Sedimentary Fill Research Articles

Fossil fuels and potential for CO 2 storage in the Slovenian part of the Pannonian Superbasin

Two Neogene sub-basins of the Miocene Extensional Pannonian Superbasin are located in Slovenia: the Mura-Zala Basin in the northeast and the Krško Basin in the east of the country. Their predominantly clastic sedimentary fill hosts diverse geoenergy resources in different geological formations. The basin evolution (e.g., very high Miocene heat flow) was not favourable for the accumulation of large amounts of hydrocarbons. Consequently, oil and gas deposits are limited to the Petišovci-Dolina field, which was discovered in 1942. The field is located along the Ormož-Selnica-Lovászi Anticline, an inverted Miocene graben structure. Currently, minor amounts of natural gas are produced from Miocene (Badenian and Pannonian) horizons, while oil production stopped in 2021. Coal deposits formed in deltaic environments during the late Pannonian and were exploited until the 1970s, in both the Mura-Zala Basin and Krško Basin. Depleted oil and gas reservoirs at depths > 800 m, saline aquifers, and deeply buried coals in the Mura-Zala Basin provide potential sites for CO 2 storage, albeit with limited volumes.

Paleogeography of Carboniferous and Permian coal formation in the Bohai Bay area, China

The sedimentary facies and sedimentology of the Carboniferous–Permian strata in the Bohai Bay area are used to develop a coal-forming paleogeography during the late Carboniferous, and early and middle Permian periods. During the Carboniferous–Permian period, the Bohai Bay area was located in the southeast margin of the large North China Basin. The sedimentary characteristics, coal-forming processes and evolution of the sediment fill are similar to those of the North China Basin but have their own unique characteristics of deposition and coal formation. This paper summarises the paleogeographic characteristics and changes in sea–land distribution, provenance and climate from the late Carboniferous to the middle Permian. Sea-level changes are considered to control the filling of the basin, the development and distribution of peat bogs, and the characteristics of coal formation. Late in the evolution of the epicontinental basin, following the end of the transgressive systems tract, the sea-level in the study area slowly declined and gradually withdrew from North China. At this time, the study area was primarily dominated by the development of shallow-water delta sedimentary systems, representing the most stable period for coal formation.

Sedimentology, lithostratigraphy, paleogeography and water level changes in a lacustrine basin: the depositional model of Lake Pannon

Advances in sedimentology and basin analysis provide the foundation for a comprehensive basin-fill model and lithostratigraphic framework of Lake Pannon, Central Europe, highlighting the dynamical changes of the depositional environments. The lake's ca. 8 Myr long evolution began with transgression and deepening, followed by normal regression, forming up to 7 km thick sediment fill. Initial coarse-grained coastal deposits are overlain by offshore to deep-water marls, with varying carbonate- and organic-matter content and include both anoxic laminites and sediment gravity-flow deposits. Later confined and unconfined turbidite systems developed due to interactions between basin-floor relief and shelf-slope progradation. Stacked deltaic cycles followed by clayey alluvial plain deposits with anastomosing and meandering sandy channel fills comprise the upper part of the succession. Repeated aggradational to progradational clinothem architectures, thickness and distribution of muddy to sandy delta lobes on the shelf, and distribution of turbidite lobes in the deep basins reflect lake-level fluctuations. While climate primarily controlled lake level, coastal sedimentation is identified as a new factor driving long-term lake-level rise. Therefore, Lake Pannon's stratigraphy demonstrates that, in contrast to marine systems, in supply-dominated endorheic lakes accommodation space is created by sedimentation.

Diversity of lakes and ponds in the forest-tundra ecozone: from limnicity to limnodiversity

ABSTRACT Arctic and subarctic landscapes have unique hydrological and limnological features and are now experiencing rapid change due to climate warming and permafrost thaw. The highly abundant lakes, ponds, and rivers across these landscapes play an increasingly important role in global biogeochemical cycles and are sentinels of environmental changes. However, studying these remote waters poses challenges for both in situ sampling and remote-sensing analysis. Here we developed a synergistic remote-sensing strategy that combined PlanetScope and Sentinel-2 satellite data to estimate limnicity (water fraction per land surface), limnodensity (density of water bodies), and limnodiversity (optical diversity of water bodies) along a boreal forest-tundra transect, from the non-permafrost to the continuous permafrost zones of western Nunavik (Subarctic Canada). Our analyses show that this region hosts 335,281 water bodies, around 90% in the 0.0001 to 0.01 km2 size range. In bedrock outcrops, large water bodies were mostly associated with glacially carved depressions (higher limnicity). In contrast, small water bodies were predominately found in sedimentary infills along valleys (higher limnodensity). The discontinuous permafrost zone had the highest limnodensity and limnodiversity. This was likely due to permafrost thaw (thermokarst), particularly the collapse, subsidence, and erosion of palsas (organic permafrost mounds), resulting in ponds with black- and brown-colored waters, and lithalsas (mineral permafrost mounds), resulting in ponds with brown, light-brown, and sometimes white-colored waters. Some of these limnodense and limnodiverse landscapes, although covering only 2 to 7% of the total area of the study region, contained over one-third (34%) of the total number of water bodies, 97% of which were <0.01 km2; they accounted for a small proportion of the total black-colored water bodies (23%), but a high proportion of the total brown- (60%) and light brown-colored water bodies (92%) throughout the region. This research underscores the utility of optical satellite remote sensing for assessing water body types and for evaluating their individual and distinct aquatic responses to climate change. The dataset may be used to improve the modeling of carbon fluxes by better categorizing small water bodies affected by organic or mineral soil type settings. This is an important factor dictating biogeochemical responses, with effects on albedo, climate feedbacks, and ecosystem dynamics in the boreal forest-tundra region. The framework developed here may be applied to landscapes elsewhere in the world that have high densities of water bodies of variable size and optical properties.

Towards a quantitative lithostratigraphy of Pleistocene glaciofluvial deposits in the southern Upper Rhine Graben

Abstract. The sediment fills of large terrestrial basins offer an opportunity to study and reconstruct regional-scale landscape history over time. An example of such a basin is the Upper Rhine Graben in central Europe, whose proximal, southern part has so far only sporadically been investigated sedimentologically. Three new drillings in close proximity have recovered the upper ∼ 40–60 m of the Quaternary sedimentary infill near the eastern graben margin north of Freiburg, Germany. Grain sizes, the rounding and shape of clasts, and the petrographic composition of the deposits have been determined and statistically analysed. The cored intervals consist of glaciofluvial gravels derived from and deposited by the Rhine system. While no consistent trends of the morphometric properties could be found, we succeeded in distinguishing two subunits within the topmost stratigraphic unit (Neuenburg Formation, Fm) based on compositional (i.e. gravel petrographic) data. An upper subunit (Hartheim Subformation, Sfm) enriched in lithologies representative of the Alpine orogen could be separated from a lower subunit (Nambsheim Sfm) that is enriched in lithologies of an outer-Alpine origin. We correlate these findings with a shift in the pattern of meltwater discharge from the Rhine glacier lobe that may have delivered more Alpine material into the study region during the last than during the penultimate glaciation and highlight the value of quantitative approaches and appropriate statistical evaluation for gravel petrographic studies.

Hydrocarbon Potential Evaluation of Chad Basin, Northeastern Nigeria Using High-Resolution Aeromagnetic Data

A cost-effective and non-intrusive aeromagnetic geophysical technique was utilized to reduce exploration uncertainty in the Chad Basin, which is believed to have significant hydrocarbon potential despite limited exploration due to its remote and challenging terrain. By analyzing various derivatives and magnetic attributes extracted from filtered and enhanced aeromagnetic data, the study aimed to highlight potential areas for hydrocarbon generation and preservation, allowing for more focused and detailed geophysical exploration efforts. This study produced several key maps, including a total magnetic intensity map (ranging from -168.7 to 224.8 nT), a reduction to equator map (ranging from -156.8 to 207.9 nT), and depth analysis, which helped delineate the structural framework and sedimentary thicknesses within the basin. Quantitative interpretation of these maps, along with the analytic depth map (ranging from 22.1 to 5649.3 m), tilt depth map (ranging from -76.50 to 80.40), and first and second vertical derivatives maps (ranging from -0.097 to 0.086 nT/m and -0.000240 to 0.000236 nT/m, respectively), was employed to detect geological features and thick sedimentary fills sufficient to create or trap hydrocarbons. Depth estimates indicate that the shallow sources range between 22 and 230 m, while deeper sources fall between 2747 and 6000 m, suggesting sufficient sedimentary fill for hydrocarbon generation. The basin is characterized by large sedimentary deposits that are bounded by structural features such as folds, faults, and fractures. The northern part of the basin, trending towards the northwest, eastern edge, and parts of the south, showed active structural features, including anticlines, synclines, and fractures, which are essential for petroleum trapping. These findings, coupled with the identified thicknesses and favorable structural disposition, suggest that the Chad Basin holds high potential for hydrocarbon accumulation, making it a prospective region for further exploration with more detailed geophysical methods.

Hybrid turbidite-contourite system on the upper-slope continental margin of the offshore southern Tanzania

Cretaceous-Cenozoic hybrid turbidite-contourite (HTCs) systems on the upper-slope region of the northern Rovuma Basin, southern offshore Tanzania have been poorly studied. HTCs have been widely studied from several places due to their petroleum prospectivity, link to geohazards, and potential to help understand deep marine circulation processes and past climates. We have studied 3D seismic data into the northern Rovuma Basin to establish variation and orientation of seismic facies, architectural elements and geomorphologies (based on RMS amplitude maps) characterizing the Cretaceous-Cenozoic HTCs linked to channelized sediment transport and deposition. Two different migration patterns for channelized systems are recognized. They include Cretaceous-Middle Miocene and Middle Miocene-Holocene systems migrating toward SE and NW, respectively. Timing of change in migration trends coincides with change in traverse directions of major submarine channels that allowed sediment transportation by gravity flows. Trajectory of the submarine channels shifted from S-N to SW-NE and approximately W-E during the Middle Miocene, agreeing with the change in channel fills migration trends. The trajectory shift, for the revealed submarine channels was caused by tectonic activity linked to East African Rift System, so does the distribution and migration trends of the HTCs. The study area has hydrocarbon accumulations in the Oligo-Miocene sandstones containing HTCs characterized by a clearly defined depositional system with high RMS amplitudes. The Middle Miocene-Early Pliocene interval has a clear depositional configuration as well, but its low RMS amplitude indicates dominance of fine-grained HTCs with limited reservoir potential. The Late Pliocene-Holocene interval has very high RMS amplitude, but its chaotic configuration implies the presence of poorly sorted sedimentary fills having limited reservoir potential as well. This may be one of the reasons for hydrocarbon discoveries in the study area being limited within the Oligo-Miocene sandstones, and not the younger stratigraphic levels.

STRATIGRAPHIC DRILLING IN THE NORTHEASTERN LAPTEV SEA: MAIN RESULTS AND FURTHER DEVELOPMENT

The Russian sector of the Eastern Arctic is characterized by large basins with thick sedimentary filling, primarily on the shelf and continental slope of the seas of the Arctic Ocean. A number of geological, geophysical, and geochemical features point to a hydrocarbon potential. At the same time, the age and composition of the sedimentary infill of the shelf basins have been controversial until now due to the lack of wells drilled in the shelf area. Six stratigraphic wells were drilled with core sampling in the eastern Laptev Sea (Anisin–Novosibirsk block owned by Rosneft) with a depth of 100 to 199.5 m during the Rosneft Stratigraphic Drilling in Arctic (RoSDAr) project in 2021. The results of complex biostratigraphic studies of the core show that the oldest strata in the well sections are Upper Barremian – Lower Aptian deformed silty mudstones (folded basement assemblage) overlain with angular unconformity by sands, silts, and clays of the Paleocene. The wells also penetrate the Eocene, Oligocene, and Miocene-Quaternary clastic rocks. A comprehensive analysis of stratigraphic drilling and seismic data refines the geological models of the region and provides better understanding of its hydrocarbon potential. The data show that Cenozoic strata play a more significant role in the sedimentary cover of the Laptev Sea than was previously assumed.

Chapter 2. Tectonics, Climate and Sedimentation in the Albertine Rift

The tectonically active early continental Albertine Rift basins are dynamic entities, constantly evolving through time. Periods of crustal extension cause rift valley floor subsidence to create accommodation space and accumulate sediment in basinal depositional centres (‘depocentres’). Periods when stress fields change across a rift can move the maximum rupture along main rift bounding faults to shift depocentre locations over time, often producing a series of syn-rift phases in basin development. In the Albertine Rift, the Lake Edward basin displays superb structural geomorphology that, in this study, could be mapped across the whole width of the rift valley. Often cited in the literature as a classic asymmetric half-graben, it is now clear that this basin is undergoing a change in rift phase, developing into an extremely asymmetric graben with a faulted eastern flexural arch. Tectonics does not operate alone, but forms a coupled dynamo with climate, that together drive and control the sedimentary fill of an early continental rift basin. The theoretical effects of this are modelled for Lake Edward to indicate basinal deposition when tectonics and climate are in, and out, of phase. Finally, the ‘sedimentary geodynamic elements’ that might be expected to characterise early continental rift basins are outlined.

Geothermal resources of Hungary: a play-based review

In this paper we review the geothermal resources of Hungary using the geothermal play concept and its scale-dependent hierarchical categorization. The Pannonian Basin belongs to an extensional domain play type, with two main plays: the porous Neogene basin-fill sediments and the fractured–karstified Paleozoic and Mesozoic basement rocks. Both plays can be divided into hydrostatic and overpressured play segments. The most widely utilized play level in the hydrostatic segment of the porous Neogene sediment play comprises laterally extended, highly permeable sandstone layers storing low-salinity thermal water with average flow rate of c. 900 l min −1 and temperatures between 50 and 100°C in the depth range of 1–2 km. The other prosperous play level is represented by the fractured–karstified Mesozoic carbonates in the hydrostatic segment of the basement play having elevated temperatures (90–120°C) and several thousand l min −1 flow rates. The play level related to fractured Paleozoic rocks is less important due to its limited extent. The overpressured segment of the basement play may have high flow rates but it is still an untapped resource as exploitation is limited by high overpressure, high temperatures (170–200°C) and highly saline hot waters.

Martian Chaos terrain fracture geometry indicates drainage and compaction of laterally heterogeneous confined aquifers

The interlocking plateaus of martian chaotic terrain have long been inferred to relate to Hesperian outflow-channel megafloods. Numerous hypotheses have been invoked to explain the formation of the hundreds-of-kilometer-scale depressions that chaoses are found in, and the mechanisms by which the fractures formed. Hypotheses range from mechanisms involving water, e.g., ice melt, overturn of sediment-covered paleolakes, or submarine landslides, to purely magmatic processes, such as caldera formation, to exotic endmembers including clathrate decomposition. These interpretations of martian chaos are largely based on photogeological mapping of individual chaoses, and have mostly neglected analysis of the chaos fracture network and its relationships with the chaos basin. Here, we show, based on analysis of 35,964 fracture blocks across 18 different chaoses and 6 terrestrial analogs, and supported by novel volumetric measurements of chaos terrain deposits and intervening void spaces, that the geometry of martian chaoses is best explained by depressurization and compaction of an underlying confined aquifer. Block size distributions are incompatible with magma chamber collapse analog experiments. We show that sedimentary fill in chaos basins is inhomogeneously distributed, with layers thickening towards the chaos center, as in terrestrial sedimentary basins. The relationship between fracture block thickness and area is explained by the same power law that describes fracture spacing and layer thickness in weak terrestrial sandstones. The presence of some chaoses with blocks that are higher than surrounding plains implies repressurization of some sub-chaos aquifers. Hesperian-aged water or ice may remain within ∼1–3 km of the surface beneath these landforms.

Ambient vibrations of a deep maar resonator

We introduce non-invasive seismic methods for identifying and characterizing maar sedimentary infills. We conducted a dense ambient vibration survey and employed state-of-the-art 3D resonance analysis techniques to map the lateral extent and depths of the sedimentary layers, a challenge with traditional geophysical methods due to unfavorable aspect ratios (depth > lateral dimension). The ambient vibrations of maars are predominantly driven by normal mode motions due to 3D resonance of crater infills. Dense station coverage enabled detailed images of the normal mode shapes revealing infill symmetries. The resonance results in extreme ground motion amplification, with factors reaching up to 30 on the vertical component, challenging conventional beliefs about site effects and methodologies based on widely used horizontal-to-vertical spectral ratios. These results are supported by numerical simulations of the maar's seismic response. The observed response is so specific that it can be used to identify partly eroded maar structures in the field.

RECONSTRUCTION OF THE SUBSIDENCE DYNAMICS AND PALAEOTEMPERATURE REGIME OF THE NORTHERN MARGIN OF THE SIBERIAN PLATFORM

The formation mechanisms of sedimentary basins are considered as a response of deep processes in the mantle, therefore they carry important information about the geodynamics and thermal regime of the lithosphere. For different sectors of the northern margin of the Siberian Platform, the dynamics of sedimentation and subsidence was reconstructed. The analysis of subsidence curves shows that during the Late Paleozoic the sedimentary infill formed in the foreland basin environment. In the Late Permian–Early Triassic time, in the central and western sectors, the subsidence was accelerating due to the development of a thick trap complex; after the Permian and Triassic boundary the subsidence slowed down. During the period of trap magmatism, an anomalously high subsidence rate up to 4.8 km/Ma in the central and up to 0.5–1.1 km/Ma in the eastern and western parts was reconstructed. The high rate and short duration of accumulation of volcanogenic sediments can be explained by an episode of short-term extension under the influence of a plume, followed by a long period of thermal subsidence. Numerical modelling of the temperature regime near mafic intrusive bodies was carried out, which showed that when determining the paleoheat flow, the influence of trap intrusions can be traced up to 400–500 m from the contacts. Estimates of the paleoheat flow for the Permian–Triassic stage of tectonic evolution of the eastern sector were obtained. It was calibrated using the PetroMod software package, based on laboratory measurements of modern values of vitrinite reflectance for rock samples from wells, modern temperature and heat flow in the sedimentary cover. It was determined that trap magmatism occurred at temperatures increased to 100 mW/m2, while the mantle component of the heat flow reached 38–72 mW/m2; it is several times higher as compared to modern one. The obtained paleoheat flow estimates for the Late Permian–Early Triassic stage appear to correspond to anomalously high values of modern continental rifts.

Hydrodynamic Modeling of Khenifiss Coastal Lagoon, Southern Atlantic Coast of Morocco: Implications for Sediment Infilling

Hydrodynamic Modeling of Khenifiss Coastal Lagoon, Southern Atlantic Coast of Morocco: Implications for Sediment Infilling

Along-strike variation in volcanic addition controlling post-breakup sedimentary infill: Pelotas margin, austral South Atlantic

Abstract. We investigate, using observations from seismic reflection data, the lateral variability in breakup extrusive magmatic addition along the strike of the Pelotas segment of the austral South Atlantic rifted margin and its control on post-rift accommodation space and sediment deposition. Our analysis of regional seismic reflection profiles shows that magmatic addition on the Pelotas margin varies substantially along strike from extremely magma-rich to magma-normal within a distance of ∼300 km. Using 2D flexural back-stripping, we determine the post-rift accommodation space above top volcanics. In the north, where volcanic seaward-dipping reflectors (SDRs) are thickest, the Torres High shows SDRs up to ∼20 km thick, and post-breakup water-loaded accommodation space is much less than in the south, where magmatic addition is normal and SDRs are thinner. We show that post-breakup accommodation space correlates inversely with SDR thickness, being less for magma-rich margins and more for magma-normal/intermediate margins. The Rio Grande Cone, with large sediment thickness, is underlain by small SDR thicknesses allowing large post-breakup accommodation space. A relationship is observed between the amount of volcanic material and the two-way travel time (TWTT) of first volcanics: first volcanics are observed between 1.2 and 2.2 s TWTT for the highly magmatic Torres High profile, while, in contrast, for the normally magmatic profiles in the south, first volcanics are observed between 4.2 and 6.5 s TWTT. The observed inverse relationship between post-breakup accommodation space and SDR thickness is consistent with predictions by a simple isostatic model of continental lithosphere thinning and magmatic addition melting during breakup. The methodology that we use in this paper provides a new approach for investigating the complex magmatic and sedimentary evolution of rifted continental margins.

Evaporitic–lacustrine mudstone laminites and prodelta mudlobes – continuity and change in the Hartmann's Valley interval, Murray formation, Gale crater, Mars

ABSTRACTThe sedimentary fill of Gale crater on Mars is dominated by lacustrine strata that are the focus of investigations into surface processes, climate change and habitability early in the planet's history. This study focuses on the lower part of the explored portion of the Murray formation on Aeolis Mons (Mount Sharp) in the Pahrump Hills and Hartmann's Valley field areas. At Pahrump Hills, sedimentary features and geochemical attributes of exposed mudstones suggest accumulation in an underfilled lake basin in which lake levels, shorelines and salinities fluctuated greatly at various temporal scales. The immediately superjacent stratigraphic interval, designated by the rover team as the Hartmann's Valley member, has previously been interpreted as an aeolian‐deposited sandstone interval. This fresh examination of all available data, however, suggests that the Hartmann's Valley member is strongly dominated by the same mudstone facies that compose most of the underlying Pahrump Hills member. The one novel facies element encountered in the Hartmann's Valley member are undulose bedded to convex bodies of mudstone that are oriented roughly north–south, suggestive of sediment supply from a northern fluvial source. Mudstones analogous in scale and character to these undulose mudstones occur on Earth in multiple modern and ancient lacustrine successions, and are related to deposition of prodelta mud lobes. The mudstones of the Hartmann's Valley member record a continuation of the underfilled evaporitive lake system proposed previously for the underlying Pahrump Hills member but with somewhat more variable environmental conditions. Hartmann's Valley mudstones contain more abundant matrix CaSO4, suggesting more severe evaporitic conditions, whereas the interbedded undulose bedded mudstones signify intermittent freshening and buildout of mud‐dominated deltas into the lake. The textural similarities between Pahrump Hills and Hartmann's Valley strata suggest that the Gale lacustrine system operated at a stable depositional mode with similar environmental parameters during both stratigraphic intervals.

Multi-proxy analysis of an Early Neolithic wooden well in a pastoral landscape in eastern Bohemia

Abstract Some of the most remarkable Neolithic finds encountered in central Europe are wells with a wooden construction. These features provide unusual insights into Neolithic societies, their subsistence strategies and the landscape they inhabited. In the last fifteen years, four Early Neolithic wells out of a total of seven such wells known since the 1970s have been discovered in Czechia. One of them is the well at Ostrov, the wooden construction and sedimentary infill of which have made it possible to study diverse topics by taking a multi-proxy approach using a range of complementary methods. The study presented here compares different periods of the well’s existence, examines the carpentry skills of the first farmers, investigates sedimentary processes, reveals details about the use and decline of the well, addresses its location relative to that of the settlement, and reconstructs the environment of the well itself and the surrounding landscape. The water well at Ostrov is a highly unusual find because it probably existed outside of a settlement. The grooved wooden lining used is identical to that of previously investigated wells inside settlements, as are the processes of its use and decline. However, environment-related indicates that the Ostrov well was located in an open landscape with sparse vegetation and was perhaps only used by-passing herdsmen.

On the role of non-equilibrium heat transfer in the filled fracture-rock matrix system

Understanding heat transfer processes in fractured porous media is critical for characterizing thermal behaviors and improving the operation efficiency of geothermal energy. The field observations have shown that many fractures are filled with sediment infilling rather than being fully open, but heat transfer in such a filled fracture-rock matrix system has received less attention to date. Since multiple domains are involved in such a system and the fracture is highly permeable even with sediment infilling, local thermal equilibrium may not be reached instantaneously. In this study, a fully coupled analytical model is proposed and developed to investigate the role of transient local heat transfer in the filled fracture-rock matrix system and analyze the spatiotemporal thermal distributions in each domain. The results indicate that multiple thermal properties of the rock matrix, such as average volumetric thermal capacity and thermal conductivity, have significant impacts on the spatiotemporal thermal distribution in the fracture. The temperatures of the pore water and sediment infilling in the fracture are sensitive to flow velocity, thermal conductivity of the rock matrix, and volumetric thermal capacities of the fluid and rock matrix. The thermal transfer coefficient has moderate interaction effects with other parameters according to the sensitivity analysis.

Seismic stratigraphy and petroleum prospectivity in the Northern Rovuma Basin, offshore Tanzania

The upper slope area of the Northern Rovuma Basin has been poorly studied and little is known about its development and petroleum prospectivity. Interpretation of wellbore, 2D and 3D seismic reflection data in this area has allowed identification of seismic features reflecting key factors for understanding the development of the Cretaceous-Holocene stratigraphy and distribution of petroleum system elements. Our results show that infill of sediment into the basin was due to an interplay of three major factors. These are the sea level variations, extensional tectonics and sediment gravity flows. The Miocene and Pleistocene-Holocene tectonic events triggered gravity flows that supplied sediments to the basin. The resultant deposits include slides, slumps, debrites and turbidites some of which contain potential reservoirs that are interpreted to have been charged by the Permo-Triassic Karoo shales and Cretaceous-Cenozoic source rocks. These reservoirs are contained in both stratigraphic and structural traps with localized combinations in some places, and are encased by deep marine shales. Some of the potential reservoirs are positively inverted and compartmentalized, and they contain several bright and flat spots suggesting hydrocarbon accumulations within the Miocene and Oligocene intervals. It has also been revealed that major gravity flows and bottom currents, that supplied and distributed sediment to the basin, were confined in three long-lived channelized systems that were initiated during the Cretaceous (due to rapid regression), and the Oligocene and Pleistocene periods (due to rapid uplift). The channels migrated toward the southeast, with some shift toward the northeast, and had overall northeast traverse direction perpendicular to the shoreline. The reported gravity flows eroded previously deposited sediment in most places causing several unconformities in the whole Cretaceous-Holocene stratigraphy. Seismic stratigraphic interpretation and facies analysis have proved useful in the identification of key petroleum system elements and improve understanding of sedimentary fill evolution of the study area.

Miocene ice sheet dynamics and sediment deposition in the central Ross Sea, Antarctica

Drill cores from the Antarctic continental shelf are essential for directly constraining changes in past Antarctic Ice Sheet extent. Here, we provide a sedimentary facies analysis of drill cores from International Ocean Discovery Program (IODP) Site U1521 in the Ross Sea, which reveals a unique, detailed snapshot of Antarctic Ice Sheet evolution between ca. 18 Ma and 13 Ma. We identify distinct depositional packages, each of which contains facies successions that are reflective of past baseline shifts in the presence or absence of marine-terminating ice sheets on the outermost Ross Sea continental shelf. The oldest depositional package (&amp;gt;18 Ma) contains massive diamictites stacked through aggradation and deposited in a deep, actively subsiding basin that restricted marine ice sheet expansion on the outer continental shelf. A slowdown in tectonic subsidence after 17.8 Ma led to the deposition of progradational massive diamictites with thin mudstone beds/laminae, as several large marine-based ice sheet advances expanded onto the mid- to outer continental shelf between 17.8 Ma and 17.4 Ma. Between 17.2 Ma and 15.95 Ma, packages of interbedded diamictite and diatom-rich mudstone were deposited during a phase of highly variable Antarctic Ice Sheet extent and volume. This included periods of Antarctic Ice Sheet advance near the outer shelf during the early Miocene Climate Optimum (MCO)—despite this being a well-known period of peak global warmth between ca. 17.0 Ma and 14.6 Ma. Conversely, there were periods of peak warmth within the MCO during which diatom-rich mudstones with little to no ice-rafted debris were deposited, which indicates that the Antarctic Ice Sheet was greatly reduced in extent and had retreated to a smaller terrestrial-terminating ice sheet, most notably between 16.3 Ma and 15.95 Ma. Post-14.2 Ma, diamictites and diatomites contain unambiguous evidence of subglacial shearing in the core and provide the first direct, well-dated evidence of highly erosive marine ice sheets on the outermost continental shelf during the onset of the Middle Miocene Climate Transition (MMCT; 14.2−13.6 Ma). Although global climate forcings and feedbacks influenced Antarctic Ice Sheet advances and retreats during the MCO and MMCT, we propose that this response was nonlinear and heavily influenced by regional feedbacks related to the shoaling of the continental shelf due to reduced subsidence, sediment infilling, and local sea-level changes that directly influenced oceanic influences on melting at the Antarctic Ice Sheet margin. Although intervals of diatom-rich muds and diatomite indicating open-marine interglacial conditions still occurred during (and following) the MMCT, repeated advances of marine-based ice sheets since that time have resulted in widespread erosion and overdeepening in the inner Ross Sea, which has greatly enhanced sensitivity to marine ice sheet instability since 14.2 Ma.