Fan Delta Research Articles

Shales of Palaeo-Mesoproterozoic Vindhyan Basin, central India: insight into sedimentation dynamics of Proterozoic shelf

AbstractThe Vindhyan Supergroup represents the largest Proterozoic sedimentary basin fill in the Indian shield. In addition to some significant palaeobiological discoveries, the sedimentary sequence of the Vindhyan, particularly its argillaceous intervals, holds crucial information for our understanding of sedimentation dynamics in Proterozoic clastic shelves. Here we attempt an extensive, although not exhaustive, review of the physical characteristics of six argillaceous (shale) intervals (Arangi, Koldaha, Rampur, Bijaygarh, Rewa and Sirbu shale) from the Son valley sector, Vindhyan Basin, augmented with new observations to unravel the status of current understanding in terms of palaeo-flow dynamics, shelf sedimentation processes and dispersal pattern, depositional cyclicity and basinal tectonics. The sedimentary attributes of Vindhyan shales reveal their deposition largely in relative bathymetry fluctuating from distal shoreface or inner shelf (near to fair-weather wave base) to distal shelf below storm wave base. More often than not, the Vindhyan shelf was storm-infested and the operation of both storm-generated return flow and Coriolis-force-guided geostrophic currents are documented from different stratigraphic intervals of argillaceous successions. The thick arenaceous intervals interrupting the deposits of the Koldaha, Rewa and Sirbu shales at multiple stratigraphic levels indicate the presence of a fan delta and braided fluvial system during intermittent regressive stands of sea level or event deposition during a sea-level highstand, respectively. Based on facies pattern and flow vectors, a rift-related half-graben model is inferred for Arangi and Koldaha shale and a low-gradient stable-shelf model with well-defined energy gradient is proposed for successions from Rampur shale onwards.

Diagenesis of the Cretaceous glutenite and its control on the reservoir porosity in the Fangzheng depression, Northeast China

The reservoir of glutenite has obvious anisotropy characteristics, so diagenesis has a significant impact on its physical property of the reservoir. In view of unclear control factors for densification of the Cretaceous glutenite reservoir in the Fangzheng depression, the diagenesis type of glutenite reservoir and its impact on the physical property of reservoir in the research area were studied by core analysis, electronic probe analysis, scanning electron microscope (SEM) analysis, X-ray energy spectrum analysis, and X-ray diffraction (XRD) analysis. The results showed that there are four types of diagenesis, compaction, dissolution, cementation, and metasomatism. The glutenite reservoir experienced a relatively strong mechanical compaction, which seriously damaged the original pores of the reservoir, with a decrease of 15.97%. This is the most important cause of the densification of the Cretaceous glutenite reservoir. Due to the injection of other hydrocarbon fluids, a large amount of organic acid entered the reservoir through residual pores and fractures, which promoted the dissolution of minerals such as potassium feldspar, formed secondary pore zone, improved the glutenite reservoir performance, and increased the porosity by 6.79%. The primary and secondary pores are filled by cementation with a porosity reduction of 6.53%, which is another key factor for reservoir densification. Through the analysis of the physical property of glutenite reservoir, it is believed that the high-quality Cretaceous reservoir in the Fangzheng depression is mainly developed in the subaqueous distributary channel in frontal fan delta near the oil-source fault. The frontal fan has a high primary porosity and is the material basis for the formation of the reservoir.

Late Eocene to Late Miocene palaeoecological and palaeoenvironmental dynamics of the Ereğli‐Ulukışla Basin (Southern Central Anatolia)

The Ereğli‐Ulukışla Basin which is the focus of this study is situated at the south‐eastern edge of the Central Anatolian Cenozoic basins (Tuzgölü, Haymana, Çankırı‐Çorum, and Sivas), and is divided into two sub‐basins, the Aktoprak (AT) and Hacıbekirli‐Tepeköy (HT). These sub‐basins mainly comprise a stratigraphically discontinuous and laterally variable series, represented by ‘fluvio‐lacustrine’ siliciclastic and carbonate sediments deposited over a wide range of environments, including meandering and braided rivers, coastal fluvial and fan deltas, mixed carbonate‐siliciclastic shores, dry lake flats, and coal‐bearing swamps. In the Ereğli‐Ulukışla Basin, higher palaeotopographic conditions existed in the AT because of the uplift of the Central Anatolian Plateau during late Middle Miocene (Serravallian)‐early Late Miocene (Tortonian) and the subsequent uplift of the Taurus Mountains in the latest Miocene (Messinian) as deduced in the Tepeköy region (northeast) of the HT sub‐basin. Diversity and abundance of archaic pollen (Normapolles) in the pollen biostratigraphy decreased from the Eocene to Oligocene, while forms with advanced angiosperm morphology (post‐Normapolles), were observed with the increase in post‐Normapolles during the Miocene. The dominance of woody angiosperms in the pollen assemblages, and increasing variety and abundance of ‘open herbs’ and shrub pollen from the Early Miocene to Late Miocene defines an important change in flora. Furthermore, the palaeoclimatic conditions changed from humid‐subtropical to warm‐temperate during the sediment deposition in the Ereğli‐Ulukışla Basin. Recurrent arid phases during the Late Miocene are indicated by the deposition of reddish caliche conglomerates in broad dry lake flats (HT), and evaporites in local playa lakes (AT), respectively.

A late Paleozoic extension basin constrained by sedimentology and geochronology in eastern Central Asia Orogenic Belt

According to sedimentary structure, petrology and sequence analysis from seven sections (S1–S7) across the West Ujimqin basin, the late Carboniferous to Permian sedimentary facies have been recognized and summarized as four sedimentary systems, i.e. the late Carboniferous-early Permian sedimentary system (SA) comprising the alluvial fan–delta–littoral facies, the late Carboniferous sedimentary system (SB) including the littoral facies–delta facies–platform margin facies, the early Permian sedimentary system (SC) characterized by delta front and prodelta facies, and the middle Permian sedimentary system (SD) with alternations of littoral and delta facies. According to the spatial and temporal distribution of the four sedimentary systems, the basin filling process can be divided into three stages. The first stage (324–290 Ma) is dominated by bidirectional terrigenous sediments containing the SA from alluvial fan to delta and littoral facies in the northwestern and the SB from littoral–delta to platform margin facies in the southern, respectively. The second stage (290–270 Ma) is characterized by delta front and prodelta facies of the SC marked by thick-bedded matrix-supported conglomerate, rapid accumulation of terrigenous sediments and volcanic debris, syn-sedimentary deformation and slump. The third stage (270–255 Ma) formed the SD with the alternations of littoral and delta facies, which is represented by complex terrigenous clasts and intra-basin carbonate. These shallow and proximal sedimentary systems from fan delta to littoral facies indicate that there was not oceanic sedimentary system in the eastern CAOB during the late Carboniferous to Permian except for some small red sea basins, which provides convictive evidence that the Paleo-Asian Ocean (PAO) had closed before the late Carboniferous. Detrital zircon dating reveals bidirectional provenances of the West Ujimqin basin, indicating that it was a limited basin between two uplifts, which implies presence of the late Paleozoic “basin and uplift” tectonic framework that developed on the eastern CAOB during the late Paleozoic.

Sedimentary architecture and provenance analysis of a sublacustrine fan system in a half-graben rift depression of the South China Sea

Research on the sedimentary architecture and provenance of sublacustrine fans is crucial not only to better understand the gravity flow evolution in lacustrine basins but to successfully locate hydrocarbon reservoirs. This study targets at a sublacustrine fan with a large petroleum reserve that has been revealed by drilling within an Eocene lacustrine succession in the Fushan Depression, northern South China Sea. The sedimentary architecture of the sublacustrine fan was investigated through the integration of core, well logs and 3D seismic data, and its provenance was identified by detrital zircon UPb dating. The examination of 117 m long continuous drilling core reveals four major lithofacies in the sublacustrine fan deposits, which are interpreted as deposits of two types of gravity flows (cohesive debris flows and turbidity currents). The cohesive debris flows developed in the lower section are mainly composed of massive gravelly mudstones with various floating clasts and high clay content, whereas the turbidity currents in the upper section are characterized by parallel to ripple bedding and normal graded bedding. These observations reflect a transformation from cohesive debrites to turbidites from deep to shallow water environments. In addition, provenance analysis of 648 detrital zircon UPb ages yield a well-defined relationship between potential provenance areas and sublacustrine fan deposits in the deep lake. The UPb age pattern of the fan is similar to that of northern fan delta deposits, but different from sediments from the western and southern deltas, suggesting that the sublacustrine fan was sourced from the north. Therefore, a deep-lacustrine depositional model is proposed for the sublacustrine fan, showing a gravity-driven evolution process from fan delta front in the northern slope into cohesive debrites and then turbidites in the lake center. This was mainly controlled by fault-related topography and sediment supply. This study highlights the effective use of the detrital zircon UPb dating method to identify the provenance direction of sublacustrine fans, and the proposed depositional model may be applicable to reservoir prediction in other lacustrine basins.

Permian to early Triassic tectono-sedimentary evolution of the Mahu sag, Junggar Basin, western China: sedimentological implications of the transition from rifting to tectonic inversion

The Permian to early Triassic terrestrial successions in the Mahu sag constrain the tectonic evolution of northwestern edge of the Junggar basin. This study analyzes the sequence stratigraphy of the Mahu sag in order to understand the interplay between tectonic process and the sedimentary fill of the basin. It uses detailed analysis of drill cores, geophysical well logs, 2D seismic reflection profiles and isopach maps. Sixteen lithofacies are grouped into three facies associations: fan delta, fluvial delta and lacustrine. The Permian to Triassic strata are organized into two second-order transgressive-regressive (T-R) sequences, further separated into transgressive systems tracts (TST) and regressive system tracts (RST). Based on seismic profiles, paleogeographic facies distribution and isopach maps, two stages of tectonic evolution are recognized: 1) early Permian syn-rift to middle Permian post-rift; 2) late Permian to early Triassic tectonic inversion. During the early Permian, sediments of TST1 record two cycles of depositional system transition from fan delta to deep lacustrine setting within the half-graben structure shown by 2D seismic profiles. At this time, tectonic mechanical subsidence exceeded sediment supply. The middle Permian post-rift stage (RST2) is characterized by gradual and slow peneplanation, which is documented by sediment supply exceeding thermal subsidence, so that the location of depocenter shifted and the depositional system transitioned from lacustrine to fan delta setting. Late Permian-early Triassic tectonic inversion is demonstrated by a striking change of the sediment dispersal patterns along the Hong-Che, Ke-Bai and Wu-Xia fault zones and alluvial fan deposition at the base of TST2. Tectonism is the main factor controlling sediment dispersal, paleogeographic evolution and hence hydrocarbon accumulation, providing a new perspective to oil and gas exploration and development in the Mahu sag.

The role of fault reactivation in the development of tropical montane lakes

AbstractThis work details the role of fault reactivation in the development of tropical montane lakes by using basin morpho‐structural analysis and seismostratigraphic studies. The upland lakes are severely faulted sinkholes, whose faults penetrate the Quaternary sedimentary units. Four main stages are related to the lake formation: (i) an Early Proterozoic tectonic deformation of the rocks along the southern border of the Carajás Structure, where the lake is placed; (ii) differential erosion by – and building of – the formation of the South Carajás Hill; (iii) Fe‐rich crust formation by weathering and gravitational collapse faults following the E–W plateau border and the start of Violão Lake formation during the Pliocene–Pleistocene; and (iv) episodic fault‐fracture reactivation by gravitational collapse causing pulses of subsidence in the lake and outlining its faulted borders. Dissolution of the lateritic crust and erosion by runoff drainage under wet climate conditions were coeval with fault activities, which allowed the deposition of relatively thick clastic deposits organized in three main seismostratigraphic units associated with major lake‐level fluctuations. Initial fault reactivation under low‐level water started lacustrine basin development with deposition of prograding fan deltas related to the main drainage. A second fault reactivation by gravitational collapse increased the lake accommodation space and resulted in the deposition of fine‐grained sediments from dilute interflows or overflows until 36 000 cal year BP. At about 31 000 cal year BP, rapid decreases in the lake water level under redox conditions at the sediment/water interface allowed widespread siderite formation. A third gravitational collapse episode was responsible for the increase in the lake area and depth and the returning of clastic/organic deposition up to the present. This tropical montane lake can be seen as a representative example for understanding the formation of other upland lakes controlled by fault reactivation. © 2020 John Wiley & Sons, Ltd.

Spatial and temporal variations in depositional systems in the Kazusa Group: insights into the origins of deep-water massive sandstones in a Pleistocene forearc basin on the Boso Peninsula, Japan

A detailed chronostratigraphic framework established by the mapping of tephra key beds and application of oxygen isotopic data allows assessment of the synchroneity and diachroneity of depositional systems formed in coastal and deep-water environments. This framework also allows estimation of the timing of active delivery of coarse-grained sediments beyond the shelf margin in relation to relative sea-level changes. The depositional processes of deep-water massive sandstones (DWMSs) are still enigmatic; their formation is a result of active delivery of sands in association with the supply of organic carbon into deep-water environments. DWMSs are also important as reservoirs for hydrocarbon explorations. This study investigated the origins of DWMSs in the upper Umegase, Kokumoto, and Chonan formations (in ascending order) of the Pleistocene Kazusa Group on the Boso Peninsula, central Japan. Each formation contains several packets of DWMSs that are interpreted to have formed in response to the progradation of gravelly shelf-margin deltas or fan deltas during the falling and lowstand stages of relative sea-level changes controlled primarily by glacioeustasy. The development of DWMSs and associated sandstone beds is interpreted to have been induced by hyperpycnal flows, in association with sediment gravity flows that were initiated by breaching and/or collapse of sandy substrates on the shelf-margin deltas or fan deltas. The timings of the initial and final deposition of the packets vary within and between the formations, and are considered to have been controlled by the interaction between allogenic and autogenic processes operating in the gravelly shelf-margin deltas or fan deltas. A muddy horizon that contains the Lower–Middle Pleistocene Subseries boundary (the base of the Chibanian Stage) in the Kokumoto Formation is also underlain and overlain by the packets and represents a deposit formed in a condensed section in an upper slope environment. This depositional setting may have favored the development of the Global Boundary Stratotype Section and Point (GSSP) for the Lower–Middle Pleistocene Subseries boundary in the formation.

Sedimentary Facies, Provenance and Geochronology of the Heshangzhen Group: Implications for the Tectonic Evolution of the Eastern Jiangnan Orogen, South China

AbstractThe Neoproterozoic Jiangnan orogen plays an important role in the study of the Precambrian tectonic evolution of South China. The tectonic nature of the Neoproterozoic sedimentary basins is still controversial, due to poor understanding of the sedimentary sequences and the lack of geochronological data. Here, we present sedimentological, provenance and geochronological data from the Heshangzhen Group in the eastern Jiangnan orogen. Sedimentological analysis shows that the Luojiamen Formation was deposited in a submarine fan, and the overlying Hongchicun Formation was deposited in front of a fan delta. The youngest detrital zircons constrain the lower Luojiamen and Hongchicun formations with ages of 827.3 ± 8.4 Ma and 825 ± 12 Ma, respectively. The sandstones of the Luojiamen Formation are characterized by a large number of intermediate to felsic volcanic grains, suggesting a volcanic arc source. In contrast, quartz and sedimentary lithic grains increase in the Hongchicun Formation, showing a new input from a collisional orogenic source. Detrital zircon from six sandstone samples in the Luojiamen and Hongchicun formations yield similar age spectra of 930–820 Ma with a peak at ca. 845–860 Ma, with one main cluster at 930–820 Ma. Detrital zircons of 930–845 Ma show a positive value of ∊Hf (t) (+2.4 to +11, mean +7.6), which is similar to the volcanic arc of the nearby Shuangxiwu Group. There are a minor group of zircons with U‐Pb ages ranging from 820 Ma to 845 Ma from the middle part of the Luojiamen Formation and Hongchicun Formation, with ∊Hf (t) values between –20 to +2.4, which are consistent with the characteristics of the Shuangqiaoshan Group. within light of the bidirectional paleocurrents in the Luojiamen Formation, it is speculated that the zircons of 820–845 Ma were recycled from the Shuangqiaoshan Group, which is derived from a continental arc to the northwest. Our data suggests that the Luojiamen Formation was formed in an inter‐arc basin, while the Hongchicun Formation was formed in an accretionary wedge‐top basin. When juxtaposed with the conglomeratic characteristics at the bottom of the Luojiamen Formation, it is believed that the unconformity represented by the ‘Shen Gong Movement’ reflects the rapid erosion and accumulation process of island arc volcanic material. The disconformity between the Luojiamen and Hongchicun formations is the imprint of transition from inter‐arc basin to accretionary wedge‐top basin, which represents the collision between the Shuangxiwu arc and the Yangtze Plate.

Correction to: Chronological evolution of the channel functional units in association with palaeo-hydrogeomorphological environment in the ancient delta fan of Subarnarekha basin, India

The assessment of chronological evolution of the channel functional units is an imperative aspect to understand the channel avulsion nature and planform change. In this study, the channel functional units (channel, aggradational and abandoned) and their distinct micro-morphologies have been assessed through the landuse and landcover classification, terrain analysis, lithostratigraphic records and fluctuating flow regimes in the ancient delta fan of the Subarnarekha basin. The distinct micro-morphological features of the functional units have been formed and evolved under the dominance of fluvial environment coupled with the fluctuating strength of Indian summer monsoon (ISM) and regression phase of sea-level since 6000 years before present (YBP). However, the borehole lithostratigraphic records reveal that the ancient delta fan was formed under the different fluvio-marine depositional environments of the marine transgression, regression and stillstand phases since 32,200 YBP. The riverbed of the recent course is ascended than the palaeo-courses due to declining trends of water discharge and sediment load in the last four decades as well as during the late Holocene mega-drought event. The channel unit and abandoned unit have been transformed into the aggradational unit with micro-morphologies of point bar, fill-terrace, and natural levee under the influence of channel avulsion and bulk of sediment deposition related to the fluctuating flow regime and base level of erosion. The micro-morphological features (marshes, oxbow lakes and meander neck-cuts) of the abandoned unit have been modified from the channel unit after diversion of the recent course from the palaeo-course owing to extreme discharge and valley drowning during lowstand.

Layered mound, inverted channels and polygonal fractures from the Makgadikgadi pan (Botswana): Possible analogues for Martian aqueous morphologies

Layered mounds and inverted channels with polygonal fractures from the Ntwetwe Pan in the Makgadikgadi Basin (central Botswana) have been herein investigated. These morphologies are from an evaporitic basin (the Makgadikgadi Basin) that is the remnant of an ancient Pleistocene lake and is currently part of the world’s largest evaporitic system.The mounds in the Ntwetwe Pan are characterized by a layered structure and low relief (max. 5 m above the pan floor) and can be in excess of 2 ​km wide. The mounds consist mainly of loose (non-lithified) sand and silt with high moisture contents, even during the dry season. Geophysical investigations have shown that groundwater processes, particularly those related to the capillary fringe that rises and conveys moisture through the mounds, are factors that make mound sediments resistant to wind erosion.The inverted channels, identified in the southern part of the Ntwetwe Pan, are characterized by gentle reliefs and depressions, which depend upon the distribution of calcretes and indurated sediments. Large scale (up to 100 ​m wide) polygonal fractures localized at the front of the channels, disappear at the transition with the present-day pan floor.We consider that these particular mounds, within the Ntwetwe Pan, are remnants of the strandline of the paleo-Makgadikgadi Lake, and that the inverted channels represent distributary channels of a relict fan delta, formed by an ephemeral river, most likely the paleo-Boteti River, during a Lake Paleo-Makgadikgadi highstand stage. We consider that large scale (up to 100 ​m wide) polygonal fractures, located on the channel-mouth lobes, represent large-scale desiccation cracks formed by rapid water evaporation from delta deposits.The results of this investigation highlight the importance of the paleo-drainage system and its interactions with the water table and wind-deflation as main geomorphological factors within salt pan environments. The mounds in the Makgadikgadi pans also show strong geomorphic similarities to spring mounds on the surface of Mars, localized in equatorial layered deposits (ELDs). These ELDs mounds are considered to result from cyclical groundwater upwelling, evaporation and wind deflation. The geological processes that resulted in the formation of mounds within the Makgadikgadi pans may, therefore, help to explain how similar layered deposits formed on Mars and confirm existing theories.

Seagrass-related carbonate ramp development at the front of a fan delta (Burdigalian, New Caledonia): Insights into mixed carbonate-siliciclastic environments

Past shallow-water carbonate environments of the main island of New Caledonia (NC) have been subject to high terrigenous influx derived from the erosion of ultramafic obducted nappes and are therefore a relevant case study for characterizing neritic carbonate production in mixed carbonate-siliciclastic systems under a tropical climate. More particularly, we focused on Burdigalian carbonate sedimentary records cropping out on the western coast of NC, in the Népoui area. Based on a comprehensive sedimentological study of cores and outcrops, we established a new depositional model of an alluvial fan to carbonate ramp transition. Shallow-water (euphotic) carbonate production was dominated by seagrass-related biota and corals derived from small-sized bioconstructions. Extensional tectonics and associated normal faulting, driven by post-obduction isostatic rebound, favored carbonate ramp aggradation and preservation. The carbonate ramp was incised by conglomerate-filled terminal distributary channels, which indicate that terrigenous inputs remained significant during marine transgression and did not inhibit the development of seagrass and scleractinian carbonate factories. Phytal substrates induced by seagrass and/or macro-algae seafloor colonization strongly controlled the nature of carbonate production and promoted the accumulation of foraminiferal-coralline algal sediments. Seagrass development at the front of the fan delta is interpreted to have controlled the preservation of a diverse and significant carbonate production by reducing water turbidity and by limiting the risk of suffocation for filter-feeding biota in such a high terrigenous influx setting.

Diagenesis effects on the conglomerate reservoir quality of the Baikouquan Formation, Junggar Basin, China

Large accumulations of oil and gas have been found in fan delta conglomerate reservoirs in the upper Triassic Baikouquan Formation in the Mahu Sag at the northwestern margin of the Junggar Basin. To effectively explore strongly heterogeneous, high-quality, conglomerate reservoirs, their deposition, diagenesis, and genetic mechanisms must first be thoroughly studied. Analyses of cores, thin sections, fluid inclusions, oxygen isotopes, logging, physical properties data, X-ray diffraction, scanning electron microscopy, and cathodoluminescence confirm that the conglomerates have high feldspar contents as well as volcanic fragments that comprise a variety of micro-lithofacies. The heterogenous reservoir properties include permeability values of less than 1 mD, 1–10 mD, and higher than 10 mD, which correspond to 44.19%, 37.06%, and 18.75% of the reservoir, respectively. The tight reservoirs, mostly developed in the fan delta plain, have experienced extensive compaction and/or calcite cementation and consist of only a few secondary pores. Reservoirs with high porosity and permeability developed in subaqueous channels and experienced relatively weak compaction. These reservoirs contain large numbers of secondary pores that were mainly formed by the dissolution of K-feldspars and volcanic rock fragments. Comprehensive studies of sedimentation and diagenesis in the Baikouquan Formation indicate that these high porosities originated from the chronological coupling of the following three important geological processes: (1) Conglomerate reservoirs with better sorting and roundness and lower mud content are mainly developed in subaqueous distributary channels and have higher porosity and permeability than reservoirs with poorer sorting and roundness. (2) Strong dissolution of K-feldspar and volcanic debris occurred in reservoirs with good original physical properties, forming large numbers of secondary pores. Acidic fluids from source rocks in the Fengcheng Formation led to dissolution. (3) The byproducts of dissolution, which consist mostly of mixed-layer illite/smectite and illite, reduced porosity and permeability. In reservoirs with good original physical properties and fault development, dissolution plays an obvious role in improving physical properties in such relatively open diagenetic systems.

Soft-sediment deformation structures in alkaline lake deposits of Lower Permian Fengcheng Formation, Junggar Basin, NW China: Implications for syn-sedimentary tectonic activity

Soft-sediment deformation structures (SSDS) are an important tool for interpreting paleoseismicity and depositional environments in ancient basin successions. The northwestern margin of Junggar Basin is a key region for understanding the paleogeography and basin attribute of the Junggar Basin during the early Permian. In the Lower Permian (Kungurian) Fengcheng Formation, nine lithofacies are grouped into fan delta, fluvial delta, and shallow, deep and alkaline lacustrine facies associations. Vertical transitions of the sedimentary environments show that the lake basin experienced expansion during deposition of the Lower (P1f1) and Middle (P1f2) members and the shrinkage during the Upper Member (P1f3), which is consistent with the paleogeographic distribution of lithofacies in different members. Conventional cores show a wide variety of SSDS, including ductile (folds, convolute lamination, and load structures), hybrid ductile-brittle, and brittle deformation structures (microfaults, breccias, boudinage and sedimentary dikes). SSDS mainly occurred in a still and deep lacustrine environment. These deformation structures were not formed in any specific lacustrine environment, as there is no difference with the undeformed sedimentary units of the same sedimentary facies. Thus, the triggering mechanism is interpreted as intermittent earthquakes. Lake expansion under arid condition and SSDS intervals with vertical repetition and possible lateral continuity indicate that most seismicity was during the Middle Member (P1f2), corresponding with the main activity on basin-bounding normal faults. The enhanced faulting at this time generated accommodation, creating lacustrine conditions in the basin depocenter. It is thus clear that the early Permian Mahu sag represents an active rift basin with bounding faults, and is not a foreland basin.

Using remote sensing techniques to interpret geomorphological features along the east coast of the Red Sea, at Yanbu, Saudi Arabia

Yanbu is the second largest port and population settlement on the Saudi Arabian Red Sea coast. With the increasing development of its nearby coast, the geomorphological characteristics of the region must be studied in detail in order to inform future developments of the region. This study examines the region’s suitability for future development. A high-resolution map of the coastal area under study was drawn by analysing Shuttle Radar Topography Mission-Digital Elevation Model (SRTM-DEM) data and Advanced Spaceborne Thermal Emission and Reflection Radiometer-Digital Elevation Model (ASTER-DEM) data, using remote sensing images from Landsat satellites. Landsat ETM+ images taken in 2000 and 2015, alongside remote sensing analyses, field observations, and geological mapping, were used to describe the geomorphological and topographical characteristics of the Yanbu coast. Both principal component analysis (PCA) and false colour composite (FCC) were the most effective remote sensing techniques for mapping the geomorphological characteristics of the coastal plain. The true colour of the combination bands 3, 2, and 1 was the best at showing the areas and features of coral reefs. Thus, the main geomorphological units in the study area were identified, including wadi systems, dunes, alluvial fans and fan deltas, fluvial terraces, sabkhas, coral reefs, platform reefs, islands, sharms, and sea heads.

Chronological evolution of the channel functional units in association with palaeo-hydrogeomorphological environment in the ancient delta fan of Subarnarekha basin, India

Chronological evolution of the channel functional units in association with palaeo-hydrogeomorphological environment in the ancient delta fan of Subarnarekha basin, India

Seismic sedimentology, facies analyses, and high-quality reservoir predictions in fan deltas: A case study of the Triassic Baikouquan Formation on the western slope of the Mahu Sag in China's Junggar Basin

This study examines problems that are related to large spatial variations in the physical properties of fan-delta sandstone in the Baikouquan Formation on the western slope of the Mahu Sag. This study conducts high-resolution sequence stratigraphy, sedimentary-microfacies identification, seismic-sedimentology analyses, and seismic inversions of high-quality reservoirs by comprehensively utilizing geophysical log data, cores, thin sections, and three-dimensional seismic data. A fourth-order sequence stratigraphic framework of the study area is established through these methods, enabling us to define the sedimentary filling processes that were related to multistage transgression and regression in the Huangyangquan and Xiazijie fan deltas. According to this study's results, the fourth-order sequences SSQ3 and SSQ5 were the development sequences of high-quality reservoirs. Feldspar-dissolution effects produced a secondary porosity-development zone, which favors relatively high-porosity and -permeability physical traps. Sedimentary microfacies, such as distributary and interdistributary channels in the fan-delta plain, alongside subaqueous distributary channels, estuarine mouth bars, and sheet sand in the fan-delta frontal areas, are successfully identified. The results suggest that the fan-delta front is the most favorable subfacies belt for reservoir development in the study area. By using the vertical boundary of the fourth-order sequence stratigraphy and the horizontal boundary of the sedimentary subfacies as the constraint conditions, we perform a facies-controlled seismic impedance inversion, in which the layers are divided to improve the accuracy of the reservoir predictions. Subsequently, five potential regions of high-quality reservoir development are predicted in the fourth-order sequences SSQ3 and SSQ5, and three well positions are proposed. Subsequent exploration drilling achieved industrial oil flow, thereby confirming these predictions from seismic sedimentological analysis.

Coupling of strike-slip faulting and lacustrine basin evolution: sequence stratigraphy, structure, and sedimentation in the North Yellow Sea Basin (West Bay Basin offshore North Korea), eastern China

The North Yellow Sea Basin in offshore areas of eastern China provides a unique opportunity to document the interaction between the paleo-Eurasian and circum-Pacific tectonic domains and the coupled relationship between Tanlu Fault strike-slip activity, intrabasinal tectonics and sedimentation. This study combines well data, three-dimensional (3-D), and two-dimensional (2-D) seismic data to make regional tectonics interpretations, and delineate the sequence stratigraphy, geological structure and sedimentary history of the basin's Eastern depression, particularly focusing on the influence of Tanlu Fault strike-slip activity on basin evolution. The Eastern depression data record the development of five second-order stratigraphic sequences, both the Mesozoic and the Cenozoic fault systems with basement F1, F2 and F3 faults, and the deposition of various deltaic, fan delta, lacustrine, and subaqueous fan facies associations. The F1 and F3 faults controlled the NW- and NE-trending secondary faults and associated Mesozoic sedimentation within the depression, while the F1 and F2 faults jointly controlled the development of NE- and near-E-W-trending secondary faults and associated Cenozoic sedimentation. The results indicate that the plate movements and Tanlu episodic, strike-slip faulting generated a left-lateral stress field in the Early Cretaceous, that switched to a right-lateral stress field during the middle Eocene to Oligocene. This transformation produced secondary shear stress fields in the North Yellow Sea Basin and generated NE-trending rifting superimposed on the previous NW-trending rift generation, and controlled the related structural geology and sedimentation in the Eastern depression of the basin. This proposed explanation of a tectonic regime transformation model, coupled with Tanlu strike-slip movements, could also provide new insights into the differences in gaps that occur in the stratigraphic record for the North Yellow Sea Basin and adjacent areas in eastern China.

Geochronology and sedimentology of the Huashan Group in the northern Yangtze Block: implications for the initial breakup of the South China

Middle Neoproterozoic sedimentary sequences are widespread in South China and provide crucial insights into the geological evolution of sedimentary basins related to the breakup of the Rodinia supercontinent. The Huashan Group is a key Neoproterozoic stratigraphic unit in the northern Yangtze Block, South China; however, its depositional age and tectonic setting of deposition are debated. Here, we report zircon U–Pb geochronology and Hf isotope data for a tuff from the second section of the Hongshansi Formation near the bottom of the Huashan Group. Zircon U–Pb geochronology yields a 206Pb/208U age of 836 ± 4 Ma (MSWD = 0.74, n = 29). Zircon Hf isotope ratios have eHf(t) values of + 3.1 to + 5.4 and TDM2 ages range from ca. 1.5 to 1.4 Ga, which indicates that juvenile materials derived from the mantle were involved in their host magmas. Combined with previous research, the Huashan Group was deposited from ca. 830 to 800 Ma from bottom to top, and it contains alluvial fan, fan delta, and semideep to deep lacustrine facies, which represent early sedimentation into a continental rift basin. Rifting and basin formation began at ca. 830 Ma in South China, which is coeval with the initial breakup of the Adelaidean Rift in southeastern Australia. The Huashan Group was deposited during the first and the second episodes of a superplume associated with the breakup of the Rodinia supercontinent.

Characteristics and Influence Factors of Es3 Reservoirs in Gubei Sag

There are many provenance systems in Gubei sag of Es3. Es3 is one of the main oil-bearing horizon of oil and gas exploration in gubei sag. Because of the great depth, the reservoir property is relatively poor. Influenced by factors such as sedimentary type and diagenesis, the reservoir characteristics of different provenance systems are different. The sedimentary type not only restricts the original physical properties, but also influences the late diagenesis. In the same diagenetic stage, there are differences in the physical properties of different sedimentary types, in the same sedimentary type there are also have many differences between different sedimentary microfiches. The fan delta is the best, and the second is the underwater fan; the best part of the fan delta is the river channel and estuary sand bar in the front of the fan delta. The influence of different provenance system by depth, rock characteristics, the moving distance of different factors, in the stage of diagenesis, diagenetic types and other aspects are different, these factors continue to transform the reservoir. Ultimately these factors lead to the Kendong and Gudao provenance systems have the best reservoirs, Changdi second, Chengdong worst.