In the southern margin of the Alboran Sea, several submarine landslides (ranging from 0.01 to 15 km³ in volume) are preserved within the sedimentary (contouritic) cover of the past million years. Historical earthquake records indicate that regional seismicity is predominantly associated with strike-slip faults, which exhibit minimal or no vertical displacement, thereby limiting the potential for significant tsunami generation. Consequently, submarine landslides emerge as the primary candidates for tsunami triggering in the area. To better understand the occurrence of submarine landslides and their associated risks in the Alboran Sea, three French research projects were conducted: (i) the ANR Albamar project (2018-2023), (ii) the CNRS-IRD Alarm project (2018-2021) and the (iii) French fleet cruise Albacore (2021, https://doi.org/10.17600/18001351). The purpose of this communication is twofold: (i) to present the major findings of these projects and (ii) to analyze the causal factors of a selected landslide event.

The spatial distribution of submarine landslides does not appear to be directly linked to the active Al Idrissi Fault System (AIFS), which has been responsible for three moderate earthquakes (6.0 < Mw < 6.4) over the past 30 years. Instead, the head scarps of landslides exhibiting seafloor expressions, located west of the AIFS, coincide with the edges of the thickest contourite drifts in this margin. This observation suggests that landslide initiation may be related to localized high sedimentation rates, which potentially induce elevated pore water pressures at the drift edges, driving upward fluid flow. Furthermore, the edges of these contourite drifts are intersected by blind thrust faults, which were initiated during the Tortonian due to Eurasian-African plate convergence. Evidence of recent activity along these faults implies that tectonic processes could also facilitate fluid migration. These combined mechanisms—sedimentation-driven fluid overpressure and tectonically induced fluid flow—likely act to reduce effective stresses along the contourite edges, thereby preconditioning the slopes to a metastable state. Although the spatial separation between the investigated landslides and the AIFS does not provide direct evidence for earthquake-triggered failures, the possibility of long-distance earthquake effects on fluid-influenced metastable slopes remains an open question. This is further supported by the presence of pockmarks, which indicate fluid expulsion in the region. The integration of sediment core data, including age dating of recent landslides, with in situ geotechnical measurements collected during the Albacore cruise, has significantly improved our understanding of the timing and mechanisms of landslide events. For the most recent landslides, which are dispersed across tens of kilometers, sediment drape analyses suggest ages ranging from 5 to 6 kyr. This likely points to a period of increased landslide activity during that time.

How to cite: Lafuerza, S., d'Acremont, E., Emmanuel, L., Rabaute, A., Vidil, L., and Leroy, S. and the Albacore Team: Submarine landslides in the southern margin of the Alboran Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14810, https://doi.org/10.5194/egusphere-egu25-14810, 2025.

Submarine landslides are hazardous events capable of triggering deadly tsunamis and destroying costly seafloor infrastructure worldwide. Accurate landslide dating provides insights into their origins, recurrence patterns, and potential links to climate change. However, a comprehensive record of well-dated submarine landslides is currently lacking, limiting our ability to analyze past slope failures and quantify future risks.

This study investigates the morphology and timing of Tuaheni North, a significant landslide within the Tuaheni Landslide Complex on New Zealand's Hikurangi Margin. We provide insights into the timing and style of Tuaheni North’s slope failures, which may help identify their causes and recurrence patterns. Our analysis reveals a clear correlation between two major source volumes from Tuaheni North and corresponding downslope mass transport deposits (MTDs), indicating two distinct events. An intermediate layer separating the stacked MTDs suggests a significant time gap between the failures.

We introduce a novel method for dating submarine landslides that does not rely on sediment core analyses. Instead, we use seismic and bathymetry data to map bottom simulating reflections (BSRs) beneath the slide-impacted seafloor. BSRs are non-stratigraphic reflections marking the base of the temperature-sensitive gas hydrate stability zone. Submarine landslides disturb the sediment temperature field, and BSR depth serves as a proxy for dating these disturbances. Our findings suggest that Tuaheni North underwent several slope failures, displacing approximately 11.2 km³ of sediment. We estimate the ages of the two major slope failures at ~37 ka and ~23 ka, highlighting a substantial time gap between them.

New Zealand's Hikurangi Margin, known for its extensive gas hydrate and landslide activity, has over 2,200 recently identified slope failures. The 2-D age-dating method developed in this study can be applied to similar regions where gas hydrates and landslides coexist, both within New Zealand and globally. Additionally, we offer a publicly available interactive Windows application to facilitate similar studies.

How to cite: Portnov, A., Hillman, J., Watson, S., Cook, A., Laake, A., and Lobo, F.: Style and timing of the Tuaheni North landslide off the Hikurangi Margin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9031, https://doi.org/10.5194/egusphere-egu25-9031, 2025.

Continental margins sedimentary records reveal regional climate-ocean trends and identify mass transport deposits (MTD) and reflect the regional paleoclimate and paleoseismicity. This study used two radiocarbon-dated piston cores collected from the shelf edge (122 m) and mid-slope (588 m) offshore Israel at the southeastern Mediterranean Sea. CT scanning showed Holocene sediment evolution, capturing a shift in grain size and geochemistry, while detecting MTD units. The core from the shelf edge recorded the post glacial sea level flooding at 10-11 ka BP, with early Holocene sediments marked by coarser grains, high biogenic material, and abundant foraminifera. Sapropel S1, dated to 6-9 ka BP, is characterized by low Ti/Al, high Si/Al, and high TOC, reflecting increased Nile discharge and precipitation in the source region.

Benthic foraminifera disappearance in the slope core indicated bottom water anoxia, interrupted by re-oxygenation linked to the ~8.2 ka BP cold event. Toward the mid-Holocene, increased Ti/Al and Fe ratios indicate higher weathering rates in the Nile watershed due to reduced rainfall and vegetation, correlating with regional aridification caused by orbital changes.

Four MTD units with higher bulk density and reduced porosity were accompanied with higher Ca/Fe ratios. Radiocarbon dates within these units indicated the deposition of recycled older sediments from the early Holocene, while the mass transport events occurred between 6.2 and 1.8 Ka BP. Distinct changes are also observed in the benthic foraminifera taxonomy in association with the MTD including the total number of individuals per gram dry sediment (BF/g), species richness, dominance, and species composition. Furthermore, within all the MTD units a noticeable increase in broken BF shells and older radiocarbon ages, which indicate on recycled sediment turbulent mass transport.

How to cite: Bookman, R., Harmon, Y., Makovsky, Y., Kanari, M., Boaretto, E., Garrett, E., and Avnaim-Katav, S.: Continental slope processes reflected in a Holocene multi-proxy record at the southeastern Mediterranean , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16394, https://doi.org/10.5194/egusphere-egu25-16394, 2025.

Marine geophysical surveys provide crucial data and information for monitoring purposes and engineering application support on coastal and marine environments. Habitats associated to these specific natural contexts represent highly sensitive ecosystems that have been constantly threatened by human activities over the past few decades. Indeed, as stated by the European Commission, the 79% of the European coastal seabed is disturbed due to bottom trawling. Moreover, due to the ever-increasing demand of food and resources from the sea, issues as pollution, biodiversity loss, seabed damage, the spread of non-indigenous species, and similar phenomena are ever more serious. For this reason, the Marine Strategy Framework Directive (MSFD) were defined in 2008 by the European Commission to protect and keep safe its coasts, seas, and the ocean, ensuring their sustainable use. To this aim, marine geophysical techniques provide valuable tools for the assessment of biocenosis health status and distribution on a large scale. On the other hand, also engineering and industrial applications, such as offshore renewable energy production, onshore facilities, pipe installations or harbour maintenance, require high-resolution bathymetrical and sea-floor data for safe and sustainable operations, only obtainable with geophysical surveys.

Concerning the nearshore environment investigation, standard marine survey techniques used so far consist of methodologies exploiting the propagation of acoustic waves in the water column, i.e., Side Scan Sonar (SSS), Single and Multi-beam Echo Sounder (SBES/MBES) and Sub-bottom Profiler (SBP). Moreover, camera acquisitions and sub-marine stereo-photogrammetry are increasingly used for the analysis of seafloor morphology, although limited to optimal water conditions. Recently, thanks to the AI techniques improvements, Machine Learning (ML) techniques, coupled with GIS software, represent valuable tools for interpreting and mapping sub-merged morphological features on geophysical data using a multidisciplinary approach.

In this context, our research proposes a Computer Vision implementation using Convolutional Neural Networks (CNNs) for the detection and classification of marine morphological features in nearshore sectors of the Italian coastal environment.  Two different CNNs algorithms were used for the automatic segmentation and classification considering one considering the most marine morphological features of the study area and recognizable on SSS orthomosaics. The latter were acquired in two coastal sites of the Apulia Region (Southern Italy): Torre Guaceto Beach (Brindisi), on the Adriatic coast, and Leporano beach (Taranto) on the Ionian seaside. The first CNN algorithm is U-Net while the second one is a Mask-RCNN-based algorithm, already used in previous works to detect Beah Litter items on the emerged section of a beach. The training datasets were suitably processed to make them available for both algorithms, which process data in a slightly different way. Moreover, the training dataset based on the nearshore environment of the Apulian coastal sector will make it possible to map seabeds with similar morphological characteristics. This multidisciplinary approach represents an early stage of a first and promising integration tool to the classical manual image screening of marine seafloor morphology on a large homogeneous seabed, characterizing most of the Mediterranean coasts. Further development will concern additional geophysical surveys that will increase the dataset for a higher detection accuracy.

How to cite: Sozio, A., Scardino, G., Parisi, F., Pirulli, G., Fiscarelli, A., Barracane, G., and Scicchitano, G.: Machine Learning techniques for the detection of geomorphological features in nearshore environments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8547, https://doi.org/10.5194/egusphere-egu25-8547, 2025.

The CORSUB project aims to explore and investigate unidentified morphological features located between 75 and 100 meters depth off the Punta Licosa Promontory (Tyrrhenian Sea, Campania, Italy), on submerged terraces. These features were firstly observed during a survey in 2004,where a biogenic origin was hypothesized, but no further research had been conducted. The CORSUB project adopts an interdisciplinary, integrated approach that combines geophysical, stratigraphical, sedimentological and palaeontological analyses to investigate the formation, evolution, and ecological significance of these submerged morphologies.

As part of the “TREMOR” oceanographic cruise, organized by the Italian National Research Council (CNR) aboard the CNR research vessel Gaia Blu in December 2024, the CORSUB team collected high-resolution multibeam bathymetry data, chirp profiles, and box-corer sediment samples (n=4) from the project areas.

The preliminary results indicate that the anomalous morphologies are located between 75 and 85 meters depth and consist of clusters of subcircular features, with sub-metric diameters. Interestingly, the edge is sunken, while the central area is gently raised. Chirp profiles revealed that the sedimentary cover over these features is relatively thin, with a rocky substrate likely corresponding to the Cilento Flysch Unit identified beneath. 

Box-corer samples revealed a composition of coarse detrital sand and gravel at the top, predominantly biogenic in origin, transitioning to muddy-sandy sediment at the base. Notably, all samples contained dead, centimeter-sized boxwork rhodoliths, ranging from 8 to 20 cm above the top of the box-corer. Live rhodoliths were found in only one sample, and these showed clear evidence of ongoing mudding.

These preliminary findings suggest several potential interpretations. The observed structures may have a biogenic origin, possibly linked to the development of rhodolith beds in the past. Alternatively, their location on the flanks of the submerged terraces may indicate a strong correlation with glacial and post-glacial sea-level changes. The morphologies could have originated as erosional features during the Last Glacial Maximum, when sea levels were as much as 120 meters lower than today, subsequently providing a substrate for biological colonization as sea levels rose during the deglaciation and into the Holocene.

The ongoing analyses of both remote sensing data and collected samples, which also include dating, will allow for a more accurate determination of the nature and evolutionary history of these structures.

CORSUB is funded as part of the PRIN 2022 program under Mission 4 of the Italian Piano Nazionale di Ripresa e Resilienza (PNRR). Principal Investigator: Professor Valentina Alice Bracchi. A special thank to the scientific crew of the TREMOR survey.

How to cite: Bazzicalupo, P., Tonielli, R., Grande, V., Innangi, S., Basso, D., Felsani, M., Vernazzani, D., Gherardi, S., Di Martino, G., Cuffaro, M., Sacchi, M., Aiello, G., and Bracchi, V. A.: Anomalous Seafloor Morphologies: Insights from the CORSUB Project (Tyrrhenian Sea, Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18832, https://doi.org/10.5194/egusphere-egu25-18832, 2025.

The bending of a subducting plate leads to extension in its upper crust through faulting. The geometry of these faults represents the convergence orientation (i.e., normal or oblique). The Eratosthenes Seamount (ESM) in the eastern Mediterranean is a natural laboratory for unraveling the tension of a subducting plate. While most of the basin is covered by extensive sedimentation that obscures the faulting pattern, ESM stands out above its surrounding relief and provides a window into the faulting pattern close to the subduction trench of the Cyprus Arc. Previous studies provided reliable sedimentologic, structural, and tectonic constraints for ESM development and incipient collision with the Cyprus arc. However, the lack of high-resolution bathymetric data prevented its quantitative geomorphological analysis. The present study analyses the bathymetry of ESM and its surrounding trench and encircling cliffs through geomorphological and statistical methods. Results show that fault orientations and extensional nature confirm previous indications of tension across the bending plate. Nonetheless, it challenges the claim for incipient collision. The pattern and distribution of slope channels and slides attest to ongoing directional instability despite the lack of an immediate sediment source. Combined analysis of the seamount and cliffs indicates an overall northward tilt that developed since the early Pliocene.

How to cite: Nelaev, A., Freiman, S., Lazar, M., and Schattner, U.: Using quantitative seafloor geomorphology to unravel the deformation of Eratosthenes Seamount at the verge of subduction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4558, https://doi.org/10.5194/egusphere-egu25-4558, 2025.

The Cotentin Peninsula (CP), located in north-western France, represents the northern extension of the North Armorican Domain (NAD), which forms a structural rim in the central Channel. The NAD, including the Cotentin and the Channel Islands, has been shaped by major geodynamic processes such as the Icartian (~2 Ga), Cadomian (~580 Ma), and Hercynian (~300 Ma) orogenies. Subsequently, the development of Meso-Cenozoic sedimentary basins, although modest in extent and thickness, further influenced the area. The NAD, in particular, experienced differential evolution due to extensive Meso-Cenozoic sedimentation, and successive Cenozoic tectonic inversions associated with the Alpine orogeny. The area is also characterized by the evolution of the Channel River and its associated troughs.

The English Channel reflects complex interactions between tectonics and surface processes. Moderate and diffuse seismic activity, including historical earthquakes near Jersey, highlights the region’s ongoing deformation (e.g. Beucler et al., 2021). The strongest tidal currents in Europe takes place in the Alderney Race, between Alderney and the CP. They greatly participate in shaping the morphology of the submarine floor (Furgerot et al., 2019).

While onshore fault-controlled Meso-Cenozoic sedimentary basins are well-studied, their offshore counterparts remain less understood, despite geological mapping efforts in the 1970’s. Recent high-resolution multibeam bathymetric data and seismic reflection surveys (EMECHAT1 in 2022 and EMECHAT2 in 2024) have provided new insights into the submarine structural framework, especially around the Cap de la Hague and in the central English Channel. These studies have identified major faults, including the La Hague Offshore Fault (LHOF) and the La Hague Deep Faults (LHDF1 and LHDF2), and refined the location of sedimentary basins (Kaci et al, 2024).

The seismic profiles offer crucial information about the geometry of geological layers, seismic facies, and apparent thickness, as well as fault characteristics such as alignment, dip, and displacement. These data also reveal the interactions between tectonics and sedimentation in the central Channel, highlighting the evolution of the Channel River system. Additionally, the 51 rock cores collected during EMECHAT2 will establish a stratigraphic framework for dating seabed units and understanding associated geological events.

The project aims to explain the differential post-Hercynian evolution of the northern and southern compartments by producing a marine geological map off the north-western Cotentin, extending onshore data, and analyzing the interactions between faults, sedimentary basins, and troughs (especially the Hurd Deep and the La Hague Trough). A final goal is to pinpoint ongoing deformation to confirm or refute the presence of active faults in this area and to correlate them with historical and instrumental seismic activity.

This work, part of a thesis on Channel troughs funded by UBO and ASNR (ex IRSN), contributes to understanding the geomorphological and tectonic dynamics at the land-sea interface in this key region.

How to cite: Thomas, J., Graindorge, D., Duperret, A., and Baize, S.: Geomorphological and Tectonic Evolution of the central English Channel: Insights from High-Resolution Marine Geophysical Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6982, https://doi.org/10.5194/egusphere-egu25-6982, 2025.

The Axial Channel is a prominent geomorphological feature seen on the present-day bathymetry of the southern North Sea. The 150 km long depression extends from the Norfolk Banks in the north to the Dover Strait in the south. It is believed to be a remnant of a large and complex drainage system that existed during the late Pleistocene, when ice sheets occupied parts of the North Sea region during three major glaciations: the Elsterian/Anglian (MIS12), Saalian/Wolstonian (MIS10-6) and Weichselian/Devensian (MIS5d-2) glaciations. The existence of these ice sheets was accompanied by a large fall in global sea level, causing the southern North Sea region to emerge and become isolated from the Atlantic. As a northern drainage route was blocked by coalescing ice sheets during their maximum expansion, glacial meltwater but also river water from the major West-European rivers (e.g. Scheldt, Meuse-Rhine, Elbe) followed a southern drainage route towards the Dover Strait. Understanding the evolution of the present-day Axial Channel is crucial to understanding the paleogeographic changes that affected the region over the course of multiple glacial-interglacial cycles.

A first step in understanding this evolution was performed by analysing the present-day bathymetry of this region and mapping the preserved geomorphological features. Available offshore bathymetry data were compiled in the region from 53° to 51° latitude North. This included the EMODnet Digital Bathymetry (DTM) map, at 20 m resolution, supplemented by high-resolution (up to 1 m resolution) bathymetry blocks from the UK Admirality Seabed Mapping Service (UK Hydrographic Office data ©Crown copyright and database right), covering most of the eastern part of the study area. Furthermore, in the framework of the WALDO project, seismic reflection data, including multi-channel sparker and high-resolution parametric sub-bottom profiler (TOPAS) data, have been gathered in the Axial Channel region.

Our bathymetric mapping revealed numerous geomorphological features on the plateau in the western part of the Axial Channel region. Our preliminary interpretation suggests a glacial origin for some features, such as the observed elongated deeps and north-south oriented scours. Furthermore, multiple palaeovalley systems, including a major west-east system, on this same plateau are witnesses of dry, not fully marine inundated periods in the southern North Sea. Our mapping further revealed multiple incisional phases shaping the present-day Axial Channel, including a distinct western escarpment, i.e. the eastern edge of the plateau. The seismic-reflection data were gathered to further investigate the incisional and infilling stages. It revealed additional incisional phases that could not be observed from bathymetric data alone. Furthermore, the reflection data allowed several infilling stages to be discerned in the northern part of the Axial Channel region, while no infilling sediments could be identified towards the south. This study illustrates the importance of combining bathymetric and seismic data to understand the evolution of large geomorphological features such as the Axial Channel.

How to cite: Vervoort, M., Kyriakoudi, D., Plets, R., Mestdagh, T., Missiaen, T., and De Batist, M.: The geomorphology of the Axial Channel, southern North Sea: a complex glacio-fluvial and marine story, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10243, https://doi.org/10.5194/egusphere-egu25-10243, 2025.

The southern North Sea region has been profoundly impacted by dynamic climatic fluctuations during the Quaternary. Global sea levels varied significantly during the Last Glacial Cycle (115-11.7 ka BP), globally dropping by ∼130 m below present levels at the Last Glacial Maximum (ca. 26 to 19 ka BP). These environmental shifts resulted in diverse glacial and post-glacial depositional environments, the remnants of which are now sparsely and patchily preserved offshore. This study specifically examines the Late Pleistocene and Holocene depositional systems southeast of Dogger Bank and Oyster Ground to unravel their intricate sedimentary and geomorphological evolution.

To achieve this, we integrated high-resolution 2D acoustic reflection data, acquired through the WALDO project surveys between 2022 and 2023 with extant lower-resolution petroleum exploration 3D seismic data. This multi-scale dataset enabled the detailed mapping of the primary stratigraphic units and key geomorphological features preserved in the region. The regional stratigraphy is dominated by glacial-age sequences and numerous buried valley-like incisions that erode the older stratigraphic units. The incisions are highly complex, showing significant variations in dimensions and orientation, and multiple infill phases. Cutting from levels around 35-50 m below MSL down to 90 m below MSL, the incisions illustrate diverse morphologies, including straight, meandering and braided patterns. They reflect shifts in hydrodynamic conditions, sediment transport pathways, and the interaction between glacial, fluvial, and marine processes. Even though previous studies in adjacent areas identified similar features, our data reveal unrecognised complexity in channel morphologies and infill, offering new insights into the glacial and post-glacial processes.

Our findings illustrate that the region experienced a multi-stage geological evolution since the last glaciation. Although the erosional and depositional processes that shape such features are crucial for paleolandscape reconstruction, they are often challenging to identify. A preliminary interpretation suggests their genesis may have resulted from glacial processes (e.g. subglacial or proglacial meltwater channels), with later modification by fluvial activity after deglaciation. These findings underscore the interplay between ice sheet dynamics, sea-level oscillations, and climatic variability in shaping the region during the last glacial period and Holocene. Integrating 2D and 3D datasets has proven invaluable for accurately mapping these depositional systems, offering a more detailed paleolandscape reconstruction.

How to cite: Kyriakoudi, D., Vervoort, M., Plets, R., Mestdagh, T., Missiaen, T., and De Batist, M.: Buried Late Pleistocene and Holocene channel systems in the southern North Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9756, https://doi.org/10.5194/egusphere-egu25-9756, 2025.

The Amazon River culminates in one a deep-sea fan up to 10 km thick, a dynamic setting in which the rapid deposition of organic-rich sediment drives linked processes of methanogenesis, fluid migration and venting, gas hydrate formation, and large-scale slope instability. Growth of the fan over the last 8 Ma has been accompanied by its gravitational collapse on shale detachments to form extensional and compressional belts across the shelf and upper slope (<2250 m water depth), and by recurrent slope failure to form fan-wide megaslides. The upper slope compressional belt contains a ‘leaky’ gas hydrate system characterised by elongate bottom-simulating reflection (BSR) patches that are aligned with the crests of thrust-fold anticlines, and in places rise towards sub-circular seafloor fluid vents. Ongoing fluid venting from the fan is indicated by sea surface oil slicks reported on the shelf and upper slope, and water column gas flares observed on multibeam imagery obtained in 2016 across part of the thrust-fold belt. The extent of degassing across the vast fan area in water depths of 2500-4500 m is unknown due to a lack of water column data below the compressional front. The 2023 AMARYLLIS-AMAGAS I campaign acquired acoustic data (multibeam imagery, Chirp profiles) along multiple transects of the fan in water depths of 100-4200 m, and cores and heat flow data from sites in the thrust-fold belt. Here we present information on fluid expulsion from the Amazon fan based on seafloor data both from the campaign, and 3D seismic datasets on the upper slope (ANP Brazil). Multibeam imagery reveal hundreds of water column gas flares in water depths of 100-1900 m, with a peak in abundance near the upper limit of the MHSZ (565 ± 65 m water depth). Gas is observed to rise from areas of smooth seafloor in places, but mainly from sub-circular mounds and depressions. Bathymetric grids from multibeam and 3D seismic (4-50 m resolution) were used to capture sub-circular seafloor morphologies for morphometric analysis using a semi-automated training approach. Over 500 features were identified in water depths of 275-2265 m, identified as domes (59%), complex forms (28%) and depressions (13%); the vast majority (>96%) are <50 m in relief (mean 16 m) and <1 km wide (mean 500 m). Cores of alternating lighter hemipelagic and darker muds interpreted as mud extrusion were recovered both from domes and depressions; gas hydrates were cored in several domes with gas flares. Subbottom data reveal chaotic facies defining structures deeply-rooted in thrust-folds. We interpret the seafloor features as differing expressions of relatively small-scale mud volcanism, many actively venting gas. Our results indicate widespread fluid expulsion from the Amazon fan within the extensional and compressional belts, and a lack of evidence for venting in greater water depths. The primary control on degassing of the fan appears to be gravity tectonism, which provides pathways for fluid escape within and above the MHSZ. This is a contribution to studies of gas hydrate dynamics and slope stability in the context of the MEGA project (ANR-22-CE01-0031).

How to cite: Praeg, D., Migeon, S., Guizan Silva, C., dos Reis, T., Augustin, A., Trevisan, J., Dano, A., Gay, A., Ketzer, M., Palhano, P., Pivel, M., Poort, J., Stranne, C., and Unnithan, V.:  Seafloor evidence of structurally-controlled fluid expulsion from the upper Amazon deep-sea , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19454, https://doi.org/10.5194/egusphere-egu25-19454, 2025.

The expulsion of gas-rich fluids from submarine sedimentary accumulations may result in the formation of seafloor depressions, or pockmarks, of metric to kilometric size. Methane flux drives biogeochemical processes favouring the precipitation of authigenic carbonates, which over time can form seafloor pavements of high acoustic reflectivity. In deep waters, it has been proposed that seafloor morphology may be influenced by gas hydrate formation and dissolution to form depressions of complex internal relief, referred to as ‘gas hydrate pockmarks’. In contrast, seafloor vents of positive relief are typically assumed to record sediment expulsion as mud volcanoes. The central province of the Nile fan, which contains evidence of a gas hydrate system, provides an interesting setting to study the morphology of seafloor fluid vents : in addition to a dozen mud volcanoes (kilometric widths), it contains hundreds of smaller (decametric widths) sub-circular high-backscatter features that have been shown to correspond to fractured carbonate pavements. Originally referred to as pockmarks, many of these features have been found to be of metric-scale positive relief. Here we present a morphometric analysis of pockmark-like features across the central Nile fan using available multibeam sonar and 3D seismic seafloor datasets. Seafloor morphologies were captured for analysis using a semi-automated training approach adapted to data types : multibeam data (20-25 m grids of bathymetry and backscatter) were used to capture high backscatter patches across an 1135 km² area of the mid- to lower slope (water depths 1525-2395 m); 3D seismic seafloor data (8 m grid) were used to capture sub-circular features (of +ve or -ve relief) across a 3275 km² area of the upper slope (water depths 137-1655 m). Water column data indicate the upper limit of the methane hydrate stability zone (MHSZ) to lie in depths of 1230 ± 25 m. We identify a total of 1309 pockmark-like features in water depths of 189-2382 m, comprising three main morphotypes : negative relief (depressions, 70%), mixed relief (complex or flat, 18%) and positive relief (domes, 12%). Their depth distribution shows a striking relationship with the MHSZ limit : of 971 features above the MHSZ, almost all (93%) are depressions, with widths of 58-408 m and depths up to 20 m; in contrast, of 338 features within the MHSZ, almost all are of positive or mixed relief (43% and 50% respectively), with widths of 54-790 m and relief up to 20 m, while only 7% are depressions. We suggest pockmark-like features within the MHSZ to be carbonate pavements formed above gas hydrate pockmarks, their domal or mixed relief and fractured character reflecting the evolution of near-surface gas hydrate lenses. Depressions above the MHSZ are pockmarks uninfluenced by gas hydrate dynamics. Interestingly, almost all features within the MHSZ lie outwith an area of bottom simulating reflection (BSR) patches indicating the presence of gas and/or gas hydrates at depth. Our findings suggest a key role of gas hydrate dynamics on the morphology of deep-water fluid vents. This study is a contribution of the MEGA project (ANR-22-CE01-0031).

How to cite: Migeon, S., Praeg, D., Trevisan, J., Dano, A., Ketzer, M., and Römer, M.: Morphology of pockmark-like features relative to the methane hydrate stability zone on the central Nile deep-sea fan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11655, https://doi.org/10.5194/egusphere-egu25-11655, 2025.

The Neogene evolution of the Pelotas Basin, located off the southern coast of Brazil and Uruguay, presents an intriguing case of high terrigenous sedimentation in an area without major river systems. This unusual sedimentation is exemplified by the Rio Grande Cone, one of the largest submarine fan-like feature on Earth. While most continental margins with high terrigenous input are associated with large deltas and rivers, the Pelotas Basin defies this pattern, making its sedimentary pathways enigmatic. To understand the region’s sedimentary history, we analyze 13 exploratory wells and 700 seismic lines to perform seismic-stratigraphic and clinoform analysis. Our findings reveal three distinct depositional environments: (1) on the shelf, upper Miocene to Pliocene fluvial channels delivered sand onto a mud-dominated shelf; (2) on the slope, sediment instability led to structural deformation and several phases of mass transport deposition; (3) on the slope and abyssal plain, large contourite drifts formed due to the reworking of sediments by bottom currents. Clinoform analysis shows that deltaic environments existed on the inner platform during the Neogene, with three separate shelf-slope sedimentary pathways. However, the limited extent of these incised valleys suggests that additional sedimentary pathways may have contributed to sediment transport into the basin. We propose that the desiccation of an epicontinental sea over the La Plata Basin during the Miocene played a key role in enabling the influx of large volumes of fine sediments into the region. The drying of this sea likely allowed for the transport of sediments via the La Plata plume, which carried sediment-laden water into the margin. Additionally, the intensification of ocean currents during the middle Miocene contributed to the formation of contourite drifts and submarine megaslides, such as the Rio Grande Cone. In summary, the Neogene evolution of the Pelotas Basin was driven by a combination of factors: anomalous fine sediment input, sea-level changes, slope instability, and the intensification of bottom currents. These processes led to the creation of submarine megaslides and widespread contourite drifts, providing new insights into the complex evolution of the SW Atlantic margin.

How to cite: Tagliaro, G., Britzke, A., Campeche Gama, M., Bonifatto, G., Bauli, P., Negrão, A., and Jovane, L.: Neogene evolution of the margin adjacent to the La Plata River Delta: Sedimentary pathways, clinoforms and the origins of the Rio Grande Cone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3319, https://doi.org/10.5194/egusphere-egu25-3319, 2025.

In the Krishna-Godavari (K-G) offshore basin, India, a 130 m thick fracture-filling and near-seafloor paleo-cold seep-related gas hydrate-bearing layer (GHBL) was encountered by drilling at Site NGHP-01-10 (Site 10) and nearby piston sampling of authigenic carbonates and shells. Our analyses of drilling cores and pore-water show that authigenic carbonates and shells are widely distributed within 200 mbsf at Site 10, with two separate intervals of high chloride concentrations up to 663 mM. This indicates that the GHBL is a young system of multistage formation related to periodically active cold seeps. This study combines core, well logging and seismic data to gain insight into the fine characteristics and detailed formation process of such a thick system. Seismic imaging of new chimney-like structures, growth faults and multiple stacked mass transport deposits (MTDs) illustrates that the system is located in the chaotic reflection strata. Synthetic seismogram shows that multiple MTDs repeatedly control the paleo-cold seeps and further influence the hydrae system. Based on a buried vent with a high amplitude reflection consistent with seafloor polarity, and its high density and high velocity similar to authigenic carbonates, a new and larger paleo-cold seep-related hydrate system is defined to the southeast of Site 10. These two thick systems probably formed in stages due to the clear stratifications on the seismic data, 2D anisotropic saturations and internal chimney-like structures. They are originated from diapirism and growth faulting, and their lateral extent depends on the fracture zone width of the anticline ridge. After formation, they are then buried by multiple MTDs and have already been upshifted by sedimentation. Although the cold seep near Site 10 is not active and the hydrate system is currently only in the chloride diffusion stage, the underlying gas accumulation means that new hydrate systems and cold seeps may form in the future. Our results suggest that the processes of formation, sedimentation, upward shift and diffusion of hydrate systems have been circulating near Site 10, which could better interpret the formation and dynamic evolution of the multilayered or thick GHBL found at drill sites around the world.

How to cite: Qian, J.: Characteristics of periodically active cold seep-related gas hydrate systems in the Krishna-Godavari offshore basin, India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5721, https://doi.org/10.5194/egusphere-egu25-5721, 2025.

Geochemical and oceanographic studies using in-situ measurements have long established the presence of groundwater flow to the seafloor, which likely originates in the deeper sub-bottom. This raises the question: What is the impact of such a flow on the sediment stratigraphy as imaged by high-resolution seismic data? In this study from the Gulf of St. Lawrence (Atlantic Canada), high-resolution seismic data indicate the presence of localized dome-shaped, semi-transparent features (50-200 m-wide, <15 m-long) that do not extend to the seafloor. In proximity to these structures, low-salinity pore water has been extracted from a 3-m-long gravity core. A pore water transport model constrained using geophysical and geochemical data indicates a potential freshwater source at 60-80 m depth, but also suggests freshwater advection from a depth of 30 m sub-bottom depth, which is where the seismic structures are visible. We, therefore, interpret the dome-shaped features as a consequence of sediment deformation caused by groundwater fluid flow. In this regard, the dome-shaped features resemble fluid plumes observed in seismic reflection profiles elsewhere, but here they are often of large dimensions (1 km-wide), extend through the sediment package to the seafloor and are often related to gas. Furthermore, similar features in sub-bottom profiles often appear to be neglected in descriptions and interpreted as artefacts. Given that the dome-shaped features are only present in specific parts of the basin where the advection is supposed to be strongest, we argue that similar features observed elsewhere are possibly not artifacts and should be considered as deformational features related to fluid flow and potentially even offshore freshened groundwater. Easy access to freshwater resources becomes increasingly challenging nowadays in many parts of the world, particularly in coastal regions. It is therefore important to have additional indicators that can help detecting the presence of offshore freshened groundwater and especially locations with active advection, which can then be sampled in more detail.

How to cite: Schulten, I., Maselli, V., Hensen, C., King, E., Schmidt, M., Müller, T. H., Micallef, A., Berndt, C., Brown, C. J., Cordoba-Ramirez, F., Elger, J., Hölz, S., Kotliarov, A., Kurylyk, B., Michael, H., Robert, K., Yu, S., and Nedimovic, M.: Can offshore groundwater flow within shelf sediments generate fluid deformation structures?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12205, https://doi.org/10.5194/egusphere-egu25-12205, 2025.

We present findings from the first academic high-resolution, high-density (3.125x6.25 m line spacing) conventional 3D seismic reflection data (550 km²) acquired on the shallow New Jersey continental shelf. This dataset enables us to identify and describe geomorphological evidence of coastal and marine processes during the Miocene. By combining seismic geomorphological analysis (performed on 3D data in map view) with quantitative geometric analysis of clinoforms (performed on 2D seismic profiles), we examine the interplay between change in margin architecture and dominant processes during major climatic perturbations, including the Miocene Climate Optimum (MCO, 17 - 13.8 Ma), and subsequent global cooling during the Middle Miocene Climate Transition (MMCT, ca. 13.8-12.8 Ma).

Our analysis shows that during the pre-MCO, clinoforms exhibited moderate lateral shifts of rollover points basinward (up to ~7 km; up to 6 km/Myr) with mostly flat clinoform rollover trajectories. Sediment thicknesses were similar on clinoform topsets and bottomsets. During the MCO, clinoforms transitioned to high aggradation-to-progradation ratios with steep rollover trajectories. In stark contrast, the MMCT and post-MMCT intervals are marked by rapid dramatic progradation (up to 35 km in 0.4Myr) and flat to falling rollover trajectories. During the MMCT, sediments primarily bypassed the topset domain. Topsets of the post-MMCT interval are, however, thick and are associated with relatively small-scale, low-angle clinoforms that we interpret as subaerial delta fronts.

Surprisingly, we have not detected signs of subaerial exposure, such as incised valleys, fluvial or tidal channels, barrier islands and beaches, etc., during the pre-MCO, the MCO, and the MMCT intervals. The first signs of subaerial exposure appeared ~12 Ma, where we identified remnants of meander bends within a NNW-SSE-trending channel belt. This channel belt appears to be truncated by an overlying fluvial system trending NW-SE comprising relatively narrow (~20-120 m), up to ~10-12 m deep anastomosing, low-sinuosity channels. The NW-SE fluvial system also cuts through a series of >10 km-long, tens-of-meters-wide, closely spaced, parallel linear to arcuate, positive-relief features. We interpret these as beach ridges that formed on the regressive coast (as opposed to the Holocene transgressive New Jersey coast). Our seismic analysis suggests the Lower to Middle Miocene paleoshelf topsets remained submerged until at least the late Middle Miocene (ca. 12 Ma) following the MMCT and drop in global mean geocentric sea level, which resulted in major shifts in shelf processes and stratal architecture.

How to cite: Mukhatzhanov, A., Mountain, G., Miller, K., and Browning, J.: Miocene coastal and shelf processes inferred from the geomorphological analysis of 3D seismic reflection data offshore New Jersey, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13468, https://doi.org/10.5194/egusphere-egu25-13468, 2025.

Pockmarks, seafloor depressions, provide valuable insights into subsurface fluid migration and geological processes, representing a critical factor in seafloor morphological evolution. This study investigates the distribution and morphology of pockmarks in the Northwestern Sicily offshore (Sicily Straits) by integrating 2D seismic reflection profiles, multibeam bathymetric data, and advanced analytical techniques. Our primary aim is to discriminate actively degassing pockmarks and examine their spatial relationships with geological structures and stress-field-oriented tectonic features.

              While previous studies emphasized the role of subsurface fluid migration mechanisms, our findings highlight a significant correlation between pockmark locations and structural highs, with pockmarks clustering along the flanks of folds demarcated by fault zones. This spatial association suggests that structural elements act as primary conduits for fluid migration, focusing fluid escape at specific seafloor locations.

              To achieve these insights, we employed machine learning-based seismic attribute analysis and bathymetric processing. One toolchain automatically extracted seismic anomalies indicative of fluid pathways, such as bright spots, acoustic blanking zones, and gas chimneys. Another toolchain used morphometric wavelength analysis to classify and map pockmarks, enabling detailed morphological and spatial characterization.

              Our results reveal that while oceanographic processes such as the Adventure Bank Vortex play a role in shaping the morphology of elongated pockmarks, their spatial distribution is primarily influenced by structural controls. These findings refine the previous interpretations and provide a more nuanced understanding of the interplay between tectonic and oceanographic factors in shaping pockmark fields. This study underscores the importance of integrating structural, morphometric, and fluid-migration analyses to comprehensively assess pockmark dynamics and their implications for seabed evolution and geohazards.

How to cite: Srivastava, E., Caldareri, F., Maiorana, M., Parrino, N., Chinmoy Kumar, P., and Sulli, A.: Structural and Oceanographic Controls on Pockmark Distribution and Morphology in the Northwestern Sicily Offshore: Insights from Seismic and Machine Learning Approaches , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1055, https://doi.org/10.5194/egusphere-egu25-1055, 2025.

Seismic data around the crest of the Bonga North Field is only of questionable quality because of recent shale flows, uplift and faulting. A 3D seismic data was reprocessed to improve seismic resolution across the diapirs. A well in the field encountered several gas flows which were neither predicted nor fully understood. Better knowledge of potential fluid pathways in the shallow section at Bonga North field is therefore required to help de-risk future drilling operations. The information derived from the 3D high resolution seismic data, well logs and end of well reports were used for this project. The shallow faults and other potential fluid migration pathways in and around the crest of the structures were mapped to better predict and mitigate potential hazards above the reservoir section. Eight stratigraphic units were mapped and analyzed for potential geohazards. Semblance slices, seafloor topography maps, dip/traverse sections and sub-volume sculpturing were created to capture the study intervals and observe structural and amplitude variations. The results showed that the Bonga North Field is highly faulted with fault density increasing towards the crest of the shale-induced structure where the BN3 well is situated. Faults are partially sealing and extend to the seafloor. The seafloor and near-surface assessment revealed potential hazards, including pockmarks (fluid escape features), shale intrusions, gas chimneys and near-surface faulting. In the subsurface; faults, shallow water flow (SWF), expulsion chimneys and seismic amplitude anomalies which may be indicative of shallow gas-filled sands were identified as the main geohazards. The BN1 and BN2 wells were drilled without problems but the BN3 well is closest to all these hazards. It is therefore recommended that; (1) the drill centers be moved farther to the northwest where there is lower risk of encountering hazards, (2) a high resolution seabed survey be conducted, (3) a working gas sensor, ROV and camera monitor be incorporated into the well drilling operations, (4) a kill-weight mud be made available to ensure well control and prevent blow-out in future wells.

How to cite: Ejairu, K.: Analysis of fluid movement along faults and shale diapirs in deep water settings, Bonga North Field, OML-118, offshore, Niger Delta. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-66, https://doi.org/10.5194/egusphere-egu25-66, 2025.

This study focuses on the 3D seismic investigation of high-amplitude elliptical reflections (HAER) within Miocene stratigraphic interval, in Western Patras Gulf, in a sedimentary basin that is affected by salt tectonics.

Miocene basins across Western Greece have been attributed to the formation of foreland and piggy-back basins of a westward advancing fold-and-thrust belt. The base and top of the Miocene basin in the study area are marked by two regional unconformities. The lower unconformity has formed during Burdigalian, following uplift related to an early compressional phase. The upper unconformity is related to the sea-level fall during the Messinian Salinity Crisis (MSC). A salt diapiric wall of NW-SE orientation along the eastern side of the basin is interpreted of Triassic age. The different deformation style between the underlying Miocene and the overlying Pliocene – Quaternary strata indicates that the salt wall went through at least two stages of re-activation, one during late Miocene and another one during Pleistocene. Seismic stratigraphy and neighboring outcrop data onshore Kephalonia Island, reveal a basin infill ranging from fluvial to lagoonal and progradational deposits to more hemipelagic mud-dominated deposits towards the top.

HAER are structures of circular to elliptical shape, that appear as patches of high amplitude anomalies at the upper Miocene stratigraphic level. Due to their seismic signal, indicative of hard lithologies, they are interpreted as methane-derived authigenic carbonates (MDAC), precipitated on top of paleo-pockmarks. Our interpretation infers that those paleo-pockmarks develop through the gas escape along a fault network associated with a late Miocene diapiric re-activation.  The presence of those paleo-pockmarks, combined with the underlying Mesozoic sequence, raises two major questions: 1) the origin of the paleo-pockmarks is thermogenic or biogenic, and 2) is it possible for the Miocene subsidence to result in thermal maturation of Mesozoic source rocks in the area?

A preliminary thermal maturity modeling indicates that there is a late kick during Neogene, and thus, a thermogenic origin for the paleo-pockmarks seems reasonable. This is also supported by multiple present-day oil seeps and gas-escape structures along Western Greece. The absence of paleo-pockmarks within the Pliocene – Quaternary section is attributed to the extensive erosion during MSC and the reduction of Pliocene - Quaternary sedimentation rates.

How to cite: Stathopoulou, A., Papatheodorou, G., Tripsanas, E., Oikonomopoulos, I., Kokkalas, S., Geraga, M., and Stefatos, A.: Upper Miocene paleo-pockmarks and their correlation to methane-derived authigenic carbonates through 3D seismic data in External Western Patras Gulf, Greece, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16254, https://doi.org/10.5194/egusphere-egu25-16254, 2025.

Seabed fluid flows refer to the migration of gases and liquids through the seabed and seawater and is often associated with energy resources, benthic ecosystems, global climate and marine geohazards. Pockmarks are 'crater-like' depressions on the seafloor formed by fluid seepage. Two high-resolution marine remote sensing surveys (sub-bottom profiling, multi-beam bathymetry and side-scan sonar) have been conducted in the inner Thermaikos and central Patras Gulfs, each characterized by distinct geological settings. These new datasets have revealed acoustic anomalies indicative of gas-charged sediments and potential gas seepages.

The Thermaikos Gulf is in the northern part of the Aegean Sea, northeastern Greece. The Thermaikos Basin is part of the wider Axios basin, which extends from North Macedonia territory to the North Sporades Islands. It is characterized by extensive sedimentary deposits derived from major rivers, including Axios, Aliakmonas and Loudias and features moderate tectonic activity. Moreover, a gas field, the Epanomi Gas Field with gas and small quantities of light oil, have been discovered, onland, southeast of the Gulf. The Patras Gulf, a semi-closed basin situated in western Greece, lies within one of the most seismically active areas in the Mediterranean. It is controlled by extensive faults forming an asymmetric graben. An active and very well-documented pockmark field is located at the southeastern part of the Patras Gulf.

Seismic profiles acquired in the inner Thermaikos Gulf, have, for the first time, unveiled shallow zones of acoustic turbidity and enhanced reflectors in two distinct areas: near the city of Thessaloniki and in the western part of the inner gulf. Moreover, a pockmark and several intrasedimentary gas pockets were identified in the northern part and across extensive portions of the region, respectively. The dataset, obtained from the central Patras Gulf, revealed elongated seabed depressions exhibiting underlying columnar disturbances. These features were accompanied by gas flares detected in both seismic profiles and side-scan sonographs, indicative of gas emissions that appear to reach the sea-air interface. Furthermore, a new pockmark field was discovered at depths ranging from 70 to 90 meters, with no apparent association to the major faults of the Gulf. Ground-truthing surveys further documented the presence of bacterial mats and gas bubble emissions, reinforcing the evidence of active seepage activity.

Acknowledgments. The Thermaikos project is founded by the Athanasios C. Laskaridis Charitable Foundation.

How to cite: Giannopoulos, N., Papatheodorou, G., Christodoulou, D., Geraga, M., Dimas, X., Hubert-Ferrari, A., and Caterina, B.: Gas-charged sediments and seabed related features in Thermaikos and Patras Gulfs, Greece: New findings and preliminary results, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17204, https://doi.org/10.5194/egusphere-egu25-17204, 2025.