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Coastal dunes are invaluable natural resources that bu er upland areas. Vegetation is key in dune development and stabilization. Dunes form with sufficient wind, sand source, and obstruction; plants are the ideal obstruction. Storms o en erode foredunes and coastal managers replant vegetation to re-establish the necessary obstruction for sand accretion and dune growth. We used a wind tunnel to examine the effect of planting density on bedform formation under constant 18.5 mph (8.25 m/s) winds for 30 min. We filled 1m x 1m x .3 m deep boxes with sand and then planted Ammophila breviligulata plugs in two densities commonly used in management, 12 inches (30.5 cm) and 18 inches (45.7 cm) on center. Sand was supplied by a downwind 1-inch sand bed to mimic backshore transport. We measured the morphology of each plant and used a 3D sensor to record the topography of the bedforms that formed in association with each plant. e bedforms did not vary in volume or basal area as a function of planting density, but biomass was a significant predictor of volume, with larger plants producing larger bedforms. We observed all accretionary bedforms in our low-density treatment, but both erosion and accretion in the high-density treatments potentially due to an inaccurate measure of pre-experiment base height or interactions among neighbors causing greater turbulent kinetic energy with tighter spacing. Bedform height, accretionary or erosive, did not vary by density, row, plant width, or biomass. The bedform shape, measured as the length to width ratio did vary by density; plants in the low-density treatment, despite being morphologically the same, produced bedforms with longer tails. These differences are likely a function of wind back ow and plant interaction interrupting ow, both of which are reduced with a lower planting density. The bedforms created at the onset of planting are thought to carry over through the life of the dune, such that understanding how density affects bedform shape should be considered when making management decisions.

Linear aeolian bedforms are the most abundant bedform type in modern Earth sand seas and are very common in our Solar System. Despite their abundance, the long-term development of these bedforms and its impact upon the resulting sedimentary architecture in the geological record is still poorly understood. The aims of this paper are to study the exposed record of an ancient linear megadune in order to discuss the factors that impact the development and sedimentary architecture of aeolian linear bedforms. The outcrops of the ancient Troncoso Sand Sea (Barremian, Neuquen Basin, Argentina) provide a unique opportunity to access a preserved megadune record with an external body geometry that unequivocally confirms its linear morphology. Architectural analysis of the bedform record reveals significant differences for several aspects of cross-stratified set bodies and bounding surfaces and allows for the identification of three architectural complexes. Insights from deterministic models, analysis of set body relative chronology and distribution suggest that complexes result from distinctive phases in bedform development. It also clearly shows that the megadune’s construction was achieved by expansion from a core, where the oldest deposits are located, and that its development was characterized by sustained growth and strong longitudinal dynamics. Factors that impact the development and architecture of linear bedforms are identified, discussed, and compared to bedforms of transverse dynamics. Finally, a scheme of expected styles of sedimentary architecture for linear bedforms is presented. This case study shows how growth can be a critical factor conditioning linear bedform architecture and indicates how the preservation of certain styles of sedimentary architecture in the geological record may not be as unusual as previously thought., Centro de Investigaciones Geológicas

[Our study present a hydraulic failure model that accounts for the styles of intra‐MTC deformation process. The genetic links identified between MTC and spatially‐focused fluid flow indicate that, as well as disturbing the deep seafloor, MTC may also create important deep‐sea biodiversity hotspots. , Abstract Lateral spread and submarine creep are processes that occur near the headwalls of both terrestrial landslides and submarine mass‐transport complexes (MTCs). Both submarine creep and spread deposits may contain giant (km‐scale) coherent blocks, but their transport processes remain poorly constrained. Here we use seismic reflection data to determine the geometry, scale, and origin of a Late Miocene mass‐transport complex (MTC) located in the Kangaroo Syncline, offshore NW Australia. We show that this large remobilised mass of carbonate ooze is ca. 170–300 m thick and covers an area of at least 1,050 km2. The deposit is defined internally by two distinct seismic facies: (a) large, upward‐tapering blocks (210–300 m thick, 170–210 m wide and 800–1,200 m long) with negligible internal deformation, which decrease in height and spacing along the transport direction (identical, but in situ, seismic facies forms undeformed slope material immediately updip of the deposit headwall); and (b) troughs (160–260 m thick, 190–230 m wide and 800–1,200 m long) comprising moderately deformed strata, which contain ‘v’‐shaped, pipe‐like structures that extend upwards from the inferred basal shear surface to the top surface. The lack of deformation within the blocks, and their correlation to adjacent in situ deposits, suggests they underwent limited transport (ca. 50 m–70 m). The relatively high degree of deformation within the intervening troughs is attributed to the vertical expulsion of fluids and sediment during hydraulic failure of the sediment mass. We present a hydraulic failure model that invokes evacuation of the lower slope by a precursor MTC and which formed the space to trigger the lateral spread. Our study also provides new insights into the genesis and rheology of subaqueous lateral spreads. The genetic links identified between mass wasting and spatially focused fluid flow, as well as disturbing the deep seafloor, indicate that submarine landslides may also create important deep‐sea biodiversity hotspots.]

Thick (>100 m-thick), highly bioturbated storm-influenced shallow-marine deposits are not frequent in the stratigraphic record, but they tend to be common in aggradational to retrogradational successions. Individual storm-event beds have typically low preservation potential in these successions, yet depositional settings are characterized on the basis of storms processes. Here we present a sedimentological study of a thick, bioturbated exhumed succession deposited during the early post-rift stage of the Neuquen Basin (Argentina) and compare its stratigraphic record with examples worldwide, in order to discuss the potential factors controlling the total overprint of storm-event beds during several million years. The Bardas Blancas Formation being 170–220 m thick in the study area is dominated by muddy sandstones and sandy mudstones, and it also includes subordinate proportions of clean sandstones and pure mudstones, collectively representing different environments of a storm-influenced shoreface-offshore system. The offshore transition and proximal offshore strata invariably comprise intensely bioturbated deposits, with only a few preserved HCS-sandstone beds. The unit shows for most of its thickness a long-term aggradational pattern spanning 7–10 Myr and is associated with low riverine influence. By combining the observations and interpretations of the Bardas Blancas Formation with other subsurface and exhumed intensely bioturbated, shallow-marine successions, we dispute the general assumption that these are associated with low frequency or low magnitude of storms. Alternatively, we argue that the long-lived efficiency of benthic fauna on overprinting most if not all the storm-event beds that reached the offshore-transition sector, results from the combination of several factors: deposition in relatively confined marine depocentres, persistent low riverine influence, and long-term aggradational stacking pattern. As these conditions can develop in a variety of basin styles, such as rift, early post-rift, and foreland settings, the recognition of thick, bioturbated successions as the ones discussed here can be used to infer more realistic constrains for depositional models and better predict facies distribution in such storm-influenced systems., Centro de Investigaciones Geológicas

The Pleistocene Mississippi sediment routing system has experienced significant drainage reorganizations in response to Northern Hemisphere glaciation. Geologically recent (

Innovative science benefits from diversity of thought and influence at all waypoints along the scientific journey, from early education to career-length contributions in research and mentorship. Scientific societies, like the Society for Sedimentary Geology (SEPM), steward their innovators and the direction of the science, thereby defining the societal impact and evolution of a discipline. They are uniquely positioned to promote the representation and success of all scientists, including those from minoritized populations, through proactive advocacy, and inclusive mentorship, awards, and leadership. We introspectively review available records of SEPM membership, leadership, awardees, and editorial boards to identify areas for growth and begin a dialogue about how the society and its members can work together to better reflect our community. In the last decade, SEPM has seen a decline in membership, while representation and recognition of scientists from minoritized groups has remained low. Awards and honors have overwhelmingly gone to men, even in the last ten years, and very few women or people of color are in leadership roles. SEPM has recently taken positive steps towards becoming more inclusive (e.g,. the Code of Professional Conduct); however, much more work is needed. We provide recommendations for swift actions that SEPM and its members should undertake for the society to become a diverse, inclusive, and equitable environment where all scientists thrive. The systemic changes needed will take continuous effort, which must be shared by all of us, to build an enduring legacy that we can be proud of.

Conditional facies modeling combines geological spatial patterns with different types of observed data, to build earth models for predictions of subsurface resources. Recently, researchers have used generative adversarial networks (GANs) for conditional facies modeling, where an unconditional GAN is first trained to learn the geological patterns using the original GANs loss function, then appropriate latent vectors are searched to generate facies models that are consistent with the observed conditioning data. A problem with this approach is that the time-consuming search process needs to be conducted for every new conditioning data. As an alternative, we improve GANs for conditional facies modeling by introducing an extra condition-based loss function and adjusting the architecture of the generator to take the conditioning data as inputs, based on progressive growing of GANs. The condition-based loss function is defined as the inconsistency between the input conditioning value and the corresponding characteristics exhibited by the output facies model, and forces the generator to learn the ability of being consistent with the input conditioning data, together with the learning of geological patterns. Our input conditioning factors include global features (e.g. the mud facies proportion) alone, local features such as sparse well facies data alone, and joint combination of global features and well facies data. After training, we evaluate both the quality of generated facies models and the conditioning ability of the generators, by manual inspection and quantitative assessment. The trained generators are quite robust in generating high-quality facies models conditioned to various types of input conditioning information.

Geological facies modeling has long been studied to predict subsurface resources. In recent years, generative adversarial networks (GANs) have been used as a new method for geological facies modeling with surprisingly good results. However, in conventional GANs, all layers are trained concurrently, and the scales of the geological features are not considered. In this study, we propose to train GANs for facies modeling based on a new training process, namely progressive growing of GANs or a progressive training process. In the progressive training process, GANs are trained layer by layer, and geological features are learned from coarse scales to fine scales. We also train a GAN in the conventional training process, and compare the conventionally trained generator with the progressively trained generator based on visual inspection, multi-scale sliced Wasserstein distance (MS-SWD), multi-dimensional scaling (MDS) plot visualization, facies proportion, variogram, and channel sinuosity and width metrics. The MS-SWD reveals realism and diversity of the generated facies models, and is combined with MDS to visualize the relationship between the distributions of the generated and training facies models. The conventionally and progressively trained generators both have very good performances on all metrics. The progressively trained generator behaves especially better than the conventionally trained generator on the MS-SWD, MDS plots, and the facies proportion metrics. The training time for the progressively trained generator is much less (39.2%) than that for the conventionally trained generator. This study demonstrates the superiority of the progressive training process over the conventional one in geological facies modeling, and provides a better option for future GAN-related researches.

The term base-of-scarp is proposed for those submarine deposits controlled by a fault and physically disconnected from their more proximal counterpart located on the footwall, although genetically linked to it. These systems differ from conventional fault-controlled deltas, such as shoal- and Gilbert-type, because they are entirely subaqueous and lack equilibrium morphology — a steady-state in which the system grows in size without altering its shape. We present field examples of faut-controlled base-of-scarp deposits from the Crati Basin and the Messina Strait (southern Italy) consisting of clastic wedges with primary inclined bedding. Beds are composed of immature coarse-grained gravel and sand, lack structures representative of wave-action, and reflect gravity-driven processes such as debris flow, debris fall, and high-density turbidity currents. A diagram for fault-controlled deposits is presented, including their steady- and unsteady-states, and the conceptual conditions under which a base-of-scarp system might evolve into Gilbert-type or shoal-water systems.

Contractional features characterise the toe domain of mass-transport deposits (MTDs). Their frontal geometry is typically classified as frontally-confined or frontally-emergent. However, it remains unclear how frontal emplacement style and contractional strain within an MTD can vary along strike. We use bathymetry and 3D seismic reflection data to investigate lateral variability of frontal emplacement and strain within the toe domain of the Haya Slide in the Makassar Strait. The slide originated from an anticline flank collapse, and the toe domain is characterised by a radial fold-and-thrust belt that reflects southwestwards emplacement. The frontal geometry of the slide changes laterally. In the S, it is frontally-confined, associated with a deep, c. 200 mbsf, and planar basal shear surface. The frontal geometry gradually changes to frontally-emergent in the W, associated with a shallow, c. 120 mbsf, and NE-dipping, c. 3o, basal shear surface. Strain analysis shows c. 8-14% shortening, with cumulative throw of the thrusts that increases along strike westwards from c. 20-40 to c. 40-80 m. We show that even minor horizontal translation of MTDs (c. 1 km) can result in marked lateral variability in frontal geometry and strain within the failed body, which may influence their seal potential in petroleum systems.

Understanding the evolution of submarine channel-lobe systems on salt-influenced slopes is challenging as systems react to seemingly subtle changes in sea-floor topography. The impact of large blocking structures on individual deep-water systems is well documented, but understanding of the spatio-temporal evolution of regionally extensive channel-lobe systems in areas containing modest salt movement is relatively poor. We use 3-D seismic reflection data to map Late Miocene deep-water systems offshore Angola within a c. 450 ms TWTT thick interval. Advanced seismic attribute mapping tied to standard seismic stratigraphic, seismic facies analysis and time-thickness variations, reveals a wide variety and scale of alterations to sediment routing and geomorphology. Five seismic units (SU1-SU5) record a striking change in sediment pathways and structural relief within eight evolving minibasins. Observations within these units include gradual channel diversion through lateral migration during times of relatively high structural growth, opposed to abrupt channel movement via avulsion nodes during times of relatively high sediment accumulation. The results of the study led to the development of conceptual models for influences on deep-water systems during characteristic structural development in the contractional salt domain, these stages being initiation, maturity, and decay. The initiation stage contains small-segmented folds with mostly system bypass, while the maturity stage contains linked high-relief structures and prominent minibasins leading to ponding, large-scale diversion and localized slump deposits derived from nearby highs (SU1-SU3). The less studied final stage of topographic decay contains decreased length and relief of structures leading to a more complicated array of channel-lobe bypass, diversion, ponding and subtle control on avulsion nodes (SU4-SU5). These observations contribute to the understanding of channel-lobe stacking, routing and control over transition zones in tectonically active areas, ultimately improving our general understanding of the effects of significant through to subtle sea-floor topography, and can be a guide in other salt-influenced basins.

Short communication on international disparities in open access practices of the Earth Sciences community

Mass flows evolve longitudinally during emplacement, but can also vary laterally by forming discrete flow cells with different rheological states separated by shear zones. Despite being documented in many field and subsurface studies, the initiation, translation, and cessation of the flow cells remain unclear. We use five, high-quality post-stack time-migrated (PSTM) 3D seismic reflection datasets to investigate the evolution of flow cells in a seabed mass transport complex (MTC), the Gorgon Slide, on the Exmouth Plateau, offshore NW Australia. The slide originated from a 30 km-wide, NE-SW trending headwall scarp that dips steeply (c. 30o) seaward, and was translated to the NW over a basal-shear surface that deepens downslope (up to 500 m below seafloor). The slide is dominated by chaotic seismic facies with discrete packages of coherent reflectors, which is interpreted as a debrite that carried megaclasts (c. 0.05-1 km-long) derived from the headwall domain. The morphology and orientation of the basal-shear surface focused the pathway of the slide, resulting in clustering of megaclasts in proximal parts of the translation domain. The megaclasts cluster became an obstacle to flow, which resulted in the formation of two flow cells (Cells A and B) separated by a longitudinal shear zone. The interaction between the two cells is recorded by sinuous shear bands within, and ridges on the top surface of, the slide. Along the longitudinal shear zone, the shear bands and ridges of Cell A were dragged downslope, due to Cell A impeding the movement of Cell B. This interaction suggests that Cell B travelled faster, and/or further, than Cell A, due to the absence of any flow obstacles. The abrupt cessation of Cell A is recorded by positive seabed relief, whose amplitude decreases updip. The transport processes of the Gorgon Slide show how entrainment and abrasion of megaclasts induced velocity perturbations during emplacement causing: (i) changes to the flow rheology, and (ii) initiation and cessation of flow cells. A better understanding of how flow cells evolve during MTCs transport may help to refine modelling of the potential impact of MTCs on submarine structures (e.g. pipelines, cables, etc.).

Mudstone studies that use a large spacing (>5km) between datapoints provide little insight into the architecture and depositional process variability at kilometre scale. This often leads to the assumption that mudstones are laterally homogenous at kilometre and sub-kilometre scales. To better understand the lateral variability of mudstones at kilometre scale, the Mancos Shale in the eastern part of Utah, USA (Book Cliffs) was examined. The Mancos Shale was deposited on a storm-dominated, low-angle shallow-marine ramp along the western shoreline of the Western Interior Seaway. Here, a combined petrographic, sedimentological and sequence stratigraphic approach was used to analyse two 43-47 m thick time-equivalent sections at a 1.6km across-strike spacing. Oriented samples were collected at 2m intervals through each measured section. Five 5m – 12m thick coarsening-upward parasequences were identified. The lower four parasequences are interpreted to be the distal deposits of the updip Aberdeen Member and the fifth parasequence is interpreted to be the basal distal parasequence of the overlying Kenilworth Member. Depositional processes including turbidity currents, linked debris flow/turbidity currents, wave-enhanced sediment-gravity flows, hyperpycnal flows and suspension settling have been identified from the samples collected. The products of these flows (beds) stack to form bedsets which display an upward increase in the lateral continuity of beds and a coarsening-upward trend. This is interpreted to reflect a change from occasional current-deposited beds with depositional breaks to more frequent varying energy conditions with fewer hiatuses. These bedsets show considerable spatial and temporal variability which is interpreted to be a result of subtle seafloor topography. Based on the bedset and parasequence stacking patterns and the temporal variability of depositional processes, the lower four parasequences are split into two parasequence sets. The lower parasequence set is interpreted to be storm-wave-dominated with fluvial influence and the upper parasequence set lacks the fluvial influence.

A large portion of freshwater and sediment is exported to the ocean by a small number of major rivers. Many of these megarivers are subject to substantial anthropogenic pressures, which are having a major impact on water and sediment delivery to deltaic ecosystems. Due to hydrodynamic sorting, sediment grain size and composition vary strongly with depth and across the channel in large rivers, complicating flux quantification. To account for this, we modified a semi‐empirical Rouse model, synoptically predicting sediment concentration, grain‐size distribution, and organic carbon (%OC) concentration with depth and across the river channel. Using suspended sediment depth samples and flow velocity data, we applied this model to calculate sediment fluxes of the Irrawaddy (Ayeyarwady) and the Salween (Thanlwin), the last two free‐flowing megarivers in Southeast Asia. Deriving sediment‐discharge rating curves, we calculated an annual sediment flux of urn:x-wiley:jgrf:media:jgrf21236:jgrf21236-math-0001 Mt/year for the Irrawaddy and urn:x-wiley:jgrf:media:jgrf21236:jgrf21236-math-0002 Mt/year for the Salween, together exporting 46% as much sediment as the Ganges‐Brahmaputra system. The mean flux‐weighted sediment exported by the Irrawaddy is significantly coarser (D84 = 193 ± 13 μm) and OC‐poorer (0.29 ± 0.08 wt%) compared to the Salween (112 ± 27 μm and 0.59 ± 0.16 wt%, respectively). Both rivers export similar amounts of particulate organic carbon, with a total of urn:x-wiley:jgrf:media:jgrf21236:jgrf21236-math-0003 Mt C/year, 53% as much as the Ganges‐Brahmaputra. These results underline the global significance of the Irrawaddy and Salween rivers and warrant continued monitoring of their sediment flux, given the increasing anthropogenic pressures on these river basins.

Submarine fans are formed by sediment-laden flows shed from continental margins into ocean basins. Their morphology represents the interplay of external controls such as tectonics, climate, and sea-level with internal processes including channel migration and lobe compensation. However, the nature of this interaction is poorly understood. We used physical modelling to represent the evolution of a natural-scale submarine fan deposited during an externally forced waxing-to-waning sediment supply cycle. This was achieved by running five successive experimental turbidity currents with incrementally increasing then decreasing sediment supply rates. Deposits built upon the deposits of earlier flows and the distribution of erosion and deposition after each flow was recorded using digital elevation models. Initially, increasing sediment supply rate (waxing phase) led to widening and deepening of the slope channel, with basin-floor deposits compensationally stepping forwards into the basin, favouring topographic lows. When sediment supply rate was decreased (waning phase), the slope-channel filled as the bulk of the deposit abruptly back-stepped due to interaction with depositional topography. Therefore, despite flows in the waxing and waning phases of sediment supply having nominally identical input conditions (i.e. sediment concentration, supply rate, grain size etc.), depositional relief led to development of markedly different deposits. This demonstrates how external controls can be preserved in the depositional record through progradation of the basin floor deposits but that internal processes such as compensational stacking progressively obscure this signal through time. This evolution serves as an additional potential mechanism to explain commonly observed coarsening- and thickening-upwards lobe deposits, with abrupt transition to thin fine-grained deposits. Meanwhile within the slope channel, external forcing was more readily detectable through time, with less internally driven reorganisation. This validates many existing conceptual models and outcrop observations that channels are more influenced by external forcing whilst internal processes dominate basin floor lobe deposits in submarine fans.

International audience; Sediment flux signals from source to sink in foreland basins preserve a record of tectonics, sea level and climate through erosion and sedimentation. However, longitudinal sediment transport often occurs in foreland basins, thus removing part of the orogenic material flux from foreland basin records. Here we use mass balance calculation and stratigraphic simulations of sediment fluxes for the Taiwan orogen to provide an order of magnitude estimate of how much orogenic material may bypass a foreland basin. Our results indicate a significant, potentially more than 50%, mismatch between sediment volume currently preserved in the basin and the amount of material presumably eroded from the orogen since the onset of collision in Taiwan. This suggests either a significant overestimation of average erosion rates over the period concerned with orogenic development of Taiwan, or it supports previous paleogeographic work suggesting that longitudinal sediment transport in the paleo-Taiwan Strait served as a major bypass conduit of importance for the establishment of a steady state orogen. We identify candidate submarine topography in the South China Sea that may preserve Taiwan's missing erosional mass.

High-resolution bathymetry, seismic reflection, and piston core data from a submarine channel on the western Niger Delta slope demonstrate that thick, coarse-grained, amalgamated sands in the channel thalweg/axis transition to thin, fine-grained, bedded sands and muds in the channel margin. Radiocarbon ages indicate that axis and margin deposits are coeval. Core data show that bed thickness, grain size, and deposition rate strongly decrease with increasing height above channel thalweg and/or distance from channel centerline. A 5 times decrease in bed thickness and 1–2 ψ decrease in grain size are evident over a 20 m elevation change (approximately the elevation difference between axis and margin). A simplified in-channel sedimentation model that solves vertical concentration and velocity profiles of turbidity currents accurately reproduces the vertical trends in grain size and bed thickness shown in the core data set. The close match between data and model suggests that the vertical distribution of grain size and bed thickness shown in this study is widely applicable and can be used to predict grain size and facies variation in data-poor areas (e.g., subsurface cores). This study emphasizes that facies models for submarine channel deposits should recognize that grain-size and thickness trends within contemporaneous axis-margin packages require a change in elevation above the thalweg. The transition from thick-bedded, amalgamated, coarser-grained sands to thin-bedded, nonamalgamated, finer-grained successions is primarily a reflection of a change in elevation. Even a relatively small elevation change (e.g., 1 m) is enough to result in a significant change in grain size, bed thickness, and facies.

*----- NOTE: This paper has been accepted in Quaternary Science Reviews as of June 8, 2020 -----* Deep sediment cores from long-lived lake basins are fundamental records of paleoenvironmental history, but the power of these reconstructions has often been limited by poor age control. Uranium-thorium (U-Th) dating has the potential to fill a gap in current geochronological tools available for such sediment archives. We present our systematic approach to U-Th date carbonate-rich sediments from the ~100 m drill core from Lake Junín, Peru. The results form the foundation of an age-depth model spanning ~700 kyrs. High uranium concentrations (0.3--4 ppm) of these sediments allow us to date smaller quantities of material, giving us the opportunity to improve sample selection by avoiding detrital contamination, the greatest factor limiting the success of previous U-Th dating efforts in other lake basins. The dates from 174 analyses on 55 bulk carbonate samples revealed significant scatter that could not be resolved with traditional isochrons, suggesting that at least some of the sediments have not remained closed systems. To understand the source of noise in the geochronological data, we first apply threshold criteria that screen samples by their U/Th ratio, reproducibility, and d234U initial value. We then compare these results with facies types, trace element concentrations, carbonate and total organic carbon content, color reflectance, mineralogy, and ostracode shell color to investigate the causes of open system behavior. We find that the greatest impediment to U-Th dating of these sediments is not detrital contamination, but rather post-depositional remobilization of uranium. After examining U-Th data in these contexts, we identify samples that have likely experienced the least amount of alteration, and use dates from those samples as constraints for the age-depth model. Our work has several lessons for future attempts to U-Th date lake sediments, namely that the samples geologic context is equally important as the accuracy and precision of analytical measurements when determining the age of sample materials. In addition, we caution that significant geologic scatter may remain undetected if not for labor intensive tests of reproducibility achieved through replication. As a result of this work, the deep sediment core from Lake Junín is the only continuous record in the tropical Andes spanning multiple glacial cycles that is constrained entirely by independent radiometric dates.

A sediment core spanning the last ~50 ka from Lake Junín (Peru) in the tropical Andes reveals abrupt climatic events on a centennial-millennial time scale. These events, which involved the near-complete disappearance of glaciers below 4700 masl in the eastern Andean cordillera and major reductions in the level of Peru’s second largest lake, occurred during the abrupt warmings recorded in Greenland ice cores known as Dansgaard-Oeschger (DO) interstadials. Lake Junín is the first record to document the response of Andean glaciers to serial DO events, and also reveals the magnitude of the hydroclimatic disruptions in the highest reaches of the Amazon Basin that were caused by a weakening of the South American summer monsoon during abrupt arctic warming. Ongoing warming in the Arctic could lead to significant reductions in the precipitation-evaporation balance in the tropical Andes with deleterious effects on the sustainability of a densely populated region of South America.

The impact of carbon capture and storage (CCS) in mitigating anthropogenic emissions of greenhouse gases is potentially great, but its success is strongly dependent on identifying suitable geological storage sites. One of the key uncertainties in this regard is the degree of compartmentalization of the target storage horizon. Many studies have examined reservoir compartmentalization in oil and gas fields and its implications to hydrocarbon production, but few have looked at compartmentalization from the perspective of CCS storativity. Using case studies from the oil and gas industry, this paper examines the predictability of reservoir compartmentalization and the techniques used to assess it. It then focusses on stratigraphic compartmentalization in saline aquifers, a major category of potential carbon storage sites, examining in particular the Triassic Bunter Sandstone Formation of the UK North Sea. It is clear that the analysis of stratigraphic, seismic and fluid compositional data can provide early evidence of reservoir compartmentalization. The available data indicate that the Bunter Sandstone has a low risk of stratigraphic and structural compartmentalization. However, the presence of compartments in oil and gas fields is often confirmed only once well production data are available. As such, though the broad likelihood of compartmentalization in a CCS site can be forecasted, understanding its exact nature may be dependent on injection data.

Spatial point-pattern analyses (PPAs) are used to quantify clustering, randomness, and uniformity of the distribution of channel belts in fluvial strata. Point patterns may reflect end-member fluvial architecture, e.g., uniform compensational stacking and avulsion-generated clustering, which may change laterally, especially at greater scales. To investigate spatial and temporal changes in fluvial systems, we performed PPA and architectural analyses on extensive outcrops of the Cretaceous John Henry Member of the Straight Cliffs Formation in southern Utah, USA. Digital outcrop models (DOMs) produced using unmanned aircraft system-based stereophotogrammetry form the basis of detailed interpretations of a 250-m-thick fluvial succession over a total outcrop length of 4.5 km. The outcrops are oriented roughly perpendicular to fluvial transport direction. This transverse cross-sectional exposure of the fluvial system allows a study of the system’s variation along depositional strike. We developed a workflow that examines spatial point patterns using the quadrat method, and architectural metrics such as net sand to gross rock volume (NTG), amalgamation index, and channel-belt width and thickness within moving windows. Quadrat cell sizes that are ~ 50% of the average channel-belt width-to-thickness ratio (16:1 aspect ratio) provide an optimized scale to investigate laterally elongate distributions of fluvial-channel-belt centroids. Large-scale quadrat point patterns were recognized using an array of four quadrat cells, each with 237× greater area than the median channel belt. Large-scale point patterns and NTG correlate negatively, which is a result of using centroid-based PPA on a dataset with disparately sized channel belts. Small-scale quadrat point patterns were recognized using an array of 16 quadrat cells, each with 21× greater area than the median channel belt. Small-scale point patterns and NTG correlate positively, and match previously observed stratigraphic trends in the fluvial John Henry Member, suggesting that these are regional trends. There are deviations from these trends in architectural statistics over small distances (hundreds of meters) which are interpreted to reflect autogenic avulsion processes. Small-scale autogenic processes result in architecture that is difficult to correlate between 1D datasets, for example when characterizing a reservoir using well logs. We show that 1D NTG provides the most accurate prediction for surrounding 2D architecture.

Over the last decade, an increasing number of studies have used lake sediment DNA to trace past landscape changes, agricultural activities or human presence. However, the processes responsible for lake sediment formation and sediment properties might affect DNA records via taphonomic and analytical processes. It is crucial to understand these processes to ensure reliable interpretations for “palaeo” studies. Here, we combined plant and mammal DNA metabarcoding analyses with sedimentological and geochemical analyses from three lake-catchment systems that are characterised by different erosion dynamics. The new insights derived from this approach elucidate and assess issues relating to DNA sources and transfer processes. The sources of eroded materials strongly affect the “catchment-DNA” concentration in the sediments. For instance, erosion of upper organic and organo-mineral soil horizons provides a higher amount of plant DNA in lake sediments than deep horizons, bare soils or glacial flours. Moreover, high erosion rates, along with a well-developed hydrographic network, are proposed as factors positively affecting the representation of the catchment flora. The development of open and agricultural landscapes, which favour the erosion, could thus bias the reconstructed landscape trajectory but help the record of these human activities. Regarding domestic animals, pastoral practices and animal behaviour might affect their DNA record because they control the type of source of DNA (“point” vs. “diffuse”).

Submarine slopes prograde via accretion of sediment to clinoform foresets, and degrade in response to channel or canyon incision, or mass-wasting processes. The timescales over which progradation and degradation occur, and the large-scale stratigraphic record of these processes, remain unclear due poor age constraints in subsurface-based studies, and areally limited exposures of exhumed systems. We here integrate 3D seismic reflection and borehole data to study the geometry and origin of ancient slope canyons developed within Late Mesozoic strata of the Måløy Slope, offshore Norway. Slope degradation and canyon incision commenced during the late Kimmeridgian, coincident with the latter stages of rifting. Later periods of canyon formation occurred during the Aptian-to-Albian and Albian-to-Cenomanian, during early post-rift subsidence. The canyons are straight, up to 700 m deep and 10 km wide on the upper slope and die-out downdip onto the lower slope. The canyons trend broadly perpendicular to and crosscut most of the rift-related normal faults, although syn-filling fault growth locally helped to preserve thicker canyon-fill successions. The headwalls of the oldest (late Kimmeridgian) canyons are located at a fault-controlled shelf edge, where younger canyons overstep this fault, which was inactive when they formed, extending across the paleo-shelf. Downslope, Aptian-to-Albian canyons either erode into the older, late Kimmeridgian-to-Barremian canyon-fills, forming a complicated set of unconformities, or in the case of the Albian-to-Cenomanian canyons, die-out into correlative conformities. Boreholes indicate that the canyon bases are defined by sharp, erosional surfaces, across which we observe an abrupt upward shift from shallow- to deep-marine facies (i.e. late Kimmeridgian canyons), or deep marine to deep marine facies (Aptian-to-Albian and Albian-to-Cenomanian canyons). Missing biostratigraphic zones indicate the canyons record relatively protracted periods (c. 2-17 Myr) of structurally enhanced slope degradation and sediment bypass, separated by >10 Myr periods of deposition and slope accretion. The trigger for slope degradation is unclear, but it likely reflects basinward tilting of this tectonically active margin, enhanced by incision of the slope by erosive sediment gravity-flows. The results of our study have implications for the timescales over which large-scale slope progradation and degradation may occur on other tectonically active slopes, and the complex geophysical and geological record of these processes. We also show that canyon formation can cause large volumes of margin-derived sediment to bypass proximal sub-basins within rifted terrains, an important process not currently captured by marine rift-basin tectono-stratigraphic models.

Local low-density basement anomalies are an important part of a rift basin’s inherited structural framework that can influence basin stratigraphy. Large granitic intrusions can cause local alterations in the basement’s density and often spatially correlate with fault-bounded highs (blocks) or convex-shaped regional flexural highs due to their isostatic responses. We investigate the influence of local low-density basement anomalies on the deposition of the fluviodeltaic Fell Sandstone Formation in the northern Pennine rift basin, northern England. The integration of a variety of data sources has enabled regional correlation of the Fell Sandstone Formation with basinal, time-equivalent stratigraphy. Spatial variations in the preserved facies, palaeocurrent and sedimentological characteristics of the Fell Sandstone are documented and the most important controls upon these variations are considered. Along the eastern margin of the granite-cored, flexural Cheviot High, the Fell Sandstone fluvial system is locally confined by the High leading to preservation of ~98% well-sorted sandstone. In the Northumberland-Solway Basin, the Fell Sandstone fluvial system is less confined, leading to sediment dispersal and downstream reduction of net sand. Based on this study, proximity to the dominant clastic sediment source, regional subsidence variations and basin palaeotopography are considered important controls upon spatial variations across the Fell Sandstone Formation. Regional subsidence variations and basin palaeotopography in the northern Pennine Basin are influenced by the Cheviot High and the Maryport-Stublick-Ninety Fathom fault system, which bounds the Northumberland-Solway Basin and the Lake District and Alston Blocks. Both the Cheviot High and the Lake District and Alston Blocks are structures caused by the isostatic responses of local granite-induced low-density basement anomalies. This study shows that flexural highs can act as baffles to fluvial systems, locally confining them and leading to the deposition of high quality reservoir. Fault-bounded highs can act as barriers and their deep bordering half-graben troughs can act as confines for clastic sediment, leading to starvation further down system.

Speleothems can offer insights into terrestrial life because their formation is critically dependent on soil-microbial ecosystems. Here we report the wide distribution of miniature paleo-speleothems from the ~635 Ma Doushantuo cap dolostone in South China in order to understand the recovery of terrestrial life after the terminal Cryogenian Marinoan snowball Earth glaciation. The cap dolostone was deposited during the initial transgression following deglaciation, but subsequently developed extensive karstic cavities or sheet-cracks when the cap dolostone was brought to the phreatic zone during post-glacial rebound. The sheet-cracks were filled with multiple generations of cements, including isopachous dolomite formed in the phreatic zone and speleothems formed in the vadose zone. The paleo-speleothems are millimeters-centimeters in size and include stalactites, stalagmites, helictites, moonmilk, flat crusts, and botryoids. The speleothems were silicified by subsequent hydrothermal processes, which also precipitated the chalcedony and quartz in the sheet-cracks and occurred before a renewed transgression in which ~632 Ma shales overlying the cap dolostone were deposited. The wide distribution of paleo-speleothems indicates the presence of an active soil-microbial ecosystem in the earliest Ediacaran Period and in the aftermath of the Marinoan snowball Earth.

IN REVIEW IN "FRONTIERS IN EARTH SCIENCE" (30 Aug 2019). Constraining the avulsion dynamics of rivers and submarine channels is essential for predicting the distribution and architecture of sediment, organic matter and pollutants in alluvial, deltaic, and submarine settings. Submarine channels are well known to be more aggradational than rivers, and aggradation of the channel, levee, and floodplain are key forcing mechanisms for avulsion. We create a geometric channel-belt framework relating channel, levee, and floodplain stratigraphy that allows comparative analysis of avulsion dynamics for rivers and submarine channels. We utilize 52 channel cross sections within this framework to provide avulsion criteria for submarine channels and how they differ from rivers. Superelevation and a new channel-floodplain coupling metric are the two key parameters that control channel-belt thickness in both rivers and submarine channels. While rivers can only superelevate an amount equivalent to 1 channel depth above the floodplain prior to avulsion, submarine channels are more stable during aggradation, with superelevation values commonly >3 channel depths. Channel-floodplain coupling in rivers is weak, with floodplain aggradation being negligible compared to channel aggradation. However, floodplain aggradation is more significant for submarine channels, resulting in stronger channel-floodplain coupling. The combination of enhanced superelevation and strong channel-floodplain coupling results in channel-belts for submarine channels that can be as thick as ~ 10 channel depths, while fluvial channel belts are limited to 2 channel depths. We interpret that levee aggradation and thus superelevation is promoted by turbidity current overspill. Floodplain aggradation is also influenced by overspill and hemipelagic sedimentation. As a submarine channel reaches aggradation that would cause a river to avulse, the submarine channel is stable because the flow has far less potential energy to create an avulsion because turbidity currents have ~50x less density contrast between flow and ambient fluid as compared to rivers. The Amazon channel showcases this stability, with a channel belt that is ~ 5 channel-depths thick for more than 400 streamwise km, more than twice the aggradation that a river is capable of.

Submarine fans are important components of continental margins; they contain a stratigraphic record of environmental changes and host large accumulations of oil and gas. The grain size and volume of sediment supply to fans is thought to control the heterogeneity of deep-water deposits; predicting spatial variability of sandy and muddy deposits is an important applied challenge in the characterization of fans. Here, we use DionisosFlow stratigraphic-forward models to evaluate the sensitivity of submarine-fan deposition to a range of grain sizes, with corresponding diffusion coefficients ranging from 10 to 100 km2/kyr for coarse sand to silt/clay, and discharges. In general, finer grains are transported farther in our models because they have larger diffusion coefficients. Coarser grains typical of a sand-rich fan tend to pile up and compensationally stack at the mouth of a proximal feeder channel. Finer grains tend to be distributed across the model domain; however, finer load resulted in fewer channel avulsions because finer sediment did not build topography as high as coarser sediment. Increasing sediment-gravity-flow discharge resulted in a thicker depositional system; however, relatively coarse sediment piled up at the mouth of the feeder channel, which created a slope that promoted basinward sediment transport. Our modeling results can be applied to predict the overall geometry, stacking, and grain-size distribution of submarine fans. Improved understanding of grain-size and discharge controls also informs interpretation of the stratigraphic record of submarine fans. For example, outcrop observations of heterogeneity and compensational stacking of depocenters can be quantitatively related to changing boundary conditions, namely changes in the caliber and overall supply of sediment delivery to deep-water basin margins.

Mass-transport complexes (MTCs) dominate many salt-influenced sedimentary basins. Commonly in such settings, halokinesis is invoked as the primarily trigger for MTC emplacement. Despite being very well-imaged in seismic reflection data, we know little of how MTCs vary in terms of their sedimentological character, which may relate to their provenance, or their triggers. We use high-quality 3D seismic reflection and well data to study MTCs preserved in a salt-confined, supra-canopy minibasin in the northern Gulf of Mexico to interpret six MTCs that together constitute >60% of the minibasin-fill volume. We define three main tectono-sedimentary phases in the development of the minibasin: (1) initial minibasin subsidence and passive diapirism, during which time deposition was dominated by relatively large-volume MTCs (c. 25 km3) derived from the shelf-edge or upper slope; (2) minibasin margin uplift and steepening, during which time small-volume MTCs (c. 20 km3), derived from the shelf-edge or upper slope, were emplaced; and (3) diapir burial and late-stage active diapirism, during which time very small volume MTCs (c. 1 km3) were emplaced, locally derived from minibasin flanks or their roofs. We present a generic model that emphasises the dynamic nature of minibasin evolution, and how MTC emplacement relates to halokinetic sequence development. Although based on a data-rich case study, our model may be applicable to other MTC-rich, salt-influenced sedimentary basins.

Studies of near-seabed datasets show that salt tectonics controls the distribution and architecture of deep-water reservoirs in many salt-influenced basins. It is typically difficult, however, to study the distribution and stratigraphic evolution of depositional systems preserved at deeper, economically significant depths, reflecting poor seismic imaging of steeply dipping strata flanking high-relief salt structures. 3D seismic and borehole data from the Santos Basin, offshore Brazil allow us to identify a range of depositional elements that form the building blocks of three main tectono-stratigraphic phases. During the first phase, channel systems and lobes were confined within updip minibasins and to the hangingwalls of salt-detached faults. During the second phase, channel systems and lobes filled updip minibasins to bypass sediment downslope, with coarse clastic deposition then occurring in downdip minibasins, >100 km from the coeval shelf margin. Syndepositional seafloor relief caused: (i) channel system deflection and diversion around salt-cored highs; (ii) channel system uplift and rotation on the flanks of rising salt structures; (iii) lateral and frontal confinement of channel systems. During the final phase, rising salt walls dissected previously deposited deep-water systems, with MTCs deposition becoming increasingly important. Our results have important implications for post-salt prospectivity in the Santos Basin and other salt-influenced sedimentary basins, with a range of reservoirs and trapping styles present in this underexplored interval. More specifically, we show that large volumes of clastic sediment were not trapped behind the ‘Albian Gap’, a salt-controlled depocenter dominating the north-western basin margin, but were instead delivered further basinward.

This paper addresses the Jurassic–Cretaceous stratigraphic evolution of fore-arc deposits exposed along the west coast of the northern Antarctic Peninsula. In the South Shetland Islands, Upper Jurassic deep-marine sediments are uncomformably overlain by a Lower Cretaceous volcaniclastic sequence that crops out on Livingston, Snow and Low islands. U-Pb zircon ages are presented for the upper Anchorage Formation (153.1 ± 1.7 Ma) and the Cape Wallace granodiorite of Low Island (137.1 ± 1.7 Ma) as well as 40Ar/39Ar ages of 136–139 Ma for Low Island andesites. Data are also presented for a U-Pb age of 109.0 ± 1.4 Ma for the upper volcanic succession of Snow Island. In combination with published stratigraphy, these data provide a refined chrono- and litho-stratigraphic framework for the deposits herein referred to as the Byers Basin. Tentative correlation is explored with previously described deposits on Adelaide and Alexander islands, which could suggest further continuation of the Byers Basin towards the south. We also discuss possible correlation of the Byers Basin with the Larsen Basin, a sequence that shows the evolution of foreland to back-arc deposits more or less contemporaneously with the fore-arc to intra-arc evolution of the Byers Basin.

Accepted open-access publication available at: https://doi.org/10.1029/2019GL085524 Barrier island response to sea-level rise depends on their ability to transgress and move sediment onto and behind the barrier, either through flood-tidal delta deposition, or via overwash. Our understanding of these processes over decadal or longer timescales, however, is limited. Here we use a recently developed barrier island model (BRIE) to better understand the interplay between tidal dynamics, overwash fluxes, and sea-level rise on barrier coasts and barrier island stratigraphy. Model results suggest that in micro-tidal environments with large alongshore sediment transport fluxes, tidal inlets are ephemeral and migrate rapidly. These conditions lead to effective deposition of flood-tidal deltas and allow inlets to constitute most of the landward sediment flux. Whether barrier islands can survive sea-level rise depends on the combined landward sediment flux from overwash and flood-tidal delta deposition, likely making barrier islands with artificially stabilized inlets (via jetty construction or maintenance dredging) more vulnerable to sea-level rise.

The Maastrichtian-Danian transgression was one of the most extensive Atlantic-derived marine incursions in Patagonia. This study examines its stratigraphic record and origin in the Magallanes-Austral Basin, revealing an interplay of sedimentation, tectonism, and base-level changes, which contribute to our understanding of foreland basin dynamics. We present a multidisciplinary approach from a relatively poorly documented sector (51°38’-53°50’S) of the basin. This approach includes facies and provenance analysis, palynology, sequence stratigraphy, and U-Pb geochronology. These techniques enable us to evaluate the role of climate, tectonics, and eustasy on the transgression, as well as providing insight into the growth of the Southern Patagonian Andes. A first shallowing-upward cycle (late Campanian to late Maastrichtian) is represented by the transition from outer shelf and upper slope deposits (Fuentes and Tres Pasos formations) to shoreface and deltaic environments (Rocallosa and Dorotea formations), favoured by high erosion rates in the fold-thrust belt and eustatic sea-level drop. A subsequent deepening-upward cycle (late Maastrichtian to Paleocene) records the Atlantic transgression, manifested by estuarine deposits in an incised valley (uppermost Dorotea Formation) and deep-water turbidites (Chorrillo Chico Formation and Cabo Naríz beds). Palynological results suggest a temperate palaeoclimate (~6-17°C) during the Maastrichtian-Danian, which agrees with significant cooling of the South Atlantic Ocean at this time. Therefore, relative climatic optima are not a driver of marine ingression. The stratigraphic and tectonic evolution of the succession studied suggests that flexural and dynamic subsidence promoted marine incursion into the Magallanes-Austral Basin. Provenance data indicate sediment input to the basin from the Southern Patagonian Batholith, Rocas Verdes Basin remnants, Tobífera Formation, and metamorphic terranes exposed in the hinterland of the Southern Patagonian Andes during the early Maastrichtian. However, by the Paleocene, sediments derived from the hinterland had been structurally dammed during basinward propagation of the fold-thrust belt.

Pyroclastic density currents (PDCs) are a life-threatening volcanic hazard. Our understanding and hazard assessments of these flows rely on interpretations of their deposits. The occurrence of stratified layers, cross-stratification, and bedforms in these deposits has been assumed as indicative of dilute, turbulent, supercritical flows causing traction-dominated deposition. Here we show, through analogue experiments, that a variety of bedforms can be produced by denser, aerated, granular currents, including backset bedforms that are formed in waning flows by an upstream-propagating granular bore. We are able to, for the first time, define phase fields for the formation of bedforms in PDC deposits. We examine how our findings impact the understanding of bedform features in outcrop, using the example of the Pozzolane Rosse ignimbrite of the Colli Albani volcano, Italy, and thus highlight that interpretations of the formative mechanisms of these features observed in the field must be reconsidered., In this study, Smith and colleagues employ analogue experiments to show the controlling parameters on sediment bedforms in pyroclastic density current deposits. The findings are applied and validated on natural deposits.

The presence of sand injections has proven to enhance the likelihood of hydrocarbon traps within siliciclastic successions. Through the development of large interconnected networks of sills and dykes, sand injection complexes provide a volume of porous and permeable rocks within the low permeability host units. Overall, the formation of sand injection complexes requires extensive fracturing and hydrofracturing, which can be particularly pronounced when sand injections are coupled with brittle tectonic deformation. In exceptional circumstances, this process may threaten the integrity of the reservoir top seal thereby preventing further hydrocarbon accumulation. Studying exceptional exposures along the coastal area of Santa Cruz in California, we report evidence for top seal failure associated with injection episodes. Two distinct sand injection episodes are proposed. A first event, datable to Late Miocene, allowed for large volumes of sand to be emplaced within the top-seal units followed by accumulation of hydrocarbons within newly injected sandstones. Later, a series of brittle tectonic events, associated with San Andreas/San Gregorio Fault System, caused remobilisation and accumulation of sand along newly formed fault planes. This combination of pervasive brittle deformation and sandstone injection along fault structures, as this detailed case study documents, can disrupt the integrity of a host unit, leading to the overall failure of a top seal and leakage of hydrocarbons.

Submarine landslides (slides) are ubiquitous on continental margins. They can pose a major hazard by triggering tsunami and damaging essential submarine infrastructure. Slide volume, which is a key parameter in hazard assessment, can change after initiation through substrate and/or water entrainment. However, the erosive capacity of slides is uncertain. Here, we quantify slide erosivity by determining the ratio of deposited (Vd) to initially evacuated (Ve) sediment volumes. Slides that gain volume through erosion = Vd/Ve>1. We apply this method to a large (500 km3), seismically imaged slide offshore NW Australia, and review Vd/Ve ratios for other large slides worldwide. Nine of the 11 slides have Vd/Ve>1 (median value=2), showing that emplaced volumes increased after initial failure. The Gorgon Slide is the most erosive slide currently documented (Vd/Ve=13), possibly reflecting its passage across a highly erodible carbonate ooze substrate. This new approach to quantifying erosion is important for hazard assessments as substrate-flow interactions control slide speed and run-out distance. The variations in slide volume also have important implications for submarine infrastructure impact assessments, including more robust tsunami modelling.

During the Last Glacial Maximum (LGM; ~23,000 to 19,000 years ago or ka) and through the last deglaciation, the Great Basin physiographic region in the western United States was marked by multiple extensive lake systems, as recorded by proxy evidence and lake sediments. However, temporal constraints on the growth, desiccation, and timing of lake highstands remain poorly constrained. Studies aimed at disentangling hydroclimate dynamics have offered multiple hypotheses to explain the growth of post-LGM lakes; however, a more robust understanding is currently impeded by a general paucity of spatially and temporally robust data. In this study, we present new data constraining the timing and extent of lake highstands at three post-LGM age pluvial lakes: Lake Newark, Lake Surprise, and Lake Franklin. This data is used in concert with previously published data for these basins and others from the Northern Great Basin including Lakes Bonneville, Chewaucan, and Lahontan to compare the timings of lake growth and decay over a large spatial scale and constrain how regional hydroclimate evolved through the deglaciation.

The term hydrothermal dolomitization (HTD) has been widely applied to describe fault-controlled dolomitization. HTD can occur at any depth from a range of different fluids, even though it is often associated with the burial realm. To date, many studies have failed to identify a source of fluids for HTD, often invoking “deep-seated brines”. Consequently, there is a gap in our knowledge as to the likely source of water and magnesium for the formation of hydrothermal dolostone. The Middle Cambrian Mount Whyte Formation displays exceptionally preserved m- to km-wide non-stratabound dolostone bodies with stratabound terminations within a bioturbated mudstone facies. Dolomitization is fabric-destructive and shows a wide range of crystal sizes (40-800 µm). Texturally, dolomite crystals can be subdivided into different phases that are all post-dated by bedding-parallel stylolites. This cross-cutting relationship suggests a shallow depth of dolomitization (< 1 km). All the dolomite types exhibit a narrow range of both negative δ18Odolomite (-15.08‰ to -17.78‰) and seawater-like δ13Cdolomite values (-1.04‰ to 0.43‰) and enriched Fe and Mn concentrations. Both the temperature and calculated δ18Owater of the dolomitizing fluids display a wide range of values depending on their location within the dolostone bodies, from 130 to 235oC and -3 to +6 ‰, respectively. The δ18Owater is substantially heavier than Middle Cambrian seawater, and correspondingly, 87Sr/86Sr ratios are elevated (av. 0.7106) compared to the host limestone (av. 0.7094). These lines of evidence are suggestive of very hot, crustal-related dolomitizing fluids. The REE+Y profiles observed in both RD1 and RD2 (positive Eu anomaly, enriched LREE and depleted HREE) are typical of ultramafic-hosted fluids. Together with the presence of a subduction complex below the WCSB (>10 km), identified from lithoprobe data, this suggests that magnesium-rich fluids were sourced from these Paleoproterozoic subducted serpentinites. The liberation of magnesium was most likely through interactions between serpentinites and CO2 enriched fluids created during either metasomatism or recycling of seawater. The presence of enriched Ti and Yb concentrations and cogenetic relation between dolomite and quartz corroborates this idea. The approximate depth of the subducted serpentinites is also in good agreement with the interpreted depth of the fluid, inferred from the measured fluid temperature. To transport such deep-seated fluids to the shallow sub-surface required vertical, permeable conduits such as faults. Since dolomitization coincided with rifting, fluids could have rapidly ascended into the Mount Whyte Formation by seismic events along crustal-scale faults which are now largely obscured by thrusting. The shallow depth of dolomitization would also explain the pervasive dolomitization of mud-dominated facies, as replacement occurred whilst there was sufficient porosity and permeability retained in these rocks. The very hot, high salinity of the dolomitizing fluids and the high reactive surface area in the mudstone helped to accelerate dolomitization. In summary, this study describes an alternative model for the source of Mg for HTD, providing a solution to the problem of mass balance between the volumes of observed dolostone formed by HTD from hot, saline, so-called crustal fluids. Such a model could be widely applicable to other settings that are underlain by ancient oceanic crust.

Seafloor topography affects the sediment gravity flows that interact with it. Understanding this interaction is critical for accurate predictions of sediment distribution and paleogeographic or structural reconstructions of deep-water basins. The effects of seafloor topography can be seen from the bed scale, through facies transitions toward intra-basinal slopes, to the basin scale, where onlap patterns reveal the spatial evolution of deep-water systems. Basin-margin onlap patterns are typically attributed to allogenic factors, such as sediment supply signals or subsidence rates, with few studies emphasizing the importance of predictable spatio-temporal autogenic flow evolution. This study aims to assess the autogenic controls on onlap by documenting onlap styles in the confined Eocene-to-Oligocene deep-marine Annot Basin of SE France. Measured sections, coupled with architectural observations, mapping, and paleogeographical interpretations, are used to categorize onlap styles and place them within a generic stratigraphic model. These observations are compared with a simple numerical model. The integrated stratigraphic model predicts that during progradation of a deep-water system into a confined basin successive onlap terminations will be partially controlled by the effect of increasing flow concentration. Initially thin-bedded low-density turbidites of the distal lobe fringe are deposited and drape basinal topography. As the system progrades these beds become overlain by hybrid beds and other deposits of higher-concentration flows developed in the proximal lobe fringe. This transition is therefore marked by intra-formational onlap against the underlying and lower-concentration lobe fringe that drapes the topography. Continued progradation results in deposition of lower-concentration deposits in the lobe off-axis, resulting in either further intra-formational onlap against the lobe fringe or onlap directly against the hemipelagic basin margin. Basinal relief is gradually reduced as axial and higher-volume flows become more prevalent during progradation, causing the basin to become a bypass zone for sediment routed down-dip. This study presents an autogenic mechanism for generating complex onlap trends without the need to invoke allogenic processes. This has implications for sequence-stratigraphic interpretations, basin subsidence history, and forward modeling of confined deep-water basins.

With the increasing use of detrital geochronology data for provenance analyses, we have also developed new constraints on the age of otherwise undateable sedimentary deposits. Because a deposit can be no older than its youngest mineral constituent, the youngest defensible detrital mineral age defines the maximum depositional age of the sampled bed. Defining the youngest “defensible” age in the face of uncertainty (e.g., analytical and geological uncertainty, or sample contamination) is challenging. The current standard practice of finding multiple detrital minerals with indistinguishable ages provides confidence that a given age is not an artifact; however, we show how requiring this overlap reduces the probability of identifying the true youngest component age. Barring unusual complications, the principle of superposition dictates that sedimentary deposits must get younger upsection. This fundamental constraint can be incorporated into the analysis of depositional ages in sedimentary sections through the use of Bayesian statistics, allowing for the inference of bounded estimates of true depositional ages and uncertainties from detrital geochronology so long as some minimum age constraints are present. We present two approaches for constructing a Bayesian model of deposit ages, first solving directly for the ages of deposits with the prior constraint that the ages of units must obey stratigraphic ordering, and second describing the evolution of ages with a curve that represents the sediment accumulation rate. Using synthetic examples we highlight how this method preforms in less-than-ideal circumstances. In an example from the Magallanes Basin of Patagonia, we demonstrate how introducing other age information from the stratigraphic section (e.g., fossil assemblages or radiometric dates) and formalizing the stratigraphic context of samples provides additional constraints on and information regarding depositional ages or derived quantities (e.g., sediment accumulation rates) compared to isolated analysis of individual samples.

The strata of arid continental basins commonly comprise evaporitic sediments deposited in sabkha settings combined with clastic sediments derived from aeolian, fluvial and/or lacustrine settings. The sedimentary character of these mixed successions and the degree to which evaporitic strata influence their composition, both contribute towards the economic potential of the evaporitic and the clastic component. This work describes, interprets, and provides predictive models for the preserved deposits of sabkha settings that interact with contemporaneous and competing arid continental environments, using the Permian Cedar Mesa Sandstone Formation of the Colorado Plateau, USA, as a case study. Detailed analysis of the sediments reveal a number of distinct sedimentary successions in which the interplay of clastic and evaporitic strata describe deposition in continental sabkha-influenced settings that gradually become drier with time. Each succession is separated from the subsequent one by a sudden ‘wetting’ of the setting in which sediments were deposited. The drying upwards successions show two distinct assemblages, an aeolian erg-margin sabkha, and a lacustrine-margin sabkha. For both settings, the preserved strata demonstrate that the intercalation of clastic and evaporitic sediments on the small (facies) scale is prevalent to such a degree that it would have economic implications for the exploitation of both resources. However, in the lacustrine marginal sabkha, the interbedding of evaporitic and clastic sediments at a larger (association) scale is significantly rarer, with dominantly evaporitic strata giving way to dominantly clastic strata abruptly in upward succession. These observations are considered in the context of climatic variation to construct models of the interplay between climate, clastic and evaporitic sediment supply, and accommodation space. The models provide a means of subsurface prediction where sediments are deposited in similar settings, and the observations provide important new insight for the interpretation and exploitation of economic continental sabkha sediments in the subsurface

Mass transport complexes (MTCs) are one of the most sedimentologically and seismically distinctive depositional elements in deep-water depositional systems. Seismic reflection data provide spectacular images of their structure, size, and distribution, although a lack of borehole data means there is limited direct calibration between MTC lithology and petrophysical expression, or knowledge of how they may act as hydrocarbon reservoir seals. In this study, we evaluate the lithological and petrophysical properties, and seismic characteristics of three deeply-buried (>2300 m/7546 ft below the seabed), Pleistocene MTCs in the northern Gulf of Mexico. We show that: (i) MTC lithology is highly variable, comprising a mudstone-rich debrite matrix containing large (4.5 km3/1.08 mi3), deformed, sandstone-rich blocks; (ii) MTCs are generally acoustically faster and are more resistive than lithologically similar (i.e. mudstone-dominated) slope deposits occurring at a similar burial depth; (iii) MTC velocity and resistivity increase with depth, likely reflecting an overall downward increase in the degree of compaction; and (iv) the lowermost 15-30 m (49-98 ft) of the MTCs, which represent the basal shear zones, are characterised by relatively high P-wave velocity and resistivity values, likely due to shear-induced over-compaction. We conclude that detailed analysis of petrophysical data, in particular velocity and resistivity logs, may allow recognition of MTCs in the absence of high-quality seismic reflection data, including explicit identification of the basal shear zone. Furthermore, the relatively thick basal shear zone, rather than the overlying and substantially thicker MTC itself, may form the primary permeability barrier and thus seal for underlying hydrocarbon accumulations.

The most popular model for submarine unconfined lobate deposits has the following attributes: (1) a single feeder channel that delivers sediment, (2) a set of distributary channels present only in the proximal part of the lobate body, and (3) unchannelized tabular deposits present in the middle and distal part of the lobate deposit. This model has become a standard to guide interpretation of outcrop and subsurface examples of submarine lobate deposits. In this contribution, three well imaged subsurface lobate deposits are described that display three markedly different morphologies, all of which differ from the “standard” model. All three lobate examples are buried by less than 150m of muddy sediment and imaged with high resolution 3D reflection seismic data of similar quality and resolution. Distinctively different distributary channel patterns are present in two of the examples, and no distributaries are imaged in a third example. We conclude that if channels are not imaged, it is because channels are not present. The different distributary channel patterns are interpreted to have resulted from different processes: (1) a lobate deposit that is pervasively channelized by many distributaries that have avulsed from numerous nodes is interpreted to result from mud-rich, stratified, turbulent flows ; (2) an absence of distributaries in a lobate deposit is interpreted to result from collapse of mud-poor, turbulent flows remobilized from littoral drift; and (3) a lobate deposit with only a few, long, straight distributaries without avulsions is interpreted to be dominated by debris flows (laminar flows) . Reconciling 3D seismic morphologies with observations of channels, scours, and amalgamation zones in outcrops is problematic. It is concluded from this study that, when characterizing unconfined deep water deposits, multiple models with significant differences in predicted permeability structure should be considered.

Carbonate rocks are important archives of past ocean conditions as well as hosts of economic resources such as hydrocarbons, water, and minerals. Geologists typically perform compositional analysis of grain, matrix, cement and pore types in order to interpret depositional environments, diagenetic modification, and reservoir quality of carbonate strata. Such information can be obtained primarily from petrographic analysis, a task that is costly, labor-intensive, and requires in-depth knowledge of carbonate petrology and micropaleontology. Recent studies have leveraged machine learning-based image analysis, including Deep Convolutional Neural Networks (DCNN), to automate description, classification and interpretation of thin sections, subsurface core images and seismic facies, which would accelerate data acquisition and reproducibility for these tasks. In carbonate rocks, this approach has been applied primarily to recognize carbonate lithofacies, and no attempt has been made to individually identify and quantify various types of carbonate grains, matrix, and cement. In this study, the applicability and performance of DCNN-based object detection and image classification approaches are assessed with respect to carbonate compositional analysis. The training data comprised of more than 13,000 individually labelled objects from nearly 4000 carbonate petrographic images. The dataset is grouped into six and nine different classes for the image classification and object detection tasks, respectively. Even with a small and relatively imbalanced training set, the DCNN was able to achieve an F1 score of 92% for image classification and 84% mean precision for object detection by combining one-cycle policy, class weight, and label mixup-smoothing methods. This study highlights the inefficiency of image classification as an approach to replicating human description and classification of carbonate petrography. By contrast, DCNN-based object detection appears capable of approaching human speed and accuracy in the area of carbonate petrography because it is able to individually locate and identify different carbonate components with greater cost-efficiency, speed, and reproducibility than conventional (human) petrographic analysis.

The aim of this work is to identify main impact factors affecting variations in the geomorphology of the Mariana Trench which is the deepest place of the Earth, located in the west Pacific Ocean: steepness angle and structure of the sediment compression. The Mariana Trench presents a complex ecosystem with highly interconnected factors: geology (sediment thickness and tectonics including four plates that Mariana trench crosses: Philippine, Pacific, Mariana, Caroline), bathymetry (coordinates, slope angle, depth values in the observation points). To study such a complex system, an objective method combining various approaches (statistics, R, GIS, descriptive analysis and graphical plotting) was performed. Methodology of the research includes following clusters: R programming language for writing codes, statistical analysis, mathematical algorithms for data processing, analysis and visualizing diagrams, GIS for digitizing bathymetric profiles and spatial analysis. The statistical analysis of the data taken from the bathymetric profiles was applied to environmental factors, i.e. coordinates, depths, geological properties sediment thickness, slope angles, etc. Finally, factor analysis was performed by R libraries to analyze impact factors of the Mariana Trench ecosystem. Euler-Venn logical diagrams highlighted similarities between four tectonic plates and environmental factors. The results revealed distinct correlations between the environmental factors (sediment thickness, slope steepness, depth values by observation points, geographic location of the profiles) affecting Mariana Trench morphology. The research demonstrated that coding on R language provides a powerful and highly effective statistical tools, mathematical algorithms of factor analysis to study ocean trench formation., 10 pages, 12 figures

Present-day catchments adjacent to sedimentary basins may preserve geomorphic elements that have been active through long intervals of time. Relicts of ancient catchments in present-day landscapes may be investigated using mass-balance models and can give important information about upland landscape evolution and reservoir distribution in adjacent basins. However, such methods are in their infancy and are often difficult to apply in deep-time settings due to later landscape modification. The southern Barents Sea margin of N Norway and NW Russia is ideal for investigating source-to-sink models, because it has been subject to minor tectonic activity since the Carboniferous, and large parts have eluded significant Quaternary glacial erosion. A zone close to the present-day coast has likely acted as the boundary between basin and catchments since the Carboniferous. Around the Permian-Triassic transition, a large delta system started to prograde from the same area as the present-day largest river in the area, the Tana River, which has long been interpreted to show features indicating that it was developed prior to present-day topography. We performed a source-to-sink study of this ancient system in order to investigate potential linkages between present-day geomorphology and ancient deposits. We investigated the sediment load of the ancient delta using well, core, two-dimensional and three-dimensional seismic data, and digital elevation models to investigate the geomorphology of the onshore catchment and surrounding areas. Our results imply that the present-day Tana catchment was formed close to the Permian-Triassic transition, and that the Triassic delta system has much better reservoir properties compared to the rest of Triassic basin infill. This implies that landscapes may indeed preserve catchment geometries for extended periods of time, and it demonstrates that source-to-sink techniques can be instrumental in predicting the extent and quality of subsurface reservoirs. publishedVersion

Pyroclastic currents are catastrophic flows of gas and particles triggered by explosive volcanic eruptions. For much of their dynamics, they behave as particulate density currents and share similarities with turbidity currents. Pyroclastic currents occasionally deposit dune bedforms with peculiar lamination patterns, from what is thought to represent the dilute low concentration and fluid‐turbulence supported end member of the pyroclastic currents. This article presents a high resolution dataset of sediment plates (lacquer peels) with several closely spaced lateral profiles representing sections through single pyroclastic bedforms from the August 2006 eruption of Tungurahua (Ecuador). Most of the sedimentary features contain backset bedding and preferential stoss‐face deposition. From the ripple scale (a few centimetres) to the largest dune bedform scale (several metres in length), similar patterns of erosive‐based backset beds are evidenced. Recurrent trains of sub‐vertical truncations on the stoss side of structures reshape and steepen the bedforms. In contrast, sporadic coarse‐grained lenses and lensoidal layers flatten bedforms by filling troughs. The coarsest (clasts up to 10 cm), least sorted and massive structures still exhibit lineation patterns that follow the general backset bedding trend. The stratal architecture exhibits strong lateral variations within tens of centimetres, with very local truncations both in flow‐perpendicular and flow‐parallel directions. This study infers that the sedimentary patterns of bedforms result from four formation mechanisms: (i) differential draping; (ii) slope‐influenced saltation; (iii) truncative bursts; and (iv) granular‐based events. Whereas most of the literature makes a straightforward link between backset bedding and Froude‐supercritical flows, this interpretation is reconsidered here. Indeed, features that would be diagnostic of subcritical dunes, antidunes and ‘chute and pools’ can be found on the same horizon and in a single bedform, only laterally separated by short distances (tens of centimetres). These data stress the influence of the pulsating and highly turbulent nature of the currents and the possible role of coherent flow structures such as Görtler vortices. Backset bedding is interpreted here as a consequence of a very high sedimentation environment of weak and waning currents that interact with the pre‐existing morphology. Quantification of near‐bed flow velocities is made via comparison with wind tunnel experiments. It is estimated that shear velocities of ca 0·30 m.s−1 (equivalent to pure wind velocity of 6 to 8 m.s−1 at 10 cm above the bed) could emplace the constructive bedsets, whereas the truncative phases would result from bursts with impacting wind velocities of at least 30 to 40 m.s−1., Sedimentology, 66 (5), ISSN:0037-0746, ISSN:1365-3091

The Essaouira-Agadir Basin (EAB) of Morocco contains the most extensive exposure of Aptian to Lower Albian strata onshore the NW African Atlantic Margin. This paper documents the first high-resolution, multi-disciplinary stratigraphic approach for the Aptian to Lower Albian on the NW African Atlantic Margin. Previous biostratigraphic work almost exclusively relied on long-distance correlation of ammonoids to the Mediterranean – Caucasian Realm. Recent biostratigraphic work has questioned some of the previous interpretations, highlighting significant faunal endemism and complications with correlation to other key Aptian sections. This study focuses on 5 key sections: Tiskatine, Id Amran, Assaka, and DSDP 416/370. Distribution of ammonoids, foraminifera, and calcareous nannofossils are reported from a bed-by-bed collection made at Tiskatine. The analysis of foraminiferal and calcareous nannofossil assemblages enable correlation to standard zonation schemes; but also highlights the urgent need of revision and future work on the integration of these schemes across disciplines. The study, further, includes δ13Ccarb, δ13Corg, and total organic carbon (TOC) data that is compared to reference material from the Vocontian Basin. The combined litho-, bio-, chemo-, and sequence stratigraphic analysis establishes a robust chronostratigraphic framework for regional and super-regional correlations and a type section is proposed for the Aptian of NW Africa at Tiskatine.

Traditional sequence stratigraphic models provide limited understanding of internal complexity and variability when applied to mixed siliciclastic-carbonate strata accumulated in tectonically active settings. Coeval Lower Pleistocene (Gelasian) shallow-marine, mixed siliciclastic-carbonate depositional wedges accumulated within an active piggy-back basin along the southern Italy fold-and thrust-belt are characterized by similar internal architecture of sequences but different stacking patterns. In particular, four coastal wedges (up to 30 m thick each), just a few kilometers (~2 km) apart from each other, show aggradational versus progradational stacking patterns related to their location within a deforming piggy-back basin. In all the studied sections, mixed siliciclastic-carbonate strata form isolated sedimentary wedges organized into three vertically stacked transgressive–regressive sequences bounded by sharp flooding surfaces. Aggradational versus progradational internal architecture results from (1) local syndepositional compressive and/or extensional tectonics controlling differential uplift and subsidence, and (2) sediment supply characterized by a combination of intrabasinal and extrabasinal siliclicastics and carbonates. Aggradation occurs in areas showing a balance between both accommodation and sediment supply, and siliciclastic and carbonate fractions. Progradation is typical of supply-dominated areas located close to the active anticline, and dominated by the carbonate fraction. The present work documents the local variability of stratal stacking patterns and sediment supply (siliciclatic-carbonate ratio). We highlight the limitations of using sequence architectures and systems tracts for base-level changes and basin reconstructions in tectonically active settings. It is of great importance not only to correctly interpret the stacking pattern, but also to increase our understanding of the type of sediment (siliciclastic versus carbonate) and sedimentation rate, sedimentation loci, and subsurface prediction.

Submerged flanks of volcanic islands are prone to hazards including submarine landslides that may trigger damaging tsunamis and fast-moving sediment-laden seafloor flows (turbidity currents) that break critical seafloor infrastructure. Small Island Developing States are particularly vulnerable to these hazards due to their remote and isolated nature, small size, high population densities and weak economies. Despite their vulnerability, few detailed offshore surveys exist for such islands, resulting in a geohazard ‘blindspot’, particularly in the South Pacific. Understanding how these hazards are triggered is important; however, pin-pointing specific triggers is challenging as most studies have been unable to link continuously between onshore and offshore environments, and focus primarily on large-scale eruptions with sudden production of massive volumes of sediment. Here we focus on a situation where volcanic sediment supply produces a long-term elevation over a “normal” regime, which is more similar to the long-term elevated sediment production cases at many sites (volcanic or not) where human-induced vegetation change over-supplies sediments to coastal margins. We address these issues by integrating the first detailed (2 m x 2 m) bathymetry data acquired from Tanna Island, Vanuatu with a combination of terrestrial remote sensing data, onshore and offshore sediment sampling, and documented historical events. Mount Yasur on Tanna has experienced low-magnitude Strombolian activity for at least the last 600 years. We find clear evidence for submarine landslides and turbidity currents, yet none of the identified triggers are related to major volcanic eruptions, in contrast to conclusions from several previous studies. Instead we find that cascades of non-volcanic events (including outburst floods with discharges of >1000 m3/s, and tropical cyclones), that may be separated by decades, are more important for preconditioning and triggering in chronic sediment oversupply regimes such as at Tanna. We conclude with a general model for how submarine landslides and turbidity currents are triggered at volcanic and other heavily eroding mountainous islands. Our model highlights the often-ignored importance of outburst floods, non-linear responses to lands-use and climatic changes, and the complex interactions between a range of coastal and tectonic processes that may overshadow volcanic regimes.