Sedimentary Facies Associations Research Articles

Paleogene-Neogene ring-shaped sedimentary system and reservoir characteristics in the Western depression of the Qaidam Basin

The Paleogene-Neogene strata in the Western Depression of the Qaidam Basin represent a primary focus for oil and gas exploration and development. Influenced by both terrigenous clastic influx and endogenic carbonate deposition, these strata exhibit significant variation in sedimentary systems and reservoir characteristics. This study comprehensively examines the depositional patterns and reservoir properties of the Paleogene-Neogene sequence across the inner, middle, and outer belts of the basin, employing core analysis, thin section petrography, and physical property assessment of reservoirs. Key findings include 1) The development of a concentric sedimentary system in the Western Depression during the Paleogene-Neogene period, characterized by increased carbonate mineral content and decreased clastic material from the periphery to the center of the basin. 2) Varied sedimentary facies associations across different zones, with the outer belt dominated by fan delta and braided river delta deposits, and the middle and inner belts characterized by near-shore shallow lacustrine carbonates and algal mat deposits, and offshore semi-to deep-lacustrine fine sediments, respectively. 3) The outer belt exhibits reservoirs with favorable physical properties and connectivity, while the inner and middle belts show high heterogeneity, indicating potential for lithological traps and shale oil exploration. These insights offer scientific guidance for further investigation into the depositional systems of lacustrine basins in the Western Depression of the Qaidam Basin and for identifying promising reservoirs.

Seismic-aseismic impact on marine depositional dynamics and sedimentary architecture: Study on multilayer-multiscale SSDS in Proterozoic Rohtas Limestone, India

The present study explores a diverse suite of soft-sediment deformation structures (SSDSs) preserved at multiple levels within the Mesoproterozoic carbonate succession of Rohtas Limestone in the Vindhyan Supergroup of India. The carbonate succession shows lithological heterogeneity, characterized by a sharp change of facies association and depositional environment. Three layers of SSDS, traced over 57 km, demarcate the lower lagoonal from upper open shelf deposits. Contorted laminae, load casts and flame structures, convolute laminae, ball and pillow structures, accordion folds and pillar structures within the limestone beds infer liquefaction-fluidization and plastic deformation. The lateral continuity, vertical repetition and confinement of SSDS beds at the interface of lagoon and open shelf deposits indicate the role of seismicity on facies succession. The SSDS beds show lateral variation in thickness and structures, depending on the distance from epicenter. The seismic trigger was accompanied by sudden deepening of the depositional environment and related marine transgression. The coarsening up packages within the lagoonal succession comprise load cast and flame structures, syn-sedimentary faults and intraclastic conglomerates. The open shelf succession shows several fining up cycles, with multiple load and flame structures with intraclastic conglomerate at the top. Origin of SSDS in association of the coarsening up sequence, and fining up cycle infers that intrabasinal tectonics and storms were the triggering agents for lagoon and open shelf successions respectively. The seismite in the studied succession not only reveals the seismicity during the Proterozoic, but also changed the sedimentary facies association, which may use as a diagnostic criterion for the identification of seismite. This study also highlights that seismic and aseismic impacts on sedimentary architecture and paleoceanography evolution.

Modelling the coupled heterogeneities of the lacustrine microbialite-bearing carbonate reservoir of the Yacoraite Formation (Salta, Argentina)

The Yacoraite Formation is a complex lacustrine microbialite-bearing carbonate formation whose heterogeneity is due to different sedimentary facies associations and several microbialite geobodies. The bi-variate plurigaussian geostatistical method is applied to simulate in parallel these two types of heterogeneity in a 3D reservoir-scale geological model. Each variable is simulated by a complete plurigaussian method based on geological interpretation and field observations and quantifications. They are coupled through the occurrence of the microbialites within the sedimentary facies and associated into combined facies giving a one-glance representation of the reservoir heterogeneity, then used to constrain the porosity simulation.

Depositional model of the Member Deng-2 marginal microbial mound-bank complex of the Dengying Formation in the southwestern Sichuan Basin, SW China: Implications for the Ediacaran microbial mound construction and hydrocarbon exploration

Recent advances in hydrocarbon exploration have been made in the Member Deng-2 marginal microbial mound-bank complex reservoirs of the Dengying Formation in the western Sichuan Basin, SW China, where the depositional process is regarded confusing. The microfacies, construction types, and depositional model of the Member Deng-2 marginal microbial mound-bank complex have been investigated using unmanned aerial vehicle photography, outcrop section investigation, thin section identification, and seismic reflections in the southwestern Sichuan Basin. The microbialite lithologic textures in this region include thrombolite, dendrolite, stromatolite, fenestral stromatolite, spongiostromata stone, oncolite, aggregated grainstone, and botryoidal grapestone. Based on the comprehensive analysis of “depositional fabrics–lithology–microfacies”, an association between a fore mound, mound framework, and back mound subfacies has been proposed based on water depth, current direction, energy level and lithologic assemblages. The microfacies of the mound base, mound core, mound flank, mound cap, and mound flat could be recognized among the mound framework subfacies. Two construction types of marginal microbial mound-bank complex have been determined based on deposition location, mound scale, migration direction, and sedimentary facies association. Type Jinkouhe microbial mound constructions (TJMMCs) develop along the windward margin owing to their proximity to the seaward subfacies fore mound, with a northeastwardly migrated microbial mound on top of the mud mound, exhibiting the characteristics of large-sized mounds and small-sized banks in the surrounding area. Type E’bian microbial mound constructions (TEMMCs) primarily occur on the leeward margin, resulting from the presence of onshore back mound subfacies, with the smaller southwestward migrated microbial mounds existing on a thicker microbial flat. The platform margin microbial mound depositional model can be correlated with certain lateral comparison profile and seismic reflection structures in the 2D seismic section, which can provide references for future worldwide exploration. Microbial mounds with larger buildups and thicker vertical reservoirs are typically targeted on the windward margin, while small-sized microbial mounds and flats with better lateral connections are typically focused on the leeward margin.

Sediment core analysis using artificial intelligence

Subsurface stratigraphic modeling is crucial for a variety of environmental, societal, and economic challenges. However, the need for specific sedimentological skills in sediment core analysis may constitute a limitation. Methods based on Machine Learning and Deep Learning can play a central role in automatizing this time-consuming procedure. In this work, using a robust dataset of high-resolution digital images from continuous sediment cores of Holocene age that reflect a wide spectrum of continental to shallow-marine depositional environments, we outline a novel deep-learning-based approach to perform automatic semantic segmentation directly on core images, leveraging the power of convolutional neural networks. To optimize the interpretation process and maximize scientific value, we use six sedimentary facies associations as target classes in lieu of ineffective classification methods based uniquely on lithology. We propose an automated model that can rapidly characterize sediment cores, allowing immediate guidance for stratigraphic correlation and subsurface reconstructions.

Salinity origin in the coastal aquifer of the Southern Venice lowland

Groundwater salinization can be natural and anthropogenic in origin, although it often results from a combination of both, especially in low-lying coastal regions that are hydraulically controlled. This study proposes a method to assess the origin of salinity using environmental tracers in porewater, like Cl− and Br−, combined with depositional facies associations detected in sediment cores. Such integrated approach was tested in a target area south of the Venice Lagoon (Italy), where groundwater salinization is triggered by multiple mechanisms due to the complexity of the hydro-geomorphological environment. Batch tests were performed on sediment core samples from boreholes to quantify major anions and total inorganic N. Cl− and Br− porewater concentrations coupled with sedimentary facies association provided insights into the origin of groundwater salinity from a variety of sources, including past and present seawater intrusion, agricultural leaching, and evaporites. The strengths and limitations of the integrated approach are discussed to provide a pathway for improving water resource management and planning measures to prevent groundwater salinization in coastal areas.

Machine learning-supported seismic stratigraphy of the Paleozoic Nubia Formation (SW Gulf of Suez-rift): Implications for paleoenvironment−petroleum geology of a lacustrine-fan delta

-Steeply dipping prograding fan deltas possess high reservoir quality facies that could be excellent targets while exploring for hydrocarbons. Due to their complex stacking nature, and limited examples, delineating their architectural elements is still challenging. In this paper we mainly performed sedimentary facies analysis; applying various disciplines e.g. sequence stratigraphy, seismic stratigraphy, GR-log motifs, and seismic waveform segmentation; so as to adequately depict the reservoir heterogeneity and quality of the Paleozoic Nubia clastics in West Esh El Mallaha Concession (southwest Gulf of Suez rift). Organic maturity prediction, to confirm the hydrocarbon charging from source units to reservoir intervals, was also of most importance in this study. Accordingly, 1D basin model was established to define the past geologic events; subsidence, and thermal maturity; and their controls on sedimentary basin evolution and associated petroleum potential. We utilized several key-information scales; e.g. wireline logs, and seismic profiles. Linking different disciplines applied in this study points to a successful integrated reservoir characterization workflow capable of unfolding ancient environments and the associated hydrocarbon potential. The results show that Nubia Formation was built during the lowstand−transgressive phase of a 3rd order depositional sequence. It encompasses fluvio-lacustrine system with eight sedimentary facies associations; form source to sink. Fluvial channels and mouth bars, settled in subaerial and subaqueous settings respectively, represent the most significant reservoir facies in the area. Given best hydrocarbon-reservoir quality, the deltaic mouth bars ought to attract attention of further oilfield development plans and be considered while investigating similar settings. • Integrated facies analysis, and established depositional model, depicting reservoir architectural elements; heterogeneity. • TOC calculations and 1D-basin modeling confirming hydrocarbon charging from source-prone intervals to reservoir zones. • Lacustrine deltaic mouth bars representing best reservoir facies ought to be tested and considered in similar settings. • Combined facies analysis and basin modeling devoting to robust insight into environments and associated petroleum potential.

Sedimentary Facies of the Cimanuk River Delta on the North Java Coastal Area and Its Geotechnical Properties

Understanding the sedimentary facies and their engineering properties in the Cimanuk river delta is very important to support the regional infrastructure development and the environmental assessment of the north Java coastal area. This research is aimed to characterize the sedimentary facies association and its geotechnical properties of the Cimanuk delta, Indramayu, West Java. Methods included geotechnical boring and Cone Penetration Tests with pore water measurement (CPTu). The results show that the subsurface condition of the Cimanuk delta comprises several sedimentary facies development and boundaries, namely the delta plain, delta front, and prodelta. The delta plain consists of the fluvial channel sands and marsh-lagoon; the delta front consists of beach ridge, and the prodelta is of clay to silt thickening towards the northeast. The fluvial channel consists of fluvial sand and silt, dense and hard with SPT N value of 30 and cone resistance, qc of 2,000-10,000 kPa. The beach ridge comprises beach sand and sandy silt, loose to very dense, with qc value of 500-16,000 kPa and SPT N value of 30. The delta plain sandy silt has a variable consistency from very soft to hard with SPT N value of 1-37, and qc value of 300- 4,900 kPa. The prodelta clay and silt consist of very soft to medium consistency, with qc value of 200- 3,000 kPa and SPT N value of 1-8. The prodelta clay-silts engineering properties are very soft to a soft consistency. When development occurs in the marsh-lagoon and prodelta facies, particular caution must be taken. The vertical, lateral, and spatial sedimentary facies and their geotechnical properties can provide information for spatial planning in the coastal region.

Trace Fossils and Sedimentary Depositional Environment: A Case Study from Early Permian Barakar Formation, Raniganj Basin, India

Behavioral responses of organisms with respect to changing environment have a wide area of research possibility. For a palaeontologist it is a challenge to interpret the organism-sediment interaction from the study of the trace fossils preserved in the ancient rock record. The ethological significance which is derived out of different intentional or accidental activities of the organisms may be preserved within the rock and is largely controlled by the substrate stability, grain size of the sediments, energy and rate of sedimentation of the driving process, types of nutrients and its supply, salinity, temperature and oxic/sub-oxic/an-oxic conditions etc. So, the viability of this study in sensu stricto depends on the preservation potential of the organism as a whole or in parts or its activities (indirect evidences) on or within the substrate upon which they have survived thousands and millions of years ago. The indirect evidences of the organism’s activities may be its locomotory/respiration/feeding/resting/dwelling/predating traces etc. which have different nomenclature based on their morphological classification. The study area encompassing the major river section of the Barakar, Khudia, Ajoy holds partly enriched and partly impoverished trace fossils within the sedimentary rocks hosting huge reserves of coal. There are several concepts regarding the depositional setting of the studied basin like formerly interpreted fluvio-lacustrine depositional model to recently reinterpreted fluvio-tide-wave dominated depositional model. Several invertebrate traces have been recorded from the study area namely Planolites, Thalassinoides, Ophiomorpha, Palaeophycus, Cylindrichnus, Diplocraterion which indicates diverse environmental settings ranging from supratidal/intertidal/subtidal to continental shelves whereas other solo/uniform traces observed like Chondrites, Skolithos, Rhizocorallium etc. are indicator of shallow subtidal to marine quite water setting. Here the additional challenges include the lack of ample exposures, weathered exposed rock sections, inaccessible mine cut sections, absence of body fossils and controversial identification of trace fossils in differential erosive surfaces. This chapter in short has tried to mitigate these problems by the integrated sedimentary and ichnological facies association studies in delineating the depositional environment of the studied basin.

Anatomy of a diamondiferous gravel barrier spit at the palaeo‐Orange River mouth, south‐western Namibia

ABSTRACTThe sedimentary facies architecture of a Plio‐Pleistocene diamond‐bearing gravel barrier spit within the palaeo‐Orange River mouth in south‐western Namibia has been revealed during onshore mining activities. Four sedimentary facies associations build this ancient coastal landform and have been interpreted, from a seaward to landward direction, as sediments in: (i) the foreshore, represented by an intertidal beach; (ii) a subtidal spit platform on which the spit developed; (iii) storm‐constructed spit head recurves on the landward side of the spit; and (iv) an estuarine back‐barrier. This sedimentary record reflects an evolving spit that grew in response to a combination of marine and fluvial processes in a wave‐dominated, high‐energy coastal regime. Here, the southern Atlantic Ocean aggressively dispersed sediment delivered by a Plio‐Pleistocene Orange River, ensuring that the fine‐grained sediments were removed to allow only the gravel fraction to build up along the coastline. This extreme dispersal of sediment also precluded the construction of a classic delta; hence sediment storage offshore of the river mouth was limited and spit growth was dependent on the direct supply of river sediment. In response to the intermittent supply of sediment, spit growth and decay alternated during periods of sediment abundance and starvation, respectively. During positive sediment budget, the spit extended northward and cut off parts of the mainland to form an estuarine back‐barrier. Foreshore and spit head progradation was sustained under these conditions, and formed a beach‐ridge plain with a topographic expression of several coast‐parallel ridges that curved at the spit head into the back‐barrier. Spit extension and recurve development were controlled by a combination of high sediment supply, a vigorous longshore drift and powerful waves approaching from various directions. This Plio‐Pleistocene coastal landform in Namibia offers a depositional model relevant to gravel‐dominated barrier spits near river mouths along wave‐dominated clastic coasts.

Hydrocarbon Prospectivity of Surma Group in Sylhet Area in Context of Sequence Stratigraphy

This research focuses on studying the Surma Group sediments with an integrated approach of using wireline logs and 2D seismic data from Sylhet structure and outcrop analogy from the Zaflong-Tamabil-Jaintiapur area to explain the geological evolution in the context of sequence stratigraphic framework and its implications to identify the hidden potential of hydrocarbon traps that remains overlooked. The 'SYL-07' well logs divided the encountered sedimentary strata by sequence boundaries (SB) and flooding surfaces (FS) into an upper third-order Lowstand System Tract (3_LST), followed by the third-order Highstand System Tract (3_HST), and underlying third-order Transgressive System Tract (3_TST) which correspond to the Tipam, Boka Bil, and Bhuban formations, respectively. The 3_HST has further been subdivided into fourth-order sequences. Well-to-seismic ties helped in identifying the sequence boundaries in the regional context. Three new prospects in the nose and flank area of the Sylhet structure have been detected based on seismic attributes and log responses. Seismic sweetness attribute anomalies confirmed the existence of these prospects. Rigorous fieldworks provided nineteen facies and seven sets of sedimentary facies associations and helped to establish the sedimentological stacking patterns and corresponding depositional environments. About 2250m lithocolumn constructed from field data revealed four third-order sequence stratigraphic system tracts roughly corresponding to Renji (3_LST), Bhuban (3_TST), Boka Bil (3_HST), and Tipam (3_LST) formations in the bottom-up order, while the obtained facies associations aid in identifying four fourth-order sequences including fourth-order system tracts in the 3_HST. The lithologic column corresponds well with the seismic sections and validates the seismically interpreted third-order system tracts and fourth-order sequences. However, the high-frequency fourth-order system tracts can only be correlated with the log motif patterns due to sub-seismic resolution. The erosional remains of the fourth-order sequences in 3_HST, for instance, the coarsening upward shoreface and shelfal facies topped by transgressive shale, have yielded potential future drilling sites based on seismic attribute and log response analysis. The analogy of field data with well log and seismic data helped the overall evaluation of the hydrocarbon prospectivity of the area. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 11(1), 2022: 95-110

Late Paleoarchean to Neoarchean sedimentation on the Singhbhum Craton, eastern India: a synthesis

Subaerial rise of Earth's first continents took place 3.3–3.2 Ga years ago. This had significant influence on the ocean, atmosphere, and biosphere. Two important sedimentological consequences of continental emersion were (1) development of terrestrial (alluvial fan–fluvial–aeolian) depositional systems and (2) formation of shallow-marine sedimentary basins near the continental margin. Late Paleoarchean–Neoarchean terrestrial deposits, including development of an extensive paleosol around 3.2 Ga, and Meso–Neoarchean shallow-marine deposits have been reported from the Singhbhum Craton, eastern India from several localities. However, lateral and vertical changes in sedimentary facies associations and stratigraphic correlation between these terrestrial to shallow-marine sedimentary deposits have not yet been investigated. In this paper, we have reviewed the sedimentological characteristics of Late Paleoarchean to Neoarchean (3.2–2.8 Ga) stratigraphic successions of the Singhbhum Craton and have discussed sea level change and mode of stratigraphic sequence building. Our analysis shows that Singhbhum granitoid complex was emplaced around 3.3 Ga in an intracontinental setting, resulting in high continental freeboard conditions that triggered terrestrial (alluvial fan–braided fluvial) sedimentation (Dhosrapahar Formation). Continental sedimentation continued until ca. 3.0 Ga. In the eastern (Simlipal Group), western (Birtola Formation), and southwestern (the Mankarchua, Mahagiri, and Keonjhar formations) parts, shallow-marine sedimentation occurred after 3.0 Ga as a result of transgression. However, in the northern part (Dhanjori Formation), continental sedimentation prevailed throughout the Archean. These Late Paleoarchean to Neoarchean terrestrial and near-coastal successions of Singhbhum Craton should be the prime targets for intense geobiological research.

Facies analysis and distribution of Late Palaeogene deep‐water massive sandstones in submarine‐fan lobes, NW Borneo

Deep‐water massive sandstones (DWMS) are characterized by large volumes of sand accumulations which are considered as potential reservoir intervals in deep‐marine environments. Lithological variations and bed thickness statistics are used to interpret the distribution of massive sandstones in a deep‐marine fan‐lobe system. These massive sandstones are interpreted based on lithological heterogeneities and detailed facies analysis in seventeen exposed sections of the Late Palaeogene deposits in Sabah, NW Borneo. Sedimentary logs containing details of lithology textures and structures were used to recognize nine sedimentary facies of DWMS. These lithofacies were then grouped into three sedimentary facies associations: (1) massive facies association with basal part of turbiditic Bouma sequence, (2) massive facies association having soft‐sediment deformation structures, and (3) massive facies association with erosional features. The facies analysis portrays inner to middle submarine fan deposition and was later applied to reconstruct the distribution of a channel‐lobe complex. Individual sandstone bed thicknesses vary from 1 m to more than 8 m and the number of massive sandstones in submarine lobes range from less than 10% to more than 50%. The thicknesses of massive sandstones in channels are more than 8 m, whereas distal lobes have thicknesses from 1–2 m only. These sandstones are concentrated in channels, proximal and medial lobe settings that can also be verified from calculating the average of all maximum thickness of massive sand intervals that is, 8.91 m. The lithological heterogeneities and the processes associated with the deposition of these massive sandstones are vital for potential hydrocarbon reservoirs in the deep‐marine environments around the globe.

Ichnology and Sedimentology of the Lower Cretaceous Wabiskaw Member (Clearwater Formation) Alberta, Canada

Identifying facies and paleoenvironmental interpretation of the rock record is complicated due to the interplay of independent variables (i.e. wave-, river- and tidal-input) in marginal- and shallow-marine environments. This study integrates sedimentology and ichnology to characterize the depositional environments of the Lower Cretaceous Wabiskaw Member. The deltaic and strand plain shoreface-offshore deposits of Wabiskaw Member of Clearwater Formation of northeast Alberta provide an excellent case study to evaluate the ichnological and sedimentological characteristics associated with laterally and vertically variable stresses in wave-influenced nearshore settings. The Wabiskaw Member is studied using four sedimentary facies associations (Ten sedimentary facies). Facies association 1(FA-1) consists of massive, sharp-based mudstones and lenticular sandstone with small-scale soft-sediment deformation features, syneresis cracks and small-scale oscillation ripples. The ichnological suite mainly includes small grazing and deposit-feeding traces, representing the Phycosiphon Ichnofacies. Facies association 1(FA-1) is interpreted to record deposition in a prodeltaic setting. Facies association 2 (FA-2) is fine-to-medium-grained sandstone and thin mudstone with current, oscillation and combined flow ripples. The low angle and trough cross-beds, soft-sediment deformation structure, mud chips and coal debris are common. The trace fossil suite includes sporadically distributed deposit-feeding traces belonging to the Rosselia Ichnofacies. This facies association is interpreted to be deposited in the delta front to a mouth bar setting. Facies association 3 (FA-3) is gray to bluish-gray mudstone with minor sandstone interbeds (massive, planar parallel to hummocky cross-stratified). FA-3 is moderate to highly bioturbated. The ichnodiversity and abundance is high with dominant horizontal and subordinate vertical traces, including the dominance of deposit and detritus feeding traces representing the archetypal Cruziana Ichnofacies ichnological suite. Facies association 3 (FA-3) is interpreted as being deposited in a storm-influenced offshore environment. Facies association 4 (FA-4) is upper fine to fine-grained glauconitic sandstone with minor mudstone interbeds at the base. Physical sedimentary structures including massive and planar (horizontal and low angle), hummocky, and swaley crossing-stratification. FA-4 is heavily burrowed with a diverse suite of horizontal and vertical traces of deposit and detritus-feeding structures, representing a proximal expression of Cruziana Ichnofacies. Facies association 4 (FA-4) represents distal lower to middle shoreface deposition. The Wabiskaw Member deltaic (prodelta-delta front) deposits, producing characteristic sedimentological-ichnological signatures, distinguishing these deposits from related strand plains. In addition to characteristic deltaic traits (e.g. soft-sediment deformation structures, fluid mud and syneresis cracks), these deposits commonly contain comparably stressed low-diversity and diminutive trace-fossil suites. On the other hand, fully marine strand plain shoreface-offshore complexes are characterized by comparably robust trace fossils with high ichno-diversity and bioturbation intensities.

Recognizing key sedimentary facies and their distribution in mixed turbidite–contourite depositional systems: The case of the Pacific margin of the Antarctic Peninsula

AbstractInterplay of deep‐water sedimentary processes is responsible for building a myriad of features and deposits across mixed turbidite–contourite systems, from <5 cm beds to >200 km long sedimentary drifts. Investigations of the spatial and temporal variability of their sedimentary facies and facies associations is crucial to reveal the dynamics between along‐slope bottom currents and down‐slope turbidity currents, as well as their impact on drift construction and channel erosion. This study focuses on extensive modern mixed (turbidite–contourite) systems, developed across the continental rise of the Pacific margin of the Antarctic Peninsula. Nine sediment cores were sampled and analysed, through grain size and geochemical methods, to study the sedimentary facies at high‐resolution (ca 1 to 20 cm). Three main facies associations have been identified across distinct morphological features (i.e. mounded drifts and trunk channels), comprising intercalations of hemipelagites, bottom current reworked sands (which include fine to coarse‐grained contourites) and gravitational facies (turbidites and mass‐transport deposits). These facies associations reflect fluctuations of the background sedimentation, oscillations of the bottom‐current velocity and of the frequency of gravity‐driven currents. The sedimentary record features cyclic alternations during the Late Quaternary (>99 kyr), suggesting that variations between along‐slope bottom currents and down‐slope turbidity currents are strongly linked to glacial–interglacial cycles during Marine Isotope Stages 1 to 6. Sedimentary records affected by bottom currents on polar margins, such as those of the Antarctic Peninsula, are essential to decipher the facies and facies sequences of bottom‐current deposits, as the low degree of bioturbation throughout most of the sediments allows us to observe the original sedimentary structures, which are poorly preserved in similar deposits from other continental margins.

Holocene evolution and depositional model of a bayhead delta, Lake Illawarra, Australia

AbstractExtensive research into the evolution of wave‐dominated estuaries has been documented since the 1960s. However, there has only been limited research on the prograding bay‐head deltas that are the primary drivers for the rate and stage of estuary evolution. This paper presents the findings of a high‐resolution spatial study into the evolution of the Macquarie Rivulet bayhead delta in the Lake Illawarra barrier estuary. The delta’s evolution has been established based on sedimentological analysis of 74 cores, two 14C ages and 45 amino acid racemization ages. This study intersected two Pleistocene and 10 Holocene sedimentary facies associations representing both the retrogradational and progradational phases of delta development. The distribution of bayhead delta facies associations in shallow barrier estuaries is initially controlled by the antecedent morphology, but, in contrast to deeper estuaries, this influence decreases as sedimentation proceeds. Changing relative sea level also has a major control on facies distribution with transgressive facies deposited as relative sea‐level rises being replaced by prograding deltaic facies during the highstand and subsequent minor relative sea‐level fall. Fluvial sediment supply and river flood events affect the rate of delta progradation, and produce low and high flow sediment deposits within the overall deltaic sequence. The low tidal flux in barrier estuaries, the muddy cohesive nature of the sediments and the prevalence of bioturbation means that primary sedimentary structures are rarely preserved in these bayhead delta facies. The depositional model of bayhead delta evolution shown by the Macquarie Rivulet delta would be widely applicable to other similar barrier estuary settings.

Geophysical 3D-static reservoir and basin modeling of a Jurassic estuarine system (JG-Oilfield, Abu Gharadig basin, Egypt)

• The estuarine architecture is just depicted via facies-constrained 3D modeling. • Heterogeneity of Khatatba complex reveals five sedimentary facies associations. • Basin modeling confirms hydrocarbon charging from Khatatba shales to reservoirs. • Bars comparison with modern-ancient analogues verifies sufficient characteristics. • Given best reservoir quality, estuarine bars deserve testing in similar settings. Inadequate delineation of reservoir-heterogeneities, along with charge-timing confirmation, can considerably mislead exploration-development phases of petroleum. Therefore, precisely depicting the reservoir-architecture is crucial for avoiding exploration failures. To this end, integrated approach of various facies analysis and modeling-related disciplines; e.g. seismic facies, and GR-log motifs; was applied, in this study, to develop a depositional-model capable of aiding in stochastically-mapping reservoir heterogeneity and quality of the Jurassic estuarine depositional-system at JG-Field. To overcome the issue of sparse well control and scarcity of promising discoveries from deep-buried intervals in the study area, stochastic 3D-geocellular reservoir modeling, constrained by seismic attribute analysis, was performed to render a lateral prediction of different facies constituting the Jurassic succession. Predicting organic maturities and retrieving past geologic processes controlled sedimentary basin evolution were also a matter of importance to confirm hydrocarbon-charging to reservoir intervals. Accordingly, 1D-basin model was established so as to complete the story of petroleum system analysis in the area. We utilized dataset of seismic, log, core, and thin-section data; and applied both object-based and pixel-based, SIS (Sequential Indicator-Simulation) and SGS (Sequential Gaussian-Simulation), stochastic modeling algorithms upon simulating rock and fluid properties. The results show that the Jurassic succession constitutes a third-order depositional sequence of fluvio-estuarine units, subdivided into five sedimentary facies-associations. Fluvial and tidal-bar facies associations enrich medium-grained sandstones, deposited in subaerial and subaqueous conditions respectively, featuring significant reservoir quality. Given best reservoir-quality, and considerable thickness, the tidal sand-bars ought to catch attention of future development strategies and be considered for investigation in similar settings.

Genetic types of mudstone in a closed-lacustrine to open-marine transition and their organic matter accumulation patterns: A case study of the paleocene source rocks in the east China sea basin

Organic mudstone can be a high-quality source rock in petroleum basins. The accumulation patterns of various types of mudstone can also serve as a useful record of paleogeography. Due to the impact of tectonic movements, the East China Sea Basin (ECSB) saw its deposition setting transform from closed-lacustrine to open marine settings. This provides an opportunity to explore organic matter accumulation patterns within such a transformation setting. This study classified the constituent mudstones according to their differences in composition and sedimentary structure as follows: coaly mudstone or carbonaceous mudstone, calcareous mudstone, clayey mudstone, and siliceous mudstone. Considering the different sedimentary structures, siliceous mudstone can be subdivided into laminated, wavy, and slumped mudstones. Using integrated multiple indices of the paleo-environment, which includes clay mineral content, trace mineral content, and micro-paleontology assemblages, we reconstructed the paleography setting during the Paleocene and inferred that during this time, the ECSB was characterized by sedimentary differentiation. We discerned two different organic mudstone accumulation patterns by combining the results from rock-eval pyrolysis and paleo-environmental indices: 1) A closed-lacustrine mudstone accumulation pattern characterized by abundant sediment supply and dominated by allogenous mudstone formation by the flocculation process. The fresh to slightly salty water environment provided adequate nutrition to microorganisms and an appropriate temperature led to the increased accumulation of type II 1 and II 2 kerogen. 2) An open-marine mudstone accumulation pattern which revealed a sediment-starved setting. The flocculation process and fine-graded turbidities were the main processes leading to mudstone accumulation. More plants were concentrated in shallow water with declining salinity, leading to peat and mass carbon mudstone accumulation. • Classified the mudstone into six types according to its genesis difference. • Build the relationship between the paleo-environment and the abundance/types of organic matters. • Restore the mudstone distribution and the sedimentary facies association evolution process. • Put out the organic matter accumulation pattern in the transition setting.

Seismic stratigraphy, sedimentary facies analysis and reservoir characteristics of the Middle Jurassic syn-rift sediments in Salam Oil Field, north Western Desert, Egypt

The Middle Jurassic syn-rift sediments (Khatatba Formation) of the Western Desert, Egypt hosting potential reservoir intervals are prospective targets for hydrocarbon exploration and development campaigns. However, their depositional evolution and factors controlling distribution of the best reservoir faces are not very well-constrained. This work integrates seismic, well logs and conventional core dataset in order to define the syn-rift sedimentary patterns and their impact on distribution and quality of the reservoir facies. Khatatba Formation comprises two discrete units; the lower unit constitutes lower progradational and upper retrogradational sedimentary packages that are interpreted in terms of discrete rift phases. Nine sedimentary facies associations (FA) were recognized and their stacking patterns are governed by the rift evolution and the interplay between variation in fault offsets and sediment supply. Distal sand bar sandstones, marine shales and organic-rich shales were accumulated during periods of high subsidence. Successive alternation between shallow and deep facies at the base of the lower unit reveals repeated short periods of progradation and retrogradation with an overall progradational trend reflecting an elevated rate of sediment supply.Episodic fault-controlled retrogradation and progradation continued during the deposition of the Khatatba upper unit where the progradational deltaic facies changes upward into retrogradational marine sediments and aggradational-progradational aeolian and shoreface sandstones. Five hydraulic flow units (HFUs) were identified and their distribution is mostly controlled by the rift evolution. The lowest reservoir quality HFU4 and HFU5 are often associated with the retrograding distal facies accumulated during highest rates of subsidence. These zones do not contribute to more than 10% of the reservoir flow capacity. On the other hand, the progradational deltaic facies accounts for approximately 85% of the reservoir flow capacity in both lower and upper Khatatba units.

Sedimentary processes in the Discovery Gap (Central–NE Atlantic): An example of a deep marine gateway

Paleoceanographic studies of abyssal bottom currents are often complicated by low current speeds and sedimentation rates, resulting in sediment condensation or erosion. However, increased rates of erosion and deposition may occur where bottom current velocities change as they pass through deep marine gaps and gateways. Despite this, the depositional processes in these gateways and their paleoceanographic implications remain poorly understood. Based on new sedimentological, hydrological and geophysical (high resolution seismic and bathymetry) data from Discovery Gap (Azores–Gibraltar Fracture Zone) collected during the 43rd cruise of the R/V Akademik Nikolaj Strakhov in 2019, the key sedimentary processes occurring in the Late Quaternary have been determined. Two depressions with depths exceeding 5300 m in the centre and south of Discovery Gap have been identified, the latter filled with contouritic deposits. These depressions are separated by a roughly N–S trending central sill at 4860 m and a sediment filled terrace at 4720 m water depth. Elongated NE–SW trending highs and sills, are present in the north and south of the study area. Their importance in controlling the flow of water through Discovery Gap is determined by the presence of erosion at the base of these highs with adjacent sheeted or mounded contourite drifts. Pelagic, hemipelagic, reworked pelagic/hemipelagic and fine-grained contourite sedimentary facies have been identified. The sedimentary facies associations point to remarkable variability in the Antarctic Bottom Water (AABW), linked to glacial–interglacial changes, and its intermittent influence in Discovery Gap during the Quaternary. During glacial intervals (MIS 6, 4 and 2) and at their terminations there was enhanced bottom current activity coeval with higher terrigenous content, and increased carbonate dissolution. The results of this study improve our understanding of sedimentary processes in abyssal environments and highlight the value of the sedimentary record in deep marine gateways for interpreting the interaction of bottom water with abyssal morphology. Future work in other modern deep gaps is essential to shed more light on how deep gaps form and to fully reconstruct deep-water paleocirculation within oceanic basins.