Atlantic Margin Research Articles

Detailed composition and physical properties analyses of surficial and sub-surface fined-grained sediments from the Continental Shelf and Upper Slope Sediments Offshore Southern New England, USA

In recent years, detailed geological characterization of the seafloor and shallow sub-surface on the northern U.S. Atlantic margin have been an important component of multi-disciplinary ocean acoustics and environmental sensing projects to support experiment planning and inform geoacoustic models of sound propagation. Comprehensive surficial sediment and core sampling across shallow continental shelf, shelf-edge, and upper continental slope sites offshore southern New England provide the opportunity to evaluate the importance of many sediment characteristics that impact sound propagation through the seabed. Beginning in the mid-shelf New England Mud Patch and continuing into deeper water, we have begun to develop a detailed understanding of the composition and physical properties of the shallow sediment column record using a combination of surficial and sub-surface sediment sampling tools, coupled with an extensive suite of discrete laboratory analyses. Quantitative data on sediment density, porosity, mineral and biogenic composition, and grain size distribution provides both valuable input parameters for geoacoustic models and helps establish a framework for interpreting independently derived measurements and modeling results. The physical, biological, and other environmental sediment characteristics can be integrated with existing geological assessments of the region and used to investigate ocean and sub-surface acoustic propagation. [Work supported by the Office of Naval Research.]

The Mechanical Nature of the Lithosphere Beneath the Eastern Central Atlantic Hotspots

AbstractThe Eastern Central Atlantic (ECA) region includes the Azores, Canary, Cape Verde, Great Meteor, and Madeira hotspots. These hotspots exhibit a large variety of characteristics and are rooted in the lithosphere ranging in age from newly created at the Mid Atlantic Ridge to Jurassic at the NW Africa Atlantic margin. Therefore, the ECA region represents an excellent scenario to investigate in an integrated way the effects of hotspots on the mechanical structure of oceanic lithosphere. Here, we calculate the effective elastic thickness (Te) of the lithosphere from an analysis of gravity and topography. Azores hotspot is characterized by a Te < 10 km, whereas the Great Meteor, Cape Verde, and Madeira hotspots have intermediate Te (15–30 km) values. In contrast, the Canary hotspot is characterized by a much higher Te (>50 km), forming the largest and most prominent mechanical feature in the ECA. All the hotspots except Canary show standard elastic thickness values when compared to average values for the same age lithosphere and to other oceanic areas in the world. The high strength of the Canary hotspot may be related to the highly depleted mantle composition in the area. The comparison between the elastic thickness distribution and the upper mantle seismic velocity structure shows no correlation between the Te estimated at the ECA hotspots (with the exception of Azores) and the presence of low shear‐wave velocity anomalies in the underlying mantle. This lack of correlation suggests a negligible effect of upper mantle temperature anomalies on the flexure of the ECA region.

Tracing the legacies of anthropogenic landscape transformation in the Iberian atlantic margin: Historical and geoarchaeological investigations in the Bidasoa estuary (Basque Country)

Human activity is a primary factor of environmental transformation in coastal and estuarine areas. The appropriation and exploitation of a given space and its resources is conditioned by socially driven practices, which are of a different nature depending on the historical contingencies and result in a variety of material imprints. This paper addresses the history of human-environment interactions in an estuary of the Iberian Atlantic Margin, and their long-term effects on the local morphosedimentary and hydrological dynamics. The study, based on an interdisciplinary combination of historical documentary sources, field survey, and core sampling, highlights the dynamic evolution of these interactions, with five main groups of human practices related to the estuarine environment: fisheries; port and road infrastructures; hydraulic infrastructures; land reclamation; and urban and industrial expansion. Hence, three main historical phases are outlined, with gradually increasing human impacts. The 16th century is characterised by a relatively low impact, based on the exploitation of fisheries and hydraulic structures. The 17th-18th centuries reflect an extensive land reclamation. Finally, the 19th-20th centuries are marked by the impact of urban and industrial expansion. These results provide a valuable pathway for the reflection on the manifold and dynamic nature of human-environment interactions, with multiple geological, ecological, and anthropogenic processes converging in the present-day layout of the estuarine environments.

Detrital zircon age signatures of the Mesozoic in the Lusitanian Basin and implications for the evolution of Iberia–Newfoundland conjugate margins

AbstractNew detrital zircon age results from the Lusitanian Basin are integrated with published data for the Mesozoic of west Iberia and eastern Canada (4959 concordant ages). Zircons in new samples are either mainly Devonian‐Permian, Cryogenian‐Ediacaran or reveal a combination of these two age populations, showing secondary to minor Mesoproterozoic‐Archean ages. Statistical tools applied to the compiled age data allow grouping the samples according to age signatures and explain main features of the age spectra. Age signatures are determined by the abundance of zircon: (1) recycled from terranes involved in Pangea amalgamation; (2) associated with Acadian‐Variscan crystalline rocks (~420–310 Ma), which becomes younger from the Laurentian to the Gondwanan sides of the orogen; (3) associated with post‐collisional events (~300–285 Ma) that affected different terranes and were exhumed in major structures controlling basin formation; and (4) resulting from Mesozoic magmatism (~145 Ma) with a stronger imprint in the west Atlantic margin.

Ignition of the southern Atlantic seafloor spreading machine without hot-mantle booster

The source of massive magma production at volcanic rifted margins remains strongly disputed since the first observations of thick lava piles in the 1980s. However, volumes of extruded and intruded melt products within rifted continental crust are still not accurately resolved using geophysical methods. Here we investigate the magma budget alongside the South Atlantic margins, at the onset of seafloor spreading, using high-quality seismic reflection profiles to accurately estimate the oceanic crustal thickness. We show that, along ~ 75% of the length of the Early-Cretaceous initial spreading centre, the crustal thickness is similar to regular oceanic thickness with an age > 100 Ma away from hot spots. Thus, most of the southernmost Atlantic Ocean opened without anomalously hot mantle, high magma supply being restricted to the Walvis Ridge area. We suggest that alternative explanations other than a hotter mantle should be favoured to explain the thick magmatic layer of seaward dipping reflectors landward of the initial mid-oceanic ridge.

Geophysical evidence for lithospheric scale asymmetry and inherited mantle in the SE Brazilian-Angola and Newfoundland-Iberia rifted margins

Rift systems in the central South Atlantic and the southern Northern Atlantic margins exhibit anomalous wide ocean-continent transitions, extreme thinning of the continental crust, and scarce volcanism indicative of low magmatic budgets during rifting and breakup, characteristic of magma-poor rifted margins. While numerous studies investigated the crustal architecture at these magma-poor rifted margins, the nature of the underlying mantle lithosphere remains virtually unknown. In this work, we have interpreted seismic tomography and electromagnetic data with the aim of comparing large-scale aspects and mantle geophysical anomalies at these conjugate rifted margins. The data exhibits low electrical conductivity and high P-wave velocity in the mantle underlying the Iberia and the Angolan margins, while the Newfoundland and SE-Brazil margins show a lack of high-velocity mantle and exhibit higher electrical conductivity. The P-wave tomography values at middle lithospheric depths are suggestive of an oceanward lateral continuity of rigid lithospheric mantle at both the Iberian and Angola margins that may correspond to an anomalous mantle. Rifting-induced delamination at the onset of Atlantic opening is supported by previous geochemical studies. In addition, low electrical conductivity areas may indicate dry mantle conditions, which can be caused by inherited subcontinental mantle, and/or pre-to syn-rift magmatic extraction. A lack of high-velocity and high electrical conductivity in the mantle under the Newfoundland and Santos-Campos margins suggest a relatively weaker and newly formed mantle, in agreement with the removing and/or initial absence of a strong middle-to-lower inherited lithosphere beneath those margins. Therefore, the geophysical observations support different types of the nature of the middle mantle lithospheres flooring the two conjugate, magma-poor rifted margins.

Assessment of the Geomorphological Heritage of the Costa Branca Area, a Potential Geopark in Brazil

The Atlantic margin of South America is considered passive and stable. However, there are some local points of discordance within the Brazilian coastal region with more than 7490 km of extension, where there is only one tectonic relief. These sites are located in a marginal sedimentary basin in which there is a small area of Quaternary tectonic relief, which makes it scientifically relevant at an international level. The present work proposes using two methods for quantifying the geomorphological heritage of this area. The main difference between the methods is the use of aesthetic values together with scientific ones as central values in one of the methods, while the other method focuses only on scientific values. The quantitative evaluation performed here allowed for the identification of seven geomorphosites with one method and only four with the other. Considering the results obtained, meetings were held with civil society and with the state and local municipalities which presented the possibility of creating a geopark, given the area’s importance for understanding the history of the Earth and potential as a priority area for geoconservation.

A Seismic Facies Analysis to Determine the Relative Age and History of the Al Idrissi Mud Volcano from Offshore Larache Located in the NW Moroccan Atlantic Margin

Formed on top of the Gulf of Cadiz, the Al Idrissi mud volcano is the shallowest and largest mud volcano in the El Arraiche mud volcano field of the northwestern Moroccan margin. The development and morphology of mud volcanoes from the El Arraiche mud volcanoes group have been studied at a large scale. However, the time interval related to their formation period still needs to be better understood. In this regard, we interpreted and analyzed the seismic facies from the 2D reflection data of the GEOMARGEN-1 campaign, which took place in 2011. The aim was to identify the seismic sequences and draw the Al Idrissi mud volcano system to determine the formation period of the Al Idriss mud volcano. And as a result, the Al Idrissi mud volcano system is made of both buried and superficial bicone and was identified along with the Upper Tortonian to Messinian-Upper Pliocene facies. As the initial mud volcano extrusive edifice, the buried bicone was formed in the Late-Messinian to Early-Pliocene period. However, the superficial bicone, as the final extrusive edifice, was included in the Late Pliocene. In this case, the timing interval between the buried and superficial bicone is equivalent to the Late-Messinian to Upper-Pliocene period. Therefore, the latter corresponds to the Al Idrissi mud volcano formation period.

Oblique rifting along transfer zones: The structural evolution model revealed by physical modeling

Oblique rifting is a common process that acts during the rupture of continental masses and can evolve to the passive margin stage. The inter-rift (or intra-rift) interaction can occur by transfer zones (TZs). These zones can be formed at the most diverse scales and, on a large scale, can result in the development of oblique rifts. To understand how TZs nucleate and evolve at the plate scale, we simulated, through physical modeling, the development of oblique transfer zones that connect two parallel rifts (with no lateral overlap) developed orthogonally to the extensional direction. Our results showed that obliquity and rheology could play an important role in the structural architecture of rifts that originated in such a structural environment. When the obliquity ranges from low to intermediate (i.e., 20°≤ α ≤ 45°), these rifts can be compartmentalized into two main structural domains - extremity, and central regions - with diachronic evolution and distinct kinematics. Extremity regions are characterized by oblique-slip deformation with intense rotation/tilting of the substrate. The central region is dominated by transcurrent (and oblique-slip) deformation with the presence of marginal plateaus, pull-apart, and oblique basins. Small variations in the obliquity (around 5°) are enough to affect parameters like faults' dip and geometry, and depocenters’ width and depth, thereby promoting changes in the morphology, geometry, architecture, and configuration of TZs. In a more mature stage, and on a continental scale, the TZs evolve into oblique rifts whose margins are composed of oblique and transcurrent fault segments (transfer/transcurrent) that together define a typical zig-zag geometry. The sizes and numbers of these segments depend on the obliquity and the rheology. Transcurrent fault segments are more common when the obliquity is 20° and 25°, in the model with quartz sand only. The modeling data presented here can be compared with the equatorial Atlantic margin of South America, assuming that it may represent an important plate-scale oblique transfer zone (20°) developed between the South and Central Atlantic.

Species acclimatization pathways: Latitudinal shifts and timing adjustments to track ocean warming

Poleward distributional shifts and phenological adjustments are universal ecological responses to ocean warming. Though they are commonly addressed as independent processes, phenology usually depends on the latitudinal location where an organism lives. Such interaction can mask the actual impacts of warming and may even constrain the ability of a species to cope with ocean warming. We propose a framework to analyse alternative acclimatization pathways that accounts for pure distributional shifts, pure phenological adjustments, and mixed response. We tested this analysing drivers of observed changes in the spawning of horse mackerel (Trachurus trachurus) and Atlantic mackerel (Scomber scombrus) in northeast Atlantic in 1992–2019. Since species had contrasting population trajectories, data from the same survey is suitable to test whether shifts are driven by warming or density-dependence. Species showed contrasting responses to warming; horse mackerel spawned earlier (11.7 ± 1.5 days/°C of warming), whilst Atlantic mackerel shifted northward (367 ± 22 km/°C of warming). The narrower reproductive thermal niche of horse mackerel resulted in a tight coupling between latitude and timing of spawning that is consistent with geographical attachment, and an acclimatization constrained to an earlier phenology. The northward shift of Atlantic mackerel might be associated to its wider thermal reproductive niche, which enables prolonged migrations and almost synchronous spawning along the Atlantic margin. Results support our framework underpinning that acclimatization can combine or exclude timing and poleward shift, which could depend on species traits. These new insights are useful for fisheries management and to improve habitat projections under climate change.

Stratigraphic and sedimentary constraints on presalt carbonate reservoirs of the South Atlantic Margin, Santos Basin, offshore Brazil

Stratigraphic and sedimentary constraints on presalt carbonate reservoirs of the South Atlantic Margin, Santos Basin, offshore Brazil

Community composition of mussel associates at deep-sea methane seeps in the Gulf of Mexico and the US Atlantic Margin

Efforts to understand and preserve the methane seep communities of the Gulf of Mexico and the US western Atlantic margin begin with an understanding of biodiversity and community composition. In this study, 10,143 individuals representing 63 different taxa were sampled from mussel-beds surrounding methane seeps at various depths within two different ocean basins. Diversity in mussel beds was highest at Baltimore Canyon, the shallowest site sampled in the Atlantic. Although only four species were sampled at more than one site, species composition was most alike among sites found at similar depths; the two deepest sites sampled, Florida Escarpment and Blake Ridge, showed a 9.6% similarity. However, depth is not the only predictor of similarity: Baltimore Canyon and Chincoteague are both located in the Atlantic Ocean at different depths but had a 5.3% similarity in species composition. The high diversity of individuals sampled among these sites emphasizes the importance of preserving seep communities, which provide essential nursery habitats and primary production that establish a food source for many migratory species within the deep-sea ecosystem. Not only is the diversity of seep communities unique and important to the deep sea, but seeps may be beneficial to the overall health of our Earth’s ecosystem through the support of commercial fisheries and the sequestering of methane.

Challenges and opportunities for hydrocarbon exploration within the Mesozoic sub-basalt plays of the Norwegian Atlantic Margin

The sub-basalt domain of the Norwegian continental shelf (NCS) is one of the last remaining hydrocarbon exploration frontiers in Europe. While there is an established geological and tectonic framework, little has been published that addresses the remaining hydrocarbon exploration risks/uncertainties. Unlike the Faroe Shetland Basin and Rockall Trough, at the time of writing, there are currently no industry-drilled sub-basalt well penetrations on the Norwegian continental shelf. Numerous potential Mesozoic sub-basalt hydrocarbon plays exist on the NCS but, due to the lack of industry-drilled sub-basalt penetrations, there is a perceived large exploration risk. By using cross-border analogues, basin modelling workflows and integration of available seismic data the main uncertainties across the NCS are outlined including charge timing, structural definition, and details of reservoir presence. Generically the Late Cretaceous and Middle Jurassic intervals are potential plays which may be present on the Norwegian Margin. However, there is considerable uncertainty on their depth and preservation. Although significant challenges and uncertainties remain, the authors believe that the integration of well results, consideration of basin modelling driven heat flow estimates and new 3D seismic data may open sub-basalt opportunities for a new exploration frontier on the NCS. Thematic collection: This article is part of the New learning from exploration and development in the UKCS Atlantic Margin collection available at https://www.lyellcollection.org/topic/collections/new-learning-from-exploration-and-development-in-the-ukcs-atlantic-margin

Styles of slope instability on a Quaternary sub-arctic continental margin: The northwest flank of the Storegga Slide

Submarine landslides are widely recognised around the Northeast Atlantic margin, some of which forming vast slide complexes. On the mid-Norwegian margin, the Storegga Slide complex has been active since the early Pleistocene, first as a regional event (Slide W) at 1.7 Ma, and later culminating in the Storegga Slide sensu stricto at 8.2 ka. By interpreting high-quality seismic data, this work investigates slope instability styles, and their geneses, on the northwest flank of the Storegga Slide complex. Seismic and borehole data prove: i) the presence of two new landslides formed prior to Slide W, ii) that mass-transport complexes occurred during the evacuation of sediment oozes, iii) the existence of a series of cracks on the seafloor, denoting modern slope instability. Fluid accumulation in glacial-marine deposits was a primary factor promoting early instability; fluid pipes increase in number below the oldest landslide deposits, with most pipes terminating at their glide planes. Furthermore, mathematical models show that vertically stacked intervals with weak layers, and older landslide deposits, are able to promote further instability. This work thus suggests episodic fluid flow as the primary factor promoting long-term instability near the Storegga Slide complex. As a corollary, we reveal the stability of the continental slope to still be precarious, at present, on the northwest flank of the Storegga Slide.

Canada’s maritime frontier: the science legacy of Canada’s extended continental shelf mapping for UNCLOS

Canada ratified the United Nations Convention on the Law of the Sea (UNCLOS) in 2003. With that ratification is an obligation to submit data and information to the U.N. pertaining to the limits of the country’s extended continental shelf (ECS); the portion of the juridical continental shelf that extends beyond 200 nautical miles. A team of Canadian scientists, managers, and legal experts that included representation from three Federal Departments (Natural Resources Canada, Fisheries and Oceans Canada, and Global Affairs Canada) with additional support from other departments, spent 13 years compiling and acquiring data to provide the scientific evidence to support delineation of Canada’s seaward most maritime limit. The submission has the potential to provide Canada with 2.4 million km2of additional submarine landmass in the Atlantic and the Arctic oceans over which Canada exercises sovereign rights for the purpose of exploring and exploiting its natural resources. Specific information such as the tectonic framework of the continental margin, the geomorphology of the margin and in particular the continental slope, the geologic nature of adjoined ridges, rises, and plateaux, and sediment thickness within adjacent basins are examples of fundamental pieces of geoscientific information needed to substantiate Canada’s outermost maritime limits. This paper highlights a number of segments of Canada’s continental margins to showcase this scientific evidence and how it is applied in the UNCLOS context. In doing so, the paper demonstrates the geologic complexity of Canada’s margins as illustrated in scientific publications that have resulted from these new data collections, while at the same time presenting new scientific evidence and interpretations. This collection of data and information provides a wealth of new knowledge in Canada’s offshore regions. The massive data compilation in the Atlantic led to conception of continental margins, in a source-to-sink scenario, as having an equilibrium base level or graded form, comparable to river systems. Departures from this shape relate to the interplay of sedimentary processes and in particular to those processes that do not fit the source-to-sink paradigm. For example, a significant part of the Atlantic margin is shown to be heavily influenced by along-slope geostrophic currents that generated massive contourite drift deposits. These deposits reflect lateral transport of sediment that had a significant impact on the morphology of the margin. The role of mass transport processes in shaping continental margins is also highlighted, and in particular the collapses of entire segments of the margin were observed. The prominent role mass failure processes play in delivering sediment to the adjacent abyssal plain is also critical in the ECS context. These observations challenge the entrenched notion of a continental margin comprising a shelf, slope, and rise and in particular the concept of the “continental rise”. Prior to 2006, regions of the Arctic Ocean seaward of the Canadian landmass had fewer than 5000 km of seismic reflection data. The massive efforts of Arctic coastal States to map their margins for ECS purposes have led to a leap in technological advances to acquire data in ice-covered seas and have led to a wealth of new geoscientific knowledge. Perhaps foremost amongst this knowledge is demonstration that Canada Basin is indeed a fully developed ocean basin, albeit significantly infilled with sediment. Based on this knowledge and identification of related structures, new realistic tectonic scenarios for opening of the Amerasia Basin are proposed that include a significant component of transform or strike-slip motions. With seismic velocity and rock sample information, the continental nature of Alpha and Mendeleev ridges has been substantiated. Even bathymetric data were lacking in the Arctic and new editions of seafloor maps now support grids of 500 m spacing; although some regions remain sparse. Once thought to be relatively stagnant, sedimentary processes such as found in many ocean basins were discovered in the Arctic Ocean. Evidence of geostrophic currents, sediment mass failures, and deep-sea turbidity current channels were found to be ubiquitous, even in the deepest parts of the Arctic’s basins.

The Vaza-Barris River: A late Quaternary decoupled accumulation-erosion model for rivers of the NE Brazil Atlantic passive margin

Limited insight is available regarding the links between the upstream-downstream fluvial response to climate changes and alluvial-coastal base-level factors in the passive Atlantic margin of tropical South America. This work attempts to characterize the last glacial-interglacial fluvial response of a typical semi-arid Brazilian Northeast River that drains Central-East Brazil's highlands. We integrate the full extension of the Vaza-Barris River alluvial plain record with the alluvial-coastal plain subsurface record. We used digital elevation models, satellite imagery, cores drill description, high-resolution seismic data, optical luminescence, and AMS 14C dating of alluvial terraces Five terrace levels, in the upstream provinces, and three terrace levels in the Coastal-alluvial province were identified. In the continental margin adjacent to the Vaza-Barris river-mouth, incised-valleys in the coastal shelf. Morphosedimentary proxies indicate that periods of aggradation and incision alternated during the late Quaternary due to different inland and eustatic dominant factors. We also estimate that the estuary stored a sediment fill of approximately ∼55 m since the late Pleistocene,. Thus, climate change and sea-level variations differentially controlled the fluvial response and the morphology of the adjacent continental margin along the fluvial system. The decoupled accumulation/erosion upstream-downstream patterns can be used as a model to be tested in fluvial systems of the passive margin of the Brazilian Northeast.

A new species of Attinopora (Bryozoa, Cinctiporidae) from the early Miocene of Atlantic Patagonia

Cinctiporidae is a family of cyclostome bryozoans that ranged from the Paleocene to Recent; however, they also include a questionable record from the Upper Cretaceous of South Africa. Most cinctiporids occur in the Paleocene to Pleistocene strata of New Zealand and the Chatham Islands, with only two living species now found in New Zealand. This study confirms the presence of cinctiporid bryozoans in South America with the description of a new fossil species, Attinopora atlantica sp. nov., based on specimens found in early Miocene deposits of the Monte León Formation, along the Atlantic margin of Argentine Patagonia. Attinopora atlantica sp. nov. differs from the other known species of Attinopora in having a much higher number of zooids per annular ring. The presence of cinctiporids in the early Miocene of Patagonia supports hypothesized biogeographical links between South America and Australasia during the early Neogene.

Palynofloras, palaeoenvironmental change and the inception of the Paleocene Eocene Thermal Maximum; the record of the Forties Fan, Sele Formation, North Sea Basin

The Paleocene–Eocene Thermal Maximum (PETM) has previously been recorded in marine density flow sedimentary rocks of the Forties Member, Sele Formation, North Sea Basin. Two cored well sections with existing δ 13 C records were analysed for their total palynofloras. Using statistically defined microplankton groups and diversity data, the Sele Formation Unit S1 depositional sequence and its maximum flooding surface was identified in both wells. This highlighted that deposition of the Forties Fan complex began significantly earlier than the inception of the PETM in the proximal fan area. Palynofloras from the Central and West Axial fairways of the Forties Fan have previously been used to indicate increased rainfall, erosion and onset of Forties Fan deposition at the PETM inception. However, winterwet floodplain communities typify the coeval East Axial Fairway, whereas the dominance of swamp-derived communities in the West and Central Axial Fairway sediments reflects source palaeogeography overriding the regional winterwet climate signal. Palynofloras reflecting regional increased seasonality and lower moisture availability increase immediately before the PETM CIE onset, but reflect climate warming over the hyperthermal. However, there is no correlation between Forties Fan initiation and the PETM. NE Atlantic margin basin flank uplift in response to synrift volcanism is indicated as the driving mechanism behind Forties Fan inception. Supplementary material : Raw data, DCA graphs for microplankton, pollen and spore data and δ 13 C data for well 22/6-1 are available at https://doi.org/10.6084/m9.figshare.c.6080873

Neural net detection of seismic features related to gas hydrates and free gas accumulations on the northern U.S. Atlantic margin

Bottom-simulating reflections (BSRs) that sometimes mark the base of the gas hydrate stability zone in marine sediments are often identified based on the reverse polarity reflections that cut across stratigraphic layering in seismic amplitude data. On the northern U.S. Atlantic margin (USAM) between Cape Hatteras and Hudson Canyon, legacy seismic data have revealed pronounced BSRs south of the deepwater extension of Hudson Canyon and more subtle ones from offshore Delaware south to Cape Hatteras, where the reflections sometimes follow stratigraphic layering. Using high-resolution seismic data acquired during the 2018 Mid-Atlantic Resource Imaging Experiment and a supervised neural net, we identify seismic features associated with gas hydrates and/or the top of gas between Hudson Canyon and Cape Hatteras. Using seismic attributes especially sensitive to the presence of gas, we train a neural network algorithm on seismic data from an area with strong BSRs and then apply the model to the rest of the data set. The results indicate that gas hydrate and/or shallow free gas are significantly more widespread on the northern part of the USAM than previously known. Seismic indicators of gas extend landward from the 2000 m isobath to the upper continental slope in sectors with (offshore Virginia) and, to a lesser extent, without (offshore New Jersey) pervasive upper slope methane seeps. Higher sand content and intermediate sediment thickness, factors related to the container size and gas charge in a petroleum systems framework, are associated with more robust gas indicators.

New Model of Coastal Evolution in the Ria de Vigo (NW Spain) from MIS2 to Present Day Based on the Aeolian Sedimentary Record

Galician Rias are fluvial valleys that were flooded during the last marine transgression in the Atlantic margin. The study of fossil dunes in the Cies Islands, a small archipelago in the mouth of the one of the rias (Ria de Vigo), allowed us to reconstruct the coastal evolution from the end of the Late Pleistocene to the present day. During this period, sea-level was 100 metres below the present one and the shoreline located about 5–10 kilometres away. About 15,000 years ago, sea-level rise began, radically modifying the coastline. This started with a gradual advance of large dune fields on both sides of the valley. The aeolian accretion continued until the Late Holocene, finishing when the sea reached its present level.