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The Early‐Middle Jurassic is one of the crucial coal‐forming geologic periods in the world and an important target for hydrocarbon exploration in the Turpan‐Hami Basin, China. The paleoenvironment and vegetation reconstruction of the Early‐Middle Jurassic have been investigated using elemental geochemistry and palynological analysis to reveal paleoclimate evolution. A total of 48 genera of pteridophyte spore and 35 genera of gymnosperm pollen were identified, and 5 palynological assemblages were longitudinally divided, which showed significant differences in geochemical behaviours. The paleoenvironment was a transition from suboxidation to anoxia and then to an oxidation environment under freshwater conditions. The paleowater in the northern Taibei Sag was deeper than that in the southern part during the Middle Jurassic, which coincided with the sedimentary background of the sublacustrine fan in the north and the shallow braided river delta in the south. The paleovegetation evolved from mixed lowland–upland forest in the Hettangian‐Toarcian, to lowland fern forest in the Aalenian‐Bajocian, to upland conifers forest in the early Bathonian, to upland Cheirolepidiaceae forest in the late Bathonian‐Callovian. The Toarcian and Bathonian‐Callovian arid climate and the Hettangian‐Pliensbachian and Aalenian‐Bajocian warm‐humid climate were responses to the continued global warming events and the intensification of the East Asian monsoon circulation, respectively. The influence of the Bathonian‐Callovian aridification event on the sedimentary response in the southern Taibei Sag will be delayed due to the gradual southward migration of the depositional centre. [ABSTRACT FROM AUTHOR]

Hyperpycnal flow deposits, one of the most important deep‐water gravity‐flow deposits in lacustrine basins, have become the research focus in recent years. However, the sedimentary characteristics and depositional model of hyperpycnal flow deposits in lacustrine basins remain unclear due to the differences of depositional settings between lacustrine and marine environments. Hyperpycnal flow deposits observed in the middle of the third member of the Shahejie Formation (Es3z) in the Bonan Sag, Bohai Bay Basin, Eastern China, provide a rare case study to reveal the characteristics and depositional model in lacustrine basins. For the first time, detailed core analysis, high‐resolution 3D seismic data, petrology and grain size analysis were used to unravel the characteristics and depositional model of hyperpycnal flow deposits in this study. Twelve lithofacies, six bed types and four bedsets (corresponding to feeder channel, distributary channel, levee and lobe) were recognized from detailed facies analysis. Plant fragment, an important identification mark for hyperpycnal flow deposits, can be classified into three types: completely broken plant fragments, partially broken plant fragments and complete leaves. The proximal part of the deposit develops a small amount of scattered and completely broken plant fragments in massive or spaced stratified pebbly sandstone and massive sandstone due to strong erosion of sustained high‐density turbidity current. The medial part of the deposit is dominated by laminated partially broken plant fragments in planar laminated or rippled sandstone due to suspended settling of sustained high‐density turbidity current and quasi‐steady low‐density turbidity current. Layered partially broken plant fragments with some complete leaves are common in the upper part mud rich division of hybrid event bed and laminated siltstone in the distal part of the deposit. The distribution pattern of hyperpycnites is controlled comprehensively by palaeogeomorphy and sediment supply. Palaeogullies determine the provenance direction of hyperpycnal flow. The formation of synsedimentary faults and troughs control the transport routing patterns. Local micro‐palaeogeomorphy and depression areas further restrict the distribution of sand bodies. During the early stage of deposition with insufficient sediment supply, sediments are transported to the deep basin along confined faulted troughs forming elongated sandy bodies. During the late stage of deposition with sufficient sediment supply, sediments are transported to the deep basin without confinement accumulating fan‐shaped sandy bodies. This study offers insight for enhancing the recognition criteria of hyperpycnites, as well as their depositional model in lacustrine basins. [ABSTRACT FROM AUTHOR]

With potential hydrocarbon source rocks, the Mesozoic Lower Cretaceous interval in the Aitegle Sag of the Yingen-Ejinaqi Basin in China has a bright petroleum exploration prospect. Considering the scarcity of wells in Aitegle Sag, we have systematically carried out the research on the sequence structure and sedimentary system evolution of the Lower Cretaceous based on seismic, core, and logging data, guided by the Vail classic sequence stratigraphy, and innovatively introduced the self-organizing mapping neural network (SOM) learning algorithm to assist in seismic geological analysis. The results are as follows: (1) after RMSAmp, LyapIndex, FrctDim, and InfoEntr clustering, five zones are divided, which are corresponding to five seismic facies (showing medium-strong amplitude and parallel-subparallel reflection; medium-strong amplitude and wedge-shaped divergent reflection; medium-strong amplitude and continuous-relatively continuous, parallel-subparallel reflection; strong amplitude and continuous sheet-like or blank reflection; and weak amplitude and mound-shaped chaotic reflection, respectively), and interpreted as five subfacies including delta plain front, prodelta-shallow lake, semideep lake, deep lake, and sublacustrine fan. (2) The Lower Cretaceous formation includes one second-order sequence, three third-order sequences (SQ2–SQ4), and six system tracts. In the SQ2–SQ4 circle, the delta system formed by sediments from southeast varies remarkably in the progradational zones in different system tracts, and tectonic movements and sediment supply control the sequence stratigraphy in the study area as major factors. (3) It is feasible to apply SOM learning algorithm to seismic attribute clustering analysis. This method effectively realizes the combination of geophysical methods based on big data analysis and geological problem analysis, which not only strengthens the use of seismic data but also ensures the effectiveness and reliability of clustering results. These findings offer basic data and scientific supports for the exploration and development of unconventional reservoirs (e.g., shale and tight oil/gas reservoirs) in the Aitegle Sag and also provide new ideas for studying the sequence-sediment in the target zones in the fault basin regions with scarce wells. [ABSTRACT FROM AUTHOR]

Coarse‐grained subaqueous fans are vital oil and gas exploration targets in the Bohai Bay basin, China. The insufficient understanding of their sedimentary processes, depositional patterns, and controlling factors restricts efficient exploration and development. Coarse‐grained subaqueous fans in the Yong'an area, Dongying Depression, are investigated in this study. These fans include nearshore subaqueous fans, and sublacustrine fans, and their sedimentary processes, depositional patterns and distribution characteristics are mainly controlled by tectonic activity and paleogeomorphology. Nearshore subaqueous fans developed near the boundary fault during the early–middle deposition stage due to strong tectonic activity and large topographic subsidence. Early sublacustrine fans developed at the front of the nearshore subaqueous fans in the area where the topography changed from gentle to steep along the source direction. While the topography was gentle, sublacustrine fans did not develop. During the late weak tectonic activity stage, late sublacustrine fans developed with multiple stages superimposed. Frequent fault activity and related earthquakes steepened the basin margin, and the boundary fault slopes were 25.9°–34°. During the early–middle deposition stage, hyperpycnal flows triggered by outburst floods developed. During the late deposition stage, with weak tectonic activity, seasonal floods triggered hyperpycnal flows, and hybrid event beds developed distally. [ABSTRACT FROM AUTHOR]

While Ediacaran cap dolostones research is a hot topic, detailed sedimentological analysis of barite‐bearing cap dolostones remains scarce. Here, new data are presented from Xiangerwan in northern Three Gorges, South China, to illustrate the sedimentary characteristics, depositional environment and formation mechanism of the barite‐bearing cap dolostone. In ascending order, the succession is divided into: (i) pebbly dolostone; (ii) dolostone with unusual sedimentary structures (for example, sheet cracks and tepee structures); and (iii) barite‐bearing facies. The gravels of the pebbly dolostone record the slow relative sea‐level rise during post‐glacial transgression, with a local terrestrial influence. Sheet cracks and tepee structures represent water escape structures in the supratidal and upper intertidal zone, and gently wavy stromatolites in barite‐bearing facies are deposits typical of the upper intertidal zone. In addition, primary radial length‐slow dolomite cements were originally precipitated at the seafloor. In general, the cap dolostone was formed in a shallow‐water ramp environment. The form and sedimentary characteristics of barites indicate a primary (syngenetic) origin and help to divide the barites into bladed (Type I) and needle‐like (Type II) variants. With the ongoing melting of the Marinoan glacier and water density stratification, the cap dolostone was gradually precipitated, accompanied by exotic gravels input. The stratification persisted, and special sedimentary structures were widely developed. Phosphorus and barium ions were brought up from the deep basin by upwelling, indicated by the flourishing stromatolites and barite fan deposition. Above the sediment–water interface, the Type I barite first grew upward from substrates, then the Type II barite could grow either in the reverse 'V‐shape' cavities between and within the Type I barite clusters, forming rhythm layers with bedded dolomite, or scattered in the laminae of stromatolites or surrounding dolomite. Finally, the formation of barite fans indicates the end of cap dolostone deposition and deeper water sedimentation. [ABSTRACT FROM AUTHOR]

The study on morphology and distribution of sublacustrine fan are necessary for the exploration of oil and gas, which could help to effectively predict the reservoirs of sublacustrine fans. In this paper, the distribution and geomorphology of sublacustrine fans of Dongying Formation in Liaoxi uplift (Bohai Bay Basin, East China) and their controlling factors (including shape and formations) have been analyzed in detail based on seismic, core, and logging data. The main conclusions achieved in this study are: (1) During the sequence of the third member of Dongying Formation (SQd3), two types of sublacustrine fan, including channelized fan (in channel shape) and non-channelized fan (in tongue shape and lobe shape), developed on the eastern slope of Liaoxi uplift, which inherited the characteristics of sediments structural maturity in braided river delta front (good sandstone sorting and high structural maturity); (2) Steep slope was favorable for forming tongue shape sublacustrine fans with large ratio of length and width, while gentle slope tended to deposit lobe shape fans; high mud content tended to form stable channels with strong erosion on the slope end, while high sand content tended to form continuous lobes with lobe shape; (3) In the basin with uplift, the beneficial combination among provenance, relative lake level change and paleomorphology, determines the development and distribution of sublacustrine fan, and the sublacustrine fan deposits are mainly concentrated in the TST. The Yanshan fold belt in the west provided sufficient sediments to the Liaodong Bay during LST for the development of a sublacustrine fan in the east slope of Liaoxi uplift since the Liaoxi uplift sunk into the water, with the result that the deposition of braided river delta front can overlap the uplift. The incised canyons in the Liaoxi uplift provided the channels for sediments entering into the eastern slope, and the main sedimentary location of lacustrine fans was between two stages of faults. This study could provide a theoretical basis for researching the characteristics and distribution of other sublacustrine fans in similar basin backgrounds. [ABSTRACT FROM AUTHOR]

Turbidites have been recognized as significant reservoir units in both marine and lacustrine basins. This study was conducted on the Eocene Dongying Sag (Bohai Bay Basin, East China) using sediment cores, well logs, seismic data, and petrography to investigate the diagenesis and reservoir quality of lacustrine turbidites controlled by climate-driven base-level changes. The early forced regression within a third-order sequence stratigraphy can be divided into rising and falling stages of fourth-order base-level changes. Throughout these stages, extrabasinal turbidites were triggered by river floods and comprised the main channel, distributary channel, lobe, and lobe fringe. Intrabasinal turbidites only occurred during the falling stage, which were caused by sediment failures and corresponded to tongue deposits. Compared to extrabasinal turbidites, intrabasinal turbidites possess enhanced anti-compaction capabilities, reduced clay matrix content, and higher carbonate cement content. Climate-driven base-level changes dominated the diagenesis of lacustrine turbidites. From the rising to falling stage, the climate transitioned from humid to arid conditions. This caused a decline in the formation of clay-sized sediments that were subsequently transported into deep-water environments, thereby enhancing mechanical compaction of extrabasinal turbidites. Stacking patterns of channel complexes changed from vertical aggradation to lateral migration, reducing the occurrence of carbonate cementation near channel amalgamation and sandstone–mudstone interfaces. Therefore, these processes controlled by base-level changes led to a decrease in carbonate cement content and mechanical compaction, simultaneously promoting dissolution in extrabasinal turbidites during burial. Additionally, falling base-level facilitated rapid progradation of clinothems and delta collapse, resulting in the development of limited-scale tongues characterized by lower sorting and clay matrix content inherited from the delta front. Tongues, despite their enhanced resistance to compaction, were surrounded by thick-layer deep-water mudstones, contributing to strong carbonate cementation during burial. This study confirms that extrabasinal turbidites during the falling base-level possessed better reservoir quality, thereby providing guidance for the exploration of gravity flow sandstone reservoirs in lacustrine basins. • There are two triggering mechanisms of gravity flows during the early forced regression. • Extrabasinal turbidites during the falling base-level possessed better reservoir quality. • Climate-driven base-level changes dominated the diagenesis of lacustrine turbidites. [ABSTRACT FROM AUTHOR]

The connection between deltaic clinothem growth and the formation of down-dip deep-water systems on continental margins has been extensively discussed as a crucial component of sequence stratigraphic theory. However, in lacustrine settings, the growth of deltaic clinothems and outlying deep-water fans remains comparatively poorly understood. In the southwestern Bozhong Sag, Bohai Bay Basin, China, both lacustrine deltas and outlying sub-lacustrine fans were developed during the Oligocene, providing an opportunity to investigate the connection between lacustrine deltaic clinothem growth and the formation of outlying sub-lacustrine fans in deep-lacustrine systems. We employ 3D seismic data, well data, core data, and sandstone grainsize data to analyze the stacking patterns and internal architectures of these two sedimentary systems in the lower and upper successions of our study interval, SQE d 2 L. In addition, elemental geochemical parameters were utilized to reveal the paleoclimatic signature of the different stratigraphic successions. Our results suggest that there are two main types of deltaic clinothem stacking patterns in the lower and upper successions of SQE d 2 L, respectively: (1) in the lower succession, progradational to aggradational stacking patterns have a flat to steeply rising rollover trajectory, and (2) in the upper succession, aggradational to progradational and degradational stacking patterns have a slightly rising to flat and slightly falling trajectory. Meanwhile, the sub-lacustrine fans with straight channels and thick lobe complexes are coupled with progradational and aggradational (PA) deltaic clinothems in the lower succession. In the upper succession, small-scale sub-lacustrine fans with sinuous channels and thin lobe complexes are coupled with aggradational to progradational and degradational (APD) deltaic clinothems. The sediment connectivity between lacustrine deltas and sub-lacustrine fans stands in stark contrast to their counterparts in marine basins (such as marine APD clinothems coupled with large-scale deep-water fans, while marine PA clinothems rarely produce deep-water fans). In addition, two contrasting paleoclimatic stages have been identified in SQE d 2 L, namely the earlier humid stage in the lower succession and the later semiarid climatic stage in the upper succession. A comprehensive analysis of the differences between lacustrine and marine basins indicates that climatic variations play a pivotal role in deep-lacustrine deposition. Consequently, a climate-cycle-driven, sediment-supply-dominated sedimentary model of delta-to-fan sediment connectivity is proposed that incorporates the efficiency of terrigenous sediment dispersal into deep-lacustrine floors and the architecture of sub-lacustrine fans. The findings of this study further refine the implementation of the sequence stratigraphy paradigm and enhance the understanding of delta-to-fan sediment connectivity in deep-lacustrine depositional systems. • The scale of deep-water fans is coupled with various lacustrine deltaic clinothems. • Sediment connectivity of delta-to-fan in lacustrine basins is opposite to marine. • Climatic variations regulate sediment-supply and deep-lacustrine deposition. • Humid climates led to increased sediment connectivity between deltas and fans. [ABSTRACT FROM AUTHOR]

Unusual sedimentary deposits such as stromatolites, thrombolites, dendrolites, and giant ooids are widely distributed in the Permian–Triassic boundary (PTB) successions of shallow platform facies worldwide. These microbial fabrics, however, are rarely present in the same section. The genesis of these PTB microbialites and the oceanographic conditions linking to the end-Permian mass extinction still remain disputed despite intense study. Here, we report a stromatolite-dendrolite-thrombolite-giant ooid association from the PTB beds of the Yudongzi section on the northwestern margin of the Yangtze Platform, South China, which was situated in low latitudes during the Permian-Triassic (P-Tr) transition. The Yudongzi microbialites rest on an irregular contact with underlying Permian bioclastic limestone and are comprised of lower bedded stromatolite, digitate dendrolite, upper bedded stromatolite, and thrombolite units. The bedded stromatolite is characterized by undulating laminated structures and various amalgamated and layered clots. The digitate dendrolite is made up of digitate-like branches, formed by clots distributed in an arched arrangement, and characterized by abundant branching dendroids. The thrombolite displays distinct clotted textures that comprise a mixture of dark-colored microbial fabric and light-colored interstitial sediment. In microbialite, columnar structures identified as Gakhumella -like calcimicrobe are very abundant. Each individual of Gakhumella -like structure has densely arranged segments forming a columnar- to fan-shaped micro-structure. Single segments are arch-shaped and form a thin chamber between segments. Coccoid-like, bacterial clump-like, and other spheroidal aggregates are also commonly present and suggestive of a biogenetic origin for the Yudongzi microbialites. Moreover, distinct aragonite crystal fans are also for the first time found in the PTB microbialites in South China, suggesting that the fans may have resulted from high inorganic carbon concentrations, and thus high levels of carbonate dioxide in the seawater. The Yudongzi microbialites are capped by shelly grainstone and a massive giant oolite, implying that the demise of the Yudongzi microbialites may be due to destruction by strong wave currents in a high energy setting. Some ooids are coated unevenly by micritic laminae (or envelopes) indicating the possibility of a microbe-related origin. These microbial-coated giant ooids, together with the massive microbialites, may imply the long-term of microbial bloom in the oceans immediately after the end-Permian extinction. The co-existence of abundant Gakhumella-like microorganisms and oxygen-dependent invertebrates, together with some coccoid-like spheroids, aragonite cement crystal fans, and pyrite framboids indicative of oxygen-poor conditions, implies that oxygenation state of the PTB microbialites is much more complex than previously recognized, demonstrating need for continued multidisciplinary examination of facies changes associated biotic mass extinction. [Display omitted] • PTB microbialite complex comprises bedded stromatolite, digitate dendrolite, thrombolite and giant ooids. • Microbial fabrics include undulating laminated structures, digitate-like branches, and clotted textures. • Ooids are coated by micritic laminae indicating the possibility of a microbe-related origin. • Columnar structures identified as Gakhumella are very abundant and belong to the benthic Pleurocapsale cyanobacteria. • Aragonite crystal fans are distinct, and may have resulted from high bicarbonate in the seawater. [ABSTRACT FROM AUTHOR]

The evolution of alluvial fans is controlled by the tectonic setting and climatic fluctuations. This study focused on the Lidian alluvial fan in the northern piedmont of Zhongtiao Shan, north China, to study the fluvial responses to paleoenvironmental changes since the late Last Glacial Maximum. In combination with series of accelerator mass spectrometry (AMS) 14C dating data on fan sediments, sedimentary analyses indicated that the primary fan accumulation was controlled by episodic millennium-scale debris and sheet flood flow related aggradation during 13.3–13.0, 12.7–11.3, 6.2–4.5, and 4.5–2.8 cal ka BP. Between the accumulation periods, the fan process was dominated by aeolian paleosol-and-loess sequence development and the reworking of fan clasts. Considering regional hydraulic conditions and sediment flux, we proposed that the millennium-scale episodic debris flow related fan aggradation during 13.3–13.0, 12.7–11.3, and 4.5–2.8 cal ka BP was controlled by high-volume sediment influx of the permafrost and physical weathering during cold events. The millennium-scale sheet flood-dominated fan aggradation event during 6.2–4.5 cal ka BP was related to the abrupt coarsening and high sediment yield forced by tectonic uplift. We also suggest that the scattered distributed channelized floods and debris backfilling sediments within the fine-grain layers indicate that the deposition of irregular fan lobe accumulation coincided with hydraulic shifts over shorter temporal scales. [ABSTRACT FROM AUTHOR]

Turbidite strata are common along faulted margins of half-graben lacustrine basins, but complex lobe evolution may cause significant variability and uncertainty in the spatial distribution of turbidite sand bodies. This study integrates core samples, seismic and well log data from the Dongying Depression lacustrine basin in East China, and uses these data as inputs to a reduced-complexity stratigraphic forward model of turbidite fan lobe evolution. Data-unconstrained sensitivity analysis is used to investigate sensitivity of fan-lobe spatial distribution to fault-related subsidence rate, basin-margin slope, sediment input volume, and sediment input volume oscillation period. A data-constrained multiple-scenario approach then varied parameters within defined uncertainty ranges to generate a series of best-fit models to predict optimal reservoir presence locations. Results indicate that syn-rift segmentation of the Shengbei fault leads to spatial and temporal variation of fault-related subsidence in the hanging wall basin. External controls exert systematic impact on the spatial distribution of both smaller-scale flow beds and larger-scale fans on basin floor. Higher rates of fault-related subsidence and smaller sediment input volume produce more laterally confined fan lobe distribution. Higher basin-margin slope gradient produces more laterally clustered turbidites, but does not change fan lobe location, indicating break of slope is a more significant control on fan location. Multiple scenario reservoir presence probability maps suggest that bypass-dominated middle and inner fan areas, and smaller lengths of retrogradation-dominated feeder channels are most promising reservoir locations. • Syn-rift fault segmentation lead to spatial-temporal variation of fault-related subsidence in the hanging wall basin. • External controls impact the spatial distribution of both smaller-scale flow beds and larger-scale fans on basin floor. • Some middle-to-inner fan areas and sections of the lobe feeder channels have best reservoir presence probability. [ABSTRACT FROM AUTHOR]

Zeolite minerals are widely developed in clastic rock reservoirs around the world, and their behavior during diagenetic evolution affects the performance of the reservoirs. Zeolite can fill the primary intergranular pores in a cemented manner and can also undergo alteration and postdissolution to increase pores during the diagenesis process, while quantitative research is still quite limited at present. For this purpose, this paper takes the typical zeolite-rich Jiamuhe Formation (P 1 j) in the deep layer of the Shawan Sag, Junggar Basin, as an example and carries out a series of sedimentological, petrological, mineralogical and geochemical analyses to quantitatively evaluate the effect of zeolite alteration on the reservoir. The results indicate that the deep P 1 j reservoir contains fan-delta facies sandstone and conglomerate, and its storage space is mainly zeolite intercrystalline pores and remaining intergranular pores. The zeolite mineral type is almost all laumontite, with very low analcite and heulandite contents (<1%). The volcanic glass provided by the medium–basic volcanic rock debris (andesite and corresponding tuff), with the continuous increase in temperature and the supply of alkali metal ions, is eroded into laumontite via clinoptilolite and heulandite. In the process of zeolite alteration, zeolite minerals appear as zonal characteristics in the vertical direction. The intercrystalline pores formed by the dehydration of zeolite minerals are the most important factors for the development of high-quality deep reservoirs. Based on a large number of statistical analyses of zeolite cementation and intercrystalline pores within the cementation, a unit change of zeolite can cause a unit change in the intercrystalline pores of 22.16%. Supposing that the laumontite mineral content of the reservoir is 30%, the porosity can be increased by 6.6%. This can provide theoretical guidance for the change in the porosity of zeolite alteration in zeolite-rich reservoirs under similar backgrounds and improve the academic understanding of this point, which is exceedingly crucial. For instance, the Permian sand-conglomerate reservoirs in the northwestern margin of the Junggar Basin also have similar zeolite alteration pathways, and the porosity can be quantitatively increased by 8.8% (the zeolite cementation is approximately 40%). Laumontite (21%) in high-quality reservoirs of the Yingcheng Formation in the Changling Sag, Songliao Basin, can increase the porosity by 4.5%. • Reservoirs dominated by remaining intergranular pores and intercrystalline pores are controlled by lithology and zeolite. • Quantitative assessment of the degree of porosity change induced by laumontite by utilizing high-resolution image data. • Reveals the intercrystalline pore formation mechanism and the influence the form of pores. [ABSTRACT FROM AUTHOR]

Although hydrocarbon gases are widely distributed in the shallow strata of marine deep-water areas, it is generally believed that these shallow gases have little potential to form large gas accumulations due to unfavorable conditions, especially for effective trap development. Based on a comprehensive analysis of the latest geological exploration data of the deep-water areas of the Qiongdongnan Basin, this study reports a large lithologic trap that developed in the shallow Ledong Formation with burial depths of 200–600 m below the seafloor (mbsf). Systematically, this work investigates the development model of the trap and its gas accumulation mechanism. The results indicate that during the Pleistocene, sediment mainly from the southern Kunsong Uplift was transported to the Qiongdongnan Basin due to confined canyon geomorphology and developed a large channelized submarine fan in the deep-water areas. The roof of the submarine fan was cut and eroded and laterally sealed by overlying muddy channels, resulting in a dome-shaped structure, which was further covered by the Pleistocene tight mudstones forming the Ledong lithologic trap. The Yacheng coal-measure source rocks in the deep-water areas had high gas yields, which resulted in increased pressures and promoted deep gas migration into shallow reservoirs along a combined migration pathway including sand strata, structural ridges, faults, fissures, and gas chimneys. The gas accumulated in the Ledong trap as a result of the decreases in temperature and pressure. After the deep gases charged the Ledong strata, migration was blocked by the overburden consisting of Pleistocene tight mudstones, whose seal capacity was significantly enhanced by overlying gas hydrates in the deep-water areas. Meanwhile, the seawater in deep-water areas compacts the underlying cap rocks through its own weight, which enhances the seal capacity of cap rocks. In shallow reservoirs, thermogenic gases may mix with microbial gases from shallow marine source rocks, and some thermogenic gases may be reformed by microorganisms to form secondary microbial gases. The shallow Ledong gas reservoir connects the underlying gas reservoirs and the overlying gas hydrate reservoirs and vertically consists of a continuous hydrocarbon enrichment zone, which significantly expands exploration targets in the deep-water areas of the Qiongdongnan Basin. Additionally, the development model of the shallow Ledong lithologic trap and its gas accumulation mechanism may have general significance for hydrocarbon exploration in marine deep-water areas worldwide. • The shallow submarine fan has favorable conditions for developing lithological traps. • Thermogenic and microbial gases provide sufficient gases to the shallow trap. • Various lateral and vertical channels consist of effective gas migration pathways. • Overlying seawater and gas hydrates enhanced the seal capacity of cap rocks. • Shallow gas reservoirs markedly expand exploration targets in marine deep-water areas. [ABSTRACT FROM AUTHOR]

Intrabasinal subaqueous uplifts around small positive structural units are important targets of high-quality reservoirs in the Eocene Bohai Bay Basin (BBB). The western BBB was filled with sediments from northern and southern source regions. The southern sources are the Paleozoic rocks deposited in marine and costal settings, which are widely exposed along the Chengzikou uplift and stacked with Mesozoic igneous rocks. The northern sources are pre-Cambrian metamorphic rocks from the western Shaleitian uplift. To determine the origin of the Eocene sediments in the intrabasinal subaqueous uplift, eight sediment samples were collected from drill cores in the Shaxinan structural belt of Shanan sag, western BBB for detrital zircon U–Pb dating. We conduct detrital zircon U–Pb dating to shed new light on Eocene provenance evolution and analyze sediment dispersal characteristics of the lacustrine beach-bar sandstones by integrating lithology, wire-line logs and 3-D seismic data in the Shaxinan structural belt. The obtained ages vary between the Archaeological and Mesozoic (2692 ± 42 Ma to 79.8 ± 1.0 Ma). Dominant provenance for the Shahejie Formation has evolved temporally, that is, from the early Shaleitian uplift to the late Chengzikou uplift. The beach-bar sand bodies developed on the subaqueous uplift in the Shahejie Formation (from base to top: member 3 of the Shahejie Formation, Es 3 , and members 1 and 2 of the Shahejie Formation, Es 12), while the gravel-rich fan delta-beach bar sand bodies mainly from the northern Shaleitian uplift in the Es 3 transitions to the mixed sand-mud braided delta-beach bar sand bodies mainly influenced by southern Chengzikou uplift in the Es 12. Types of intrabasinal subaqueous uplift (gentle palaeoslope), strong hydrodynamic environment, abundant multiple sediment provenance and the Eocene-Oligocene evolution collectively control beach bar sediment dispersal patterns in the deposit area. • Dispersal characteristics of multi-provenance systems. • Evaluate the adjacent S2S systems to predict potential deposit around the intrabasinal subaqueous uplift. • Reveal the dispersal patterns of beach-bar sedimentary systems and their spatial-temporal evolution. [ABSTRACT FROM AUTHOR]

The Pearl River Mouth Basin in the South China Sea is one of the most important offshore petroliferous basins in China. Specifically, the shelf-edge delta and slope fan systems in the deepwater area of the Baiyun Sag have been regarded as the most important objects for hydrocarbon exploration, and the sequence stratigraphic structure, sedimentary evolution, and "source to sink" relationship between them is an important basis for predicting favorable areas for hydrocarbon exploration. In this study, the sequence stratigraphic structure and sedimentary system of the Late Oligocene Zhuhai Formation in the Baiyun Sag of the Pearl River Mouth Basin were studied based on a comprehensive dataset that integrated seismic, logging, and core data. A total of four third-order sequences were determined in the second-order composite sequence (CS3) according to nature of unconformities. Within each third-order sequence, the characteristics of different sedimentary systems were successfully identified. Within CS3-1 and CS3-2 the transgressive systems tracts (TST) are relatively thick, and the highstand systems tracts (HST) encompass mainly the outer-shelf deltaic deposits with thin foresets. As for CS3-3 and CS3-4, the lowstand systems tract (LST) and falling-stage systems tracts (FSST) are dominated by shelf-edge deltas and slope fans deposits, whereas the TST are very thin. The depositional evolution and "source to sink" relationship between the shelf-edge deltas and associated slope fans are revealed as follows: there are mainly three stages of shelf-edge deltas, and their sedimentary paleo-water depths were 794.9 m, 822.6 m, and 556.8 m, with progradation angles of 8.5°, 7.7°, and 5.7°, respectively; the thick delta front (200–500 m) and slump deposit are the main identification features of the shelf-edge delta. During the period of LST, although the progradation angle of the shelf-edge delta was the largest, there were few slope fans or only mud-rich slope fan deposits in the front of the delta due to the influence of relative sea-level rise, and during the period of FSST, the slump and redeposition of the delta front sand bodies provided the sand source for the formation of the slope fans, thus forming the sand-rich fans. Moreover, according to the root mean square amplitude slices and 3D seismic profile, it was found that the slope fans in this area are directly related to the development of the channels between the deltas and slope fans; generally, the larger and denser the channel, the larger the slope fan area. • Sequence and sedimentary characteristics of the shelf-edge and the deltaic progradation structures. • The source to sink relationship between shelf-edge deltas and slope fans within the system tract. • Constraints of sea level change, tectonic movement and sediment supply. [ABSTRACT FROM AUTHOR]

Open-framework gravels (OFGs) form common lithofacies of alluvial fans. However, inferences of their mechanisms of transport and deposition, and of controls on their distribution in alluvial-fan successions, remain difficult, limiting our ability to interpret the environmental significance of such deposits and to predict their distributions in ancient successions. From an applied standpoint, such predictions are important in the development of hydrocarbon reservoirs and remediation of aquifers hosted in alluvial-fan strata. To elucidate our understanding of formative conditions of different types of OFGs, a study has been undertaken on the Quaternary Poplar Fan, in the endorheic Heshituoluogai Basin, China. Based on observations from outcrops and trenches on the Poplar Fan, eight different types of OFGs are identified: these lithofacies types account for 7% of the total deposits of the fan. During high flow stages, OFGs are deposited in association with supercritical sheet-like flow (type 1), unconfined streamflow (type 2), and flow in groundwater-fed channels (type 3). During low flow stages, OFGs are associated with trough cross-stratification (type 4) and sigmoidal cross-stratification (type 5); these types occur over the entire fan. At the fan margins, OFGs are associated with gulleys (type 6), especially at the distal fan toe. Other OFG types are associated with bank collapse (type 7) or intercalated with aeolian deposits (type 8). A model is proposed to account for the distribution of different types of OFGs across the fan, wherein types 1, 2 and 4 seen in the medial fan are dominant. This provides a framework for the identification, prediction and correlation of OGFs in subsurface alluvial-fan successions. • Detailed description and particle-size analysis of eight types of openwork gravels are presented. • The distribution of openwork-gravel types across the fan surface and in subenvironments and elements is determined. • A facies model is proposed to account for the occurrence of openwork gravels of different origin in alluvial-fan successions. [ABSTRACT FROM AUTHOR]

Under the guidance of the source-to-sink system model, we conducted multi-scale research, characterizing the provenance features, transport pathway, convergence mode, sand body architecture, and controlling factors of the channelized submarine fan developed in the Huangliuformation, Dongfang block, Yinggehai basin by combining both macro and micro methods. Zircon U–Pb dating, heavy minerals, and source area lithologic geological analysis confirmed that the provenance input for the upper member of the Huangliuformation mainly originated from a northwest mixed provenance system, which includes the Red River, Lam River, and Ma River drainage area. Based on 3D seismic and well logging data, seismic interpretation and sand body tracking were performed to further reveal that the ancient delta sediments were transported along the Yingxi slope and converged on the seafloor in the central depression to form a submarine fan. Detailed seismic sedimentological analysis also confirmed that the submarine fan is characterized by a strong gravity flow channelization. The thickness of the sand body varies significantly and its spatial structure is highly heterogeneous. The channels in the area were divided into four types: main channel, medial channel, migrated channel, and distal channel, according to genetic type and morphological characteristics. The submarine fan system was divided into six stages, exhibiting various channel and lobe developments and distributions. The evolution of the multi-stage channelized submarine fan was closely related to the sediment provenance, sea level rise and fall, and paleogeomorphology. Our research is important for the natural gas field exploration and sand body reservoir evaluation in DongFang block,and have typical case value for deep-water channelized submarine fan deposition in the South China Sea. • Provides systematic source-to-sink analysis of the channelized submarine fan. • Reveal the northwest multi-provenance system from the rock and dating analysis. • Sea level change and paleogeomorphology influence the sediment dispersal pathways. • Identify two reservoir groups, six evolution stages and four types of channels. • Shed new light on the sedimentary mechanism model of the Dongfang channelized fan. [ABSTRACT FROM AUTHOR]