Basin Floor Research Articles

Giant sediment-wave field and supercritical flows in a distally steepened ramp, Fort Payne Formation (Lower Mississippian), Kentucky–Tennessee, U.S.A.

ABSTRACT Sediment waves are common in confined to unconfined settings on modern marine slopes and basin floors worldwide. Their morphology and stratal patterns show that many of them migrate upslope and upflow, a characteristic thought to record Froude-supercritical flow conditions associated with sediment gravity flows and density cascades. Few sediment waves of this type have been observed in the ancient rock record. This study reports the discovery of a giant (> 20,000 km2) sediment-wave field in Lower Mississippian carbonates and shales of the Fort Payne Formation in Tennessee and Kentucky, U.S.A. Sediment waves are present in the clinothem slopes and basin floor of a distally steepened ramp as seismic-scale bedforms ranging from 100 to 700 m long and 15 to 50 m high. Dominant facies include crinoidal shales, packstones, and rudstones. Many of the beds are sharp-based and graded, indicating sediment-gravity-flow deposition. Upslope-inclined rudstones (backsets) and wavy beds with upflow and downflow laminae are common and indicate supercritical flow conditions. These observations and interpretations are in stark contrast to previous interpretations of crinoidal bioherms and Waulsortian-type mounds. Basin physiography, a cool-water heterozoan carbonate factory and coastal upwelling were key factors in establishing a rapidly prograding ramp characterized by high rates of sediment production and basinward shedding. Sediment gravity flows and density cascades transported crinoidal grains downslope and entrained crinoids that inhabited the slope. Flows frequently reached Fr-supercritical flow conditions that led to the formation of sediment waves similar to those on modern marine slopes. This sediment-wave field is one of the first to be documented in the ancient rock record, and its extent is enormous. The near absence of other reported ancient examples must be due to misinterpretation (mounds, slumps) and the problem of observational scale and resolution. Sediment waves are often larger than outcrops. Lack of recognition of sediment waves in subsurface seismic sections is probably due to misinterpretation and insufficient resolution. Perhaps this study demonstrates the need for revisiting and updating existing facies models of carbonate-sediment transport and depositional processes across slopes and basin floors.

Evolution of Sequence Stratigraphy and Paleogeography, Case Study: M2 Member of the Muara Enim Formation

Sequence stratigraphy related to accommodation space as an area of potential sediment accumulation that is influenced by fluctuations in sea level and subsidence of the basin floor. Paleogeography, on the other hand, is the study of physical geographic features and their evolution throughout geological periods. The aim of this work is to shed light on the relationship between paleogeographic evolution and sequence stratigraphy, as well as coal accumulation in the South Sumatra Basin. The method used are geophysical logs and cores analysis to determine the system tracts, types of system tracts, and stratigraphic sequences, lithofacies and sedimentary facies analysis, paleogeographic analysis using modified single-factor and multi-factor and them mapped using IDW as a geostatistical method. The results indicate that the study area comprises four system tracts, namely TST-1, HST-1, TST-2 and HST-2. In TST-1 and TST-2, the rate of peat formation is balanced with the rate of accommodation space formation, resulting in continuous and very thick coal accumulation. In HST-1 and HST-2, the rate of accommodation space formation exceeds the rate of peat formation, leading to continuous coal accumulation that is quite thick to very thick. Sequence 1 consists of lagoon and tidal/mouth/distal bar paleogeographic unit with sand/shale ratio range 0.217 to 0.247. Sequence 2 consists of lagoon paleogeographic units with sand/shale ratio range 0.046 to 0.05.

Modeling glaciation of the Hellas Basin, Mars, for a ‘cold and icy’ late Noachian Paleoclimatic scenario

Global climate models (GCM) predict snow accumulation/glaciation on the Hellas basin eastern rim, where Amazonian glacial landforms are observed. We explore GCM results for Late Noachian-Early Hesperian higher atmospheric pressure/higher obliquity/faint young sun conditions, assess accumulation rates, and use these as input to an ice sheet model. We assess ice sheet growth, thickness, basal temperatures, basal melting water volumes, flow/sliding-ice velocities and the fate of basin floor glacial ice/meltwater. We conclude that significant volumes of glacial ice (with shear-induced basal melting) could have flowed down the basin wall and onto the basin floor, covering the majority with glacial ice. Late Noachian water budgets of up to 1000 m global equivalent layer (GEL) and Hellas floor ice sequestration are implied. Subsequent emplacement of Hesperian volcanic plains superposed on the ice may have caused melting (contact/deferred) and deformation (loading-induced flow/diapirism), potentially accounting for several observed basin floor geologic units.

River-fed basin-fill and hyperpycnites in an island-arc setting: The Silurian–Devonian Kekexiongkuduke Formation from Western Junggar, China

Sediments from land are primarily transported into basins through hyperpycnal flow, which plays a significant role in the process of basin filling. Various models of hyperpycnites have been proposed. This study examines a Silurian–Devonian basin-fill sequence in NW China to validate existing models and presents a visually compelling case demonstrating the process of basin filling through flood-dominated river discharge.The Utubulak Member of the Kekexiongkuduke Formation can be subdivided into three parts, representing basin floor, slope and shelf environments, collectively representing a regressive basin fill sequence. The lower part consists of flood-related turbidites contain or encompass material of terrestrial and marine origin, their sustained and pulsed velocity structures are similar to river discharge. These turbidites may result from basinal hyperpycnal flow or retrogressive failures of the shelf-edge (hyperpycnal) delta. The middle (slope deposits) contains bi-graded hyperpycnite bed interpreted commonly attributed to deposition by river floods exhibiting the classical waxing-waning configuration. Additionally, fine-grained deposits resulting from river-generated, dilute hyperpycnal or hypopycnal plumes are observed interbedded with the basin turbidites or slope background deposits. In the upper part, the presence of thick-bedded sandstones indicates that sustained hyperpycnal flow can transport sands to the shelf-edge/shelf, facilitating deep-water sand delivery. The vertical distribution of the various flood-related facies in basin floor, slope and shelf strata emphasize the complexity of hyperpycnites in different settings, and particularly highlighting challenges associated with their recognition in basin deposits.The investigated succession accumulated in an island-arc setting which provided a favorable condition for a river-fed turbidite system to develop. The narrow shelf facilitated transport of sediments by hyperpycnal flows directly into the basin, while erosion of high mountains promoted a high sediment supply for hyperpycnal flow. And a river-fed turbidite system commonly developed during the late stages of basin filling.

Sources and composition of organic matter as a tool for understanding the complex variation in paleoenvironments and the connectivity of an epicontinental basin: The Miocene in the northern Pannonian Basin

Epicontinental basins are extremely prone to major paleogeographic changes, and this will directly affect any organic matter (OM) preserved in the depositional record. In this study the Middle–Late Miocene successions in the northern Pannonian Basin System were investigated via sedimentological, petrographic, and geochemical analyses of cores from the Danube Basin to reveal the interplay of factors driving the character of the OM. In the late Middle Miocene (~12.3 Ma), the Central Paratethys Sea maintained normal marine salinity, with dysoxic bottom waters in a distal basin floor environment rich in aquatic OM. The last rifting phase followed during the Late Miocene and led to formation of the deep Lake Pannon. Like seawater, the brackish lake water still also contained sulfate. These open lacustrine deposits (~11.6–10.0 Ma) reveal OM sourced from submerged/floating macrophytes and algae, and humid conditions are indicated by the preponderance of deciduous trees and shrubs on shores. The study identifies hybrid event beds (HEBs) on Lake Pannon's floor (~10.0–9.3 Ma), with currents redepositing mud and OM, resulting in similarities between the Middle Miocene and Late Miocene successions. Turbidite deposition (~9.3–9.0 Ma) from the paleo-Danube induced a shift in OM, replacing algae with terrestrial input. Complete isolation from the main water masses of Lake Pannon (~9.0–8.9 Ma) altered its sources of OM, transitioning from algae to macrophytes, and caused a drop in salinity, likely associated with a humidity peak. The subsequent deltaic dominance (~8.9–8.6 Ma) features well-developed topset lakes, swamps, and floodplain forests, reflecting warm temperate to subtropical climates. The Middle–Upper Miocene deposits studied here are source rocks with fair to very good richness and poor to fair generative potential, and contain kerogen types III and IV, while type II is rare. The rapid paleoenvironmental changes observed over the order of ~100 kyr caused the complete switching of OM type and delivery, giving an indication of the complexity of epicontinental basins.

Interpreting environments of deposition from facies analysis of outcrop versus seismic reflection data: A cautionary tale from the Mount Messenger Formation, Taranaki Basin (New Zealand)

The lower part of the Mount Messenger Formation, which crops out along the North Taranaki coast (North Island, New Zealand), is widely regarded to display classic examples of exhumed basin floor fan strata. This interpretation is supported by numerous publications on the sedimentary facies and depositional environments inferred for these strata, which are exposed in coastal cliff exposures about 20 m high with limited lateral extent. Consequently, for almost three decades, this succession has served as an analogue and training ground for geoscientists investigating the features of basin floor fan deposits and their reservoir characteristics. Here, we bring together seismic stratigraphy and seismic geomorphology of 2D and 3D seismic reflection datasets, as well as photogrammetric models based on images collected using uncrewed aerial vehicle (UAV) drones from selected locations along the outcrop belt to challenge this paradigm. We analyzed seismic reflection data in an area immediately offshore and down-dip of the strata exposed in the coastal outcrop and found no objective criteria for submarine fan depositional elements based on accepted seismic stratigraphic criteria. Furthermore, mapping of seismic reflectors revealed large submarine channel systems (up to 3 km wide and up to 200 m deep) within the lower part of the Mount Messenger Formation. Submarine channel depositional elements (less than 250 m wide and 25 m thick) are also observed to incise through the outcrops, but they are generally below seismic resolution. In the context of the regional geology, we conclude that the lower Mount Messenger Formation accumulated as continental slope sediments cross-cut by channels rather than as basin floor fans. This study issues a cautionary tale about applying facies analysis to outcrop with limited 3D exposure to interpret sedimentary environments. The spatial distribution of facies and architectural elements viewed in seismic data are invaluable for testing the veracity of facies interpretations.

Sedimentary facies analysis of a thin-bed-dominated turbidite succession in the Miocene Temburong Formation, Kampung Bebuloh, Labuan Island, Malaysia

Thin-bedded turbidites are important hydrocarbon-bearing reservoirs in many mature fields throughout the world. The type of turbidite depositional setting strongly influences vertical and horizontal continuity of the reservoir. However, distinguishing between lobe and levee associated thin-bedded turbidites remains challenging due to their generally similar facies characteristics. This study aims to contribute some insights to this problem by conducting a detailed bed-scale facies analysis on the Early Miocene Temburong Formation exposed at Kampung Bebuloh, Labuan Island, Malaysia, which may uncover features that can help in differentiating between both depositional types. Six facies are recognized in the Temburong Formation, which are interpreted as low density turbidites (F1–F4), hybrid event beds (F5), and sustained turbidites (F6). Detailed facies and ichnology analysis reveal features which are consistent with a lobe fringe deposit rather than levee-associated environment interpretation, including tabular bed geometries, presence of hybrid event beds, and the absence of thick-bedded channel-fill sandstones. Five facies associations are identified and interpreted as representing sub-environments within an overall lobe depositional setting. A diverse trace fossil assemblage, comprising the Nereites ichnofacies is consistent with a deep marine environment. Further identification of the Paleodictyon and Nereites sub-ichnofacies indicates a distal turbidite system setting, most likely lobe fringe. Based on the thick accumulation of FA2 and FA3 and no distinct observable vertical trend, the Early Miocene Temburong Formation in Labuan is interpreted as turbidites deposited at the fringes of lobe complexes rather than a single lobe fringe. Earlier works into the Temburong Formation in SW Labuan proposed a middle slope to proximal basin floor setting where the thin-bedded intervals were interpreted as potentially representing either levee deposits or the fringes of confined lobe deposits. Conversely, the Temburong Formation at Kampung Bebuloh exhibits characteristics of an unconfined lobe setting, suggesting an evolutionary change in depositional conditions over time.

Contemporary formation of ice-wedge pseudomorphs during the expansion of a thermokarst lake in Old Crow Flats, Yukon, Canada

Ice-wedge pseudomorphs (IWPs) are thermokarst structures that form by the secondary infilling of cavities left by the slow melting of ice wedges. Contemporary IWP formation in periglacial environments informs our understanding of past processes and dynamics implied by their presence in the stratigraphic record. However, contemporary IWPs are seldom studied as they are difficult to locate and observe due to the general lack of surface expression and because they can deform with time or be confused with sediment wedges. This study presents detailed information about the morphology and soil composition of IWPs that formed beneath a thermokarst lake in Old Crow Flats, northern Yukon (Canada), and provides the first conceptual model of lacustrine IWP development. Seven IWPs were unearthed along a transect perpendicular to a former eroding lakeshore in a recently (2019), partially drained lake basin. The IWPs were between 76 cm and 122 cm high and had varying morphologies, generally forming triangles pointing down or T shapes. They had a much higher organic matter content and were composed of slightly coarser sediment than their host sediment, characteristics that were shared by basin floor surface sediment found in the near-shore zone (<15 m) of the former lake. Within five meters of the former shoreline, some troughs showed pronounced subsidence due to the melting of remnant wedge ice following lake drainage. Based on ice-wedge dimensions, bank height, shore erosion rates, and field measurements of sublake active-layer thickness prior to lake drainage, it is likely that ice wedges were entirely melted by the development of the sublake active layer, prior to talik development. Together, the results indicate that the IWPs formed within 5 to 10 m of the eroding shore bank, 9 to 18 years after lake submergence, and were filled with the organic-rich lacustrine sediment that accumulated in the near-shore zone due to sediment sorting by wave action following the erosion of peaty polygonal tundra. This study highlights that IWPs can form during the natural evolution of thermokarst lakes in regions with stable permafrost and are not necessarily indicators of conditions leading to generalized permafrost degradation.

Environmental controls on the generation of submarine landslides in Arctic fjords: Insight from Pangnirtung Fjord, Baffin Island, Nunavut

High-latitude fjords are susceptible to hazardous subaerial and submarine mass movements such as rock avalanches and landslides. Geophysical surveys in the fjords of Baffin Island (Nunavut) have shown widespread evidence of submarine landslides, but their timing and triggers remain relatively unconstrained, limiting our ability to understand the environmental controls on the wide range of landslides occurring in high latitude fjords. Using bathymetric, sub-bottom, and sediment core data, this study seeks to generate a comprehensive understanding of the distribution, morphology, lithology, and timing of submarine landslides in Pangnirtung Fjord (SE Baffin Island, Nunavut). These results are used to evaluate the influence of different environmental controls on the generation of submarine landslides in Arctic fjords. We identified 180 near-surface submarine landslides, most of which are relatively small (∼ 0.13 km2), with elongated depletion zones and wide deposits dispersed along the basin floor of the fjord. Landslide ages, calculated from radiocarbon dating and 210Pb/137Cs activities, indicate that 8 of the 11 dated landslides occurred in the last 200 years. Four types of environmental controls were identified, which are believed to have preconditioned or triggered the observed landslides: 1) 51% of landslides, by area, are associated with subaerial sources and extend offshore of debris flow channels and fans; 2) 23% are initiated in shallow-water (< 40 m), are non-subaerially influenced, and may have been triggered by nearshore processes and sea-ice loading; 3) 13% are located in deeper waters (>40 m) and associated with sills and moraines, suggesting they are older deposits associated with the retreat of the ice sheet in the fjord; and 4) 13% are offshore of river deltas, likely associated with delta progradation; they form the largest landslide deposits in the fjord. This research suggests that the main triggers for submarine landslides in high-latitude fjords are climatically influenced (rainfall, floods, subaerial debris flows, and sea ice loading). Consequently, the predicted increase in the frequency of subaerial debris flows and river floods due to anthropogenic climate change will likely result in an increase in the recurrence of these types of submarine landslides. Additional monitoring efforts will be then needed to fully evaluate how future climate will impact the submarine landslide hazard across the Arctic.

Facies analysis for the Neoarchean Itchen and Sherpa formations of the Winter Lake greenstone belt, Slave craton, Northwest Territories, Canada

Facies analysis for the Neoarchean Itchen and Sherpa formations of the Winter Lake greenstone belt, Slave craton, Northwest Territories, Canada

Readjustment of fluvial systems to Quaternary tectonic disruption in the Central Afar (Ethiopia)

The Afar region constitutes the diffuse triple junction adjoining the Red Sea, Gulf of Aden, and Main Ethiopian Rifts. Extension in the Afar is distributed between on-axis, magmatic crustal spreading, and off-axis, amagmatic extension, such as in Dobe graben. The timing of initiation and development of these amagmatic grabens is key to understanding the final stages of continental extension/breakup in central Afar. All major graben-bounding faults in central Afar cut through the Quaternary Afar Stratoid Series, constraining the ages of initiation to younger than approximately 1 million years. The Afar Stratoid Series presents a widespread thick lava unit that smoothed and infilled the topography created by the prior 30 Ma of deformation. The ∼1 Ma top surface of the Afar Stratoid Series serves as a regional marker predating most Quaternary deformation. The initiation of a particular fault (or location along a graben-bounding fault) begins a process of local lowering of base level – this is recorded in the landscape as a knickpoint that incises the paleo drainage in the footwalls of the grabens, connecting it to the basin floor with a deep canyon. The rate at which knickpoints retreat upstream permits a space-for-time approach to assessing initiation. This study develops and applies a landscape evolution model to estimate relative maturity and age of drainage basins by measuring the long profile response to tectonic forcings over intermediate timescales in central Afar. This is applied under the assumption that faulting postdates Afar Stratoid Series emplacement. The model is calibrated by analysis of stream longitudinal profiles and terrestrial cosmogenic nuclide (TCN) analysis of samples collected in the field. Longitudinal stream valley profiles are mapped through remote sensing and photogrammetry, and TCN concentrations are assessed to calculate the uplift rate along the graben-bounding faults. Results indicate that faulting of Dobe Graben in the central Afar initiated in the southeast and propagated to the northwest. Along the southern margin of Dobe Graben, ages of 503 ± 116 ka were calculated for fault initiation at Hann Canyon in the southeast, and 339 ± 80 ka at Ishyilu Canyon to the northwest. These timing constraints have implications for competing tectonics models for central Afar. The general approach developed for modeling knickpoint retreat has broader utility beyond Afar, allowing for application to extensional tectonic regimes elsewhere where similar geological and surface constraints exist.

Contemporary and relic waters strongly decoupled in arid alpine environments

Deciphering the dominant controls on the connections between groundwater, surface water, and climate is critical to understanding water cycles in arid environments. Yet, persistent uncertainties in the fundamental hydrology of these systems remain. The growing demand for critical minerals such as lithium and associated water demands in the arid environments in which they often occur has amplified the urgency to address these uncertainties. We present an integrated hydrological analysis of the Dry Andes region utilizing a uniquely comprehensive set of tracer data (3H, 18O/2H) for these environments, paired directly with physical hydrological observations. We find two strongly decoupled hydrological systems that interact only under specific hydrogeological conditions where preferential conduits exist. The primary conditions creating these conduits are laterally extensive fine-grained evaporite and/or lacustrine units and perennial flowing streams connected with regional groundwater discharge sites. The efficient capture and transport of modern or “contemporary” water (weeks to years old) within these conduits is the primary control of the interplay between modern hydroclimate variations and groundwater aquifers in these environments. Modern waters account for a small portion of basin budgets but are critical to sustaining surface waters due to the existence of these conduits. As a result, surface waters near basin floors are disproportionally sensitive to short-term climate and anthropogenic perturbations. The framework we present describes a new understanding of the dominant controls on natural water cycles intrinsic to these arid high-elevation systems that will improve our ability to manage critical water resources.

Seismic attributes and instantaneous spectral analysis-based temperature-porosity simulations: An example of imaging shale gas-bearing basin floor fans of early-cCretaceous delta sequences, Southeast Asian Basin

Basin floor fans (BFF) of deltaic depositional systems are important stratigraphic traps, which are sourced by the regionally developed meandering channel belts and associated deposits of point bar facies. The vertical and lateral changes in the tectonics and sea level adversely affect the temperature (θ) and porosity constraints of petroleum plays within BFF of the lowstand system tracts. These fluctuations impact the sedimentary controls on thickness, lithology-impedance contrast, phase, and frequency of BFF. As a result of the reliance on full-spectrum seismics, quantifying thin-bedded stratigraphic wet gas-bearing intervals (WGI) and light oil-bearing intervals of petroleum systems becomes extremely difficult. This study utilizes seismic attributes and instantaneous spectral analysis-based temperature-porosity reservoir simulations (TPRS) to quantify the BFF of the Early-Cretaceous delta of the Miano gas field, Central Pakistan. The 47-Hz peak-tuned frequency component of spectral decomposition [SpecDecomp] images a 154 km2 NEE-SWW traversed and regionally developed stratigraphic prospect. Linear regression of R2 > 0.80 between spectral decomposition-based tuning frequency of 47-Hz and gross reservoir thickness of BFF validates the presence of gas-bearing shales. The 47-Hz wavelet-based TPRS has resolved the phase reversals and seismic-doublet signatures for thin-bedded shale PETROS at θ of 170°F to 200°F and porosities of 22 % to 32 % of WGI within BFF. TPRS at 47-Hz SpecDecomp profile between the frequency bandwidth spectrums of 12–62-Hz has reappraised the exact morphology of the continental shelf, shelf-slope, and BFF. A 21 m thick aggradational parasequence of BFF was deposited at an angle of 2° during the onset of subsidence and rapid fall, followed by a subsequent standstill of sea-level at θ of 170 to 200°F, ∼26 to 35 % porosities, and laterally fractured subsidized regimes of WGI.. A 20 m thick retrogradational fluvial-dominated facies was deposited at an angle of 35° during a rising followed by a standstill of sea level at a θ of 140 to 165°F, ∼08 % to 18 % porosity, and poorly fractured uplifted compressional regimes of light oil-bearing intervals. The aggradational WGI of Lowstand System Tracts was completely embedded by retrogradational shales of transgressed system tracts from the top of the aggradational and laterally. The uncertainty analysis has prevailed with a moderate-to-good R2 > 0.75 for BFF and a very poor R2 < 0.1 for fluvial-dominated point bar traps. Our workflow has implications in terms of exploring the tectonics and stratigraphic frameworks within the petroleum systems for imaging the most productive zones in a single snapshot of 47-Hz tuning frequency.

Interaction between magmatism and polygonal faults revealed by three-dimensional seismic data in the Zhongjiannan Basin, South China Sea

The features of magmatism and polygonal faults are unveiled through a comprehensive analysis of high-resolution and reprocessed three-dimensional (3D) seismic data covering 1200 km2 in the Zhongjiannan Basin, South China Sea. These structures influence the hydrocarbons formation and migration, and the interaction between them is significant for hydrocarbon exploration. We identified magmatic bodies, including eight volcanoes, fifty sills, and a single igneous diapir, are mainly developed in three stages: 27.9–23 Ma (between T70 and T60), around 11.6 Ma (T40), and after 5.3 Ma (T30). The polygonal faults, characterized by linear, polygonal, and radial configurations, are extensively distributed within Miocene and Quaternary sediments. In the platform, polygonal faults manifest linear or polygonal attributes, while in the basin floor, they show a polygonal shape. Particularly, above volcanoes and the igneous diapir, the polygonal faults exhibit radial configurations. However, among volcanoes, few polygonal faults are discerned based on the coherence attribute slice. The controlling factors influencing the distribution of polygonal faults are the lithological disparity, temperature, and pressure. Radial fault formation is promoted by volcanoes and igneous diapir through differential compaction. The resultant vertical pathways formed by volcanoes and overlying radial faults play a crucial role in adjusting pressure differentials or water discharges. Consequently, these pathways disrupt the requisite conditions for the formation of polygonal faults among volcanoes. In the basin floor, magma intrusion occurs along the planes of polygonal faults, giving rise to inclined, spoon-shaped, and bowl-shaped sills. As weak zones, polygonal faults worked as connectors for sills at different depths. Hence, pre-existing polygonal faults are considered pathways facilitating magma migration from the lower Miocene to Pliocene strata, ultimately contributing to sill formation in shallow sediments. This study advances our understanding of the intricate interaction between polygonal faults and magmatism within sedimentary basins.

Late Neogene and Quaternary Lacustrine History of the Great Salt Lake-Bonneville Basin

The Great Salt Lake-Bonneville basin has contained lakes for many millions of years and has been hydrographically closed for most of its history. Lakes in the lacustrine system have ranged from saline to fresh, and from shallow to deep. Tectonics, specifically crustal extension, which began roughly 20 million years ago as part of the formation of the Basin and Range Province, is the cause of lake-basin formation. Much of the rock record of lakes from Miocene time is faulted and has been eroded and/or buried. Pliocene and Quaternary lakes are better known. For much of the past ~5 Ma the basin has probably appeared similar to today, with a shallow saline terminal lake in a dry desert surrounded by mountains. Freshwater marshes and fluvial systems existed on the basin floor during part of the past ~5 Ma, probably were caused by the lack of inflow from the upper Bear River during the Neogene Period and most of the Pleistocene Epoch (that river was diverted into the basin during the Late Pleistocene), combined with a warm and dry climate. The largest deep-lake cycles were caused by changes to a cold and wet climate, which affected the water budget of the lake system and were correlated with periods of global glaciation. Based on limited data, the total length of time deep lakes existed in the basin is thought to be less than 10% of the past ~773 ka. Lake Bonneville, the most-recent of the deep-lake cycles, was probably the deepest and largest manifestation of the lake system in the history of the basin. Named deep-lake cycles during the past ~773 ka, are Lava Creek (~620 ka), Pokes Point (~430 ka), Little Valley (~150 ka), Cutler Dam (~60 ka), and Bonneville (~30 -13 ka). Of the Quaternary deep-lake cycles, only Lake Bonneville is represented by lacustrine landforms, outcrops, and cores of offshore deposits; no landforms from older deep-lake cycles exist (some may be buried under Lake Bonneville deposits but are not visible at the surface), and pre-Bonneville lakes are represented by sediments in limited outcrops and drill holes (including a set of cores taken by A.J. Eardley in the mid 20th century). During the past ~773 ka, deep-lake cycles were correlated with changes in the total volume of global glacial ice; the available evidence indicates that prior to ~773 ka deep-lake cycles were rare.

Neogene evolution of the margin adjacent to the La Plata River Delta (Pelotas Basin): Sedimentary pathways and the origins of the Rio Grande Cone

AbstractContinental margins that exhibit high terrigenous input are generally located near deltas that are capable of transporting large quantities of sediments into the basin. However, in rare cases, high terrigenous sedimentation occurs in regions deprived of major riverine systems where the sedimentary pathway is enigmatic. One such case is the Neogene of the Pelotas Basin of Brazil and Uruguay, adjacent to the La Plata River mouth. Since the Miocene, anomalous sedimentation formed a giant progradational wedge, the Rio Grande Cone, one of the largest submarine fan‐like features on Earth. To understand the Neogene evolution of the margin and the origins of the Rio Grande Cone, here we present a seismic‐stratigraphic framework based on well‐logs and 2D seismic data. Three depositional environments are identified: (1) on the shelf, upper Miocene to Pliocene fluvial channels delivered sand deposits on the mud‐dominated shelf; (2) on the slope, sediment instability resulted in structural deformation and multiple phases of mass transport deposition and (3) on the lower slope and basin floor, large contourite drifts formed by sediment reworking. We classify the Rio Grande Cone as a megaslide complex, due to its depositional and structural setting. Local deltaic systems were active on the shelf in the Neogene, but the limited size of their paleo‐drainage systems in comparison to the volume of sedimentation in the margin suggests that an additional sedimentary pathway existed. In this sense, the demise of an epicontinental sea over the La Plata Basin during the Neogene likely enabled the input of large volumes of fine sediments into the margin, via the La Plata plume water. We suggest that the desiccation of this epicontinental sea and the intensification of ocean currents since the middle Miocene explains the anomalous Neogene terrigenous influx into the SW Atlantic margin.

Transformation of dense shelf water cascade into turbidity currents: Insights from high-resolution geophysical datasets

Dense shelf water cascade (DSWC) is a common oceanographic phenomenon on many continental shelves. Previous studies indicate that the DSWC could shape seabed physiography and carry seawater, sediment, and organic carbon a long distance from the continental shelf to the basin floor. However, it remains enigmatic how these DSWC's interact with seabed geomorphology and travel long distances from the shallow to deep marine environments. In this study, we employed high-resolution multibeam bathymetry, 2D and 3D seismic reflection, core description, and sediment grain size data from the Gippsland Basin, southeast offshore Australia. The continental shelf of the central Gippsland Basin stores sediment supplied by the along-shelf transported DSWC. By calculating the sediment motion threshold, we demonstrate that the DSWC is capable of entraining sediment from, and forming dense bottom nepheloid layers above, the seabed. Seismic reflection data reveal that cyclic steps are common on the shelf and slope, indicating a downslope-transported, supercritical current-dominated environment. Core observation and grain size analyses reveal that coarse-grained, Ta-typed turbidites are the major facies, indicating the presence of high-intensity downslope-traversing turbidity currents. Thus, supercritical turbidity currents are the dominant sedimentary process in the central Gippsland Basin. We illuminate that DSWC can interact with pre-existing seabed bathymetry created by a buried submarine landslide, resuspending sediment and igniting downslope-transported turbidity currents. The presence of numerous cyclic steps indicates that the turbidity current can evolve into a supercritical regime upon ignition, leaving complex seabed geomorphology and allowing the forming currents to travel across the shelf and extend more than 80 km down the lower slope. As revealed by our literature review, we imply that the transformation of DSWC into turbidity currents should be a common sedimentary process on outer continental shelves globally, significantly sculpting the seabed morphology and facilitating sediment and other marine particles transportation from shallow to deep sea.

Sedimentology and sequence stratigraphy of shallow and deeper marine Miocene deposits: A case study from the St. Paul and Gebel El‐Zeit blocks, Gulf of Suez, Egypt

AbstractMarginal and deeper marine facies typify the Miocene exposures along the western margin of the Gulf of Suez rift basin. The stratigraphic setting of these facies is a subject of debate and confusing at best. Integrative sedimentological and sequence stratigraphic study of successions exposed in the St. Paul and El‐Zeit blocks provides insight into the lateral relationships between the two facies and their evolution, a topic that is not fully understood. The St. Paul block, located at the basin margin, has thin shallow marine facies, while the succession of El‐Zeit block, situated near the basin axis, consists of basal conglomerates, thin shallow marine carbonates, thick deeper marine shale and marginal evaporites. The facies architecture of these successions is interpreted as belonging to two different depositional models: a fan‐delta/lagoon system followed upwards by an alluvial fans/sabkha‐tidal flat system in the St. Paul hangingwall basin, and carbonate–siliciclastic–evaporite systems on the hangingwall dip‐slope ramp of El‐Zeit block. These models may help understanding the sedimentary history of other similar blocks in the rift basin. The studied facies show many striking features such as deposition during tilting of fault block, abrupt facies and thickness variations, coarse clastic shedding, erosion channel filling, onlapping of high standing blocks and evaporite accumulation. These features are the result of major tectonic events that triggered the formation of unconformities at different hierarchical levels during the late early to middle Miocene. These unconformities subdivide the Miocene facies into five depositional sequences separated by basin‐wide erosional boundaries. This division greatly improves the age control of marginal marine facies. It affords new insight into the evolution of marginal marine facies along the western margin of the basin in relation to deeper facies in the basin centre. Facies and thickness changes in these tectonically induced sequences indicate that basin floor irregularities, subsidence rates, climatic changes, variable sediment influx, sea‐level/brine‐level changes and basin isolation/connection to the Mediterranean Sea are also important factors responsible for their evolution.

Spatiotemporal patterns of land surface temperature and their response to land cover change: A case study in Sichuan Basin

Land surface temperature (LST) is a critical geo-parameter in terrestrial environmental interaction processes, directly related to land cover change (LCC) which modifies surface energy balance. In this study, LST data from 2003 to 2019 were reconstructed in the Sichuan Basin with average R2 of 0.85 (daytime) and 0.91 (nighttime), effectively filling in the missing pixels and reducing the noise components. Emerging hot spot analysis (EHSA) and land cover transfer matrix were utilized to analyze the multi-patterns of LST spatiotemporal evolution and responses to LCC. Results indicate that LST hot spots are concentrated in low-altitude basin floor and are dominated by sporadic hot spots. Cold spots are mainly in marginal high-elevation mountains, but the dominant pattern varies with time scale. The largest proportions of hot and cold spots are found in summer (>46 %) and autumn (>29 %), respectively. Moreover, the significant upward and downward trends of LST cold and hot spots are most prominent in western plain and marginal mountains, respectively, and have the largest coverage in summer and autumn, respectively. In total LCC area, cropland-to-forest (CF), cropland-to-impervious (CI), and forest-to-cropland (FC) account for 93.55 %. Among them, CI significantly promotes the aggregation and upward trend of daytime LST hot spots. CF and FC have the strongest effect of aggregating LST cold spots and cooling LST in daytime, with CF being more effective. The information can serve as a reference for regional planning and climate change mitigation measures.

Seismic geomorphology of the basin floor area in the Northern North Sea: evolution of the Frigg submarine channels and their influence on sediment distribution

Seismic geomorphology of the basin floor area in the Northern North Sea: evolution of the Frigg submarine channels and their influence on sediment distribution