Objective The formation of sedimentary systems within straits is intricately linked to the unique topographical constraints that influence both facies characteristics and sediment distribution patterns. Although current research mainly focuses on narrow straits （less than 50 km wide） ， where sedimentation is dominated by tidal processes， wider straits introduce more complex hydrodynamic dynamics， leaving many aspects of the sedimentation processes yet to be fully understood. Methods This study focuses on the Bohai Strait （a shallow strait with a width of 106 km） and is based on an extensive dataset of surface sediment grain sizes， combined with four shallow seismic profiles， to characterize the sedimentary environment within the Bohai Strait. Additionally， a regional ocean modeling system （ROMS） simulation was employed for winter （December 2020⁃February 2021） to better understand the hydrodynamic processes influencing sediment dynamics and control over sediment distribution within and surrounding the Bohai Strait. Results Our results reveal significant differences in sediment dynamics between the northern and southern parts of the strait. The northern region exhibits a high-energy environment dominated by erosion， whereas the southern region displays a lower-energy environment conducive to deposition. Surface sediment types vary spatially， with coarser grains predominating in the north and narrow regions， with finer grains observed on both sides （east⁃west） and in the south. A large-scale， sandy flood-tidal delta appears around the Laotieshan Channel in the north. The asymmetric tidal currents flowing in and out of the channel are likely responsible for this feature， and ebb-tidal delta is not prominent. In contrast， the southern part of the strait exhibits two distinct sedimentary systems：（1） Shandong mud wedge： This system lies along the coast of the Shandong Peninsula， shaped by the substantial sediment supply from the Yellow River and the influence of coastal currents. （2） Scour troughs and sandy tidal deltas： These smaller features are attributed to the protective effect of islands present in the southern strait， combined with the abundant supply of fine-grained sediments. Conclusions This study highlights the critical role of the complex topography of the strait in the confinement in shaping regional sediment transport dynamics and the resulting distribution of sedimentary systems.

Objective The catastrophic failure of large submarine landslides can result in the deformation and destruction of thousands of square kilometers of seafloor， transporting hundreds to thousands of cubic kilometers of submarine sediments. This process dramatically reconstructs the seafloor topography of the continental shelf-slope region and has a profound impact on subsequent submarine sedimentation processes. Methods The topographic features of different large submarine landslides were qualitatively described using multibeam bathymetric and seismic reflection data， and the key geometric parameters of the submarine landslide top surface， such as area and volume， were quantitatively characterized. Based on the scale， morphological features， and formation mechanisms of the associated reliefs on the submarine landslide top surface， these landslides were separated into three categories： head evacuation zone， locally negative accommodation associated with internal fault systems， and locally negative accommodation associated with internal deformation blocks. The mechanisms of the three types of negative accommodation on the subsequent turbidity current system are then discussed separately. Results Firstly， the head evacuation zone is typically associated with hundreds to thousands of square kilometers of negative accommodation， which acts as a "funnel" during sediment transport along the continental margin， effectively capturing and concentrating subsequent turbidity currents while enhancing the transport efficiency of gravel and coarse sand and playing a crucial role in the accumulation of marine organic matter. Secondly， the striped negative accommodation associated with internal fault systems and the irregular negative accommodation associated with internal deformation blocks can regulate the sedimentation dynamics of subsequent turbidity currents， such as constraining flow direction， enhancing erosion intensity， and forcing channels to avulse. Finally， the negative accommodations associated with the submarine landslide top surface may produce synergistic effects， influencing the sediment filling and evolution of sedimentary basins and the distribution of sedimentary centers over millions of years. Conclusions The investigation of the morphological characteristics of submarine landslide top surfaces and their controlling effects on the subsequent turbidity currents sedimentary dynamic process can provide key geological information for clarifying the transport process of marginal sediments， identifying the distribution of sand-rich reservoirs in deep-sea sedimentary basins， and predicting the development range of catastrophic turbidity currents.

Objective A typical gravity-flow sedimentation set is present in the Ordovician Lashizhong Formation at the western margin of the Ordos Basin. This study investigated the formation process of gravity flows in the third member of the Lashizhong Formation with the aim of summarizing the sedimentary characteristics and evolutionary pattern， and to establish a sedimentary model. Methods Outcrop observation， thin-section examination， grain size analysis and paleocurrent measurement were used in the analysis. Results Eight kinds of lithofacies and six litho-facies associations were found in the study area： horizontal bedded shale （A1）； lens-shaped massive bedded calcirudite （B1）； lens-shaped parallel-bedded sandstone （B2）； lens-shaped cross-bedded sandstone-siltstone （B3）， wedges of cross-bedded sandstone-siltstone （C1）， graded beds of sandstone-siltstone （D1）， parallel-bedded siltstone （D2）， and bedded pebbly sandstone （D3）. These indicate channel axis deposition （B1）， vertical aggradation channels （B2， C1， A1）， distributary channels （B3， C1， A1）， proximal lobes （D1， A1）， distal lobes （D2， A1） and mass transport deposits （D3）. Channel axis deposition， vertical aggradation channels， distributary channels， proximal lobes and distal lobes have been successively developed in the lowest part of the Third member of the Lashizhong Formation， which is divided into five stages. The middle and upper parts of the Third member of the Lashizhong Formation show the development of mass transport deposits， proximal lobes and distal lobes， and is divided into seven stages. Conclusions The evolution of these strata is closely related to the type and energy of gravity flow. At the initial stage， gravity flow was dominated by debris flow， then， as the debris flow energy weakened， turbidity current dominated. The vertical aggradation channels were developed during multi-stage periods of erosion and sedimentation. Distributary channels and lobes then developed with further weakening of the turbidity flow. Tectonic movement increased the sand content of sediment supply， leading to the initial development of massive transport deposition followed by large-scale lobes with higher sand content. The vertical evolution of gravity flow sedimentation was governed by a combination of factors， including sea-level fluctuations， sediment supply and its composition， as well as tectonic movement. An initial rise in sea level followed by a sub-sequent fall are suggested by a decrease and then increase in the scale of gravity flow development. Variations in sediment supply types gave rise to diverse sedimentary units， including channel-axis deposition composed mainly of calcirudite， as well as vertical aggradation channels， distributary channels， proximal lobes and distal lobes mainly comprising fine sandstone and siltstone. Moreover， the magnitude of sediment supply significantly impacted the morphological features， dimensions and sand-to-mud ratio of these sedimentary units. During the depositional period of the Lashizhong Formation， relatively subdued tectonic activity facilitated the formation of a channel-lobe system that is relatively modest in size compared to the scale typically encountered in exploration contexts. The interplay of the above factors ⁃ sea-level changes， sediment-supply dynamics， and tectonic setting ⁃ together shaped the architectural complexity and distribution patterns of the gravity flow deposits in the basin. Understanding these controls is crucial for accurate reservoir characterization and prediction in hydrocarbon exploration and production. This study helps in the understanding of gravity-flow evolution in the study area， and provides a theoretical reference for oil and gas exploration.

Objective Organisms are extremely responsive to the environments in which they live， and the traces they create are the result of interactions between organisms and their environment. To a certain extent， the traces reflect the properties of the depositional environment. Biological sedimentary structures are a powerful tool in understanding the ecology and depositional processes of modern coastal sedimentary environments. Methods The composition and distribution of modern biological traces in the tidal flat environments of the Pearl River Delta were studied by field observations and 3D reconstruction. Results The key understanding obtained by the study was that the distribution of organisms in the supratidal， intertidal and subtidal varies greatly， and the biological traces are mainly distributed in the intertidal zone. In the supratidal zone， mainly Ligia oceanica and Uca arcuata are present. The main traces are Uca arcuata level feeding traces， excretion traces， trackways， and intra-layer I-shaped dwelling burrows. Biological traces in the intertidal mud flat environment mainly include feeding， excretion， trackways and I-shaped dwelling burrows of Uca arcuata， crawling traces and Y-， U- and I-shaped dwelling burrows of Periophthalmus cantonensis， and trackways and I- and Y-shaped dwelling burrows of Orisarma dehaani. Biological traces in the mixed intertidal flat environment mainly include excretion traces and intra-layer I-， U-， and Y-shaped dwelling burrows of Perinereis aibuhitensis， Y-， U- and I-shaped dwelling burrows of Ligia oceanica， and crawling traces of Vittina coromandeliana and Neritina pulligera. Biological traces in the sandy intertidal environment include feeding and excretion traces of Ocypode cordimand and intra-layer I-shaped dwelling traces. The subtidal environment was not accessible for observation and no biological traces were found. Conclusions The study of modern intertidal biological traces in the Pearl River Delta supplements modern sedimentological data on tidal flat environments in the Pearl River Delta， and provides modern empirical evidence for palaeoichnology and palaeoenvironmental reconstruction.

Objective A large number of Thalassinoides trace fossils developed in the Cambrian strata of Henan province. We studied the morphology and distribution characteristics of different ichnospecies and analyzed the sedimentary environment-controlling factors. Methods Based on lithology and ichnography， the morphology， size， disturbance depth， and disturbance intensity of Thalassinoides in this area were combined with sedimentary environment parameters. Results The dense network Thalassinoides suevicus features Y-shaped branches with enlarged intersections， developed in the intertidal zone where water is turbulent and oxygen is abundant. Sparse Thalassinoides horizontalis Type 1， which is Y-shaped long branches with large diameters， formed in the shallow water area in front of the oolitic beach with abundant oxygen and nutrients due to water turbulence. Thalassinoides horizontalis Type 2， T-shaped short branches with smaller diameters， occurred in deeper waters on the seaward side in front of the oolitic beach. The three-dimensional， boxwork burrows of Thalassinoides bacae， featuring vertical tubes， branches， and thick lining walls， developed in interbeach-confined seas and deep subtidal zones where oxygen and nutrients were deficient. Conclusions The variation in different ichnospecies and morphologies of Thalassinoides is controlled by factors such as water depth， water kinetic energy， nutrients， and oxygen content of the sedimentary environment. The trace maker adopted different strategies to cope with the changing sedimentary environment.

Objective Clarifying the provenance composition and evolution of the Lower Jurassic Badaowan Formation and Sangonghe Formation in the Dongdaohaizi Sag， Junggar Basin， has important guiding significance for studies of the sedimentary filling response in this region of the Lower Jurassic. Methods A detailed analysis was conducted on the source characteristics and evolutionary processes of the Badaowan Formation and Sangonghe Formation based on the composition of sandstone debris， the geochemical characteristics of whole-rock elements， and U-Pb ages of detrital zircons. Results It was found that the sandstone samples from the Lower Jurassic in the study area were mainly composed of feldspathic lithic sandstone， with an average content of 37.7% of tuff and basalt lithic debris in the thin sections， along with a small amount of metamorphic rock debris. After standardization of shale samples in North America， the Badaowan Formation samples showed no significant differentiation between light and heavy rare earth elements. The Sangonghe Formation exhibited slight enrichment of light rare earths and depletion of heavy rare earths. The age distribution of detrital zircons in the sandstone samples in the Badaowan Formation is mainly concentrated in three ranges： 280-330 Ma， 400-440 Ma and 490-520 Ma； the Sangonghe Formation is dominated by three peak age ranges： 280-350 Ma， 380-430 Ma and 460-520 Ma， with similar age compositions. Conclusions A comprehensive analysis of provenance characteristics indicated that the Badaowan Formation in the Dongdaohaizi Sag is mainly sourced from the Kela Meili provenance system in the eastern Junggar Basin， and the western Urho and Karamay provenance regions had little influence. During the depositional period of the Sangonghe Formation， the western region began to supply resources， but the eastern Kela Meili provenance system remained the main source of materials in the study area. In the Middle Jurassic， the influence of the western provenance increased， and the Che-Mo paleo-uplift was formed. The Donghaizi Sag was jointly influenced by two major provenance systems. The parent rocks in the Lower Jurassic provenance area of the Dongdaohaizi Sag are mainly intermediate acid magmatic rocks and basic magmatic rocks， and the provenance is mainly from the transitional and recirculating zones of the recycled orogenic belt. The tectonic setting is dominated by continental island arcs， which is consistent with the mixed-source background formed by oceanic continental subduction around the Junggar Basin， and following closure of the ocean basin. In the context of this tectonic setting， during the sedimentation period of the Badaowan Formation the Dongdaohaizi Sag was influenced by the East Kela Meili source， forming a shallow-water delta lake sedimentary system. Distributary channel sand bodies were extensively developed， but the physical properties were poor， with few favoring hydrocarbon accumulation. During the sedimentation period of the Sangonghe Formation， the Dongdaohaizi Sag was influenced by two major source systems， east and west， and a shallow-water delta lake system developed together with underwater distributary channel microfacies composed mainly of medium and fine sandstones， as well as a small amount of estuarine dam microfacies with physical properties favorable to hydrocarbon reservoir development.

Objective To clarify whether the western edge of the Kaijiang-Liangping trough is connected to the eastern platform margin of the Pengxi-Wushengtai Depression in the north of the Late Permian Changxing-Early Triassic Feixianguan period in northwestern Sichuan Basin， and to determine the sedimentary facies distribution pattern of the Jiangyou-Jiange Formation in northwestern Sichuan Basin and the Changxing Formation-Feixianguan Formation in the periphery area， and to analyse the evolution process of sedimentary filling to indicate further oil and gas exploration work. Methods Based on the latest drilling， field outcrop， and seismic data， this study systematically analyzed the distribution of lithofacies and paleogeography during the deposition of the Changxing Formation-Feixianguan Formation in the Guangyuan-Jiangyou area， based on the stratigraphic and sedimentary facies division and comparison. Results The intersection area of the Changxing Formation-Feixianguan Formation can identify six sedimentary facies： shelf basin， slope， platform edge， open platform， restricted platform， and evaporative platform. Based on the sedimentary records of the front slope of the platform， the western edge of the Kaijiang-Liangping trough and eastern edge of the Pengxi-Wusheng intra-platform depression were clearly merged to form a unified platform edge belt in the Cilinbao-Shangsi area in northwestern Sichuan Basin. The platform edge belt and front slope show a northwest finger shaped interdistribution， rather than a simple smooth belt distribution. The intersection area of the two troughs in the Changxing Formation presents a sedimentary pattern of two troughs interlocking from southwest to northeast. The connecting area of the platform margin zone developed a northwestern fingered reef beach， developing bioclastic shoals in the 1^st member and biological reefs and shoals in the 2^nd member of the Changxing Formation at the platform edge zone. During the sedimentary period of the 1^st and 2^nd members of the Feixianguan Formation， the sedimentary pattern of Changxing depositional period was inherited； however， in the 1^st member of Feixianguan Formation， only local platform edge oolitic beaches were formed owing to sea flooding. In the stage of the late 1^st to 2^nd member Feixianguan Formation， platform edge oolitic beaches gradually developed and expanded in scope with an overall eastward migration. The slope in front of the platform was prone to sliding and sedimentation. During the sedimentation period of the 3^rd member of the Feixianguan Formation， the sea trough gradually filled， and the finger shaped platform edge zone disappeared， forming a unified restricted platform. Only the local development of oolitic beach. The research area was filled and flattened during the depositional period of the 4^th member of the Feixianguan Formation， forming an evaporative platform facies. The platform margin zone in this region did not migrate northwestward along the finger shaped platform margin zone， but rather exhibited eastward migration characteristics. Conclusions The determination of the Changxing-Feixianguan connectivity and the definition of five sedimentary filling evolution stages in the Kaijiang-Liangping trough and Pengxi-Wusheng intra-platform depression supplements a new understanding of the sedimentary pattern and filling evolution process in the intersection area of the Changxing-Feixianguan trough. It also provides ideas and references for oil and gas exploration in this area.

Objective The beach facies dolomite reservoir in the Middle Permian Qixia Formation， central Sichuan Basin， has significant potential for oil and gas exploration， but relatively little systematic study has been reported on its diagenetic sequence and pore evolution. Methods The petrology and pore genesis of the Qixia Formation were investigated by core observation， thin section analysis， cathodoluminescence examination and image recognition techniques， to delineate diagenetic variations and pore evolution in the different lithologies. Results In the Gaoshiti area， four types of rock are identified in the Qixia Formation： micrite limestone， micrite grain limestone， sparite grain limestone， and residual grain dolostone. Four types of reservoir space are observed： intergranular dissolved pores， intragranular dissolved pores， fractures and vugs. Each rock type has undergone distinctive diagenesis： the type and intensity of dissolution vary in the different lithologies. The two kinds of granular limestone are mainly dissolved by meteoric water， and the residual granular dolomite is more strongly dissolved by meteoric water. On this basis， dolomitization and burial period dissolution occur. Recrystallization is more pronounced in the residual grain dolomite， whereas compaction and pressure dissolution is more evident in micrite grain limestone. The key diagenesis and stages influencing pore development vary between the different rock types： the pores in the two types of granular limestone are mainly formed by quasi-syngenetic dissolution， then partially destroyed by compaction and cementation during the burial stage. The dissolution and dolomitization in the parasyngenetic stage result in the formation and preservation of the pores in the residual granular dolomites； dissolution and tectonic fracture at the burial stage are beneficial supplements， but cementation during the shallow burial stage destroys the pores. Conclusions The varied diagenesis has caused different pore evolution， forming four lithologies with a decreasing extent of pore development： residual grain dolostone （plane porosity： 2.10%）， sparite grain limestone （plane porosity： 1.24%）， micrite grain limestone （plane porosity： 0.41%） and micrite limestone （compact）.

Objective Current domestic and international research on bauxite oil and gas reservoirs is limited in scope. The bauxite reservoir with high-yield industrial gas flow discovered in the Taiyuan Formation， Longdong area， southwestern Ordos Basin， represents a significant advance in the exploration for bauxite gas reservoirs， and the recent identification and production tests of bauxite rock series in the Benxi Formation in the Linxing area at the northeastern margin of the basin suggests promising exploration potential.Further natural gas exploration and development in the bauxite series in the Linxing area requires a comprehensive analysis of the fundamental geology of the sedimentary environment， including the mineral composition， reservoir pore properties and the structure of the bauxite series. In addition， it is essential to identify the factors that control the development of bauxite and which areas are most conducive to such activity. Methods A comprehensive analysis of the sedimentary environment， reservoir characteristics and sedimentary model of the Benxi Formation bauxite rock series in the Linxing area was conducted using logging， seismic data， X-ray diffraction， casting thin sections， scanning electron microscopy， major and trace elements， high-pressure mercury injection， N₂ and CO₂ adsorption and conventional physical properties， and other experimental methods. Results The bauxite rock series in the study area is characterized by a high concentration of diaspore and clay minerals， and has a distinctive three-stage vertical structure. The lower portion is rich in iron， the middle zone contains a higher aluminum content， and the upper section has a lower iron concentration. The pore types include predominantly dissolution pores typically ranging between 2 nm and 50 nm， along with intercrystalline pores， organic pores and microfractures. The sorting and connectivity of the pores are relatively good， with average porosity 3.64% and average permeability 7.24×10^-3 μm². Conclusions The thickness of a bauxite rock series depends upon the sedimentary environment and karst paleogeomorphology. A shallow-water sedimentary environment with high temperature and high humidity， low oxygen levels and alternating marine and terrestrial conditions is optimal for its formation and preservation. A slope， or buried pit， is a crucial area for exploration and development. This understanding provides a geological foundation for the exploration and development of natural gas in bauxite with comparable geological background in this region.

Objective The 5th member of the Ordovician Majiagou Formation in the southern Sulige gas field primarily consists of karst reservoirs， with proven reserves exceeding 100 billion cubic meters. However， during development， severe water production and complex gas-water relationships have been observed， and the distribution patterns and controlling factors of gas and water remain unclear， significantly constraining the release of the gas production potential of the region. Methods Based on formation water geochemical analysis， various chemical parameters （i.e.， Na⁺/Cl^-， desulfurization， Mg²⁺/Ca²⁺， Na⁺/Ca²⁺ and Na⁺ + Cl^-/Mg²⁺ coefficients） were analyzed to determine the formation environment of the water. The distribution patterns of gas and water were then studied by identifying the water-bearing intervals in individual wells， and by cross-well gas reservoir profile comparisons and the planar distribution of different formation water types. Finally， the controlling factors of gas-water distribution were explored in relation to the hydrocarbon source rock， karst reservoir heterogeneity and structural features. Results The total salinity of formation water （total dissolved solids） in the 5th member of the southern Sulige gas field is relatively concentrated （mean 83 598.7 mg/L）， with slightly acidic pH. The water type is predominantly CaCl₂， and exhibits low chloride-sodium coefficients， low desulfurization coefficients， low magnesium-calcium coefficients， low sodium-calcium coefficients and high metamorphism coefficients， all indicating good formation sealing favorable for gas reservoir preservation. These parameters show similar characteristics over the area， controlled by the karst reservoirs. The formation water is classified into three types， based on genetic differences， spatial distribution and reservoir properties： Type I （structural low-position water）， Type II （isolated lenticular water） and Type III （low-permeability trapped water）. Type I is mainly developed in karst areas， controlled by karst residual hill units， with a unified gas-water interface， and is the primary region for high-efficiency wells. Type II is sporadically distributed and influenced by the planar distribution of karst depressions and troughs， with moderate reservoir properties， representing a potentially favorable exploitation zone. Type III indicates poor reservoir properties. Conclusions The distribution of formation water is controlled by three factors： hydrocarbon source rock， karst reservoir heterogeneity and local structures within individual karst units. Insufficient hydrocarbon supply from the source rock is the fundamental reason for the development of formation water. The heterogeneity of the karst reservoir dictates the gas-water distribution pattern， and local structures have resulted in gas-water differentiation， with a unified gas-water interface within the same karst unit.