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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]

Sequence architectures along the margins of rift basins are still poorly documented compared to passive continental margin settings. The Eocene Shahejie Formation on the rift margin of the Dongying Depression records a complex sequence stratigraphic distribution of conglomerate, sandy conglomerate, sandstone and mudstone. These facies have been mainly attributed to fan delta and marginal subaqueous fan depositional settings that developed during segmented fault activity along the rift margin. We utilize three‐dimensional (3D) seismic data, conventional cores, and wireline log data to dissect the overall wedge‐shaped upper sub‐member strata of the Shahejie Formation's fourth member. The study interval is a third‐order sequence formed between 45.4 and 42.5 Ma and contains a lowstand–transgressive systems tract (LST–TST) and a highstand systems tract–falling‐stage systems tract (HST–FSST). We found that the LST–TST developed several huge amalgamated depocenters along the Chennan border fault; whereas, these depocenters gradually diminished or even disappeared during the HST–FSST period, illustrating less significant control by the border fault. Through calculations of strata growth rates, we confirmed that the segmented activity of the border fault influences the stratigraphic distribution and facies evolution during these two periods. Specifically, deep‐water depositional systems, represented by marginal subaqueous fans were widely developed in the LST–TST period and were influenced by overall strong tectonic activity, including retrogradational (R) and aggradational (A) patterns. However, the aggradational to progradational (AP) deltas and progradational to degradational (PD) deltas dominated the generally muted tectonic activity setting during the HST–FSST. Additionally, influenced by localized segmented fault activity, these systems tracts exhibit incomplete vertical development, resulting in spatial variability in stratigraphic stacking patterns. [ABSTRACT FROM AUTHOR]

The significance of beach-bar reservoirs, which are intricately linked to unconventional hydrocarbon reservoirs, has gained increased attention. This study elucidates the complex mechanisms governing the formation, spatial distribution, and morphological characteristics of beach bars in Qinghai Lake, NW China, highlighting the interplay of lake-level fluctuations, wind wave dynamics, sediment provenance, and terrain gradient. Our findings reveal that large-scale lake-level fluctuations primarily dictate the initial formation settings of beach bars, while small-scale fluctuations refine their internal stratification and sedimentary features. Wind wave dynamics play a critical role in defining suitable depth zones for beach bar development, influencing their morphology and resulting in distinct sedimentary characteristics across different lake zones. Furthermore, the study categorizes beach bars into three main systems based on sediment provenance--bedrock, alluvial fan (fan delta), and braided river systems--each exhibiting unique compositional and structural attributes. Terrain gradient around the lake significantly affects beach bar formation, with areas having a gradient less than 0.7° being particularly favorable. This research advances our understanding of lacustrine beach bar dynamics, offering insights into their potential as indicators of past environmental conditions and their implications for hydrocarbon exploration. The comprehensive analysis of controlling factors provides a foundation for predicting beach bar distribution and contributes to the broader field of sedimentary geology by integrating multi-disciplinary approaches to study lacustrine sedimentary processes. [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]

The Paleogene Shahejie and Dongying formations of the eastern Bohai Bay Basin contain >500 m fluvial-deltaic deposits and >600 m deltaic-lacustrine deposits, both of which are important for oil and gas exploration. This study aims to figure out the deposition system distribution within the sequence stratigraphy and predict the exploration target. Sequence boundaries are recognized by unconformities in the seismic profiles and abrupt changes in the well-logging curves (acoustic, spontaneous potential, natural gamma-ray and resistivity), and two second-order and five third-order sequences (SQs1, SQs3 in the Shahejie Formation and SQd1-SQd3 in Dongying Formation) are identified. Four types of depositional system and distribution are determined by well-logging profiles, cores, relative sand content and root-mean-square seismic attributes. The SQs3 sequence is predominantly fan deltas and lacustrine deposits, the SQs1 sequence is predominantly shallow lacustrine deposits, the SQd3 sequence is predominantly braided-river delta, semi-deep lacustrine, and turbidite fan, and the SQd2 sequence is predominantly braided-river delta deposits, whereas the SQd1 sequence is predominantly braided-river deposits. The controlling factors are determined by basin subsidence simulation and fossil data of biological palynology, indicating that tectonic activity is the main controlling factor in SQs3 and SQd3 while climate is the main controlling factor in the SQs1, SQd2 and SQd1 sequences. Combined with the physical properties of sandstone, it is concluded that the beach bar in the SQs1 sequence, turbidite fan in the SQs3 and SQd3 sequences, and thick sandstone in the SQd2 sequence are the important exploration targets. [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]

The 4th member of Xujiahe Formation (Xu4) in the western Sichuan Depression is a typical porous tight sandstone reservoir. Finding reservoirs with relatively high porosity controlled by sedimentation and diagenesis is crucial for successful tight gas exploration. In this study, the Xu4 sandstone was studied by diverse methods, including outcrop and core observation, logging data interpretation, thin section and cathodoluminescence examination, scanning electron microscopy analysis, and X-ray diffraction, to determine sedimentary and diagenetic characteristics and to discuss their impact on the sandstone reservoir quality. During the depositional period of Xu4, subaqueous distributary channel sandstone of braided river delta front developed extensively under controls of bidirectional provenance (LASP and SASP), mainly consisting of litharenite and sublitharenite, with low feldspar and high rock fragments volume, respectively. Strong compaction and carbonate cementation have largely destroyed primary porosity, while secondary pores constitute the main pore space in the Xu4 sandstone. The sediment provenance, sedimentary microfacies and A/S determine the clastic composition of sandstone, genetic type and thickness of sand bodies, furthermore affect the subsequent diagenetic variations. The larger the thickness of the sand body indicates a higher-energy depositional environment, coarser grain size, better sorting, and lower shaliness content of the sandstone during deposition period. This results in stronger resistance to compaction of the sandstone, which is conducive to the preservation of primary pores and dissolution of organic acids, resulting in better physical properties of sandstone. Among them, the physical properties of the sandstones of the Xu4s and Xu4x are better than those of the Xu4z; moreover, LASP's sandstone is superior to SASP. It is worth noting that subaqueous distributary channel sandstones with thickness exceeding 13 m in Xu4s and Xu4x from LASP represent favorable areas for high-quality reservoirs. The work can be used as a reference for the exploration and evaluation of similar tight sandstone gas in the world. • The sediment provenance determines the rock type of the reservoir. • High-energy sedimentary environment is the premise of forming high quality reservoir. • A/S affects the difference of stacking pattern and thickness of sand bodies. • The diagenesis of porous tight sandstone is influenced by sedimentary conditions. [ABSTRACT FROM AUTHOR]

Reservoir architecture is often heterogeneous and can affect the migration and accumulation of hydrocarbons. The Triassic Baikouquan Formation in the Mahu oilfield presents a unique opportunity to use seismic data for fan delta channel and lobe belt characterization in an area with a sparse well spacing of about 800–1200 m. The Baikouquan Formation comprises coarse-grained lacustrine fan delta units deposited by traction and debris flows. The occurrence, distribution, and morphology were investigated using petrography, frequency spectrum decomposition, stratal slices, seismic forward modeling, and wireline logs. Fan-shaped lobe complexes and distributary channel complexes (sixth-order architectural units) exhibiting relatively large lateral and vertical variation were identified from 45- and 60-Hz seismic profiles. Channel and fan-shaped lobe belts (fifth-order architectural units) were investigated by integrating provenances, architectural elements from individual wells, the ratio of conglomerate to formation, cross section analysis, and seismic stratal slices. Four channel belts and three fan-shaped lobe belts were recognized, occurring in six evolutionary stages. It was discovered that these channel and lobe belts had distinct geomorphological traits. Reservoir architecture and distribution was governed by paleogeomorphology, fluctuations in accommodation space, and sediment supply. The identified fifth-order architectural units are useful for reservoir modeling and contribute to remaining oil development. This study indicates the suitability of seismic sedimentology for characterizing reservoir architecture in areas with sparse well spacing. • Seismic forward models are established to guide the interpretation of subsurface reservoir architecture. • Quantitative analysis of the fan delta complex is performed using frequency-division seismic profiles. • Reservoir architecture is governed by paleogeomorphology, fluctuations in accommodation space, and sediment supply. [ABSTRACT FROM AUTHOR]

The Silurian–Devonian transition experienced dramatic changes of climates, global carbon cycles and faunas, but detailed documentation of the environments and biotas during this transitional interval in the South China Block is needed. The upper Silurian–Lower Devonian sequence of Qujing, Yunnan, southwestern China, represents one of the rare stratigraphic records of this transition in the South China Block. In this study, the Xiaxishancun Formation of Qujing, a unit generally considered earliest Devonian in age, is studied in terms of sedimentology and ichnology. The results show that the Xiaxishancun Formation typically records the deposition of hyperpycnal flow systems, which have been rarely reported in the Paleozoic. Three facies associations, including mudstone-dominated association, heterolithic association, and sandstone-dominated association, represent different parts of the channels and lobes of hyperpycnal subaqueous deltas on the shelf. Nineteen ichnogenera and 32 ichnospecies were distinguished in the Xiaxishancun Formation, and grouped into two ichnoassemblages, the Lockeia - Ptychoplasma - Oravaichnium ichnoassemblage in hummocky/swaley cross-stratified sandstones, and the Cruziana - Diplichnites - Monomorphichnus ichnoassemblage in thin rippled sandstone beds. The hyperpycnal depositional processes of the Xiaxishancun Formation created nutrient-rich, oxygen-rich, siliciclastic environments that supported diverse benthic ecosystems. Our study provides new insights into the understanding of marginal-marine environments and biotas of South China, immediately following the Silurian–Devonian transition event. • 32 ichnospecies reported from the Lower Devonian Xiaxishancun Formation. • Ichnoassemblages are helpful to analyze the sedimentary process of hyperpycnites. • Hyperpycnites developed in South China during the earliest Devonian. • Inceased terrestrial inputs improved Early Devonian marine community. [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 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]

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 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. [ABSTRACT FROM AUTHOR]

Alluvial fans are usually constructed through episodic flood events. Despite the significance of these ephemeral floods on the morphodynamics of alluvial fans, depositional responses to the variations in flood conditions are still poorly documented. This greatly limits the ability to interpret ancient sedimentary successions of fans and the associated flood hydrodynamics. The Quaternary Poplar Fan from endorheic Heshituoluogai Basin provides an optimal case for addressing this issue. Based on the variations in facies associations and flood conditions, three depositional stages – namely; lobe building stage, channel building stage and the abandonment stage – are identified. During the lobe building stage the Poplar Fan is predominately constructed through incised channel flood, sheetflood and unconfined streamflood, with coeval development of distal surficial ephemeral ponds. The channel building stage is characterized by the development of gravelly braided rivers. However, only scour pool fill deposits are preferentially preserved in the Poplar Fan. During the abandonment stage, erosional lags and aeolian sands randomly occur throughout the fan, while gully deposits can only be found in the distal fan. The distinctive facies architecture of the Poplar Fan is likely to be the result of periodicity of climate fluctuations between wetter and drier conditions during the Late Pleistocene to Holocene. The ephemeral floods formed under wetter conditions usually show high discharge and sediment concentrations which facilitate the lobe building processes. During the drier periods, only gravelly braided rivers can be developed through ephemeral floods as the intensity and frequency in precipitation, discharge and sediment concentrations of the flood flows significantly decrease. The abandonment stage of the fan may occur between recurring flood episodes or during the driest periods. Furthermore, the long‐term (105 to 106 year) geomorphic evolution of the Poplar Fan shows the influence of tectonic activities. The ongoing thrust uplift tectonic activities have caused destruction of the fan but can also facilitate the fan‐head trench/incision of the fan, which in turn facilitate the progradation of the fan. This study proposes a new depositional model for alluvial fans constructed through episodic flood events, which shows the character of both sheet‐flood dominated and stream‐flow dominated end members of alluvial fans. These findings supplement the understanding of the variability of the alluvial fans and provide means to characterize rock record of alluvial fans and their associated flood and climate conditions. [ABSTRACT FROM AUTHOR]

Deep‐water deposits in marine basins have recently received considerable research attention. However, the controls of sediment transported to deep‐lacustrine environments are comparatively understudied. In this study, we utilize field‐based outcrop data to investigate the variability of sediment distribution and its controlling factors in the Lower Cretaceous synrift Xiguayuan Formation in the Luanping Basin. Two fan‐delta systems with variability dominate the measured outcrop sections. At the lithological scale, the ratio of conglomerate to strata in the Xiyuan fan‐delta system is 87%, and the average thickness of individual coarse‐grained layers is ~1 m; the corresponding values in the Caoying fan‐delta system are 52% and 0.4 m. In addition, sand‐rich gravity‐flow deposits are developed in front of the Xiyuan fan delta, whereas mud‐rich mass transport deposits (i.e., sliding block and slumping debris) are found in front of the Caoying fan delta. At the stratigraphical scale, a delta succession in the Xiyuan section characterized by sand‐rich facies from proximal to distal parts is developed in a relatively steep slope setting. In the Caoying section, however, a delta succession characterized by sand‐rich facies in the proximal to middle parts is found in addition to a mud‐rich distal part developed in a gentle slope setting. Differential sediment supply resulted in significant variation in the sediment distribution pattern. In particular, the grain size of the fan‐delta front controls that of the deep‐lacustrine gravity‐flow deposits fed by them. This study highlights the variability of sediment supply and their control on sediment partitioning in continental rift and marine basins. [ABSTRACT FROM AUTHOR]

Hyperpycnites are extrabasinal turbidites related to hyperpycnal flows which form during river floods. Compared to intrabasinal turbidite systems in deep marine or lacustrine settings, hyperpycnites in shallow lakes settings are not understood. In this work, we studied the typical sedimentary characteristics of shallow lacustrine hyperpycnal flow deposits in outcrops of the Luanping Basin, Northeast China. Based on the sedimentary architecture and analysis of the facies associations in these outcrops, the hyperpycnites can be classified into the following three types: (a) bedload‐dominated erosional channel deposits, (b) bedload‐ and suspended‐load‐dominated channel‐to‐lobe transitional deposits, and (c) suspended‐load‐dominated lobe deposits. The erosional channels in proximal locations are filled by mud clasts, parallel‐laminated sandstones, massive sandstones, cross‐bedded sandstones, massive siltstones, and mudstones. The channel‐to‐lobe transitional deposits in a middle location are composed of parallel‐laminated sandstones, cross‐bedded sandstones, mud clasts near internal erosional surfaces, ripple cross‐bedded sandstones, massive siltstones, and mudstones. The lobe deposits in distal locations are composed of ripple cross‐bedded sandstones, massive siltstones, and mudstones. The sedimentary process of the shallow lacustrine hyperpycnal flows shows obvious response to periodic flood energy fluctuations. Gentle slope, small capacity of flood discharges and semiarid paleoclimate may be the possible reason for the observed sedimentary architecture of the shallow lacustrine hyperpycnal flow deposits. Therefore, this study offers new insights into the sedimentology of shallow lacustrine deposits in rift basins. [ABSTRACT FROM AUTHOR]

In recent years, shallow-marine fans have attracted considerable attention because they may serve as valuable targets in hydrocarbon exploration. By integrating 3-D seismic, well log, core, and other measured data, this study analyzed the sedimentary characteristics and factors controlling the deposition of shallow-marine fans in Member #1 of the Huangliu Formation in the Yinggehai Basin. Four depositional elements were recognized in the channel-lobe complexes (CLCs), channel-fill sandy debrites, channel-fill turbidites, sand-rich lobe deposits and mud-rich lobe deposits. The channel-fill sandy debrites, which are characterized by low root-mean-square (RMS) amplitude in plan view and deep V-shaped reflections in seismic profile, are commonly located in the internal regions of CLCs. They have widths ranging from 1 to 2 km and single sandbody thicknesses exceeding 25 m. A cored interval from a channel-fill sandy debrite comprising several ungraded sand units revealed massive fine-grained sandstones with floating mud clasts and muddy rip-up clasts. In contrast, the channel-fill turbidites are characterized by low or high RMS amplitude in plan view and shallow V-shaped or vermiform-shaped reflections in profile. They have a small-size frontal splay at the terminus, thus forming a lobe-channel-lobe depositional style. The width of a channel-fill turbidite is usually less than 0.5 km, and the single sandbody thickness is no more than 20 m. A cored interval of channel-fill turbidite consisted of very fine-grained sandstones containing incomplete Bouma subdivisions T a –T b. The sand-rich and mud-rich lobe deposits are characterized by high RMS amplitude and low RMS amplitude with continuous sheet reflection patterns, respectively. The deposition of the shallow-marine fans was significantly influenced by sea-level fluctuations and paleogeomorphology. When sea level fell rapidly, gravity flows with higher erosive energy and velocity tended to form widely developed large-scale channel-fill sandy debrites and sand-rich lobe deposits. When sea level rose, small-scale channel-fill turbidites were dominant because of relatively decreased gravity flow energy. Distinct variations of reservoir characteristics, including mean grain size, mud content, and pore-throat radius, were controlled by sea-level fluctuations. From the period of rapid sea-level fall to the period of rising sea level, the gravity flows may have been increasingly diluted due to sufficient mixing with ambient seawater, resulting in a gradual transformation from sandy debris flows into turbidity currents. In addition, changes in gradient caused by irregular paleogeomorphology may have significantly triggered different depositional styles. With a steeper gradient, the CLC is dominated by a channelized-lobe depositional style; however, a lobe-channel-lobe depositional style prevails under a gentler gradient condition. Taking the reservoir characteristics and depositional styles into consideration, it is suggested that the sandy debrites, with better physical properties, constitute favorable hydrocarbon reservoir intervals. The shallow-marine fans in this study may serve as a distinctive analogue to similar gravity flow deposits in other basins worldwide. • Four depositional elements were recognized in the channel-lobe complexes. • Each depositional element shows distinctive seismic, well log, and core expressions. • Depositional variations are controlled by sea level fluctuations. • The irregular paleogeomorphology exert a fundamental control over depositional styles. • Sandy debrites represent a preferable hydrocarbon unit than turbidites. [ABSTRACT FROM AUTHOR]

The geomorphological evolution and sediment dispersal processes of the Liaodong Bay Depression (LBD), a strike-slip and extensional composite basin in the Dongying Formation, were studied using 3D seismic, drilling, and logging data in an attempt to understand the diversity of sand-controlling factors and the complexity of the sand dispersal processes. The LBD was mainly supplied by sediments from the eastern side, which originated in the Yanshan Fold system (comprising the Dashi River, Liugu River, and Lin River systems) and sediments from the western side, which originated from the Jiaoliao Uplift system (comprising the Daqing River and Fuzhou River systems). Different sediment provenances had various sediment supply capacities depending on the composition of the source rocks. Sediments were injected into the basin through the channels identified from two interpreted southwest-to northwest-orientated seismic sections. Strata of the Dongying Formation could be divided into three sequences, and comprised shallow-deep lacustrine deposits, braided river delta deposits, fan delta deposits, and sublacustrine fan deposits. Based on the established sequence stratigraphic framework, the strata thickness distribution and sequence of geomorphological evolution could be restored from 3D seismic data of the LBD. By analyzing the distribution and migration of depocenters and the distribution of channels, sediment pathways in the basin could be determined under high flux sediment supply. In terms of five interpreted seismic sections from north to south, we demonstrated that in addition to immense changes in tectonic depositional style in the eastern areas of the basin, the sediment dispersal processes in different areas exhibited prominent discrepancies in sediment accumulations from diverse depositional systems. Tectonic activities, efficient sediment provenance, distribution of channels, and sequence geomorphology jointly controlled the sediment dispersal processes in the deposition areas and determined the potential reservoir distribution. • Geomorphological evolution and sediment dispersal of a bay depression was studied. • Strata thickness and sequence-geomorphology was restored from 3D seismic data. • Distribution of incised valleys and sediment pathways in the basin were determined. [ABSTRACT FROM AUTHOR]

Taking some steam flooding experimental area in the western depression of the Liaohe Basin in China as an example, it quantitatively evaluates the flow units of the sedimentary facies in fan delta front and analyzes the influences of the flow units on the development of the oilfields. Comprehensive analysis of multifarious data such as geology, core analysis and well logs indicates that porosity, permeability and FZI are key parameters for classification and evaluation of the reservoir flow units. Then using SPSS cluster analysis software platform, cluster analysis are conducted on reservoir physical properties of cored wells, and based on which discriminant analysis are performed to obtain the discriminant formula. The discriminant analysis of reservoir physical properties of the wells without core data is based on fine interpretation of well logging data. Combined with the results of cored wells, the classification and evaluation of the flow units has been completed in the target layer of ​​the whole study area. Finally the flow units are divided into four classes, namely, Class A, Class B, Class C and Class D. Classes A and B flow units represent high-quality reservoirs. The flow units are mainly controlled by sedimentation. Classes A and B are mainly sedimentary microfacies of underwater distributary channel and distributary mouth sand bar. The paper proposes five principles of judging the rationality of flow units, describes the development characteristics of different classes of flow units on section and plane, analyzes the influence of flow units on oilfield development and suggests countermeasures. Specially, in the process of steam flooding, target injection layers should be optimized and steam injection pressure should be effectively controlled to prevent steam channeling; when planning infill wells, injection and production wells should be deployed in the same class of flow unit to ensure good connectivity; the development of remaining oil should focus on Classes A and B flow units, and meanwhile pay more attention to the fine interpretation results of well logging data. • The classification and evaluation method of flow units combined with genetic analysis and clustering analysis. • Key parameters optimized for classification and evaluation of the reservoir flow units. • Five principles of judging the rationality of flow units. • Analyzing of the influences of flow units on oilfield development and suggests countermeasures. [ABSTRACT FROM AUTHOR]

In recent years, enriched hydrocarbon reservoirs have been largely founded in the Lower Triassic Baikouquan Formation, in the Mahu Depression of Junggar basin, northwestern China. Accordingly, the sedimentologic complexity of associated deposits has been extensively studied, though most of them focused on local oil‐producing fields separately. In this research, a detailed sedimentary study of the entire Mahu Depression has been conducted, which include several aspects of sedimentary characteristics, sediment provenance, evolution, and controls of the coarse‐grained fan‐delta system. According to facies features recognized from cores, thin sections, well logs, and seismic data, three sedimentary facies associations were identified: upper fan‐delta plain, lower fan‐delta plain, and fan‐delta front. Furthermore, four depositional systems (Xiazijie, Haungyangquan, Karamay, and Xiayan fan‐delta) around the Mahu Depression were recognized by the distribution of heavy mineral assemblages and change of ZTR index (percentage of Zircon, Tourmaline, and Rutile in the total transparent heavy mineral assemblage). Based on the analysis of facies and sediment provenance, the temporal and spatial distribution of the fan‐delta system were reconstructed associated with the variation of net/gross ratio. As characterized by decreasing‐upward of net/gross ratios and fining‐upward trend of grain size, the evolution of the fan‐delta succession showed an overall retreating pattern which was mainly controlled by lake level rising and rapid tectonic subsidence. Within the retreating pattern, hydrocarbons were trapped in the middle deposits with reservoir space produced by fan‐delta front and lower fan‐delta plain, which were encased between the top transgressive lacustrine mudstones and the bottom debris‐flow deposits produced by upper fan‐delta plain. These findings of the research throw light on the phenomena that the stratigraphy trap for hydrocarbon accumulation could be constructed by retreating, coarse‐grained fan‐delta systems. [ABSTRACT FROM AUTHOR]

Abstract The Ledong Submarine Fan in the western Qiongdongnan Basin runs parallel to the continental slope, with an area of over 10,000 km2 and maximum thickness of greater than 2000 m. Using bulk rare earth element (REE) compositions of the sediments and detrital zircon U-Pb age data, we analysed the provenance of the Ledong Submarine Fan and its regional tectonic implications. The zircon grains in the Ledong Submarine Fan show a wide range of shapes, from prismatic crystals to oval grains with mostly rounded corners, indicating the long transport distance of these zircon grains prior to deposition. The zircon ages have a wide range from 27 to 3006 Ma, with five major age peaks at ca. 27 Ma, 88 Ma, 256 Ma, 415 Ma and 785 Ma, along with a number of subordinate age peaks at ca. 1024 Ma, 1376 Ma, 1879 Ma and 2374 Ma. These age distribution patterns are similar to those from the Red River at Yen Bai. The total REE content range is between 87.72 and 210.38 mg/g in the Ledong Submarine Fan. The chondrite-normalized REE patterns show light REE (LREE) enrichment and weakly negative Eu anomalies, which are similar to those in the Red River at Hanoi. The evidence from zircon U-Pb ages and REE geochemistry indicates that the provenance of the Ledong Submarine Fan is the Red River System. The development of the Ledong Submarine Fan indicates that a rapid subsidence occurred in the western Qiongdongnan Basin during the late Miocene, and the strike slip reversal of the Red River Fault from sinistral to dextral motion was the key factor that induced gravity flow to form the Ledong Submarine Fan. Highlights • Detrital zircons and REE from the sediments in the continental slope-parallel Ledong Submarine Fan were examined. • The source of the Ledong Submarine Fan sediments was from the Red River System. • The development of the Ledong Submarine Fan has implication for the tectonic activity of the Red River Fault. [ABSTRACT FROM AUTHOR]

Abstract: The origin of the fourth member of the Eocene Shahejie Formation in the northern steep slopes of the Minfeng Sub‐sag, Dongying Sag, China, was investigated by integrating core studies and flume tank depositional simulations. A non‐channelized depositional model is proposed in this paper for nearshore subaqueous fans in steep fault‐controlled slopes of lacustrine rift basins. The deposits of nearshore subaqueous fans along the base of steep border‐fault slopes of rift basins are typically composed of deep‐water coarse‐grained sediment gravity‐flow deposits directly sourced from adjacent footwalls. Sedimentation processes of nearshore subaqueous fans respond to tectonic activities of boundary faults and to seasonal rainfall. During tectonically active stages, subaqueous debris flows triggered by episodic movements of border‐faults dominate the sedimentation. During tectonically quiescent stages, hyperpycnal flows generated by seasonal rainfall‐generated floods, normal discharges of mountain‐derived rivers and deep‐lacustrine suspension sedimentation are commonly present. The results of a series of flume tank depositional simulations show that the sediments deposited by subaqueous debris flows are wedge‐shaped and non‐channelized, whereas the sediments deposited by hyperpycnal flows generated by sporadic floods from seasonal rainfall are characterized by non‐channelized, coarse‐grained lobate depositional bodies which switch laterally because of compensation sedimentation of hyperpycanal flows. The hyperpycnal‐flow‐deposited non‐channelized lobate depositional bodies can be divided into a main body and lateral edges. The main body can be further subdivided into a proximal part, middle part and frontal part. Normal mountain‐derived river‐discharge‐deposited sediments are characterized by thin‐bedded, fine‐grained sandstones and siltstones with a limited distribution range. Normal mountain‐derived river‐discharge‐deposited sediments and deep‐lacustrine mudstones are commonly eroded in the area close to boundary faults. A nearshore subaqueous fan can be divided into three segments: inner fan, middle fan and outer fan. The inner fan is composed of debrites and the proximal part of the main body. The middle fan consists of the middle part of the main body and lateral edges, normal mountain‐derived river‐discharge‐deposited fine‐grained sediments and deep‐lacustrine mudstones. The outer fan comprises the frontal part of the main body, lateral edges, and deep‐lacustrine mudstones. Based on the non‐channelized depositional model for nearshore subaqueous fans, criteria for stratigraphic subdivision and correlation are discussed and applied. [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]

Shallow-marine fans have been analyzed for sedimentary characteristics and genetic mechanisms far less commonly than deep-marine fans. Based on outcrop observations, this study reveals that large-scale submarine fans in the Middle Triassic Baise area, south China, consisted of a braided channel-levee facies complex in the inner fans; sinuous channel-levee facies complex, overbank facies and crevasse splay facies in the medial fans; and sand sheet facies in the outer fans, which present different lithology assemblages and depositional successions. The lithofacies of dominant massive sandstone, secondary graded sandstone and laminated sandstone from bottom to top is similar to the Bouma sequence, indicative of gravity flow processes. However, the laminated sandstones mostly bear sedimentary structures of gutter casts, wave-generated ripple marks, hummocky cross-bedding, wave-generated cross-bedding and ripple bedding, and were thus attributed to frequent storm reworking processes. Moreover, discontinuous deposition recorded by abrupt sediment grain-size changes, distinct interfaces and divergent paleocurrent orientations occurred between the laminated sandstones and the underlying massive (or graded) sandstones. Accordingly, storm reworking processes together with abundant fossils of Daonella , Ammonite and Crinoidea indicate a shallow-marine paleo-environment. As a whole, this study provides a good example of large-scale shallow-marine fans and laminated sandstones resulted from storm reworking. [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 gravity flow deposit were mainly developed in the lowstand systems tract (LST) of the first member of Upper Miocene Huangliu Formation (E hl) in Dongfang area, Yinggehai Basin, has become a valuable target for gas exploration and production. The gravity flow sedimentary characteristics of lithofacies associations, sedimentary texture, seismic facies and logging facies were described in detail on the basis of integrated analysis of cores, logging and seismic data. The sedimentary microfacies types composed of neritic sandbar, continental shelf mud, main channel, bifurcated or cross-cutting distributary channel, overspill, and natural levee are revealed under the constraint of high resolution sequence stratigraphic framework in the E hl. The gravity flow deposit system in the LST is divided into three evolution stages corresponding to periods of three parasequence sets. The gravity flow deposit was induced in the early LST, expanded rapidly in the middle LST and decreased slightly in the late LST. But its developing scale decreased sharply in the transgression systems tract (TST) and finally vanished in the highstand systems tract (HST). This spatial evolution rule is constrained by the integrated function of sediments supply of the Vietnam Blue River in the LST, the development of local gradient change in sea floor (micro-topography, i.e., flexure slope break), and the fall in relative sea level. On the basics of the deep study of the coupling relationship among the three main control factors, the sedimentary model is established as an optimal component of 'source-channel-sink' for shallow marine turbidite submarine fan. [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]

Field investigation and laboratory research on flysch of the Liufengguan Group in Qinling indicate the following: (1) Sandstone of the Liufengguan Group is categorized as feldspathic lithic graywacke with a minor amount of lithic graywacke in the QFR triangular diagram. Grain size ≤0.3 mm. Bedding plane structures such as groove casts and suspected flute casts can be found at the bottom of the sandstone. It is inferred that currents may have come from the southeast during deposition. Bedding structures such as ripple marks, graded bedding, parallel bedding, small-scale cross bedding, climbing bedding, suspected convolute bedding, microlamination and sliding structures have also been observed, which are of indicative significance. It is thought that the Liufengguan Group has the sedimentary characteristics of bedding, bedding plane structures and lithological assemblages of deep-sea low-density turbidity current deposits. The vertical succession of the Bouma sequence in the inner fan subfacies zone is generally incomplete: the assemblage of Ta and Tabc is commonly seen; the succession of the middle fan subfacies zone is relatively complete; and divisions Te and Tb are common in the outer fan subfacies zone. (2) The flysh of the Liufengguan Group is a sequence of deep-sea argillaceous-arenaceous submarine fan deposits, in which the authors recognize the inner, middle and outer fan subfacies and also nine types of lithofacies: normal graded sandstone (A1), medium- to thick-bedded, fine-grained sandstone (A2), medium- to thick-bedded and massive siltstone (A3), thin-bedded, fine-grained sandstone and mudstone (B1), irregular interbeds of thin-bedded, fine-grained sandstone and siltstone (B2), thin-bedded, fine-grained sandstone (C1), very thin-bedded, fine-grained sandstone (D1), olistostromes (E1) and deep-sea mudstone (F). The inner fan consists of four microfacies: natural levee (A1), water channel (A2, A3) and olistostromc (E1); in the middle fan there also occur four microfacies, i.e., branch channel (B1), branch channel (B2), interdistributary bay (D1) and olistostrome. The outer fan is made up of the branch channel (C1) and sheet sand (D1) microfacies, which alternate vertically with sediments of deep-sea plain subfacies (F). There occur fining- and thin ning-upward channel deposits in the outer-fan subfacies zone of the submarine fan of the Liufengguan Group observed in this study. The quartz content of the graywacke of the deposits is all higher than 40% and may reach as high as 60%. Therefore, on the basis of the aforementioned features, this flysh should be formed in a passive continental-margin tectonic environment. [ABSTRACT FROM AUTHOR]

Abstract: The North Qilian Shan is an accretion–collision orogenic belt in the northeastern margin of the Tibetan Plateau that connects the North China plate to the north with the Tethyan orogenic assemblage to the south. Its Early Paleozoic temporal–spatial tectonic evolution has been extensively studied, but the nature and tectonic setting of its Silurian deposition is poorly understood. Our new petrological analysis suggests that the clast composition of fan conglomerates is complex. In the Danbanshan and Zhongdabanshan sections, abundant lenticular conglomerate beds contain mainly subrounded–rounded metamorphic clasts; whereas the Tongziba and Haichaoba sections contain volcanic, chert, limestone, ultramafic and granitoid clasts. However, in the Sunan area, clast types are relatively simple, dominated by basalt and granitoids, and at Tongziba gabbro and basalt clasts are subrounded and angular, indicating two different types of provenance. Ultramafic, limestone and abundant chert clasts in the Haichaoba and Tonghe conglomerates indicate an ophiolitic source, whereas subrounded–rounded quartzite and granitoid gneiss clasts were probably derived from the Central Qilian basement. Geochemical data from the volcanic and granitoid clasts suggest an arc-related source and their zircon U–Pb ages of 515–429Ma suggest that the arc magmatism did not end in the Mid-Silurian. Sandstone petrology and detrital modes suggest that the Silurian sediments were deposited in a forearc basin. Paleogeographic reconstructions inferred from NNW–NNE paleocurrent data indicate that an island arc was present off the southern margin of the Silurian basin, and that southward subduction of oceanic crust between North China and the Qilian Shan was active or continued in the Silurian. [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]

Studying the fundamental influence of basin-floor topography on the growth and morphology of sedimentary systems has largely focused on submarine fans; however, in lacustrine settings, only a limited number of studies are primarily concerned with confined sublacustrine fans, although such fans can form high-quality hydrocarbon reservoirs. By using recently acquired three-dimensional seismic data, a series of unusual confined and semiconfined sedimentary units with seismic reflection patterns different from those of previous studies have been identified. The identified sedimentary units are developed in the Paleogene succession on the northern slope of the Bonan uplift, Bohai Bay Basin, China, and are characterized by either vermicular-like chaotic progradational reflections or coupled vermicular-like and progradational seismic reflections in the dip direction and channel-shaped bidirectional onlap reflections along strike directions. Through restored paleogeomorphology, six elongate incised valleys (V-1 to V-6) with diverse scales on the uplift slope are clearly documented. The identified sedimentary units were deposited within these incised valleys. The units identified in this study are considered "confined" or "semiconfined" based on the following several aspects, they: 1) were deposited within elongate depocenters along dip directions; 2) are clearly separated from each other by topographic highs along strike directions; 3) have belt-shaped sediment dispersal patterns in planar view; and 4) have the thickest deposits primarily distributed in the middle and distal parts. Through comparing sedimentary landforms, feeder systems, seismic reflection characteristics and spatial distribution patterns between sedimentary systems, the confined and semiconfined systems identified in this study display both similarities to and profound differences from previously studied confined sublacustrine fans and are here considered a new unusual type. We anticipate this work may serve as a useful reference for confined sedimentary system research in other types of sedimentary basins. • A series of unusual confined and semiconfined sedimentary units were identified in this study. • The identified confined systems are characterized by distinct seismic reflections in dip and strike directions. • All the identified units are deposited within elongate depocenter and separated from each other. [ABSTRACT FROM AUTHOR]

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. • Fourth-order sequence stratigraphic framework of the Baikouquan Formation. • Fan-delta sedimentary microfacies identification and seismic sedimentary filling processes analysis. • Facies-controlled seismic impedance inversion and interpretation of high-quality reservoir. [ABSTRACT FROM AUTHOR]

As an inevitable result of fluvial-deltaic avulsions, abandoned distributary channels and associated lobes form an important component of coastal marine systems, serving as a sediment source and sink for the adjacent delta region. The distinct differences between normal tidal flats and abandoned channel systems restrict the application of classic intertidal mud flat morphological theory to the study of the evolution of abandoned channels. Herein, a quantitative model based on the concept of mass conservation was proposed to describe the infilling processes for an abandoned channel. Sediment cores and elevation profiles from an abandoned channel of the Yellow River delta (China), along with hydrodynamic observational data, are used to constrain a numerical approach and test model performance. The modeled accumulation thicknesses are satisfyingly consistent with those derived from sediment cores. The model results indicate that the tide-delivered sediment flux and channel water depth are the dominant variables governing the variation in accumulation thickness in the abandoned channel, whereas the channel shortening rate largely impacts the depositional area rather than depositional thickness. By contributing to steady deposition on the mud flat, tide-associated landward sediment deposition formed a steep profile near the estuary, while the final four years of deposition represent only a quarter of the total deposition compared to that from the first five years owing to a decreasing depositional rate. The model-derived sediment volume indicates that shore-parallel flow is significant in shaping mudflat morphology, especially in the late stages, while the shortening of tidal channels leads to shrinking of the mud flat and sediment volumes. Despite its limitation to residual channels, our model presents a new approach for quantitative interpretation of the geomorphic evolution of an abandoned river channel with finite boundary conditions, providing a good reference to apply to other large deltaic systems. • A model was proposed to quantify the in-filling process of an abandoned channel. • Landward flux and channel depth are dominant variables for the in-filling process. • Shore-parallel flow shapes the mudflat morphology at the late stage of abandonment. • The abandoned channel acts as a sediment sink in the deltaic depositional system. [ABSTRACT FROM AUTHOR]

• The Guaizihu sag has undergone five stages of evolution corresponding to five rift-related sedimentary units. • The north and south sub-sags were connected with each other to form a unified one during late rift climax substage. • The lack of deep-water sedimentary facies during the greatest tectono-subsidence phase was due an arid environment. • There are three typical filling patterns in the tectono-sedimentary evolution of the Guaizihu sag. Distinguished from most existing rift basin evolutionary models, the succession of deep-water deposits in the Guaizihu sag were mainly developed during rift initiation instead of the greatest tectonic subsidence phase. This paper focuses on the detailed analysis of rift-related sequence stratigraphy and sedimentary evolution in this continental rift sag, and discusses tectonic and climatic controls on filling patterns. The deposits of the Guaizihu sag can be ascribed to four major depositional systems: alluvial fan and fan delta, braided delta, sublacustrine fan and shallow to deep lacustrine deposits. They are in part contemporaneous and some succeeding each other, forming five sequence units and corresponding substages of basin evolution: (i) rift initiation, (ii) early rift climax, (iii) middle rift climax, (iv) late rift climax, and (v) late syn-rift substages. With the onset of fault movement and hot-humid climate conditions, the first substage is characterized by a number of poorly linked depocenters, which consist of alluvial fan, fan delta and deep lacustrine deposits with organic-rich mudstones. The second substage is associated with an enhanced activity of border faults and block rotation. This unit is dominated by lacustrine deposits, but fan or braided delta and sublacustrine fans also can be observed. The third substage is marked by the maximum subsidence rate and shallow lakes fringed by fan and braided deltas. The arid environment is likely to be the main factor controlling the lithofacies and filling characteristics of this unit. During the fourth substage two early sub-sags gradually converged to form a uniform one. The relative tectonic quiescence and climate fluctuations (sub-humid to sub-arid) favored carbonate deposition. The late syn-rift unit, which is dominated by fine-grained deposits, is a consequence of degradation of source area (mostly tectonic). This study shows that the effects of tectonics and climate on lacustrine sedimentation are intimately interwoven. Tectonism determines the sag structure, stratigraphic architecture, and spatial distribution pattern of depositional systems. Climatic conditions superimposed on tectonics tends to be the major control on sediment supply, lithofacies types and sedimentary features. [ABSTRACT FROM AUTHOR]

Compared to first rift phase (RP1) or single rift basins, the relationship between fault behaviours and depositional architecture during the second rift phase (RP2) remains insufficiently understood in multiphase rifts. This study attempts to provide implications for tectono-sedimentary signatures during the RP2 in multiphase rift evolution, according to an integrated analysis of 3D seismic reflections, wire logs and cores from the Lufeng Depression in the Pearl River Mouth Basin, South China Sea. The four recognised third-order sequences, ESQ1-4, define a two-stage tectono-sedimentary evolution, including an early (ESQ1-2) and a late stage (ESQ3-4) of the RP2 (38–33.8 Ma) in the Lufeng Depression. Fan-deltaic, braided deltaic sandstone-prone and lacustrine mud-prone deposits are interpreted from the basin margin towards to the central areas. During the early stage of the RP2, two relatively steep dipping E-W striking faults in the northern area were very active, undergoing rapid reactivation with a high displacement, while other faults were less active, had low displacements with respect to the extension direction and possibly represent pre-existing fault geometries. Two tectono-depositional signatures are identified during the early stage of the RP2: 1) facilitation of newly captured axially-dominated deltaic systems in the rapidly reactivated fault propagated areas, as a more uniform distribution of connected and elongated depocentres establishes an axial-supply drainage catchment; 2) sustained previous drainages from the end of the RP1 showed an increase of dip-slope sourced systems in low-displacement faulted-controlled areas, i.e. these areas lack fault-controlled topographic re-organisation but show establishment of a hanging dip-slope. The late stage of the RP2 is characterised by a low-accommodation basin as faulting activities totally waned, and thus large-sized shallow-water deltaic systems and long-distance transported sandstones are promoted. This study highlights the distinctive stratigraphic architectures and associated sediment dispersal patterns induced by progressive fault activity during the RP2 cycle. Furthermore, the proposed depositional signatures may be used as a reference when studying less data-rich multiphase rifts elsewhere. • Tectono-depositional patterns of the second rift phase (RP2) cycle are described in the Lufeng Depression. • Axially-dominated deltaic systems are facilitated in the rapidly reactivated fault areas in the early stage of the RP2. • An increase of dip-slope sourced systems is developed in low-displacement faulted areas in the early stage of the RP2. • Large-sized shallow-water deltaic systems are promoted during the late stage of the RP2. • A two-stage tectono-sedimentary motif of the RP2 in the multiphase rifts is proposed. [ABSTRACT FROM AUTHOR]

Sediment routing in deep-water settings can be significantly different in lacustrine basins from their well-studied marine counterparts, which has been largely overlooked during the past decades. The seismically well-imaged lacustrine clinothems in the Eocene Dongying Depression provide a good opportunity to bridge the deep-water sediment partitioning with clinothem architecture and shelf-edge trajectories, which have been studied through the integration of 3D seismic data and well-logging data. In the study area, the Eocene delta-complexes are architecturally manifested as alternating aggradation dominated (AC) and progradation dominated clinothems (PC). The Eocene Dongying clinothem architecture has been documented in terms of shelf–edge trajectory angle (θ sht), edge-to-toe distance (ETT), aggradation height (Ah), progradation distance (Pd) and maximum foreset angle (γ mfa). Aggradation dominated clinothems are characterized by ascending shelf-edge trajectories with thick and widespread sand-prone bottomsets, suggesting higher efficiency of sediment delivery into the outlying lake floor. Progradation dominated clinothems, in contrast, are characterized by flat to slightly descending trajectories and generally by a lack of bottomsets. Alternations of rising and flat to slightly descending trajectories accompanied with different clinothem types probably indicate frequent relative lake level changes (on time-scales of 100s of kyr). Further analysis of seismic images and extensive well-logs suggest the distal aggradational bottomsets are generally consist of sub-lacustrine channel-lobe systems, whereas sediment slide, slump blocks occur in slope to slope toe areas of progradation dominated clinothems, which indicate varied processes of deep-water sediment transport associated with different clinothem types and shelf-edge trajectories. Lake-level, sediment supply, water salinity and density change induced by humid-arid climate cycle are suggested to be main factors controlling clinothems stacking pattern and sediment dispersal into deep-lacustrine. Humid climate are considered to be related with strongly aggradational clinothems, during which sediment can be directly transported to the distant bottomset areas due to increased sediment concentration and energy in river discharge. Whereas during dry periods, progradation dominated clinothems start to build under stillstand or falling lake level conditions, sediment generally accumulates at river mouth and collapses due to sediment overload or fault activity. Therefore, a relationship between deep-lacustrine depositional process and climatic signature was established which may provide new thoughts in both the study of deep-water sequences and deep-water exploration in lacustrine basins. • Alternation of two different growth styles of lacustrine clinothems is identified. • Strongly aggradational clinothems suggest increased deep-water sediment delivery. • Strongly progradational clinothems suggest limited deep-water sediment delivery. • Climate-cycle controls clinothem patterns and associated deep-water processes. [ABSTRACT FROM AUTHOR]

Taking He146 Development Unit of Shinan Oilfield in Dongying Depression as an example, the quantitative architectural model of turbidite reservoir is studied by using local dense well pattern and production performance data. The turbidites in the study area are mainly turbidite fans and turbidite channels. The area of a single turbidite-fan belt is 0.08–0.8 km2, with long-axis length of 162–900 m, width of 120–620 m, and thickness of 2–25 m. The scale of turbidite-fan belt is positively correlated with its thickness. The morphological parameters of turbidite-channel belts could be counted in logging and seismic data. The width of turbidite-channel belt is positively correlated with its thickness. Its thickness is 2.4–9.6 m, with an average of 6.3 m. The width of turbidite-channel belts is about 612–1212 m (estimated from seismic and logging profiles), with an average of about 884 m. The thickness of a single channel story is 1.5–5.8 m, the inclination angle of the bottom of the channel story is 0.9–2.4°, width of a channel stories is 120–450 m. The variation of channel-story thickness between two wells is fitted to a better linear function with the distance between wells in the cross section of channel stories. High production wells and corresponding injection wells are basically parallel or intersected with low angle to the extension direction of channel. The ideal projection distance is within 150 m, and the projection distance can exceed 150 m in the superimposed area of main body of turbidite-channel. • Turbidity channels and turbidite fans are identified by core and particle size data in the study area. • Quantitative architectural characteristics of deep-lake turbidite belts are identified by logging and seismic data. • Quantitative architectural characteristics of channel stories are described by dense-drilled wells and production data. • Distribution of channel stories is described by their quantitative characteristics in the anatomical area. • The influence of channel geometric characteristics on production efficiency is evaluated. [ABSTRACT FROM AUTHOR]

Reconstruction of sediment-dispersal patterns not only provides insight into paleogeographic evolution, but also sheds light on facies and reservoir prediction. By integrating core, wireline logs, and 3D seismic data, seismic sedimentologists have discovered several advantages to sediment-dispersal reconstruction and paleogeographic-environment analysis. We have subdivided the third member of the Shahejie Formation (Es3) of the southeastern Zhanhua Sag (Sanhecun Block) into three third-order sequences, namely SQ1, SQ2, and SQ3 from bottom to top. The facies architecture was analyzed by using the seismic sedimentology approach based on 3-D seismic data. Seismic RMS-amplitude stratal slices reveal different characteristics of the lobes among the southwest gentle slope, southern slope-break belt and north fault-controlled slope from source to sink. On the basis of an integrated analysis of well log, core data, seismic facies based on RMS attributes, three depositional environments (e.g., "fan-delta", "turbidite" and "lacustrine" facies) have been recognized. Seismic RMS-amplitude stratal slices indicate that the depositional environments of these sequences evolved from medium-sized gravel-rich fan-delta and turbidite-fan deposits to small-scale mud-rich fan-delta deposits, and lastly to large-scale sand-rich fan-delta deposits. The changes of relative lake level and sediment supply rate control the lithology and size of different depositional systems. This study also suggests that the temporal and spatial evolution and distribution of depositional systems are influenced significantly by paleotopography and slope break in the systems tracts of different sequences of the Es3 in the southeast Zhanhua Sag, Bohai Bay Basin. In addition, fan-delta-front deposits could also be considered as future potential exploration targets because they are relatively sand- or gravel-rich, given the reconstruction of the sediment-dispersal pattern. • Three sequences of the third member of the Shahejie Formation (Es3) in the Sanhecun Block, Zhanhua Sag have been established. • Seismic sedimentology based on stratal slicings is documented as an example. • Sediment-dispersal patterns are illustrated by stratal slicings. • Evolution of fan-deltas are influenced by paleotopography. • Fan-delta front, with the sand- or gravel-rich deposits, could be considered as future potential exploration targets. [ABSTRACT FROM AUTHOR]