Multibeam Bathymetry Data Research Articles

McDonald Islands Phonolitic Lavas: Evidence for Zonation of the Kerguelen Plume

AbstractThe McDonald Islands, together with Heard Island and the Kerguelen Archipelago, are volcanic islands on the mostly submerged Kerguelen Plateau, and the products of the long‐lived Kerguelen mantle plume (at least 130 Myr; Coffin et al., 2002, https://doi.org/10.25919/jw5f‐ad35). The first multibeam bathymetry data acquired around the Heard and McDonald islands reveal > 70 sea knolls surrounding the McDonald Islands and three sea knolls north of Heard Island. Rocks dredged from McDonald Islands sea knolls include fresh vesicular phonolitic lavas, phonolitic obsidian, phonolitic pillow fragments, and one basanite. These are the first phonolites sampled from the seafloor on the Kerguelen Plateau. Dredging of one sea knoll north of Heard Island recovered basaltic lavas. Lavas from the sea knolls are young, returning 40Ar/39Ar plateau ages of 73.7 ± 15.1 ka to 7.0 ± 2.7 ka for McDonald Islands sea knoll phonolites and 9.0 ± 1.3 ka for the Heard Island sea knoll. We define a new magma series, the McDonald Series, characterized by low εHf (−3.9 to −4.4) and lower Δ207Pb/204Pb (4.5–4.8) and Δ208Pb/204Pb (79–85) than all other lavas on the Kerguelen Plateau. This newly defined series is the product of a relatively young (Pleistocene‐Holocene) phase of volcanism produced by a distinct component of the Kerguelen mantle plume. We propose that McDonald Series phonolites together with 53.4 Ma lavas previously dredged from Ninetyeast Ridge provide evidence for zonation of the Kerguelen mantle plume.

Architectural development of a land-attached carbonate platform in the African–Arabian Desert Belt: the late Pleistocene to Holocene evolution of the Al Wajh Platform, NE Red Sea, Saudi Arabia

ABSTRACT Carbonate platform architectures are indicators of environmental changes, such as sea level, climatic variations, and tectonic influence, which all control platform evolution. While analog studies on modern carbonate platforms have predominantly focused on tropical settings, limited attention has been given to arid and semiarid environments, although many ancient carbonate sequences were developed under these settings. This study aims to bridge this gap by investigating the Al Wajh carbonate platform lagoon in the NE Red Sea, Saudi Arabia, using geophysical and remote-sensing data to unravel its architecture and development since the last interglacial highstand (MIS 5e). We collected and analyzed sub-bottom profiles extending over 675 km and airborne lidar multibeam bathymetry data covering an area of 1700 km2. Surface sediment samples and vibracores with a maximum penetration of three meters were integrated to strengthen our interpretation. Furthermore, a recently published Red Sea sea-level curve was used to establish an age model and supplemented by available climate data to reconstruct depositional models. The Al Wajh lagoon is a “bucket” structure hosting five distinct depositional units since the late Pleistocene: U0 (pre-MIS 5e and MIS 5e), U1, U2, U3, and U4 (MIS 1), which are composed of five hydroacoustic facies, ranging from mounded to wavy laminated facies. Based on combining climate data, sea-level curves, and platform topography with our geophysical data, we conclude that the lagoon hosts carbonate, siliciclastic (fluvial and eolian), and potentially evaporitic deposits of open-marine and playa-lake origin. Intriguingly, karst architecture (i.e., sinkholes, caves, and collapsed cavities) is absent despite intermittent pluvial episodes and exposure during the late Pleistocene. Data analysis indicates that the Al Wajh lagoon architecture and development since the late Pleistocene are controlled by a combination of antecedent topography, sea-level variation, climate fluctuation, siliciclastic influx, carbonate production, and reef growth and drowning. Finally, insights from this study enhance our understanding of the architecture and sedimentary infill of ancient land-attached carbonate platforms deposited in a mature rift basin under alternating arid and pluvial climate settings.

Morphology and evolution of submarine canyons around the Zhongsha Platform, South China Sea: Implications for sedimentary processes in a modern isolated carbonate setting

Recent high-resolution multibeam bathymetry and seismic data from the platform-top to the abyssal plain of the Zhongsha Platform allow for a detailed investigation of the morphologies, spatial distribution, and trigger mechanisms of submarine canyons, submarine landslides, and associated sedimentary features along modern isolated carbonate slopes. The newly observed Zhongsha Canyon System provides a natural laboratory for reconstructing the source-to-sink sedimentary processes in a pure carbonate setting. This study reveals that there are thirty-four submarine canyons at water depths between 300 and 4100 m on the northern and western slopes of the Zhongsha Platform. Two morphologically different submarine canyon types are identified: (1) dendritic canyons, which exhibit abundant tributaries with scallop-shaped failures at the canyon heads, and (2) linear canyons, which feature rare tributaries with elongated failures at the canyon heads. The dendritic canyons are more complex in morphology than the linear canyons as a result of the interaction among numerous tributaries. Canyon initiation and evolution pass through three phases: (1) initial stage: off-platform sediment transport and platform margin failures contribute to erosive gravity flows; (2) developmental stage: initiation and incision of submarine canyons along platform margin failures; and (3) mature stage: numerous mature canyons along the platform margin. Off-platform sediment transport, density cascading, gravity flows, monsoon currents, and deep circulation play an essential role in shaping the slope morphologies. In addition, submarine landslides are extensively observed along the entire slope of the Zhongsha Platform at water depths of 600 to 4200 m, including canyon-wall failures, slope landslides, canyon-front landslides, and slope-toe failures based on their location and genesis. These processes can steepen the platform slopes by upward retrogressive and downward progressive erosion. On a larger scale, the persistent submarine canyons and occurrence of landslides around the Zhongsha Platform contribute to the uniqueness of this landscape among modern carbonate slopes. The morphologies and evolutionary processes of Zhongsha Canyon System present significant differences from the global carbonate submarine canyons in terms of their dimensions and trigger mechanisms. The findings of this work provide novel insights into the morphological features and sedimentary processes of submarine canyons in modern isolated carbonate platform settings.

Lacustrine mass movements in active tectonic settings: Lake tsunami sources in New Zealand's South Island

Lake tsunamis generated from subaerial and subaqueous mass movements can pose a significant hazard to lakeshore communities. However, current knowledge of lake tsunamis is derived from a limited number of studies, primarily in low-seismicity settings such as Switzerland and Norway. Underrepresented are studies from active tectonic settings, characterised by high relief, high sediment yields, and frequent seismic shaking that is likely to produce episodic subaerial and subaqueous mass movements with the potential to produce lake tsunamis. This study seeks to address this gap in our understanding through an examination of four lakes in the active tectonic region of New Zealand's South Island (Lake Rotoiti, Lake Rotoroa, Lake Brunner, and Lake Mapourika). High-resolution multibeam bathymetry and high-resolution seismic reflection data were used to identify and characterize the landforms and sediment associations of large and potentially tsunamigenic mass movements. A qualitative evaluation of the tsunamigenic capacity of the identified mass movements was undertaken using established empirical relationships between mass movement volumes and run-up heights. The bathymetric and seismic surveys have revealed 16 previously undocumented mass movements capable of generating lake tsunami. Fluvial deltas and bedrock slopes proximal to active faults were the most prevalent mass movement source areas, with the largest mass movements identified being a 49 Mm3 delta collapse and a 110 Mm3 subaerial mass movement in Lake Rotoroa. The findings suggest the origin and characteristics of the potentially tsunamigenic mass movements identified were strongly influenced by the high rates of delta progradation, frequent seismic activity, and the preconditioning and displacement by active faults, typical of active tectonic settings. Our results provide new insights into the heterogeneity of lacustrine mass movements and the drivers of lake tsunami hazards in underrepresented high-seismicity regions. The findings illustrate the importance of developing regionally specific insights into lake tsunami susceptibility and may inform the direction of more detailed lake tsunami hazard assessment in New Zealand.

Dissimilarity of megabenthic community structure between deep-water seamounts with cobalt-rich crusts: Case study in the northwestern Pacific Ocean

As anthropogenic disturbance on deep-sea seamount ecosystems grows, there is an urgent need for a better understanding of the biodiversity and community structure in benthic ecosystems, which can vary at local and regional scales. A survey of the benthic megafauna on two adjacent deep-water seamounts in the northwestern Pacific Ocean was conducted, which are covered by cobalt-rich crusts, to assess the biodiversity patterns and dissimilarity of assemblage composition. Based on a multidisciplinary dataset generated from video recordings, multibeam bathymetry data, and near-bottom currents, environmental and spatial factors impacting the megabenthic communities were explored. Results showed that these two deep-water seamounts were dominated by hexactinellids, crinoids, and octocorals. The seamounts were able to support diverse and moderately abundant megafauna, with a total of 6436 individuals classified into 94 morphospecies. The survey covered a distance of 52.2 km across a depth range of 1421–3335 m, revealing multiple distinct megabenthic assemblages. The megabenthic communities of the two deep-water seamounts, with comparable environmental conditions, exhibited similarities in overall density, richness, and faunal lists, while dissimilarities in the relative abundance of taxa and assemblage composition. No gradual depth-related change in terms of abundance, richness, or species turnover was observed across the two seamounts, despite the statistical significance of depth in structuring the overall communities. The spatial distribution of megabenthic communities displayed a discontinuous and patchy pattern throughout the two deep-water seamounts. This patchiness was driven by the interactive effects of multiple environmental factors. Near-bottom currents and microhabitat features were the primary drivers influencing their dissimilarities in megabenthic community structure. This case study on the megabenthic community structure of two adjacent seamounts with cobalt-rich crusts can serve as an environmental baseline, providing a reference status for the conservation and management of seamount ecosystems, particularly valuable for areas being considered for deep-sea mining.

Interaction between active tectonics, bottom-current processes and coral mounds: A unique example in the NW Moroccan Margin, southern Gulf of Cadiz

The NW Moroccan Margin has a complex geological evolution, being located close to the transition zone between the Azores – Gibraltar Fracture Zone and the western front of the Betic–Rif collisional orogen. The interaction between tectonic, halokinetic and fluid flow processes with bottom-current activity shapes the seafloor and influences the distribution of seafloor biological communities (such as the cold-water coral mounds) and deep-water sedimentation. The aims of this work are to study the interaction of the paleo-oceanographic and morpho-tectonic processes that generated the various seafloor features of the NW Moroccan Margin. To achieve this, high-resolution multibeam bathymetry and parasound data acquired in the “ALBOCA II” cruise have been used, complemented by high-resolution 2D seismic reflection data and the EMODnet bathymetric compilation.Several morphological features were identified in the margin, which are related to different processes of sedimentary (contourites and sediment waves), structural (faults and diapirs), gravitational (slide scars, mass transport deposits), fluid migration (mud volcanoes and pockmarks) and biogenic (exposed and buried coral mounds) nature. The structural features (e.g., strike-slip faults) have a major control on the seafloor morphology and, consequently, on the development and evolution of the sedimentary systems in the study area.The evolution of the NW Moroccan Margin during the late Quaternary has been controlled by climatic variations and tectonic activity. The action of these factors has been dominant in distinct parts of the study area where: i) contourite terraces developed when climatic and oceanographic changes were the prevalent factor, ii) mounded and confined contourite drifts and local mass transport deposits formed when the major control was tectonic activity.

Arctic puzzle: Pioneering a northern shrimp (Pandalus borealis) habitat model in Disko Bay, West Greenland

Recent advancements in spatial modelling leverage remote sensing data and statistical species-environment relationships to forecast the distribution of a specific species. Our study focuses on Disko Bay in West Greenland, recognized as a significant marine biodiversity hotspot in the region. We conducted comprehensive analyses using multiple datasets spanning from 2010 to 2019, incorporating shrimp and fish surveys, commercial shrimp fishery catches, high-resolution (25 × 25 m) multibeam bathymetry and backscatter data along with a medium-resolution (200 × 200 m) bathymetric model, measured and modelled oceanographic data, and satellite chlorophyll data. Through multivariate regression analysis, we tested the significance of various physical factors (seafloor depth, sediment class, bottom water temperature, bottom water salinity, bottom current velocity, space, and time), biological factors (chlorophyll a, Greenland halibut (Reinhardtius hippoglossoides)), and anthropogenic impact (shrimp fishery; standardized catch per unit effort) on the density of northern shrimp in the area. Our results indicate a significant association between northern shrimp density, seafloor depth, and sediment class, explaining 36 % of the variation in shrimp density. Subsequently, we developed a high-resolution (optimized) spatial linear mixed–effect model to map the distribution of northern shrimp across Disko Bay, representing the first model of its kind developed for an Arctic area. The optimal habitat for northern shrimp is characterized by medium-deep waters (approximately 150–350 m), turbulent conditions, and mixed sediments, predominantly located in the northern and southern regions of Disko Bay. Notably, the northern region hosts a relatively diverse benthic community, with northern shrimp and sponges as the primary contributors of epibenthic biomass. This novel high-resolution model significantly enhances our understanding of the physical drivers and detailed spatial patterns influencing the distribution of northern shrimp in the Arctic.

Controls on Bending‐Related Faulting Offshore of the Alaska Peninsula

AbstractOceanic plates experience extensive normal faulting as they bend and subduct, enabling fracturing of the incoming lithosphere. Debate remains about the relative importance of pre‐existing faults, plate curvature and other factors controlling the extent and style of bending‐related faulting. The subduction zone off the Alaska Peninsula is an ideal place to investigate controls on bending faulting as the orientation of the abyssal‐hill fabric with respect to the trench and plate curvature vary along the margin. Here, we characterize faulting between longitudes 161°W and 155°W using newly collected multibeam bathymetry data. We also use a compilation of seismic reflection data to constrain patterns of sediment thickness on the incoming plate. Although sediment thickness increases over 1 km from 156°W to 160°W, most sediments were deposited prior to the onset of bending faulting and thus should have limited impact on the expression of bend‐related fault strikes and throws in bathymetry data. Where magnetic anomalies trend subparallel to the trench (<30°) west of ∼156°W, bending faults parallel magnetic anomalies, implying that bending faults reactivate pre‐existing structures. Where magnetic anomalies are highly oblique (>30°) to the trench east of 156°W, no bending faults are observed. Summed fault throws increase to the west, including where pre‐existing structure orientations are constant (between 157 and 161°W), suggesting that another factor such as the increase in slab curvature must influence bending faulting. However, the westward increase in summed fault throws is more abrupt than expected for gradual changes in slab bending alone, suggesting potential feedbacks between pre‐existing structures, slab dip, and faulting.

Unstable geomorphologic fabric impacted by excess magmas and propagating rifts in the central West Philippine Basin

The central West Philippine Basin (WPB) comprises three contrasting geomorphologic provinces, the mantle-plume type Benham Rise in west, the volcanic arc-type Kyushu-Palau Ridge (KPR) at the east limit, and the in-between central rift hosting the deepest (∼7874 m) rifted seafloor. However, their morphic transit and dynamic interactions remain elusive owing to the insufficiency of relevant data. By incorporating new and previous multibeam bathymetry data fully enveloping the central rift, we synthesized a 3-band, 3-segment seafloor fabric of the central WPB and deduced its formation mechanisms. The bathymetry documents prominent across- and along-axis variations and variable landform assemblages, including: 1) overall trends of abyssal hill lineation swing counter-clockwise from ∼N100/105°E at a distance of 100 km from the fossil rift valley to ∼N85/95°E at a distance of ∼30/50 km, then clockwise to ∼N100/140°E in the rift valley, which recognizes three irregularly bands (I, II, and III ripping into II) and a rotatory spreading fabric; 2) the rift valley narrows westward from ∼85 km wide near the KPR to ∼25 km at Centric Deep, and then fades out to further west, synchronously from magmatic to amagmatic then to failed, indicating a northwestward propagating stirred by the KPR volcanism. Moreover, it is found in the middle segment that three major transform faults bend southwesterly into Southern Band I with their concaves pointing to the Benham Rise. Behaving as pseudo-faults, they are likely triggered by the former magmatism of the Benham Rise. Lying just at the intersection of a relict nodal basin and the western tip of the later PR, the Centric Deep might have resulted from overprinting amagmatic extension on former pull-apart. Thus, the geomorphic fabric featuring high spreading instability reflects strong magma-tectonic intervention by excessive magmatism of mantle plume and subduction arc.

Shallow structure and late quaternary slip rate of the Osaka Bay fault, western Japan

The Osaka Bay is situated at a seismically active region north of the Median Tectonic Line and east of Awaji Island in western Japan, known as part of the Kinki Triangle and the Niigata–Kobe Tectonic Zone. Dense distribution of active faults and high geodetic strain rates characterize the region, posing a major seismic hazard potential to the coastal and metropolitan areas of the Kansai region. To investigate the shallow structure and recent deformation history of active faults in the Osaka Bay, we acquired 15 high-resolution seismic profiles using a Mini-GI airgun and a Boomer as active sources, together with multi-beam bathymetry data across the Osaka Bay Fault. Our seismic sections image a ~ 0.1 to 3.7 km-wide asymmetric anticline forelimb above the Osaka Bay Fault at shallow depths, coupled with a ~ 2.6 km-wide syncline to the west, and a broad, ~ 11 km-wide syncline in the footwall to the east. The synclinal axial surface at shallow depths measured in this study ranges 75°–89°. We observe the vertical displacement of the Osaka Bay Fault increasing northwards along strike. The sediment thickness on the hanging wall, however, is variable, modified by non-tectonic processes such as by tidal currents, affecting the geometry of growth strata. The most recent deformation by the Osaka Bay Fault reaches to near the seafloor by active folding, with large vertical offsets of 8–14 m over the last ~ 11 ka, and 5–11 m over the last ~ 5 ka. By combining with previously reported borehole age data, the average uplift rate on the Osaka Bay Fault is estimated to be ~ 1.0 to 1.7 m/ka during the Latest Pleistocene to Holocene. The inferred slip of the Osaka Bay Fault during the Holocene is likely to account for > 5% of the regional geodetic strain accumulation within the Kinki Triangle. Further studies to evaluate the Holocene slip rates of regional faults are necessary to assess the seismic hazards and the internal strain budgets within the Kinki Triangle and the Niigata–Kobe Tectonic Zone.Graphical abstract

Potential triggers and development processes of submarine landslides in the Xisha Trough Basin, South China Sea

Both submarine landslides and submarine canyons can transfer large amounts of terrigenous quantities from the continental shelf to the deep sea. In some cases, they can have a close relationship to their spatial distribution, formation and evolution. Submarine landslides on the shelf–slope can provide early depressions for submarine canyons, representing the early stage of submarine canyons. The continuous downcutting process during the evolution of submarine canyons can steepen the gradient of the canyon sidewalls, which can lead to the occurrence of submarine landslides. However, the role of submarine canyons in the initiation of slope failure has been overlooked. In this study, high-resolution multibeam bathymetry data, submarine image data and 2-D seismic data were used to investigate two adjacent submarine landslides developed on the northern slope of the Xisha Trough and the spatiotemporal relationship of these landslides to the Central Canyon. We identified a steep downslope between the submarine landslides and the Central Canyon. The Central Canyon formation age was much earlier than those of the submarine landslides. The Central Canyon is filled with modern submarine landslide deposits. The characteristics of the multiple failure scarps indicate retrogressive failure of the submarine landslides. We suggest that the submarine landslides developed on the northern slope of the Xisha Trough Basin have finally been captured by the Central Canyon. We determined that the emptying of sediments at the end of the northern slope of the Xisha Trough Basin caused by the development of the Central Canyon caused the end of the northern slope of the Xisha Trough Basin to lose support, which may have affected the slope stability and could have even played a role in the initiation of submarine landslides. Consequently, the slope area along the Central Canyon may be susceptible to slope instability and slope failure processes.

Morphotectonics of the Raman-Panikkar-Wadia seamount chain in the Laxmi Basin, Eastern Arabian Sea

The Laxmi Basin, which is a deep ocean basin situating adjoining to the northwestern continental margin of India, contains a linear seamount chain consisting of the Raman Seamount, Panikkar Seamount and the Wadia Guyot, located over the axial basement high in the Laxmi Basin representing the Panikkar Ridge. The geomorphology of this seamount chain was studied by earlier researchers; however, its characteristic geophysical signatures, possible genesis and age of formation remains to be clearly established. We attempted for a detailed understanding of the morphological characteristics and the geophysical signatures over the spatial extent of these seamounts using a fresh set of multibeam bathymetry data and sea-surface gravity and magnetic anomalies, complemented by the existing seismic reflection sections. Based on the seafloor and basement topography signatures observed together from the multibeam bathymetry data and the seismic reflection sections, we infer that all the three seamounts are associated with the presence of surface/subsurface secondary peaks on their central parts. The free-air gravity anomaly maps show that the seamounts are associated with a very short wavelength gravity high, superimposed on the short wavelength gravity low representing the Panikkar Ridge. The magnetic anomaly maps suggest that all these seamounts are associated with complex magnetic signatures. Based on the presence of morphological features that are generally associated with the volcanic activity and by considering the above complex geophysical signatures and the updated magnetic isochron map of the Laxmi Basin, we support multiphased volcanic origin for the Raman-Panikkar-Wadia seamount chain, emplaced at an age younger to 63.28 Ma.

Reconstruction of the Maërl habitat to better understand its ecological integrity

Maërl habitats are composed of coralline red algae species that can live freely rolling on the seabed and forming nodules, the so-called rhodoliths, or incrusted forming coralligenous habitats. Maërl habitats are generally distributed in the Mediterranean at a depth of between 30 m and 70 m and are considered one of the most emblematic Mediterranean seabeds. In the present study, the complex structure of maërl habitats was investigated to i) characterise the relief features and classify the different sediments, ii) to estimate the abundance of the coralline red algae (both rhodoliths and encrusting ones) and iii) to analyse the biodiversity of the species inhabiting the habitat. Data were obtained from an approximately 11 km-long transect, using non-intrusive sampling methods, integrating information from video images collected using the Remotely Operated Vehicle LIROPUS (IEO_CSIC), and multibeam bathymetry and backscatter data. Video images were used to reconstruct (using GIS) the habitat structure and characteristics. Throughout the transect, a strong relationship between habitat characteristics and the effect of trawling activity and the geomorphology of the studied area was observed. The closed area to fishing activity showed a high abundance of rhodoliths in well-structured megaripples reliefs. Contrarily, the areas affected by fishing showed an important destructuring of the relief with a low density of rhodoliths. Last, the muddy bottoms showed areas with no characteristic features and no rhodoliths. All this information has allowed to reconstruct the maërl habitat in the Blanes continental shelf (NW Mediterranean) and analyse the fragmentation of the assemblages seen in the video to assess its good environmental status (GES), and finally to identify the level of ecological integrity of this vulnerable habitat.

Highlighting broad-scale morphometric diversity of the seabed using geomorphons

Morphometric diversity is an important component of overall seabed geodiversity. Automated methods for classification of morphometric features (ridges, peaks, valleys etc.) provide a convenient way of classifying large volumes of data in a consistent and repeatable way and a basis for assessing morphometric diversity. Here, we apply ‘geomorphons’, a pattern recognition approach to morphometric feature classification, to 100 m resolution multibeam bathymetry data in the Barents and Norwegian Seas, Norway. The study area spans depths from a few metres to nearly 6000 m across several geological settings. Ten unique morphometric features are delineated by the geomorphon analysis. From these results, we compute the variety of features per 10 km2. This simple ‘geomorphon richness’ measure highlights broad-scale morphometric diversity across the study area. We compare the richness results with terrain attributes and across physiographic regions. Our results provide new regional insights, which together with more detailed information will help guide follow-up surveys as well as identifying diversity hotspots, which may require special management.

Basin-scale interaction between post-LGM faulting and morpho-sedimentary processes in the S. Eufemia Gulf (Southern Tyrrhenian Sea)

The integrated interpretation of high-resolution multibeam bathymetry, seismic profiles and backscatter data in the S. Eufemia Gulf (SEG; Calabro-Tyrrhenian continental margin, south-eastern Tyrrhenian Sea) documents the relationship between postglacial fault activity and morpho-sedimentary processes. Three systems of active normal faults that affect the seafloor or the shallow subsurface, have been identified: 1) the S. Eufemia fault system located on the continental shelf with fault planes mainly oriented N26E-N40E; 2) the offshore fault system that lies on the continental slope off Capo Suvero with fault planes mainly oriented N28E-N60E; 3) the Angitola Canyon fault system located on the seafloor adjacent to the canyon having fault planes oriented N60E-N85E. The faults produce a belt of linear escarpments with vertical displacement varying from a few decimeters to about 12 m. One of the most prominent active structures is the fault F1 with the highest fault length (about 9.5 km). Two main segments of this fault are identified: a segment characterised by seafloor deformation with metric slip affecting Holocene deposits; a segment characterised by folding of the seafloor. A combined tectono-stratigraphic model of an extensional fault propagation fold is proposed here to explain such different deformation.In addition to the seabed escarpments produced by fault deformation, in the SEG, a strong control of fault activity on recent sedimentary processes is clearly observed. For example, canyons and channels frequently change their course in response to their interaction with main tectonic structures. Moreover, the upper branch of the Angitola Canyon shows straight flanks determined by fault scarps. Tectonics also determined different sediment accumulation rates and types of sedimentation (e.g., the accumulation of hanging wall turbidite deposits and the development of contourite deposits around the Maida Ridge). Furthermore, the distribution of landslides is often connected to main fault scarps and fluids are locally confined in the hanging wall side of faults and can escape at the seabed, generating pockmarks aligned along their footwall.

Initiation and evolution of an isolated submarine canyon system on a low-gradient continental slope

Submarine canyons are important conduits transferring large volumes of sediment, nutrients, and pollutants from the continental shelf to deep-water basins. However, the mechanisms initiating submarine canyons and the factors influencing their evolution are still poorly understood. Here, we use multibeam bathymetry and two-dimensional seismic reflection data to investigate the origin and development of a submarine canyon system on the northern South China Sea margin. Our results show a submarine canyon system lying at a water depth of 400–1200 m on a relatively low-gradient (<0.5°), open continental slope. At the bottom of this canyon system, buried canyons undercut a mass-transport complex (MTC 1), whose top surface is early Pliocene in age. No other modern or buried canyons, channels and gullies are observed outside the area spanned by MTC 1. Such an observation demonstrates that pre-existing slide scars can capture gravity flows by providing accommodation space for sediment transported onto the lower continental slope, thus facilitating the development of pre-existing channels above MTCs. Lateral accretion packages identified on the southwest walls of several submarine canyons suggest they migrated northeastward due to the influence of contour currents. In addition, the presence of several basal erosional surfaces and smaller-scale MTCs in the canyons confirms they have undergone multiple cut-and-fill cycles, which were likely controlled by relative sea-level changes. The relative high sea level recorded at present ultimately led to the preservation of the studied canyon system on the continental slope. The results not only demonstrate the crucial role of submarine landslides in the initiation of submarine canyons, but also highlight how relative changes in sea level influence the evolution of submarine canyons on low-gradient continental slopes.

Submarine landslide susceptibility assessment along the southern convergent margin of the Colombian Caribbean

Submarine landslides are a mixture of rock, sediment, and fluids moving downslope due to a slope's initial event of mechanical failure. Submarine landslides play a critical role in shaping the morphology of the seafloor and the transport of sediments from the continental shelf to the continental rise in the southern margin of the Colombian Caribbean. Two fundamental considerations can be highlighted: first, mass transport complexes produced by submarine landslides encompass significant portions of the stratigraphic record; second, these mass movements could affect underwater infrastructure. The mapping of the Southern Caribbean seafloor using 3D seismic surveys and multibeam bathymetry data in an area encompassing 59,471 km2 allowed the identification of 220 submarine landslides with areas ranging between 0.1 and 209 km2. Distinctive characteristics were found for submarine landslides associated with canyon walls, channel-levee systems, tectonically controlled ridges, and the continental shelf break. The analysis of the relationship between submarine landslides and seafloor morphological features made it possible to estimate a mass movement susceptibility map that suggests the following considerations: first, structural ridges and adjacent intraslope subbasins related to the South Caribbean Deformed Belt are more likely to be submarine landslide hazards; second, the continental shelf break and channelized systems produce a moderate submarine landslide hazard potential; and third, deep marine systems with a slope less than 5° show the lowest submarine landslide hazard potential. This work contributes to the understanding of submarine landslides in the study area through the presentation of conceptual diagrams that provide additional visual elements facilitating the level of abstraction necessary for visualizing bathymetric data. Likewise, the mass movement susceptibility map presented herein gives insights for future studies that seek to evaluate geohazards in the southern Colombian Caribbean margin.

Imprints of post-glacial sea-level changes in the Visakhapatnam Bay (VB) basin: first documentation from multibeam bathymetry data

Imprints of post-glacial sea-level changes in the Visakhapatnam Bay (VB) basin: first documentation from multibeam bathymetry data

Miocene to Quaternary geodynamic evolution of the southern section of the Burdur-Fethiye Shear Zone and its offshore continuation, eastern Mediterranean

The main interrelated structures of the eastern Mediterranean are shaped by the complex tectonic regimes including active subduction, uplift, and progressive counterclockwise rotation. The Hellenic Arc, the Anaximander Mountains, the Western Taurides, the extensional western Anatolian graben, the Burdur-Fethiye Shear Zone and the Rhodes Basin are these structures located in one of the most tectonically active regions. The Burdur-Fethiye Shear Zone is a 75- to 90- km wide and 300-km-long transtensional left-lateral shear zone developed during the formation of the Aegean back-arc extensional system and the thrusting of Western Taurides. In this study, fault kinematic analysis, and DEM and earthquake data characterize the tectonic controls of the southern section of the Burdur-Fethiye Shear Zone. The high-quality multibeam bathymetry data, their processing and interpretation with the onshore structures and an integrated interpretation with multichannel seismic profiles allowed the geodynamic evolution of the Burdur-Fethiye Shear Zone, Rhodes Basin and environs to be evaluated. Despite the heated debates regarding the presence of the zone, the latest offshore data reveals again that the continuation of the subduction transform edge propagator (STEP) fault between the Hellenic and Cyprus arcs comes into play as the Burdur-Fethiye Shear Zone on land.

A study of volcanic rocks and ferromanganese crusts through marine geophysical methods integration in the north portion of Cruzeiro do Sul Rift in the Rio Grande Rise

The Rio Grande Rise (RGR) is an extensive structural high located in the South Atlantic Ocean, target of increasing exploratory interest. During the last decades, considerable attention has been given to its genesis, dynamic, regional tectonic, and composition. Some studies indicate the presence of volcanic rocks, mainly basaltic, related to their volcanic origin and Ferromanganese Crusts, boosting the research and economic interest. This study suggests the location of volcanic rocks and FeMn crusts at the north portion of Cruzeiro do Sul Rift within the RGR, characterizing the local geology and distribution pattern. We used multibeam bathymetry, sidescan sonar, dredges, and magnetic field data to integrate and better constrain the results. The magnetic field data highlighted the location of probable basaltic rocks, agreeing with the published literature, which was afterward confirmed by dredge samples. Their magnetic anomalies displayed the predominance of reverse polarization and less frequent normal polarization anomalies. FeMn crusts need a large volume of magnetite to cause anomalies in the local magnetic field, which does not happen in the RGR. There, they have reduced thickness and are frequently eroded, as displayed by the bathymetry, sidescan sonar, and geological data. Magnetic lineaments at the Rift margin defined a zone with a series of normal faults. During the Rift formation, transcurrent movements caused an intense fracturing, providing pathways for magma intrusion. Therefore, the fault zone could be related to the primary magnetic anomalies as a function of the magma intrusion and the occurrence of the rifting process and seafloor spreading. The new data presented in this paper brings valuable data for the comprehension and exploration effort of the RGR.