Depositional Model Research Articles

Hybrid-driven MRF seismic inversion for gas sand identification: A case study in the Yinggehai Basin

The Yinggehai Basin displays anomalies characterized by heightened levels of temperature and pressure. It represents a depositional model of a submarine fan with gravity-driven flow, demonstrating significant lateral reservoir heterogeneity and intricate spatial distribution of the gas reservoir. Identifying gas formations using elastic parameters as indicators relies on stable seismic inversion results. This requires regularization to alleviate ill-posedness in the inverse problem and to construct model features of the subsurface medium. Markov Random Field (MRF)is an effective soft-constrained regularization method. It enhances the marginal features of inversion results by penalizing the objective function with the gradient of neighborhood points. However, the standard MRF method relies only on the parameter model-driven and has poor applicability in areas with strong lateral inhomogeneity or complex depositional processes. In this research paper, we propose a novel approach to seismic inversion that integrates MRF neighborhood drive and incorporates both seismic data and a parametric model. Multi-order MRF neighborhoods are constructed by using seismic data in the horizontal direction (including horizontal diagonal) and parametric model data in the vertical direction (including vertical diagonal). The model-driven results are also utilized to couple seismic data and improve the stability of the hybrid-driven MRF inversion. In addition, we select the P-impedance as the parameter for inversion due to its heightened sensitivity towards gas formation within the study region. Consequently, we utilize the inversion results to delineate the presence of sandstone in the target layer and discern any indications of gas formation. The implementation of this method in the field has demonstrated its capability to enhance the stability of inversion outcomes, effectively integrating the lateral consistency of seismic data with the vertical precision of parametric model data. This approach significantly improves reservoir heterogeneity characterization and enhances accuracy in identifying sandstone and gas.

3D stochastic simulation of a deep-water turbidite system: An example from the Los Molles Formation, southern region of the Neuquén Basin, Argentina

A recurring challenge in geological modeling is bridging the gap between different scales. For example, difficulties arise when connecting outcrop data through production to exploration scale models. An object-based stochastic simulation was performed using outcrop data from the Arroyo La Jardinera area in the southern region of the Neuquén Basin, Argentina. This simulation involved four depositional sequences in a vertical succession that includes turbidites and associated deep marine facies. The aims of this study are (a) to determine the best geological model consistent with field and aerial image data; (b) to validate the application of object modeling to determine facies distribution; (c) to evaluate uncertainties from models based on scarce data. The studied interval covers a transgressive (J1) to regressive succession (J21, J22, and J23) of basin plain to slope depositional settings, featuring sandy and gravelly turbidite channels, turbidite lobes and interlobes, lobe fringes, and muddy slope and basin plain. Each depositional sequence model was constructed using specific input parameters for architectural elements, with lithological proportions based on sedimentary logs. The J1 sequence includes basin plain, lobe fringe, and minor lobe deposits; J21 features turbidite lobes, fringes, and subordinate channels; J22 accommodates turbidite channels scoured into muddy slope facies; and J23 encompasses gravelly and sandy turbidite channels carved on muddy slope facies. The geostatistical modeling of outcrop data has allowed building a quantitative sedimentological model useful for understanding subsurface facies heterogeneity in both exploration (vertical) and production (horizontal) scales.

Timing and geometry of the Chemehuevi Formation reveal a late Pleistocene sediment pulse into the Lower Colorado River

The Chemehuevi Formation is a distinctive 50−150-m-thick wedge-shaped Pleistocene sedimentary unit deposited by the Colorado River. It lines the perimeters of the river’s floodplains and bedrock canyons for more than 600 km between the mouth of the Grand Canyon and the delta region in the Gulf of California. The formation is composed of a basal tan to light-yellowish-brown and pale-orange mud-dominated facies overlain and interbedded by a light-yellow-brown sand-dominated facies. The unit is one of two extensively exposed aggradational packages in the Lower Colorado River corridor, in addition to a series of other smaller alluvial terrace deposits. The Chemehuevi Formation appears to represent the response of a fully integrated Colorado River system to a significant perturbation, in contrast to the Bullhead Alluvium, which is likely a unique result of Pliocene river integration. The aggradation of the Chemehuevi Formation in the Lower Colorado River corridor may be similarly due to a unique event in the Colorado River system, or it may instead be a well-preserved sedimentary sequence recording typical behavior of the Colorado River below the Grand Canyon in the late Pleistocene. As such, multiple causal mechanisms have been proposed, but no study to date has conclusively explained the Chemehuevi Formation. To help resolve its timing, duration, and origin, we applied post-infrared infrared stimulated luminescence, carbonate U-Th series, and zircon sensitive high-resolution ion microprobe U-Th series geochronology to determine the ages of key exposures of the unit over a wide spatial area. These new data demonstrate that the Chemehuevi Formation was deposited ca. 110−90 ka. The depositional ages collectively overlap, suggesting that deposition occurred rapidly relative to the resolution of the geochronometers. The new depositional timing coincides with a shift from glacial to interglacial conditions after the marine isotope stage 5-6 transition. This observation is consistent with a climate-induced sediment pulse as a causal mechanism, yet correlations with similar deposits in the Colorado River headwaters or in neighboring catchments appear elusive. Potentially, climate transitions between glacial and interglacial periods induced a sediment pulse from hillslopes of the Colorado River system that resulted in the Chemehuevi Formation. An alternative or additional explanation is that the Chemehuevi Formation represents release of lava dam−impounded sediment in the Grand Canyon. The surface geometry of the Chemehuevi Formation projects upstream to the approximate location of lava dams, and the largest possible lava dam impoundment (the Upper Prospect dam) is comparable in volume to the formation. The lava dam hypothesis appears to be a possible explanation for the Chemehuevi Formation. However, tying deposition to a specific lava dam or series of lava dams remains challenging due to discrepancies in timing and volume. The combined effects of a series of lava dams may have led to the Chemehuevi Formation, as the last Pleistocene lava dam eruption coincides with the onset of deposition. Alternatively, the formation may result from the combined effects of both regional climate transitions and the lava dams that created a transient reservoir to compound a climate transition−driven sediment pulse. The geochronologic data presented here do not allow us to distinguish between the lava dam or climate transition hypotheses but will need to be reconciled with any future proposed depositional model.

Source rock and petrophysical evaluation of the Late Cretaceous Haymana Formation, Haymana Basin, Central Anatolia, Turkey

This study investigates the petroleum potential of the mudstones of the Late Cretaceous Haymana Formation in the Haymana Basin, Turkey. Lithofacies, pore structure, and source rock characteristics of the mudstones are examined using stratigraphical, sedimentological, petrophysical, and organic geochemical methods along four stratigraphic sections and other sampling sites. The depositional model presents a facies distribution within a submarine fan system. According to bulk mineralogy, the identified lithofacies are mixed mudstone, mixed siliceous mudstone, marl, mixed carbonate mudstone, argillaceous/siliceous mudstone, and clay-rich siliceous mudstone. XRD and mercury intrusion measurements suggest that the macropores (> 50 nm) of the mudstones formed by dissolution of calcite, while mesopores (2 nm-50 nm) developed around the clay/quartz/feldspar. Of the analysed samples, no lithofacies class is distinct with any specific range of porosity or permeability, which suggests a strong heterogeneity in pore throat size, mineral content, and grain size. The black shale from the northwest of the basin with 1.19% TOC, 0.07 mg/g S 1 , 1.01 mg/g S 2 , and 441°C T max is a relatively more mature source rock although it still exhibits poor petroleum potential. Overall, the TOC values (avg. 0.38%) of the mudstones suggest organic-poor rock characteristics for the Haymana Formation in the studied parts of the Haymana Basin.

Microfacies Analysis and Depositional Model for the Black River -Trenton Carbonates (Ordovician) of Southern Ontario, Canada

This study documents the detailed microfacies depositional environment of the Ordovician Black River and Trenton limestone Groups in Lake Simcoe area of southern Ontario, resting unconformably on Precambrian basement. Local Precambrian 'highs' complicate the overall facies pattern and lithofacies patterns define local shoal, intershoal and basinal environments. Detailed microfacies and facies analysis in large quarries in the Lake Simcoe area are used to infer various carbonate environments by comparison with analogous modern and ancient ramps. Fifteen microfacies are grouped into six microfacies associations based on composition, grain size and texture. Relative energy levels, and depositional environments for these are then inferred. These environments resemble the Recent Arabian Shelf of the Persian Gulf for the Black River Group, and the Recent West Florida Shelf for the Trenton, though other Recent ramps like South Australia are also comparable. The vertical arrangement of facie\s in the Lake Simcoe area forms repetitive cycles, which can then be traced laterally into adjacent areas, complicated by the effects of sea-floor topography and possibly by synsedimentary faulting.

Sedimentary processes and patterns in deposits corresponding to freshwater lake-facies of hyperpycnal flow – An experimental study based on flume depositional simulations

Abstract The article establishes a depositional model for lacustrine hyperpycnal flow by examining dynamics, transport factors, and laminae formation. The results show that several typical experimental phenomena such as fluid front mixing, double flow division, underwater leap, water skiing, and “new head” can be observed in the flume experiment. Based on the experimental observation of the flow process, three modes of transport of hyperpycnal flow in freshwater lake basins are summarized: bottom-bed loading, suspended loading, and uplift loading. Further, the change of fluid properties in hyperpycnal flow is summarized in three stages: a high-concentration stage, a low-concentration stage, and an uplifting stage. There are two main factors affecting the long-range transport of hyperpycnal flow: (1) the concentration difference between the head deposits and the ambient water body and (2) shear force of turbulence in the upper part of hyperpycnal flow. The simulation experiments of hyperpycnites laminae show that the laminae change from continuous to intermittent with the increase of the transportation distance. It is clear that the mode of transport of the hyperpycnal flow has a controlling effect on the degree of development of the laminae. Eventually, a depositional model of lake-facies hyperpycnal flow under experimental conditions was constructed.

Description of the Late Holocene South‐east Saline Everglades, Florida palustrine depositional environment with comparisons to other Holocene environments

AbstractA transgressive palustrine depositional model is described for the South‐east Saline Everglades, Florida. The origin, development and termination of freshwater carbonate mud (marl) deposition along the very low gradient Late Pleistocene carbonate ramp are responses to changing rates of rising sea level during the Late Holocene. The onset of the Late Holocene is defined by a decrease in the rate of sea‐level rise from between 2 and 3 to <1 mm year−1. Freshwater marl deposition began with this decrease ca 3165 ± 187 year BP, in a shallow (<0.3 m deep), ephemeral wetland that developed landward of a fringing mangrove forest and is maintained by seasonal Everglades water delivery. Sedimentation kept pace with sea‐level rise forming a 1.2 m thick wedge shaped, landward thinning deposit. The rate of global sea‐level rise began to accelerate ca 1900, the Anthropocene Marine Transgression, and presently the regional rate is 9.4 mm year−1. Saltwater encroachment rates >80 m year−1 are driven by sea‐level rise. Saltwater encroachment resulted in retreat and transformation of coastal communities and their biogenic facies, resulting in a decrease in freshwater wetlands and marl production. Inundation ponding, mangrove overstep and the beginning of submergence are the responses to the accelerating rate of sea‐level rise, however, small scale topographic and tidal ingress differences create considerable variability between Biscayne Bay and Florida Bay coastal basins. The freshwater marl producing habitat will probably be lost within 55 years, and submergence within the next century at the present rate of sea‐level rise. The unique South‐east Saline Everglades depositional environment is compared to other Holocene palustrine depositional environments.

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

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

تحليل السحنات الرسوبية وتوصيف الخزانات لتكوينات حواز والمومنيات من العصر الأوردوفيشي وتكوين عوينات وأنين من العصر الديفوني، منطقة 176-4، حوض مرزق، جنوب غرب ليبيا

The Ordovician to Devonian succession in the in Murzuq Basin represents the most important part of the lower Paleozoic terrigenous Al Gargaf siliciclastic group, which consists of several formations such as the Ordovician Hawaz, Melaz Shuqran and Mamuniyat Formations and the Devonian Tadrart and Awainat Wanin Formations. Different integrated methods were used and implemented in order to understand lithology and sedimentary structures of the Ordovician, Silurian and Devonian formations. Firstly, intensive geological field trips were carried out and special attention was focused on Ordovician and Devonian reservoir sandstones and the Silurian source rocks. Secondly facies analysis and sequence stratigraphy methods were applied to figure out a simple sequence stratigraphic division of the Ordovician to Devonian succession based on outcrop sections, well logs and interpreted seismic sections. As a result of the petrographic field investigation and facies analysis based on seismic interpretation of the several seismic lines in the study area. Sequence boundaries of the Ordovician and Devonian succession on all seismic sections were identified by using specific reflection terminations such as onlap and erosional truncations features. 13 seismic facies were recognized, divided and classified for each of the examined stratigraphic formations (4 facies in Hawaz, 5 facies in Melaz Shuqran and Mamuniyat formations and 4 facies in the Tadrart and Awainat Wanin). A seismic facies classification chart was made on the basis of the classified seismic facies scheme, since depositional systems and types of seismic facies differ in each stratigraphic succession. Depositional sequences of sedimentary environments were identified from well logs and available 2D seismic sections and sequence stratigraphic frameworks were constructed for the Ordovician and Devonian formations. Based on the facies analysis and sequence stratigraphy interpretations, two different order sequences in the Ordovician to Devonian succession have been found and identified: The major sequences are possibly 2nd-order sequences in time duration. They are clearly traceable on all seismic sections. May be minor sequences are possibly 3rd-order sequences, and they are not traceable on all seismic sections clearly, but are recognized on well logs or outcrop sections. Eventually, all obtained information and that results were plotted on the different maps for each examined section to construct a depositional model and to estimate the maximum distributions of each formation separately on the basis of depositional system interpretations. Keywords: Murzuq Basin, Al Gargaf siliciclastic group, Ordovician to Devonian succession, depositional system and seismic facies

Facies variability and depositional cyclicity in central Northern Switzerland: insights from new Opalinus Clay drill cores

The Opalinus Clay, a silty to sandy claystone formation, Early to Middle Jurassic (Toarcian and Aalenian) in age, has been selected as the host rock for deep subsurface disposal of radioactive waste in Switzerland. Over the past thirty years, numerous geotechnical, mineralogical, and sedimentological studies have been conducted on the Opalinus Clay within the framework of the Nagra (National Cooperative for the Disposal of Radioactive Waste) deep drilling campaigns and the Mont Terri Project, an international research program dedicated to the study of claystone. The present study aims to unravel the variability of the lateral and vertical facies of the Opalinus Clay in central Northern Switzerland and to place this variability in a regional and basinal context. Analyses of new cores drilled in central Northern Switzerland, including petrographic, mineralogical (X-ray diffraction, multi-mineral interpretation), geochemical (X-ray fluorescence), statistical (non-metric multidimensional scaling analysis), and bedding dip and azimuth data, shed new light on the depositional facies and the spatial and temporal variability of the Opalinus Clay. Petrographic descriptions encompass nine new drill cores using a revised subfacies/facies classification scheme based on texture (colour, grain size, bedding) and composition (mineralogy). Particularly, one new subfacies (SF6) is described and interpreted as mass-wasting deposits. The drill cores are correlated laterally using specific marker horizons. This correlation is achieved by combining thorough facies investigations with lithostratigraphy, biostratigraphy, and chemostratigraphy. Six to seven small coarsening-upward cycles and two long-term coarsening-upward sequences can be interpreted as regressive trends. The observed trends are influenced by the interplay between sediment supply, eustatic sea level change, synsedimentary subsidence, but also the palaeogeographic configuration in an epicontinental sea, provenance and delivery of sediments, current dynamics and climate change. Finally, combined results show that the current dynamics in the Opalinus Clay has been underestimated until now and new depositional models, including the occurrence of drift deposits, are discussed.

Ramp Depositional Model in an Intracratonic Basin: The Cambrian Sedimentary Successions in Yanshan Area, North China

Ramp Depositional Model in an Intracratonic Basin: The Cambrian Sedimentary Successions in Yanshan Area, North China

Sedimentology and structure of the Paleogene Nummulitic series of Corsica: Reconstruction of the southern termination of the western Alpine foreland basin

AbstractNummulitic Limestones deposits are preserved along the tectonic contact between the Variscan basement and Alpine units of Corsica. These marine carbonates, dated from the Late Palaeocene to the Middle Eocene, were deposited within a foreland flexural basin that is considered to be the southern continuation of the Alpine foreland basin of southeast (SE) France. However, in contrast with the Nummulitic Limestones of SE France, those of Corsica are far less documented. This field‐based study constrains the sedimentology, stratigraphy and structure of the Nummulitic Limestones of Corsica in three localities (Balagne, Corte and Sari‐Solenzara) to identify factors that controlled foreland basin development and to clarify its significance within the early alpine orogen. The microfacies, microfaunal assemblages and siliciclastic fractions are characterised throughout the succession at each locality. The results indicate the existence of an important Variscan basement relief to the west of the basin (West Corsican Massif) that supplied early alluvial fans found at the base of the foreland succession in the northernmost Balagne area. Continuous high clastic input strongly reduced the development and diversity of the overlying Nummulitic Limestones facies and fauna. Further south, limestones in the Corte and Sari‐Solenzara areas are thicker and contain richer fauna. Three depositional models corresponding to the carbonate ramp system are proposed for the Nummulitic Limestones and used to construct paleogeographic maps illustrating the transgressive evolution of the Corsican foreland basin from the Early to the Late Eocene. Based on our results and available regional tectonic data and LT thermochronological data, we propose that the Nummulitic marine transgression took place within a continuous foreland basin encompassing southern Corsica and SE France during the early development of the western alpine arc.

Heterolytic tide-dominated sedimentary facies and depositional environment: An Example from the Boka Bil formation, Sitapahar anticline, Bangladesh

The Baraichari Shale Formation, which is equivalent to the Boka Bil Formation, is well exposed within the Neogene sequence of the Sitapahar Anticline in the Chittagong-Tripura Fold Belt, Bengal Basin, Bangladesh. Regardless of its importance in hydrocarbon accumulation, a comprehensive facies analysis is essential to understand and explain the heterogeneity within different depositional architectural elements. The purpose of this work is to delineate the lithofacies characteristics, depositional environment heterogeneities and propose a generic depositional model for the Middle to Late Miocene shallow marine sediments of the formation. The sedimentary facies were investigated at three outcrops along the Kaptai–Chandraghona road cut sections of the Sitapahar anticline. The formation is composed of dark to bluish-gray shale, silty shale, yellowish brown siltstone, and gray to yellowish brown fine-to medium-grained sandstone. Eight distinct sedimentary facies have been identified and were categorized into three facies associations: subtidal or estuarine, mixed flats with tidal creeks, and tidal mud flats. The subtidal facies, predominant in the middle member, consists of fine to medium-grained ripple cross-stratified sandstone-siltstone, herringbone cross-stratified sandstone, and trough cross-stratified sandstone, indicating sub-tidal channel deposition. Mixed flats with tidal creeks exhibit heterolithic facies, suggesting energy level changes in intertidal to sub-tidal zones influenced by tidal currents. Tidal mud flats are predominantly laminated shale/mudstone and lenticular laminated sandstone-siltstone, reflecting deposition during tide transitions in the intertidal zone. Fining upward cycles within the formation indicate progressive progradation or changes in inner tidal flats conditions during regressive periods. These depositional settings serve as analogs for equivalent subsurface reservoirs and contribute to the construction of reservoir models with greater accuracy.

Sedimentary dynamics and depositional model for mud accumulation in deep lake basins: A case study in the Upper Triassic Chang-7 Member, Ordos Basin, northern China

Shales in deep lake basins have become the main focus of continental shale oil and gas exploration. In order to highlight the sedimentary dynamics of mud deposition in deep lake basins, a combination of core observation, thin section examination, X-ray diffraction, and QEMSCAN (quantitative evaluation of minerals by scanning electron microscopy) was used to analyze the depositional characteristics of mudrocks in the Chang-7 Member from the Yanchang Formation (Upper Triassic) in Ordos Basin, and to establish a depositional model for mud accumulation in deep lake basins. This study recognizes four mudrock lithofacies in the Chang-7 Member: (1) the laminated silt-bearing mudstone, which generally develops a binary composition of “silt–clay” or a ternary composition of “silt–clay–organic matter”; (2) the graded mudstone, mainly composed of dark gray and gray-black mudstone sandwiched by silt-bearing mudstone; (3) the massive mudstone, internally showing a uniform distribution of quartz, clay, and carbonate minerals, with also a small amount of organic detritus; and (4) the laminated shale, which is generally composed of clay laminae, and organic laminae of the former two. Sediment supply, topographic slope, and flood intensity combine to control the evolution of gravity flows and the transport and deposition of the mudrock in the Chang-7 Member. The influence of orogeny provides terrain gradient, water depth, abundant sediments at source areas, and triggering mechanism for the formation of gravity flows. Floods triggered by wetting events provide the impetus for sediment transport. Mud deposition in the Chang-7 Member was mainly related to the transport and sedimentation of mud by hyperpycnal flows and rapid sedimentation by buoyant plume flocculation. A comprehensive evolutionary model for shale accumulation in the deep lake basin is established by integrating various triggering mechanisms and mud transport sedimentary processes.

Newly discovered diamictite and cap carbonate couplet in the southern Alxa Block, northwestern China: Implications for stratigraphic correlation and Marinoan glaciation

Neoproterozoic glaciogenic diamictite and cap carbonate couplets have played a pivotal role in understanding glacial-interglacial cycles and establishing regional stratigraphic correlation. The Alxa Block in northwestern China preserves a sequence of Neoproterozoic diamictites along its southern margin, but the age and origin of the succession remain debatable due to the lack of discovery of cap carbonate. We report newly discovered cap carbonates that overlie the diamictites of the Shaohuotonggou Formation in the Longshoushan region in the southern Alxa Block. Based on detailed geological investigations, we identified massive diamictites, stratified diamictites, and cap carbonates in the lower part of the formation. The presence of ice-rafted dropstones, bullet-shaped and facetted clasts, glacial striations, and relatively low chemical index of alteration values of sedimentary matrix support a glaciogenic origin of the diamictites. The 2- to 2.6-m-thick cap carbonates are mainly composed of thinly laminated microcrystalline dolomites and show sheet cracks, cemented breccias, and tepee-like structures at the basal part of the unit. These features and their consistently negative δ13C values (−5.2‰ to −2.2‰) are characteristic of Marinoan-age cap carbonates (ca. 635 Ma). The quasi-continuous deposition of the massive diamictites, stratified diamictites, and cap carbonates suggests that the formation of this couplet was closely related to the Marinoan glaciation and subsequent deglaciation. We propose a three-stage depositional model for the glaciogenic succession and recommend that the diamictite and cap carbonate couplet in the Alxa Block provides a credible mark of the Cryogenian−Ediacaran boundary for further stratigraphic correlation and investigation.

Facies controls and tectonic evolution on oil accumulation and entrapment in the Cenomanian Abu Roash G member, northern-central Egypt: Deltaic and channel sandstones as good reservoirs

Along northern-central Egypt, the oil accumulation and entrapment were mainly controlled by variable parameters including the stratigraphic architecture, sedimentary features, and tectonic evolutions. The present paper presents a new model for oil occurrences in the Abu Roash G Member (Cenomanian) along Gindi, Abu Gharadig and to a few extents the Beni Suef basins, in the northern-central part of the Western and Eastern Deserts of Egypt. The studied concessions include the Wadi El Rayan, East Bahariya and El Diyur (Gindi basin and Abu Gharadig basins, Western Desert) and the Ghariboun (Beni Suef Basin, Eastern Desert) fields. Twenty sedimentary facies were recorded from the studied subsurface sections of the Abu Roash G Member and grouped into three facies associations. A new depositional model is achieved where estuarine, open marine, deltaic distributaries, and tidal channel deposits are the main facies associations recorded in the studied Abu Roash “G". These deltaic and channel deposits occurred as an arch like form between open marine and estuarine deposits. These deltaic and tidal channel sandstone deposits act as a good reservoir to accumulate oil from nearby areas. As well, these areas were subjected to the well-known Syrian arch compressional deformation that affected northern Egypt during the Mesozoic, up to late Senonian time. A regional NE-SW oriented fold system took place, forming NE-SW oriented ridges in addition to the dextral strike-slip movement that took place along these ridges because of this compressional deformation.To sum up, oil accumulation in the studied Abu Roash G Member was mainly controlled by facies distribution mainly of channel sandstone enhanced by the tectonic movements (Syrian Arc System) affecting the areas studied.

Sedimentology and stratigraphy of lower Cretaceous fluvial to shallow marine deposits on the central Atlantic passive margin: The Aaiun-Tarfaya Basin, Morocco

This paper presents the first integrated regional outcrop-based sedimentological study of the northern Aaiun-Tarfaya Basin located in Morocco (NW Africa). The Lower Cretaceous Tan-Tan Formation has been subdivided into six new members and placed within a sequence stratigraphic framework that includes two incomplete depositional sequences. Strong thickness variations of individual lithostratigraphic units from north to south suggest differential subsidence during sedimentation and/or the existence of major topography on the basal unconformity that the succession onlaps. The results provide valuable insights into the timing of local tectonics in the Western Anti-Atlas and the control on the evolution of the sedimentary system. Deposition of each of these six units is interpreted to be the result of a complex interplay between an overall eustatic sea-level rise during the early Cretaceous, sediment delivery controlled by tectonic movements in the Western Anti-Atlas and Reguibat Shield and periods of differential subsidence in the basin. The results document the style of evolution of a back-stepping wave-dominated system feeding into the Central Atlantic during the passive margin phase. The improved facies and depositional models together with improved understanding of the evolution of the delta have significant implication for exploring the deep-water equivalents offshore.

OSL re-dating and paleoclimate of Laoya Cave in Guizhou Province, southwest China

Laoya Cave is a significant prehistoric human site in Guizhou Province, Southwest China, and optically stimulated luminescence (OSL) and a Bayesian depositional model were used to update the chronology of the cave. Six OSL samples were dated to 16.7 ± 1.2, 18.0 ± 1.1, 28.8 ± 2.3, 32.1 ± 2.8, 57.7 ± 6.5, and 74.0 ± 5.9 ka, respectively, and the Bayesian deposition model has provided a coherent chronological framework, revealing boundaries with median ages of 18.5, 25.0, 27.5, 28.6, 29.9, and 74.4 ka for Boundaries 1/2, 2/3, 3/4, 4/5, 5/6, and 6/9, respectively. By comparing the new chronological framework with the related records of paleoclimate and human activities, we gain insight into the relationship between the environment and Paleolithic hominins at different times. During relatively warmer periods, humans tend to spread, while in relative colder climates, they tend to rely more heavily on caves and employ hunting strategies with an equal age distribution. These survival strategies help humans prevent the threats of cold weather. Additionally, the analysis of OSL dating results uncovers a discrepancy between OSL and accelerator mass spectrometry radiocarbon (AMS 14C) dating methods, with AMS 14C dates generally appearing older at later ages (<∼30 ka). This phenomenon may be due to disturbances caused by human activity, and OSL dating may recognize this to some extent.

The dominant influence of muddy bottom currents on organic-rich fine-grained sedimentary rocks: The lower Congo Basin, west Africa

The Madingo Formation in the Lower Congo Basin (LCB) of West Africa is a fine-grained strata, which is considered to be the most promising source interval during the drift stage. Despite the extensive studies of the internal sedimentary characteristics of the Lower Mading Formation (LMF), muddy bottom currents have not been previously identified in this area. Extensive seismic (2D and 3D data), wire - line measurements and cutting samples in the LCB offer a unique opportunity to study the influence of muddy bottom currents depositional system on organic matter, and related depositional environment of the region and its depositional model of organic rich fine-grained strata. This study aims to unravel the influence of muddy bottom currents on organic matter enrichment within the LMF and build a depositional model. In combination with drilling and thin sections analysis, the M-1 member suggests the initiation and cessation of muddy bottom currents. Utilizing 3D seismic data inversion techniques, geochemical analysis, and sedimentological assessment, we studied the effect of muddy bottom currents on organic matter enrichment from the perspectives of paleoproductivity, preservation conditions, terrigenous input, and total organic carbon (TOC) distribution. Results show that muddy bottom currents have a significant impact on the redistribution of shallow water shelf sediments. They promote the transportation of nutrients and organic matter to deep water shelves, improving paleoproductivity. Most notably, terrigenous input is a key factor affecting organic matter distribution, resulting in dilution effects in deep water shelf bottom current influence areas, but conducive to the preservation of deep organic matter in low-lying areas of shallow water shelf. Muddy bottom currents have a weaker influence on the preservation environment of deep water shelves, but they have a significant effect on redox indicators (eg. U/Th, Ni/Co, V/Cr). Specifically, they reduce the enrichment in particulate elements. We established the depositional models of organic-rich fine-grained sedimentary rocks for the M-1 and M-2 members in LCB. These insights not only provide practical depositional models for marine sources rocks in the LCB, but also improves the general understanding of marine organic matter accumulation in muddy bottom currents environments. Furthermore, they serve as a reference for the study of organic-rich fine-grained sedimentary rocks in similar basins.

Carbonate‐rich megabeds within a Triassic siliciclastic deep‐water system, West Qinling orogenic belt, Central China: Character, processes and implications

AbstractDeep‐water megabeds are a particular type of sediment gravity flow deposit that are anomalously thick and often of distinctive composition compared to the deep‐water strata within which they are embedded. Pure siliciclastic or carbonate megabeds have been widely reported from deep‐marine systems. Less documented are carbonate‐rich mixed megabeds with abundant carbonate clasts in a siliciclastic matrix, which are embedded in siliciclastic deep‐water systems. Here, such examples are reported from outcrops of the Lower Triassic in the West Qinling orogenic belt, central China, with a focus on the character, processes and implications of these carbonate‐rich megabeds. Based on regional geology and characteristics of the encasing siliciclastic turbidites and autochthonous micritic limestones, these megabeds are inferred to have been deposited in a deep marine trough. The megabeds are thick (1 to ca 10 m) compared to surrounding beds (commonly less than 1 m), and are of mixed composition, comprising both siliciclastic grains and shallow‐water carbonate clasts. These megabeds are commonly characterised by a distinctive bipartite or tripartite vertical succession of facies. A complete (tripartite) sequence consists of a basal clast‐supported conglomeratic division (Division I), an intermediate matrix‐supported conglomeratic division (Division II), and an upper normally graded and/or laminated sandy division (Division III). These divisions are interpreted to be deposited from evolving debris flows transitioning to turbidity currents during a single flow event, and are the result of flow deceleration and dilution. The megabeds show variability over very short lateral distances (several tens to a few hundred metres), possibly related to surface relief on the debritic portion of the deposit. A new depositional model is proposed for the mixed deep‐water system, with frequent siliciclastic turbidite deposition within this elongate basin from axially flowing turbidity currents, and episodic deposition from laterally‐supplied carbonate‐rich megaflows that eroded and incorporated the substrate during transport.