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.

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.

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.

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 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 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.

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.

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.

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.

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.