, T., Grevemeyer, I., Dannowski, A., Marjanovic, M., Hilbert, H.-S., Robinson, A., Li, Y., and Teagle, D.: Site survey for potential MoHole drilling sites in the Guatemala Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8488, https://doi.org/10.5194/egusphere-egu23-8488, 2023.

As the world warms due to rising greenhouse gas concentrations, the Earth system moves toward climate states without historic precedent, challenging societal adaptation. One way to investigate these unprecedented conditions is to study past climates and ecosystems that shar similarities to our current and future ones. One such period is the Eocene (~56 – 33 Ma), during which the climate changed from a hot-house to a greenhouse state, comprising a wide range of atmospheric CO2 concentrations. However, our knowledge of the Eocene climate evolution is incomplete because of a lack of terrestrial records covering the entire period. To address this gap in our understanding, we propose to obtain drill cores at Geiseltal in Eastern Germany as part of the International Continental Scientific Drilling Program (ICDP).

This former lignite quarry is famous for its exceptionally well-preserved Eocene mammal fossils, but its potential as a climate archive has not yet been explored due to the lack of existing drill cores. By drilling a maximum of three cores, we aim to create a spliced 100-120 m long record comprising the entire Eocene archived in Geiseltal as an alteration of lignite seems intercalated with fluvial strata. High-resolution, multi-proxy analyses of the obtained sediments will allow to generate a unique record of (sub)orbital climate variability under various atmospheric greenhouse gas concentrations. The integration of newly developed paleoclimate records with the existing paleoecological data will further help to inform how the terrestrial ecosystems reacted to long-term as well short-term changes, e.g., during hyperthermals. To advance this project, we welcome scientific input from a wide range of disciplines (e.g., stratigraphy, sedimentology, paleolimnology, paleobotany, paleontology, and organic/inorganic geochemistry) as well as are actively seeking interested groups and individuals to collaborate with us on this project.

How to cite: Kaboth-Bahr, S., Bahr, A., and Zeeden, C.: A proposal for drilling “Geiseltal” – a near complete terrestrial section of the Eocene in Central Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9391, https://doi.org/10.5194/egusphere-egu23-9391, 2023.

The Neoproterozoic Era (1000 - 541 Ma) is one of the most dramatic in Earth history: metazoans evolved, the supercontinent Rodinia formed and broke apart, the global carbon cycle underwent high-amplitude fluctuations, oxygen concentrations rose and climate experienced at least two episodes of worldwide glaciation. However, the discontinuous and fragmented nature of outcrop-based studies has hindered developing quantitative models of Earth system functioning during that Era. The Geological Research through Integrated Neoproterozoic Drilling (GRIND) project begins to rectify this scientific shortcoming by obtaining 13 cores through the archetype successions that record this environmental and biogeochemical change.

The specific targets are the Ediacaran-Cambrian transition (ECT; c. 560-530 Ma) in south Namibia (Nama Group), strata of west Brazil (Corumbá Group), and South China (Doushantuo, Dengying and equivalent formations). Drilling in Namibia and Brazil is complete, and drilling in China will commence in 2023. The work aims to 1) construct a highly resolved temporal framework that will lead to the development of age models for the ECT; 2) refine the patterns of biotic evolution of organic-walled and mineralised microfossils, metazoans and trace fossils, and identify the links between and test hypotheses about biological evolution and environmental change, and 3) using fresh, unweathered samples, determine the palaeoenvironmental and biogeochemical conditions that led to the rise of oxygen and distinguish cause-and-effect relationships and basin-specific versus global-scale secular trends in geochemical and stable isotope patterns.

We present sedimentological data from the characterised split cores from Namibia and Brazil, which are permanently archived at an in-country repository as well as the Federal Institute for Geosciences and Natural Resources in Germany. All cores will be available for future research, education and national capacity building activities and mark the first step towards creating an on-shore core archive that will match in stature that of the IODP.

How to cite: Rose, C., Prave, T., Baillie, I., Cantine, M., Kasemann, S., Macdonald, F., Mesli, M., Nduutepo, A., Pruss, S., Trindade, R., and Zhu, M.: Grinding through the Ediacaran-Cambrian Transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9523, https://doi.org/10.5194/egusphere-egu23-9523, 2023.

Marine sediments, obtained from cores and captures from deep sea and continental shelf sites of West Antarctica, contain rich records of latest Miocene to Present glacial and deglacial processes and conditions at the margin of the West Antarctic ice sheet (WAIS). The materials we are investigating were recovered from a) Resolution Drift on the Amundsen Sea continental rise (water depths >3900m), b)the continental shelf in the Amundsen Sea, Wrigley Gulf, and Sultzberger Bay (water depths <1000m). Resolution Drift cores were drilled by IODP Expedition 379 (Gohl et al., doi:10.14379/iodp.proc.379.2021) in sediments dominated by compacted clay and silty clay, with conglomeratic intervals of ice-rafted detritus (IRD) and downslope deposits. The shelf sediments were recovered by piston core, trigger core, and Smith McIntyre Grab (SMG) during USA research cruises of the RVIB Nathaniel B Palmer (1999, 2000, 2007) and USCGC Glacier (1983). The shelf samples are non-compacted clay, containing abundant cobbles, pebbles and biogenic fragments.

Our research focuses upon rock clasts, detrital apatite and zircon, felsic volcanic tephra, and micro-manganese nodules separated from marine and glaciomarine clay. The rock clasts and detrital minerals represent samples of continental crust that we characterise according to rock type, petrology, geochemistry, and geo-thermochronology [U-Pb, (U-Th)/He, and fission track methods]. These characteristics illuminate solid Earth processes, including the development of subglacial topography . We compared clasts’ petrology and age data to the exposed onshore geology and thermochronology of bedrock, and determined that ≥90% of clasts likely originated in West Antarctica. Therefore the materials can be used to assign roughness, erodibility, and heat production factors for subglacial bedrock, which constitute boundary conditions used by ice sheet modelers.

Rhyolite ash and fragments provide new evidence for explosive eruptions (dated ca. 2.55 to 2.92 Ma; feldspar ⁴⁰Ar/³⁹Ar) delivered to sea as airfall, IRD, and possible subglacial water transport. Silicic eruptions produce ash and aerosols that may screen solar energy, and provide bio-available nutrients that produce phytoplankton blooms leading to sequestration of carbon. The rhyolite dates coincide with the end of a Pliocene warm period recorded in IODP379 cores (Gille-Petzoldt et al., 10.3389/feart.2022.976703). Our work in progress seeks to obtain higher resolution geochronology in order to determine whether silicic continental volcanism occurred in response to ice unloading due to deglaciation (cf. Lin et al., 10.5194/cp-18-485-2022) and whether erupted products contributed to latest Pliocene significant cooling and WAIS re-glaciation.

Another distinctive sediment constituent is micro-manganese nodules of unusual form. Whereas typical micro-MN nodules are dark, formed of concentric layers, this form is pale in color, ‘barbell’ shaped, and transparent in transmitted light. Scanning electron microscopy shows these to be microcrystalline Mn-oxide with embedded grains of quartz and feldspar, which likely served as seed material.  Mn-oxides form by authigenesis at/near the seafloor surface, requiring  high oxygen concentrations in the bottom water and low sedimentation rates, generally associated with the end of glacials/during interglacials (Hillenbrand et al. 2021, 10.1029/2021GL093103). Work is in progress to determine whether Mn oxides formed through passive accretion upon seed grains or microbially-mediated precipitation from Mn-oxyhydroxides or colloids, of possible relevance for coastal carbon budgets.

How to cite: Siddoway, C. S., Thomson, S. N., Cavosie, A., Alfaro, J., and Iverson, N.: Inventory of ice-rafted clasts and sediment constituents that pertain to dynamic ice-margin processes and biological productivity, Amundsen Sea region, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9728, https://doi.org/10.5194/egusphere-egu23-9728, 2023.

In the southwest Japan, located at the eastern edge of Eurasian plate, dehydrated water from subducting Philippine Sea Plate from the Nankai Trough issues without magmatic activity as thermal brines. Those brines contain high amounts of mantle derived components, and mercury may be one of those components. Mercury contamination is found in shallow groundwaters (>0.1 µg/kg) and soils (>200 µg/kg) along peripheral active faults of Osaka Basin, where subducting slab from the Nankai Trough appears deeper than the surroundings. Occurrence of the mercury contaminated groundwater also corresponds to the areas of deep low frequency tremor, which is known as a phenomenon occurring in relation to dehydration from subducting slab.

In order to specify the source(s) of mercury above described, mercury concentration and stable isotopes were analyzed for the sediments down to 2200 mbsf (meters below seafloor) taken from drilled cores at Kumano-nada basin IODP Site 0002, where accreted oceanic and forearc sediments are deposited. The mercury concentration, ranging 30-240 µg/kg, except three of 330-820 µg/kg of samples taken from ≥2000 mbsf. The range of 30-240 µg/kg is the same as those of surface sediments of ocean bottom of the study area. The high concentrations seemed due to high contribution of volcanogenic materials. The mercury stable isotopes values, –0.26 to –0.83 ‰ for δ²⁰²Hg and no shift of Δ¹⁹⁹Hg and Δ²⁰¹Hg, indicating geogenic origin without biogenic and/or photochemical alteration. The isotope values are in the similar range of those in the shallow groundwater in the Osaka Basin. The isotope values of δ²⁰²Hg are slightly smaller than that of mantle (0 ‰). These observations would be direct evidence that the mercury deposited in the subducting slab comes up with upwelling fluids.

Ocean scientific drillings have dissolved material cycles and the associating geological phenomenon, especially related to volcanic and seismic activities, at convergent margins related to subduction factory. From the point of views of concentration of useful elements, subduction factory is an important role for formation of ore deposits mainly via magmatic and the associating hydrothermal activities, which also cause the contamination of toxic elements. However, this study gives possible contamination of hydrosphere and pedosphere with toxic elements via non-volcanic tectonic activity.

How to cite: Takeuchi, A. and Masuda, H.: Recycling mercury at a convergent margin from Nankai Trough to southwest Japan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10280, https://doi.org/10.5194/egusphere-egu23-10280, 2023.

Since rare earth elements and Yttrium (REY) were considered critical resources in modern technological and economic industries, deep-sea sediments in the world oceans have started to gain attention as an essential source of REY. In particular, recent studies have discovered that deep-sea sediments in the western North Pacific Ocean near Minamitorishima island have the highest REY concentrations (over 5,000 ppm of REY). In this study, our goals are to identify the existence potential of REY-rich sediment in the South Pacific Ocean and investigate REY abundance and distribution characteristics depending on lithofacies. We acquired the sediment samples from seven sites (U1365, U1366, U1367, U1368, U1369, U1370, U1371) recovered from Integrated Ocean Drilling Project (IODP) Expedition 329. The sediment samples were analyzed for bulk chemical composition, mineral composition, and sedimentary facies. The results indicate that REY concentrations ranged from 53 to 4,177 ppm. U1365 and U1366 sediments showed extremely high REY abundances over 2,000 ppm. On the other hand, U1368 and U1371 sediments showed the lowest contents of REY, less than 200 ppm. Based on the geochemical results, the sediments were divided into six lithofacies: Bioapatite-rich clay, Fe or Mn-rich clay, zeolitic clay, pelagic clay, siliceous ooze, and calcareous ooze. Bioapatite-rich clay with high P₂O₅ content contained the highest REY peak layers (1,141 ~ 4,177 ppm). We observed abundant fish teeth debris in the sediments composed of biogenic calcium phosphate. Fe or Mn-rich clay contained an average of 1,073 ppm of REY, indicating the second-highest abundance among the six lithofacies. XRD analysis and wet sieving results suggested that Fe or Mn originated mainly from goethite derived from hydrogenous and hydrothermal origins. Zeolitic clay and pelagic clay contained an average of 729 ppm and 344 ppm of REY, respectively. In addition, siliceous ooze and calcareous ooze showed an average of 152 ppm and 130 ppm of REY, respectively. These results imply that clay deposits are expected to have high REY contents than biogenic ooze. In addition, it implies that the main host phases of REY from deep-sea clay in the South Pacific are bioapatite and Fe or Mn (oxyhydr)oxides.

How to cite: Kim, Y., Hong, S. K., Kim, Y.-M., Lee, C., and Hong, S.-H.: Rare earth elements and Yttrium (REY) abundances and distribution characteristics depending on lithofacies in the South Pacific sediment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10613, https://doi.org/10.5194/egusphere-egu23-10613, 2023.

Temperature is one of the important parameters to understand complex dynamics, because temperature of the crust is changed by some events such as volcanic activities and a passage of high temperature fluid, which affects physical property, chemical cycle and also microbiosphere. Therefore, information about temperature allow us to understand the dynamics of the active subduction zone.

IODP Site C0023, located at the tip of subduction zone in the Muroto transect of the Nankai Trough, was drilled by IODP Expedition 370. There, we measured the vitrinite reflectance which is an index of the maximum temperature experienced by the sediments. Comparing the measured reflectance and the model values calculated by assuming the past heat flow, it was found that Site C0023 experienced a higher heat flow than the present, which was approximately 160 mW/m². However, the vitrinite reflectance is significantly higher than that in the above model just below the décollement, which suggested that another thermal anomaly originated directly under the décollement in addition to the high heat flow from the basement. With assumptions on the temperature of the heat source and the duration of heating below the décollement, we calculated the vitrinite reflectance in different models.

As a result, it was found that heat source temperature of 200˚C and heat generation duration of 500-1000 years are required just below the décollement to explain the depth distribution of the measured values. At Site C0023, a high pore pressure zone is distributed just below the décollement, which can serve as a path for fluids from deeper part. Considering that the temperature at the depth corresponding to the seismogenic zone in the Muroto area of the Nankai Trough is approximately 200˚C, and that a specific high temperature has not been confirmed just below the décollement of C0023 at present, the origin of the high-temperature fluid would be the deep seismogenic zone. Furthermore, the advection of high-temperature fluids is thought to be intermittent. In other words, the high reflectance just below the décollement is considered to indicate the advection of the high-temperature fluid from deep to shallow areas at the time of past earthquakes.

How to cite: Kamiya, N., Kinoshita, M., Lin, W., Hirose, T., Yamamoto, Y., Bowden, S. A., Tsang, M.-Y., and Tonai, S.: High temperature fluid flow through active décollement at the Nankai subduction zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10649, https://doi.org/10.5194/egusphere-egu23-10649, 2023.

The ICDP STAR drilling project (Strain Meter Array) is a joint research project among different institutions that aims to study the fault slip behaviour of the low angle Alto Tiberina Fault (ATF) in the Northern Apennines, Italy. The ATF is an active low-angle normal fault (mean dip 20°) whose activity and mechanics is still debated. Therefore, STAR drilled and instrumented six shallow boreholes, providing an excellent opportunity to study creep at local scale and over periods of minutes to months, poorly constrained by other geophysical instruments.

Two drilling campaigns were made in Fall 2021 and in Summer 2022, drilling a total of six 80-160 m deep vertical boreholes. Each borehole was instrumented with seismometers (three-component (3C) borehole geophones) and strainmeters (Gladwin Tensor Strainmeters, GTSM).  Strainmeters are the only instruments capable of measuring small creep events, as has been demonstrated near other creeping faults, such as the creeping section of the strike-slip San Andreas fault near Parkfield.

Two boreholes drilled the Mesozoic-Paleogene, Umbria-Marche carbonate succession (Maiolica, Marne a Fucoidi, Scaglia Bianca, Scaglia Rossa and Scaglia Variegata formations). The other four boreholes encountered the Neogene marls and turbidite sandstones (Schlier and Marnoso-Arenacea formations). Upon completion of the drilling operations, a suite of downhole logging measurements was performed in each borehole, comprising: total gamma ray, full wave sonic, electrical conductivity and temperature, caliper, resistivity, optical and acoustic borehole images. The sondes recorded data only in the deepest portion (open section) of the wellbore, except for the total gamma ray that run also in the cased section. The objective was to record the physical properties of the rocks in situ, and to reconstruct the spatial distribution and characteristics of the fractures (i.e. partially open, closed, thickness) and their connection with the geological structures mapped on the surface. 

Here we present a preliminary analysis of the logging data. In the carbonate units (i.e. Maiolica and Scaglia Rossa) the gamma ray shows low and flat curve (less than 30 cps) and P-wave velocity about 3 km/s. In the sandstone-marly units (Marnoso-Arenacea), encountered in three boreholes, the gamma ray records high values (about 80-100 cps) correlated mainly to marly intervals and P-wave velocity of 3-3.5 km/s. The hemipelagic marls of the Schlier Formation are characterized by high gamma ray (mean value of 80 cps) and by an average P-wave velocity of 3.5 km/s. These values will be compared with the results of laboratory analysis of samples, collected in similar lithologies, as well as with the results of logging performed in deeper wells drilled for commercial purposes. Through this comparison, we will evaluate the effect of depth (i.e. pressure) on the main physical properties of sedimentary rocks. The physical properties, in combination with the orientation and geometry of the discontinuities (fractures, veins, bedding), acquired by downhole logging, will contribute in building-up improved 3-D geological models of the ATF.

How to cite: Akimbekova, A., Barchi, M. R., Chiaraluce, L., Johnson, W., Mariucci, M. T., Mirabella, F., Montone, P., Pierdominici, S., and Urbani, M.: ICDP STAR drilling project in Italy: preliminary analysis of geophysical downhole logging data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10947, https://doi.org/10.5194/egusphere-egu23-10947, 2023.

We report preliminary results from drill cores and logging from the ICDP Drilling the Ivrea-Verbano zonE (DIVE) project, Hole DT-1b in Ornavasso (Val d’Ossola, northern Italy). Characterized by pronounced geophysical anomalies, the exposed Ivrea-Verbano Zone in the Italian Alps represents an archetypal lower continental crust section. The first phase of DIVE is dedicated to the drilling and the petrological and geophysical characterization of the lowermost continental crust. Specifically, Hole DT-1b was set in the in the hinge zone of the Massone Antiform to explore the pre-Permian lithologies of the lower continental crust. Hole DT-1b was drilled using the diamond double tube continuous wireline coring method, from October 6 to December 10, 2022, and the retrieved rock cores were inspected and classified by the DIVE drilling project science team. Core recovery was effectively 100% throughout the entire drill hole. In total, 578m of the upper part of the lower continental crust in the Ivrea-Verbano Zone were drilled and cored.

Here we summarize on site visual core descriptions and preliminary geophysical logging and microbiological investigations. The cores mostly consist of amphibolites and garnet-bearing metapelites with variable presence of migmatitic structures, and with local high and low temperature shear zones, pegmatitic dikes, and open fractures.

Continuous monitoring of borehole fluids and gases (OLGA and miniRuedi devices, see EGU abstract by Dutoit and coworkers), and a suite of borehole logging measurements (see abstract by Li, Greenwood, Caspari and coworkers) were performed. They match very well the core logs performed on site (magnetic susceptibility and natural gamma radiation). The most prominent, directly observable deformation feature was a high-temperature foliation, with a dip angle between 30 and 60° in the upper part of the hole, becoming increasingly steeper in the deeper part.

Along the entire drill hole fractures and open cracks were observed, some of them filled with precipitates of quartz, carbonates, sulphides and oxides. These fractures are potentially promising hosts for microbial communities and are currently under investigation. Additional samples for microbiological studies were taken every 20m from the drill cores and are currently cultivated for further investigations.

Hole DT-1b provides detailed insights into the compositional, structural and geophysical variation of metasedimentary continental lower crust, including the distribution of sulphides. Relamination of metamorphic pelitic and mafic rocks may produce an important reservoir of sulphur bearing minerals in the lower continental crust. Further results emerging between abstract submission and the conference will be presented.

How to cite: Müntener, O., Hétenyi, G., Greenwood, A., Ziberna, L., Zanetti, A., Pistone, M., and Giovanelli, D. and the DIVE Drilling Project Science Team: Preliminary results from the ICDP - DIVE project: Hole DT-1b (Ornavasso, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11174, https://doi.org/10.5194/egusphere-egu23-11174, 2023.

Ostracod shells are small aquatic crustaceans (0.3 - 5 mm) capable of recording climatic and environmental changes at high-resolution in sedimentary archives of modern and ancient lakes. Their stable low-Mg calcite shell mineralogy makes them ideally suited for targeted geochemical analyses. Therefore, ostracods represent the best candidate to develop a new carbonate clumped isotope (∆₄₇) lacustrine paleothermometer that disentangles and quantifies the effects of global climate changes at regional scale. To establish the relationship between ∆₄₇ and the temperature for ostracod shells, three different species were collected in monitored environments at 4°C and 12°C and one was cultivated in the lab at 23°C. Our results show a linear regression between ostracod-∆₄₇ and calcification temperature that is in agreement with previous published calibrations. This implies that ostracods are an equally-good recorder of (paleo)temperatures as other carbonaceous micro- or macrofossils from the marine realm. Moreover, we report the absence of a consistent offset between the species Eucypris virens and Bradleystrandesia fuscata coming from the same environment and precipitated at the same temperature. This observation suggests the absence of a vital effect at the genus and species level. Samples from shallow Lake Trasimeno (Italy) cover the last 50000 years and confirm the ability of the ostracod clumped-isotope thermometer as well as the absence of vital effect in the fossil record. The new paleothermometer identifies warmer/colder and humid/dryer conditions during Greenland Interstadial and Greenland Stadial/Heinrich events respectively.

These findings show that the ostracod-∆₄₇ thermometer has several advantages that makes it an attractive tool for scientific drilling: (i) It is independent of ostracod species and geography. Hence, one can also use endemic species.  (ii) It is applicable throughout geological time, as extinct species can be used. (iii) Temperature reconstructions for all environments where ostracods live are within reach. We emphasize that also high-diversity lacustrine environments are suitable for ∆₄₇ analysis, by mixing shells of different species together. This is of particular importance when working with small samples size from sediment cores.

The establishment of this new lacustrine proxy enables precise paleoclimatic reconstructions from different climate belts. It opens the door to new high-resolution continental paleoclimate and paleoenvironmental reconstructions and therefore has the potential to be a key tool in future lacustrine drilling in the ICDP framework.

How to cite: Marchegiano, M., Peral, M., Venderickx, J., Martens, K., García-Alix, A., Goderis, S., and Claeys, P.: The ostracod clumped-isotope thermometer: A new tool to quantify continental climate change., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11373, https://doi.org/10.5194/egusphere-egu23-11373, 2023.

In our study we investigate the subsurface velocity structure of the Cheb Basin (Czech Republic) based on shallow high-resolution 2D seismic data collected in the years 2014-2020. The Cheb Basin is a small intracontinental basin, located in the north-west part of the Bohemian Massif and at the western end of the Cenozoic Eger Rift. The basin and underlying crustal structure are the subject of the ongoing International Continental Scientific Drilling Program (ICDP) “Drilling the Eger Rift''. Our surveys aim to investigate the up to 350-m-thick Miocene and Quaternary sediments and the bedrock, made of Paleozoic Variscan units and post-Variscan granites.

Four datasets were collected, each with a 480-m-long split-spread of single geophones at 2 m spacing. The 2014 dataset was acquired with a 10 m source interval, mainly with a weight-drop source and partly with a SISSY source, resulting in an almost 3 km long profile. The 2017, 2020 line 1 and 2020 line 2 datasets were shot with a buffalo gun at a 20 m source interval. Their lengths are 2 km, 0.8 km and 1 km respectively.

We present the traveltime tomography output for all 4 profiles, which brings important information about the subsurface. The results give us insight into the velocities of the sediments, which in this area mainly range from 600 m/s to 2500 m/s. The bedrock is observed with velocities up to 4500 m/s and is present at a depth of around 250 m below the surface. This velocity information is complimented by the preliminary results of the ongoing reflection processing.

How to cite: Banasiak, N. and Bleibinhaus, F.: Seismic structure of the Cheb Basin from high resolution surveying – traveltime tomography results, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11508, https://doi.org/10.5194/egusphere-egu23-11508, 2023.

The projections of future scenarios under the current trend of global climate change demand a better understanding of the long-term ice-ocean-tectonic interactions, and in particular the potential meltwater contributions from modern ice sheets. The sensitivity of the Greenland Ice Sheet to polar amplification, changes in ocean heat transport and deteriorating perennial sea ice conditions makes the Northeast Greenland margin one of the most critical locations to understand the impact of future climate change on ice sheet instability and associated sea level rise. The development of oceanic gateways controlling the long-term water mass exchanges between the Arctic and Atlantic oceans, notably the Fram Strait and the Greenland-Scotland Ridge, have played a pivotal role for the Cenozoic evolution of the Northeast Greenland regions. In Northeast Greenland, ice-ocean-tectonic interactions and coupling between the ice sheet, ocean and sea ice are readily observable today, but geological records that can illuminate long-term trends are lacking. Consequently, NorthGreen MagellanPlus workshop was organised at the Geological Survey of Denmark and Greenland in collaboration with Aarhus (Denmark) and Stockholm (Sweden) universities in November 2022 as an international effort to develop Mission Specific Platform (MSP) proposals on Northeast Greenland margins under the umbrella of the European Consortium for Ocean Research Drilling (ECORD). For three days, seventy-one participants (56 in person + 15 online) discussed the key scientific questions and primary targets for scientific drilling in Northeast Greenland. Three pre-proposals have been initiated during the workshop targeting Morris Jesup Rise, Northeast Greenland continental shelf and Denmark Straight.

How to cite: Pérez, L. F., Knutz, P. C., Hopper, J., Seidenkrantz, M.-S., and O'Regan, M.: Scientific drilling in Northeast Greenland: Greenland Ice Sheet sensitivity to polar amplification and long-term ice-ocean-tectonic interactions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11575, https://doi.org/10.5194/egusphere-egu23-11575, 2023.

The ICDP Drilling the Ivrea-Verbano zonE project (DIVE), aims at unravelling long-standing fundamental questions on the nature of the continental lower crust, its lithological correlation with geophysical anomalies and the characteristics of the underlying physical and chemical rock properties. Borehole geophysics provides an excellent opportunity and is the method of choice to explore the origin of geophysical anomalies, observed within the Ivrea-Verbano Zone, and their link to lithologies of the lower crust across several spatial scales. The first borehole of the DIVE project DT-1b in Ornavasso, Val’d Ossola (Italy), drilled into the Massone antiform, has been completed in December 2022 at a depth of 578.5 m. Geophysical borehole experiments comprising a suite of downhole logging and vertical seismic profiling (VSP) measurements have been conducted in two stages. A select set of first-look logs were collected to a depth of 315 m and a full suite at the end of drilling. The drilled rock types are metapelite, metapsammite, schist, gneiss, amphibolite, and, in places, migmatite and pegmatite. Several fractures are encountered within the drilled rock mass, exhibiting a NW-SE orientation and a variation of dip angles as identified by acoustic televiewer data. The acoustic televiewer data also show a couple of breakout zones, which may allow to constrain the current stress field orientation after carefully analyzing the impact of the topography. Preliminary results of the wireline logs suggest that they broadly correlate with the different rock types. Notably, the amphibolites as well as some of the more pelitic migmatites and gneiss exhibit locally high values of magnetic susceptibility of the order of 1000 10^-6 SI. These values are confirmed by magnetic susceptibility measurements performed on drilled cores on-site with a self-built manual core scanner. Such high values have been reported in previous studies for amphibolites and mafic granulites in the Ivrea-Verbano zone and are most likely related to pyrrhotite and magnetite. Apart from the amphibolites, for most of the other rock types encountered, a weak correlation between magnetic susceptibility and the natural gamma radiation can be observed. The sonic P-wave velocities and preliminary P-wave velocity estimates of the VSP data are generally consistent. The average P-wave velocity estimate from the VSP is 5.3 km/s and slightly lower than the average estimate of 5.6 km/s obtained from the sonic logs. An integrated analysis of the complete set of the borehole geophysical data is currently undertaken to classify the rock mass with respect to their geophysical responses and to systematically delineate the underlying major factors of influence governing these responses.

How to cite: Li, J., Greenwood, A., Caspari, E., Pierdominici, S., Kück, J., Baron, L., and Venier, M. and the DIVE Drilling project Science team: Drilling the Ivrea-Verbano zonE project: DT-1b borehole geophysics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11796, https://doi.org/10.5194/egusphere-egu23-11796, 2023.

Lake Bosumtwi was created after a meteorite impact 1.07 Ma ago in an area that is highly susceptible for climate changes due to shifts of the tropical rain belt, as well as variation in dust dynamics. The sedimentary sequence records such changes in the tension field between the North African Monsoon (humid, wet) and the Harmattan (dry and dusty winds from the Sahara) and has been intensively studied. Drilling in 2004, supported by the International Continental Scientific Drilling Program (ICDP), recovered downhole logging data and sediment cores that allow for the analysis of the complete ~300 m lacustrine sequence. Yet, detailed climatic and environmental reconstructions for the record have not been completed, mostly due to the absence of a robust age model beyond 500 ka. In 2022, we obtained core scanning natural gamma ray data of the ~300 m lacustrine sedimentary sequence. Based on this data, we are generating an astronomical age model that can be directly compared to the independently dated sections, but extends farther back in time. Our age model will provide critical chronologic context for the numerous existing and new proxy data that illuminate past changes in climate, environment, and ecosystems. This breakthrough will allow a robust framework to analyse climatic interferences with archaeological findings that might shed new light on habitat availability for our ancestors in tropical Western Africa.

How to cite: Vinnepand, M., Zeeden, C., Noren, A., Kaboth-Bahr, S., Gosling, W., Kück, J., and Wonik, T.: Extending the age model for Lake Bosumtwi (Ghana) to reconstruct West African climate and dust dynamics during the last million years, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11822, https://doi.org/10.5194/egusphere-egu23-11822, 2023.

At IODP Site U1407 (SE Newfoundland Ridge, IODP Expedition 342) a 270-m-thick sedimentary succession of Cretaceous and Paleogene age has been recovered. The two holes U1407A and B contain the transition from the reef basement to fine grained (hemi-)pelagic marls at ~270 mCCSF. The basal, incomplete short-cores of these two holes revealed a number of shallow-water fossils such as gastropods, corals, rudists and larger foraminifera (orbitulinids; Norris et al., 2014) from the top of the reef. In addition, a well-developed Cenomanian-Turonian Boundary (CTB) with its typical black shale expression of the Oceanic Anoxic Event 2 is represented in the cores. Here, we present a high-resolution carbon isotope record of the 40-m-thick succession from the top of the reef to the bathyal CTB black shales. Beside the typical δ¹³C anomalies associated with the CTB we identified the decline of δ¹³C values related to the top of the Albian-Cenomanian boundary interval and the Mid-Cenomanian Event. We further present new biostratigraphic results based on calcareous nannofossils as well as ⁸⁷Sr/⁸⁶Sr isotope ages for the top of the reef analyzed on Orbitulina. These new data in combination with the identified, stratigraphically well-calibrated events allow for a detailed comparison with other mid-Cretaceous records around the world and provide new insights into the subsidence history of the western Atlantic margin off Newfoundland.

Reference:
Norris, R.D., et al. 2014. Site U1407. Proceedings of the Integrated Ocean Drilling Program, Volume 342, doi:10.2204/iodp.proc.342.108.2014.

How to cite: Bornemann, A., Friedrich, O., Moriya, K., and Scher, H.: The Albian to Turonian record of IODP Site U1407 (SE Newfoundland Ridge), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11937, https://doi.org/10.5194/egusphere-egu23-11937, 2023.

In 2023, the GEOREAL hydraulic stimulation experiment will be conducted at the KTB deep crustal lab in Windischeschenbach/Germany that originated from the Continental Deep Drilling Program of the Federal Republic of Germany (https://www.gfz-potsdam.de/ktb-tiefenlabor/). The two 4 and 9.1 km deep boreholes were drilled between 1987 and 1994, followed by a long-term experimental program between 1996 and 2005, providing key knowledge on in-situ geomechanical processes and the subsurface at the KTB site. This also led to the foundation of the International Continental Scientific Drilling Program (ICDP) in 1996.

GEOREAL aims at addressing research topics relevant for characterizing the geothermal potential of the metamorphic basement. The two KTB wells provide direct access to a petrothermal fluid reservoir at crustal depth and at temperatures ≥100°C at >3 km depth in the low-permeability rock, typical for large parts of the Earth's crust in Germany. These ambient pressure and temperature conditions are representative for a deep geothermal reservoir and have been extensively studied in the past. GEOREAL builds upon three major injection experiments between 1994 and 2005, during which 150–400 microearthquakes were located in close proximity to the stimulation intervals. The largest induced earthquake of M=1.2 occurred during the phase of highest flow rate. Most of the observed events had M∼0.

The GEOREAL hydraulic stimulation experiment aims at further refining the adaptive reservoir stimulation concept employing near-real-time microseismic monitoring with direct feedback on hydraulic parameters. It will include a series of hydraulic tests at depths ≥3.9 km to investigate the effect of pressure build-up and release, the role of continuous and periodically varying flow rates, the effect of relaxation phases and maximum injection pressure on the spatial propagation of induced earthquakes and the temporal evolution of their magnitudes. This procedure was successfully applied during the 2018 and 2020 geothermal stimulations in Helsinki, Finland. Using a double packer assembly, controlled injection in 15–20 m-long depth intervals, identified through logging will be performed. The goal of GEOREAL is to enhance hydraulic reservoir properties in the KTB pilot hole while avoiding noticeable seismic events. A unique seismic monitoring network will be set up with a 12-level geophone chain in the KTB main hole at only ~300 m distance to the stimulation interval to monitor the fluid injection with high precision. In addition, ≤40 seismometers will be installed surrounding the KTB, including several 45–150 m deep boreholes, and their data transmitted in real-time for rapid evaluation. With this setup, we expect a significantly higher number of locatable microearthquakes than observed during previous injection experiments at the KTB and thus more detailed information on the spatio-temporal propagation of the induced seismicity. A further goal of GEOREAL is to improve existing best practices for technical implementation and to reduce potential risks associated with the technology, thus improving the acceptance of deep geothermal energy in Germany.

How to cite: Boese, C., Dresen, G., Kück, J., Bohnhoff, M., Harms, U., Kamrani-Mehni, S., Zimmermann, G., Sass, I., and Holzförster, F.: GEOREAL: An adaptive stimulation experiment at 3.9 km depth at the KTB deep crustal lab, Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12721, https://doi.org/10.5194/egusphere-egu23-12721, 2023.

Immiscible sulphide liquids, preserved as magmatic sulphide droplets, are believed to strongly control the partitioning behaviour of chalcophile trace elements [1-2]. Hence, the chemical composition of sulphide droplets can be used to understand the fractionation processes of chalcophile elements in magmatic systems that reached sulphide saturation. We carried out LA-ICP-MS analysis of sulphide droplets from gabbros of the lower oceanic crust recovered by deep ocean drilling from mid-ocean ridge spreading centres in the Pacific (ODP147), Indian (ODP176, ODP179, IODP360) and the Atlantic (OPD209 and IODP305) Oceans. For comparison, sulphide droplets from mid-ocean ridge basalts from the East Pacific Rise, Mid-Atlantic Ridge and Southwest Indian Ridge were analysed. Our results show that most gabbros host abundant large magmatic sulphide droplets (mostly above 100 µm up to 1 mm) significantly exceeding those from the related lava units [2-4]. The droplets are commonly associated with or incorporated in olivine or clinopyroxene suggesting an early-stage sulphide saturation but are locally also incorporated in Fe-oxides indicating a later-stage formation during magma cooling [4-5]. The Ni contents of sulphide droplets hosted in gabbros from Hess Deep (Pacific Ocean) are highly variable ranging from ~10 µg/g to weight % levels. Nickel is also strongly controlled by olivine fractionation, and thus can be seen as a parameter indicating whether sulphide saturation was reached before or after the onset of olivine crystallisation. Due to the highly variable Ni contents and in combination with petrographic observations, we suggest that the magma reached early sulphide saturation at Hess Deep, as typically seen in mid-ocean ridge magmatic systems. However, the variable Ni contents in the sulphide droplets indicate that the magma was sulphide-saturated over a longer time span. Alternatively, the magma may frequently switch between being sulphide undersaturated and saturated, due to decreasing pressure during magma ascent accompanied by crystal fractionation at different levels in the crust. Generally, the trace element composition of the sulphide droplets hosted by gabbros from the different drill sites overlap. However, there are significant differences in the compositions of sulphide droplets from lava samples and from associated gabbroic xenoliths [4]. Thus, analysis of droplets from lavas alone provide an incomplete picture of the chalcophile element evolution of the magmatic system. We find no clear differences in sulphide composition with spreading rate or degree of melting as suggested for the silicate melt portion. Instead, the composition of sulphide droplets indicates that fractionation during magma ascent in the crust is the main driver that causes the observed chemical variations, which is part of ongoing investigations.

[1] Wood, B. J. and Kiseeva, E. S. (2015), Earth and Planetary Science Letters, 424, 280-294. [2] Patten, C. et al. (2013), Chemical Geology, 358, 170–188. [3] Peach et al. (1990), Geochimica et Cosmochimica Acta, 12, 3379-3389. [4] Keith, M. et al. (2017), Chemical Geology, 451, 67–77. [5] Jenner, F. E. et al. (2010), Journal of Petrology, 51, 2445-2464.

How to cite: Schäfer, W., Keith, M., Regelous, M., Klemd, R., and Kutzschbach, M.: How scientific ocean drilling helps to decode chalcophile trace element behaviour in mid-ocean ridge magmatic systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12837, https://doi.org/10.5194/egusphere-egu23-12837, 2023.

The mobile Drilling Information System (mDIS) is ICDP’s (Internal Continental Scientific Drilling Program) database management software, initially designed for the acquisition of data gained during a drilling campaign. It is now in use for three years and is by far exceeding its intended application. MDIS has now been installed in core repositories with varying requirements and it is currently been tested for the use as a laboratory data collection application.

The system is based on 25 years of sample and data management at ICDP. It is a database backed web application that is entirely based on open-source code, is platform-independent and has a responsive design. Beyond the basic data registration and management, mDIS provides functionality for QR code label-printing, data export and report generation. Application specific XML export supports International Generic Sample Number (IGSN) registration and data visualization in the “Corelyzer” software (https://cse.umn.edu/csd/corelyzer). Third party software can interface the mDIS through its REST application programming interface (API). Version 3 of the mDIS software features an updated, consistent data model and n:m relations.

Driven by the pandemic, the “expedition mDIS” has mostly been installed as a SaaS (software as a service) variant hosted on a shared ICDP server rather than an offline virtual box application on a personal computer. This solution facilitates training and enhanced support by the ICDP-OSG, it provides continuity by the use of a single project database throughout the project lifespan, and it provides uncomplicated data access to scientists that are currently off-site. Next to the design of further print labels, reports and entry masks for borehole measurements, the most significant extension for the “expedition mDIS” is a digital visual core description allowing for printing a stratigraphic column while simultaneously filling the database. Inspired by a user, our next plan is to develop an add-on for managing sample requests in mDIS.

MDIS has now been implemented in several core repositories (“curation mDIS”), amongst them the Bremen Core Repository (BCR) of the International Ocean Discovery Program (IODP), were curators face up to several thousand samples a week during sample parties. The simultaneous input and processing of large amounts of data lead to new challenges in terms of data handling and database performance. The mDIS has been supplemented with modules to curate and store different sample types, to design and adapt sample series, to add a contact data base and adaptable reports. One of the most important add-ons is the so called “sample-sheet”, which facilitates fast data entry and automated printing of sample labels during large sampling parties.

For more information please visit the ICDP homepage (https://www.icdp-online.org/support/data-samples), the mDIS Documentation website (https://data.icdp-online.org/mdis-docs) or contact us directly. MDIS is open source and as such available for all projects and everybody who is interested.   

How to cite: Heeschen, K., Kunkel, C., Lorenz, H., Bender, V. B., Kuhlmann, H., and Behrends, K.: News on ICDP’s data management system mDIS: experiences, adaptions and extensions after three years of field application and core repository installation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13942, https://doi.org/10.5194/egusphere-egu23-13942, 2023.

The need for constraining future climate scenarios requires a better understanding of how the cryosphere responded to ocean-climate conditions that were warmer than present. The Greenland shelf margins store thick sedimentary packages that may offer detailed information pertaining to ice-ocean-climate dynamics and Arctic ecosystems. A wealth of seismic data acquired since the early nineties has generated numerous subsurface maps and geomorphic studies of expanded sedimentary archives located proximal to the Greenland Ice Sheet. While paleoclimate reconstructions of ice sheet and ocean dynamics have largely been based on North Atlantic deep-water records, the Greenland continental margin will be the focus of forthcoming International Ocean Discovery Program missions such as Exp. 400, NW Greenland margin. The aim of this presentation is to provide an update of the late Cenozoic marine successions that form key targets for understanding cryospheric behavior during warm climate periods, in particular the Miocene-Pliocene interval characterized by contourite drifts and hemipelagic sequences. The significance for pushing knowledge frontiers on Northern Hemisphere climate evolution and Earth System modelling will be discussed. 

How to cite: Knutz, P., Perez, L., and Nielsen, T.: Late Cenozoic sedimentary systems offshore West Greenland providing new insights to ice-ocean interactions during periods of enhanced climate warming, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14109, https://doi.org/10.5194/egusphere-egu23-14109, 2023.

The Ivrea Verbano Zone (IVZ) is one of the most complete crust upper-mantle geological references in the world, an area that the Drilling the Ivrea-Verbano zone project (DIVE) aims to study. Associated with the IVZ, the Ivrea Geophysical Body (IGB) is of particular interest, as it is a structure beneath the IVZ characterized by high seismic velocities and a strong gravity anomaly. Recent studies across the IGB indicate that dense mantle rocks are located at depths as shallow as ca. 3 km. Several geological, geochemical and geophysical studies are planned, including the drilling of a 4 km deep borehole that will cross the crust–mantle transition zone, and provide, for the first time, geophysical in situ measurements of the IGB.

In preparation for the drilling campaign, a seismic survey was performed in October 2020 in collaboration with GFZ Potsdam, Université de Lausanne, and Montanuniversität Leoben. In this study, we present results from a shallow seismic survey across the Blamuccia Peridotite, where the prospective drill site is planned. The survey was carried out with a fixed spread of 200 vertical geophones and 160 3C-sensors, spaced at 11 m along three sub-parallel lines 50-80 m apart. Vibroseis source points were at 22 m stations along a 2.2 km line utilizing a 12-140 Hz 10 s linear sweep with 3 s listening time.

Through the application of 3D traveltime tomography, a shallow velocity model was obtained. The model shows a good correlation with the surface geology and can outline the east and west boundaries of the peridotite body; however, it is not deep enough to interpret its relationship with the mantle. Velocity analyses performed through the tomography process show that the peridotite body must have a P-wave velocity at least greater than 7.3 km/s, which is consistent with the high velocities measured in several laboratory studies from samples throughout the area.

Seismic data show a lack of reflectors from the peridotite body, which could be interpreted in two ways: The peridotite body is attached to the mantle, or its structure is such that reflections from its boundaries cannot be detected by our seismic survey due to its limited aperture. However, a deep reflector was observed in some shot gathers, originating from a depth between 2-3 km from sea level. This corresponds well to the depth of the crust-mantle transition estimated from gravity and receiver function surveys. The shallow 3D velocity was used for the application of refraction statics and the development of a deeper velocity model to perform 3D pre-stack depth migration. Extreme topography, high P-wave velocities, and vertical geological structures present a challenge for the imaging process.

How to cite: Pasiecznik, D., Greenwood, A., Hetényi, G., and Bleibinhaus, F.: 3D Tomography across the Balmuccia Peridotite, Ivrea Zone, Italy - Project DIVE, phase two, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15184, https://doi.org/10.5194/egusphere-egu23-15184, 2023.

The Iberian margin is a well-known source of rapidly accumulating sediment that preserves a high-fidelity record of millennial climate variability. Previous studies of piston cores and IODP Site U1385 demonstrated that surface, and deep-water climate signals from the region can be correlated precisely to the polar ice cores in both hemispheres and with European terrestrial sequences. The continuity, high sedimentation rates, and fidelity of the climate signals recorded in Iberian margin sediments make this region a prime target for ocean drilling. The primary objective of IODP Expedition 397 was to extend these remarkable paleoclimate records beyond the range of existing piston and IODP cores -- currently limited to the last 1.5 million years. To this end, we recovered a total of 6176.7 m of core at four sites (U1586, U1587, U1385, and U1588) arranged along a bathymetric transect (4691, 3479, 2590 and 1339 mbsl, respectively) to intersect each of the major subsurface water masses of the eastern North Atlantic. The bathymetric transect provides an opportunity to study the history of deep-water circulation, ventilation and carbon storage in the deep eastern North Atlantic and its relationship to changing atmospheric CO₂. Sediments from all sites display strong cyclicity in bulk sediment properties, permitting the development of orbitally-tuned time scales and correlation with classic Mediterranean cyclostratigraphy. We will report on existing results from Site U1385 drilled during Expedition 339, new preliminary results from Expedition 397 sites (including the reoccupation of Site U1385), and discuss the future potential of Iberian margin sediments for providing benchmark paleoclimate records for the late Miocene through Quaternary. 

How to cite: Hodell, D., Fatima, A., and Carlos, Z. and the IODP Expedition 397 Scientists: Benchmark sedimentary records recovered from the Iberian margin during IODP Expedition 397 , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16019, https://doi.org/10.5194/egusphere-egu23-16019, 2023.

The use of µEDXRF elemental mapping provides access to data on relatively large core sections within a reasonable time at high spatial resolution down to 20 µm, enabling to link macroscopic to microscopic information, and providing an objective tool to select areas of interest for more sophisticated data acquisition by EPMA, LA-ICP-MS etc. Textural features can be visualized, that hardly are identified with the naked eye e.g. interstitial silicates in massive chromitites of the Bushveld Complex, South Africa. The application of automated mineralogy provides access to local paragenetic changes and to modal analyses of selected areas. Automated mineralogy based on µEDXRF has to overcome a number of obstacles due to aspects of diffraction, depth of information and grain boundary effects. Tools have been developed to limit these aspects within an acceptable error frame by combining the information of two opposing detectors to reduce the side effects of diffraction. By applying a supervised endmember based classification using the spectral angle mapper algorithm of the ENVI hyperspectral software, phase distribution maps can be produced. Within a well-known system such as the UG-2 chromitite mineral names can be attributed to the identified phases. Exceptions exist for very fine grained secondary phases which might show mixed signals. Well-identified phases can be segmented and grain size, shape and orientation of individual grains can be obtained supported by diffraction signals of single grains. Chemical information can further be extracted for individual minerals, individual grains and bulk area corresponding to the modal mineralogy for any selected area. This offers a new approach to interprete (Verb fehlt?) complex textures by comparing chemical and mineralogical aspects of individual textural pattern. The example of mottled UG-2 chromite shows that the hosting silicates of the chromititebasically orthopyroxene and anorthite-rich plagioclase, but within stringers phlogopite, anorthite-poor plagioclase, potassic feldspar, amphibole, quartz with local enrichment of apatite and sulphides, show differences in grain size and chemistry of the chromite. EPMA investigations on chromite show that Cr/(Cr+Al), Mg/(Mg+Fe), and Cr/Fe is controlled by the chemistry of its hosting oikocryst silicates plagioclase or orthopyroxene. The appearance of late inter-oikocryst phlogopites induces a metasomatic loss of titanium in the chromite. By applying several steps of µEDXRF data reduction and phase masking, these changes in chromite chemistry can be visualized despite of the relatively large spot size of 20 µm for large areas. Using this information the metasomatic impact within a continuously µEDXRF mapped half drill core can be visualized and quantified. 

How to cite: Rammlmair, D., Nikonow, W., and Goldmann, S.: Highlighting the metasomatic impact on mottled UG-2 chromitites from the Bushveld Complex (South Africa)  by large-scale µEDXRF mapping., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16429, https://doi.org/10.5194/egusphere-egu23-16429, 2023.

Units of the up to 3.7 km thick Moodies Group (~3.22 Ga) in the Barberton Greenstone Belt, South Africa and Eswatini, comprise some of the oldest well-preserved sedimentary strata on Earth, deposited within only a few million years in pro-deltaic to alluvial settings, with a dominance of tidal deltas and coastal plains. They consist of widespread quartzose, lithic, tuffaceous and arkosic sandstones, polymict conglomerates, common siltstones and shales, and rare BIFs and jaspilites, all interbedded with rare dacitic air-fall tuffs and several lavas. Moodies strata preserve abundant sedimentary structures and represent a very-high-resolution record of Paleoarchean surface processes. Microbial mats, early diagenetic vadose-alteration zones and tidal rhythmites are locally common. Moodies strata provide a unique opportunity to investigate the conditions under which bacterial life spread and thrived in coastal-zone and terrestrial settings on early Earth.

The ICDP Barberton Archean Surface Environments (BASE) Project drilled November 2021 to July 2022 eight inclined boreholes of 280 to 497 m length each through steeply inclined or overturned Moodies Group strata. The unweathered and continuous core record was complemented by sampling in three several-km-long tunnels and by detailed surface mapping. Two to three rigs operated concurrently, delivering twenty to sixty m of high-quality core daily. This core was processed in a large, publicly accessible hall in downtown Barberton. An exhibition provided background explanations for visitors and related this fundamental-geoscience research project to the geology of the Barberton-Makhonjwa Mountains World Heritage Site. The archive half of the core, nearly 3 km total, remained in South Africa, the working half is curated at the ICDP core repository in Berlin, Germany. We show preliminary cross sections, overall core photographs and representative lithologic descriptions.

How to cite: Heubeck, C. and Beukes, N.: Geologic framework and first results from ICDP BASE drilling in the Moodies Group (~3.22 Ga), Barberton Greenstone Belt, South Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17266, https://doi.org/10.5194/egusphere-egu23-17266, 2023.

The characteristics of half-precession (HP) cycles (~9,000 - 12,000 years) are still poorly understood, despite their appearance in numerous records. Previous studies on European terrestrial and marine records indicate a connection of the HP-signal to low latitudes. Here, we investigate HP-cycles in equatorial regions to study the assumed origin of this signal.

Spectral analysis, evolutive approaches and correlation techniques are used on records from ODP Sites 662 and 663 to identify the HP-signal in elemental ratios reflecting e.g. terrigenuous input and/or bioproductivity. Filters have been designed to remove the classical orbital cycles (eccentricity, obliquity, precession), in order to isolate the HP-signal and to determine the temporal evolution of its presence and amplitude.

We present first results of a larger project which has the overall objective to characterize the HP-signal across the Mid-Pleistocene Transition (MPT) at Sites 662 and 663. Over the course of the MPT, the ~100 kyr-eccentricity cycles supersede the 41-kyr obliquity as the primary driver of climate forcing. As precession is modulated by eccentricity, a similar relationship may be assumed for HP and eccentricity. Our preliminary analyses show an enhanced HP-signal in the younger, 100-kyr eccentricity world, but also in the late MPT which is partly influenced by the 41-kyr obliquity cycle. Cyclostratigraphic investigations of high-resolution XRF data will provide a clearer insight into the presence, amplitude and role of HP during the MPT and the late Pleistocene.

How to cite: Ulfers, A., Zeeden, C., Kaboth-Bahr, S., Westerhold, T., and Röhl, U.: Cyclostratigraphic investigations with special emphasis on half-precession signals using XRF-data from ODP Site 663 (Eastern Equatorial Atlantic), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17472, https://doi.org/10.5194/egusphere-egu23-17472, 2023.

High-resolution depositional archives were identified in the contourite drifts developed on the mid-upper slope of the western continental margin of Svalbard (Bellsund and Isfjorden drifts, Vestnesa and Svyatogor ridges) under the persistent effect of the West Spitsbergen Current (WSC). The sediment drifts contain very similar stratigraphic sequences characterised by depositional marker beds (Heinrich-like and meltwater related deposits) outlining a synchronous, almost simultaneous response of the Svalbard-Barents Sea paleo-ice sheet to changing climatic conditions. These observations strengthened the idea that the WSC, transporting warm Atlantic Waters to the Arctic ,was one of the major drivers of the Arctic climate variability and cryosphere evolution in the area.

The considerations made above, inspired the writing of Proposal IODP 985-Full2 that was motivated by the necessity of retrieving continuous, high-resolution, and datable depositional sequences containing the record of the palaeoceanographic characteristics and cryosphere evolution during the past climatic transitions that followed the opening of the Fram Strait in the Arctic. Such data are greatly needed to better constrain global climate connections, forcing mechanisms and climate models. The general objective of 985-Full2 is the reconstruction of the variability of the WSC and its influence on climate changes particularly during key climate transitions (i.e. the late Miocene–Pliocene transition, late Pliocene–Pleistocene Transition, Mid-Pleistocene Transition, Mid-Brunhes Transition, and sub-orbital Heinrich-like events), its impact on the Arctic glaciations, ice shelves development and stability, and sea ice distribution over last 5.3 Ma.The proposal submitted in April 2020 was approved in May 2022 and scheduled as IODP Exp. 403 (June 4^th to August 2^nd, 2024).

How to cite: Lucchi, R. G., Buenz, S., Plaza Faverola, A. A., Vadakkepuliyambatta, S., Knies, J., Rebesco, M., and St. John, K.: The high-resolution paleoclimatic record of the western margin of Svalbard (Proposal IODP 985-Full2), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17524, https://doi.org/10.5194/egusphere-egu23-17524, 2023.

The Deccan volcanic province is extensively studied for the occurrence of the K–Pg boundary, Cretaceous mass extinction, associated climate change and biotic crises. The Late Cretaceous volcaniclastic sediments occurring in between the lava flow, known as bole beds, are often overlooked. These bole beds, however, are useful to understand the paleoenvironmental conditions during non-eruptive phases of Deccan volcanism. A comprehensive study involving field, petrography and mineralogical investigations focuses on a few cm to a few m-thick bole beds of variable lateral continuity.

Field observations of bole beds reveal red to green colour and variable geometry i.e., massive, bedded, lensoid etc. Petrographic study reveals differences in textural and mineralogical characteristics of red and green boles. Red boles show an incipient to moderate degree of pedogenesis. The incipiently pedogenised red boles show the dominance of volcanic lithic fragments (lathwork, microlitic and vitric), scoria, plagioclase, and pyroxene. The moderately pedogenised red boles, show dominance of altered basaltic clasts (100 μm to 5 mm), iron glaebules, alteromorph and oxidized fragments set in the fine-grained clayey groundmass. The green bole, however, shows poor pedogenesis, with predominance of volcaniclastic fragments, plagioclase, pyroxene and opaques. The volcanic glasses and minerals in green boles are thoroughly replaced by green clay. X-ray diffraction study shows presence of hematite and 14 Å smectite in red bole. The green bole, however, contains 10 Å celadonite and 14 Å smectite as major clay minerals. FTIR and VNIR spectroscopy further confirm the slight difference in composition of smectite associated with bole beds, i.e., Fe, Al-rich smectite in red boles and Fe, Mg-rich smectite in green boles. Although the original material for forming red and green boles is basalt-derived, the distribution pattern of green boles is not as extensive as red boles. This indicates difference in the paleoenvironment of formation of the two bole beds. The study of red bole suggests its formation in oxic, subaerial conditions. The relatively thick red bole units (up to a few m), showing gradational contact with lower basalt and distinct pedogenic features, mark prominent breaks in Deccan eruptions. However, the cm-scaled red bole units, showing uneven boundary with lower basalt, and containing abundant volcaniclastic fragments, indicate minor breaks in volcanism. Green boles, on the contrary, indicate confined suboxic conditions in local depressions on the Deccan lava flow.

How to cite: Singh, P., Banerjee, S., and Pande, K.: Paleoenvironmental implications of interbasaltic volcaniclastic sediments within Late Cretaceous Deccan volcanics, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-710, https://doi.org/10.5194/egusphere-egu23-710, 2023.

During the transition from the Paleozoic to the Mesozoic, marine communities went through major changes in clade composition and proportions. A significant shift happened in the proportion between the Paleozoic Evolutionary Fauna and the Modern Evolutionary Fauna. The Permian-Triassic transition also marks the establishment of molluscs as the most diverse and dominant group in marine benthic environments. At the end-Permian, gastropods experienced a mass extinction as all other marine clades, but they showed a remarkable proliferation in the Triassic. As a result, the global species and genus diversity exceeded their maximum diversity during the Permian. However, not all gastropod clades contributed to the remarkable Triassic diversification. Similar to the shift in clade proportions between the Paleozoic and Modern Evolutionary Fauna, the clade proportions within Gastropoda changed at the Permian-Triassic transition as a result of differential diversification and selective extinction. The change in the proportional diversity of individual gastropod clades is most evident in the dwindling of the order Pleurotomariida (Vetigastropoda). Although Pleurotomariida was one of the most diverse and abundant Late Paleozoic gastropod groups, they diversified poorly during the Triassic recovery period compared to other groups. Gastropod diversity peaked in the Carnian (Late Triassic), but many newly evolved Carnian taxa could not pass the upper Carnian boundary, indicating an extinction event in the Carnian. A previous analysis of occurrence data in the Paleobiology Database (PBDB) indicates that among the marine clades, gastropods suffered most from the Carnian biotic crisis. Here, we analyze the generic range through data from the most comprehensive global Triassic gastropod list (2177 species, 429 genera) and the PBDB. The range-through data suggest high extinction rates in the Carnian (45%) compared to extinction rates during previous Triassic ages (5%). The Carnian extinction rates were higher than in the Rhaetian (35%). If singletons are excluded from the analysis, the Carnian still shows the highest extinction rate (16%) when compared with the Early and Middle Triassic ages (1–3%), but lower than in the Rhaetian (33%). Origination rates continuously decrease throughout the Triassic. Shareholder quorum subsampling analysis of the PBDB data indicates that generic extinction rates rose in the Carnian, peaked in the Norian and remained high in the Rhaetian. The analyses of both, range through and occurrence data show persistently high extinction rates throughout the Late Triassic. Altogether the Late Triassic biotic crises seem to impact gastropod diversity as much as the end-Permian mass extinction event.

How to cite: Karapunar, B. and Nützel, A.: Gastropod diversity dynamics at the Paleozoic–Mesozoic transition and the impact of the Carnian biotic crisis on gastropod diversity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1070, https://doi.org/10.5194/egusphere-egu23-1070, 2023.

The 24 species of crocodylians, including crocodiles, alligators, caimans, and the gharial, represent the extant diversity of Crocodyliformes. These species poorly reflect the past diversity of this group. Indeed, extinct crocodyliforms include hundreds of species adapted to semi-aquatic but also to terrestrial and marine environments. Characterization of the factors driving the macroevolutionary history of Crocodyliformes has been difficult partially because of this ecological disparity. Indeed, studies working at a global scale (i.e. at the scale of the Crocodyliformes or more inclusive) have yielded ambiguous or even contradictory results. This highlighted the need for smaller-scaled studies, both from a phylogenetic and stratigraphic point of view.

The work presented here is part of this new framework. It focuses on an extinct group of crocodyliforms, the Notosuchia, at a specific time interval, the Cretaceous-Palaeogene (K-Pg) crisis. This group was chosen because of three characteristics that made it relevant for deciphering the factors explaining extinction/diversification events: (1) it is homogeneous regarding the living environments: almost all notosuchians were fully terrestrial; (2) it exhibits a high degree of ecological diversity with diets ranging from strict herbivory to specialized carnivory, including omnivory; and (3) it crosses a major crisis event, the K-Pg crisis. We tested the impact of body size, using skull length as a proxy, and local palaeotemperature, on the survival/extinction, coded as a binary response variable, at the K-Pg crisis using the phylogenetic logistic regression (PLR). We also investigated the evolution of body size throughout notosuchian evolutionary history and its relationship with diet. The analyses were performed on several sets of dated supertrees of Notosuchia: two different node dating methods were used on two different topologies. Furthermore, each species was dated by randomly picking an age included in its stratigraphic interval and 100 supertrees were produced for each sets (400 in total). This allowed to account for the effect of the stratigraphic and phylogenetic uncertainties. Finally, to assess the effect of the Adamantina Formation, of uncertain age and from which a high number of specimens come from, we performed the PLR analyses on all 4 sets of supertrees, including or not all the species belonging to this formation.

We found that local palaeotemperature does not explain the survival/extinction while body size do when all the species from the Adamantina Fm are considered to have faced the crisis: the larger notosuchians were, the higher their probability of survival was. Furthermore, Notosuchia showed a trend towards larger body sizes during the Cretaceous. This trend is driven by the apparition of specialized carnivorous species having significantly larger body sizes than omnivorous ones. Thus, diet rather than just body size might explain the survival/extinction of notosuchians at the K-Pg crisis. Because the relationship between survival and body size is only significant when all the species belonging to the Adamantina Fm are considered to have faced this crisis, we corroborates previous studies which found this formation to have a Laggerstätten effect.

How to cite: Aubier, P., Jouve, S., Schnyder, J., and Cubo, J.: Diet diversity might explain the differencial survival of Notosuchia (Crocodyliformes) at the Cretaceous-Palaeogene crisis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2567, https://doi.org/10.5194/egusphere-egu23-2567, 2023.

The Smoking Hills Formation of Arctic Canada represents a Cretaceous metalliferous black shale named after auto-combusting exposures in Ingniryuat, Northwest Territories. This area was also named The Smoking Hills by the Franklin Expedition after the ever-present clouds of sulphuric acid smoke produced. Similar burning Cretaceous mudstones occur in Yukon, and northern Alberta, as well as western Greenland (as recorded in the Viking Sagas). These burning shales reflect deposition during OAE 2 and 3 events across the Arctic region. Metal in the Smoking Hills Formation are enriched over 1000x average shale values. The metal concentrations strongly correlate with heulandite content, an alteration product of volcanic glass, suggesting an origin related to volcanic loading. Abundant bentonite beds in the Smoking Hills Formation support deposition during active volcanism. This is further consistent with the eruption history of the High Arctic Large Igneous Province to the north, or Cretaceous arc related volcanics to the west. These metals are now being recycled into the otherwise modern pristine Arctic environment, generating hyper acidic waters (recording negative pH values) with extremely high metal concentrations orders of magnitude higher than safe drinking levels. Cretaceous eruptions are still driving widespread deleterious environmental impact today.

How to cite: Grasby, S., Percival, J., Smith, R., Galloway, J., and Bringué, M.: Volcanos – the gift that keeps on giving, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2881, https://doi.org/10.5194/egusphere-egu23-2881, 2023.

The Paleocene – Eocene Thermal Maximum (PETM) was a global hyperthermal event during which temperatures increased by 6 - 8° C within a few thousand years at the Paleocene - Eocene boundary, and lasted about 250 ka resulting in ocean acidification, anoxia, and marine extinctions. The PETM coincided with the opening of the North Atlantic and the emplacement of the North Atlantic Igneous Province (NAIP). However, because of the short duration of the PETM compared to NAIP volcanism (several Ma), the contribution of NAIP volcanism to these environmental changes is unclear.

Previous studies have used mercury (Hg) enrichments in Paleocene - Eocene sediments as a proxy to link the timing and intensity of NAIP volcanism to the environmental changes at the PETM. However, published Hg and Hg/TOC profiles across the PETM from various locations are different, indicating that Hg is affected by processes other than volcanism. Here we use tellurium (Te), a volatile trace element that is highly enriched in volcanic gas relative to crustal rocks, as an alternative proxy for NAIP volcanism. Te and other trace element concentrations were measured by ICP-MS in sediments from the Fur Formation in Denmark and DSDP Site 550 in the North Atlantic, which span the PETM. Sediments of both study sites are enriched in Te with averages between 200 to 300 ppb and thus exceeding estimated average crustal concentrations of 1 – 5 ppb drastically. In both locations, Te and Te/Nb ratios increase abruptly at the level of the carbon isotope excursion (CIE) onset, remain high during the PETM ‘body’, and decrease towards the end of the main North Atlantic ash phase. The Te variations are not correlated with trace element proxies for anoxia or productivity. The Te data support recent Hg isotope data indicating a brief intense phase of NAIP volcanism initiating at the onset of the δ¹³C excursion and lasting for a few 100 ka. The coincidence of the main volcanic pulse and the CIE onset suggests that the source of the light carbon may be volcanic, rather than metamorphic.

How to cite: Baumann, N. B., Regelous, M., Regelous, A., Adatte, T., Thibault, N. R., Schultz, B. P., and Haase, K.: PETM onset triggered by intense volcanism in the North Atlantic: evidence from tellurium, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5127, https://doi.org/10.5194/egusphere-egu23-5127, 2023.

The Tunguska Basin in East Siberia (Russia) hosts an extensive network of thick sills, part of the Siberian Traps Large Igneous Province. High-precision geochronology links the initial phase of sill emplacement to the end-Permian cascade of environmental catastrophes that almost expunged life on Earth (Dal Corso et al., 2022). The end-Permian atmosphere was impacted by a voluminous cocktail of gases, from CO₂ and SO₂ to halocarbons. Multiple lines of evidence suggest that sills emplaced within the evaporitic and coal-rich series of the Tunguska Basin acted as major contributors to this outgassing. Basin-scale observations and thermal modelling provide evidence of thermogenic gas production and release (Svensen et al., 2018). For the Tunguska sills, whole-rock geochemistry (Callegaro et al., 2021) and micro-analyses track multiple processes of magma host-rock interaction occurring at different levels across the plumbing system and the volcanic basin. Whole-rock trace elements and radiogenic isotopes reveal assimilation of variable crustal lithologies, from the crystalline basement to evaporites and carbonates in the Tunguska Basin. Assimilation of anhydrite-dominated evaporites is confirmed by whole-rocks sulfur isotopes. Assimilation of halogen-dominated evaporites is tracked by detailed mineral analyses of dolerite sills. We found widespread evolved late-stage pockets among the larger plagioclase and clinopyroxene crystals in the Tunguska dolerites. These pockets filled with an evolved, volatile-rich minerals, dominated by biotite and quartz, with minor K-feldspar, chloro-apatite, Cl-rich amphibole, sulfides and occasional baddeleyite and zircon. Biotite in the pockets is extremely enriched in Cl, especially at the rims. Plagioclase surrounding the pockets shows highly albitic rims. These compositions are widespread across the Tunguska Basin, where sills intruded halite- and anhydrite-rich evaporites, and suggest extensive mobilization of crustal halogens and sulfur associated with the emplacement of the sills, along with previously demonstrated thermogenic carbon production. Notably, most investigated sills are geochemically correlated with the phase of Siberian Traps magmatism coeval with the main extinction horizon (Callegaro et al., 2021).

Callegaro S., Svensen H.H., Neumann E.R., Polozov A.G., Jerram D.A., Deegan F.M. Planke S., Shiganova O.V., Ivanova N.A. & Melnikov N.V., 2021. Geochemistry of deep Tunguska Basin sills, Siberian Traps: correlations and potential implications for the end-Permian environmental crisis. Contrib. Mineral. Petrol., 176, 49.

Dal Corso J., Song H., Callegaro S., Chu D., Sun Y., Hilton J., Grasby S.E., Joachimski M.M. & Wignall P.B. 2022. Environmental crises at the Permian–Triassic mass extinction. Nat. Rev. Earth Environ., 3(3), 197–214.

Svensen H.H., Frolov S., Akhmanov G.G., Polozov A.G., Jerram D.A., Shiganova O.V., Melnikov N.V., Iyer K. & Planke S. 2018. Sills and gas generation in the Siberian Traps. Phil. Trans. R. Soc. A., 376:20170080.

How to cite: Callegaro, S., H. Svensen, H., H. Heimdal, T., Deegan, F. M., Jerram, D. A., Polozov, A. G., and Planke, S.: Magma-evaporite interaction in doleritic sills from the Siberian Traps: insights from whole-rock and mineral data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5285, https://doi.org/10.5194/egusphere-egu23-5285, 2023.

Sediment cores from the Mid-Norwegian Margin, IODP Expedition 396 recovered several glendonite (calcite) pseudomorphs after cold-water ikaite, CaCO₃•6H₂O, within sediments deposited during the Paleocene-Eocene Thermal Maximum hyperthermal and the early Eocene greenhouse. This presents an apparent climate paradox, since during this time interval, deep sea bottom water temperatures are not believed to have been lower than c. 10 °C anywhere on Earth, mostly much warmer (Meckler et al., 2022 and references therein), far above temperatures typical for natural ikaite formation (Vickers et al., 2022 and references therein). The glendonites are found in close association with ash horizons from the nearby North Atlantic large igneous province (NAIP), with some actually in the infill of a hydrothermal. This, coupled with the presence of glendonites in sediments of the same age from Svalbard and Denmark (Spielhagen and Tripati, 2009; Vickers et al., 2020), may point to volcanically-driven climate and environmental changes in this region, perhaps on temporal and spatial scales hitherto unresolved by global-scale datasets.

Here, we present reconstructed ikaite crystallisation temperatures from clumped isotope palaeothermometry and biomarker sea surface and air temperature reconstructions from glendonite-bearing horizons in ash-rich sediments at four IODP Expedition 396 sites. We find that the glendonites indicate bottom water temperatures considerably lower than the majority of other localities so far studied for this time interval (0 – 10 °C). The biomarker signals are harder to interpret, but may indicate sea surface and air temperatures significantly lower than many other studies across this time interval. We discuss possible causes and mechanisms for this cooling, and the conditions driving ikaite growth, focussing on whether these both may be linked to NAIP volcanism.

How to cite: Vickers, M. L., Bernasconi, S. M., Peterse, F., Sluijs, A., Ullmann, C. V., Longman, J., Stokke, E. W., Frieling, J., Bajnai, D., Clementi, V. J., Harper, D., Nelissen, M., Brinkhuis, H., Planke, S., Jones, M. T., and Science Party, I. E.: Volcanically driven short-term, regional-scale cooling during the early Paleogene Greenhouse?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5465, https://doi.org/10.5194/egusphere-egu23-5465, 2023.

The end-Permian mass extinction (EPME) is the largest extinction event of the Phanerozoic, but the specific causal pathways, especially in the terrestrial realm, are unresolved. Malformed pollen and spores recovered from the EPME interval have been taken as indicators of extreme environmental stress in terrestrial ecosystems. However, whether they relate to volcanism-driven ozone-layer deterioration and enhanced ultraviolet-B (UV-B) flux, or volcanogenic toxic pollutants including mercury and acid rain, or some combination of the two, remains unclear. Here, we take advantage of a novel palynological proxy, which utilises the ability of land plants to adjust the concentration of protective UV-B-absorbing compounds (UACs) in the outer wall of their reproductive propagules in response to changes in ambient UV-B flux. We analysed UAC abundances in ca. 800 pollen grains from an independently-dated Permian-Triassic boundary section in southern Tibet, in order to infer changes in UV-B-radiation flux at the Earth’s surface during the EPME. Our data reveal an excursion in UACs that coincides with a spike in mercury concentration and a negative carbon-isotope excursion in the latest Permian deposits, suggesting a close temporal link between large-scale volcanic eruptions, global carbon- and mercury-cycle perturbations, and ozone-layer disruption. Because enhanced UV-B radiation can exacerbate the environmental deterioration induced by massive magmatism, ozone depletion is considered a compelling ecological driver for the terrestrial mass extinction.

How to cite: Jardine, P., Peng, H., Marshall, J., Lomax, B., Bomfleur, B., Kent, M., Fraser, W., and Lui, F.: Direct evidence for elevated UV-B radiation and ozone layer disruption during the end-Permian mass extinction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5978, https://doi.org/10.5194/egusphere-egu23-5978, 2023.

The Triassic-Jurassic transition, from the Norian to the Hettangian (corresponding to the Rhaetian), was a critical timespan marked by a series of global environmental perturbations, most notably the end-Triassic mass extinction event (201.6 Ma). Here, we present palynological, mineralogical, geochemical, and sedimentological data obtained from new core material spanning the Upper Triassic to Lower Jurassic in the northeastern Paris Basin. Together, these data give new insights into the link between terrestrial and marine extinctions, and their respective driving mechanism. The Boust core (Lorraine, France) provides a complete succession of marginal marine sedimentation. The δ¹³C_org record from Boust reveals two major C-isotope excursions that, based on the available biostratigraphy, correspond to the Negative-1 (Marshi) and Negative-2 (Spelae) negative isotope excursions. While the Marshi excursion is marked by high abundances of dinoflagellate cysts, the Spelae excursion is marked by an influx of acritarch species. The two excursions bracket an interval of strongly diminished tree pollen abundances and proliferation of fern spore taxa, marking the extinction interval associated with the ETME and forming an equivalent to the Triletes Beds in Germany. This subdivision is confirmed by sedimentological and geochemical results as well as by lithological changes, which are reflecting the development of the depositional environment during the Rhaetian.

How to cite: Kuhlmann, N., van de Schootbrugge, B., Thein, J., Franz, S.-O., and Colbach, R.: Geochemical and palynological evidence for a two-phased end-Triassic mass extinction in the Paris Basin (Lorraine, France), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6742, https://doi.org/10.5194/egusphere-egu23-6742, 2023.

The end-Triassic mass extinction (ETE) ranks as one of the ’Big Five’ biotic crises in Earth history. The processes that led to the ecosystem collapse are thought to have been triggered by the volcanism of the Central Atlantic Magmatic Province (CAMP). However, there is an ongoing debate about which environmental effect was the main trigger for the extinction. Our research aimed to produce a new uranium isotope dataset from the Triassic-Jurassic boundary section of Csővár and to carry out Earth system modelling to understand the role of anoxia in driving the extinction and/or delaying the subsequent biotic recovery.

The uranium isotope ratio (δ²³⁸U) is a novel paleoredox proxy as its application dates back only a few years. The main advantage of the method is that δ²³⁸U measured in limestone is a global proxy, i.e. it provides information on the redox conditions of the whole ocean rather than that of the local basin. It can be used to reconstruct the proportion of the global seafloor that was under anoxic conditions during the deposition of the studied sediment. Our δ²³⁸U measurements were performed on the NEPTUNE Plus™ MC-ICP-MS instrument at the Institute for Nuclear Research (ATOMKI) in Debrecen. The obtained data represent only the second δ²³⁸U dataset from the Triassic-Jurassic boundary worldwide.

The studied Csővár section is suitable for uranium isotopic analyses as the deposition took place in an oxic environment and was continuous across the boundary interval, as proven by biostratigraphy of multiple fossil groups and cyclostratigraphy. The section is of international importance as it was among the first sections in the world where the TJB event was recognized in the carbon isotope record.

We detected a major negative uranium isotope anomaly immediately below the Triassic-Jurassic boundary, which is a global signal and indicates widespread marine anoxia. This anomaly coincides with the previously detected carbon isotope anomaly and Hg peaks, which are associated with the volcanism of the CAMP and mark the extinction horizon. Our results support the hypothesis that volcanism indirectly induced anoxia in the ocean, which may have played a role in triggering the marine ETE.

Using the geochemical data (δ¹³C, Hg, δ²³⁸U) and the astrochronological age constraints of the section, we modelled the coupled behaviour of carbon, phosphorus and uranium cycles after volcanic carbon emissions. The model allowed us to estimate when the anoxic conditions were the most severe in the ocean. Our results suggest that anoxia did not reach its maximum extent during the extinction but only about 200-250 kyr later, when approximately 13% of the global ocean floor may have been depleted in oxygen. This delayed peak of anoxia is probably the result of the later, extrusive phase of the CAMP marked by the prominent Hg peak of the section. Our geochemical and modelling results suggest that marine anoxia played a key role in hindering the biotic recovery after the end-Triassic extinction.

This research was supported by the National Research, Development and Innovation Fund (Project No. K135309).

How to cite: Somlyay, A., Palcsu, L., Kiss, G. I., Clarkson, M. O., Kovács, E. B., Vallner, Z., Zajzon, N., and Pálfy, J.: Extensive anoxia after the end-Triassic mass extinction: uranium isotope evidence from the Triassic-Jurassic boundary section at Csővár, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7978, https://doi.org/10.5194/egusphere-egu23-7978, 2023.

The Cenomanian–Turonian Oceanic Anoxic Event (OAE 2: 94 Ma) marked one of the most severe episodes of climate and environmental change during the Cretaceous Period. The primary feature of this interval was widespread marine anoxia/euxinia, leading to deposition of organic-rich, thinly-bedded, mudstones across the world’s oceans, which in turn caused a pronounced positive shift in δ¹³C of seawater that is recorded (and characterizes) OAE 2 strata worldwide. The event was also marked by climate warming (with superimposed cooling pulses), biotic stress, and terrestrial perturbations such as increased continental weathering. However, the majority of studied records of OAE 2 were deposited in deep-marine Atlantic and Tethyan settings or European epicontinental basins. Thus, the record of environmental change in other locations or environments is less clear.

The Western Interior Seaway (WIS) represented a marine corridor across North America that connected the Arctic and Atlantic marine realms. Thus, understanding the environmental and oceanographic changes in the WIS during OAE 2 is crucial to resolving the wider impact of the event across the global marine realm. Several previous works have focused on sites towards the southern end of the WIS (e.g., Pueblo, Iona Core). In this study, we present a new multi-proxy geochemical dataset from a site in the central–northern part of the Western Interior Seaway: Pratts Landing (western Alberta, Canada). Previous palynological studies have highlighted a southward migration of boreal dinoflagellates during the Plenus Cold Event midway through OAE 2, as well as increased input of terrestrial organic matter. Here, we correlate these data with information from redox, nutrient, and volcanic proxies, and compare the Pratts Landing record with other deep- and shallow-marine records of OAE 2 to gain a wider perspective over the environmental changes that operated in different settings during that time interval. This viewpoint is key for understanding the differences and complexities in how surface phenomena were disturbed during OAE 2, and interpreting geochemical records of different settings during that time interval.

How to cite: Percival, L., van Helmond, N., Plint, G., Papadomanolaki, N., Gao, Y., Goderis, S., and Claeys, P.: Geochemical records of environmental change in the central Western Interior Seaway during the Cenomanian–Turonian Oceanic Anoxic Event (OAE 2), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8959, https://doi.org/10.5194/egusphere-egu23-8959, 2023.

The end-Permian mass extinction, the largest biological crisis in Earth history, is currently understood in the context of Siberian Traps volcanism introducing large quantities of greenhouse gases to the atmosphere. We reconstructed the late Permian to Middle Triassic atmospheric CO₂ record by applying the carbonate paleosol pCO₂ barometer to soil carbonates from sections in northwest China (Xinjiang Province), north China (Henan and Shanxi Provinces), Russia (South Ural foreland basin), South Africa (Karoo Basin), and the United Kingdom (Dorset). Atmospheric pCO₂ shows an approximate 4-fold increase from mean concentrations of 412–919 ppmv in the late Permian (Changhsingian) to maximum levels between 2181 and 2610 ppmv in the Early Triassic (late Griesbachian). Mean CO₂ estimates for the later Early Triassic are between 1261–1936 ppmv (Dienerian) and 1063–1757 ppmv (Spathian). Significantly lower concentrations ranging from 343 to 634 ppmv are reconstructed for the latest Early to Middle Triassic (Anisian). In parallel to the reconstructed rise in greenhouse gas levels, low-latitude sea surface temperatures (SST) increased by 7–10 °C, from 25–28 °C to >35 °C (Joachimski et al., 2020). With the decrease in pCO₂ in the late Spathian to Anisian, SSTs decreased as well (Sun et al., 2012). Thus, pCO₂ as well as SSTs persisted at high levels for almost 5 m.y.

In contrast, pCO₂ reconstructed using the photosynthetic carbon isotope fractionation suggest much lower atmospheric pCO₂ (e.g. Shen et a. 2022), inconsistent with significant warming, while modeling studies suggest up to a 13-fold increase in pCO₂ (e.g. Cui et al. 2021). Most important, the 5 m.y. long episode of elevated pCO₂ suggests that negative feedback mechanisms such as silicate weathering, the most effective mechanism by which to extract CO₂ from the atmosphere and to buffer Earth’s climate, were not effective enough to reduce atmospheric pCO₂ to pre-crisis levels. Instead, marine authigenic clay formation (i.e., reverse weathering) may have been an important component of the global carbon cycle keeping atmospheric pCO₂ at elevated levels during this critical time interval.

References: Cui et al. 2021, PNAS, V. 118, No.37, e201470118; Joachimski et al. 2020, GSA Bull., 132, 427-443; Shen et al. 2022, Nat. Geosc., 15, 839-844; Sun et al. 2012, Science, 338, 366-370.

How to cite: Joachimski, M., Müller, J., Gallagher, T., Matthes, G., Chu, D., Mouraviev, F., Silantiev, V., Sun, Y., and Tong, J.: Atmospheric CO2 history of the late Permian and Early Triassic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9038, https://doi.org/10.5194/egusphere-egu23-9038, 2023.

A large volume of intrusive sills of the Siberian Traps Large Igneous Province (STLIP) is found in the Tunguska Basin, Siberia. These rocks intrude evaporite, carbonate and siliciclastic lithologies, which are sometimes rich in organic material and bear massive coal layers. The interaction of hot basaltic magma with the cold country rocks is considered to have released large volumes of thermogenic volatiles that altered atmosphere composition and had a serious impact on climate and biodiversity (e.g., Svensen et al. 2019). Previous high precision isotope dilution thermal ionisation mass spectrometry (ID–TIMS) U-Pb dates obtained on zircon, baddeleyite and perovskite suggest that the intrusive activity lasted from ca. 251.9 Ma until 251.0 Ma (Burgess et al., 2017). However, the total duration of the intrusive magmatic history, as well as its spatial extent, are not well explored in terms of high precision geochronology, since zircon from a mere 17 sills have been dated at highest precision by ID-TIMS so far.

To enhance the temporal control on the STLIP intrusive history, we extracted accessory minerals from sill samples of 5 borehole sites that have been characterised geochemically (low-Ti basalt, Callegaro et al., 2021), to perform U-Pb ID-TIMS dating. These boreholes are situated between Bratsk and Tura, in an area for which no ID-TIMS geochronology is available so far. These boreholes will help to fill the gap on the western part of the STLIP dataset presented by Burgess et al. (2017). For three boreholes, we were able to extract baddeleyite and/or zircon from three/four stratigraphic levels. First U-Pb data of baddeleyite indicate predominantly young U-Pb dates, in the range of 251.5 Ma down to 250.0 Ma, with a tendency to minor discordance and a range in dates that exceeds expectation for a single growth population. Curiously, the geochemical characteristics of samples analysed from the same boreholes (Callegaro et al., 2021) are interpreted as potentially earliest stage of the STLIP, a mismatch with our preliminary U-Pb dating results. Given the doubts about the robustness of baddeleyite against Pb-loss during secondary processes, we hope to directly compare baddeleyite and zircon U-Pb dates in selected samples. Should the accuracy of baddeleyite U-Pb dates be confirmed through similarly young zircon U-Pb, this would mean that STLIP intrusive activity and related volatile injection (including Hg) into the atmosphere significantly post-dated the Permo-Triassic Boundary and extended into the Lower Triassic (Griesbachian-Dienerian). This fact would question the assumption that Hg spikes in the sedimentary record of South China are necessarily synchronous and can be used as time markers for the biological crisis at around the PTB.

References:

Burgess, S.D., et al. Initial pulse of Siberian Traps sills as the trigger of the end-Permian mass extinction. Nat Commun 8, 164 (2017). https://doi.org/10.1038/s41467-017-00083-9

Callegaro, S., et al. Geochemistry of deep Tunguska Basin sills, Siberian Traps: correlations and potential implications for the end-Permian environmental crisis. Contrib Mineral Petrol 176, 49 (2021). https://doi.org/10.1007/s00410-021-01807-3

Svensen H.H., et al. Sills and gas generation in the Siberian Traps. Phil. Trans. R. Soc. A. 376 (2018). http://doi.org/10.1098/rsta.2017.0080

How to cite: Paul, A. N., Ramezani, J., and Schaltegger, U.: Extending the geochronological record of intrusive rocks of the Siberian Traps Large Igneous Province, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9228, https://doi.org/10.5194/egusphere-egu23-9228, 2023.

The final ~0.5m interval of the Cretaceous-Paleogene (K-Pg) boundary at Bidart (France) constitutes the “Deccan benchmark” interval characterized by taphonomic and geochemical proxies of ocean acidification linked with Deccan volcanism. Planktic foraminifera census and morphometric data reveal a concurrence of dwarfed species, thinner test walls, high test fragmentation of planktic foraminifera and increased relative abundance of Guembelitria spp. Together, these evidences point toward severe biotic stress and a likely calcification crisis in planktic foraminifera in the final ~0.5m (~58 ky) of the late Maastrichtian at Bidart.

In the sediment-water interface, the benthic foraminiferal assemblage increase to a dramatic >100,000 tests/gram, indicating a sediment-starved horizon at the KPB. Interestingly, a sharp increase in the relative proportion of heavily calcified genera like Cibicidoides spp. (~51%), Steinsioeina spp. (~10%) and Coryphostoma spp. (~9%) is also recorded at the KPB. The taphonomic angle to such a record is rejected as the benthic foraminifera fragmentation index does not record the ‘acidification’ event as significantly. Similarly, morphometric analysis reveals average sizes of thick-walled genera like Cibicidoides spp., Steinsioeina spp., Gyroidinoides spp., Praebulimina and Coryphostoma spp. increasing at the KPB and ~0.3m below it. A possible explanation for such a biotic advantage for the individuals building heavily calcified tests could be a carbonate super-saturation led by the extinction of pelagic calcifiers at the KPB. In the benchmark, rare occasions of dwarfing and reduced absolute abundances of calcareous benthic foraminifera imply a lower degree of environmental stress. Similarly, census analysis of agglutinated benthic foraminifera records an increased population within the benchmark, indicating a change in community structure.  Whether such a change is a response to acidification or an artifact of preservation is currently under investigation. Our results support an acidification that was restricted to the surface ocean and resulted in severe (planktic) crisis, with limited effect on benthic foraminifera. This is consistent with a lack of benthic foraminifera extinctions across the K-Pg boundary.

How to cite: Patra, S., Kesen, K., and Punekar, J.: The late Maastrichtian calcification crisis in Bidart (France): a benthic environment perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9769, https://doi.org/10.5194/egusphere-egu23-9769, 2023.

Mercury (Hg) and more recently tellurium (Te) are indicator of large-scale volcanism in marine sediments and provide new insights into relative timing between biological and environmental changes, mass extinctions and delayed recovery. Several studies evaluated the relationship between Hg anomalies in sediments and LIP activity across mass extinction horizons. The bulk (80%) of Deccan Trap eruptions occurred over a relatively short time interval in magnetic polarity C29r. U-Pb zircon geochronology reveals the onset of this main eruption phase 350 ky before the Cretaceous-Tertiary (KT) mass extinction. Maximum eruption rates occurred before and after the K-Pg extinction, with one such pulse initiating tens of thousands of years prior to both the bolide impact and extinction, suggesting a cause-and-effect relationship.

We present a comprehensive high-resolution analysis of Deccan Traps Hg-Te loading, climate change and end-Cretaceous (KPB) mass extinction from a transect, which includes 30 sections deposited in both shallow and deep environments. In all sections, results show that Hg concentrations are more than 2 orders of magnitude greater during the last 100ky of the Maastrichtian up to the early Danian P1a zone (first 380 Ky of the Paleocene). Hg anomalies generally show no correlation with clay or total organic carbon contents, suggesting that the mercury enrichments resulted from higher input of atmospheric Hg species into the marine realm, rather than organic matter scavenging and/or increased run-off. Significant and coeval Hg enrichments are observed in multiples basins characterized by proximal and distal, as well as shallow and deep-water settings, supporting a direct direct fallout from volcanic aerosols. Hg isotope data from Bidart confirm a direct Hg fallout from volcanic aerosols. Te/Th ratios measured in the Goniuk (Turkey), Elles (Tunisia), Gubbio (Italy) and Wadi Nukhul (Egypt) sections show the same trend as Hg/TOC and are consistent with a volcanic origin, albeit a minor extraterrestrial contribution of Hg to the boundary cannot be excluded. Te and Hg are however not correlated with iridium contents in the KPg interval and are consequently not related with impact and maximum eruption rates occurred before and after the K-Pg extinction, with one such pulse initiating tens of thousands of years prior to both the bolide impact and extinction

How to cite: Adatte, T., Regelous, M., Khozyem, H., Spangenberg, J. E., Keller, G., Karabeyoglu, U., Schoene, B., and Khadri, S. F. R.: Timing and Tempo of Deccan volcanism relative to the KPg extinction revealed by Mercury and Tellurium anomalies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11057, https://doi.org/10.5194/egusphere-egu23-11057, 2023.

This study explores sedimentological and stratigraphical implications of glauconites within the upper Cretaceous Mahadek Formation exposed at the Umsohryngkew River section in Meghalaya, India. The succession is overall fining upward, with sandstone dominating the lower part and calcareous shales and limestone bands constituting the upper part of the Mahadek Formation. Glauconite occurs within the impure limestone and shale beds of the upper part of the sequence. The glauconitic section gradationally passes upward to K/Pg boundary above the Mahadek Formation. Textural, mineralogical and chemical analyses were carried out to understand the origin of the glauconite. Petrographic investigation reveals three main types of glauconites, a) pellet b) vermiform c) infilling within bioclasts. The glauconite appears dark green and the long dimension of the glauconite grain averages 200 µm. Occasionally, the glauconite grains may be as long as 500 µm. The glauconite pellets show sharp boundaries and exhibit internal cracks. The content of glauconite grain  is nearly 15-20 % of the rock volume. These are sub-rounded to rounded in shape without showing evidence of transportation. X-Ray Diffraction on air-dried samples reveals very prominent (001) basal reflection at 10.23 Å, with reflections of (020), , , (003) and (060) planes at 4.52 Å, 4.23 Å, 3.66 Å, 3.27 Å, 5.51 Å respectively. On glycolation, the (001) peak shifts from 10.23 Å to 9.95 Å, while  and (003) reflections collapse into one single peak. The peaks get narrower, more symmetrical and sharper after heating the samples at 400^oC. Also, the  and (003) reflections show separations into 3.33 Å and 3.30 Å reflections respectively. The X-Ray diffraction characteristics confirm the pure nature of glauconite devoid of any interstratification. FEG-SEM imaging of glauconite grains shows a perfect lamellar structure and corroborates the X-Ray diffraction patterns of glauconites.  Further, the electron microprobe analyses data show average K₂O content of the glauconite is 6.5 %, suggesting an evolved variety. The Fe₂O_3(total) content varies from 2.9 % to 16.8 %, with an average of 9.9 %. While the average content of Al₂O₃ is 20.3%. The K₂O vs Fe₂O₃ plot (r²= 0.7) shows a strong positive correlation. The inverse correlation (r² = 0.8) between Fe₂O₃ and Al₂O₃ suggests the replacement of Al by Fe at octahedral sites. The averages of MgO, SiO₂ are 3.5% and 52.6% respectively. The evolved glauconite within the shelfal Mahadek Formation demarcates the stratigraphic condensation at the top of the transgressive deposits. The formation of glauconite in the late Cretaceous Mahadek Formation is significant because of its stratigraphic preference close to the K/Pg boundary.

How to cite: Borgohain, D., Phukan, S., and Banerjee, S.: Glauconitization within the late Cretaceous Mahadek Formation and its stratigraphic implications., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11099, https://doi.org/10.5194/egusphere-egu23-11099, 2023.

The Cenomanian–Turonian boundary (CTB; ~94 Ma) marks a period of extreme climate warming, the highest sea-levels of the Phanerozoic, and a turnover in marine microfossils and macroinvertebrates. This boundary interval is marked by black shales that mark a global carbon cycle perturbation and the Oceanic Anoxic Event-2. However, the identification of OAE-2 is complicated by the frequent absence of black shales and/or age diagnostic fossil species, and diagenetic overprinting of δ¹³C data. This warrants a systematic investigation of other biostratigraphic indicators of the OAE-2 crisis. This study investigates the stratigraphic utility of a microgastropod-dominated shell bed as a key marker within the OAE-2 interval.

A regional lensoidal microgastropod-dominated shell bed (2 to 10 cm thick) is observed in the shallow marine carbonate sequence the of Bagh group of sediments (Narmada basin) in the Karondia, Soyla, Jeerabad, and Rampura outcrops near Manawar, India. Previous reports suggest a Turonian age based on ammonite biostratigraphy. We test the hypothesis that the microgastropods indicate biotic stress in shallow marine environments due to OAE-2. The age diagnostic planktic foraminifera are absent. However, low-diversity benthic and planktic foraminifera assemblages with low oxygen-tolerant species confirm biotic stress in Nodular Limestone Formation. Microfacies studies indicate a low-energy supratidal to upper intertidal environment of deposition for the Nodular Limestone Formation, which bears the microgastropod shell bed. The occurrence of microgastropods in association with opportunist planktic foraminifera (e.g., Muricohedbergella, Planoheterohelix) indicate a pioneering palaeocommunity of generalists that colonized new ecospace on the shelf created by the late Cenomanian-early Turonian transgression in the Eastern Narmada Basin. Similar and coeval microgastropod shell beds have been reported from the Tethyan marginal sites of the Western Saharan Atlas of Algeria (Whiteinella archeocretacea zone, CTB interval), Eastern Desert of Egypt (Vascoceras proprium zones, lowermost Turonian) and Upper Benue Trough, Northeastern Nigeria (Turonian). The diachronous occurrence of microgastropod shell beds at various Tethyan marginal sites may be due to a regional offset in the timing of marine incursion. 

How to cite: Charthamkudam Prakasan, S., Punekar, J., and Singh, B.: Eustatic and environmental implications of a microgastropod shell bed in the Cenomanian–Turonian boundary interval in the Narmada Basin (India), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11120, https://doi.org/10.5194/egusphere-egu23-11120, 2023.

The end-Triassic mass extinction (ETME; c. 201.6 Ma), one of the so-called “big-five” mass extinctions in the Phanerozoic era, is associated with widespread marine anoxia, ocean acidification, global warming, carbon cycle perturbations (δ¹³C) and an extinction of diverse marine and terrestrial groups. This extinction is frequently linked to the volcanic activity in the Central Atlantic Magmatic Province (CAMP) which is often cited to explain e.g., the correlative negative carbon excursions across many sections, mutagenesis of land plants by Hg-toxicity, and enrichment of Hg/TOC. Despite this, the exact identification of a volcanic signal in many of these sections is not well constrained. In this study we present high-precision platinum group element (PGE: Ir, Ru, Pt, Pd) and Re data for the Triassic-Jurassic boundary succession at the Kuhjoch section (Austria). These are the first results from our new analytical setup using high-pressure asher digestion, isotope dilution and multi-collector inductively-coupled plasma mass spectrometry for precise determination in low concentration (e.g. ppt) samples such as sediments. The PGE and Re concentrations and patterns vary significantly with stratigraphy. The c. 13 m of clayey sediments above the onset of the extinction (marked by the c. 16 cm thick T-bed) show pronounced enrichment in Pt, Pd and Ir concentrations relative to the under- and overlying carbonate dominated stratigraphy. Their PGE patterns are non-chondritic with Pd/Ir and Pt/Ir similar to CAMP basalts. Normalised for lithology (Al₂O₃), however, there are no significant variations in Pt, Pd and Ir values below, within and above the clayey sediments. Re and Ru are, however, depleted compared to the other PGEs in the clayey interval, something also observed in some CAMP basalts. One possibility is therefore to interpret the PGE-rich, clayey sediments, including the main extinction interval in the basal portion, as recording increased weathering of CAMP basalts. As the PGE enrichment increases up through the T-bed, this could show that the onset of CAMP weathering and mass extinction would have therefore coincided. However, further work is needed to identify the relative role of CAMP volatile emission during volcanic activity versus post-eruption weathering of basalts.

How to cite: Mortensen, H., Andreasen, R., Bodin, S., Sanei, H., Ulrich, T., Richoz, S., Lindström, S., Luguet, A., Tanner, L., and Tegner, C.: Platinum-group elements of the Kuhjoch section (Austria) link the onsets of weathering of the Central Atlantic Magmatic Province and the end-Triassic mass extinction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11171, https://doi.org/10.5194/egusphere-egu23-11171, 2023.

Mercury concentration anomalies in sedimentary successions are widely considered as proxies for volcanism and together with negative carbon isotope (δ¹³C) excursions, are a common feature of many Permian-Triassic boundary (PTB) sections ^1,2. On the basis of a temporal overlap of these geochemical excursions with the Permian-Triassic mass extinction (PTME) interval and PTB at the stratigraphically condensed Meishan PTB Global Stratotype Section and Point (GSSP), Hg and/or C- isotope excursions occurring stratigraphically close to the PTB are often used as chemostratigraphic markers for the extinction interval ². However, several studies indicate that near-PTB Hg anomalies vary in their stratigraphic occurrence and expression ³; a point also noted for PTB δ¹³C records ⁴. Permian – Triassic sedimentary successions are also frequently characterized by an unconformity straddling the PTB and/or by stratigraphic condensation, questioning the robustness of PTME correlations based on these geochemical markers. This study investigates the terminal Permian to earliest Triassic Hg and δ¹³C record, coupled with U-Pb zircon geochronology, for two stratigraphically continuous deep-water marine sections in the Nanpanjiang Basin, South China. The results show an interval of significant Hg enrichment stratigraphically close to the PTB, which is coeval with the nadir of a negative δ¹³C excursion spanning the Changhsingian to Induan. U-Pb zircon geochronology of volcanic ash beds interbedded with sediments in the studied sections indicate that the onset of this Hg anomaly postdates 251.82 ± 0.060 Ma, and that the peak of the Hg anomaly (and nadir of the negative δ¹³C excursion) is of Griesbachian age (between 251.59 ± 0.052 Ma and 251.67 ± 0.079 Ma). The peak of the Hg anomaly and nadir of the δ¹³C excursion in these stratigraphically continuous marine successions post-date both the PTB (251.90 ± 0.024 Ma) and mass extinction interval (251.94 ± 0.037 Ma – 251.88 ± 0.031 Ma) as determined from the Meishan GSSP ⁵. Our results indicate that stratigraphical correlation of the extinction interval based on Hg anomalies and/or δ¹³C excursions occurring stratigraphically close to the litho- or bio-stratigraphically determined PTB should be interpreted with caution. Furthermore, this study emphasizes the importance of precise and accurate U-Pb zircon ages for stratigraphic correlation between spatially disparate localities, especially during periods of notable environmental perturbations and biotic turnover such as the Permian-Triassic transition.

References

1             Korte, C. & Kozur, H. W. Carbon-isotope stratigraphy across the Permian-Triassic boundary: A review. J Asian Earth Sci 39, 215-235 (2010). https://doi.org:10.1016/j.jseaes.2010.01.005

2             Shen, J. et al. Evidence for a prolonged Permian-Triassic extinction interval from global marine mercury records. Nat Commun 10, 1563 (2019). https://doi.org:10.1038/s41467-019-09620-0

3             Sial, A. N. et al. Globally enhanced Hg deposition and Hg isotopes in sections straddling the Permian-Triassic boundary: Link to volcanism. Palaeogeogr Palaeocl 540, 109537 (2020). https://doi.org:10.1016/j.palaeo.2019.109537

4             Shen, S.-Z. et al. A sudden end-Permian mass extinction in South China. GSA Bulletin 131, 205-223 (2019). https://doi.org:10.1130/B31909.1

5             Burgess, S. D., Bowring, S. & Shen, S. Z. High-precision timeline for Earth's most severe extinction. Proc Natl Acad Sci U S A 111, 3316-3321 (2014). https://doi.org:10.1073/pnas.1317692111

How to cite: Edward, O., Paul, A. N., Bucher, H., Adatte, T., Schaltegger, U., and Vennemann, T.: Mercury (Hg) anomalies and carbon isotope excursions as a stratigraphic marker for the Permian – Triassic mass extinction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11420, https://doi.org/10.5194/egusphere-egu23-11420, 2023.

The Cretaceous-Palaeogene (K-Pg) boundary interval is marked by the mass extinction of more than 50% of the larger more specialized Cretaceous planktic foraminifera, followed by the extinction of ~33% generalist species (short-term survivors) (Keller and Abramovich, 2009 Punekar et al., 2014). Adaptation strategies identified in Cretaceous planktic foraminifera assemblages within this biotic-stress interval include changes in the community structure through shifts in abundance of species and diversity decline. Changes on a species level are reported as inter- and intra- specific dwarfing, malformation and test-wall thinning. Guembelitria cretacea is typically small sized triserial species identified as the only long-term survivor of this event. Through this study, we test the ocean acidification hypothesis of the late Maastrichtian planktic stress by understanding the link between species carbonate demand and their survivorship at the K-Pg boundary.

Four-dimensional X-ray microscopy (FDXRM) scans of pristine Cretaceous planktic morphogroups (the globotruncanids, the rugoglobigerinids and the planoheterohelicids) from pristine late Maastrichtian zone CF4 of DSDP 525A (South Atlantic) yield the most accurate estimation of their respective test calcite volume. The average test weights and the FDXRM reference estimates together suggest that the scaling of calcium carbonate for globotruncanids, planoheterohelicids, rugoglobigerinids, w.r.t. the guembelitrids is 10-269ug, 6-28ug and 9-60ug respectively. This scaling is significant in context of the observed survivorship of these morphogroups across the K-Pg boundary interval. The new results establish a preliminary link between the carbonate demand, ocean acidification related carbonate crisis (especially in the late Maastrichtian biozone CF1) and the survivorship of these morphogroups. However, other detrimental environmental factors in this critical stress interval cannot be ignored.

How to cite: Kesen, K. and Punekar, J.: Survivorship of Planktonic Foraminifera in the Cretaceous-Palaeogene Transition: A Carbonate Demand Perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11589, https://doi.org/10.5194/egusphere-egu23-11589, 2023.

Large-scale volcanic activity during the formation of large igneous provinces (LIPs) were contemporaneous with almost every mass extinction event in Earth’s history, and LIP activity is believed to have caused or contributed to at least three, if not all, Big Five mass extinctions. However, compared to the marine fossil record, the effects of the volcanism on the terrestrial plant record is still poorly understood. Extinctions in the animal record during major biotic crises in Earth history are not mirrored by comparable major changes in land plants. Despite being sedentary organisms land plants have evolved adaptations to cope with adverse changes in the environment which may provide autecological advantages compared to animals. Despite their remarkable resilience, land plant communities were still affected in multiple ways during LIP-induced extinction events. During the end-Triassic mass extinction (201.56–201.36 million years ago) emissions of greenhouse gases, sulfur dioxide and aerosols, halocarbons, polycyclic aromatic hydrocarbons, Hg and heavy metals from magmatic activity, as well as sea-level changes, during the emplacement of the Central Atlantic Magmatic Province (CAMP) are considered to have severely stressed land plants. This is exemplified by major changes in ecosystem structure in palynological records, a rise in microscopic charcoal abundance indicating increased wildfire activity, enhanced reworking of palynomorphs indicating increased soil erosion, acid rain damages on macroplant leaves, and increased abundances of abnormal spores and pollen indicating mutagenesis from Hg-toxicity and/or ozone layer depletion. Several of these land plant responses have also been observed during other extinction events contemporaneous to LIP activity. Here, we compare and discuss some of the changes in common between different biotic crises to evaluate whether there is a common pattern or not.

How to cite: Lindström, S., Galloway, J. M., Tegner, C., Bos, R., and van der Schootbrugge, B.: Land plant responses during extinction events linked to large volcanic eruptions – is there a common pattern?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12194, https://doi.org/10.5194/egusphere-egu23-12194, 2023.

The Central Atlantic Magmatic Province (CAMP) eruptions are generally regarded as the main driver of major environmental change and mass-extinction across the Triassic-Jurassic (T-J) boundary (~201.3 Ma). CAMP emissions have been invoked as the main trigger for the formation of abnormal pollen and spores during the end-Triassic crisis that may have led to forest dieback and proliferation of pioneer species. Proposed scenarios include extensive climate change leading to wildfire activity, acid rain, and increased UV-B radiation due to ozone depletion. More recently, volcanogenic mercury (Hg) has been implicated in the occurrence of mutations in fern spores. However, Hg-dynamics in deep-time remain poorly understood and require further examination. Here, we explore a new long-term (Rhaetian to Sinemurian) bulk Hg-concentration record combined with Hg-isotope data to understand the link between floral turnovers and the Hg-cycle.

Shallow marine sediments sampled from the Schandelah-1 core in northern Germany contain a record of cyclical shifts in malformed fern spores coinciding with fluctuations in carbon isotopes, increased levels of weathering, and Hg-enrichments. Similarly, increased mutagenic spore abundances with accompanying Hg-isotope records confirm the volcanogenic origin of Hg at the T-J boundary, showing a sharp positive excursion in mass-independent fractionation (MIF) of odd-numbered Hg-isotopes. Hettangian cyclicity is clearly reflected in the Hg-isotopic signals, showing positive excursions in mass-dependent/independent fractionation records (d²⁰²Hg and D¹⁹⁹Hg) during periods of sedimentary Hg-enrichment. In addition, the Hettangian Hg-isotopic signature clearly deviates from Rhaetian signatures, which hints at climate-controlled mechanisms being responsible. Atmospheric Hg-loading via volcanism can explain the synchronous enrichments of Hg concentrations at the T-J boundary interval in multiple sites across the globe. In contrast, the origin of this periodic Hg-loading is more difficult to pinpoint, but it becomes clear that Hg is showing shifts in speciation and closely tied to terrestrial vegetation development. Orbitally induced changes to the regional hydrological regime, resulting in increased wildfire activity, monsoonal intensity, and soil erosion, potentially redistributed Hg stored in soil and/or bedrock reservoirs causing a shift to more mobile Hg-species. Overall, this shows a more dominant role of climate-induced Hg-remobilisation, rather than direct volcanic emissions, to disturbance in terrestrial vegetation.

How to cite: Bos, R., Zheng, W., Lindström, S., Sanei, H., Waajen, I., Fendley, I., Mather, T., Sluijs, A., and van de Schootbrugge, B.: Climate-driven Hg-remobilisation triggering long-term disturbance in vegetation following the end-Triassic mass-extinction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12914, https://doi.org/10.5194/egusphere-egu23-12914, 2023.

Continental breakup in the NE Atlantic was associated with mafic magmatism recorded by basalt flows, volcanogenic sediments, magmatic underplates, and intrusive sheet complexes in the nearby sedimentary basins and continental crust. The voluminous magmatism is concomitant with the global hot-house climate in the Paleogene, and the injection of magma into organic-rich sedimentary basins is a proposed mechanism for triggering short-term global warming during the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma). IODP Expedition 396 drilled 21 holes along three transects on the mid-Norwegian continental margin to sample 1) Paleogene sediments along the Vøring Transform Margin and in hydrothermal vent complexes, and 2) basalt deposits from the Vøring Marginal High into the oceanic Lofoten Basin. A total of 2 km of core were recovered, including more than 350 m of basalt, 15 m of granite, and 900 m of late Paleocene to early Eocene sediments. Wireline logging data were recorded in eight holes. All the sites were located on industry-standard 2D and 3D seismic data. In addition, high-resolution seismic data were acquired in 2020 and 2022 over all the 21 Expedition 396 boreholes and 5 legacy ODP/DSDP sites using R/V Helmer Hansen. The seismic surveys included three P-Cable 3D cubes covering the 14 boreholes on the Modgunn (5), Mimir (5), and Skoll (4) transects. A comprehensive core-log-seismic integration program is ongoing for each site, based on an integration of high-resolution biostratigraphy, core and log based petrophysical data, and seismic modelling. The expedition recovered the first sub-basalt cores on the mid-Norwegian continental margin, recovering 15 m of granite. It furthermore collected the first samples from an Outer High at Site U1574, recovering both pillow basalts and hyaloclastites. These cores documented a shallow marine depositional environment of the emergent Eldhø volcano located near the foot of the Vøring Plateau. Finally, we drilled five holes through the upper part of a hydrothermal vent complex with a very expanded Paleocene-Eocene Thermal Maximum (PETM) interval dominated by biogenic ooze and volcanic ash deposits, documenting the temporal correlation of intrusive breakup magmatism in the Vøring Basin and a major hypothermal event. Collectively, the Expedition 396 sample archive offers unprecedented insight into tectonomagmatic processes in the NE Atlantic, including links to both rapid and long-term climate variation in the Paleogene.

How to cite: Planke, S., Berndt, C., Zarikian, C. A. A., Huismans, R. S., Bünz, S., Faleide, J. I., Lebedeva-Ivanova, N., Zastrozhnov, D., and Scientists, E.: Breakup Magmatism and Paleogene Paleoenvironment: Initial Results from IODP Expedition 396 on the Mid-Norwegian Continental Margin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13260, https://doi.org/10.5194/egusphere-egu23-13260, 2023.

The end-Permian mass extinction occurred during an interval of extreme global warming caused by enormous greenhouse gas emissions from Siberian Traps volcanism. A common concomitant effect of global warming is ocean deoxygenation which can be observed in geological and modern times. In the case of the end-Permian mass extinction, marine anoxia has long been postulated as one of the key killing mechanisms. However, causes for the Permian-Triassic (P-T) deoxygenation are under debate. Two frequently invoked scenarios are eutrophication and ocean stagnation.

We present geochemical data from two P-T carbonate sections across the Paleotethys Ocean. Productivity-related proxies (reactive P, TOC and trace elements) indicate high organic matter and P export to the sediments during the late Permian. A decrease in all these proxies during the C. yini conodont Zone suggests a decline of marine primary productivity at the study sites, approximately 30 kyr prior to the main marine extinction interval. Moreover, C/P ratios document a switch from intense P-recycling to efficient P-burial. Above the C. yini conodont Zone, Ce-anomalies (measured on the carbonate fraction of our samples) shift from negative to positive revealing deoxygenation of the local water columns.

Our proxy data imply that low productivity coincided with anoxic conditions at the study sites, hence not supporting a eutrophication scenario as a cause for the intensification of anoxia. Instead, we argue that ocean stagnation caused a stably stratified water column with reduced mixing, upwelling, overturning and ventilation. Regenerated P was trapped in the deeper, aphotic zones of the stagnant Paleotethys Ocean and was not available for photosynthesis.

We suggest that those settings of the Paleotethys Ocean represented by our study sections (deep slope and distal carbonate ramp) were characterized by high productivity and well-ventilated conditions during the relatively cool late Permian. Prior to the marine extinction interval, conditions switched to a low-productivity-anoxic state which persisted into the Early Triassic. This productivity collapse likely resulted in food shortage for higher trophic levels further stressing heterotrophic organisms before and during the extinction event.

How to cite: Müller, J., Sun, Y., Yang, F., Regelous, M., Fantasia, A., and Joachimski, M.: Marine primary productivity and redox conditions during the Permian-Triassic transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13316, https://doi.org/10.5194/egusphere-egu23-13316, 2023.

In the Siberian Traps Large igneous province (LIP), the emplacement of magma in sedimentary strata led to explosive release of volatiles and the formation of large pipe structures with explosion craters. Of the hundreds of pipes present, several still have preserved crater lake sediments, representing the only known end-Permian sedimentary archive proximal to the Siberian Traps. Here we present new data from a core from the best studied crater lake section, the October pipe/crater located west of Bratsk in East Siberia. The S26 core contains 505 meters of sediments and in order to investigate the geochemical processes in the lake and the possible role of brine influx from the breccia pipe below, we have analysed carbon isotopes, the mercury content, δ³⁴S and δ⁵⁶Fe in pyrite and δ⁵⁶Fe in magnetite, from the breccia pipe and crater sediments. In addition, reference samples from two other breccia pipes and relevant sedimentary strata from the Tunguska Basin were analysed for comparison. Our previous work has shown that the lake was saline, stratified and anoxic/euxinic, with up to 4 wt.% TOC, and abundant framboidal pyrite. The sediments are dominated by sandstone and siltstone, sourced from the material ejected during the pipe formation, and have not experienced heating above ca. 50 °C. The basal deposits are coarse and contain reworked magnetite-apatite ore that originally precipitated from hydrothermal fluids within the upper parts of the pipe. The sediments are calcite-cemented and the volcanic minerals altered to clays and zeolites, with occasional oxidized zones showing that the water level fluctuated, in accordance with rapid subsidence resulting from dissolution of deeper-seated Cambrian evaporites. New results show a marked shift in the isotope systems from the breccia pipe and into the basal lake deposits. The δ³⁴S shifts from background sedimentary values (+20-30‰) in the pipe breccia, to -7-0‰ in the lower half of the lake sediments followed by an increase to +20 ‰ towards the top of the lake. The trend is evident in the δ⁵⁶Fe in magnetite as well, with a 0.4 ‰ negative shift from the breccia and into the lake sediments, followed by an upward increase in the stratigraphy. We suggest that basinal brines rich in iron and sulphate were partly reduced in the stratified lake, leading to pyrite precipitation and isotope fractionation. The data shows the interplay between lake processes and fluid seepage from a hydrothermal system, making these deposits unique for understanding the consequences of LIP formation.  

How to cite: Svensen, H. H., John, T., Polozov, A. G., Callegaro, S., Jones, M. T., Newton, R. J., Fristad, K. E., and Planke, S.: Carbon, sulphur, and mercury geochemistry in a crater lake in the Siberian Traps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14142, https://doi.org/10.5194/egusphere-egu23-14142, 2023.

The extensively studied Cretaceous-Palaeogene (K-Pg) boundary mass extinction of planktic foraminifera (~66 Ma) has been linked with two catastrophic triggers: the Chicxulub impact (Gulf of Mexico) and Deccan volcanism (India). All the studies of the past three decades have focused on the climate shifts and faunal stress at the K-Pg boundary, and in the final ~200 ky preceding it. However, it is critical to study the events that precede the age and influence of Deccan volcanism to gain perspective on the true magnitude of the biotic crisis at the boundary. This study presents a new high-resolution (at 20-cm intervals) climate and faunal dataset of the entire late Maastrichtian record at the DSDP Site 525A (Walvis ridge, South Atlantic). The DSDP Site 525A offers a relatively continuous sediment record of the late Maastrichtian with near-pristine planktic foraminifera for faunal and stable isotopic analyses, excellent magnetostratigraphy and potential for cyclostratigraphy.

            Our results reveal sediments spanning biozones CF1 through CF7 of the Maastrichtian, a duration of ~6 myr. The updated biozone boundaries have been used to infer the relative ages of the observed faunal and climate shifts. The seven important late Maastrichtian climatic events (E1-7) are clearly identified in stable isotopic (δ¹³C and δ¹⁸O) records of planktic (Rugoglobigerina rugosa) and benthic foraminifera (Cibicidoides cf.). Of these, events E-2, E-4 and E-6 represent relatively warmer climate, whereas events E-1, E-3, E-5 and E-7 are colder climate. Events E-2, E-4 and E-7 correspond to the globally recognized Deccan warming event, mid-Maastrichtian event (MME) and Campanian-Maastrichtian Boundary Event (CMBE), respectively. Based on isotope records, the late Maastrichtian corresponds with four climate shifts. Faunal analysis reveals these events are bracketed within four biozones (CF1-4) and have a species richness of ~50 planktic foraminifera. The census analysis reveals a slightly decreasing diversity in E-4 followed by a uniform diversity in E-3. Further, E-2 witnessed a sharp fall in the diversity trend that reduced to an all-time low of ~20%. Most planktic species (globotruncanids) get extinct in E-2 following the diversity drop. However, Hedbergella spp., Pseudoguenbelina costulata, P.  hariaensis, Heterohelix globulosa, H. rajagopalani, Globigerinella aspera, and Globotruncana arca manage to survive through E-2 and were present in high abundance (~10%). Our long-term study suggests an overall stress built up in the background that must have aided in the K-Pg boundary mass extinction.

How to cite: Singh, B., Punekar, J., Spangenberg, J., and Keller, G.: Late Maastrichtian climatic shifts and faunal upheavals at DSDP Site 525A (South Atlantic): Understand the K-Pg boundary crisis in the long-term perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14240, https://doi.org/10.5194/egusphere-egu23-14240, 2023.

The end of the Pliocene (~2.5-3 Mya) saw a period of biotic turnover in marine ecosystems with significant losses in marine megafauna (36% of genera globally) including the giant apex predator, Otodus megalodon. This recently identified extinction event coincided with a period of notable climatic change, with glaciation of the Northern Hemisphere causing a drop in global sea level. A positive correlation has been found between extinction probability and those genera that had high energy requirements and were associated with coastal, shelf habitats. As such, it has been hypothesised that these extinctions may have been driven by sea level drop resulting in loss of shelf area and a reduction in the neritic zone, a highly productive feeding habitat.

Megafauna, and particularly apex predators, are known to play important trophic roles in extant communities yet the ecological consequences of losing these large taxa from marine ecosystems in currently not well understood. Using a trait-based inference model, we reconstructed food webs to assess the impact of this Pliocene extinction event on North Atlantic trophic community structure and dynamics. The model distributes trophic links using rules based on optimal foraging theory and functional traits assigned to every trophic species (e.g., body size, depth distribution and feeding habit). Through analysing the differences in food web topology pre- and post- megafaunal extinction event, we identify consistency in structure and connectedness between taxa within the webs. However, diversity changes within trophic levels and a decrease in competition in the Pleistocene indicates this turnover event did result in changes to the marine ecosystem makeup. Furthermore, our results show that the trophic role held by O. megalodon in the Pliocene appears to have been lost in the Pleistocene, with no other taxa taking its place.

In addition to these findings, we also consider alternate hypotheses that may have impacted megafaunal extinction other than shelf loss. As the North Atlantic possesses areas of long continental shelf, neritic zone habitats may have only been shifted, not lost. Consequently, other factors may have played a more significant role.

How to cite: Shipley, A., Aze, T., Pimiento, C., Beckerman, A., Dunne, J., Shaw, J., and Dunhill, A.: Ecosystem structure changes following a marine megafaunal Pliocene extinction and the role of continental shelf habitat loss, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14272, https://doi.org/10.5194/egusphere-egu23-14272, 2023.

The Permian witnessed the extensive development of cherts from the palaeoequator to the northern high latitudes. However, large-scale chert deposition was abruptly terminated in the latest Permian, resulting in the Early Triassic "chert gap". Deepwater sedimentary successions in South China across the Permian-Triassic transition recorded the shift from radiolarian- and spicule-bearing siliceous units to carbonate/siliciclastic facies in the equatorial Tethys. In order to constrain the onset time of the chert production crisis and understand its nature, we carried out sedimentological, palaeontological, and geochemical analyses on two deepwater sections along the northern margin of the South China Block. Our results suggest that chert production in equatorial latitudes was already weakened in the Clarkina changxingensis conodont zone. The final collapse of the chert factory occurred in the Clarkina yini - Hindeodus praeparvus/Clarkina zhangi Zone and was accompanied by a significant decrease in SiO₂ content, which predated the negative carbonate carbon isotope excursion and climate warming but coincided with a sharp decline in primary productivity. Combined with Si box model results, our study suggests that global warming cannot maintain a multi-million-year chert gap. Instead, the loss of siliceous skeleton producers was the primary cause of the Early Triassic chert demise.

How to cite: Yang, F., Sun, Y., Frings, P., Luo, L., Eh, J., Wang, L., Huang, Y., Wang, T., Müller, J., and Xie, S.: Collapse of Late Permian chert factories in the equatorial Tethys and the nature of the Early Triassic chert gap, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14371, https://doi.org/10.5194/egusphere-egu23-14371, 2023.

Major volcanic eruptions like the Deccan have long been invoked as causes of global mass extinctions. Deccan volcanism erupted ~ 600,000 km³ over the span of ~ 700 ka contemporaneously with the end-Cretaceous mass extinction. It has been difficult to establish a correlation between eruption size and extinction intensity because the frequency of eruptions and extent of degassing of individual flows is not well constrained. For example, the eruption of the same amount of lava by high frequency, low effusion flows is less likely to result in a mass extinction than by eruption of low frequency, high effusion flows. This is due to volcanic eruptions outgassing climate perturbing gases SO₂ and CO₂. When in the atmosphere, SO₂ and CO₂ could lead to a global climatic catastrophe capable of driving the extinction observed in planktic foraminifera that preceded the end-Cretaceous mass extinction by 200 ka. To determine the role Deccan volcanism played on the extinction it is critical to constrain the eruptive and effusive rates of Deccan eruptions. In addition to SO₂ and CO₂, volcanoes also emit volatile metals, e.g., Cd, Re, Hg, that form aerosols preserved in contemporaneous sediments. Trace metals, such as Cd, accumulate in sediments, where the excess Cd reflects the intensity of volcanic emissions. In such instances, high frequency, low effusion rate eruptions result in low Cd enrichments, whereas low frequency, high effusion rate eruptions result in high Cd enrichments in sediments. To constrain the eruption tempo of the Deccan, we have performed measurements of elemental abundances on the stratigraphically well-preserved KPg section at Elles, Tunisia. In this report, we conducted a high-resolution study of ~ 90 samples covering ~ 20 ka above the KPg boundary to ~ 350 ka below the KPg boundary. Elemental compositions for ~ 50 elements of Elles sediments were obtained by solution ICP-MS. In some samples, particularly sediments from 100 ka period preceding the boundary, Cd enrichments were eight times that of the upper continental crust (UCC). A lack of correlation between Cd and TOC, Zn, P₂O₅, and Mo below the boundary suggest the Cd enrichments are not from an influx of biogenic detritus nor from organic burial. Above the boundary, normal shale Cd values representing 25 ka are interpreted here to represent the period between the Ambenali and Poladpur phases. Cadmium as a tracer relates foram-based chronology with the intensity of the Deccan eruption.

How to cite: Sillitoe-Kukas, S., Humayun, M., Adatte, T., and Keller, G.: Cadmium as a tracer of volcanism at the Cretaceous-Paleogene boundary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16993, https://doi.org/10.5194/egusphere-egu23-16993, 2023.

Tasmania was located at 62-74° S in the Triassic, a position today occupied by the frozen rocky Antarctic continent. Sedimentary archives of the Triassic from Tasmania present a unique opportunity to examine a high latitude archive of a world that was in a significant state of climatic and environmental flux from the end-Permian mass extinction (~252 Ma) to the Late Triassic, Norian Manicouagen bollide impact, ~214 Ma . Here we present new sedimentological and geochemical data spanning these major events from two core records (~300m each) located in Bicheno, Eastern Tasmania. These cores represent deposition of organic rich sediments in a coastal environment, that spans the Permo–Triassic boundary through the Norian. This data includes new carbon isotopes, charcoalfied wood abundances, sedimentological evaluation and pXRF data. The Permo-Triassic Event (PTE) is marked by a -6‰ excursion in δ¹³C_TOC  with a change from Upper Parmeener Marine sequence limestones to more organic rich Upper Parmeener Freshwater sequences which includes mudstones, volcanic sandstones and tuffs. The Earliest Triassic is relatively condensed suggesting a relatively cold interval, with low sedimentation following on from the PTE. Other notable events include the Carnian Pluvial Event (CPE), with a marked increase in the abundance of charcoalified fossil wood, a -4‰ δ¹³C_TOC excursion and increased weathering suggesting significant changes to the hydrological cycle and the climate during this interval. There is also evidence of the Middle Norian Event with a -4‰ δ¹³C_TOC  excursion. This sedimentological and chemostratigraphic record from Tasmania represents a unique high latitude Southern Hemisphere record of climate change through the Triassic with evidence of significant paleoclimatic and environmental change near the South Pole.

How to cite: Al Suwaidi, A., Fox, C. P., Lestari, W. A., Ghosal, I., and Rigo, M.: Wildfires, Weathering and Warming: A High Latitude Southern Hemisphere paleoclimate record of the Triassic from Tasmania, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17314, https://doi.org/10.5194/egusphere-egu23-17314, 2023.

Discovery of impact glass in deep water at El Penon, NE Mexico, revealed a 2m thick impact spherule deposit during excavation of an 8m thick late Maastrichtian sequence ^[1]. The impact spherules are pristine and undisturbed in the late Maastrichtian. Marly sediments prevailed at the base followed mainly by small rip-up clasts overlain by a 10cm thick layer, which consists only of amorphous molten glass containing occasional planktic foraminifera. Large impact glass spherules 3-5mm in size followed and gradually reduced in size. Up-section the impact spherule size gradually reduced (2mm) but remained abundant and devoid of sediments. Near the top, spherules reduced in size and abundance mixed with marls, ending the impact deposit quietly. Marls and marly limestones followed. Preliminary age determinations identified the impact based on various indicators. 1) Biostratigraphy: First appearance of planktic foraminifer Plummerita hantkeninoides zone CF1 age ~200-kyr pre-KPB. 2) U-Pb dating of Deccan volcanism ~230-kyr pre-KPB. 3) Mercury anomalies of Deccan volcanism EE6 ~215-kyr pre-KPB. 4) Cyclostratigraphy ~230-kyr pre-KPB^[2]. Impact glass spherules are ubiquitous in the late Maastrichtian of NE Mexico and the impact is believed to be the source. But these spherules are almost always reworked from older into younger sediments, which eliminates age control. Nevertheless, the reworked Chicxulub impact spherules were always believed the source – but this is no longer tenable. The discovery of pristine impact spherules in NE Mexico at the much older age of 200-kyr to 230-kyr places the Chicxulub impact outside the realm of the KPB mass extinction. However, we know since 2003 the Chicxulub crater predates the KPB, although this fact was always neglected. New mercury data from a dozen localities in NE Mexico reveals further evidence that the Chicxulub impact is linked to the older impact crater. Our data supports Deccan volcanism as primary cause for the KPB mass extinction.

References:

[1] Keller et al., 2009, Journal of the Geological Society, London

[2] Keller et al., 2020, Global Planetary Change

How to cite: Keller, G., Grasby, S., and Adatte, T.: Chicxulub Impact Predates the KPB Mass Extinction by 200-230 kyr;Deccan Volcanism, Mercury and Climate change are main causes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17344, https://doi.org/10.5194/egusphere-egu23-17344, 2023.

The Paleocene-Eocene Thermal Maximum (PETM) around 56 Ma was associated with 5-6 °C global warming, resulting from massive carbon release into the ocean–atmosphere system. One potential driver of hyperthermal conditions was the North Atlantic Igneous Province (NAIP), as both volcanic degassing and thermogenic volatile release during contact metamorphism during its emplacement were large potential emitters of carbon. Despite a broad temporal correlation between NAIP activity and the PETM, the exact relationship is obscured by multiple climate forcings, imprecise geochronological data, uncertainties in the timing and magnitude of volatile fluxes from volcanic and thermogenic sources, and limited availability from crucial NAIP localities that could constrain these unknowns. Here we present new seismic and borehole data for the Modgunn hydrothermal vent complex in the Northeast Atlantic (IODP Sites U1567-U1568). Stable carbon isotope stratigraphy and dinoflagellate cyst biostratigraphy reveal a negative carbon isotope excursion coincident with the appearance of Apectodinium augustum in the vent crater infill. Modern examples of submarine explosion craters suggest they have filled in within decades to centuries, so the preservation of the PETM onset within the Modgunn vent suggests an extremely close temporal correlation between the crate formation and the onset of hyperthermal conditions. Furthermore, the majority of the craters across the entire NAIP are likely to have vented in very shallow water, implying that the vast majority of emitted CO₂ and CH₄ gases directly entered the atmosphere during eruptions. These findings add considerable weight to the hypothesis that thermogenic degassing aided the initiation of the PETM.

How to cite: Jones, M., Berndt, C., Planke, S., Zarikian, C. A., Frieling, J., Millett, J. M., Nelissen, M., and Brinkhuis, H.: Shallow-water hydrothermal venting at the Paleocene-Eocene Thermal Maximum onset, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17367, https://doi.org/10.5194/egusphere-egu23-17367, 2023.

Extensive magmatism during the NE Atlantic break-up generated about 6-10 million cubic kilometers of magma in the Paleogene. Magmatic degassing and explosive discharge of thermogenic gases by contact metamorphism is implicated in triggering the Paleocene-Eocene Thermal Maximum (PETM; 56 Ma). In 2022, the CAGE22-5 research cruise collected high-resolution seismic, sub-bottom profiler, and multibeam data across the central and northern Vøring Plateau to tie IODP Expedition 396 Sites U1571 to U1574. One high-resolution P-Cable 3D seismic cube (10.3 by 1.8 km) was collected on the Skoll High, covering both sites U1571 and U1572. The data were fast-track processed with a bin size of 6.1 x 6.1 m. Four Cenozoic sedimentary horizons and the Top Basalt horizon were subsequently interpreted, followed by horizon attribute analyses. The Top Basalt horizon reveals unprecedented details of the nature of the volcanic paleosurface. A faulted and eroded lava horizon characterizes the southeastern part of the cube at 150-250 m below sea floor (bsf) around the U1571 site location. In contrast, in the northwestern part of the cube, the Top Basalt attribute maps reveal a pitted surface and lobate structures with linear ridges with characteristic inter-ridge spacings of a few tens of meters. The pitted basalt surface is mapped in an area of about 5.5 km2 at depths of 250-350 m bsf and drilled by Site U1572. About 270 individual pits have been mapped with radius ranging from about six meters, within the horizontal resolution of the data, to about 50 meters with a mean radius of c. 16 meters. The holes are interpreted as rootless cones, which comprise volcanic craters resulting from the explosive reaction between lava flows which flow over water-saturated sediments. The dimensions of the rootless cones in the Skoll 3D survey are comparable with the field analogue of rootless cones mapped in the Myvatn lake area of NE Iceland. Unlike at Myvatn and at other field analogues, the Skoll3D data allow unique 3D imaging of the rootless cones revealing internal structures and geometries including the base of the cone structures. The cone depths vary from meters to a few tens of meters. The lobate structures are interpreted as separate subaerial lava flows with compressional ridges. These lava flows are similar to outcrop analogue lava flows and compressional ridges imaged by elevation model ISN2016 with a 2x2 m resolution near the Myvatn lake. In conclusion, the interpreted patterns of the basaltic pitted surface within the Skoll3D suggest a wet terrestrial paleoenvironment during effusive volcanism. Unlike in the eastern faulted area of the survey, the extremely well imaged pitted basalt surface of the Skoll3D area did not experience significant erosion, suggesting rapid subsidence and drowning of the paleo-land surface in a low-energy coastal environment. This study demonstrates the unprecedented detail that is possible when high resolution 3D seismic data acquisition is applied to buried volcanic landscapes and opens the potential for unique associated insights in the Northeast Atlantic and further afield.

How to cite: Lebedeva-Ivanova, N., Planke, S., Millett, J. M., Bünz, S., Binde, C. M., Manton, B., Zastrozhnov, D., Berndt, C., Jolley, D. W., and Brinkhuis, H.: Terrestrial Early Eocene Volcanic Paleoenvironment of the Skoll High, Mid-Norwegian Margin, Based on New High-Resolution 3D Seismic Geomorphology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17396, https://doi.org/10.5194/egusphere-egu23-17396, 2023.

Soil is considered the largest sink of microplastics (MP) in terrestrial ecosystems. Among the expected effects of MP as hydrophobic surface addition is the likelihood that MP enhances soil water repellency. So, crucial for MP fate in soils is the interaction between MP and water. If MP is translocated by water flow and, vice versa, MP impacts water flow, to what extent? Water flow on the pore scale will be impacted with feedbacks on transport and retention of MP. However, we don’t know the extent of and conditions under which MP are transported through porous media and, if deposited, how they interplay with soil water dynamics. We hypothesize that: (i) isolated MP are displaced and translocated by air-water interfaces and (ii) local accumulation of MP is facilitated by bypassing water flow. To approach this question, neutron and x-ray imaging of MP and water in soils was utilized.

Dual neutron and x-ray imaging at the beamlines ICON (Paul-Scherrer-Institute) during repeated wetting-drying cycles was applied to trace MP-water interactions in aluminum cylinders filled with sand (0.7-1.2 mm) and MP (PET, 20-75 µm) in gravimetric contents of 0.35, 1.05 and 2.10%. The contents refer to static contact angle estimations of the mixtures resembling < 90°, 90° and > 90°. First, simultaneous neutron and x-ray tomography captured the initial dry MP configuration in samples. Subsequently, neutron radiographies of deuterated water flow through the sample of 1 ml min^-1 were recorded for 200s. After drying, repeated tomography gave insights into MP translocation.

Neutron and x-ray imaging results showed that regions of major MP content are water repellent. Water flow bypasses and MP is mainly retained. Resultant air entrapments lead to reduced water contents. In regions of minor MP content water can infiltrate. Here, the air-water interface collects isolated MP and shifts their distribution towards an enhanced accumulation.

Extrapolation of these results to natural soil systems suggests that vertical transport of MP can be limited especially at hotspots of high MP contents. Water bypasses here. This might limit the water dependent degradation processes of MP due to reductions in hydrolysis, coating and colonization by microorganisms even elongating the process of natural attenuation.

How to cite: Cramer, A., Benard, P., Anders, K., Zarebanadkouki, M., and Carminati, A.: Microplastic Interaction with Soil Water - Visualization and Quantification with Neutron and X-ray Imaging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1477, https://doi.org/10.5194/egusphere-egu23-1477, 2023.

The occurrence of microplastics (MPs) has been evidenced worldwide in various aquatic environments, and while quite many studies have been devoted to the quantification and characterisation of these MPs, the knowledge of potential leaching from MPs to water is yet limited. In the current study, a range of different MPs prepared from consumer plastic products were soaked in water for 12 weeks, and variable composition of the water leachates was continuously analysed. Majority of investigated MPs released substantial amounts of dissolved organic carbon, with the maximum of approximately 65 mg per g of MPs after the 12 weeks, and some MPs also released dissolved inorganic carbon. Additionally, up to 10 other elements were detected in individual leachates – including metals (Al, Ba, Ca, Fe, K, Mg, Mn, Na, Zn) and one metalloid (Si). Out of those, Ca, K, and Na occurred most frequently, while Ca reached the highest values (up to approximately 2.5 mg per g MPs). In general, the overall highest leaching was observed in the case of MPs comprising polyurethane, polyvinyl chloride, and acrylonitrile-butadiene copolymer as the main polymers. Another general observation is that the leaching was usually most rapid during the first few weeks of MP contact with water. Further, in order to provide a better insight into composition and properties of the leachates, non-target analysis was conducted, and dozens of chemical individuals were tentatively identified in the leachates. Considering that the amounts of some elements released from MPs were quite high, and that some of the tentatively identified compounds are considered harmful to human health and/or to the environment, the leaching from MPs to ambient water might be important from different perspectives, including toxicology as well as fluxes of carbon and metals.

How to cite: Novotna, K., Cermakova, L., and Pivokonsky, M.: Leaching of carbon, metals, and additives from microplastics to water, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2559, https://doi.org/10.5194/egusphere-egu23-2559, 2023.

Microplastics (MPs) are emerging globally distributed pollutants of aquatic environments. Nowadays, MPs are being detected in seas, oceans and freshwater bodies worldwide, even in very remote areas. Studies have reported also the occurrence of MPs in potable water. Despite the potential adverse effects on human health are still largely unknown, the presence of MPs in drinking water deserves more attention. Besides the need for elimination of MPs in natural environments, it is necessary to focus also on their fate and removability at drinking water treatment plants (DWTPs) that pose a barrier for MPs to enter water for human consumption. In our study, we decided to provide unique insight into the occurrence of MPs at two different DWTPs situated on the same river but differing in treatment technology. Quantification and characterization of MPs ≥ 1 μm was conducted not only in raw and treated water but also after each technological treatment step. The results showed that the content of MPs varied greatly between the DWTPs. There were 23 ± 2 and 14 ± 1 MPs L⁻¹ in raw and treated water, respectively, at the upstream DWTP. By contrast, 1296 ± 35 and 151 ± 4 MPs L⁻¹ were found in raw and treated water, respectively, at the downstream DWTP. The majority (>70%) of MPs were smaller than 10 μm, and irregular fragment shape prevailed over fibres. Cellulose acetate, polyethylene terephthalate, polyvinyl chloride, polyethylene, and polypropylene were the most frequently occurring materials. Total removal of MPs of 88% was achieved at the DWTP with a higher initial MP number and more complicated treatment technology consisting of coagulation-flocculation-sedimentation, deep-bed filtration through clay-based material, and granular activated carbon adsorption. These steps contributed to MP elimination by 62%, 20%, and 6%, respectively. These results contribute to filling the knowledge gap regarding the removability of different types of MPs by distinct drinking water treatment technologies operating under ordinary conditions.

How to cite: Cermakova, L., Novotna, K., and Pivokonsky, M.: Investigating microplastics at two drinking water treatment plants within a river catchment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2560, https://doi.org/10.5194/egusphere-egu23-2560, 2023.

Microplastics have been found in various places, including not only densely populated areas of China or Germany but also remote high-altitude places like the Himalayas or the Pyrenees. However, the remoteness of a place is not determined only by its altitude. The Outer Hebrides (Scotland), with a low population and minimum industry, are remote in terms of direct pollution. This study aims to analyse the occurrence and spatial distribution of microplastics in soils of the Outer Hebrides to discover the factors driving the abundance of microplastics and to find how much more or less are remote Scottish soils polluted with microplastics than inland soils of populated areas.

In the Isle of South Uist, 123 topsoil samples were collected along the western coastline and in four transects through the isle in the west-east direction. In total, 63 samples were analysed using an optical microscope to quantify the plastic microfibres visually using a semi-automatic algorithm. The amounts of microfibres were statistically processed, and their distribution was modelled for the entire archipelago.

More microplastics are present in inland soils with loamy soil texture, denser vegetation and denser roots (median = 36,900 microfibres/L) than in coastal soils with sandy soil texture, sparse vegetation and low root density (median = 3,580 microfibres/L). Their abundance is mainly influenced by soil texture, vegetation density, and root density.

With the south-western prevailing wind direction, we assume that most microfibres enter the island from the Atlantic Ocean, and the wind transports the microfibres inland to the east. Wind deflates the microfibres from coastal soils, and microfibres are deposited in inland soils. The inland soils are less susceptible to wind erosion, and the microfibres accumulate there.

Thus, the remoteness of the Outer Hebrides does not guarantee low microplastic pollution. Contrarily, the Hebridean soils are extensively more polluted than most so far studied sites. The level of pollution is comparable to only a few studies where the abundance of microplastics in the soils is similar, e.g. Beijing (China), Lower Rhine basin (Germany) or Coimbra (Portugal). However, these sites are much more populated and interconnected, which suggests a great contribution of microplastic pollution from Atlantic Ocean and a great magnitude of wind transport processes in the Outer Hebrides.

How to cite: Pavlíková, T., Pavlík, D., Divíšek, J., and Nývlt, D.: Soil susceptibility to wind erosion drives the abundance of microplastics in remote Scottish soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2670, https://doi.org/10.5194/egusphere-egu23-2670, 2023.

Since plastics were first made in the early 20 century, global plastic production has increased dramatically and annual plastic use reached 460 million metric tons (Mt) in 2019. Although the advent of plastics creates miraculous economic achievements, it brings about severe pollution at the same time. As the life cycle of plastic use worldwide is still in linear form, mismanaged plastic waste might break into microplastics and accumulate in the environment. Rivers are the main route by which plastics enter the ocean. The process may take years or decades for microplastics to reach the ocean. The ocean surface currents were responsible for the transport of plastic waste and the ocean is its ultimate destination. This study correlated the fate of marine microplastics with economic growth under the influence of climate change. Taking 1960 as a benchmark, the trend of world GDP growth coincided with the growth of annual plastic production, indicating that economic growth heavily relies on plastic-related industries. Plastics emit a high amount of greenhouse gas (GHG) through their life span, enhancing the negative impact of climate change, causing the faster weathering process to form microplastics, and further enabling the leakage into the aquatic environment. According to the OECD statistics, 1.7 Mt of plastics entered the ocean system in 2019, reaching the total accumulation of 30 Mt of plastic waste since 1970. Global warming over past decades enhances the Earth's ocean currents which induced the acceleration of ocean plastic distribution. The accelerated ocean transportation may increase plastic accumulation at the garbage patches within five gyres and the Arctic Ocean which are ultimate sinks for plastic waste in the ocean. The abundance of microplastics in the ocean interferes with the carbon fixation capacity of the ocean, forming a nexus implication between climate change, ocean currents, and marine plastic redistribution. The accumulation of marine microplastic is suggested to be a factor in aggravating the impact of climate change. To deal with the dilemma, economic growth should be decoupled with the massive use of plastic utilization to reduce plastic production and GHG emission. Moreover, higher plastic waste recycling is urgently needed to prevent extra microplastics from entering the ocean.

How to cite: Fan, C. and Lee, Y.-Y.: The circularity of marine microplastics under the influence of climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2997, https://doi.org/10.5194/egusphere-egu23-2997, 2023.

Increasing volumes of mismanaged plastic waste have resulted in millions of tons of plastics entering the environment. While recent research has made substantial progress in determining the fate and transport of microplastics (MP) in river systems and their subsequent discharge to the worlds oceans, much less is known about the subsurface fate of MP as they enter soils, (riverine) sediments and global groundwater resources. Initial studies have identified MP in selected groundwater samples and there is great interest to understand entry pathyways of MPs into soils, in particular through agricultural pathways. The mechanisms of MP release from agricultural sources such as seed and agrochemical encapsulations or sewage sludges as well as the total quantity, spatial distribution, residence time scales as well as the impact of MP on soils and subsequently groundwater ecosystems are completely unknown. There is hence a critical need to study the role of soils and groundwater systems as a long-term sink for plastic pollution, including the development of legacy risks.

Here we identify the significance of various entry pathways for MP into subsurface ecosystems, integrating experimental and model based quantifications of MP transport through streambed sediments with quantifications of MP inputs into agricultural soils through irrigation with river water. We present first results of MP impacts on the functioning of subsurface ecosystem services, by the particular example of MP exposure impacts on the behaviour of bioturbating invertebrates and the subsequent consequences for sediment biogeochemical cycling in order to draw attention to the potential risks for vital soil and groundwater ecosystem services.

We complement this site specific mechanistic process understanding with global estimates of mismanaged plastic waste accumulation in river basins to quantify MP catchment wide loads available for leakage into soils and present first results of our recently started participatory approach that aims to develop a baseline of MP pollution in aquifers across the world. Such baseline data is imperative to increase our understanding of MP fate and transport processes, MP uptake by groundwater organisms and the interaction of MP with nutrients and potential co-contaminants. Our specifically tailored protocol allows for standardized MP sampling in boreholes, springs or wells across a wide range of geological settings and land cover classes. We invite and encourage the community to contribute to this global effort in order to enable estimates of the magnitude and expected time scales of soil and groundwater MP contamination.

How to cite: Krause, S., Schneidewind, U., Wazne, M., Kukkola, A., Lynch, I., Haverson, L., Kelleher, L., Davies, G., Dendievel, A.-M., Mourier, B., Mermillod-Blondin, F., Quiñones-Rivera, Z., Simon, L., Reiss, J., Perkins, D., Robertson, A., and Gomez-Velez, J.: The Plastic Underground: Are Microplastics in the Subsurface a Ticking Time Bomb for Soil and Groundwater Ecosystems?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4405, https://doi.org/10.5194/egusphere-egu23-4405, 2023.

Seafloor sediment is an important sink for microplastics, and vertical profile of microplastic accumulation in a sediment core can provide historical pollution trend. However, microplastic pollution in coastal sediment has not been addressed well, and a few studies have investigated the trends of microplastic pollution in age-dated core sediments. In this study, the microplastics in surface sediments in urban, aquafarm and reference areas of South Korea were analyzed to evaluate the pollution characteristics of microplastic according to different sea area use patterns. In addition, the historical trend of microplastic pollution was investigated in core sediments in the urban and aquafarm areas. The abundance of microplastics in surface sediment were in order of urban area (6,887 ± 6,100 particles/kg d.w.), aquafarm area (5,121 ± 2,428 particles/kg d.w.), and reference area (2,474 ± 522 particles/kg d.w.). Polymer types were diverse in the urban area, and expanded polystyrene used for buoys was dominant in the aquafarm area. Fragment type microplastic was dominant in all three areas, and the proportion of fiber was higher in urban and aquafarm areas than in reference area. The polymer composition of fiber was different in urban (polyester 51% and polypropylene (PP) 29%) and aquafarm areas (PP 84% and polyamide 13%). These results support that the characteristics of microplastic pollution well reflect the sea area use patterns. Historical trend of microplastic pollution has increased since the 1980s and the increasing rate steeply increased around the early and mid-2000s in both the core samples. Their increasing trend reflected the influence of population or surrounding input sources (i.e. effluent discharge amount of a wastewater treatment plant). The clear increasing trend of historical microplastic pollution up to now indicates that more efforts is highly required to reduce the microplastic pollution. 

How to cite: Eo, S., Hong, S. H., Song, Y. K., Cho, Y., Han, G. M., and Shim, W. J.: Spatial distribution and historical trend of microplastic pollution in sediments from enclosed bays of South Korea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4586, https://doi.org/10.5194/egusphere-egu23-4586, 2023.

Plastic has greatly changed modern society, and it has become an indispensable material in our daily lives. Microplastics are now regarded as the serious environmental threats due to the management limitations. Saltmarshes are one of the most productive ecosystems on earth and a high-efficiency blue carbon sink. As an emerging contaminant, the load, transport and fate of microplastics are largely neglected in saltmarshes. Here, we firstly measured the mass concentration of microplastics in the sediment cores of a multi-species saltmarsh by pressurized liquid extraction and modified double-shot pyrolysis gas chromatography-mass spectrometry. The major microplastics in saltmarsh sediments were polyethylene (PE), polyvinyl chloride (PVC), and polypropylene (PP). The microplastic mass concentration in the sediment of Scirpus mariqueter was greater than Phragmites australis and mudflat. As artificial carbon, carbon content of microplastics accounts for 1.15% of total organic carbon. Overall, the results suggest that saltmarsh vegetation can efficiently drive the microplastic settling and retention. Therefore, the microplastic distribution characteristics in saltmarsh can be effected by the vegetation types and their distribution pattern.

How to cite: Zhang, Y., Wang, Y., Chen, X., Zhu, P., Jing, S., and Li, L.: Microplastic distribution characteristics and storage in a multi-species saltmarsh, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5676, https://doi.org/10.5194/egusphere-egu23-5676, 2023.

Impacts of climate change – sea level rise, more frequent storms and coastal flooding will exacerbate coastal erosion, resulting in the erosion of coastal historic landfills. These historic landfills are particularly vulnerable to such erosion as they typically have no lining or leachate management, limited information of the proportion and/or types of waste mixtures they contain and inaccurate records of their location and waste volumes. There are over 1200 coastal historic landfills in England alone, and over 10,000 such sites are at risk of release both solid waste and soluble contaminants across Europe. The contaminated matrix and solid wastes make landfills a major sink and source of microplastics and heavy metal, posing a threat to the coastal and marine environment.

We investigated heavy metal and microplastic pollution on the beach and foreshore in three coastal historic eroding landfills, East Tilbury (n = 32 samples), Lynemouth (n = 33 samples), Northam Burrows Tilbury (n = 33 samples), UK. Samples were collected every 50 meters along the shoreline, with 100g of surface soil from the landfill edge, and 1kg of beach and intertidal sediment collected from each transect. The metal concertation was measured with handheld X-ray Fluorescence (XRF). Microplastics were density separated with a zinc chloride solution (1.5 g cm⁻³), after the samples were dried and digested with hydrogen peroxide. The extracted microplastics were recorded under stereomicroscope at 50× magnification with a digital camera, and characterized with Fourier-transformed infrared (ATR-FTIR) spectroscopy.

This study is one of the first few to investigate the impacts of eroding historic landfill. Our preliminary findings suggest that eroding landfill are releasing significant amounts of microplastics and heavy metal pollution. These findings will be crucial to assess the impacts of eroding landfills, identify solutions and raise public attention to this environmental problem.

How to cite: Xue, S., Spencer, K., and Grieve, S.: The impacts of climate change on eroding coastal historic landfills, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6323, https://doi.org/10.5194/egusphere-egu23-6323, 2023.

Plastic mobilization, transport, and retention dynamics are influenced by hydrological processes and river catchment features (e.g. land-use, vegetation, and river morphology). Increased river discharge has been associated with higher plastic transport rates, although the exact relation between the two can vary over time and space. The precise role of an extreme discharge event on plastic transport is however still unknown. Here, we show that fluvial floods drive floating macroplastic transport and accumulation in river systems. We collected observational evidence during the (return period of 200 years) along the Dutch part of the Meuse. Upstream plastic transport multiplied by a factor of over 100 compared to non-flood conditions (3.3x10⁵ vs 2.3x10²), making the Meuse . Over one-third of the annual plastic transport was estimated to occur within the six-day period of extreme discharge (>3,200 m³/s). Towards the river mouth, plastic transport during the flood decreased by 90%, suggesting that the Plastic transport and accumulation on the riverbanks decreased significantly along the river, corroborating the river's function as a plastic reservoir, rather than conduit for plastic towards the ocean. We demonstrate the crucial role of floods as drivers of plastic transport and accumulation in river systems. Floods amplify the mobilization of plastics, but the effects are local and the river-scale dispersion is limited. We anticipate that our findings serve as a starting point for improving global estimates of river plastic transport, retention, and export into the sea. Moreover, our results provide essential insights for future large-scale and long-term quantitative assessments of river plastic pollution. Reliable observations and a fundamental understanding of plastic transport are key to designing effective prevention and reduction strategies.

Link to preprint

Tim van Emmerik, Roy Frings, Louise Schreyers et al. River plastic during floods: Amplified mobilization, limited river-scale dispersion, 08 August 2022, PREPRINT (Version 1) available at Research Square [https://doi.org/10.21203/rs.3.rs-1909246/v1]

How to cite: van Emmerik, T., Frings, R., Schreyers, L., Hauk, R., de Lange, S., and Mellink, Y.: River plastic during floods: Amplified mobilization, limited river-scale dispersion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9164, https://doi.org/10.5194/egusphere-egu23-9164, 2023.

Glacimarine sediment results from glaciers weathering the rock exporting silt and clay into the ocean. Such fine sediments are also exported from the Greenlandic Ice Sheet where new sources of plastic pollution like seasonal ice thawing may be releasing microplastics (MP) back to the environment. MP could be then transported to the seafloor via sediment burial and incorporated into the layers of the geological record. However, the purification and extraction of MP from such a fine-grain matrix is challenging, as the small grains remain in suspension and can form aggregates. In order to look for a footprint of the Anthropocene in Greenland, a sediment core was analyzed to generate a record of MP by comparing a pre- and post-plastic boom period. Using ²¹⁰Pb and ¹³⁷Cs dating, the chronology was established from 1861 to 2015 ±5 yrs bridging the plastic boom of the 1950s. Using a 4-step methodology developed for fine-grain matrices, MP particles were characterized via FT-IR imaging. QC/QA protocols were applied throughout the process to reduce the risk of contamination. More than 1000 particles were found in total ranging from 20 µm to 600 µm and going as far back as 1930. Nine polymer types were found, the most common being PE and PP accounting for 84% of all particles. This is the first sediment record of MP pollution in the Arctic, which shows that once thought pristine regions have in fact being polluted for a long time, which in turn implies that the impact might be greater than previously thought. In addition, this long-term accumulation in Greenlandic marine sediment could be compared to global horizons in the search for markers of the Anthropocene.

How to cite: Parga Martinez, K. B., Andersen, T. J., da Silva, V., Strand, J., and Posth, N. R.: Greenland in the Anthropocene: an archive of microplastic pollution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10534, https://doi.org/10.5194/egusphere-egu23-10534, 2023.

A visual survey using a vessel is a representative method to assess the degree of pollution of floating plastic debris in marine environments. However, the visual survey may more easily miss plastic items on and just below water (e.g. plastic bags) than above water (e.g. PET bottles). In addition, there are very limited comparison studies for floating plastic debris on the water surface and suspended plastic debris in the water column. None of the studies quantitatively determined the difference in detection rate by visual and surface trawl surveys. The aim of this study is to evaluate what could be relatively missed and underestimated by surface water visual surveys.

Floating plastic debris was monitored by visual and trawl surveys (depth of 0.5 m) in three coastal areas (rural area, GJ; aquafarm area, JH; urban and near river mouth area, SY) of Korea over the four seasons in 2022. In addition, during the visual survey of floating plastic debris in a fishing area (GH), near the river mouth of Han River, a shrimp beam trawl was used to collect plastic debris in the water column (water depth of 10 m) except for thin surface and bottom layer over three seasons in 2022. The seasonal patterns and composition of floating plastic debris in the surface water of JH, GJ, and SY were similar between the visual and trawl surveys. But, the mean densities of most plastics obtained from trawl surveys were 3 to 7 times higher than those from visual surveys. In particular, it was hard to detect small-sized, submerged, or dark-colored fishing gear with the visual survey. Patches with small items can increase the uncertainty of the visual survey. Therefore, visual surveys may underestimate the amount of marine plastic debris above and just below the water.

Various types of floating plastic debris were observed by visual survey in the surface water of GH: plastic bags/sheets (54%), expanded polystyrene pieces (18%), plastic containers (4%), strapping (3%), plastic bottles/caps (3%), discarded fishing gear (1%), and other hard plastic pieces (14%). In the water column of GH, however, plastic bags/sheets (93%) predominated and followed by strapping (4%), discarded fishing gear (1%), and other plastics (1%). These results indicate that plastic bags/sheets and strapping would mainly submerge in the water column, but expanded polystyrene pieces, plastic containers, plastic bottles/caps, and other hard plastic pieces are more likely to float rather than sink. Thus, the application of only visual surveys for plastic pollution monitoring in water may largely miss and underestimate the plastic items transported on and below water such as plastic bags and sheets.

How to cite: Shim, W. J., Jang, Y. L., Eo, S., Jeong, J., Ha, S. Y., Han, G. M., and Hong, S. H.: Comparison Studies for Surface Water Visual Survey and Surface and Water-Column Trawl for Floating and Suspended Marine Plastic Debris, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11173, https://doi.org/10.5194/egusphere-egu23-11173, 2023.

The increasing plastic pollution of the world’s oceans represents a serious threat to marine ecosystems and has become a well-known topic garnering growing public attention. The global input of plastic waste into the oceans is estimated to be approximately 10 million tons per year and predicted to rise by one order of magnitude by 2025. More than 90% of the plastic that enters the oceans is thought to end up on the seafloor, and seafloor sediment samples show that plastics are concentrated in confined morphologies and sedimentary environments such as submarine canyons. These canyons are occasionally flushed by powerful gravity-driven sediment flows called turbidity currents, which transport vast volumes of sediment to the deep sea and deposit sediment in deep-sea fans. As such, turbidity currents may also transport plastics present in the canyon and bury plastics in deep-sea fans. These fans may therefore act as sinks for seafloor plastics. Here we present a comprehensive dataset showing the spatial distribution of microplastics in seafloor sediments from the Congo Canyon, offshore West Africa. Multicores taken from 16 locations along the canyon, sampled different sedimentary sub-environments including the canyon thalweg, canyon terraces, and distal lobe. Microplastics were extracted from the sediments by density separation and the polymer type, size, and shape of all individual microplastic particles were analysed using laser-direct infrared-spectroscopy (LDIR). Microplastic number concentrations in the sediments of the distal lobe are significantly higher than in the canyon, indicating that the Congo Canyon system is a highly efficient conduit for microplastic transport to the deep sea. Moreover, microplastic concentrations of >20,000 particles per kg of dry sediment were recorded in the lobe, which represent some of the highest ever recorded microplastic number concentrations in seafloor sediments. This shows that deep-sea fans can serve as hotspots and potential terminal sinks for seafloor microplastics.

How to cite: Pohl, F., Hildebrandt, L., O’Dell, J., Talling, P., Baker, M., El Gareb, F., La Nasa, J., De Falco, F., Mattonai, M., Ruffell, S., Eggenhuisen, J., Modugno, F., Proefrock, D., Pope, E., Silva Jacinto, R., Heijnen, M., Hage, S., Simmons, S., Hasenhündl, M., and Heerema, C.: The submarine Congo Canyon as a conduit for microplastics to the deep sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12344, https://doi.org/10.5194/egusphere-egu23-12344, 2023.

Biodiverse coastal ecosystems are vulnerable to microplastic (<5 mm) pollution due to inputs from riverine and shoreline sources which pose ecological threats and have repercussions for social ecosystem services. These ecosystems may contain an aquatic canopy covering the bed, such as seagrass meadows or coral reefs that can trap particles. Despite field measurements revealing the accumulation of plastic debris in a variety of aquatic canopies, the transport and dispositional processes that drive microplastic trapping within such canopies is barely understood. Here, we investigate for the first time the prevalence of biofilmed microplastic retention by sparse and dense branching coral canopies in a hydraulic flume under unidirectional flow. Corals were replicated through 3D-printing using a scan of a staghorn coral Acropora genus, a branching coral that encompasses one-fifth of extant reef-building corals, globally.

Trapping mechanisms by coral canopies were identified, and include: a) interception of particles with the coral acting as a barrier and microplastics and settling to the bed; b) settling of microplastics on the branches or within the structure of the coral and c) accumulation in the downstream region of individual corals. Trapping efficiency was found to depend on bulk velocity and canopy density, with up to 99% of microplastics retained across the duration of the experiments. Surprisingly, sparse reefs may be as vulnerable to microplastic trapping and contamination as denser canopies under certain flow velocities, with the latter found to retain only up to 18% more microplastics than in sparser conditions. Flow velocity profiles provide insights into the relationships between canopy hydrodynamics and microplastic trapping and distribution. The results indicate coral reefs may form areas of accumulation for microplastic pollution through their observed high trapping efficiency that may otherwise have been transported greater distances.

How to cite: Houseago, R., Mendrik, F., Hackney, C., and Parsons, D.: Transport and trapping of microplastics in coral reefs: a physical experimental investigation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14119, https://doi.org/10.5194/egusphere-egu23-14119, 2023.

Despite microplastic pollution now being ubiquitous in natural environments, there remains several unknowns in terms of which zones may act as microplastics sinks. Coral reefs are the most ecologically diverse marine ecosystem, supporting 25% of all ocean species, and have high socio-economic value, offering ecosystem services such as coastal protection and tourism. However, the average cover of tropical reefs has declined by 50-75% in nearly all global regions over the last 30-40 years due to a range of anthropogenic stressors. There is growing evidence that coral reefs can entrap plastics and that microplastic (>5 mm) pollution threatens coral physiology. However, there is a lack of understanding as to the occurrence, accumulation, spatial distribution and impacts of microplastic pollution on coral ecosystems. It is, therefore, necessary that more research is undertaken within coral reefs to understand microplastic contamination levels and ensure effective mitigation measures are in place.

The islands of Con Dao, Vietnam, are 90 km from the Mekong Delta coast and are a designated national park, with a 14,000 ha marine protected area that conserves endangered wildlife and a diverse range of coral that support hundreds of fish species. Although considered pristine, Con Dao it is influenced by the Mekong River, which is one of the top contributors to marine plastic waste worldwide, posing an increasing risk to this biodiversity hotspot. Understanding the volumes and impacts of microplastic pollution in this area will allow insight into the levels of exposure and risk coral reefs in Southeast Asia, including the highly biodiverse Coral Triangle, have from increasing plastic pollution.Here, the occurrence and spatial distribution of microplastics in water and sand samples from Con Dao is presented. Reef health is also provided through photogrammetry whereby 3D reconstruction of reef sites allows analysis of coral cover and diversity, in addition to structural complexity, which is strongly correlated to reef health indicators including biodiversity, especially within tropical reef ecosystems. Potential sources of microplastics are also discussed through polymer identification by FT-IR analysis.

How to cite: Mendrik, F., Hackney, C., Cumming, V., Hung, N., Hennige, S., and Parsons, D.: Paradise lost: Microplastic pollution on a remote coral island, Vietnam, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14286, https://doi.org/10.5194/egusphere-egu23-14286, 2023.

Microplastics (mPs), defined as plastic particles that are less in 5mm in size, are ubiquitous within the marine environment. They are difficult to remove from natural water streams and persist for long periods of time, breaking down into continually smaller particles. Since the diversity of organisms that can ingest plastic particles increases as the particle size decreases, microplastics have been identified as an emerging contaminant of concern in the marine environment and the determination of the potential ecological harm caused by mPs is a key objective of the EU Marine Strategy Framework Directive (MSFD 2008/56/EC). However, the completion of a comprehensive risk assessment of this marine pollutant is prevented by the current lack of consensus on the processes influencing mP transport, uptake and exchange in the marine environment. For example, the processes driving the transport of mPs with buoyant polymers to the deepest part of the ocean are surrounded in uncertainty. The potential for mPs to accumulate within organisms and consequently the significance of trophic transfer as an uptake route for mPs is also unclear, particularly at lower trophic levels where contrasting arguments have formed on the risk of trophic transfer of mPs via zooplankton.

In this study, an integrated system of numerical models has been proposed to improve our understanding of mP processes in the marine environment by simulating the transport and ecosystem uptake and exchange of mPs at lower trophic levels in the northwest European continental shelf region. The continued refinement of the mathematical models will be presented, including the results of tests undertaken to evaluate the efficacy of empirical models for the calculation of the vertical settling velocity of irregularly-shaped particles from the perspective of mP transport modelling. Based on the current availability of data on mP distribution and uptake by lower trophic level organisms in the study area, the feasibility of model implementation will be examined as well as the significance of this research in providing information required by policy makers to complete risk assessment and implement suitable management strategies for marine mP pollution.

How to cite: Coyle, R., McKinley, J., Hardiman, G., Service, M., and Witte, U.: Modelling the Uptake and Exchange of Microplastics in Marine Ecosystems using a Novel, Integrated System of High-Resolution Numerical Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14881, https://doi.org/10.5194/egusphere-egu23-14881, 2023.

Following the discovery of microplastics (MPs) in river sediments, the number of MP studies on rivers and other freshwater systems has increased rapidly, revealing that MPs are omnipresent in all freshwater environments. The abundance of MPs in freshwater sediments seems to be affected by population density, urban centers, water flow velocity, water catchment size and position and type of sewage and waste management. However, not all of these relations are consistent. For example, while many studies report good correlations between MP source regions (highly populated and industrialized areas) and MP abundance in river sediments, others do not. This is in contrast to the concentrations in the water itself, for which better links with MP source areas were found. What all these studies have in common, is their large-scale approach, in which sediment samples are obtained over distances of tens to thousands of kilometers along the river; and at each site sediments are than retrieved either from the deepest part of the channel or from the river bank (depending on the study). Here, we study MP distribution in a section of the meandering Leie River, in a rural area, a few kilometers upstream of the city of Ghent (Belgium). Multibeam bathymetry and side-scan sonar images allowed selecting three undisturbed across-channel transects where surface sediments were retrieved. Sediment samples were analyzed for MP content, organic-matter content and grain size of the clastic fraction. Overall the MP concentrations are much (up to an order of magnitude) lower in the thalweg compared to samples near the river banks, resulting in an asymmetric distribution at the bend apex, where the thalweg approaches the outer banks. Furthermore, MP concentrations show strong correlations with the organic matter content and grain-size parameters as expected form hydrodynamic sorting. Exceptions to these correlations are the outer bank samples, where MP concentrations are lower than predicted from sedimentological characteristics. We attribute this to the more erosive character of the current in the thalweg near the outer banks, which inhibits MP deposition, but exposes fine-grained and organic-rich flood plain sediments. We highlight that the different hydrodynamic conditions across a river channel greatly influence MP distribution (with an order of magnitude), but in a sedimentologically predictable manner. Care should thus be taken in environmental studies, as local variability in MP concentration across a river bed may be larger then the large-scale variability.

How to cite: Van Daele, M., Van Bastelaere, B., Vercauteren, M., Meyer, I., and Asselman, J.: Depositional patterns of microplastics in a meandering river: a case study of the Leie River, Belgium, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16232, https://doi.org/10.5194/egusphere-egu23-16232, 2023.

The WASCAL WRAP2.0 project LANDSURF aims to calculate and compare different climatological and agrometeorological indices to support stakeholders and farmers in adapting to climate change and its impact in Africa.

This study, which was conducted in the framework of LANDSURF, focuses on the number and duration of heatwaves as rising temperature and resulting heat were found to limit crop yield and thus lower food security in different African regions. We calculated the heat wave duration index (HWDI) for reanalysis data, three regional climate models (RCMs) (REMO2015, RegCM4-7, and CCLM5-0-15) from CORDEX CORE, and their respective forcing data to validate the models over a historical climatological period (1981-2010) and investigate the change of the HWDI for three climatologies of the near-, mid-, and long-term future until 2100 using the two Representative Concentration Pathways (RCPs) 2.6 and 8.5.

How to cite: Ziegler, K., Abel, D., Weber, T., König, L., and Paeth, H.: Analyses of Heatwaves in Observational and Modelled Data for Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1312, https://doi.org/10.5194/egusphere-egu23-1312, 2023.

The Okavango rift zone/delta and the Makgadikgadi paleo-megalake form a dynamic system in northern Kalahari, where tectonic activity, climate change, sedimentation, and biota have interacted in a complex pattern. Previous research suggested that the region may have been a hotspot for hominid evolution.

Here we present results from the first scientific deep drilling project (OKAMAK) in the northern Kalahari, Botswana. Two drill cores, OKA (230 meters) and MAK (210 m), were drilled in the Okavango delta and Makgadikgadi paleolake. Cores recovered shallow and deep-water sands, muds and evaporitic lithologies of the Cenozoic Kalahari Group extending across the unconformity into the Cretaceous/Jurassic Karoo Group sandstones.

We discuss initial stratigraphy, chronologies and paleoenvironmental information for this novel sedimentary record, present hypotheses to be tested on the complex climate of the region, history of river piracy, evolution of the delta and infilling phases of Makgadikgadi and assess the international collaborative potential of this yet to be fully understood region within a future multi-platform ICDP-IODP initiative.

How to cite: Giosan, L., Canales, J. P., Ivory, S., Shen, Z., De Jonge, C., Eglinton, T., Lattaud, J., Russo, N., Haghipour, N., Filip, F., Khonde, N., Carter, A., Garzanti, E., Ando, S., Franchi, F., Kgosiemang, K., Burrough, S., Thomas, D., Mapeo, R., and Laletsang, K. and the OKAMAK Extended Team: When the desert was a lake: Tectonics, climate, river piracy and hominids in the Kalahari, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1586, https://doi.org/10.5194/egusphere-egu23-1586, 2023.

Tectonic activity impacts the environment and identifying the influence of active faulting on environmental factors, such as vegetation growth and soil formation patterns, is valuable in better understanding ecosystem functions. We applied remote sensing techniques to illustrate how tectonic activity and lithology of bedrock influence temporal and spatial patterns of vegetation and soil parameters in a climatically sensitive, fault-controlled river basin in the Kenya-Tanzania transboundary region.

The Mara River Basin lies in a region of previously unrecognised tectonic activity, characterised by subrecent extensional faulting along the Utimbara and Isuria faults. Faulting leads to spatially variable erosion and soil formation rates as well as disruption and modification of drainage systems. All these factors might be expected to exert controls on ecosystem dynamics on a range of lengths and timescales. We investigate tectonic controls on ecological processes in the Mara River Basin using a combination of geospatial mapping and multispectral image analysis. To map fault structures and to reveal signs of recent tectonic activity along the Utimbara and Isuria faults, we use high-resolution digital elevation models derived from 12m TanDEM-X data. To investigate spatiotemporal vegetation patterns and soil formation, we use a 5-year Normalised Difference Vegetation Index (NDVI) time-series, Clay Mineral Ratio (CMR) and Moisture Stress Index (MSI) derived from Sentinel 2 data. 

Whilst lithology does exert some control on ecological properties, we also observe that the downthrown hanging wall of the faults, especially directly adjacent to the escarpment, is consistently associated with a higher degree of vegetation, wetland formation and clay distribution. Analysis of spectral indices shows that the overall spatial pattern of vegetation cover is seasonally low in the flat plains and perennially high in the vicinity of more complex, tectonically influenced structures. The NDVI highlights several locations with permanently healthy vegetation along the escarpment which extend downslope for several kilometres. Our study shows that in the Mara River Basin, active normal faulting is an important stabiliser of vegetation growth patterns. We interpret this effect to be caused by favourable hydrological and pedological conditions along the escarpments and tectonically induced structures such as subrecent surface ruptures and a series of small, fault-bounded alluvial fans exposing systematically high vegetation and clay values. This implies that tectonic activity has a direct beneficial influence on ecological processes in this climatically sensitive region. As future climate change in the area is expected to lead to accelerated habitat desiccation and deterioration of vegetation quality, suitable habitats for wildlife will progressively reduce and will likely be limited to tectonically active locations. Long-term insights into tectonic processes and the interplay between geology and soils can thus be useful for recent and future ecosystem management since the understanding of an area from a geological perspective can complement the understanding of other natural processes within it.

How to cite: Ludat, A. L. and Kübler, S.: The influence of tectonic surface faulting on vegetation growth and soil formation of the Mara River Basin, East Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1589, https://doi.org/10.5194/egusphere-egu23-1589, 2023.

The study of the ancient anthropological sites of the Levantine Corridor is very significant for understanding the evolution of ancient hominins and the time of their dispersal from East Africa to the Caucasus and Eurasia (Eppelbaum and Katz, 2022a). In such geologically complex regions as the northern Levantine Corridor (in the area of ​​development of the Dead Sea Transform's pluvial basins in the Eastern Mediterranean), the application of single Earth Science methods, as a rule, is ineffective. Therefore, we analyzed in detail, for the first time, an integrated geological-geophysical data set: paleomagnetic correlation, magnetostratigraphy, and paleomagnetic and paleogeographic mapping (considering radiometric data) (e.g., Eppelbaum and Katz, 2022b), event, cyclic and eco-stratigraphy, lithological-facies analysis, and tectonic-geodynamic constructions with the attraction of the hydrospheric disturbances' data. One of the most important sites is the multi-layered site of 'Ubeidiya, located in the Kinnarot Basin. The age of this site was reviewed several times and is now determined as 1.6-1.2 Ma. Based on the numerous geological-paleomagnetic data analysis, the first integrated structural-paleomagnetic-event stratigraphic chart of the northern Levantine ancient hominin sites was developed. The results of the paleomagnetic mapping of the Sea of Galilee, Kinnarot, and Hula basins were used to construct the first palinspastic map for this region (for the period of 3.6 – 2.0 Ma). This map unmasked the tectonic-magmatic evaluation of this area and confirmed our assumption that the 'Ubeidiya Formation belonged to the Gelasian. It has been shown that the correlation of the 'Ubeidiya Formation with the Lower Matuyama Chron (C2r) is most likely correct than with its upper part (close in location to the strata with artifacts from the Evron quarry (Israel)). The correlation with the excellent radiometrically and paleomagnetically dated Zarqa section (western Jordan) (2.52 - 1.98 Ma) testifies that the 'Ubeidiya section most likely cannot be younger than this rock series. First, it follows from the event-stratigraphic and paleomagnetic correlation characteristics. The event-stratigraphic and rhythm-stratigraphic analyses indicate that the 'Ubeidiya and Erq El-Ahmar (Israel) formations do not contain a significant break and form a single sequence of the lacustrine-alluvial cycles of the Gauss and Matuyama Chrons. The analysis of finds of marine foraminifers confirms the paleogeographic relationship between the fluvial-lacustrine stratum (formation) of 'Ubeidiya and the transgressive Middle Akchagylian-Gelasian marine basin located nearby. Thus, the multifactor geological-geophysical analysis indicated that the ages of the most ancient archaeological sites of 'Ubeidiya and Zarqa correspond to the extremum of the Middle Akchagylian-Gelasian hydrospheric maximum (2.6–1.9 Ma) in contrast to the earlier suggested Middle Calabrian (1.6–1.2 Ma) age of the 'Ubeidiya site. The new proposed age may require revising the global process of dispersing hominins from Africa to the north.

References

Eppelbaum, L.V. and Katz, Y.I., 2022a. Combined Zonation of the African-Levantine-Caucasian Areal of Ancient Hominin: Review and Integrated Analysis of Paleogeographical, Stratigraphic and Geophysical-Geodynamical Data. Geosciences (Switzerland), 27, No. 1, 1-23.

Eppelbaum, L.V. and Katz, Y.I., 2022b. Paleomagnetic-geodynamic mapping of the transition zone from ocean to the continent: A review. Applied Sciences, 12, Advances in Applied Geophysics, 1-20.

How to cite: Eppelbaum, L. and Katz, Y.: Combined paleomagnetic, paleogeographic, and event stratigraphy studies increase the age of the anthropological site 'Ubeidiya in the Levantine Corridor (northern Israel) by 1.0 Ma, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1598, https://doi.org/10.5194/egusphere-egu23-1598, 2023.

Benthic foraminifera (BF) typically constitute around 50% of the eukaryotic biomass of seafloor environments and are excellent recorders of bottom water environmental and geochemical changes in the past. In the last 27.000 years, major climatic oscillations including the Heinrich Stadial 1 (HS1), Bølling–Allerød (B-A) and Younger Dryas (YD) shaped the climate of a big part of the northern hemisphere. Although the response of the ocean surface to these events is well documented, information about the response of benthic ecosystems is still limited.

To better understand how BF responded to major climatic shifts in the last 27.000 years, we analyzed the benthic foraminifera content from core GeoB9512-5 (15°29.90'N/17°56.88'W, 793 m water depth) off NW Africa. Our high-resolution sediment record covers the last 27.000 years of the eastern North Atlantic, including the Heinrich Stadial 2 (HS2), Last Glacial Maximum (LGM), HS1, B-A and YD.

Taxonomic and quantitative analyses were used to reconstruct changes in bottom water oxygenation and organic matter fluxes and show that BF assemblages shifted in coincidence with the major climatic periods documented for the North Atlantic. After the LGM, Bottom water salinity, oxygenation and quantity/quality of organic matter played a major role in BF distribution and are linked to transient changes in BF diversity in the last 27.000 years.

The LGM showed no major diversity changes for thousands of years, while BF distribution shifted rapidly during HS1, B-A and YD. Low-diversity intervals during the HS1, B-A and the last 6.000 years are typically dominated by stress species in times of oxygen decrease and high organic matter content at bottom waters. These short intervals (typically lasting 500-1300 years) are commonly intercalated by low-duration high-diversity periods, associated with higher bottom water oxygenation and relatively lower organic matter content. Additionally, relatively abundant porcelaneous BF during HS1, LGM and HS1 indicate relatively higher salinity than the observed in the last 14.000 years.

Our results show that BF at intermediate depths at the NE Atlantic off NW Africa are strongly influenced by changes in bottom water paleoenvironmental conditions potentially linked to major climatic events. Bottom water oxygenation played a major role in BF diversity, observed by alternating low-diversity periods in times of low oxic conditions and high-diversity intervals in high oxic bottom waters. At the same time, bottom water salinity favored porcelaneous BF distribution during LGM and HS1 times and increasing hyaline-calcareous BF show decreased salinity in this part of the NE Atlantic after the end of the HS1.

How to cite: Barragán-Montilla, S., Mulitza, S., Johnstone, H. J., and Pälike, H.: Response of benthic foraminiferal assemblages off NW Africa to climate change during the past 27.000 years, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2109, https://doi.org/10.5194/egusphere-egu23-2109, 2023.

The environmental and living conditions of a region are shaped by its relief, geology and climate, and control factors like hydrology and soil formation. While long-term climatic fluctuations and associated changes in environmental conditions are commonly viewed as the dominant natural factor in human evolution, the role of geological and pedological processes has so far received little attention. However, it makes a big difference to consider the effects of large-scale environmental changes in a homogeneous "static" landscape or to include the multitude of dynamic landscape factors that can lead to strong local effects with regard to the structure of the landscape and the availability of water and food.

The NE Aegean is a key region of Pleistocene hominin presence at the crossroad between Africa, Asia and Europe situated in a geologically highly unstable region. Rodafnidia, an open-air Lower Paleolithic site on Lesbos, has revealed a unique Acheulean assemblage from excavated fluvio-lacustrine deposits dated between 476 and 164 ka BP. This site and its surrounding region represent a key location to study hominin subsistence and mobility and to investigate potential trans-Aegean migration corridors during Pleistocene sea-level lowstands. Geologically, Rodafnidia is situated on middle Pleistocene fluvial sediments consisting mainly of reworked early Miocene ignimbrites, and Pliocene marly limestones and marls, whereas the wider region is characterized by strong geochemical and pedochemical contrasts including nutritionally depleted soils on ophiolitic rocks, highly productive soils on marshy coastal deposits along the Kalloni Gulf, and a series of fault-controlled thermal sulfur springs at Lisvori and Polichnitos. We hypothesize that the attractiveness of Rodafnidia site for hominin presence was influenced by the local geology and tectonic activity controlling the long-term soil nutritional status of the region. We employ a combined geological-pedological study to unravel the paleoenvironmental conditions of the wider region. Our approach offers, in return, valuable insights into hominin-landscape interaction, relevant to landuse, resource exploitation and dispersal potential.

Our systematic sampling and analysis of rocks, soil and water offers clues to the soil nutritional characteristics of the main lithological units exposed in the wider Rodafnidia area. Results reveal distinct differences in the nutritional status of soils developed on different geological substrates. While volcanic soils in the immediate Rodafnidia region and marshy soils along the coast comprise well-balanced nutritional levels, serpentinite soils dominating the ophiolitic highlands display highly problematic properties such as low Ca/Mg ratios and enhanced heavy metal concentrations. Soils on hot spring deposits are puzzling as they display both beneficial characteristics (high soil organic carbon, high calcium) and potentially harmful enhanced heavy metal levels.

In a pedological context, Rodafinidia is located in a narrow zone of highly productive, nutrient rich soils in a wider region of geologically induced nutrient deficiencies. During sea-level lowstands, hominins along with other continental fauna could have crossed terrestrial passages between western Asia and the Eastern Aegean, and sites like Rodafnidia emerge as likely beneficial locations for hominin subsistence strategies. 

How to cite: Kübler, S., Tsakanikou, P., Galanidou, N., and Iliopoulos, G.: Soil nutritional gradients as long-term proxy for hominin subsistence strategies in geologically dynamic settings: the case of Acheulean Rodafnidia on Lesbos island, NE Aegean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3287, https://doi.org/10.5194/egusphere-egu23-3287, 2023.

African Easterly Waves (AEWs) are a significant control of West African rainfall and the associated Mesoscale Convective Systems (MCSs) and squall lines embedded within them. More than 40% of the total MCSs over the region are associated with AEWs and these MCSs account for approximately 80% of the total annual rainfall over the Sahel. Approximately 60% of all Atlantic hurricanes and 80% of major hurricanes have their genesis associated with AEWs. Simulating the features of AEWs, such as their westward propagation off the east Atlantic coast, is challenging for coarse-resolution climate models. In this study, we use High-Resolution Atmospheric Model (HiRAM) to simulate AEWs and analyze their future projections by the end of the 21st century. The simulations are performed globally at a horizontal resolution of 25km. The model uses shallow convective parameterization for moist convection and stratiform cloudiness. Future projections are conducted using representative concentration pathway 8.5. AEWs are separated with respect to their periods as 3–5 and 6–9-day period AEWs, and bandpass filtering is used to filter the waves from the mean flow. HiRAM simulates the structure and propagation of the waves well; however, it tends to overestimate the associated precipitation. In the future, the AEW precipitation and intensity of the circulation will considerably increase. The northward extent of the AEW track also shows a significant increase in the future. Enhanced baroclinic overturning and eddy available potential energy generated due to diabatic heating is also observed in the future.

How to cite: Raj, J., Bangalath, H. K., and Stenchikov, G.: Future projection of the African easterly waves in a high-resolution AGCM, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4141, https://doi.org/10.5194/egusphere-egu23-4141, 2023.

The study of the mid-Holocene climate tipping point in tropical and subtropical Africa is the subject of current research, not only because there is a comparatively simple but nonlinear relationship between the change in cause (orbital forcing) and the accelerated response of the monsoon system, but also because the African monsoon is an example of a potentially positive evolution of living conditions for humans: modeling results suggest that the Sahel is expanding northward in the wake of human-induced recent global warming, with green belts spreading northward. New literature distinguishes tipping elements such as the African monsoon according to the nature of the cause and the response of the climate system. Research here focuses primarily on tipping points of the type, which is characterized by a critical slowing down and a decreasing recovery from perturbations. The African monsoon, on the other hand, is an example of the tipping point of the type, which is characterized by flickering before the transition. The two types also differ in the nature of their early warning signals (EWS). These EWS are increasingly becoming the focus of research, as they are particularly important for predicting possible tipping of climate in the future of our planet. For the African monsoon system, flickering between two stable states near the transition has been predicted by modeling, but has not yet been demonstrated on paleoclimate time series.

The paleoenvironmental record from the Chew Bahir Basin in the southern Ethiopian Rift, which documents the climate history of eastern Africa of the past ~620 ka with decadal resolution in some parts provides the possibility to examine the termination of the African Humid Period (AHP, ~15–5 kyr BP) with regard to the possible occurrence of EWS. Thanks to six well-dated short sediment cores (<17 m, <47 kyr BP) and two long cores (~290 m, <620 ka BP) we can not only study the last climate transition at ~5.5 kyr BP in detail, but also similar transitions including possible EWS long before the first occurrence of Homo sapiens at ~318 ka BP on the African continent. The analysis of the Chew Bahir record reveals a rapid (~880 yr) change of climate at ~5.5 kyr BP in response to a relatively modest change in orbital forcing that appears to be typical of climate tipping points. If this is the case then 14 dry events at the end of the AHP and 7 wet events after the transition, each of them 20–80 yrs long and recurring every 160±40 yrs, could indeed indicate a pronounced flickering between wet and dry conditions at the end of the AHP, providing significant EWS of an imminent tipping point. Compared to the low-frequency cyclicity of climate variability before and after the termination of the AHP, the flickering occurs on time scales equivalent to a few human generations and it is very likely (albeit speculative) that people were conscious of these changes and adapted their lifestyles to the rapid changes in water and food availability.

How to cite: Trauth, M. H., Asrat, A., Fischer, M. L., Hopcroft, P. O., Foerster, V., Kaboth-Bahr, S., Lamb, H. F., Marwan, N., Maslin, M. A., Schäbitz, F., and Valdes, P. J.: Early Warning Signals for the Termination of the African Humid Period(s), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5277, https://doi.org/10.5194/egusphere-egu23-5277, 2023.

Which routes did Homo sapiens take when spreading from Africa to Eurasia? The climatic conditions changed and with them the living conditions. Over the past twelve years, a research team has deciphered the complex interplay of cultural innovations, mobility and environmental changes funded by the German Research Foundation (Collaborative Research Center 806 "Our Way to Europe"). Our working group in Bonn specifically investigated when and where migration corridors or barriers existed  from a paleoecological and paleoclimatological point of view. It turned out that the Levant, as the only permanent land bridge between Africa and Eurasia during the Quaternary, was the key region as a migration corridor for modern humans. Cores from the Dead Sea Deep Drilling Project (ICDP) were investigated, in which the environmental and climate history of the last 200 ka is excellently preserved and documented. In particular, pollen analysis allows changes in vegetation cover to be identified and environmental and climatic conditions to be reconstructed. These data illustrate that the Levant could only have served as a corridor when, under more favorable conditions, for example, neither deserts nor dense forests impeded the spread of modern humans.

How to cite: Litt, T.: Paleoecology/paleoclimate of the Levant and its impact on the spread of modern humans from Africa to Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5707, https://doi.org/10.5194/egusphere-egu23-5707, 2023.

The Guinea Dome, located in the eastern tropical North Atlantic, is produced by cyclonic circulation associated with the eastward North Equatorial Countercurrent, the northward Mauritanian Current and the westward North Equatorial Current, which causes the uplift of the isotherms in the Guinea Dome. This oceanographic feature is important for the regional atmosphere-ocean dynamics, and its variability was suggested to be linked with precipitation changes in North Africa, at least at a decadal scale. Characterizing the development of the dome through the Holocene will contribute to understand the prominent environmental changes that occurred regionally during this period, as evidenced by the green-to-desert Sahara transition at the end of the African Humid Period (ca. 6,000 years ago).

A 35cm sediment multicore, extracted southwest off Cabo Verde during the iMirabilis2 scientific cruise, at a water depth of 4,394 m, is being investigated. We present planktonic foraminifera counts and X-ray fluorescence (XRF) scanning data to reconstruct palaeoceanographic and sediment input changes during the Holocene. An age-depth model for the sediment core was established with three samples dated by the radiocarbon method, indicating that the sediment was deposited from 11,180 to 1,257 calibrated years before present (cal. BP).

Planktonic foraminifera results show a gradual but important change in the assemblages throughout the core, where the abundance of species preferring warmer waters increase by 44% towards the top of the core. These results are interpreted as warming of the surface water masses during the Holocene, as a result of reduced influence of the Guinea Dome due to its change of location to a more southern position and/or as a consequence of a weakening of the dome. X-ray fluorescence scan variations along the core show that the faunal shift is encompassed by differences in the terrigenous sediment supply, indicating changes in the inland climate regime. For instance, changes in the Ti/Fe, Ti/Al and Al/Ca ratios are proxies for the fluvial/aeolian sedimentary input and the hinterland climate variability. An increase of the high river discharge indicators is displayed between 10 and 6 kyr BP, probably as a consequence of the increased precipitation that took place during the African Humid Period.

Further ongoing geochemical analyses of foraminifera shells will provide information regarding the temperature, salinity and productivity of both, the mixed layer and the sub-thermocline, which will improve the characterization of the variability that the Guinea Dome experienced during the Holocene.

How to cite: Pérez-Rodríguez, I., Hansteen, T. H., Schindlbeck-Belo, J. C., Nürnberg, D., Kutterolf, S., Huvenne, V. A. I., Barnhill, K. A., Simon-Lledó, E., Evans, S., Vinha, B., Mosquera Giménez, Á., and Orejas, C.: Holocene oceanographic variability linked to the Guinea Dome development recorded in a deep-sea sediment core off Cabo Verde, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5829, https://doi.org/10.5194/egusphere-egu23-5829, 2023.

Climate over Kenya is rather heterogeneous and exceptionally dry for a region located in the tropics. This is related to various large-scale drivers, such as Lake Victoria, the complex topography, and the vicinity to the ocean. In consequence water resources are scarce and several stakeholders depend on these. Hence, it is important to understand how precipitation amounts and patterns change under global warming. A special focus is on Mount Kenya, one of the most important freshwater towers in Kenya. To investigate these changes, we employ the Weather Research and Forecasting (WRF) model V3.8.1 to downscale a 30-year period for the present and the future climate, based on global climate simulations. The present period covers the years 1981–2010, and the future is run once for the mitigation scenario RCP2.6 and for the high-emission scenario RCP8.5 for the years 2071–2100.

Changes in precipitation and temperature are well noticeable in the region of Mount Kenya. The projection indicates an increase in precipitation for the two rainy seasons (March to May, and October to November), while precipitation is reduced in the dry season. Extreme precipitation around Mount Kenya shows increases in the future during the rainy season, whereby the two different scenarios show a similar increase in extreme precipitation. This result is a bit surprising and needs further investigation. As expected, temperatures are projected to increase over all of Kenya, and particularly along the slopes of Mount Kenya in all months. For temperature there is a clear difference in the warming between the two scenarios, as RCP8.5 shows a much stronger change in temperature than RCP2.6. The summit of Mount Kenya reaches temperatures in the future that today are found at an elevation of around 3,200 m above sea level (a.s.l.). This warming can substantially affect the endemic vegetation along the slopes of Mount Kenya. Assuming that the tree line is limited by temperature and not precipitation, as the latter is abundant, it could move from around 3,000 m a.s.l. up to 3,700 m a.s.l. The strong increase in temperature further affects the remaining glacier, which is currently an important water storage during dry months. The projected increase in precipitation over entire Kenya will therefore increase water availability and reduce fire danger. Nevertheless, the combined increase in temperature and precipitation could affect human and animal wellbeing, as heat stress may be increased.

All these results are based on a single regional and global climate model. Preliminary results indicate that the rainy season is clearly underestimated in the present simulation, compared to simulations obtained by a downscaling of the reanalysis ERA5. This indicates that important components of the atmosphere are not correctly captured by the model. These could include land-atmosphere interactions, misrepresentation of land cover, biases in sea surface temperatures and related changes in the atmospheric circulations. Thus, the atmospheric circulation and interactions with the land surface have to be assessed in further studies.

How to cite: Messmer, M., González Rojí, S. J., Raible, C. C., and Stocker, T. F.: Influence of climate and atmospheric circulation changes on water balance of Mount Kenya and surroundings, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6585, https://doi.org/10.5194/egusphere-egu23-6585, 2023.

The Arabian Peninsula was, up until recently, thought to have been depopulated during the more arid phases between MIS5 and Holocene interglacials, and in particular during MIS3 and MIS2. Within the last few years there have been five new sites dated to this arid phase, demonstrating that at the very least there were episodic occupation events on the Arabian Peninsula, and potentially refugial populations. The increasing number of sites potentially lends weight to the hypothesis for a more continuous refugial population on the Arabian Peninsula, as opposed to multiple-short lived events. The human adaptation to harsh environment during transition from humid period is a focus of this research project. Here we present preliminary dates from the newly recorded site at Wadi Asklat in Duqm, south-central Oman, where stratified lithic technology has been identified within a alluvial terrace sediment sequence. Two OSL samples at depth of 100 and 125 cm were taken to understand site chronology together with geomorphic processes. The paleoenvironmental samples were collected for palynological and pedological analyses. The preliminary clay mineral analysis identified palygorskite, illite, chlorite, smectite in layer at depth 90 to 110 cm suggesting a soil formation process. The lithic artifact at depth of 115 cm was preliminarily identified as Kombewa core with two bidirectional negatives made on crested flake. In addition, a several stratified sites have also been identified within the area, however except for the Wadi Asklat site these are at present undated. The association of many of the new sites with river terraces, including Wadi Asklat, indicate an important link between human activity and water which was no doubt heightened during arid phases. The results contribute to our knowledge of population dynamics and settlement patterns in this under-studied region of central Oman. The research is as a joint effort of ARDUQ expedition led by Archaeological Institute Prague (Czechia) and LARiO expedition led by La Trobe University Melbourne (Australia).

How to cite: Garba, R., Meredith-Williams, M., Neuhuber, S., Gier, S., and Usyk, V.: Arid occupation of south-eastern Arabia: A new Late Pleistocene site at Wadi Asklat, south-central Oman—dating and paleoenvironmental reconstruction., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8109, https://doi.org/10.5194/egusphere-egu23-8109, 2023.

North Africa is one of the most vulnerable regions on Earth to anthropogenically-driven climate change, but also one of the least equipped to deal with the consequences. Predictions of precipitation levels over the forthcoming centuries diverge, not only in magnitude, but also in the sign of change. One key aspect of this uncertainty comes from the role of Atlantic Ocean sea surface temperatures (SST), which are known to exert a strong control over precipitation in North Africa and are implicated in both the major Sahelian drought of the late 20^th century and extreme droughts associated with the Heinrich events of the last glacial period.

To better understand how African hydroclimate responds to SST variability across a range of climate states, we reconstruct changes in the ocean and atmosphere through the transition from the Pliocene epoch (when atmospheric CO₂ levels were comparable to present) into the cooler Pleistocene. We present data from Ocean Drilling Project Site 659, which is situated in the subtropical North Atlantic beneath the major modern summer Saharan dust plume. Our dust accumulation and X-ray fluorescence core scan data record repeated shifts between highly arid conditions and humid intervals with vegetated or “Green Sahara” conditions over much of northern Africa. The amplitude of these humid events is modulated by both global climate state and variability in solar insolation, with three unusually long intervals of low dust emissions (each lasting ca. 100 kyr) occurring at times when insolation variability was weak. We also present new paired alkenone-derived SST estimates and multi-species planktonic foraminiferal isotope records from 3.5–2.3 Myr ago to explore the role of North Atlantic dynamics in driving African hydroclimate variability. Our records help to develop the environmental framework needed to assess evolutionary outcomes on land and improve our understanding of the mechanisms driving precipitation variability in North Africa.

How to cite: Crocker, A., Jewell, A., Mitsunaga, B., Buchanan, S., Westerhold, T., Röhl, U., Xuan, C., Russell, J., Herbert, T., and Wilson, P.: Did the North Atlantic Ocean play a role driving Green Sahara conditions during the Late Pliocene and Early Pleistocene?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10095, https://doi.org/10.5194/egusphere-egu23-10095, 2023.

The Early Mid-Pleistocene Transition (EMPT) between 1,200–700 ka represents a major global climate transition from dominantly 41,000-year to 100,000-year glacial cycles. The forces and mechanisms behind this transition, and the response of African environments, is not well understood. The active volcanism and tectonics of the East African Rift System (EARS) add complexity to environmental systems and can erase important proxy records, inhibiting studies of lacustrine dynamics. As a result, there is minimal understanding of how this transition impacted the region’s lake systems, with implications for hominin migration. At paleolake Suguta in the northern Kenya Rift, however, flood basalts cap lacustrine EMPT-aged deposits and help preserve these strata and their valuable paleoenvironmental record. This research presents a high-resolution reconstruction of hydrological change from approximately 930 to 830 ka during the EMPT at the Suguta-Turkana Valley in the northern Kenya Rift. Paleolake dynamics are reconstructed from a 41 m sedimentary section using diatom morphology, sedimentology, and x-ray fluorescence analysis. Lake levels varied during the EMPT, particularly from ~885–830 ka, ranging from deep stratified lakes, shallow, well-mixed lakes, and complete desiccation. This record identifies hydroclimate variability at several thousand year-resolution within the Suguta-Turkana Valley during the EMPT, illuminating a period where generally little is known about terrestrial environmental change.

How to cite: Robakiewicz, E., Owen, R. B., Deino, A., Trauth, M., and Junginger, A.: Variable Hydroclimate in the Suguta-Turkana Valley, Kenya during the Early Middle-Pleistocene Transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14071, https://doi.org/10.5194/egusphere-egu23-14071, 2023.

Climate change is often linked with evolutionary processes, but the effect of this driver is mediated by the environment in which the organisms live. In relation to hominins, climatic conditions play an important role in determining the availability of resources critical to development and evolution, including water, materials for tools, and food. Over the last c. 1 million years the spatial distribution of water and vegetative resources across Africa has shifted dramatically, and in tandem. The most significant change in this time period occurred c. 300,000 years ago when the predominance of wetter conditions, and relatively more abundant vegetative resources, shifted from western to eastern Africa. Around this time Homo sapiens and Middle Stone Age technologies emerged. While the changing landscape of Africa would not have necessarily have excluded hominins from occupying particular regions, they would have altered the chances for interaction between different populations through the creation of new geographic connections. These new connections between hominin populations would have promoted different cultural and genetic exchanges, which consequently could have driven development and evolutionary processes. To understand the environmental backdrop to hominin development and evolution we need to explore the changes that occurred within the landscapes in which they lived. Here landscape scale (site specific) changes in environmental resources are considered from key locations in western and eastern Africa. These insights are then placed within the context of climate and vegetation change across the continent to develop ideas about how the changing landscapes could have facilitated, and driven, cultural development and evolutionary processes in hominins during the Pleistocene.

How to cite: Gosling, W.: Hominin life and evolution across changing African landscapes in the Pleistocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14725, https://doi.org/10.5194/egusphere-egu23-14725, 2023.

Samples of present-day aeolian dust collected with the help of various kinds of dust sampling devices are currently a widely used resource to measure distinct characteristics of aeolian transported material, such as variations in the amount of dust flux over space and/or time, chemical and mineralogical composition and isotopic signatures of the material to ultimately infer the origin of the aeolian transported sediment, to understand transport pathways and to identify the sensitivity of aeolian dust to changes in local or global climate variability. However, so far the majority of samples captured by dust traps originate from classical desert environments, such as the Saharan desert or the Australian or Asian deserts. Due to smaller sample amounts, longer depositional periods, difficulties in installing the traps, and labor-intensive trap maintenance, continuous dust-trap records from semi-arid regions are rare.

In this study we present a record of aeolian dust deposits from the semi-arid region at Lake Chala, in SE Kenya/ NE Tanzania, comprising a nearly continuous sampling period of 5 years from three different locations. The first dust traps were installed in 2016 during the ICDP DeepCHALLA drilling and deliver a monthly record of dust characteristics in the area. A combination of microscopic investigations, detailed grain-size measurements, as well as mineralogical analysis allows us to infer changes in the amount and characteristics of the monthly deposited aeolian sediments and provide a first insight into seasonal changes and fluctuations of atmospheric forcing factors responsible for dust transport and the deposition in our study area.

How to cite: Meyer, I., Verschuren, D., and De Batist, M.: Track and trace: how aeolian dust can help to understand East African climate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14878, https://doi.org/10.5194/egusphere-egu23-14878, 2023.

The analysis of ancient DNA and paleoproteomics can identify biological materials, such as fossils, construct phylogenetic relationships between extinct and extant species, and has been widely applied in archaeology and paleontology. In general, proteins degrade more slowly than DNA and could be persevered in fossils over 60 million. Although less phylogenetic information was obtained than ancient DNA, paleoproteomics analysis becomes an indispensable method for studying biological evolution and hominins behaviours with its high throughput, low cost, and low contamination. Based on several cases of applying paleoproteomics analysis in archaeological and paleontological sites from East Asia, I will present two main methods, LC-MS/MS and MALDI-TOF MS, and how paleoproteomics reveals the evolutionary history and behaviours of hominins in East Asia, aiming to provide a research background of this field.

How to cite: Xia, H., Zhang, D., and Chen, F.: Palaeoproteomics of skeletal fossils reveals hominins evolution and behaviours: several case studies from East Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15774, https://doi.org/10.5194/egusphere-egu23-15774, 2023.

The East African Rift System (EARS) is a key location for studying Plio-Pleistocene paleoclimate and hominin inhabitance. The region experienced profound reorganization during this interval as a response to volcanism, tectonics and climate change, and arguably detailed spatiotemporally coherent climate datasets could provide evidence of causal links between geologic change and hominin evolution.  However, continued tectonism, erosion, burial and volcanism obscures much of this information. Despite its rich fossil record, the Turkana basin in the northern Kenya Rift is no exception. It has been hypothesized that Lake Turkana and paleo-Lake Suguta to its south formed one 530-650 km long mega-lake before 221 ka ago, and was a major barrier for E-W dispersal of hominids and other terrestrial fauna. Here we present new information on basin development based on paleolandscape modeling and ⁸⁷Sr/⁸⁶Sr analysis on microfossils of newly discovered paleo-lake sequences in the Suguta Valley, permitting reconstruction of volcano-tectonic processes 900-700 ka ago. Contrary to previous assumptions, results suggest that two to three lakes separated by tectono-volcanic barriers formed instead of one mega-lake. These results have implications for previously formulated hypotheses about mega-lakes preventing W-E migration and exchange and suggest that during the early Middle Pleistocene E-W migrations were possible.

How to cite: Junginger, A., Kuebler, S., Rosca, C., Owen, R. B., Deino, A., Feibel, C., Trauth, M. H., and Vonhof, H.: Mid-Pleistocene volcano-tectonic fragmentation of the Turkana-Suguta Megalake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17267, https://doi.org/10.5194/egusphere-egu23-17267, 2023.

The Sicily Channel, located in the foreland area of the African plate, is a very interesting geological area in the Western-Central Mediterranean, as it has undergone different tectonic processes because of its proximity to the convergence zone with the European plate. Extension and opening of a rift zone (Sicily Channel Rift Zone, including the Pantelleria, Malta, and Linosa grabens) occurred in the lower plate of the subduction zone marked by the Gela Thrust System and the Calabrian Accretionary Wedge, respectively located south and south-east of Sicily, and the Maghrebian chain to the west. We analyzed geological and geophysical data, such as variable penetration seismic reflection profiles integrated with borehole data; these allowed us to investigate subsurface structures down to the crust-mantle boundary. The crustal profile shows a Moho deepening down to 11.8 s/(TWT) under the Gela Thrust System and going up to 8 s/(TWT) under the Linosa Graben. Moreover, the presence of several hyperbolae zones and signal anomalies have been linked to a rise of deep fluids associated with mantle uplift and, upward, to magmatic intrusions. The sub-surface also shows evidence of a N-S oriented zone, from the Gela Thrust System to the Malta and Linosa grabens, which has undergone contractional tectonic events superimposed on previous extensional structures. Throughout this area, from the Early-Middle Miocene to the Early Pliocene, an extensional event occurred in association with the slab roll-back of the African Plate. In this phase, several volcanic intrusions concentrated near the grabens’ rims suggest a relation between the extension, the Moho rising, and the magmatic manifestations.  Afterward, a compressional event in the Madrepore and Malta Grabens was registered. This event has been correlated to the advance of the Gela Thrust Front, which, according to literature bio-chronostratigraphic analysis, had three stages of advancement in Zanclean, Piacenzian and Chibanian. Furthermore, a recent contractional event caused the folding of the seafloor in the central part of the Malta Graben. This latter phase has been related to a potential change in the subduction polarity. These results provide new insights into the regional kinematic setting of the Sicily Channel, suggesting that strain located within the African Plate can be explained through the overlapping of both intra-plate (localized asthenospheric rise) and inter-plate (compression transmitted from surrounding mountain belts) processes ongoing between Europa and Africa. Indeed, the Sicily Channel structural setting resulted from the interplay of the rollback of the African slab, the consequent changes in the asthenospheric flow that caused extension and local magmatic intrusions, and the active subduction front and its potential polarity reversal that caused local and polyphased compressional pulses.

How to cite: Maiorana, M., Artoni, A., Chizzini, N., Le Breton, E., Sulli, A., and Torelli, L.: Polyphased contractions inside the Sicily Channel Rifting Zone: new evidence from seismic reflection profiles analysis and geodynamic implications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-707, https://doi.org/10.5194/egusphere-egu23-707, 2023.

The Calabrian block, along with Alboran, Kabylies and Peloritani, form isolated and enigmatic igneous/metamorphic terranes (AlKaPeCa) stacked over the Meso-Cenozoic sedimentary successions of the Apennines and Maghrebides. The long-lasting debate on the origin and evolution of such crustal terranes include different paleogeographic interpretations. Some authors considered them as: i) remnants of a micro-continent lying between Eurasia and Africa; ii) fragments of the Hercynian margin of Europe separated from Africa during Early Jurassic Alpine Tethys spreading, later detached from Corsica-Sardinia and/or Catalan-Provençal margin, and then stacked over Apennine-Maghrebian sediments during Neogene roll-back episodes; iii) portion of the Africa-Adria paleomargin deformed and involved into the orogenic pile.

Paleomagnetic data are crucial to properly reconstruct the drift of the AlKaPeCa blocks and their lasting geological history, however no paleomagnetic data could be obviously obtained from the Hercynian crystalline rocks of the AlKaPeCa. Besides the well-defined ∼20° clockwise (CW) rotation, constrained between 1 and 2 Ma and related to changes occurring in the roll-back system and spreading episodes in the Tyrrhenian Sea, the tectonic behavior of the Calabrian block during the Early Jurassic rifting episodes, the Early-mid Cretaceous transcurrent tectonics, the Late Cretaceous-early Cenozoic Africa-Europe collision, and Eocene-Miocene counterclockwise (CCW) 90° rotation of the Corsica -Sardinia block, to which Calabria was likely solidly attached, remains completely speculative.

We report on the paleomagnetism of upper Triassic-lower Miocene sedimentary rocks from the Longobucco succession that is transgressive over the crystalline Sila Massif (NE Calabria). Well-defined remanent magnetization directions carried by hematite were isolated in 10 sites (122 samples) in Jurassic rocks. Nine Toarcian and one Tithonian Ammonitico Rosso sites yielded a dual polarity “A” magnetization component whit a direction over 40° from the geocentric axial dipole (GAD) field direction, that supports a positive fold test. Five sites yielded a “B” normal polarity component NE (<40°) of the GAD direction characterized by a negative fold test. We interpret the B component as a Miocene magnetic overprint later clockwise rotated by ∼20° during the Pleistocene (1–2 Ma) rotation of Calabria. When corrected for such rotation, the A component defines a ∼160° CCW rotation of the Calabrian block with respect to Europe. Of these, ∼90° likely occurred along with Corsica-Sardinia block during its Eocene-Miocene rotation from the Provençal margin. Thus, the Calabrian block underwent an additional Cretaceous-Eocene 70° CCW rotation that we relate to Early-mid Cretaceous >500 km left-lateral transcurrent motion between Africa and Europe.

How to cite: Siravo, G., Speranza, F., and Macrì, P.: Pre-Miocene Paleomagnetic Data from the Calabrian Block Document a 160° Post-Late Jurassic CCW Rotation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1624, https://doi.org/10.5194/egusphere-egu23-1624, 2023.

We present a study of the synorogenic deposits associated with the orogenic construction of the southern Apennines. This orogen is a segment of the Alpine chain system bounding the central-western Mediterranean Sea. Southern Apennines form an orogenic belt consisting of the superposition of some successions of the downgoing Adria plate, made of shallow-water to pelagic sedimentary successions. The synorogenic sedimentation was ruled by the migration of the forebulge-foreland basin system, with the flexure of the continental part of the Adria plate since the Oligocene (forebulge stage), mainly due to the slab retreat process. The thrust front-foredeep-forebulge system migrated toward E/NE until the middle Pleistocene. We focussed our attention on the Foreland Basin System synorogenic deposits mainly consist of back-bulge, foredeep, and wedge-top basin sediments.

How to cite: Ciarcia, S. and Vitale, S.: Neogene synorogenic stratigraphic evolution of southern Apennines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1865, https://doi.org/10.5194/egusphere-egu23-1865, 2023.

The Cenozoic tectono-sedimentary evolution of the External Rif Zone (ERZ) has been studied based on an integrated analysis of twenty-two representative stratigraphic successions grouped in seven sectors from N to S: Tangier, Asilah, Chaouen, Zoumi, Ouezzane, Ourtzarh and the Prerifian Ridges. The ERZ is divided classically, from N to S, into Intrarif, Mesorif and Prerif sub-domains. Each sub-domain is subdivided further in to internal and external. The Cenozoic stratigraphic record of the ERZ can be roughly separated into five main stratigraphic intervals bounded by five main unconformities corresponding to the Cretaceous-Paleogene, Eocene-Oligocene, Oligocene-Miocene, Burdigalian-Langhian and middle-late Mioceneboundaries. Each unconformity can be related to a local or regional tectonic events: (1) the Cretaceous-Paleogene boundary unconformity to the tectonic inversion (from extension to compression) occurring in the alpine Tethys domain in the upper Cretaceous ; (2) the Eocene-Oligocene boundary to a flexure phase in the Atlas front; (3) the unconformity that marks the Oligocene-Miocene boundary can result from the starting of the nappes stacking phase in the Internal Zone; (4) the Burdigalian-Langhian boundary unconformity to the end of structuring of the Internal Zone; and (5) the middle-late Miocene boundary unconformity to the nappes stacking phase in the ERZ. The Paleogene evolution can mainly be correlated with the so-called Eo-alpine orogenic phase, while the Miocene one is related to the Mio-Alpine, both recognized in the western Mediterranean area. As a fundamental part of this research, the analysis of synsedimentary tectonics have been performed, considering tectofacies, unconformity implications and subsidence analysis. Tectofacies (such as, turbidites, slumps, mass flow deposits, synsedimentary folds and faults) are checked from the upper Ypresian succession onward, but more frequently during the Oligocene and Miocene, which point out an upward increase in the tectonic activity. Considering the ERZ as a foreland basin, the Eocene foredeep area would correspond to the Internal Mesorif and Internal Prerif sub-domains. This foredeep was represented by a complex of two “sub-geosynclines” separated by a relative bulge located in the External Mesorif. In this way, the Intrarif could represent the relative orogenic front (advanging on the Internal Rif Zone). The Eocene forebulge was located in the External Prerif, while the Gharb Basin was the backbulge of the system. During the Oligocene the depocentral area migrated southward favoring a homogenization of subsidence in the whole ERZ. In this new configuration, the foredeep would be located in the External Mesorif (formerly a relative bulge) while the External Prerif and the Gharb Basin continued to act as the forebulge and the backbulge of the system, respectively. During the early Miocene a new diversification of depocenter took place with the main foredeep in the Internal Mesorif and secondary foredeeps areas in the externalmost and internalmost Intrarif. In this period, the forebulge should be located in the middle Intrarif. Finally, during middle Miocene foredeep were located in the externalmost Intrarif and Internal Prerif while in the late Miocene depocenter migrates southward to the Extenal Prerif-Gharb areas (formerly forebulge and backbulge areas).

How to cite: Maate, S., Hlila, R., Maate, A., Martin Martin, M., Guerrera, F., Serrano, F., and tramontana, M.: Cenozoic synsedimentary tectonics in the External Rif Zone (Maghrebian Chain, Northern Morocco), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2019, https://doi.org/10.5194/egusphere-egu23-2019, 2023.

We present a study on the mud volcanoes of Bolle della Malvizza located in the Irpinia sector of the southern Apennines (southern Italy). These structures are hosted in the Upper Cretaceous-Upper Miocene Fortore succession (Lagonegro-Molise Basin) and emit mud and bubbles of methane and CO2. Mud volcanoes are focused in a narrow area of ca. 5000 m², consisting of eight main emission centres and several minor craters. We approached this research with a multidisciplinary study, including stratigraphic and structural surveys, geophysical and geochemical investigations and morphometric analyses. This study aims to investigate the origin of fluid migration and shed light on the pathways mainly controlled by faults.

How to cite: Fabozzi, C., Albanese, S., Ambrosino, M., Ciarcia, S., Cicchella, D., Natale, J., Prinzi, E. P., Verrilli, F., and Vitale, S.: A multidisciplinary study of the “Bolle della Malvizza” mud volcanoes (southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2648, https://doi.org/10.5194/egusphere-egu23-2648, 2023.

Most plate kinematic reconstructions concerning the Iberian plate imply a major (>400 km) left-lateral displacement between Iberia and Eurasia during the opening of the Bay of Biscay (Late Jurassic-Early Cretaceous). In the past, authors identified the North Pyrenean Zone (NPZ) as the domain accommodating this lateral displacement, while more recent works tend to distribute the deformation in two or three transtensional corridors located in the NPZ and in the Iberian Chain basins. Nevertheless, field evidence contrasts with such models, since no structure seems to have accommodated such huge amount of displacement. Moreover, debate exists concerning the timing of the left-lateral displacement between Iberia and Eurasia (Late Jurassic vs Early Cretaceous).

We present a review of the tectono-sedimentary and kinematic evolution of rift basins distributed across the wide Iberia-Eurasia plate boundary that recorded the Late Jurassic-Early Cretaceous rifting phase, from the Iberian Chain basins (in the southwest) to the northern part of the Aquitaine domain aligned with the Armorican Margin (to the northeast). To the first order, these basins experienced the same tectonic evolution, with an initial Permian-Triassic rifting phase related to the breakup of Pangea, and a subsequent Late Jurassic-Early Cretaceous rifting phase related to the opening of the Bay of Biscay. For this latter phase, authors have proposed contrasting kinematic models, with opening mechanisms varying between orthogonal rifting and transtensional/pull-apart tectonics. Our review allows to propose a reappraisal of the kinematic evolution of the Iberia-Eurasia diffuse plate boundary during the Late Jurassic-Early Cretaceous rifting, which consists in four phases: (i) a Late Jurassic phase of transtensional deformation localized at the borders of the system (Asturian Basin/Southwesternmost Iberian Chain basins and Armorican Margin), while the rest of the basins underwent orthogonal rifting, contemporaneous with rifting in the Bay of Biscay margins; (ii) a Neocomian phase of generalized marine regression; (iii) a Barremian-Early Albian phase of distributed left-lateral transtension, contemporaneous with crustal breakup in the Bay of Biscay; (iv) an Albian-Cenomanian phase of left-lateral transtension localized in the Basque-Cantabrian/North Pyrenean corridor, contemporaneous with ocean spreading in the Bay of Biscay, while the rest of the rift basins within the plate boundary became tectonically inactive. This evolution highlights a trend of progressive localization of the plate boundary from the Late Jurassic to the Early Cretaceous in response to the different tectonic phases of the Bay of Biscay margins. This work also allows to highlight the role of some rift basins in accommodating part of the deformation between Iberia and Eurasia which have been often disregarded, due to their position below the Cenozoic cover of the Pyrenean foreland basins, such as the Ebro and Aquitaine domains.

How to cite: Asti, R., Saspiturry, N., and Angrand, P.: Progressive localization of a diffuse transtensional plate boundary: the example of the Iberia-Eurasia plate boundary during the opening of the Bay of Biscay (Late Jurassic-Early Cretaceous), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2691, https://doi.org/10.5194/egusphere-egu23-2691, 2023.

We present a study of a Mio-Pliocene marine to a continental clastic sedimentary succession of the southern Apennines Foreland Basin System well exposed in the Miscano River in the Irpinia sector of the chain. These well-bedded wedge-top basin deposits host a significant angular unconformity between a post-evaporitic succession (uppermost Messinian-lowermost Pliocene), developed on top of the evaporite deposits related to the Messinian Salinity Crisis, and an overlying upper part of the Zanclean sediments. The unconformity witnesses a major tectonic shortening stage of the southern Apennines characterized by out-of-sequence thrusting that involved the Mio-Pliocene wedge-top basin deposits. Meio-microfaunal and nannofloral fossil assemblages were analyzed to define the depositional environments and biostratigraphy of the two successions. In addition, benthic foraminiferal and ostracod assemblages were studied in detail, and their autochthonous/allochthonous provenience was discussed from a paleoecological point of view. The relative response of these assemblages to environmental parameters, such as salinity, oxygenation, paleobathymetry and climatic changes, allowed us to reconstruct the paleoenvironmental evolution of these wedge-top basin deposits.

How to cite: Infante, A., Aiello, G., Barra, D., Ciarcia, S., Di Donato, V., Morabito, S., Prinzi, E. P., and Vitale, S.: Palaeoenvironmental reconstruction of the Mio-Pliocene succession of the Miscano River: insights on sedimentation after the Messinian salinity crisis in the southern Apennines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4235, https://doi.org/10.5194/egusphere-egu23-4235, 2023.

Hinterland basins are low-lying and often heavily populated areas at the back of orogenic belts which have significant economic and infrastructural importance. The tectonic-stratigraphic and regional characterisation of hinterland basins is fundamental for evaluating their subsurface utilisation and potential geohazards.

This study focuses on the origin and development of the Tuscan hinterland basins of the Northern Apennines. These basins have been associated with a compressional regime lasting until the Late Pliocene-Pleistocene during which out-of-sequence thrusts and back-thrusts in the inner portion of the chain accommodated the compressive stress accumulated in the frontal zones. An alternative interpretation considers the evolution of these basins in an extensional regime as an effect of large-scale back-arc processes or gravitational collapse of thickened crust following the Apennine orogeny since the Early Miocene. In this tectonic regime, the basins have been interpreted as graben, half-graben or bowl-shaped basins evolving into graben.

Our work aims to determine the tectonic-sedimentary evolution of the Valdera-Volterra Basin through the analysis of  ~271.8 km of 2D seismic reflection profiles and wireline logs from two exploration wells. The Valdera-Volterra Basin basin is an NW–SE oriented depocenter ~60 km long ~30 km wide filled with a clastic succession of Miocene-Pleistocene fluvial-lacustrine to marine deposits up to ~2 km thick.

The analysis has revealed a polyphased tectonic history of the basin with a Messinian-Zanclean compressional phase deforming the basin-infill as indicated by seismic imaging of synformal geometries and strongly tilted unconformities. Such deformation is tentatively associated with E/NE vergent blind thrusts and SW vergent blind back-thrusts. During the Piacenzian, the activity of normal border faults and the presence in their hanging wall of associated sedimentary wedges thickening towards NE suggest an extensional phase following the earlier Messinian-Zanclean compression. Broad folding of the shallow Piacenzian units in the hangingwall of the normal faults suggests the occurrence of mild positive inversion at the end of the Piacenzian/Lowermost Pleistocene?.

This tectonic history has been associated with crustal shortening in the Northern Apennines hinterland, accommodated by thrusting, that occurred discontinuously until the end of the Pliocene/Lowermost Pleistocene?. The formation of the border faults during the Piacenzian has been related to a prolongated phase of tectonic quiescence that led to the collapse of the sedimentary pile and the Pre-Neogene substrate. In this setting, the positive inversion occurred at the end of the Piacenzian/Lowermost Pleistocene? represents the last compressive event related to crustal shortening.

How to cite: Poneti, G., Scarselli, N., Benvenuti, M., and Craig, J.: Evidence of tectonic inversion in the Northern Apennines Hinterland basins, the example of the Valdera-Volterra basin (Central Tuscany), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6232, https://doi.org/10.5194/egusphere-egu23-6232, 2023.

Diverging plates are reconstructed through well-defined time-steps and direction of motion thanks to oceanic magnetic anomalies and fracture zones. None of these two oceanic features can nevertheless be used if the divergent boundaries are reactivated in orogenic belts. Convergence erases indeed the dense oceanic material and the related kinematic markers and leave as main witnesses suture zones and associated remnants of the former continental margins. The pre-orogenic plate template of the Alps remains debated for this reason, leading to debate on the size of subducted oceanic domains, and on the complex paleogeography at the Tethys-Atlantic junction. Unravelling size and fate of the pre-orogenic domain remains difficult and asks for a new, holistic restoration approach. Here we use a rift domain approach that enables us to quantify width and formation ages of margins of the Iberia-Eurasia-Adria-Africa plate boundaries. We jointly use a global kinematic restoration software (Gplates) and new rift concepts that allow us to propose a tight fit restoration and evolution of the Atlantic Tethys junction during the Mesozoic. Kinematic restorations of the Mesozoic evolution of what is now the Western Mediterranean must build on independent approaches. A first approach is the correct restoration of the major surrounding plates. A second approach is the restoration of the intra-continental extension accommodated in reactivated rifted margins that can be in the order of several hundreds of kilometers. Remnants of the former margins allow to define so-called building blocks and appear as a good base for restoration where vestiges of a standard oceanic crust are missing.

How to cite: Frasca, G. and Manatschal, G.: Mesozoic evolution of the Atlantic-Tethys junction: a kinematic description, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7288, https://doi.org/10.5194/egusphere-egu23-7288, 2023.

The Empordà basin is located in NE Catalonia (Spain), overprinting the Eastern Pyrenees where this mountain belt reaches the Mediterranean Sea. The area offers an opportunity to study cycles of orogenic evolution, from mountain building to destruction, although with some peculiar features. Following Pyrenean contractional structures that ceased in the Oligocene, earlier than in the Central and Western Pyrenees finished during the lower Miocene, the extension that depressed the Empordà basin seems to be a younger event (late Miocene-Pliocene) than the opening of the Western Mediterranean (Gulf of Lyon and Valencia trough; late Oligocene-Miocene). The regional NE-SW extensional fault systems that dominate from the Gulf of Lion to the Catalan Coastal Ranges and Valencia grabens contrast with the NW-SE normal faults in the Empordà basin, which are also associated with alkali volcanism during the Neogene. This feature is still poorly understood, together with the absence of crustal root in the adjacent relict relief of the Pyrenees despite the relatively high elevation.

To gain insights into these questions and into the detailed geochronology and mechanisms of the transition from convergence to extension, we have revisited the tectono-sedimentary record of the South-Pyrenean and Empordà basins. First, the provenance of the clastic deposits from the Paleogene to the Neogene gives information about the evolution of the sedimentary systems, as well as the tectonic changes in the source regions. This data combined with low-temperature thermochronology of source reliefs and basin sedimentary units allows characterizing part of the geodynamic evolution from the NW Mediterranean realm. Complementary, new structural data from field observations and seismic profile interpretation provide us with inferences on a new structural model of the region.

How to cite: Peris, S., Griera, A., Gómez-Gras, D., and Teixell, A.: The transition from convergence to extension in the NW Mediterranean: insights from the thermochronologic and tectono-sedimentary record in the Eastern Pyrenees and Empordà basin (NE Spain), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7642, https://doi.org/10.5194/egusphere-egu23-7642, 2023.

During the Burdigalian the North Alpine Foreland Basin, as part of the central and western Paratethys, underwent various paleogeographic and paleoenvironmental changes which led to the deposition of different sedimentary facies. For instance, the Ottnangian regional stratigraphic stage (18.2 – 17.3 Ma) was characterized by a major transgression in the beginning, with the deposition of several littoral facies along the northern coastline of the North Alpine Foreland Basin. Successively, the late Ottnangian documents the final retreat of the Paratethys Sea from the North Alpine Foreland Basin and the deposition of widely distributed fluviatile units. The outcrop Neustift in southeast Germany bears many different siliciclastic facies and shows the transition of the Ottnangian marine realm towards a riverine-deltaic environment. Despite the exceptional size and complexity of the succession, this outcrop is only poorly studied. Anyhow, this section gives unique potential for the understanding of the facies evolution during the terminal Ottnangian. In total a 70 m long and 15 m high sedimentary log was recorded together with several micropaleontological samples (1 kg each) for the reconstruction of the depositional environment and stratigraphic positioning. The micropaleontological samples yielded 164 genera of benthic foraminifera and 144 species of ostracods. Moreover, these deposits are extremely rich in macrofossils (elasmobranchia, mollusca, brachiopoda, echinoidea) which are also poorly studied. We found out, that the lowermost segment of the section belongs to the marine “Littoral Facies of Holzbach-Höch”, which deposited directly on top of a transgressive layer on the crystalline basement. Several of the observed ostracod species are new to these deposits. Large-scale cross-bedding structures show that this shallow marine environment was affected by strong tidal currents along the rocky shoreline. The fine-grained sediments with wavy and lenticular bedding on top of the littoral deposits show an ongoing transgression, with neritic foraminiferal assemblages and bioturbation. They were assigned by biostratigraphy to the uppermost Neuhofen Formation. Finally, the marine deposition is replaced by a large-scale deltaic system, resulting into the deposition of the fluviatile Ortenburg gravel. This preliminary study should draw some more attention to this unique outcrop in the North Alpine Foreland Basin and the potential for further studies in the realm of sedimentology and paleontology. 

How to cite: Drießle, T. and Hofmayer, F.: From shoreface to riverbed – Facies evolution in Burdigalian deposits of the North Alpine Foreland Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8123, https://doi.org/10.5194/egusphere-egu23-8123, 2023.

Data from the late Miocene site of Cessaniti (Vibo Valentia, Calabria, southern Italy) suggest the existence of a land connected to Africa in the central Mediterranean.

Although the site has been known since the XIX century for the abundant and well-preserved fossil echinoids of Clypeaster, in the last 20 years, Cessaniti released not only abundant remains of the Sirenian Metaxytherium serresii and rare Cetaceans (Odontocetes: Physiteroidea indet.; Mysticetes: Heterocetus cf. guiscardii) but also a consistent record of terrestrial mammals (Stegotetrabelodon syrticus, Bohlinia attica, Samotherium boissier, Tragoportax cf. rugosifrons,  ‘Ceratotherium’ advenientis, an undetermined Anthracotherid).

The stratigraphic succession outcropping at Cessaniti – “Gentile” Quarry, overlying in unconformity the Paleozoic crystalline basement, is made up of four informal units indicating a transgression from lagoonal to deep-sea environments, dated between 8.1  Ma (Chron C4n) and 7.2 Ma (nannoplankton zone CNM17). The main part of terrestrial mammals comes from the upper part of the shallow sea deposits, locally named “Clypeaster sandstones”, where almost two temporary falls in sea level, probably controlled by tectonics, are testified by the occurrence of soils and fluvial deposits. Only Stegotetrabelodon is also recorded in the underlying lagoonal deposits. The main part of the fossils was collected during quarry works by amateur palaeontologists who summarily recorded their findings. However, they notated the provenance from the upper part of the “Clypeaster sandstones” and noticed the presence of poorly preserved, oxidated echinoids. These letters are typical of the intercalated soils and fluviatile deposits, so the presence of bone beds in fluviatile deposits may be supposed.

The terrestrial mammal association has no insular adaptations nor relationships with the islands of central Italy (Tusco-Sardinian and Apulo-Abruzzi bioprovinces).  The occurrence of Stegotetrabeolodon syrticus represents the only “out of Africa and Arabia” record for the species and has plesiomorphic characters, coherent with an early arrival at Cessaniti. Giraffids suggest a westward expansion of the Pikermian biome from the Greco-Iranian  bioprovince through North Africa (where scanty remains are recorded) and then to Cessaniti. Tragoportax was widely spread in Eurasia and Africa. The new species‘Ceratotherium’ adenitis can be related to African Rhinocerontidae. The palaeoecology of the mammal association indicates a mosaic environment with open spaces, probably similar to the modern savannah but less arid, similar to that suggested for the Pikermian biome.

The stratigraphic and taphonomic data, the abundant record of the terrestrial mammals, and their palaeoecology and taxonomy support the hypothesis of a land in terrestrial continuity with North Africa. Therefore, the accumulation of floating carcasses coming from north Africa can be excluded.

How to cite: Marra, A. C.: The Lost World of Cessaniti: palaeogeographic relevance of a Late Miocene mammal assemblage from the  Central Mediterranean area., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9158, https://doi.org/10.5194/egusphere-egu23-9158, 2023.

In the Peloritani Mountains (North-Eastern Sicily, Italy), evidence of several fractured pebbles and cobbles was found in the coarse-grained siliciclastic deposits of the middle-upper Miocene San Pier Niceto Formation. The pattern of this pebble/cobble fracturing is analogous in type and orientation. These broken pebbles and cobbles appear fractured and affected by normal subparallel faults in a single clastic element, with mm- to cm offset. Such peculiar structures have been commonly associated with active tectonics in recent deposits. 
The present research is therefore devoted to the study of the middle-upper Miocene San Pier Niceto Fm. in Peloritani Mountains for i) characterizing the morphologic properties and orientation of clasts, ii) defining the spatial orientation of faults and principal stresses, iii) understanding their tectono-sedimentary genesis. The goal is to ascertain that broken clasts may or may not represent paleoseismic evidence and coseismic deformation during the initial stages of the extensional tectonics in the still active area of the Calabrian Arc.

How to cite: Maniscalco, R., Somma, R., and Spoto, S. E.: Broken pebbles and cobbles from the middle-upper Miocene siliciclastic deposits of the Peloritani Mountains (Sicily, Italy): evidence of extensional paleotectonics?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9397, https://doi.org/10.5194/egusphere-egu23-9397, 2023.

Continental subduction and collision are not merely follow-ups of oceanic subduction but mark the transition from lithospheric-scale deformation localized along the subduction interface to crustal-scale deformation distributed across the orogen. In order to unravel the processes typifying the dynamic changes from oceanic subduction to collision, we have characterized pressure-temperature (P-T) and spatio-temporal evolution of rocks on either side of the tectonic contact (Briançonnais/Liguro-Piemont contact – Br/LP contact) separating the subducted oceanic remnants from the subducted continental fragments along the length of the Western Alps. West of the contact, the Briançonnais zone is considered as a micro-continent composed of pre-Alpine basement and Paleozoic to Meso-Cenozoic cover units. East of the contact, the Liguro-Piemont zone corresponds to a nappe-stack, with three groups of oceanic (upper, middle and lower) units. The Piemont zone is pinched in between the two in the southern part of the Western Alps and correspond to the distal part of the Briançonnais continental margin.

Results indicate that the maximum temperature and pressure difference on each side of the contact is generally < 30°C and < 0.3 GPa, evidencing that (i) no significant metamorphic gap exists between both sides and that (ii) offscraping of the continental fragments occurred at the same depth as the oceanic ones. The dataset also shows a northward increase of peak P-T conditions from ~300°C-1.2 GPa to ~500°C-2.0 GPa. The preservation of similar P-T conditions on both sides of the Br/LP contact can tentatively be assigned to either (1) offscraping of the Liguro-Piemont and later of the Briançonnais at similar depths or (2) entrainment and joint burial of the Liguro-Piemont (previously accreted or subducted) fragments together with the Briançonnais margin. The latter hypothesis, however, is not supported by the ~10 My gap between the peak burial of the Briançonnais and Liguro-Piemont zones. The recurrent depth range of the various units, which reflects systematic variations of slicing and mechanical coupling along the plate interface (Herviou et al., 2022), suggests that (1) similar slicing mechanisms and strain localization prevailed during both oceanic and continental subduction and (2) shows that the Br/LP contact represents a frozen-in subduction interface. The end of high-pressure and low-temperature metamorphism and continental subduction at ~33 Ma would thus mark the stalling of subduction interface dynamics and the onset of strain distribution across the plate interface and into the lower plate.

• Herviou, C., Agard, P., Plunder, A., Mendes, K., Verlaguet, A., Deldicque, D., Cubas, N., 2022. Subducted fragments of the Liguro-Piemont ocean, Western Alps: Spatial correlations and offscraping mechanisms during subduction. Tectonophysics 827, 229267. https://doi.org/10.1016/j.tecto.2022.229267

How to cite: Mendes, K., Agard, P., Plunder, A., and Herviou, C.: Plate interface frozen at the very end of continental subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11990, https://doi.org/10.5194/egusphere-egu23-11990, 2023.

The Piemonte-Ligurian-Maghrebian Tethys or “Alpine Tethys” developed at the western tip of the Tethys Ocean between Eurasia and Gondwana. The evolution of the Alpine Tethys during the post-Pangea rifting and oceanic expansion from the Early Jurassic to the Early Cretaceous has been well documented compared to its evolution from the onset of the African-Eurasian convergence during the Late Cretaceous upward. In this contribution, based on our studies and the literature, we try to decipher the evolution of this ocean through the study of its inverted margins during Late Cretaceous-Paleocene times. In the Western Alps, the Briançonnais domain, which constituted the distal European magma-poor passive margin of the Alpine Tethys, was affected by a systemic extension in the Late Cretaceous-Paleocene. This late extension, poorly described so far, operated only a few million years before the Briançonnais encroached the SE-dipping subduction zone under the Adria microplate. In the Maghrebides transects from the Rif belt (Northern Morocco) to the Peloritani Mountains of Sicily (e.g., Bouillin, 1986; Bouillin et al., 1986) the Alkapeca (Alboran-Kabylias-Peloritan-Calabre) terranes were part of south-eastern Iberia until the Early Jurassic opening of the narrow Betic Ocean (Puga et al., 2011) or OCT domain (Jabaloy Sánchez et al., 2019). The Alkapeca blocks preserve in their “Dorsale calcaire” units remnants of the northern margin of the Alpine Tethys and then are southwestern equivalents of the Briançonnais domain, except they were fragmented and carried onto the African and south-eastern Iberia margins during the Tertiary opening of the back-arc Mediterranean basins. We observe that the Dorsale calcaire units testify to extensional deformation like the Briançonnais during the Late Cretaceous-Paleocene, i.e., when Africa-Eurasia-Iberia convergence was active and then subduction of the intervening Tethyan slab must have occurred somewhere. We propose here for the first time that the Late Cretaceous-Paleocene subduction of the Ligurian-Maghrebian slab occurred under the North African margin in the southward continuation of the Alpine subduction. Contrary to some early claims, the North African margin did not experience significant compression during the Late Cretaceous-Paleocene, which compares with the Adria margin case during the same period. During the Eocene, a Subduction Polarity Reversal occurred, which was associated with the relocation of the subduction zone along the Alkapeca blocks. This was the beginning of the Apenninic subduction, which triggered the back-arc opening of the Mediterranean basins and corresponds to the back-thrusting tectonic phase in the Western Alps.

References  

Bouillin J-P, 1986. Le « bassin maghrébin » : une ancienne limite entre l’Europe et l’Afrique à l’ouest des Alpes. Bull. Soc. Géol. Fr. (8) 2 :547-558.

Bouillin JP, et al., 1986. Betic-Rifian and Tyrrhenian Arcs : Distinctive Features, Genesis and Development Stages. Developments Geotect. 21:281-304.

Puga E, et al., 2011. Petrology, geochemistry and U-Pb geochronology of the Betic Ophiolites: Inferences for Pangaea break-up and birth of the Westernmost Tethys Ocean. Lithos 124:265-272.

Jabaloy Sánchez A, et al., 2019. Lithological successions of the Internal Zones and Flysch Trough Units of the Betic Chain. In : Quesada C and Oliveira JT (eds.), The Geology of Iberia: A Geodynamic Approach. Region. Geol. Rev. (Springer Nature Publ.)

How to cite: Farah, A., Saddiqi, O., Chabou, M. C., and Michard, A.: Extension of a lower plate passive margin coeval with subduction of the adjacent slab: The Western Alps and Maghrebides cases, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12441, https://doi.org/10.5194/egusphere-egu23-12441, 2023.

The Eastern Sardinian margin consists in a hyper-extended rifted margin, located in the western Tyrrhenian Sea, a recent back-arc basin (late Neogene). This area was affected by strong aerial erosion during the Messinian Salinity Crisis (MSC, 5.96 – 5.33 My) associated with the drop of sea level (> 1500 m) which occurred throughout the whole Mediterranean. The Gulf of Orosei and surrounding offshore areas are characterized by small and diffuse drainage systems input, where the Messinian Erosion Surface (MES) has rarely been studied while it has been in large fluvial systems (Rhone, Ebro). The MES was already found in the Cendrino valley (which flows in the Gulf) and in the East-Sardinia Basin but the link between onshore and offshore was never been studied in the area. The “METYSS 4” cruise (June 2019, R/V “Téthys II”) allowed acquiring more than 2000 km of very high-resolution (VHR) seismic data (Sparker), following a dense grid (1.5 km average profile spacing), on the Eastern Sardinian continental shelf, and especially in the Orosei Gulf area, that has been little explored until now. While the main limitation on seismic data (air-gun) interpretation is often due to the occurrence of sea bottom multiple, the limitation for Sparker data may also be due to very short shot intervals at greater water depth. The seismic trace ends where there still is signal of interest. Thus, we applied a simple method to increase investigation depth for short shot intervals (0.333 - 0.533 ms), which allowed interpretation on the continental slope. This approach consists in copying the raw data and concatenating the copied data under the raw data with a shift of 1 shot point. To constrain the MES depth on the continental slope and shelf we compared air-gun seismic data from previous METYSS surveys, where the MES has already been interpreted by a strong erosional discordance between Plio-Quaternary deposits and pre-MSC units, with the new VHR data. The restoration of the morphological features of the Orosei canyon at Messinian times shows that the former Messinian canyon network is very similar to the present-day one. The present-day canyon and its tributaries show sub-marine erosion in the talwegs. The heads of the canyons present gravitational features, highlighted by chaotic deposits near the talweg of the canyon or in-between the Plio-Quaternary strata. Offshore Arbatax, south Orosei, the seismic profiles show no significant Plio-Quaternary deposits (thickness < 0.1 sTWT), which allows polygenic pre-MSC units to occur at the seafloor. In the Gulf, we observe thick deposits (0.4 - 0.5 sTWT) on the right bank of Orosei Canyon, making it more complicated to image the MES in this area. The sedimentation rate on this margin is very low (c.a. 9 cm/ka in the Gulf of Orosei), which is consistent with previous studies on the East-Sardinian basin (3-20 cm/ka). These preliminary results will allow correlating for the first time the MES distribution from the onshore to the offshore continental slope of the Eastern Sardinian Margin in order to improve the MSC understanding in this key area.

How to cite: Sylvain, R., Gaullier, V., Watremez, L., Chanier, F., Caroir, F., Graveleau, F., Lofi, J., Maillard, A., Sage, F., Thinon, I., and Travan, G.: The Messinian Erosion Surface along the Eastern Sardinian Margin, Western Tyrrhenian: New Insights from Very High-Resolution Seismic Data (METYSS 4), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13909, https://doi.org/10.5194/egusphere-egu23-13909, 2023.

Ancient coastal carbonate depositional systems provide exceptional records of past changes in relative sea level– globally and locally (tectonics) – and of paleoenvironmental variations. Here we present new work on carbonate outcrops within the UNESCO Rocca di Cerere Geopark in central Sicily (Caltanissetta and Enna districts). They show superb sub-vertical cliffs made of Pleistocene packstones with clinoforms which provide a high-resolution record of relative sea-level changes that correlate with precession cycles. Regionally these successions deposited during Plio-Quaternary forced regression caused by late-orogenic uplift. However, their deposition within local thrust top basins was modulated by local uplift and tectonic tilting. Collectively these global, regional, and local processes are recorded by offlapping of successive depositional cycles. Moreover, the high-resolution photogrammetric surveys we developed, revealed that the underlying anticlines tilted the original beds of almost 20°. The packstones are derived from fauna: micro-habitat variations have been here traced by changes in sediment provenance, fossil assemblages, and preservation. The resultant stratal architectures reflect the interplay between the efficiency of this carbonate factory, the environmental conditions, the minute siliciclastic input, and the evolution of accommodation space. Bio- and magneto-stratigraphy were fundamental to date, the parasequences, while organic and inorganic chemistry, benthic foraminifera assemblages, as well as stable isotopes analyses (δ¹⁸O and δ¹³C) are used as environmental and climatic proxies (where possible) to reconstruct coastal dynamics (physical and biological), in relation to the tectonic history and sea-level change.
These outcrops provide analogues to interpret stratal patterns in subsurface examples where these types of strata form important aquifers – and shallow gas reservoirs.

How to cite: Forzese, M., Maniscalco, R., Nádudvari, Á., Nürnberg, D., Speranza, F., Todrani, A., Zimmermann, U., and Butler, R. W.: Coastal carbonate systems: evolving paleoclimatic and paleoenvironmental proxies to relative sea-level change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13922, https://doi.org/10.5194/egusphere-egu23-13922, 2023.

The tectonic evolution of the plate boundary between Iberia and Europe since the Variscan and more clearly since the Mesozoic rifting is at the origin of heterogeneities of densities and structure, in the crust and the mantle, which have an impact on the distribution of the current stresses and post-orogenic uplift in the Pyrenees. Here, we investigate the lithosphere structure across the Pyrenees and Western Europe using LitMod2D that integrates geophysical and petrological data sets to produce the thermal, density, and seismic velocity structure of the lithosphere and upper mantle. Of particular interest is the chemical composition of the mantle, including the degree of serpentinization near the North Pyrenean Fault (>10 km), and the shape of the lithosphere-asthenosphere boundary at a larger scale (>100 km). The topography and geophysical constraints, including LAB geometry, Vs, Vp data are well reproduced for a weak fertile Phanerozoic lithosphere. Our results suggest that accounting for serpentinization allows fitting second-order gravity and seismological features in the lithosphere, but not topography which is controlled to first-order by high lateral variability in crustal thickness and lithosphere strength.

How to cite: pajang, S., Mouthereau, F., Robert, A., and Callot, J.-P.: Lithosphere-asthenosphere structure and impact on serpentinization processes and topography across the plate boundary between Iberia and Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14651, https://doi.org/10.5194/egusphere-egu23-14651, 2023.

In recent decades, reconstructing the geometric and kinematic evolution of fold-and-thrust belts around the Mediterranean region has been one of the priority goals of the scientific community, also with the aim of energy resource retrieval. However, the frequent poor quality of subsurface constraints has sometimes led to the production of even very different geometric-kinematic evolutionary models, characterized by different amounts of shortening and deformation timing, with important implications on the kinematic reconstructions of the Africa-Europe convergence process. In this talk, I intend to propose a journey through a series of fold-and thrust belts around this region, that in recent years have been studied by the team of the Academic Lab of Basin Analysis or Roma Tre, in collaboration with many colleagues around the Mediterranean, through the integration of classical stratigraphic and structural data with the reconstruction of the paleo-thermal evolution of these structures. Particular attention will be paid to thermal modeling, constrained through different parameters of thermal and thermo-chronological evolution of both pre-orogenic and syn-orogenic sedimentary successions.

How to cite: Corrado, S.: Deciphering the Cenozoic evolution of circum-Mediterranean fold-and-thrust belts through the integration of structural and thermal maturity studies of sedimentary basins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16943, https://doi.org/10.5194/egusphere-egu23-16943, 2023.

Processes driving orogenic styles and long-term isostatic versus dynamic support of the topography have been largely debated in domains of plate convergence. The tectonic evolution of orogens reflect the interactions between mantle flow driving plates and the inherited rheology and composition of moving plates. Here we show that the tectono-magmatic evolution of the European lithospheric mantle and structure, which inherits past subduction/collision (e.g. Cadomian, Variscan) and rifting events (Tethys/Atlantic), control first-order crust-mantle coupling, plate-mantle coupling, defining Alpine-type orogens. The lack of thermal relaxation needed to maintain rheological contrasts over several hundreds of millions of years requires high mantle heat flux below Central Europe since at least the Permian. A combination of edge-driven convection on craton margins and asthenospheric flow triggered by rift propagation during the Atlantic and Tethys rifting is suggested to be the main source of heat. Timing and rates of exhumation recorded across Western Europe during the Cenozoic convergence reveal an additional control by the architecture of Mesozoic rifted margins that defined a complex array of small continental blocks with European affinity (e.g. S-Iberia, Ebro/Sardinia-Corsica) caught between the East European and West African cratons, and Adria. By 50 Ma the acceleration of orogenic exhumation, from the High Atlas to the Pyrenees, occurred synchronously with the onset of extension and magmatism in the West European Rift. Extension marks the onset of distinct orogenic evolution between Western Europe (Iberia) and the Alps (Adria) in the east, heralding the opening of the Western Mediterranean. While the details of the Cenozoic topographic history of peri-Mediterranean orogens are understood to be controlled by the rheology and architecture of rifted margins combined with changing large-scale kinematic boundary conditions (e.g. Atlas, Betics, Pyrenees, Alps), their post-10 Ma, quaternary to current surface and tectonic evolution appears to illustrate increasing control by magmatism and flow at the asthenosphere-lithosphere boundary.

How to cite: Mouthereau, F. and Angrand, P.: Tectono-magmatic and kinematic evolution of the Africa-Europe plate boundary: from Cadomian subduction to Western Mediterranean tectonics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17274, https://doi.org/10.5194/egusphere-egu23-17274, 2023.

The Mid-Pleistocene Transition (MPT) between ~1200 and ~800 ka was associated with a major shift in global climate and was marked by a change in glacial/interglacial periodicity from ~41 to ~100 kyr that resulted in higher-amplitude sea-level variations and intensified glacial cooling. The Indonesian Throughflow (ITF), which controls the exchange of heat between the Pacific and Indian Oceans, is a major component of the global climate system. On the other hand, Asian-Australian Monsoon dynamics play a key role in regional primary productivity. Therefore, reconstruction of ITF and Asian-Australian Monsoon variability during the MPT could potentially clarify the impact of the glacio-eustatic sea level changes on the climate and ecosystem of Northwest Australia. The International Discovery Program (IODP) Expedition 363 retrieved an extended, continuous hemipelagic sediment succession spanning the past two million years at Site U1483 on the Scott Plateau off Northwestern Australia.

In this study, we analyzed radiolarian assemblages in core top samples retrieved during the RV Sonne Expedition 257 and downcore samples from IODP Site U1483 to estimate the variability in regional sea surface temperatures (SSTs) during the MPT, and to explore ITF dynamics in relation to glacio-eustatic sea-level variations and tropical monsoon strength. We suggest that glacio-eustatic sea-level variations have been a key factor affecting changes in SSTs at Site U1483, primarily because the shallow and hydrogeographically complex nature of the sea means that SSTs are highly sensitive to glacio-eustatic sea-level variation. Based on comparisons with SST data from the mid latitudes off Northwest Australia and the South China Sea, we suggest that the SSTs at Site U1483 are highly dependent on prevailing climate changes in the northern hemisphere rather than changes in the climate of the Southern hemisphere. In addition, comparisons of radiolarian total abundances with X-ray fluorescence-scanning elemental data suggested that, until the onset of the MPT (~1200 ka), radiolarian productivity was higher during strong summer monsoons during interglacial periods, probably because of the high riverine runoff generated by heavy summer monsoonal precipitation. However, since ~900 ka, there appears to have been a shift in the mode of radiolarian productivity that has resulted in increased radiolarian productivity during glacial periods when the delivery of nutrients is increased due to the enhanced mixing of the upper water column in the shallow sea caused by strong trade winds. 

How to cite: Matsuzaki, K., Holbourn, A., Kuhnt, W., Gong, L., and Ikeda, M.: Variability of the Indonesian Throughflow and Australian monsoon dynamism across the Mid Pleistocene Transition (IODP 363, Site U1483), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-41, https://doi.org/10.5194/egusphere-egu23-41, 2023.

During the last decades, the Southern Ocean (SO) has been experiencing physical and chemical drastic changes which are affecting the distribution and composition of pelagic plankton communities. Coccolithophores (small-sized haptophyte algae) are the most prolific carbonate-producing phytoplankton group, playing a key role in biogeochemical cycles at high latitudes.

In this work we investigated the biogeographical distribution and calcification patterns of the ecologically dominant species Emiliania huxleyi across a latitudinal transect in the Pacific sector of the SO (from ~40°S to ~54°S). We aimed to assess the response of E. huxleyi to steep environmental gradients across the frontal system of the Antarctic Circumpolar Current.

The plankton samples were collected during International Ocean Discovery Program Expedition 383: Dynamics of Pacific Antarctic Circumpolar Current (DYNAPACC, May-July, 2019) onboard the R/V JOIDES Resolution (https://iodp.tamu.edu/scienceops/expeditions/dynamics_of_pacific_ACC.html). In situ environmental data (such as sea surface temperature, total alkalinity and pH) were measured at each sampling location.

The samples were prepared and analysed at the University of Portsmouth using a combination of electron backscatter diffraction (EBSD), Scanning Electron Microscope (SEM) and light microscopy techniques.

How to cite: Morgan, E., Saavedra-Pellitero, M., and Malinverno, E.: Effects of the Pacific Antarctic Circumpolar Current on the extant coccolithophore Emiliania huxleyi, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-464, https://doi.org/10.5194/egusphere-egu23-464, 2023.

The Great Barrier Reef is a unique environmental resource threatened by future climate change. However, it has always been unclear how this ecosystem developed in the Mid to Late Pleistocene. Work has shown that the reef developed between ~ 600-500 ka during MIS 15-13, although some records suggest a start at MIS 11 at 400 ka. There is a lack of Sea Surface Temperature (SST) records for this time for the area around the Great Barrier Reef. Furthermore, the few existing SST records do not show temperature changes during these key periods, leading researchers to suggest that factors other than temperature, such as sea-level change or sediment transport, explain the start of the reef. We used the TEX₈₆ proxy to produce a new SST record starting at 900 ka from ODP Site 820. This core is located next to the northern Great Barrier Reef. In this new record, there are SST changes that seem to match both dates for the start of the Great Barrier Reef. First, there is a period of stable SST between 700-500 ka, with no glacial cooling during this time. This could promote the development of a reef system during this time, allowing the reef more time to evolve from isolated smaller reefs to a continuous barrier reef. However, there is some suggestion based on facies analyses that even though the barrier system developed around MIS 15, the modern coral reef system was not yet fully established. Our records show that glacial temperatures during MIS 14 still are similar to SSTs from records further south. However, this trend shifts around MIS 11 when glacials became warmer. In fact, while before MIS 11, SST at ODP 820 was colder than records from the Western Pacific Warm Pool, afterwards SST was either the same or sometimes warmer than at these sites. Also, unlike other nearby records, the difference in SSTs between glacials and interglacials is reduced after MIS 11. This suggests that the northern Coral Sea might have been protected from the extremes of glacial temperature changes after the MPT. This process might have allowed the development of a continuous coral reef system by encouraging the growth of reefs even during glacials. Therefore, our research suggests that major steps in the development of the Great Barrier Reef system are linked to changes in the SSTs. Our SST record suggests that SST changes are the primary driver of reef development and other non-SST factors are less important.

How to cite: Petrick, B., Reuning, L., Auderset, A., Pfeiffer, M., and Schwark, L.: The start of the Great Barrier Reef is a result of the increased stability of Temperatures in the Mid to Late Pleistocene., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1105, https://doi.org/10.5194/egusphere-egu23-1105, 2023.

Chemical weathering of silicate rocks is a well recognized method by which carbon dioxide is removed from the atmosphere and fixed as calcium carbonates in the sedimentary record. For many years the long term cooling of the Earth during the Cenozoic has been linked to uplift, erosion and weathering of the Himalayas and Tibetan Plateau, however following scientific ocean drilling of the submarine fans in the Asian marginal seas it now seems that this region could not be responsible for cooling, at least during the Neogene. Although other factors such as burial of organic carbon and the rates of degassing during seafloor spreading may also be important, erosion and weathering of other regions may also be important in controlling global CO2 concentrations. In this study we focus on the role of New Guinea, the large (>2500 km long) orogen formed as Australia collided with Indonesia since the Mid Miocene. New Guinea comprises slices of arc and ophiolite rocks that are susceptible to weathering, and is located in the tropics where warm, wet conditions favor rapid weathering. Rainfall exceeds >4 m annually in the island center. Analyses of sediment from Deep Sea Drilling Project Sites 210 and 287 in the Gulf of Papua now allow the weathering and erosion history of the island to be reconstructed. A trend to more continental erosion since 15 Ma reflects uplift and erosion of tectonics slices of the Australian plate. At the same time chemical weathering shows increasing intensity, especially since 5 Ma, as proxied by major element ratios (K/Rb, K/Al) and clay minerals. Greater proportions of kaolinite point to more tropical weathering since the Mid Miocene. Trends to more weathering contrast with Himalayan records that show the reverse, and suggest that New Guinea may be an important component in controlling global climate in the past 15 Ma.

How to cite: Clift, P. and Mohtadi, M.: Chemical Weathering in New Guinea since the Mid Miocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1997, https://doi.org/10.5194/egusphere-egu23-1997, 2023.

The Indo-Pacific Warm Pool (IPWP) is the warmest and most dynamic ocean-atmosphere-climate system on Earth and has undergone significant climatic changes during the Pleistocene glacial periods (De Deckker et al., 2012; Lea et al., 2000; Russell et al., 2014). During the Last Glacial Maximum, the latitudinal position of the Southern Ocean fronts, both south of Africa and Australia, was shown to be critical in controlling the outflow of warm water of the Agulhas Current from the Indian Ocean and the IPWP area. Yet, there is no direct evidence for such oceanic change on the scale of the Late Pleistocene glacial-interglacial transitions.

Here, we combine sea surface temperature proxies (d¹⁸O and Mg/Ca) with the neodymium (Nd) isotopic signature to reconstruct changes in climate and oceanic circulation in the eastern tropical Indian Ocean over the last 500 ka. The most striking feature of our dataset is the oscillating Nd signal that mimics the glacial-interglacial cycles. While interglacial periods are characterized by a more significant contribution from the less radiogenic Antarctic intermediate water mass (AAIW, ~ -7 ε_Nd), glacial periods are marked by more radiogenic water mass of Pacific origin (~ -5 ε_Nd). We argue that under global cooling, the northward penetration of the AAIW has weakened due to the general slowdown of the global thermohaline circulation. Furthermore, the oscillating pattern is also recorded in the sea surface temperature and salinity, indicating the settlement of cooler and more saline surface water masses probably linked to a less expanded IPWP and weaker Leeuwin Current during glacial intervals.

We suggest that under low AAIW a less intense advective mixing occurred, allowing a deepening of both halocline and thermocline in the tropical eastern Indian Ocean. Our new proxy-derived dataset confirms results from models (DiNiezo et al., 2018), suggesting that these ocean conditions could amplify the externally forced climate changes resulting from drier atmospheric conditions and weaken the monsoon during glacial periods in the Indonesian region.

How to cite: Le Houedec, S., Tremblin, M., Champion, A., and Samankassou, E.: Changes in intermediate circulation waters along the tropical eastern Indian Ocean during quaternary climatic oscillations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2105, https://doi.org/10.5194/egusphere-egu23-2105, 2023.

During the Cenozoic (66–0 Ma) Tasmania has continuously been at a crucial geographic location. It represented the final tectonic connection between Australia and Antarctica before complete separation of both continents in the late Eocene, and therefore a barrier for circumpolar flow. Since the Eocene-Oligocene transition, the northward drifting Tasmania was bathed by the throughflow of the subtropical front, but remained an obstacle of the ideal flow path of strengthening ocean currents. The sedimentary record around Tasmania thus represents a perfect archive to record the oceanographic consequences of this regional tectonic change. We here present a new TEX₈₆ and U_K’³⁷-based SST compilation from 4 sediment cores: ODP Site 1172 (East Tasman Plateau), Site 1170 and 1171 (South Tasman Rise) and Site 1168 (western Tasman margin). We paired these reconstructions with microplankton (dinoflagellate cyst) assemblage data which reflect qualitatively the surface water conditions: nutrients, temperature, salinity. Together, the >1.300 samples portray the SST evolution around the island, from the time it was still connected to the Antarctic continent in the Paleocene to its near-subtropical location today. Trends in the SST compilation broadly follow those in benthic foraminiferal stable isotope compilations, but with some interesting deviations. Differences in SSTs on either side of the Tasmanian Gateway are small in the early Paleogene (66–34 Ma), even when the Tasmanian Gateway is considered closed. Widening of the Tasmanian Gateway around the Eocene-Oligocene transition (34Ma) immediately allows throughflow of what later becomes the Leeuwin Current, which warms the sw Pacific. Oligocene and Neogene SST trends follow those of the benthic d¹⁸O, and with continuous influence of the proto-subtropical front. While the SST evolution of Tasmania is remarkably stable in most of the Oligocene, prominent cooling steps are inferred in the Late Oligocene (26 Ma), at the MMCT (~14 Ma), in the mid-to-late Miocene (9 Ma, 7 Ma and 5.3 Ma) and in the Pliocene (2.8 Ma). The remarkably strong Neogene cooling of the subtropical front implies expansion of subpolar temperate conditions and probably gradual strengthening of the Antarctic circumpolar current. Pliocene-Pleistocene SST variability is strong over glacial-interglacial cycles. Taken together, the sites portray a complete overview of local environmental change of the subtropical front area, and provides crucial context to the history of Southern Ocean heat transport and regional climate.

How to cite: Bijl, P., Hoem, F., Hou, S., Thöle, L., Sauermilch, I., and sangiorgi, F.: The Cenozoic sea surface temperature evolution offshore Tasmania, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2802, https://doi.org/10.5194/egusphere-egu23-2802, 2023.

Late Quaternary clay mineral assemblages, radiogenic isotope, and siliciclastic grain size records collected from high sedimentation Site U1483 of the International Ocean Discovery Program (IODP), beneath the path of the modern-day Indonesian Throughflow (ITF) and Leeuwin Current of northwest Australia are studied to reconstruct sediments provenance, transport processes and ocean current behavior, and to evaluate the Australian summer monsoon over the last 500 kyr. Clay minerals are primarily composed of smectite (41–70 %), followed by kaolinite (10–28 %), illite (13.5–25 %), and minor chlorite (3–14 %). Our reconstructed model based on the clay minerals source comparison and radiogenic isotope (Sr-Nd-Pb) records suggest the Victoria and Ord rivers of the Kimberley region as the source over the past 500 kyr for Site U1483. Smectite is mainly derived from the mafic volcanic and smectite-rich Bonaparte Gulf, whereas kaolinite and illite are primarily derived from felsic igneous and metamorphic rocks, respectively, found in the drainage areas of these rivers. Chlorite is primarily contributed by the Indonesian Throughflow (ITF), with a minor contribution from the northwest Australian rivers. Variations in the clay mineral assemblages and grain size records indicate strong glacial-interglacial cyclicity, with small grain size, high smectite, and low kaolinite and illite during glacial periods, while interglacial intervals are marked by a relative increase in kaolinite and illite, mean grain size, and decrease in smectite content. (Kaolinite+illite+chlorite)/smectite and kaolinite/smectite ratios are adopted as proxies for the ITF strength and Australian summer monsoon, respectively. High values of kaolinite/smectite and (kaolinite+illite+chlorite)/smectite ratios during the interglacial intervals indicate a wet summer monsoon with high river discharge and a strong ITF and Leeuwin Current, which has the capacity to transport a relatively high percentage of large-size kaolinite and illite sediments to Site U1483. In contrast, during glacials, the low values of kaolinite/smectite and (kaolinite+illite+chlorite)/smectite ratios imply a dry summer monsoon with low sediment discharge and weak ITF and Leeuwin Current, which can majorly carry the small smectite size particles in its suspension. The mean grain size and clay/silt ratio also indicate that the strength of ITF and Leeuwin Current was weak during glacials and gained high strength during the interglacials. The proxy records’ spectral analysis indicates a strong eccentricity period of 100-kyr, an obliquity period of 41-kyr, and a precession period of 23-kyr, implying that the clay mineral input along the northwest Australian margin is influenced by both high-latitude ice sheet forcing and low-latitude tropical processes.

How to cite: Sarim, M. and Xu, J.: Late Quaternary glacial-interglacial variability of the Indonesian Throughflow and Australian summer monsoon: Evidences from clay mineral and grain size records at IODP Site U1483 of northwest Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3430, https://doi.org/10.5194/egusphere-egu23-3430, 2023.

Earth’s climate during the Neogene period changed in several steps from a planet with unipolar ice sheets to today’s bipolar configuration. Yet, time-continuous and well-preserved sedimentary archives from this time interval are scarce. This is especially true for those records that can be used for tracing the role of astronomical climate forcing. Ocean Drilling Program (ODP) Site 752 was drilled on Broken Ridge (Indian Ocean) and provides a time-continuous sedimentation history since the early Miocene in its upper portion.  To date, no astronomical-scale paleoclimate research has been conducted on this legacy ODP site. Here, we use X-ray fluorescence (XRF) core scanning data and benthic foraminifera (BF) taxonomic and quantitative analyses to reconstruct the paleoceanographic changes in the Indian Ocean since 23 Ma. Productivity-related elements from the XRF dataset, show higher productivity during the early Miocene and late Pliocene/early Pleistocene. Moreover, we found strong 405-kyr and ~110-kyr eccentricity imprints in the spectral analysis result of this XRF-derived paleoproductivity proxy. Although the precession signal is also quite remarkable in the spectral analysis results, the 4-cm resolution may not be adequate to further test the precession contribution. Bottom water oxygenation reconstructed using BF, suggest no oxygen minimum zone conditions for the late Miocene on site 752. Dissolved oxygen concentrations (DOC) indicate low oxic conditions (⁓ 2 ml/L) during this time, and relatively low stress species distribution (< 32%) along with abundant oxic species like H. boueana, C. mundulus, L. pauperata and Gyroidinoides spp. suggest predominantly high oxic conditions during the late Miocene (DOC > 2 ml/L). Meanwhile, the grain size (> 425µm) record shows an increasing trend at ~5 Ma, which indicates more current winnowing. Therefore, we argue that the drop in Mn is the result of the increase in the current winnowing, instead of the OMZ expansion. On the other hand, high-amplitude changes in Fe content from the lower Miocene to the middle Miocene, cannot be explained by eolian input, suggesting the source might be the neighbor-distanced Amsterdam-St. Paul hot spot. The source of Fe might be the neighbor-distanced Amsterdam-St. Paul hot spot. We conclude that the legacy ODP Site 752 constitutes an excellent paleoceanographic archive that allows us to reconstruct Indian Ocean dynamics since the early Miocene. New drillings on Broken Ridge with state-of-the-art scientific ocean drilling techniques will provide more detailed information and be highly beneficial for paleoclimatic and paleoceanographic research.

How to cite: Lyu, J., Bar­ra­gán-Mon­til­la, S., Auer, G., Bialik, O., Christensen, B., and De Vleeschouwer, D.: Astronomically-paced changes in paleoproductivity, winnowing, and mineral flux over Broken Ridge (Indian Ocean) since the Early Miocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5655, https://doi.org/10.5194/egusphere-egu23-5655, 2023.

The Early Middle Pleistocene Transition (EMPT) represents a fundamental reorganization in Earth’s climate system as the obliquity-dominated glacial/interglacial rhythmicity characterizing the Quaternary got progressively replaced by a high-amplitude, quasi-periodic 100 kyr cyclicity. This critical change in the climatic response to orbital cycles occurred without proportional modifications in the orbital-forcing parameters before or during the EMPT, implying a substantial change internal to the climate system. The EMPT had a severe impact on marine ecosystems. However, the trigger mechanisms and the components of the climate system involved in this global reorganization are still under debate, and high-resolution studies from the equatorial to mid-latitude shelf regions are at present rarely available.

In this study, we analyze the benthic foraminifera assemblage of an expanded section from Site U1460 (eastern Indian Ocean, 27°22.4949′S, 112°55.4296′E, 214.5 meters water depth), collected during International Ocean Discovery Program (IODP) Expedition 356 on the southwestern Australian shelf covering the EMPT. At this site, we provide a new benthic and planktonic foraminifera dataset to better define the response of the Leeuwin Current System during the EMPT on low to mid latitude shelf regions that are strongly sensitive to glacial/interglacial sea-level oscillations. Specifically, benthic foraminifera assemblage and the plankton/benthos (P/B) ratio are used to understand the bottom water community and its reaction to the Leeuwin Current System variations during the EMPT. Additionally, these data will untangle the local impact of eustatic sea-level changes in a highly dynamic setting.

Preliminary data of the microfossil content revealed a polyspecific benthic foraminifera assemblage with high diversity. The most abundant taxa are trochospiral forms (e.g., Cibicides, Cibicidoides, Heterolepa, Nuttallides, Eponides). Triserial and biserial taxa are abundant (e.g., Textularia, Spirotextularia, Gaudryina, Bolivina, Uvigerina). Planispiral tests such as Melonis and Lenticulina are also commonly present, as well as uniserial ones such as Siphogenerina, Lagena, and Cerebrina. Preservation varies significantly between glacial and interglacial intervals. Particularly, benthic foraminifera are poorly to moderately preserved during glacial stages while exhibiting moderate to good preservation in the interglacials. The variations in the P/B ratio allowed to constrain the sea-level changes along the Australian shelf. Specifically, higher and lower values of this ratio indicate highstand and lowstand phases, respectively. In this regard, foraminifera data will be integrated in a multiproxy dataset available for Site U1460 to obtain new insights on sea-level-driven environmental changes in the area during the EMPT. This, in turn, will allow to resolve the impact of local versus global climatic change across the studied interval.

How to cite: Arrigoni, A., Auer, G., and Piller, W. E.: The Leeuwin Current System during the Early Middle Pleistocene Transition (EMPT): foraminiferal assemblage and sea level reconstruction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5891, https://doi.org/10.5194/egusphere-egu23-5891, 2023.

The Agulhas leakage is an important contributor to the global thermohaline conveyor system, adding warm and saline subtropical waters from the Indian Ocean to the South-east Atlantic Ocean. It has been proposed that weaker Agulhas leakage occurred during glacial stages, but that leakage was reinvigorated during deglaciations and was, in turn, potentially important for the development of interglacial warmth.

Little is known about the longer-term evolution of Agulhas leakage during the Pliocene and Pleistocene (the last 5.3 Ma). In the Pliocene, the continental ice sheets were smaller in size, and the position and strength of key ocean and atmosphere circulation systems in the South Atlantic region were different. The Pliocene is also characterised by a series of gateway changes which are argued to have affected North Atlantic climate, but the response of the Agulhas leakage system remains unclear. It is also unclear whether the ‘early deglaciation’ signal is a specific component of the late Pleistocene 100 kyr cycles. Identifying how and when this signal developed could have important implications for understanding the impact of ocean circulation changes on the development of the mid-Pleistocene climate transition (MPT) ~1.2-0.6 Ma, when the period of the glacial-interglacial cycles shifted from ~41 kyr to ~100 kyr.

Here we present initial results from a new Cape Basin site (Site U1479, 35°03.53′S; 17°24.06′E), which was recovered by IODP Expedition 361 in 2016 from the western slope of the Agulhas Bank (Hall et al., 2016). We combine reconstructions of sea surface temperatures (using the alkenone-derived U^K₃₇’ index) and sea surface salinity (from alkenone dD analysis) with details of planktonic foraminifera assemblages, to identify and understand variability in Agulhas leakage operating across both orbital and longer timescales. There is an overall cooling of ~4°C since the Pliocene, but it is focussed around ~2 Ma and from 1.2 Ma. Orbital scale and longer-term variability in SST, sea surface salinity and Agulhas leakage fauna are also determined, demonstrating that the Agulhas leakage system has evolved across a range of timescales through the Plio-Pleistocene, especially in association with the MPT.

References

Hall, I.R., Hemming, S.R., LeVay, L.J., and the Expedition 361 Scientists, 2016. Expedition 361 Preliminary Report: South African Climates (Agulhas LGM Density Profile). International Ocean Discovery Program. http://dx.doi.org/10.14379/iodp.pr.361.2016

How to cite: McClymont, E., Caley, T., Charles, C., Starr, A., Sanchez Montes, M. L., West, M., Rossignol, L., Hall, I., and Hemming, S.: Pliocene-Pleistocene evolution of the Agulhas leakage to the Atlantic Ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7477, https://doi.org/10.5194/egusphere-egu23-7477, 2023.

The mid-Pliocene (3.3-3.0 Ma) is a time when the Earth's climate fluctuated between cold glacial conditions (marine isotope stage M2; 3.3 Ma) and periods when global temperatures were ~3°C warmer than the pre-industrial (Mid-Pliocene warm period; 3.3-3.025 Ma) when CO₂ concentrations reached ~400 ppm. Thus, the paleoclimate reconstruction of this time interval provides an analogue of the present-day and near-future climate change in a moderate pCO₂ increase scenario. Although fluctuations in benthic δ¹⁸O in the mid-Pliocene were predominantly associated with Northern Hemisphere glacial dynamics, the contribution of Antarctic ice to mid-Pliocene glacial-interglacial cyclicity is unknown. Moreover, the surface oceanographic response of the Southern Ocean to Pliocene glacial-interglacial climate change is poorly documented

We studied 2 sedimentary records from offshore west Tasmania (ODP Site 1168) and the Agulhas Plateau (IODP Site U1475), both located close to the modern position of the subtropical front (STF) in the Southern Ocean and encompassing the mid-Pliocene. The STF is a crucial surface water mass boundary separating cold, fresher subantarctic waters and warm, more saline subtropical waters and plays a key role in global ocean circulation, ocean-atmosphere CO₂ exchange and meridional heat transport.

We use lipid biomarkers, dinoflagellate cyst assemblages and benthic foraminiferal clumped isotopes to reconstruct surface and bottom oceanographic conditions over the mid-Pliocene including the M2 glaciation. We identify similar sea surface temperature (SST) changes at the two sites. Site 1168 SST cools from 18°C to 12°C and at Site U1475 from 21°C to 18°C across the M2 glaciation. Dinoflagellate cyst assemblages suggest strong latitudinal shifts of the subtropical front associated to Pliocene glacial-interglacial climate changes. However, the most profound assemblage shift occurs at the M2 deglaciation stage at both sites, suggesting strong and unprecedented surface water freshening. Preliminary clumped isotope results suggest bottom water temperatures at Site 1168 are stable around 9°C between M2 and mid-Piacenzian warm period, indicating that the enrichment in δ¹⁸O across the M2 is mainly contributed by large ice volume changes. We interpret the surface water freshening of the subantarctic zone as signaling major iceberg calving following the M2 glaciation, suggesting that the Antarctic contribution to the M2 glaciation was profound.

How to cite: Hou, S., Stockhausen, M., Toebrock, L., Sangiorgi, F., Starr, A., Berke, M., Ziegler, M., and Bijl, P.: Mid-Pliocene subtropical front variability in the Southern Ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7924, https://doi.org/10.5194/egusphere-egu23-7924, 2023.

The Southern Hemisphere Supergyre refers to the strong connections and intertwining of the southern subtropical gyres. Tasman Leakage is a fundamental part of the supergyre, as well as of the  global thermohaline circulation, as it provides a return flow from the Pacific and Indian Oceans to the North Atlantic at intermediate depths.   However, both are only relatively recently documented, and the timing and conditions of onset are not well understood.

This study characterizes the newly identified onset of Tasman Leakage in sedimentary records in and around the Indian Ocean using core descriptions and data derived from sediments.  Since much of this is legacy core material, core photographs were used to develop complementary and more continuous records to help refine the timing of onset.  These newly constructed time series based on core photographs are compared with X-ray Fluorescence time series based on core scanning provide both insight into onset of Tasman Leakage and a first test of the utility of time series based on core photos.

This effort will focus on the intermediate water pathway associated with Tasman Leakage and identify conditions at critical around the basin from at least 8 Ma at Broken Ridge and Mascarene Plateau to understand the role of Indian Ocean intermediate waters in the Southern Hemisphere Supergyre in major climate events of the late Miocene. 

This proposed work provides the first synoptic view of SHS onset using intermediate depth cores, which in turn will provide an important framework for basin-wide synthesis of Indian Ocean drilling, much of which is outside of the main pathway of the SHS.  It will also serve as a test of the utility of legacy material as primary data.

How to cite: Christensen, B., Drury, A. J., Auer, G., DeVleeschouwer, D., and Lyu, J.: Using Legacy Data to Explore the Onset and Development of the Southern Hemisphere Supergyre, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9653, https://doi.org/10.5194/egusphere-egu23-9653, 2023.

A collapse of the Atlantic Meridional Overturning Circulation (AMOC) could drive widespread changes in tropical rainfall, but the underlying physical mechanisms are poorly understood. Numerical simulations validated against hydroclimate changes during Heinrich Stadial 1(HS1) – the most recent, best-documented AMOC collapse – show a global response driven by cooling over the tropical North Atlantic. This pattern of ocean cooling is key to link changes in rainfall across the tropics with the reductions in AMOC strength. Cooling over the tropical North Atlantic drives changes over the Pacific and Indian oceans that uniquely explain the paleoclimatic evidence. A similar response is active in simulations of future greenhouse warming, but model disagreement regarding the pattern of AMOC-induced tropical cooling produces divergent rainfall predictions across the tropics. Models with responses consistent with the paleodata predict more pronounced rainfall reductions across the tropics, revealing a heightened risk of drought over vulnerable societies and ecosystems worldwide.

How to cite: DiNezio, P.: The tropical response to a collapse of the Atlantic Meridional Overturning Circulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10410, https://doi.org/10.5194/egusphere-egu23-10410, 2023.

Sediment cores (A10 and I06) were analyzed using a high-resolution X-ray fluorescence (XRF) core scanner to understand changes in paleo-sedimentary environments of the study area. Age dating reflects environmental changes from interglacial marine isotope stage 3 (MIS 3) through the last glacial maximum (LGM; MIS 2) to the Holocene. Three layers were identified in the seismic profiles as follows: unit 1 (thickness = ca. 5 m) in a homogeneous sedimentary phase; unit 2 formed by erosion; unit 3, which is parallel and continuous. XRF elemental proxy data indicate anomalous distributions of Ca/Fe, Ca/K, and Fe/Ti caused by organic substances that appear at several depths in the A10 core. Results show that the seafloor was exposed to air during the LGM. The I06 core shows characteristic anomalies at depths of 0.8, 1.5, and 2.5 m, which were caused by sediments supplied from surrounding rivers.

How to cite: Cho, J. H., Kum, B.-C., Jang, S., Lee, C., Lee, S., Son, Y. B., and Jung, S.-K.: Understanding the Changes in the Post-Glacial Depositional Environments through High-resolution Geochemical Proxies in the Central Yellow Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11089, https://doi.org/10.5194/egusphere-egu23-11089, 2023.

The Pacific Ocean hosts one of the most extensive areas of oxygen deficient waters at present with well-defined areas of oxygen minima existing both north and south of the equator along the eastern basin. This deficiency in oceanic O₂ concentrations is mainly due to a combination of upwelling induced high primary productivity and poorly ventilated intermediate waters. Across the Miocene-Pliocene the Pacific Ocean is thought to have been distinctly different with an elevated water column temperature profile, reduced Walker circulation, active deep-water formation in the north Pacific, high primary productivity, and differences in its fundamental configuration with gateway changes occurring at the eastern and western margins. Collectively, and individually, these different factors will have had implications on Pacific Ocean O₂ distribution. To better understand the past oxygenation of Pacific waters amidst this backdrop of climatic and geographical changes we reconstruct iodine/calcium ratios from planktic foraminifera across multiple Pacific Ocean sites. Our I/Ca records extending from the mid-late Miocene through to Pleistocene show the progressive reduction in oceanic O₂ content across the Pacific. We place these records in the context of changes in the Central American Seaway and the resultant changes in oceanic circulation.

How to cite: Nilsson-Kerr, K., Hoogakker, B., Reyes Macaya, D. A., and Winkelbauer, H. A.: Late Cenozoic oxygenation of the Pacific Ocean, a perspective from planktic foraminiferal I/Ca, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11804, https://doi.org/10.5194/egusphere-egu23-11804, 2023.

The Southern Ocean (SO) is a region particularly sensitive to the anthropogenic global warming because of the raising ocean temperatures, leading to latitudinal shifts of oceanographic fronts which govern the position of the South Westerly Winds (SWW) in the SO. Sediments represent a natural climate archive that allows to observe changes in Earth’s systems only affected by natural forcing. In this sense, Marine Isotope Stage (MIS) 11c (∼426–396 ka) is the most similar climate state to the ongoing climate warming that we are facing today, but quantiative climate reconstructions in the SO for this period are scarce. Radiolarians (zooplankton) live in a wide range of depths in the water column and are very abundant in sediments throughout the Neogene in the SO.  Recent radiolarian databases and transfer functions for the SO (Lawler et al. 2021; Civel-Mazens et al. 2022) enable reconstructing quantitatively past climate. For this, three sediment cores, drilled during IODP Expedition 382 and located along latitudinal gradient in the Atlantic sector of the SO (between 53.2°S and 59.4°S), were studied for their fossil radiolarian assemblage composition for the interval corresponding to MIS 11c. Application of the newly developed radiolarian transfer functions to the fossil radiolarian assemblages in these three cores enabled the reconstruction of ocean temperatures and thermal gradients in the SO during MIS 11c. These reconstructions will be used also to infer the position of the oceanographic frontal zones and the position of the SWW in this sector of the SO in the past, which are important for promoting upwelling nutrient rich bottom waters and degassing of deeply sequestered CO₂ during the interglacial maxima.

References:

Civel-Mazens, M., Cortese, G., Crosta, X., Lawler, K. A., Lowe, V., Ikehara, M., & Itaki, T. (2022). New Southern Ocean transfer function for subsurface temperature prediction using radiolarian assemblages. Marine Micropaleontology, 102198.

Lawler, K. A., Cortese, G., Civel-Mazens, M., Bostock, H., Crosta, X., Leventer, A., & Armand, L. K. (2021). The Southern Ocean Radiolarian (SO-RAD) dataset: a new compilation of modern radiolarian census data. Earth System Science Data, 13(11), 5441-5453.

How to cite: Hernández-Almeida, I., Hirt, J., and Renaudie, J.: Microfossil-based reconstruction of latitudinal thermal gradients in the Southern Ocean during MIS11c, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12026, https://doi.org/10.5194/egusphere-egu23-12026, 2023.

Today, the western Arabian Sea represents one of the most productive marine areas in the world. The high productivity in this region is governed by upwelling related to the intensity of the South Asian Monsoon (SAM). Previous studies show that high productivity has prevailed since the late Early Miocene (~15 Ma) after establishing a favorable tectonic configuration in the region. Existing productivity records have further demonstrated that upwelling intensity varied in the western Arabian Sea over different time scales. This variability has been attributed mainly to changing monsoonal upwelling intensity linked to global climatic changes. However, the abundance and contribution of individual primary producers (calcareous nannoplankton and diatoms) have never been studied in the context of upwelling and SAM changes. To fully disentangle the variability in the context of local upwelling changes and nutrient availability at ODP Site 722B, we link assemblage-based primary productivity records to the established multi-proxy framework in the region. Quantitative nannofossil assemblage records and absolute diatom abundances are examined in conjunction with existing and new planktonic foraminifer data to better constrain the temporal variation in productivity in the western Arabian Sea.

In our record, the first increase in cool and eutrophic nannofossil taxa (i.e., Coccolithus pelagicus and Reticulofenestra pseudoumbilicus) corresponds to the initial phase of sea surface temperatures (SST) cooling ~13.4 Ma. By ~12 Ma, rare occurrences of diatoms frustules correspond to the maximum abundances of Reticulofenestra haqii and Reticulofenestra antarctica, indicating higher upwelling derived nutrient levels. However, these changes ~12 Ma occur in the absence of coeval high latitude cooling, as shown by deep-sea benthic oxygen isotope records. By 11 Ma, diatom abundance increases significantly, leading to alternating blooms of upwelling sensitive diatom species (Thalassionema spp.) and eutrophic nannoplankton species (e.g., R. pseudoumbilicus). These changes in primary producers are also well reflected in geochemical proxies with increasing δ¹⁵N_org. values (> 6‰) and high C/N ratios also confirming high productivity and beginning denitrification at the same time.

Our multi-proxy-based evaluation of Site 722B primary producers thus indicates a stepwise evolution of productivity in the western Arabian Sea related to the intensity of upwelling and forcing SAM dynamics throughout the Middle to Late Miocene. The absence of full correspondence with existing deep marine climate records also suggests that local processes, such as lateral nutrient transport, likely played an important role in modulating productivity in the western Arabian Sea. We show that using a multi-proxy record provides novel insights into how fossil primary producers responded to changing nutrient conditions through time in a monsoon-wind-driven upwelling zone.

How to cite: Auer, G., Bialik, O. M., Antoulas, M.-E., and Piller, W. E.: Middle to Late Miocene responses of primary producers to monsoonal upwelling in the western Arabian Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12214, https://doi.org/10.5194/egusphere-egu23-12214, 2023.

International Ocean Discovery program (IODP) Expedition 383 Dynamics of the Pacific Antarctic Circumpolar Current (DYNAPACC) (Lamy et al., 2019; 2021) drilled a series of cores from the Pacific sector of the Southern Ocean in order to explore atmosphere-ocean-cryosphere glacial-interglacial dynamics their implications for regional and global climate changes. IODP Expedition 383 sites constitute the first continuous drill cores at key locations of the Subantarctic Pacific Southern Ocean extending through the Pleistocene and back into the Pliocene.

Here we focus on coccolith relative and absolute abundance as well as productivity variations for the last 0.5 Million year, in order to understand the nannofloral response to glacial-interglacial cycles and related changes in carbonate production and export. Our data has been generated at IODP Sites U1539 (56°09.0655′S, 115°08.038′W, ~1600 nmi west of the Strait of Magellan at 4070 m water depth) and U1540 (55°08.467′S, 114°50.515′W, ~1600 nmi west of the Strait of Magellan at 3580 m water depth), drilled at a southern and northern location in the central Pacific within the ACC, respectively. Coccolithophore diversity and coccolith numbers change dramatically in the studied cores, ranging from high values during interglacials (up to ca. 10¹¹ coccoliths per gram of sediment, as in MIS11, Saavedra-Pellitero et al., 2017) to low values during the glacials, where they are outcompeted by siliceous microfossils, mostly diatoms.

References

Lamy, F., Winckler, G., Alvarez Zarikian, C.A., and the Expedition 383 Scientists, 2019. Expedition 383 Preliminary Report: Dynamics of the Pacific Antarctic Circumpolar Current. International Ocean Discovery Program. https://doi.org/10.14379/iodp.pr.383.2019

Lamy, F., Winckler, G., Alvarez Zarikian, C.A., and the Expedition 383 Scientists, 2021. Dynamics of the Pacific Antarctic Circumpolar Current. Proceedings of the International Ocean Discovery Program, 383: College Station, TX (International Ocean Discovery Program). https://doi.org/10.14379/iodp.proc.383.2021

Saavedra-Pellitero M., Baumann K.-H., Lamy F., and Köhler P., 2017. Coccolithophore variability across Marine Isotope Stage 11 in the Pacific sector of the Southern Ocean and its potential impact on the carbon cycle. Paleoceanography, 32, 864–880, doi:10.1002/2017PA003156.

How to cite: Malinverno, E., Saavedra-Pellitero, M., Jones, A., Cerri, S., and Dunkley Jones, T. and the IODP-383 Scientific Party: Late Pleistocene-Holocene coccolithophore variations in the Subantarctic South Pacific, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13273, https://doi.org/10.5194/egusphere-egu23-13273, 2023.

The latitudinal migration of the Southern Ocean hydrographic fronts has been suggested to influence oceanographic conditions within the Indian-Atlantic Ocean gateway by restricting the amount of warm, saline water from the Indo-Pacific, transported by Agulhas Current, feeding into the South Atlantic via the Agulhas leakage. The Agulhas Current is an integral part of the global thermohaline circulation system as it acts as potential modulator of the Atlantic Meridional Overturning Circulation, which drives changes in regional and global climate, over at least the last 1.4 million years. However, the dynamics of this frontal system and associated changes in surface ocean biogeochemistry have not been explored beyond this time period due to absence of long continuous records spanning the Pliocene. Using International Ocean Discovery Program Site U1475 located on the southwestern flank of the Agulhas Plateau (41°25.61′S; 25°15.64′E; 2669 m water depth), we present high-resolution palaeoclimate records spanning the early to mid-Pliocene (~2.8 to ~5 Ma), from assemblage composition and morphometry of coccoliths, combined with oxygen and carbon stable isotopes from the bulk coccolith fraction. Our new Pliocene reconstructions offer evidence of the changing position of the subtropical front in the Southern Indian Ocean, driving variations in surface ocean conditions (e.g., nutrients, temperature, stratification), and thus biological productivity. We also explore expressions of coccolith δ¹³C vital effects from size-separated coccolith fractions together with planktic foraminifer carbon and oxygen stable isotopes from co-registered samples, that have been linked to cell size, growth rate, and calcification degree, providing empirical correlation with aqueous and atmospheric CO₂ concentrations.

How to cite: Tangunan, D., Hall, I., Beaufort, L., Berke, M., LeVay, L., Mejia, L. M., Palike, H., Starr, A., and Flores, J. A.: The early to mid-Pliocene latitudinal migration of the Southern Ocean subtropical front (IODP Site U1475, Agulhas Plateau), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17081, https://doi.org/10.5194/egusphere-egu23-17081, 2023.

The restriction of the Mediterranean–Atlantic marine connection over the Messinian stage, which led to a salinity crisis and the deposition of the youngest salt giant on Earth, impacted the composition and structure of marine biota in unprecedented ways, but its effects on the biological functions of marine organisms remains unchartered territory. By analyzing the stable oxygen and carbon isotopic composition of the otoliths of two carefully selected fish species, a pelagic (surface) and a benthic (bottom-dwelling) one, we were able to infer not only the sea surface and bottom salinity and oxygenation conditions, but also the fishes’ metabolic response to the paleoceanographic changes in the eastern Mediterranean from 7.2 to 6.5 Ma. The high salinity and stratification of the Mediterranean water column during this interval hampered the ability of the marine fishes to grow, particularly those dwelling in the sea bottom. A first event (6.82–6.81 Ma) of high temperature and salinity induced an increase in the metabolism of fishes across the water column, meaning that they consumed and respired more. Subsequent warming, increased salinity and stratification at 6.70–6.69 Ma further intensified the environmental stress for bottom-water fishes. To cope with these extreme conditions at the sea floor, benthic fishes show increased metabolic carbon despite low food availability, which implies that fishes metabolized (i.e. consumed) their own tissue to survive. The disappearance of benthic fishes in the study area after 6.8 Ma further reinforces this conclusion. Our study promotes the importance of otoliths stable isotopic analyses as tools for reconstructing complex paleoenvironmental histories.

How to cite: Agiadi, K., Vasiliev, I., Butiseaca, G., Kontakiotis, G., Thivaiou, D., Besiou, E., Zarkogiannis, S., Koskeridou, E., Antonarakou, A., and Mulch, A.: Fish starved to death by Mediterranean water-column stratification and high salinity in pre-evaporitic Messinian, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1186, https://doi.org/10.5194/egusphere-egu23-1186, 2023.

At present, the Mediterranean is connected to the Atlantic Ocean through the narrow Strait of Gibraltar (only 13 km wide). The latter, in the late Miocene, most probably did not exist, and the Mediterranean – Atlantic water exchange took place through the Betic (Southern Spain) and Rifian (Northern Morocco) corridors. Studying the evolution of such gateways is fundamental when investigating the extraordinary event known as the Messinian Salinity Crisis (5.96 – 5.33 Ma), when the connection between the Mediterranean Sea and Atlantic Ocean significantly diminished or even ceased. In this work we present a new high resolution geochemical (XRF and stable isotope) record of the Tortonian – Messinian interval of the Montemayor-1 and Huelva-1 cores located in the Betic corridor, current Guadalquivir Basin. Our new data enabled in the first place the high-resolution tuning of the 7.4 – 5.8 Ma time interval, and consequently to precisely date environmental changes and relate them to Mediterranean and global events.

Our results indicate that, at 7.17 Ma and in concomitance with a shallowing of the basin, the bottom water residence time, temperature and salinity increased. These changes have been associated with a reduction of the Mediterranean Outflow Water reaching the Guadalquivir Basin as a consequence of the restriction of the last strand of the Betic corridor connecting the Mediterranean and the Atlantic. This hypothesis is in line with the analogous changes observed in several Mediterranean Sea locations, where from 7.17 Ma a reduced Mediterranean – Atlantic connection is visible. Nonetheless, even if such reduction of the connection was feasible, the same changes in isotope record and analogous cyclicity observed both in the Guadalquivir and Alboran Basin record imply that the Mediterranean signal was still reaching the Betic gateway to some degree. In addition, the significant offset present between our and North Atlantic oxygen stable isotope records entails how the signal in the Guadalquivir basin could not have been purely Atlantic. Consequently, we conclude that a significant Mediterranean signal was still present in the Betic corridor during the Messinian.

How to cite: Bulian, F., Jiménez-Espejo, F. J., Andersen, N., Larrasoaña, J. C., and Sierro, F. J.: Evidence of Mediterranean water in the Atlantic margin during the Messinian, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2922, https://doi.org/10.5194/egusphere-egu23-2922, 2023.

Neoichnology of high energy deep-sea environments: A tool to improve gateways characterization

Olmo Miguez-Salas¹, Francisco J. Rodríguez-Tovar²

1Department of Marine Zoology, Senckenberg Research Institute and Natural History Museum, 60325 Frankfurt, Germany.

2 Department of Stratigraphy and Paleontology, University of Granada, 18071 Granada, Spain

Evolution of ocean gateways determines significant changes in deep-water dynamics affecting depositional and ecological conditions. Particularly, variations in deep-water circulation associated to closing and opening gateways induce changes in hydrodynamic energy, rate of sedimentation, organic matter availability, salinity, oxygenation, etc., affecting benthic community. Modern biogenic structures (lebensspuren), as reflecting the behavior of the tracemaker to environmental conditions (i.e., depositional and ecological) reveal as a useful tool to interpret processes affecting deep-sea depositional settings. The exploration of these deep-sea environments and the in-situ observation of tracemakers require the expensive and time-consuming deployment of short-range observation gear, in many cases with inherent limitations, such as restricted fields of view in both spatial and temporal scales. However, in recent years neoichnological information from marine epibenthic lebensspuren (i.e., traces on the seafloor) has been obtained from videos or still images captured by cameras on autonomous and remotely operated underwater vehicles transiting on or above the seafloor. This new information reveals of major interest, especially in high-energy deep-sea environments, which can be correlated with those related to gateways and paleo-gateways.

In this study we present three cases that exemplify how lebensspuren features are related to deep-sea environments that have high-energy conditions: 1) Rosette-shape traces (RST) related to echiuran feeding activities. We study two locations of the Porcupine Abyssal Plain (NE Atlantic) where the seafloor consistency is different due to sporadic high energetic gravity flows as well as the local dominant megabenthos feeding group (e.g., suspension vs. deposit feeders). The seafloor consistency appeared not to affect RST morphology while the dominant feeding group seemed to control rosette areal coverage. 2) At an abyssal site in the NE Pacific ('Station M'), high-energy periods associated with benthic storms have been related to the impoverishment of lebensspuren abundance and diversity. The local-scale erosion and re-suspension of unconsolidated surface sediment inhibits the formation of previous softground traces and led to the redistribution of organic matter resources but the trace maker remained in the deep-sea station. These findings offer a new perspective where absence of traces may not imply tracemakers absence during quick (<1 day) energetic episodes at the deep-sea. 3) At an abyssal site with a dune field in the Bering Sea, lebensspuren abundance and diversity varies from the abyssal area to the dune field. Changes in the abundance of dwelling structures seem to be related to the high energetic conditions typical of deep-sea dunes.

How to cite: Miguez Salas, O. and Rodríguez Tovar, F.: Neoichnology of high energy deep-sea environments: A tool to improve gateways characterization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7273, https://doi.org/10.5194/egusphere-egu23-7273, 2023.

How to cite: Palcu, D. V., Heida, H., Sandric, I., Popov, S., Garcia Castellanos, D., and Krijgsman, W.: The demise of Paratethys in the time of the Messinian Salinity Crisis: impact on Eurasian paleogeography and Mediterranean environments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7669, https://doi.org/10.5194/egusphere-egu23-7669, 2023.

The extreme Mediterranean sea-level drop during the Messinian salinity crisis has been known for >50 years, but its amplitude and duration remain a challenge. Here we estimate its amplitude by restoring the topography of the Messinian Nile canyon and the vertical position of the Messinian coastline by unloading of post-Messinian sediment and accounting for flexural isostasy and compaction. We estimate the original depth of the geomorphological base level of the Nile River at ~600-m below present sea level, implying a drawdown 2-4 times smaller than previously estimated from the Nile canyon and suggesting that salt precipitated under 1-3-km deep waters. This conclusion is at odds with the nearly-desiccated basin model (>2 km drawdown) dominating the scientific literature for 50 years. Yet, a 600-m drawdown is ca. five times larger than eustatic fluctuations and its impact on the Mediterranean continental margins is incomparable to any glacial sea-level fall.

How to cite: Gvirtzman, Z., Heida, H., Garcia-Castellanos, D., Bar, O., Zucker, E., and Enzel, Y.: Limited Mediterranean sea-level drop during the Messinian salinity crisis inferred from the buried Nile canyon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7864, https://doi.org/10.5194/egusphere-egu23-7864, 2023.

Restricted basins are susceptible to develop anoxia because these land-locked basins can trap nutrients and the water column can easily become stratified. The Mediterranean basin has a limited connection to the open ocean and became increasingly restricted over time, making it suitable to study effect of basin configuration on anoxia development. Enhanced runoff, related to increased North-African monsoon intensity, regularly resulted in increased productivity and/or deep-water anoxia and deposition of organic-rich sediments, the so-called sapropels. Most depositional models for sapropel formation focus on the most recent sapropels (e.g. S1 and S5), outcrop samples or individual Pliocene sapropels from ODP leg 160. Until recently, continuous and high-resolution records were lacking, whereas such records can provide important constraints on the relationship between sapropel deposition and its environmental driving forces, such as climate and basin configuration. Here we present newly acquired XRF-scanning data of redox-sensitive trace elements and estimates for total organic carbon (TOC) from a 5 Myr record of the Eastern Mediterranean Sea (ODP Site 967), where reoccurring sapropels are recorded from 3.2 Ma onwards. Based on our geochemical proxies, we reconstruct (de)oxygenation and associated basin restriction over the last 5 Myr. This record allows us to elucidate which primary processes drove sapropel formation in this basin and whether these processes changed over time. We show that the first preserved Pliocene sapropels (~3.2-3.0 Ma) are highly enriched in redox-sensitive trace elements and have TOC values up to 25%, and likely formed in a much more open (i.e. with increased water renewal) depositional environment. Such a model of Mediterranean sapropel deposition differs significantly from that of the more recent sapropels, which are deposited in a much more restricted environment. Hence, the depositional model for recent sapropel formation cannot be directly extrapolated to these older sapropel deposits.

How to cite: van der Hoeven, I., Grant, K., Rohling, E., Liebrand, D., Lourens, L., Reichart, G.-J., and Hennekam, R.: A 5-million-year record of (de)oxygenation and associated changes in basin restriction in the Mediterranean Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8524, https://doi.org/10.5194/egusphere-egu23-8524, 2023.

In the Mediterranean region, the end of the Miocene is marked by the Messinian Salinity Crisis (MSC; 5.97 - 5.33 Ma), a peculiar event that governed environmental modifications in the region, causing the deposition of large thicknesses of evaporitic rock units, dramatic hydrological and ecological crises that affected both water and land-based habitats. The onset of the MSC has been proven to be synchronous over the Mediterranean basin as demonstrated by astronomical tuning of the pre-evaporitic sedimentary successions. Among these, the Sorbas Basin plays a pivotal role for the understanding of the palaeoceanographic evolution of the Western Mediterranean Sea before the onset of the MSC. Its location within proximity of the Atlantic gateway renders the Sorbas Basin an exceptional recorder of palaeoceanographic changes just prior to the MSC. The pre-evaporitic sequence starts with Tortonian calcarenites (belonging to the Azagador Member) followed by early Messinian clays and diatomites (belonging to the Abad Member). The Lower Abad Member, consists of indurated whitish marls and softer grey marls which contrast sapropel and diatomite alterations of the Upper Abad Member. Here, we present biomarker-based sea surface temperatures (SST) using TEX₈₆ paleotemperatures recorded in the Sorbas basin for the time interval between 7.3 and 6.1 Ma. The TEX₈₆ SST estimates show a generally decreasing trend, with a 7.26 Ma to 7.11 Ma warm phase (averaging 27 °C). This warm phase is followed by ~5°C cooling (to values averaging 22 °C) after 7.11 Ma, with two distinct colder peaks, one centred around 7.09 Ma and one around 6.95 Ma. The cooling after 7.11 Ma follows shallowing and restriction in the Betic and Rifian marine gateways and is most likely controlled by global cooling characterizing the latest Miocene. In a second step, we couple the TEX₈₆ SST estimates with oxygen stable isotope ratios (δ¹⁸O) measured on the surface-dwelling planktonic foraminifera Orbulina universa to reconstruct sea surface salinity (SSS) variations at the corresponding stratigraphic levels for the study interval. The newly acquired SST and SSS data from the Sorbas Basin provide a previously unavailable record of changed environmental conditions recorded in the Western Mediterranean Basin that permit direct comparison across the Mediterranean Basin with the recently acquired Messinian Eastern Mediterranean SST and SSS changes.

How to cite: Lanterna, F., Vasiliev, I., Sierro, F. J., and Mulch, A.: Sea Surface Temperatures variations during the Messinian in the Sorbas Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9065, https://doi.org/10.5194/egusphere-egu23-9065, 2023.

The Central Paratethys Sea occupied the transition between the Alps, Dinarides and Carpathian mountains during Oligocene to Miocene times. However, its spatial and temporal evolution, i.e. southward expansion, subsequent salinity crisis, and governing mechanisms are poorly constrained. Here, we employ radiometric dating to construct the Middle Miocene absolute chronology of the evolution of the successions developed along the southwestern margin of the Central Paratethys flanking the NE Dinarides (NE Bosnia and Herzegovina) and governing mechanisms. We present three U-Pb zircon ages acquired by LA-ICP-MS from volcanic ash layers sampled in Tuzla marginal marine basin (two layers) and neighboring lacustrine Lopare Basin (one layer). Zircon grains from the lowermost ash of the playa lake in Lopare Basin yielded a U-Pb age of 15.143 ± 0.094 Ma. This indicates that despite the warm and humid global climate, the Lopare Basin and many lakes in the internal part of the Dinarides hosting similar salina-type successions recorded regional arid climatic conditions during Middle Miocene. Furthermore, this age implies synchronicity of arid with humid lakes (e.g., Sinj, Gacko) developed in the internal and external Dinarides, respectively which are orographically controlled. The U-Pb zircon age of the middle ash layer (14.12 ± 0.077 Ma) places new constraints on the marine flooding in the Tuzla Basin, i.e. along the southwestern margin of the Central Paratethys. Considering age data from previous studies the new age implies south-southeastward marine expansion of the Central Parathetys over a period of 3-4 Myrs, along the N, NE-ward flanks of the Dinarides. The demise of the Dinarides affected by the rift climax in the neighbouring Pannonian Basin and associated block rotations provided a space for the S/SE-ward marine expansion. Deposition of the uppermost ash layer sampled at the top of marine salt succession in Tuzla Basin is constrained by a U-Pb zircon age of 13.88 ± 0.11 Ma. This indicates that Salinity Crisis in Badenian was affecting the entire Central Parathehys coevally. Therefore, we correlate the evaporitic event in the Tuzla basin with the sea-level fall controlled by the global climatic Mi3b event.

How to cite: Andrić-Tomašević, N., Mandic, O., Zeh, A., Simić, V., and Vrabac, S.: Middle Miocene events in the peripheral basins of Central Paratethys (Central Europe): inferences from Tuzla and Lopare basins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9107, https://doi.org/10.5194/egusphere-egu23-9107, 2023.

The boron isotope composition of the ocean is homogeneous, but varies on multi-million year time scales, given its residence time of approximately 10 million years. To date, the secular evolution of the oceanic boron isotope budget has been difficult to constrain. The lack of knowledge on past boron isotope composition of seawater (δ¹¹B_sw) poses a major uncertainty for reliable boron-based pH and CO₂ reconstructions from Earth’s geologic past and critically limits our understanding of the global biogeochemical cycling of this important element through time. Evaporitic minerals bearing fluid inclusions – and halites in particular – present a highly appealing archive for reconstructing δ¹¹B_sw given their direct origin from seawater. However, the interpretation of their boron isotope signatures is not straightforward due to the possibility of fractionation during evaporation and crystallisation. Here we present first insights into boron isotope evolution during evaporite formation from laboratory experiments and natural modern evaporitic settings. These data enable us to place constraints on boron fractionation in ancient evaporites, offering new insights into δ¹¹B_sw during some of the key periods of the Phanerozoic.

How to cite: Jurikova, H., Gázquez, F., Branson, O., Evans, D., Dumont, M., Sendula, E., Bodnar, R., Weldeghebriel, M., Lowenstein, T., and Rae, J.: Secular evolution of boron isotope composition of seawater archived in evaporites?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9969, https://doi.org/10.5194/egusphere-egu23-9969, 2023.

During the early and middle Miocene, the Mediterranean became a restricted marginal sea with the contraction of the Mesopotamian Gateway and ultimate loss of connectivity to the Indian Ocean. Leading to the transformation of the Mediterranean into a restricted marginal marine sea . Low latitude circumglobal circulation through the basin characterized the basin for most of the Cretaceous and Paleogene. With the loss of this supply of surface and subsurface waters, dramatic changes occurred to the heat, energy, and nutrient budgets across the Mediterranean. The most affected area was the eastern basin. , As is well evidenced by the onset of sapropel formation, many other aspects of the sedimentary system changed in response to this ocean circulation rearrangement. Hemipelagic successions in southwestern Cyprus offer a window into the changes in the subsurface waters occurring in the Eastern Mediterranean through the closure of the gateway to the Indian Ocean. Dated to the late Aquitanian to the early Serravallian (22.5–14.5 Ma), this sequence is carbonate-dominated and overall continues. It exhibits sedimentation with mass transport contribution from shallow water carbonates to deeper facies. The succession exhibits fluctuation of bottom current activity, which was disrupted in the early Burdigalian by mass transports and temporarily halted during the Langhian. Phosphates are present through the entire succession, but most notably in the Langhian. Combined, these lithological characteristics indicate changes in bottom current energy and seafloor ventilation that point to two key intervals of connectivity restriction through the Mesopotamian gateway.

How to cite: Bialik, O. M., Reolid, J., Kulhanek, D. K., Hincke, C., Waldmann, N. D., and Betzler, C.: The impact of Indian Ocean - Mediterranean gateway closure on the current and nutrient regime in the Eastern Mediterranean during the early to middle Miocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12101, https://doi.org/10.5194/egusphere-egu23-12101, 2023.

Between 5.97-5.33 Ma, kilometre-thick evaporite units were deposited in the Mediterranean Basin during the so-called Messinian Salinity Crisis (MSC). The MSC was marked by a strongly negative hydrological budget, with a net evaporative loss of water exceeding precipitation and riverine runoff. Knowledge about the contemporary changes in continental and marine circum-Mediterranean environments are still limited to qualitative descriptions in terms of temperature and humidity. Here we reconstruct continental mean annual temperatures (MAT) using branched glycerol dialkyl glycerol tetraether (brGDGT) biomarkers for the time period corresponding to MSC Stage 3 (5.55-5.33 Ma) and compare them with values obtained from Δ₄₇ clumped isotope geochemistry measured on paleosol carbonate nodules found at few locations in the Mediterranean basin. Additionally, for the same time interval, we estimate sea surface temperatures (SSTs) of the Mediterranean Sea using the isoprenoidal GDGT-based TEX₈₆ proxy. The excellently preserved organic biomarkers were extracted from outcrops onshore (Malaga, Sicily, Cyprus) and offshore (DSDP core holes 124 and 134 from the Balearic abyssal plane, hole 374 from the Ionian Basin and hole 376 drilled west of Cyprus) covering a rather vast portion of the Mediterranean Basin.

Calculated MATs for the 5.55 to 5.33 Ma time interval show values around 16 to 19 ºC for the Malaga, Sicily and Cyprus outcrops. The MAT values calculated for DSDP Leg 13 holes 124, 134 and Leg 42A holes 374 and 376 are lower, around 13 to 16 ºC. Comparing the brGDGT-MAT values with Δ₄₇-MAT values from carbonate nodules, shows high congruence between both approaches. For the northern Mediterranean Δ₄₇-MAT is 20 ºC and brGDGT-MAT is 19 ºC. For Cyprus Δ₄₇-MAT is 21 ºC and brGDGT-MAT is 18 ºC. Given the very different type of the used paleoproxies, the similarity of the obtained MAT values provides a strong indication of their (cross)validity in sampled sections. Additionally, the measured δ¹⁸O values of ~33‰ (VSMOW) for the carbonate nodules used for the Δ₄₇-MAT indicate highly evaporative conditions for the two onland sites where these were collected (Northern Apennines and Cyprus).

For samples where the branched and isoprenoid tetraether index was lower than 0.4 we could calculate TEX₈₆ derived SSTs averaging around 27 ºC for all sampled locations, reaching the higher end of the values obtained in the Mediterranean region for the pre-MSC through U^k₃₇ and TEX₈₆ derived SSTs of Tzanova et al. (2015), Vasiliev et al. (2019) and Kontakiotis et al. 2022. Independent of pitfalls that may arise in using molecular biomarkers as temperature proxies, both SST estimates independently hint towards much warmer Mediterranean Sea water during the latest phase, Stage 3 of the MSC. These elevated temperatures coincide with higher δ²H values measured on alkenones and long chain n-alkanes (both records indicating more arid and/or warmer conditions than today between 5.55 and 5.33 Ma). We conclude that between 5.55 to 5.33 Ma the temperatures in the Mediterranean region was similar to present-day conditions, yet the region has suffered from excess evaporation as indicated by combined high δ¹⁸O values from carbonate nodules δ²H values from biomarkers.

How to cite: Vasiliev, I., Agiadi, K., Fiebig, J., and Mulch, A.: A drier Mediterranean region at the Miocene to Pliocene transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13297, https://doi.org/10.5194/egusphere-egu23-13297, 2023.

Closing and opening of ocean paleo-gateways strongly influenced the tectono-stratigraphic and sedimentary evolution of basins, affecting global ocean circulation, climate, sedimentary processes, and living biota. Particularly, closing and opening of ocean paleo-gateways determine significant changes in ocean dynamic affecting deepwater circulation, and then deepsea sedimentary facies and benthic community. Changes in bottom-current dynamic and their effects (e.g., erosion, nondeposition and variable rate of deposition) can cause changes in substrate features that might exert a major effect on the benthic habitat. To improve knowledge of paleo-gateways, involved oceanographic processes, and variations in the depositional systems, detailed analysis of the Contourite Depositional Systems and associated sediments controlled by deep-water circulation processes reveals of major interest. In this context an integrative ichnological and sedimentological approach is proved as a useful strategy.

This study focuses in the application of an integrative sedimentological (i.e., primary sedimentary structures, grain size analysis, microfacies, etc.) and ichnological approach to improve characterization of contourites and differentiation from other deep-sea facies associated to paleo-gateways. Examples from middle Miocene contourite deposits in Cyprus associated to the Indian Gateway, the late Miocene contourites Morocco related to the Rifian Corridor and from the Pliocene and Quaternary deposits in the Gulf of Cadiz related to the Strait of Gibraltar are presented. Changes in paleoenvironmental (ecological and depositional) conditions induced by gateways evolution, as hydrodynamic energy, rate of sedimentation, organic matter availability, affecting tracemaker community are interpreted based on integration of sedimentological and ichnological features.

How to cite: Rodriguez Tovar, F. J., Hernandez Molina, F. J., and Miguez-Salas, O.: Contourites and paleo-gateways: An integrative ichnological and sedimentological approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13517, https://doi.org/10.5194/egusphere-egu23-13517, 2023.

Paleogeographic reconstructions of the Western Mediterranean are often based on the present location of sedimentary outcrops. However, most geodynamic and biogeographic models for the region have highlighted the importance of up-to-hundreds of km of horizontal displacements of the terrains forming the western Mediterranean orogenic arcs since the early Miocene until the Pliocene. Here we update the known paleogeographic evolution for the westernmost Mediterranean, considering published biogeographic and recent new geological constraints, including paleontological, stratigraphic, tectonic kinematic data, seismic reflection lines, low-temperature thermochronological dating, detrital zircon age populations, among others. During the Burdigalian to Langhian the rocks of the Betic hinterland, corresponding to the Alboran domain, where exhumed in a forearc setting as far East as Mallorca, now located 450 to 700 km of their present outcrops. Those exhuming rocks floored sedimentary basins among an island archipelago. The land connection between Mallorca and Alboran domains continued until the Serravallian as attested by the shared fossils of vertebrate insular fauna and biogeographic data of different taxa including trap-door spiders, beetles and fresh-water planarians. The westward migration of the Alboran forearc archipelago and its overlying basins (currently forming the Betic intramontane and western Alboran basins) was concomitant to the Langhian to Tortonian opening of the Algero-Balearic back-arc basin and the retreat of the Betic-Rif subducted slab. At a smaller scale, the Granada supra-detachment intramontane basin moved > 100 km between the Tortonian and Present, implying that previously interpreted, emerged domains, like the Sierra Nevada island where either inexistent or in a different location during the Tortonian. Sediment interpreted to represent marine gateways around and through the Alboran archipelago in the westernmost Mediterranean, may have being partially deposited as far East as Mallorca, and probably migrated westwards from the Langhian to the late Pliocene in the Gibraltar straits. Of particular interest, is the Late Messinian to Late Pliocene westward migration of the Gibraltar straits documented by sedimentary onlap over erosive channels in the Western Alboran basin and marine terraces along its Betic and Rif shores. The above proposals are evolving questions concerning the Neogene paleogeographic evolution of the Western Mediterranean that may be tested by future work and drilling.

How to cite: Booth-Rea, G., Ranero, C., Azañón, J. M., Garrido, C. J., and García-García, F.: Migrating straits, basins and archipelagos: open questions about the Neogene paleographic evolution of the Westernmost Mediterranean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15310, https://doi.org/10.5194/egusphere-egu23-15310, 2023.

Contourite depositional systems (CDS) represent the sedimentary records of paleoceanographic circulation and paleoclimatic changes throughout the geological timescale. These records offer expanded but contingent information relative to their adjacent marine gateways, documenting changes in the intensity and the direction of modern-day and paleo-current pathways on multi-centennial, millennial and million-year timescales. This study investigates the late Miocene to Quaternary CDSs from the Gulf of Cadiz towards the West Iberian margin after the exit of the past Betic and Rifian corridors and most recent Strait of Gibraltar, the key gateways for the Mediterranean – Atlantic exchange trough time. A summary of the key results is presented as a representative study case for decoding the long- and short-term behaviour of oceanographic processes related to gateways and their associated overflows.

In the study area, it is well known that the Mediterranean Outflow Water (MOW) has generated a complex CDS since the full opening of the Strait of Gibraltar in the early Pliocene (5.3 Ma). Recently, an ancient CDS has also been discovered in the late Miocene, which is separated from the Pliocene-Quaternary CDS by a period of quiescence representing the restriction of bottom water circulation across the Mediterranean-Atlantic exchange during the late Messinian (~6.4 - 5.3 Ma). The late Miocene CDS was established after the final closure of the Indian Gateway (IG) and the Neo-Tethys Ocean in the Middle Miocene, followed by the inception of the Mediterranean Sea (~13.8 - 11 Ma). The final closure of the IG conditioned a wide gateway configuration for the connection between the Mediterranean Sea and the Atlantic Ocean, with the full establishment of an anti-estuarine circulation similar to the present day as opposed to its previous situation.

Interestingly, both the late Miocene and the Pliocene-Quaternary CDSs have a long common evolution that could be simplified into two stages, with an initial- and growth-drift stages. The late Miocene CDS is then buried under dominantly hemipelagic late Messinian (~6.4 - 5.3 Ma) deposits, whereas the buried-drift stage is absent for the Pliocene-Quaternary system due to the ongoing nature of the CDS’s evolution. The long-term development of these CDSs can be correlated with a coeval shallowing of sills, which determined a change from an outflow to an overflow setting across the gateways through time. These long-term variations (>5-10 My) in paleo-circulation are thus driven by the by the tectonic control on the evolution of oceanic gateways. The internal sedimentary architecture of the late Miocene and Pliocene-Quaternary CDSs indicates a complex stratigraphic stacking pattern of deposits bounded by internal discontinuities and hiatuses in response to the intermittent behaviour of the MOW at different temporal scales, which have been attributed to tectonic pulses, climatic and eustatic changes and oceanographic processes that have caused deepening/shoaling or weakening/strengthening of bottom currents through time, exerting a major effect on deepwater sedimentation and the benthic habitat.

This project was funded by the JIP#1 within the framework of “The Drifters” Research Group at Royal Holloway University of London and related to the projects, CTM2016-75129-C3 (INPULSE) and PID2021-123825OB-I00 (ALGEMAR).

How to cite: Hernández-Molina, F. J., Ng, Zhi. L., Duarte, D., Llave, E., Roque, C., Sierro, F. J., de Weger, W., de Castro, S., Rodrigues, S., Rodríguez-Tovar, F. J., Fernández-Salas, L. M., García, M., Arnaiz, Á., Roque, D., Bruno, M., and Sánchez-Leal, R. F.: Late Miocene to Quaternary Contourites Depositional Systems in the Gulf of Cadiz and West Portugal related to the Mediterranean - Atlantic exchange evolution: decoding bottom currents behaviour and oceanographic processes associated with gateways, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15668, https://doi.org/10.5194/egusphere-egu23-15668, 2023.

At the end of the Miocene, the restriction of the Atlantic-Mediterranean seaway led to the deposition of a basin-wide salt giant (of up to 2.5km in thickness) in the Mediterranean. Drawdown(s) of the water level of the Mediterranean during this Messinian Salinity Crisis (MSC) have been proposed to have occurred. However, their number, timing and amplitude are still largely debated, with estimates ranging from 200m to 2km. While an important sea level fall could have efficiently blocked the Mediterranean outflow to the Atlantic Ocean, a limited drawdown would have allowed huge export of salt from the Mediterranean to the Atlantic Ocean, and in turn to the global ocean.  These two scenarios would thus have had opposite effects on thermohaline circulation and consecutively on climate. It is therefore crucial to estimate the water level of the Mediterranean during the MSC to understand its climatic and environmental effects both on a regional and global scale.

Here we investigated the deposits drilled by ODP and DSDP expeditions that characterize the terminal phase of the MSC in deep basins of the Mediterranean.  We measured the sulfur isotopic composition (both in sulfide and sulfate bearing minerals) in these deposits to constrain the maximal depth under which they formed, building on the observation that sea level is an important factor controlling sedimentary sulfur isotopic composition. We then used these maximal depths of deposition in a paleo-bathymetric reconstruction to constrain the amplitude of the base level fall that characterized the end of the Messinian Salinity Crisis. The result of this approach suggests a minimal water level drop of 1.1km in the western Mediterranean and a 1.7km drawdown at least in the eastern Mediterranean. This imply that these two basins were disconnected at the end of the MSC, and supports the findings of studies using independent seismic markers.

How to cite: Guibourdenche, L., Heida, H., Andreetto, F., and Aloisi, G.: Late Messinian Mediterranean base level fall : insights from sulfur isotopic variations coupled with isostasy-based paleo-depth estimates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16940, https://doi.org/10.5194/egusphere-egu23-16940, 2023.

Hydrological restriction from the Atlantic Ocean and a negative freshwater balance transformed the Mediterranean Sea into a giant saline basin during the Messinian Salinity Crisis (MSC) (5.97 – 5.33 million years ago). After more than 50 years of research, it is still unclear if the deposition of nearly one million km3 of evaporite salts during this event was accompanied by a major (≥ 1.5 km) drawdown of Mediterranean sea level; and if halite deposition occurred only during this drawdown event, or also in a filled Mediterranean connected to the Atlantic.

We present evidence based on the chlorine stable isotope composition of halite for a sea level drawdown of 2 km in the eastern Mediterranean during the final stages of deposition of the Mediterranean halite layer. This is the largest sea level drop ever reported from the geological record and implies a short (~20 kyr), but nearly complete hydrological disconnection of the Mediterranean from the Atlantic. About half of the halite volume in the eastern Mediterranean was deposited during this drawdown event. Scant chlorine isotope data from the western Mediterranean, together with new estimates of western basin halite volume, suggest that the complete western halite deposit accumulated during the drawdown event. This mode of halite deposition - termed “evaporative drawdown” - had been already proposed as an evolution of the “deep-basin, shallow-water” scenario for the MSC (Hsü et al., 1973).

Chlorine isotopes indicate that the remaining half of the eastern Mediterranean halite volume accumulated prior to the drawdown, in a filled Mediterranean that received a continuous input of Atlantic waters. This halite accumulation phase lasted about 70 kyr and was driven by a restricted - but not fully blocked - outflow of deep western Mediterranean waters to the Atlantic. This model of halite deposition corresponds to the “deep-basin, deep-water” scenario for the MSC (Schmaltz, 1969). In summary, our results show that both the “deep-basin, deep-water” and the “deep-basin, shallow-water” modes of halite accumulation took place during the MSC, and that the complete deep-basin MSC halite deposit accumulated in less than 100 kyr.

Hsu, K., Ryan, W. & Cita, M. Late Miocene Desiccation of Mediterranean. Nature 242, 240–244 (1973).

Schmalz, R. F. Deep-water evaporite deposition, a genetic model. American Association of Petroleum Geologists Bulletin53, 798–823 (1969).

How to cite: Aloisi, G., Moneron, J., Guibourdenche, L., Camerlenghi, A., Gavrieli, I., Bardoux, G., Agrinier, P., and Gvirztman, Z.: Modes of deep basin halite accumulation during the Messinian Salinity Crisis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17206, https://doi.org/10.5194/egusphere-egu23-17206, 2023.

Physical connectivity between marine basins facilitates population exchange and hence controls biodiversity. The Mediterranean Sea is a semi-restricted basin with only a small two-way connection to the global ocean, and it is a region heavily impacted by climate change and biological invasions today. The massive migration of non-indigenous species into the basin through the Suez Canal, driven and enabled by climate warming, is drastically changing Mediterranean biodiversity. Understanding therefore the origin and cause(s) of pre-existing biodiversity patterns is crucial for predicting future impacts of climate change. Mediterranean biodiversity exhibits a west-to-east decreasing gradient in terms of species richness, but the processes that resulted in this gradient have only been hypothesized. By examining the fossil record, we provide evidence that this gradient developed 5.33 million years ago at the end of the Messinian Salinity Crisis, and it was therefore caused by the re-population of the basin by marine species with a dominating western source at the Mediterranean–Atlantic gateway.

How to cite: Agiadi, K., Hohmann, N., Gliozzi, E., Thivaiou, D., Collareta, A., Bosellini, F., Bianucci, G., Londeix, L., Bulian, F., Lozar, F., Mancini, A. M., Dominici, S., Moissette, P., Campos, I. B., Borghi, E., Kontakiotis, G., Zarkogiannis, S., Harzhauser, M., Camerlenghi, A., and Garcia-Castellanos, D.: Mediterranean biodiversity gradient initiated by basin restriction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17215, https://doi.org/10.5194/egusphere-egu23-17215, 2023.

Marine gateways play a critical role in the exchange of water, heat, salt and nutrients between oceans and seas. The advection of dense waters helps drive global thermohaline circulation and, since the ocean is the largest of the rapidly exchanging CO₂ reservoirs, this advection also affects atmospheric carbon concentration. Changes in gateway geometry can therefore significantly alter both the pattern of global ocean circulation and associated heat transport and climate, as well as having a profound local impact.

Today, the volume of dense water supplied by Atlantic-Mediterranean exchange through the Gibraltar Strait is amongst the largest in the global ocean. For the past five million years this overflow has generated a saline plume at intermediate depths in the Atlantic that deposits distinctive contouritic sediments in the Gulf of Cadiz and contributes to the formation of North Atlantic Deep Water. This single gateway configuration only developed in the early Pliocene, however. During the Miocene, a wide, open seaway linking the Mediterranean and Atlantic evolved into two narrow corridors: one in northern Morocco; the other in southern Spain. Formation of these corridors permitted Mediterranean salinity to rise and a new, distinct, dense water mass to form and overspill into the Atlantic for the first time. Further restriction and closure of these connections resulted in extreme salinity fluctuations in the Mediterranean, leading to the formation of the Messinian Salinity Crisis salt giant.

IMMAGE is a land-2-sea drilling project designed to recover a complete record of Atlantic-Mediterranean exchange from its Late Miocene inception to its current configuration. This will be achieved by targeting Miocene offshore sediments on either side of the Gibraltar Strait with IODP during Expedition 401 (December 2023-February 2024) and recovering Miocene core from the two precursor connections now exposed on land with ICDP. The scientific aims of IMMAGE are to constrain quantitatively the consequences for ocean circulation and global climate of the inception of Atlantic-Mediterranean exchange; to explore the mechanisms for high amplitude environmental change in marginal marine systems and to test physical oceanographic hypotheses for extreme high-density overflow dynamics that do not exist in the world today on this scale.

How to cite: Flecker, R. and Gaitonde, O. and the IMMAGE Co-I Team: Investigating Miocene Mediterranean-Atlantic Gateway Exchange (IMMAGE): the first land-2-sea drilling project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17219, https://doi.org/10.5194/egusphere-egu23-17219, 2023.

Due to the lack of drilling confirmation and the poor imaging quality of the early seismic data in deeper part, there was a great controversy on the understanding of the strata under the Cenozoic in the offshore Indus Basin: some scholars thought that the Deccan volcanic rocks were widely distributed; It is also believed to be Mesozoic sedimentary strata, but its stratigraphic framework, distribution and structural characteristics are not clear. This directly affects the evaluation of exploration potential in this area. Using the latest multi-channel seismic data, we have clearly identified Mesozoic sedimentary strata in the offshore Indus Basin. The offshore Indus basin is composed of the underlying Mesozoic rifting basin and the overlying Cenozoic passive continental margin sedimentary basin. It is a two-stage superimposed basin developed on the stretched and thinned crust of the Indian plate, drifting from the southern hemisphere to the present position together with the Indian continent. Through correlation of sea and land strata, it is found that the Mesozoic offshore Indus Basin is an offshore extension of the lower Indus Basin, and has similar stratigraphic distribution characteristics and structural characteristics to the lower Indus Basin. The correlation of seismic wave sets indicates that the Jurassic, Sembar Formation and Lower Goru Formation of Lower Cretaceous and the Upper Goru Formation of Upper Cretaceous were also deposited in the sea area. The Jurassic and Lower Cretaceous have the stratigraphic characteristics of eastern faulted and western overlapped, and the Upper Cretaceous has the characteristics of east-west double faulted. The basin rifting area expanded westward continuously during the Mesozoic. The Mesozoic strata were controlled by nearly N-S trending faults，the northern near-shore strata partially reformed by Cenozoic near E-W fault, and the western strata was influenced by the near N-S uplifting and strike-slip structure of Murray Ridge. The average thickness of Mesozoic strata is about 2000m, and the thickest can reach 12000m. The Mesozoic major depocenter is located in the southeast of the basin, the second one is in the northwest. The favorable structural types such as faulted nose, faulted anticline and anticline are mainly developed. These structures were mainly formed during the late Mesozoic compressive uplift period. Therefore, the Mesozoic in the Offshore Indus Basin has the material basis and structural geological conditions for the formation of oil and gas fields. If the favorable structure in Mesozoic can be configured with the depocenter, it will be conducive to hydrocarbon near-source charging. Like the Lower Indus Basin, the Mesozoic is also a favorable direction for petroleum exploration.

How to cite: Baohua, L., Jianming, G., Jing, L., Jie, L., Jianwen, C., and Sen, L.: Mesozoic structural characteristics and exploration potential of the offshore Indus Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1612, https://doi.org/10.5194/egusphere-egu23-1612, 2023.

According to the geotectonic analysis and seismic data interpretation, the Offshore Indus Basin is the extension of the Lower Indus Basin in the sea area, with a double-layer structure of "lower fault and upper depression" similar to that of the Lower Indus Basin in the land area. That is, the Mesozoic is a fault basin and the Cenozoic is a depression basin. On the 2D seismic profile, the Mesozoic strata are characterized by many faults, large fault throw, steep dip angle and the development of transport system. There is a great difference between the shallow water area of the northern continental shelf and the deep water area of the southern part of the Cenozoic strata. In the northern part, there are more gravity slumping faults, larger fault throw, and more developed transport systems, while in the southern part, there are fewer faults, smaller fault throw, and less developed transport systems. By comparing and analyzing the small normal faults in the passive continental margin basin of Guyana, South America, and their reservoir forming models, it can be inferred that there may be many "invisible" normal faults with small fault throw, large density and steep dip angle developed in the Cenozoic slope break area of the offshore Indus Basin. In addition, in the strike slip area of Murray Ridge in the west of the basin, the Mesozoic and Cenozoic fault transport systems are developed. The results of sea land correlation and offshore drilling core analysis show that there may be three sets of widely distributed source rocks in the Offshore Indus Basin, which are Cretaceous, Paleo-Eocene and Lower Miocene mudstones. According to comprehensive analysis, the formation of oil and gas reservoirs in the Offshore Indus Basin is mainly controlled by Mesozoic large fault transportation, Mesozoic-Cenozoic fault relay transportation, Cenozoic collapse fault transportation and "hidden" fault transportation. The types of oil and gas pools may mainly include Mesozoic "self generated and self stored" or "side generated and side stored", Cenozoic "lower generated and upper stored" in the north and east of the basin, and "lower generated and upper stored" and "self generated and self stored" in the west of the basin.

How to cite: Jianming, G., Jing, L., Baohua, L., Jie, L., Jianwen, C., and Sen, L.: Fault Transportation and Hydrocarbon Accumulation in Offshore Indus Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1937, https://doi.org/10.5194/egusphere-egu23-1937, 2023.

Atlantic Canada and its conjugate margins, the Irish, Iberian, and Moroccan margins, were subject to rifting and eventual breakup during the Mesozoic, following prior Appalachian Orogenesis from the early to mid-Paleozoic. The complexities of that older orogenesis, involving accretion and collision of Laurentian and peri-Gondwanan terranes during the closing of the Iapetus Ocean, contributed to the heterogeneous pre-rift template of the modern southern North Atlantic Ocean and the timing and extent of subsequent rift-related deformation.

In this work, we present newly-derived offshore and onshore present-day crustal thickness estimates of Atlantic Canada that are calculated using constrained 3-D gravity inversion and later reconstructed back to the onset of rifting and beyond, using GPlates and pyGPlates. In addition, deformable plate reconstructions are also used to reconstruct present-day magnetic anomalies, both onshore and offshore, back through time to track Appalachian orogenic trends beyond what can be deduced from geological field mapping alone. With the pre-rift template of the southern North Atlantic Ocean restored, we then attempt to extend these reconstructions further back in time to the Paleozoic to investigate strain localization within and between Appalachian terranes. Our results clearly reveal the fundamental influence of orogenic inheritance on subsequent rift events and the present-day variations in the crustal architecture that are observed along rifted margins. This study also provides the first quantitative assessment of Atlantic Canada’s crustal evolution from a compressive regime, to an extensional regime, to passive margin development.

How to cite: King, M., Welford, J. K., and Waldron, J.: Deformable plate reconstructions of Atlantic Canada and its conjugates back to the Paleozoic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2710, https://doi.org/10.5194/egusphere-egu23-2710, 2023.

Topographic spectra of abyssal hills from fast-spreading mid-ocean ridges have concentrations of power at Milankovitch frequencies and, in particular, around 1/(41 ka) [1].  This frequency corresponds to variations in Earth’s obliquity and is prominent in many climate records, including Pleistocene sea-level variations. Sea-level variations are understood to induce variations in magma supply to the ridge axis [2]. How might these magma-supply variations pace the faulting that creates abyssal hills?  We hypothesise that magma-supply variations introduce a perturbation to elastic plate thickness that is correlated with crustal thickness [3]. Building on Roger Buck’s theory for plate unbending and faulting at fast-spreading ridges [4], we show how thickness perturbations lead to concentrations in bending stresses in thinner parts of the plate.  These concentrations can be significant relative to background unbending stresses and may therefore pace faulting, depending on their amplitude and wavelength.  Using perturbation analysis and numerical solutions of Euler-Bernoulli beam theory, we develop predictions for fault spacing as a function of spreading rate, amplitude of magma supply variations, and other physical parameters.

[1] Huybers, Peter, et al. "Influence of late Pleistocene sea-level variations on mid-ocean ridge spacing in faulting simulations and a global analysis of bathymetry." PNAS https://doi.org/10.1073/pnas.2204761119 

[2] Cerpa, Nestor G., David W. Rees Jones, and Richard F. Katz. "Consequences of glacial cycles for magmatism and carbon transport at mid-ocean ridges." EPSL https://doi.org/10.1016/j.epsl.2019.115845 

[3] Boulahanis, Bridgit, et al. "Do sea level variations influence mid-ocean ridge magma supply? A test using crustal thickness and bathymetry data from the East Pacific Rise." EPSL https://doi.org/10.1016/j.epsl.2020.116121 

[4] Buck, W. Roger. "Accretional curvature of lithosphere at magmatic spreading centers and the flexural support of axial highs." JGR https://doi.org/10.1029/2000JB900360 

How to cite: Katz, R. F. and Huybers, P.: Unbending connects sea level to faulting at fast-spreading mid-ocean ridges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2721, https://doi.org/10.5194/egusphere-egu23-2721, 2023.