Depositional Setting Research Articles

Morphology and Depositional Processes of a Carbonate-Filled Canyon in the Carboniferous KT-II Formation of the Eastern Precaspian Basin, Kazakhstan: Insight from 3D Seismic Data

Canyons in carbonate depositional settings, as important elements of the source-to-sink system, remain poorly studied compared to those in siliciclastic depositional environments. The latest high-resolution three-dimensional seismic data, well logs, and core data at the eastern edge of the Precaspian Basin are used to investigate the geomorphology, infillings, and depositional process of a unique carbonate-filled canyon in the Carboniferous KT-II formation parallel to the carbonate platform, which is distinct from other slope-perpendicular canyons. The canyon has a total length of more than 52.3 km with a nearly N-S orientation and an S-shaped geometry, and the whole canyon can be divided into three segments by two knickpoints. The slope-parallel orientation of the canyon is mainly controlled by the palaeogeomorphology and reverse faults. Due to the collision of the Kazakh and European plates in the early-middle Visean (early Carboniferous), the canyon was formed in a northern tilted, elongated, and restricted palaeotopographic feature between uplifts. The development of reverse faults related to tectonic movement controlled the variations in the width of the canyon and the positions of the knickpoints. Tectonics controlled the orientation and formation of the canyon, while sedimentary processes contributed to its infilling. The well-seismic tie analysis indicated two distinct periods of the canyon fillings, Ss1 and Ss2, which were separated by a second-order sequence boundary. The lower part contained sediments supplied by both sides of the canyon through channels or gullies, and the upper part was dominated by a carbonate platform that prograded from the eastern side of the canyon. The evolution of the canyon can be subdivided into three stages. The increasing stage was mainly characterized by significant upslope erosion through headward retrogressive mass failures in the slope-parallel confined negative relief to form the canyon during the lowstand system tract of Ss1. Subsequently, in the early filling stage, the carbonate factory was productive during the highstand, and massive excess carbonate sediments were transported into the adjacent canyon by channels or gullies on both sides and deposited. The canyon was basically filled, and the morphology became much gentler. During the subsequent late filling stage, the carbonate platform was flooded again during the highstand, and the production rates of the carbonate factory greatly increased. The lateral progradation of carbonate platforms accelerated on the canyon of the early filling stage and further into the inner sag.

Variable Ophiomorpha ichnofabric: Improving the understanding of mouth bar environments in fan-delta complex depositional settings from the Upper Cretaceous of NW South America

Fan-delta deposits, an important sedimentary component of fan-delta complexes, are scarcely described in the ancient record because it is very difficult to distinguish them from other types of coarse-grained deposits (e.g., alluvial, fluvial, or deep marine deposits). This obstacle is overcome when a well-record of physical/biogenic sedimentary structures or fossils unambiguously marks the influence of the receiving basin. However, this is usually not the case. Here, we present the Ophiomorpha ichnofabric record as a key proxy of marine influence within a generally fluvial-dominated system for improving the paleoenvironmental understanding and reconstructing animal-substrate interplay during the evolution of a fan-delta complex. The ichnological record, together with detailed sedimentological analysis, allows us to define three ichnofabric types, distributed in four levels. The stratigraphic distribution of these features points to distal alluvial environments towards the base, dominated by debris and sheet flows deposits and locally shallow braided channels; they evolve upward into well-developed braided fluvial system whose facies arrangement is related to channel fills, locally influenced by debris flows. Subsequently, a basinward migration of the sedimentary system is recorded through the occurrence of the first level with Ophiomorpha ichnofabric A, and then ichnofabrics A and B in levels 2 and 3, respectively, suggesting marine-influenced mouth bar settings. Toward the top, another steep basinward migration is evidenced by Ophiomorpha ichnofabric C in level 4, indicating wave-dominated processes in distal mouth bars environments. The record of marine-influenced and dominated levels may indicate relative sea-level fluctuations related to local or autogenic processes at the basin scale. Furthermore, the present study demonstrates the ability of Ophiomorpha tracemaker to colonize challenging sedimentary environments.

Integrated biostratigraphy and chemostratigraphy of the Maastrichtian–Danian succession at Abu Minqar, Egyptian Western Desert: Implications for sequence stratigraphy and tectonic influence

We investigated the Maastrichtian–Danian succession at the Abu Minqar section in the Western Desert of Egypt (part from the southern Tethyan margin) using an integrated analysis of biostratigraphic (calcareous nannofossils, foraminifers, macrofauna) and chemostratigraphic data to determine the controlling factors on depositional history. The integrated microplankton biostratigraphic framework identified two prolonged hiatuses at the lower/upper Maastrichtian and the Maastrichtian/Danian boundaries. Four depositional sequences were identified and subdivided into systems tracts based on paleodepth variation evidenced by foraminiferal investigations and the comparable response of the various geochemical indices. The study also highlighted the presence of two alternated depositional styles in the study area, influenced by relative sea level, with the first style involving the deposition of aluminosilicate-enriched intervals that yield non-calcareous foraminifers in lagoonal and coastal depositional settings induced by relative sea-level fall and river rejuvenation, and the second one involving the deposition of calcareous intervals containing abundant megafossils, calcareous foraminifers, and nannofossils during a sea-level rise. Despite the occurrence of certain resemblances to the global eustatic curves, the inferred relative sea level pattern suggests that regional tectonics had a substantial role in developing the depositional history and paleoenvironmental circumstances of the southern Tethys margin. These findings help build a more comprehensive picture of the geological evolution of the southern Tethyan margin during the Late Cretaceous to Paleogene.

The upper cretaceous carbonate sediments of the Ras Budran Field, Gulf of Suez, Egypt: stacking patterns and depositional controls

The present study interprets the carbonate stacking patterns and their depositional controls in the Upper Cretaceous strata of the Ras Budran Field in the Gulf of Suez, Egypt, on the basis of integrated well logging and a geological report provided. A set of well logs was run for two wells (RB-A2 and RB-B2), comprising gamma ray, resistivity, density, neutron, sonic, and photoelectric factor. Composite logs and geological reports were also used to help deduce the lithological and biological description of the stratigraphic units under investigation. The stacking patterns of the carbonate rocks yielded three types of electro-facies. The first facies covers the lower part of the Brown Limestone (early Campanian) and reflects a cylindrical (aggrading) stacking pattern. This facies indicates keep-up carbonate deposition in a heterogeneous facies accumulated in shallow water. The second facies covers the upper part of the Brown Limestone (late Campanian) and displays a funnel (prograding) stacking pattern. This facies indicates the depositional setting of a shallow shoreline. The third facies covers the Sudr Chalk (Maastrichtian), for which a serrated stacking pattern indicates an aggradational environment. This pattern indicates a marine depositional setting both distal and deep. Therefore, the formation and evolution of the cyclical stacking pattern of the carbonate rocks reflects variations in accommodation potential that determines the environmental changes. The evolution of these deposits is mainly attributed to a combination of eustatic sea-level fluctuations and tectonic episodes within the basin.

THE OLDEST TRACE FOSSILS IN ASSOCIATION WITH EDIACARA-TYPE BIOTA IN THE UPPER VENDIAN OF THE SOUTH URALS

Trace fossils and palaeopascichnids have been studied from the Basa Formation of the Vendian Asha Group of the South Urals (southwestern periphery of the Suleiman Anticline, Shubino quarry in the Ust’-Katav city, Chelyabinsk Region. The general morphology and preservation of ichnofossils was shown to be similar to the Late Vendian-Early Cambrian subhorizontal bilobate burrows of Didymaulichnus. The paleontological remains were found to be confined to extremely shallow depositional settings and located stratigraphically below the volcanic tuff layer, the zircon from which has a U–Pb isotopic age of 578 ± 7 Ma. Until now, the first occurrence of trace fossils and the associated “Agronomic Revolution” were thought to be timed to the interval of ~560–550 Ma. Our results show that mobile benthos and biological mixing of sediments may have occurred 20–30 Ma earlier and support the hypothesis that the onset of the first “Agronomic Revolution” and the “Cambrian Explosion” were not significantly coincident in time.

Volcanism Pacing Slumping Gravity Flow Deposits during the Late Carboniferous in the Southern Margin of the Junggar Basin, China

AbstractDeep‐water gravity depositional processes and evolution in arc systems have become topics of intense research focus in recent years. This study discusses the co‐evolution of volcanism and deep‐water gravity flow deposits at the southern margin of the Junggar Basin, based on petrology, geochronology and geochemical analyses. The results show that a massive collapse of unstable sediments from the slope was triggered by volcanism, resulting in the formation of slumping gravity flows. The occurrence of volcanic beds in the slump deposits confirm that synchronous volcanism likely affected sediment instability, triggering gravity flows. The Th/Yb, Ta/Yb and Th/Ta elemental ratios, U‐Pb ages of detrital zircons and paleocurrent directions indicate that the North Tianshan (NTS) island arc represents the provenance of the Qianxia Formation. Moreover, statistical data on the pyroclastic components in the gravity flow deposits reveal an intensity index of volcanism, indicating that volcanism is strongly related to gravity flow deposits, especially in terms of the type and distribution of the deposits. A model for volcanically‐triggered deep‐water gravity flow deposits is established, in order to provide a more in‐depth understanding of the co‐evolution of volcanism and gravity flow deposits within the depositional setting of the late Paleozoic NTS oceanic subduction margin in the Junggar Basin.

Depositional Architecture and Reservoir Quality Assessment of Abu Roash (G) Dolomite, as a Low Resistivity Pay, Razzak Oilfield, Western Desert, Egypt.

Abu-Roash (G) dolomite (A/R-G) is considered one of the most prolific oil-bearing reservoirs in the Western desert. In this study, Razzak Oilfield was selected to investigate the geological and petrophysical findings of these successions that were assigned stratigraphically to the upper Cretaceous (Late Cenomanian), in the Alamein basin. Sedimentologically, three main facies groups have been recognized in the studied successions of A/R-G and include dolostone, limestone and mudstone facies; and depositional; are divided into three parts: A) Back-reef to reef crest (Reefal depositional setting) - dolostone facies group; graded to B) Inner-ramp of limestone / dolomitic limestone facies types; then C) mud-flat (intertidal setting) of calcareous mudstone facies type. Petrophysically, most of the recorded pore sizes in the dolomite zone are mesopores (≈1 micron), with scattered macropores (2-10 microns), as identified by MICP on some selected 1.5” core plugs. In general; A/R-G dolomite displays low resistivity pay (high conductivity) due to: A) The heterogeneity of moldic and vuggy pore size distributions (macropores); associated with the dominant intercrystalline-dolomite mesopores; and B) Fe-rich minerals that increase the conductivity; where most of the identified dolomite crystals are secondary, late-diagenetic stage ferroan dolomite; and confirmed that petrographically by thin-section analysis.

Lithofacies and Clay Mineral Analysis of the Upper Cenomanian Ms'ad Formation, Rutbah Area, Western Iraq

The Cenomanian succession in Rutbah City, western Iraq, is composed of siliciclastic carbonate with multicolored paleosoil layers that refer to unconformity surfaces within the Ms'ad Formation. The current study will examine the clay mineralogy and facies to determine the source of these clay minerals and depositional settings. Fifteen carbonate facies have been identified as three distinct facies associations (FA1–FA3). These FAs are supratidal to intertidal (FA1), semi-restricted lagoon (FA2), and shallow open subtidal ramp with patches of a rudist-bivalve reef (FA3). The reported Multispirina Iranica-Nezzat simplex-Chrysalidina gradata assemblage Zone within the Ms'ad Formation indicated the Cenomanian age. Clay mineral analysis displays three distinctive clay mineral assemblages; kaolinite-dominated with illite (assemblage A), R0-dominated (smectite-rich illite/smectite mixed layers) with kaolinite and illite (assemblage B), and illite-dominated (illite and illite-rich illite/smectite mixed layers) with kaolinite and R0 (assemblage C). Most of these clays are detrital, generated by weathering source rocks (igneous, metamorphic, and sedimentary) under various paleoclimatic circumstances. The Kaolinite-dominated assemblage A represents intense chemical weathering from hot, humid circumstances. Smectite-dominated R0 assemblages were created by weathering alkaline rocks in flat pedogenic soils with seasonal humidity. The source of clay minerals in the studied region was subject to a dry climate towards the end of the Cenomanian period, which encouraged physical weathering and the production of illite-rich assemblages.

Taphonomic analysis of shell concentrations in deltaic Miocene deposits of the South Caspian Basin, eastern Paratethys

ABSTRACT The depositional environment and palaeoecological conditions of a Miocene delta in the Paratethys Basin have been reconstructed based on an integrated sedimentological, ichnological and taphonomic analysis of shell concentrations. Four facies associations, i.e. delta plain, distributary channel, delta front and prodelta, are recognised. The shell concentrations, which are a characteristic feature of the Miocene successions, display different taphonomic signatures in the various parts of the delta system. Delta plain shell concentrations are characterised by unabraded shells with abundant micro-borings and thick micrite envelops formed during colonisation windows and optimum ecological conditions such as good illumination, high nutrient availability and low sedimentation rate. Distributary channel shell concentrations consist mainly of highly abraded, highly fragmented, disarticulated shells that point to long-term high-energy hydrodynamic conditions during their formation. Sporadic shell concentrations in the delta front are composed of chaotic and highly fragmented skeletal elements and co-occur with predominantly suspension-feeding trace fossils such as Arenicolites, Diplocraterion and Skolithos. They reflect a high sedimentation rate and suspension organic particles in a high-energy depositional setting. Prodelta shell concentrations are characterised by moderately fragmented, parallel-oriented shells, preserved within thin-bedded sandstones, intercalated between thick mudstone packages. These concentrations were produced by storm-induced, offshore-directed high-density currents.

Microfacies Analysis of Mixed Siliciclastic-Carbonate Deposits in the Early-Middle Ordovician Meitan Formation in the Upper Yangtze Platform in SW China: Implications for Sea-Level Changes during the GOBE

During the Early-Middle Ordovician, the Upper Yangtze Platform experienced extensive development of a distinctive set of mixed siliciclastic-carbonate deposits known as the Meitan Formation. To conduct a comprehensive study of the relationship between mixed sedimentation and sea-level changes, the Hailong section, situated at the southwest margin of the Upper Yangtze Platform in SW China, was selected as the study area due to its typical mixed sedimentary sequence. This section was effectively compared with sections in other regions. Clustering analysis of the point-count groups from the Honghuayuan and Meitan Formations revealed nine microfacies that developed during this period. Such a diverse range of microfacies provides the evidence of frequent sea-level changes in the Yangtze Platform throughout this period. Specifically, two sea-level rises were identified during the early TS.2b and early TS.3b, with the early TS.2b event occurring globally. Furthermore, four sea-level falls were observed in the late TS.2b, TS.2c, TS.3a, and late TS.3b periods. The late TS.2b sea-level fall was globally significant. From TS.2c onwards, distinct variations in sea-level changes among the Yangtze Platform, North China, Baltoscandia, Australia, and North America emerged due to alterations in the paleogeographic pattern. By comparing the sea-level curves in the Upper Yangtze Platform with the diversity curves of chitinozoans, acritarchs, and brachiopods, it became evident that environmental changes played a crucial role in the Great Ordovician Biodiversification Event (GOBE), especially during the Floian. The rising sea level and increased detrital materials fostered the development of diverse habitats, prompting organisms to adapt to varying environments. In general, rising sea levels favored increased brachiopod diversity, while falling sea levels favored enhanced planktonic diversity among chitinous and acritarch species. By shedding new light on the relationship between Ordovician sea-level changes and biodiversification in the Yangtze region, this study offers a fresh perspective on the subject from the microfacies analysis.

Early marine carbonate cementation in a relict shelf-edge coral reef North of Miami, Florida: Pseudo-coupled depositional and diagenetic modeling

Carbonate depositional and early diagenetic processes overlap in time because of the high chemical reactivity of calcite. Previous studies have modeled early diagenesis in a static depositional framework. They followed a rule-based modeling approach instead of applying rigorous thermodynamics and reaction kinetics.This study has developed a pseudo-coupled approach based on a dynamic depositional framework and reactive transport modeling for diagenesis. It has been tested for the “Pompano” reef north of Miami, Florida. The model includes five reef parasequences deposited over 9.0 kyr with five facies zones. After deposition of the first parasequence, diagenetic processes are modeled. The resulting framework forms the starting condition for depositing the next parasequence. Subsequently, its diagenetic overprint and the continued overprint in the underlying parasequence(s) are modeled. These workflow steps are repeated until all five parasequences are covered.The results show the spatial and temporal development of calcite cementation and porosity distribution. During the reef catch-up phase, cement mainly developed at the depositional surface (up to 10% of the total sediment volume). During the keep-up phase, cement abundance increases to a maximum value of ∼17%. After the reef's demise, cement forms a crust at the sediment-water interface with up to 38% of the total sediment volume. In general, controlling factors of cement distribution include facies-specific flow velocities, reef facies, relative sea-level changes, depositional gaps, and seawater salinity.The modeling results of this study are well aligned with the actual cement and porosity distribution in the Pompano reef and with other sub-recent and ancient examples described in the literature. Pseudo-coupled depositional-diagenetic modeling represents a suitable approach for quantitative porosity prediction in comparable depositional and diagenetic settings. It reduces uncertainties in prediction at inter-well to prospect scale for oil and gas exploration, geothermal exploration, and subsurface storage of CO2.

A conditional GAN-based approach to build 3D facies models sequentially upwards

This paper presents an alternative way of simulating 3D facies models using conditional generative adversarial networks (GANs) by reconstructing the 3D volume upward with customised thickness from generated 2D slices. To mimic natural fluvial reservoirs, GANs need to learn the complicated facies’ lateral and vertical sequences, connectivity patterns and spatial correlation, e.g. the distribution of channel deposits and lateral accretion packages, including channel lags and point bars in a meandering fluvial system. 3D GAN modelling remains challenging, despite some success in 3D, due to the increased data and GAN model complexity caused by the 3D training data. For example, a 3D facies model with a larger number of voxels introduces more complex geobody shapes and requires 3D convolutions that increases the computational burden compared to 2D convolutions.Our proposed conditional GAN-based framework predicts 2D upper layers slice by slice to build 3D facies models, mimicking the sedimentary process in a purely aggrading system, which is less computationally costly than generating the facies models used as training data and generating facies models directly in 3D from a GAN. Each upper layer is predicted conditionally to a lower layer that contains the facies distributions in all layers below the target using several unique training enhancements. All those methods help prevent the simulated 3D models from gradually losing realism and the preset sedimentary settings vertically while inferring the plausible evolution of the channel system. The results demonstrate that the trained conditional generator, a SPADE generator, can work as a simulator to produce unconditional 3D meandering fluvial facies models by inputting a user-defined spatial correlation strength between layers and the number of layers needed (thickness in metres) without post-processing or retraining. This framework’s performance was evaluated using a connectivity metric towards the range of avulsion scenarios that represent a range of depositional uncertainty.

A new age, provenance and tectono-sedimentary setting of the middle Dengying Formation of the terminal Ediacaran in the western Yangtze Block, South China

The widespread terminal Ediacaran Dengying Formation in the western Yangtze Block, South China, is dominated by thick marine dolomite successions deposited in shallow-water platform environments. However, a distinctive succession of mixed clastic and carbonate rocks occurs widely in the middle Dengying Formation, representing sedimentary environment variations. The absolute age of the mixed sedimentary succession is poorly constrained, and tectonic and sedimentary settings remain controversial. In this study, we report a new zircon U–Pb age of 547.3 ± 4.8 Ma from a volcanic ash bed intercalated within a mudstone succession (ca. 40–100 cm thick) in the middle Dengying Formation in the western Yangtze Block. This age is consistent with previously published ages of the middle Dengying Formation or its equivalents in the Yangtze Block and in other blocks worldwide. Field investigations show that the mudstone succession overlies above an unconformity resulted from the lower Dengying Formation weathering and shows a deepening upwards depositional succession representing a period of transgression. Mineralogical analyses show that the mudstones are composed of clay minerals (ca. 68.7%, illite and illite/smectite mixed layers), quartz (24.2%) and minor K-feldspar, indicating a high compositional maturity. Redox sensitive element results (e.g., Mo and U) indicate an increasing anoxic setting upwards. Both elemental geochemical and Lu-Hf-O isotopic analyses suggest that the siliciclastic sediments were moderately weathered (average CIA = 71) and were derived from felsic-intermediate rocks, such as granites and granodiorites (or geochemically-equivalent rocks). We suggest that the mixed sedimentary succession represents as a short-lived, regionally-correlated sea level change event, rather than a tectonic uplift event. Our geochemical data reveal that the mudstone succession accumulated most likely in a passive margin setting, supporting the proposition that the Yangtze Block was located on the periphery of the Gondwana supercontinent during the Ediacaran Period.

Fluvial geomorphic factors affecting liquefaction-induced lateral spreading

Liquefaction-induced lateral displacements represent a major geohazard in earthquake-prone regions, yet the uncertainty associated with their prediction remains notoriously high. Documented observations after recent earthquakes provide evidence that depositional environment-specific geologic conditions play a crucial role in liquefaction susceptibility, and in the severity and spatial extent of liquefaction-induced ground deformations. However, this evidence is largely qualitative in nature, which limits the potential to incorporate the effects of depositional processes and environments in the next generation of lateral spreading predictive models. This study provides a framework to quantitatively assess the relationship between depositional environment-specific geologic factors and lateral spreading by means of simple fluvial geomorphic facies models, geotechnical engineering data (e.g. Cone Penetration Test data), and geospatial analytics. Three hypotheses are introduced and tested using lateral spreading ground deformations observed following the 2011 Christchurch earthquake along the Avon and Heathcote rivers in New Zealand. The results from this study indicate that the presence of an active (i.e. with active sediment deposition) compared to inactive (e.g. abandoned) channels is the most important fluvial geomorphologic variable out of the three tested. The other two are associated with the location relative to the meander bend position, including location within the point bar (inside) or the cut bank (outside), and upstream versus downstream within a given point bar. Findings from this study show that more lateral spreading occurs within point bars, and upstream (within a given point bar) in simple meander bends. However, the presence of geomorphic complexities (e.g. cut banks connected to an incised channel or tributary and/or channel confinement) can challenge the unbiased quantification of the contribution of a single geomorphic variable to the observed lateral displacements. These findings can be applied to other fluvial environments outside of New Zealand, and the proposed framework can be implemented for other non-fluvial depositional settings.

Record of palaeoclimate across theCretaceous–Palaeogeneboundary from palaeosols in the west‐central San Juan Basin, New Mexico, USA

AbstractThe mass extinction at the Cretaceous–Palaeogene boundary is widely attributed to sudden and severe climate changes forced by bolide impact and/or flood basalt volcanism. In terrestrial depositional settings, these changes may potentially be recorded by palaeosols. To test the ability of pedogenic features to record both long‐term climate and shorter‐term changes preceding and following the Cretaceous–Palaeogene extinction event, palaeosols in the Upper Cretaceous (Maastrichtian) Naashoibito Member of the Ojo Alamo Formation and the lower Palaeocene (Danian) Nacimiento Formation in the San Juan Basin of north‐western New Mexico, USA, were examined, including data from previous studies. The fine‐grained facies of the Naashoibito Member comprises grey to greenish‐grey and red‐banded mudstones displaying pedogenic features including colour mottling, root traces, cutans, ped fabrics, pedogenic slickensides and calcareous nodules. Aside from a high‐chroma horizon at the formation base, palaeosols in the lower Nacimiento Formation are broadly similar to those observed in the Naashoibito Member. Lateral and vertical variability of the pedogenic features between correlated sections suggest that soil hydrology varied spatially and temporally from very saturated to seasonally well‐drained, with temporal variations controlled by basin sedimentation rates. Abrupt and/or catastrophic climate events precisely at the Cretaceous–Palaeogene boundary are not recorded due to an unconformity at the top of the Naashoibito Member. However, the presence of kaolinite in the clay mineral assemblage of the Nacimiento Formation, particularly near the formation base, but not in the Naashoibito Member, indicates episodic warmth and short (104 years) intervals of more intense weathering conditions during the very early Danian as compared to the late Maastrichtian. Aside from short warm intervals, the overall palaeoclimate during deposition of both formations was warm and consistently subhumid to humid and seasonal, suggesting no substantial long‐term (105–106) climate change took place across the Cretaceous–Palaeogene boundary in the San Juan Basin.

A review of the characteristics and geological settings of orogenic gold deposits of the Boule Mossi Domain: implication for gold exploration

A review of the characteristics and geological settings of orogenic gold deposits of the Boule Mossi Domain: implication for gold exploration

Facies, diagenesis, and palaeo-environment significances of the Plio-Quaternary fluvio-lacustrine deposits of Ain Cheggag region, Sais foreland basin, Morocco

Fluvio-lacustrine deposits are promising archives that afford to decipher climate and tectonic signatures, typically when evidence of changes in the depositional settings therein is remarkable. As such, the present work coveys a case study whose fluvio-lacustrine deposits may serve to provide insights into climate and tectonic controls on palaeoenvironmental settings. The study area lies in the northwestern portion of Ain Cheggag, southeastern the Sais foreland basin (northern Morocco). The lithostratigraphical analysis of Plio-Quaternary fluvio-lacustrine deposits in the area has enabled the identification of nine facies. The depositional systems are organized into three deposit units, each of which reflects a typical depositional environment. The first (lower) unit consists of detrital facies implying deposition in alluvial-dominated settings. The alternation of detrital and carbonate facies giving way to the second (middle) unit suggests sedimentation in a fluvio-lacustrine environment. Whilst being carbonate-rich, the third (upper) unit reflects a shift into lacustrine-dominated settings. Accordingly, the vertical succession of the sedimentary pile delivers remarkable insights into a general palaeo-environmental shift from alluvial settings, with enhanced pedogenesis processes, towards carbonate-dominated lacustrine conditions where early- and late-stage diagenesis processes would have prevailed. This broad shift in depositional systems is likely to be the response of palaeohydrological changes that are modulated both by the neotectonic subsidence background and, specifically, the general palaeoclimate evolution towards more humid conditions. Bioturbation, desiccation, and void-filling with internal sediments are key features of early-stage diagenesis processes, whereas cementation, micritization, recrystallization, dissolution, and iron and manganese oxidation are the main features of late-stage diagenesis altering the primary structures of the studied deposits. Finally, we highlight the significance of fluviolacustrine deposits in deciphering palaeoclimatic signatures and tectonic implications.

Petrology and geochemistry of sandstone from Lower Cretaceous Kikhla Formation, NW Libya: Implications for provenance and depositional setting.

This study aims to determine and investigate the provenance of the source rocks and the depositional setting of the Kikhla Formation, northwestern Libya. It is mainly composed of mature quartzitic sandstone alternating with conglomerate and clay. The study proved that the sandstone is yellow-white in color and commonly carries quartz granular and small fragments of silicified wood. The environmental deposition is under differing fluvial conditions and by a large braided river. Texturally, the Kikhla sandstone is poorly cemented, coarse to very coarse grained and strongly unimodal and is classified as litharenite and subarkose by the modal composition, which is supported by geochemical studies. According to petrography and geochemistry, the Kikhla sandstone was deposited in a passive continental margin basin, mainly from granitic sources. On the basis of major elements ratios, and petrographic interpretation, the source rocks are most likely recognized as Proterozoic granites that were exposed via rifting. The CIA values (73.28-93.97) indicate a high degree of chemical weathering, which could be attributed to the arid climate conditions in the source area and mainly controlled by the source-rock provenance, hydraulic sorting during transport and deposition, diagenesis and depositional environment. According to chemical investigations, sandstone exhibits significant concentrations of SiO2, Na2O> K2O, and Fe2O3, which is compatible with the modal data.

Multi-scale sedimentary facies controls on fluvial sandstone-type uranium accumulation process in the Songliao Basin, NE China

The relationship between uranium mineralisation and sedimentary facies in a fluvial depositional setting remains a challenging topic. However, the specific effect of muti-scale sedimentary facies control on meandering sandstone-type uranium enrichment is poorly understood. Based on sedimentological, geochemical, mineralogical, and petrophysical analyses, three third-order sequences (SQ1, SQ2, and SQ3) composed of four systems tracts in meandering deposits were identified in the Sifangtai Formation of the northern Songliao Basin. Four subfacies (channel, levee, flood, and abandoned channels) and seven microfacies were identified in meandering rivers, exhibiting spatio-temporal migration of sedimentary fillings. Here, uranium deposits were mainly enriched in semi-abandoned channel deposits during the lowstand systems tract (LST) period of SQ1. Stable-distributed and thick-layered industrial-grade uranium deposits occurred in a positive rhythmic rock assemblages, exhibiting high-frequency variation from thicker medium–fine sandstone to thin charcoal-rich siltstone–fine sandstone. Rapid tectonic uplift and warm-semi humid climate during early Sifangtai period controlled sequence growth and sedimentary filling. Furthermore, sequence and sedimentation during the LST period mediated the formation of uranium-rich rock assemblage and fluid migration pathway, reacting on the abundance, location, and distribution of uranium enrichment. Ultimately, a conceptual model of the sequence and sedimentary control on uranium accumulation was established in the context of meandering rivers. This model revealed that semi humid-warm climate and tectonic inversion (74.9–72.2 Ma) control meandering river, sedimentary hiatus, and charcoal-rich uranium-hosted rock series formation in the LST. Enhanced Cenozoic tectonic uplift (38.0–10.0 Ma) and continental weathering prompted uranium-rich fluids along steep paleotopography, migrated to geochemical barriers of charcoal-rich rock series, and reductive mineralisation around semi-abandoned channel deposits. Our results illustrate the importance of examining multi-scale sedimentary facies to interpret the uranium accumulation process of meandering deposits, ultimately contributing to uranium exploration in similar settings.

Integrated analysis of a mixed carbonate-siliciclastic reservoir in the Iranian Asmari intra-shelf Basin: Insights from well data, seismic profiles, and outcrops

A multidisciplinary approach (facies analysis, biostratigraphy, cyclostratigraphy, and seismic stratigraphy) was employed in this case study to assess the depositional geometry and sequence stratigraphic architecture of a mixed carbonate-siliciclastic reservoir in the Oligo-Miocene Asmari intra-shelf basin (SW Iran). The integration of both the surface and subsurface datasets provides an excellent opportunity for this analysis. Previously, this reservoir was assumed to consist of flat-lying strata with no significant gradient, primarily because of the emphasis on the lithostratigraphy correlation technique and, to some extent, biostratigraphy resolution. However, these aspects have been discussed and improved in this study. Subsurface data, including well data and seismic data, correspond to the southern flank of the Asmari Basin (Kupal Oil Field), which was compared with the exposed sections (Lar and Dashtak anticlines), exceptionally found in its northern counterpart. The Oligo-Miocene rock successions studied here are Chattian-Burdigalian in age and comprise 14 sedimentary facies distributed along different settings of a depositional profile, ranging from deep-water basin (F.1, F.2) and shallow-water carbonate platform (F.3 to 13) to continental settings (F.14). Using cyclostratigraphy, 19 significant timelines were identified along the oil field and calibrated with age dating and seismic data. The integration of well-to-seismic data ties and outcrop observations allowed for the identification of five seismic facies and four seismic packages. Consequently, the combination of these techniques and methods established a sequence stratigraphy architecture comprising four 3rd-order depositional sequences (sequence. I, II, III, IV). The transgressive system tract (TST) and highstand system tract (HST) are the main packages identified within these sequences. Due to the resolution of seismic data and the spatial position of the Oligo-Miocene depositional setting in the Kupal Oil Field, Lowstand system tract (LST) can only be observed in the sequence. I. within this sequence, three 4th-order depositional sequences (cycles. I-a, I-b, I-c) were hierarchically nested into the HST package.