Objective     As the most extensive sediment transport systems on Earth, submarine channels shaped by turbidity currents transport billions of tonnes of sediment to the deep sea.     Methods     The internal structure, sedimentary architecture, and hydrodynamics of turbidity currents are revealed by summarizing the advances of depositional dynamics in a submarine channel.     Results and Conclusion     （1） The definitions and flow properties （Re, Fr, and Ri number） of gravity current are provided. The general anatomy and structure of turbidity currents are shown by the head and body of the current, as well as the structure of velocity, density, and turbulence. （2） A review of the related literature describing sediment transport for uniform and non-uniform sediment beds and bedform development associated with open channel flow is provided. It is necessary to research the hydrodynamics of the turbidity current in submarine channel to reveal the morphology, geometry, overspilling, sediments distribution, and reservoir architecture, as well as guide deep-water hydrocarbon exploration. （3） Three main methods （field observations, experimental modelling, and numerical modelling） for studying the depositional dynamics in submarine channels are introduced. （4） The frontier areas and controversial topics in current research on depositional dynamics in submarine channels are discussed.

Significance  A large number of carbonate deposits in the Phanerozoic record information about the evolution of the environment at that time, and they represented an important carbon sink for the Earth. Today’s need for a “carbon neutral” condition has encouraged research into the development and evolution of the carbonate factory, and is an essential primary focus of contemporary carbonate studies. Carbonate factory research began later in China than in other countries； the main focus has been on the deposition and evolution of carbonate rocks. Studies of carbonate factory classification and research methods are still weak, and the understanding of the main causes of their extinction is also limited.   [Progres s ]  This summary, based on the reports of a large number of studies, examines the research progress in classification schemes and research methods for recognizing the main influences on carbonate factory development, and provides a reference to assist geologists’ deeper understanding of the carbonate factory mechanism. [Conclusions and Prospects]  It may be the development direction of carbonate factory research in the future to understand its operating mechanism, evolution process and main controlling factors from many aspects by using multidisciplinary knowledge methods, so as to make the research conclusions more accurate and explore its biological and oceanographic significance.

Significance  The widespread development of bedding-parallel fractures （BPFs） in sedimentary reservoirs is the key to improve the overall rock permeability and promote fluid flow, and it is increasingly important for unconventional hydrocarbon exploration and development.   [Progress]  Scholars at home and abroad have examined the characteristics of BPFs and their relationship with hydrocarbon migration and accumulation, identification and prediction, formation mechanism, and major controlling factors. The following conclusions have been made： （1） BPFs are characterized by high linear density and high horizontal permeability. The existence of BPFs is one of the basic conditions affecting the large-scale accumulation of hydrocarbons in unconventional sedimentary reservoirs. （2） Seismic inversion, image logging and conventional logging identification, fracture related major controlling factors prediction, geological parameter modeling, and numerical simulation prediction are commonly used to identify and predict fractures； however, there are still limitations in regards to low accuracy, high cost, and immature methods. With the application of scanning electron microscopy, automatic mineral quantitative analysis, nanometer and micron computed tomography （CT） scanning, and digital core technology, the study of BPFs has gradually entered the level of microscopization, visualization, and quantification. （3） The formation of BPFs is the result of complex factors such as sedimentary diagenesis, structure, overpressure and crystallization stress. （4） Sedimentary rock type, bedding type, mineral composition, and total organic carbon （TOC） content are the main internal factors affecting the development of BPFs. The development degree of fault and fold, the distance from fault core and fold axis, the depth of stratum burial, and the intensity of uplift and denudation are the main external factors affecting the development of BPFs.   [Conclusions and Prospects]  However, there are still lack of comprehensive, systematic and quantitative research on the comprehensive mechanism of BPFs formed by different types of sedimentary rocks and bedding, the establishment of fine identification and quantitative prediction models for different types of BPFs, and the determination of the specific relationship between BPFs and hydrocarbon migration or accumulation. These problems limit the exploration and development of fractured reservoirs to a certain extent, and are also important research directions of BPFs in the future.

Significance  Fine-grained sedimentary rock laminae represent the fundamental and distinctive unit structures in the inner layer of semi-deep and deep-lake basins, typically with a thickness of less than 10 mm.Its material composition, continuity, and geometry play an important role in the restoration of paleo-environmental changes and sedimentary mechanism. With the development of unconventional oil and gas production, mang scholars have identified diverse types of laminae in lake basins, complex sedimentary mechanisms, and numerous controlling factors that significantly impact shale oil and gas enrichment, development, and production. Therefore, further research into the fine-grained sedimentary rock laminae structure can offer valuable insights for unconventional oil and gas exploration. [ Progress ] Through the process of discovery, identification, and research on laminae, genetic mechanisms for clay mineral laminae, felsic laminae, calcareous laminae,and organic-rich laminae were determined respectively. Additionally,the coupling relationship between different environmental conditions and priority development types of laminae was summarized while expounding on the control effect of single factors on laminae. It is proposed that fine flocculation reaction serves as an explanatory theory for hydrodynamic-induced laminar formation which challenges conventional understanding that laminae are solely caused by continuous suspension settlement in still water. [ Conclusions and Prospects ] Influencing factors of laminae deposition were classified into four categories： paleoclimatic factors, palaeogeographic conditions, palaeogeological events, and other factors. During lamina deposition,different influencing factors may promote or inhibit each other,and their combination controls the material composition, continuity,and geometric featuresofthe laminae.The accurate inversion of laminae formation by using the perfect model will be the main research direction in the future, providing guidance for the further study of laminae structure in fine-grained sedimentary rocks and the research and application of unconventional oil and gas reservoirs.

  Objective   The discovery of the Anyue gas field and the Mianyang-Changning intratonic sag has attracted considerable attention to the strata near the Ediacaran-Cambrian boundary in the Sichuan Basin. The reservoirs of these oil and gas fields occur mainly in the microbial and karst porous rich dolomite of the second and the fourth member of Dengying Formation. This study discusses the impact of Cloudina skeletal remains, one of the earliest metazoan mineral skeletons, on the terminal Ediacaran carbonate reservoirs, in order to expand regional oil and gas exploration strategies.   Methods   Drilling core material from the topmost Dengying Formation of the well Luye 1, northeastern Sichuan Basin, was examined for sedimentology, diagenesis, pore types, and porosity evolution, using a combination of methods including optical microscopy, cathodoluminescence, scanning electron microscopy, and micro-CT analysis.   Results and Discussions   Abundant tubular animal fossils, diagnosed as Cloudina, were aggregated in a layer of bioclastic micrite dolomite. These fossils are preserved in a micritic to microsparitic matrix, with their body axes oriented along the bedding plane. Micritic clots and filaments of probably microbial origin were found all around. The recognized pore types include biogenic pores formed by tubular fossils, intergranular pores, inter- and intracrystalline dissolution pores, and bitumen pores. The main diagenetic processes include dissolution, cementation, and filling at different periods. The high-resolution micro-CT scan shows that the porosity of the studied material is conspicuously affected by the presence/absence of the Cloudina skeleton. Only 0.1% to 0.4% of the porosity can be attributed to the dolomitic matrix, while the contribution of the tubular fossils is more than 0.7%.   Conclusion  Cloudina aggregates can contribute a considerable amount of porosity to the terminal Ediacaran dolomite, in addition to the microbial fabrics. The presence of mineralized animal skeletons at the end of the Ediacaran not only marks a big step in biological evolution but has also profoundly changed the types of oil and gas reservoirs.

Objective  The deposits of the Lower Triassic Feixianguan Formation are widespread in the Sichuan Basin. In this formation, the Second member is dominated by brown purple mud shale. Several researchers have maintained that it was deposited in tidal flat environment, and ‘mud crack’ is one of the distinguished bases of its environment. In this study, we find that the so-called mud cracks are developed in lamellar microcrystalline granular limestone in the Second member of the Feixianguan Formation. Although they show an overall grid shape in the bedding plane, they are not ‘V’ or ‘U’ shaped in cross section. In fact, they are split grid cut by sparry calcite veins penetrating the rock, significantly different from real mud cracks. As depositional structures, they are different but have a similar morphology. We call them ‘pseudo-desiccation cracks’ to distinguish from ‘mud cracks’ in this study. Pseudo-desiccation cracks do not represent the exposed paleoenvironment, and they cannot be used to infer that the Second member of the Feixianguan Formation was deposited in a tidal flat environment. Therefore, the study regarding the features of pseudo-desiccation cracks and their forming environment will be helpful in correcting misunderstanding and recognizing a depositional environment. [ Methods and   Results  ] The structure of the studied pseudo-desiccation cracks is developed in the surface of lamellar microcrystalline granular limestones in the Second member of the Feixianguan Formation, and the study area is located in the Dagouli profile, Qingchuan county, in the northwestern Upper Yangtze region. Limestone beds are interbedded with brown purple mudstones and occur frequently as thin layers in the sequence. Field survey determined that the thickness of the limestones is 2-10 cm, and they are sheet or channel shaped. Microsection observation indicate that they are microcrystalline granular limestones and contain a large number of gastropods, ostracods, bivalves, and coprolite pellets. Flute cast and channel mold structures are developed in the limestone, which show the influence of frequent storms during deposition. Irregular quadrilaterals or pentagons are developed on the top and bottom surfaces of the laminated limestones, the result of segmentation by calcite veins under compaction and dissolution. The diagenetic compaction and tectonics is likely the dynamic inducement for the formation of pseudo-desiccation cracks.   Conclusions  This study has clarified that the so called ‘mud cracks' in the Second member of the Feixianguan Formation in the northwestern Sichuan Basin are diagenetic-epigenetic products and do not represent the exposed environment. Therefore, the Second member of the Feixianguan Formation was deposited in a shallow shelf environment under normal wave base and above storm wave base in the northwestern Sichuan Basin. The identification of pseudo-desiccation cracks is helpful for the study on the formation of reticulated limestone in the Ordovician Baota Formation. Strong compaction in the early diagenetic period indicates fast deposition rate for the overlying beds （Feixianguan Formation） or special tectonic environment （Baota Formation）. Relatively active tectonic movements in the Ordovician could promote the formation of reticulated structure in the Baota Formation.

Objective    The paleoclimate and environment have changed significantly across the Norian-Rhaetian transition （NRT, Late Triassic）, as demonstrated by carbon-isotope fluctuations and biological extinction events. However, the causes of climate perturbations and biotic crises during the NRT remain controversial. It is believed that the eruption of contemporaneous volcanisms （e.g., the Angayucham Large Igneous Province） was the main cause of paleoenvironmental changes during the NRT. The large-scale volcanic activity released a large amount of greenhouse gases, which resulted in global temperature rise, carbon-isotope perturbation, and biological crises during the NRT. At present, the majority of NRT studies have focused on the shallow marine strata in the Tethys region, but knowledge on the changes in terrestrial paleoclimate, paleoenvironment, and their driving mechanism during the NRT is extremely limited. Studies have shown that terrestrial strata can faithfully record paleoclimatic and paleo-environmental changes during geological events, such as the end-Permian mass extinction. However, previous studies mainly focused on paleobotany, sedimentology, organic carbon isotopes, and wildfires during the NRT in the Sichuan Basin, but lacked element geochemical evidence, limiting the accurate understanding of the climatic changes in this time interval and the comparison between different research methods.     Methods    To tackle this scientific question, we examined the Norian-Rhaetian section （Xujiahe section） located 4.5 km NE of Guangyuan city, northwest Sichuan Basin. Thirty-four samples were collected at a resolution of 10 cm to 2 m in the Xujiahe section for major and trace element compositions. The surface dust and weathered portions of samples were removed with a rasper and then washed with deionized water. After 8 hours of oven drying at 50 °C, samples were ground into powder using agate mortars. Sample preparations were completed in the School of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology. Analysis of major and trace elements in samples was completed at the Institute of Earth Environment, Chinese Academy of Sciences, Xi 'an. A glass bead was created by fusing 0.6 g of the powdered sample with 6 g of dry lithium tetraborate （Li₂B₄O₇） for 5 minutes at 1 000 °C. The glass bead was further scanned by an X-ray fluorescence spectrometer （WD-XRF； PANalytical, Ea Almelo, The Netherlands）. The analytical accuracy was better than 2%.     Results and Discussions    The analyzed samples have high Chemical Index of Alteration （CIA） values and Rb/Sr at 105.5, 110.2-122.5, 119, 123.4-123.45, and 137.7 m in the Xujiahe section, and low CIA values and Rb/Sr at 107, 109.5, 115.5-116.5, 121.5, and 127-135m. The uppermost part of Upper Norian successions （105.5-129.5m） have CIA values ranging from 59 to 82, with a mean of 73； Rb/Sr values ranging from 0.2 to 2.6, with a mean of 1.2； and R values ranging from 3.8 to 16.9, with a mean of 8.2. For the Norian-Rhaetian boundary interval （NRB, 129.5-135 m）, CIA values range from 59 to 63, with a mean of 60； Rb/Sr values range from 0.5 to 0.6, with a mean of 0.5； and R values range from 13.1 to 13.9, with a mean of 13.5.     Conclusions    Results show that the climate fluctuated frequently during the NRT of Xujiahe section in the Sichuan Basin. The Late Norian was dominated by warm and humid climate, which was interrupted by a short-term cooling event close to the NRB. The prevailing mega-monsoon in Pangaea during the Late Triassic may be the main trigger for the frequent climate change and NRB cooling events in the Xujiahe section, but the influence of volcanic activity and wildfire events on the paleoclimate system cannot be eliminated in this time period. To determine the precise timing of volcanic eruptions and wildfires during the NRT and how they contributed to climate change, more research is needed.

Objective  Capillary effects increase the solubility of methane in fluids in equilibrium with hydrate,which affects the gas-hydrate distribution. Revealing the influence of capillary effects on the distribution of hydrates can provide theoretical support for the study of hydrate accumulation and hydrate exploration.   Methods  A numerical model was developed to investigate and predict the influence of capillary effects on the top occurrence of gas hydrate, and applied at site ODP994.   [Results and Conclusions]  The predicted top occurrence was calculated to be about 194 m, consistent with the depth determined from chloride anomalies. The top occurrence of gas hydrate tends to be located at depths where the pore radius is locally larger compared to adjacent layers. The methane concentration in hydrate zone could be increased by capillary effects by increasing solubility of methane in fluids in equilibrium with hydrate. And dissolved methane would be more readily transported upward from hydrate zone, resulting in a shallower top hydrate occurrence. Therefore, capillary effects in gas hydrate stability zones plays a important role in determining the upper boundary of gas hydrates.

Objective  There are abundant geothermal resources in Tibet, and most hot springs or sinters are rarely enriched with elements such as B, Li, Rb, and Cs. In addition to their potential economic value, they are considered important mineral sources of salt lake resources. It is not only of basic theoretical significance but also of guiding significance to correctly evaluate the potential value of mineral resources to study the provenance, evolution, and enrichment law of B, Li, Rb, and Cs in geothermal water.   Methods  Based on the chemical composition and B and Li isotope system analysis of hot springs, rivers, and springs in the typical Yangbajing-Dangxiong rift, boiling springs were found to be mostly Na-Cl type and moderately alkaline, belonging to continental non-volcanic geothermal systems. The most obvious geochemical characteristic of hot springs is a negative δ¹¹B value, and the higher the concentration of B and Li, the more negative the B and Li isotopes are.   [Result and Conclusions] The upwelling of Earth's crust remelting residual magma fluid can reasonably explain the unique element enrichment and combination characteristics, isotope distribution law, and extremely high heat storage temperature of this geothermal system. Geothermal systems like Yangbajing-Dangxiong rift are not only a good prospect of geothermal energy development, but have also all kinds of abnormally or supernormally enriched elements such as B, Li, Rb, and Cs that can be used as mineral resources based on the coupling relationship between magmatic activity and enrichment laws of various elements.

Objective  The East China Sea Bridge is located in the important passage between Hangzhou Bay and the Yangtze River Estuary where the exchange of water and suspended sediment occurs, which has a significant impact on the distribution and transportation of the suspended sediment in the adjacent area. Therefore, the variation characteristics of suspended sediment concentration （SSC） on both sides of the East China Sea Bridge for the tidal cycle, seasonal, and interannual scales are studied.   Methods  Based on 26 days of high-quality Geostationary Ocean Color Imager （GOCI） images with 8 continuous tidal hour per day from 2011 to 2020, the inversion equation was established to transfer remote sensing reflectance to SSC in the adjacent waters around the East China Sea Bridge. In addition, combined with the ideal numerical model and the observation data of seabed sediment, the influence of the East China Sea Bridge on the changes of suspended sediment and seabed sediment distribution at different time scales was studied.   Results  The results show that the SSC on both sides of the East China Sea Bridge presents an obvious gradient distribution, with the higher value on the lee side and lower value on the upstream face of the bridge during both the flood and ebb periods. The SSC difference reaches 300%, which is related to the vertical movement caused by the lower water level on the lee side of the bridge and strengthened disturbance induced by the vortex behind the piers. During the ebb and flood maximum times, the difference in SSC between the two sides of the bridge is the largest, and the difference between the two sides at the flood slack and fall is the smallest. During the ebb period, the difference of SSC on both sides of the bridge is significantly greater than that of high tide. The gradient distribution of SSC on the two sides of the bridge is not significantly different during the ebb and flood periods in different seasons, but the concentration difference is different. The difference of SSC on both sides of the bridge in winter is less than 300 mg/L, which is less than the value in summer that reaches 500 mg/L. Spring is the transitional season, and the difference of SSC on both sides of the bridge in spring is between winter and summer. From the changes over the years, the SSC gradient on both sides of the East China Sea Bridge has little changed. Comparing the grain size changes of seabed sediments near the bridge after 11 years of bridge construction, the seabed sediments in the adjacent waters become finer, which may be related to the weakening of the current velocity due to the water blockage effect by the bridge.   Conclusion  This study concludes SSC gradient distribution between the two sides of the bridge with higher value in the leeside while lower value in the upstream face, which does not vary seasonally or annually. This study is of great significance to improve the research on the impact of cross sea bridges on the marine environment at different time scales.

Results  From this sedimentary sequence, four EM components with different provenance and sedimentary significance were analyzed by the nonparametric method. With the exception of the modern flood sediment and fine sand layers of the floodplain facies, the other layers in each stratigraphic soil unit exhibited characteristics of mixing and superposition of multi-EM components.   Conclusions  Combined with the comprehensive analysis of the macroscopic characteristics and physical and chemical properties in the field, the EM 1 component were shown to represent the far distal source aeolian sediments of the northwest monsoon dust storm and the products of the weathering and soil transformation, and the EM 2 component represents the proximal sediment of the loose sediment sandstorm in the northeast wind blown Yellow River flood plain. The EM 3 components represented the sediments of the suspended sediment of the river flood in the high water level stagnation environment, and the EM 4 components were the floodplain water of the river in the channel Sediment under dynamic action. This shows that the end member analysis of the whole sample grain size can more clearly reflect the diverse sedimentary dynamic characteristics of the Ruhe River Basin. This study has important scientific significance for a profound understanding of the evolution of the Holocene environment and surface processes in the Huaihe River Basin.   [Objective and Methods]  For a profound understanding of the evolution of the Holocene environment and surface processes in the Huaihe River Basin. Through a detailed field investigation in the Huaihe River Basin, a Holocene loess soil stratigraphic profile with multiple layers of paleo-flood stagnant sediments was found at the front of the first-level river terrace in the Zhushixiang section of the upper reaches of the Ruhe River. The section was observed and measured in detail, stratigraphic division and stratified sampling were conducted, and various index analysis and research are performed in the laboratory. In this study, based on the previous study of sedimentological properties and dating, the end member （EM） analysis method was used to analyze the grain size components and further reveal the provenance of this palaeoflood sediment sequence and the change law of its sedimentary dynamic characteristics.

Objective  Surface sediment proxies indicate modern environmental elements and thus infer paleoenvironmental evolution, but few assessment have been reported on the effect of intensive human activity on sediments, and whether this affects the indication of the climate of the area by surface sediment proxies.   Methods  In this study, 456 surface sediments from the Qilian Mountains and surrounding areas were collected and proxies such as total organic nitrogen （TN）, total organic carbon （TOC）, carbon to nitrogen ratio （C/N）, organic carbon isotope （δ¹³C_org）, carbonate carbon isotope （δ¹³C_carb） and oxygen isotope （δ¹⁸O） were analyzed. Relationships between proxies and elevation, latitude, longitude, temperature and precipitation were examined, and the influence of modern human activity on the paleoenvironmental proxies of surface sediments was explored.   [Results and Conclusions]  It was found that these proxies in the anthropogenic zone fluctuate significantly in this region and the correlation is significantly less than in other areas. This suggests that the influence of human activity has changed the indicative meaning of paleoenvironmental proxies. Systematic analysis and calculation of the relationship between surface sediments and environmental elements explored the influence of human activities on surface sediments, and clarified the use of proxies as modern environmental indicators. This provides a theoretical basis for the use of paleoenvironmental proxies in sedimentary strata to infer past climatic conditions and to analyze human activities.

Objective  The Yanchang Formation comprises the most important source rock and reservoirs in the Ordos Basin. Recent 3D seismic exploration shows that progradational reflection is widely developed in the delta-deepwater transition zone of the Yanchang Formation, which means that the previous “thousand-layer pie-like” and near equal-thickness stratigraphic division and correlation scheme would cause stratigraphic diachronistic correlation in clinoform development area. The aims of this study are to explore the establishment of isochronal division and correlation of the clinoform pattern for the Yanchang Formation, and to explore its connection and correlation with the traditional stratigraphic division scheme.   Methods  Based on the 3D seismic data, seismic profiles in the study area are carefully interpreted to obtain the shape type, migration superposition relationship and internal structure of the clinothem, guided by the theories of sequence stratigraphy and sedimentology. Well-seismic mutual calibration （i.e., drilling calibration of seismic horizon, seismic calibration of horizontal correlation of drilling profile strata）, and constrained by core facies marks, a new isochronous stratigraphic division and correlation scheme is established for the mid-upper Yanchang Formation： divided into six stages of clinothems （F1-F6） in Qingcheng, Heshui area, and five stages of clinothems （F1-F5） in the Huanxian area. In the topsets, these correspond to the traditionally stratified Chang 7 - Chang 1 oil layers.   Results and Discussions  The different stratigraphic divisions are mainly reflected in the foreset and bottomset areas. In the foresets, the strata in each clinothem are generally thicker than suggested by the traditional schemes. In the deep-water area, the newly determined F2 and F3 strata are significantly thinner than the traditional values, while the thicknesses of F5 and F6 are dramatically increased. In plan view, the isochronous stratigraphic units of each clinothem show a NW⁃SE zonation. In the study area from SW to NE there is an alternating thin-thick-thin NW-SE zonal distribution pattern. Within the clinoform pattern there are isochronous and intrinsic genetic relationships of the tracking and correlation relationships between stratigraphic division and sandstone bodies. The connectivity relationship of the sandstone bodies approximates more closely to the actual situation of underground reservoirs, which is conducive to a reasonable well pattern of oilfield development layout, and the determination of water injection horizon. The foresets indicated by the thicker strata continue to advance towards the basin depocenter, indicating the contraction and filling process of the lacustrine basin.   Conclusions  The “natural extension tracking of the topsets, marker bed constraint, and 3-D space closure test” establishes an isochronous correlation in mid-upper Yanchang Formation in the progradational development area in the SW Ordos Basin. It provides significant implication for re-understanding the stratigraphic division and correlation in the delta- deepwater areas of the Yanchang Formation, and also provides new insights for a greater understanding of the connectivity and spatial distribution of sandstone bodies, as well as the sedimentary filling process of the basin.

Objective  As an important part of the continental-margin strata, mass-transport deposits （MTDs） attract considerable attention from researchers worldwide. However, previous studies rarely related the development of MTDs to the building of depositional sequences. This study took SQ4 and SQ5 on the Late Quaternary Pearl River margin as the study objects to investigate the influence of different sequence-building backgrounds on the development of MTDs.   Methods  Through the integrated method of seismic interpretation and numerical stratigraphic forward modelling, MTDs are shown to primarily occur in the deep-water reaches of SQ4, whereas in the deep-water part of SQ5, they rarely occurred. Near the shelf-slope break, the existence of different systems tracts suggests that highstand system tracts in SQ4 are highly developed compared with their counterparts in SQ5. Based on the real condition of the Late Quaternary Pearl River margin, a total of 45 modelling experiments with varying relative sea-level changes were designed in Software DionisosFlow 2016 to investigate the development of mass-transport deposits for different backgrounds of depositional sequence building.   Results  The results prove that for high sediment supply （with sediment discharge being 5 000 km³/My and water discharge being 1 200 m³/s） and high amplitude of relative sea-level changes （up to 250 m）, the development of MTDs is sensitive to the development of highstand systems tracts during sequence building； When highstand systems tracts are longer and experience sufficient development, MTDs are easily formed in deep-water areas, which is in consistent with the real condition of MTDs within SQ4 and SQ5.   Conclusions  Moreover, the models representing SQ4 and SQ5 （Model C8 and Model E5） further explain the occurrence mechanism of MTDs. During the building of SQ4, highstand system tracts are fully developed （with the duration of highstand systems tracts accounting for 65% of the elapsed model run）, and the associated delta-shoreline systems overreach the shelf break, causing delta fronts to merge onto the continental slope and form clinothems with high reliefs and slopes； those clinothems are highly unstable and drive the occurrence of mass wasting processes, leading to the deposition of MTDs in deep water. During the building of SQ5, the development of highstand systems tracts is limited （with the duration of highstand systems tracts accounting for 40% of the elapsed model run）, and the associated delta-shoreline systems prograde to the outer shelf but do not overreach the pre-existing shelf-slope break, forming clinothems with low reliefs and slopes, which disfavor the occurrence of mass wasting processes and the development of MTDs in deep water. Those controls of different sequence-building backgrounds on the formation of MTDs in deep water provide a useful method for predicting thesubmarine depositional elements, which are important for hydrocarbon exploration and development in the future.

Objective  The Lower Jurassic Badaowan and Sangonghe Formations in the middle and eastern parts of the Fukang Depression are key intervals for oil and gas exploration, but they are restricted due to their unclear provenance.   Methods  In this study, the provenance was analyzed from rock clastic composition, paleocurrent analysis, heavy mineral composition, cathodoluminescence properties and the proportion of sandstone in the strata.   [Results and Conclusions] The study area is dominated by the Karameri Mountain provenance during the Lower Jurassic, with limited Northern Tianshan and Bogda Mountains provenance. The Sangonghe Formation was influenced by provenances inherited from both the Kalameri Mountain and the northern Tianshan, enhanced by a superposed branch provenance from the Bogda Mountains. In the study area, which has a south-dipping structural background, it is clear that the provenance changed due to the increasing east-to-west uplift of the Bogda Mountains. This southeasterly Lower Jurassic provenance is the scenario for stratigraphic-lithological traps to develop on the southern slope of the Fukang Depression. This may be greatly significant for future oil and gas exploration.

Objective  The quartz sandstone of the Changlongshan Formation in the Qingbaikou system from the Neoproterozoic was encountered during drilling in the southwestern Liaodong Bay, Bohai Sea. The in-depth study of its provenance characteristics is of great significance to the anatomy of major geological events from the Archean to Proterozoic in the North China Craton.   Methods  Five quartz sandstone samples collected from around 2 482 meters in well BD4-1a were analyzed for whole-rock geochemistry and detrital zircon U-Pb geochronology.   Results  The quartz sandstones had high SiO₂ content （88.53%-93.06%）, the chemical index of alteration （CIA） value was 69.5~71.6, the index of compositional variability （ICV） value was 0.69-3.99, and the samples displayed high compositional maturity, structural maturity, and moderate weathering. The Th/U ratio ranged from 3.46-4.92, the Cr/Zr ratio of 0.17 ~0.35. The sum of the rare earth elements （ΣREE） is （8.26-24.12） × 10^-6, the low/heavy rare earth element ratio （LREE/HREE） was 6.28~10.21, and the δEu was 0.77-1.04, which shows a weak negative anomaly. The U-Pb ages of detrital zircons ranged from 2 744-1 581 Ma； the main age peak was ~1 845 Ma, and the subordinate age peaks were ~ 2 225, ~2 340, ~2 600, ~2 725 Ma, respectively.   Conclusions  Whole-rock geochemistry indicates that the provenance mainly comes from felsic rocks of the upper crust. The 2.7-2.5 Ga detrital zircons record the growth and tectonothermal events of the continental crust in the North China Craton. The 2.2-1.8 Ga detrital zircons correspond to the crystalline basement formation during the amalgamation of the eastern and western blocks of the North China Craton, recording the geological events of the Columbia supercontinent's assembly. The 1.8-1.6 Ga detrital zircon ages likely record the breakup of the Columbia supercontinent.

Objective  Gravelly limestone is developed in Cambrian strata at the western margin of the Ordos Basin,and typical storm sedimentary structures are developed. However, there is still a lack of systematic research on its sedimentary environment, formation process, and geological significance.   Methods  This detailed study of the development of gravelly limestone and typical storm deposits in the Xuzhuang Formation at the western margin of the Ordos Basin was conducted by means of field observation and thin section observation of four sections： Wuhai Moergou, Wuhai Laoshidan, Huanxian Yinshixia and Tongxin Qinglongshan.   Results  The following conclusions have been made： （1） storm sedimentary structures （e.g., channel mold, bottom scouring surface, mound cross-bedding and parallel bedding） are developed in the study area. （2） There are four gravelly limestone facies are categorized by shape, arrangement and infill characteristics （e.g., particle-supported gravelly limestone facies； argillaceous filled gravelly limestone facies； radial gravelly limestone facies and matrix-supported gravelly limestone facies）. （3） In addition, five typical storm sedimentary sequences of the Xuzhuang Formation of the Middle Cambrian are identified at the western margin of the Ordos Basin from field-measured data, and a storm sedimentary model of the study area is established. （4） The study area was located in an epicontinental sea environment during the Cambrian and combined with previous research results, the genesis of gravel limestone is analyzed and the formation process is illustrated. It is considered that the storm wave and seismic action are the dynamic conditions for the formation of gravel limestone. Storm waves and earthquakes were the dynamic conditions for the formation of gravelly limestone. The ancient plate was located in a tropical storm belt, which was the reason for frequent storms. （5） The development of storm deposits in the study area reveals that the Ordos Basin was located in a low-latitude area near the equator during the Cambrian Xuzhuang Formation, which is consistent with the position of the North China Plate at that time established by paleomagnetism studies.   Conclusions  Through the study of storm deposits in the study area and the establishment of sedimentary models, it is of great significance for the restoration of paleoenvironment and paleogeography in the Cambrian of Ordos Basin. In addition, the formation process of gravel limestone in the study area is revealed by establishing the genetic diagram of gravel limestone in the study area.

  Objective   Multiple layer storm deposits are distributed in the Lower Permian Taiyuan Formation carbonate rocks located at the Gancaoshan zone of Xiangning county on the eastern margin of the Ordos Basin.   Methods   These are primarily distributed in limestone beds L₂, L₃, and L₄. Based on the lithology, sedimentary structure, trace fossils and sedimentary sequence, the main characteristics of the deposit sequence consisting of the eroded basement structure and bioclastic lags, graded bedding, laminated unit, bioturbation structures （trace fossils）, and marlstone or calcareous mudstone unit in carbonate rocks are discussed in detail.   Results   From the vertical component features of storm deposits sequence in different limestone beds, five types of tempestite deposit sequences were identified： Type A is comprised of a wavy bottom erosion surface and graded bedding, developing in the near shore zone above the fair weather wave base. Type B is characterized by a wavy bottom erosion surface, graded bedding, and laminated unit （Hummocky   ⁃  swaley cross-bedding） and is generated in the subtidal zone, namely the upper zone between the fair weather and storm wave base. Type C is composed of a wavy bottom erosion surface, graded bedding, laminated unit （Hummocky   ⁃  swaley cross-bedding and gently wavy bedding）, and marlstone unit, forming in the lower zone between the fair weather and storm wave base. Type D consists of a wavy bottom erosion surface with bioclastic lags, graded bedding, bioturbation structure, and marlstone unit, appearing mainly near the storm wave base. Type E consists of a slight fluctuation bottom erosion surface, thin-bedded graded bedding, ichnofossil-bearing unit, and marlstone unit, occurring in the shallow marine environment near/below the storm wave base.   Conclusion   This result not only provides new understanding of the Lower Permian Taiyuan Formation carbonate rocks and their sedimentary environment in the Ordos Basin, but also can provide evidence of sedimentary environment analysis and palaeogeographic reconstruction for the exploration and development of oil and gas resources in these strata.

Objective  There is large potential of oil and gas resource from the Jurassic Shaximiao Formation of the eastern slope in the Western Sichuan Depression, and the internal structure of the single sandbodies restrict the prediction of high-quality reservoirs, and consequently affects the evaluation of the natural gas enrichment characteristics in this area. The order of the architecture boundary, architecture-element, and architecture-element assemblies in the study area are not yet clear. There is a lack of relevant understanding of how the architecture-elements and their assemblies control the reservoir heterogeneity from the different architecture boundary levels.   Methods  In this study, the types of sedimentary facies were determined to provide the foundation for the study of the sandbody architecture. Based on the data of field outcrops, cores, logs, and experimental measured analysis, detailed research on the type and characteristics of the sandbody architecture of the meandering river from the Shaximiao Formation of Western Sichuan Depression was carried out, and the effect of sandbody architecture on the reservoir heterogeneity under the constraints of multilevel architecture boundary was discussed.   [Results and Conclusions]  The architecture-elements in the study area were divided into H_PB, H_CH, M_CS, M_CL, M_CA, and M_FM. Based on the vertical stacking pattern of architecture units and the sedimentary characteristics of vertical sequence, the architecture-element assemblies are divided into three types, including homogeneous assemblage （Type I）, homogeneous+ compound （Type II）, and compound assemblage （Type III）. Type I assemblage mainly occurs in the Zhongjiang-Huilong area of the study area, and the Type I assemblage and Type II assemblage mainly occur in the Third member of Shaximiao Formation, and the reservoir heterogeneity is relatively weak. Based on the above research on the types and characteristics of sandbody architecture, the analysis on the characteristics of reservoir heterogeneity under the control of different levels of architecture boundary, and the discussion of the controlling factors that sandbody architecture impact on the reservoir heterogeneity under different levels of architecture boundaries, the model of controlling the reservoir heterogeneity under the architecture boundary constraints of 3~5 levels of architecture is established. The reservoir plane heterogeneity is controlled by the 5 level' architecture boundary, and the reservoir heterogeneity under the 5 level' architecture boundary is controlled by the rising of based-level and structure subsidence. The reservoir inter-layer heterogeneity is controlled by the 4 level' architecture boundary, and the reservoir heterogeneity under the 4 level' architecture boundary is controlled by the slope and erosion. The reservoir intra-layer heterogeneity is controlled by the 3 level' architecture boundary, and the reservoir heterogeneity under the 3 level' architecture boundary is controlled by the hydrodynamic condition, channel sinuosity, degree of channel migration, deposited load, discharge, and diagenesis.

Objective  The reactions between sulfates and sedimentary organic matter are typical organic⁃inorganic interactions in sedimentary basins. During the early stage of catagenesis, the thermal evolution of sedimentary organic matters would be influenced by the presence of sulfate. Investigations on thermal evolution of aromatic fraction compositions in the corresponding system will improve the understanding its geochemical behaviors.   Methods  In this study, the effect of sulfate on the thermal evolution of kerogen was investigated by hydrous pyrolysis. The source rock and the corresponding sulfur-bearing kerogen were sampled from the Pingliang Formation on the southwestern margin of the Ordos Basin.   Results  Experimental results showed that the presence of sulfate promotes the yields of soluble organic matters, as well as the generation peak of aromatic fractions in the early stage. Moreover, the organosulfur compounds, might be oxidized by sulfate during the early stage of catagenesis, which led to the decreasing of generation of dibenzothiophene. It would result in the significant discrepancies of aromatic fraction compositions between two group experiments. Therefore, there was a stage of oxidative degradation between sulfate and sedimentary organic matter before hydrocarbon generation peak. In this stage, the majority of production is polar organic compounds, such as oxygen-bearing compounds. Dibenzothiophene was derived from organosulfur compounds.   Conclusions  These understandings enlarged the reaction region between sulfate and sedimentary organic matters to the gypsum-bearing source rock during catagenesis with lower thermal stress.

Objective  To clarify the cause of the different compositions of the individual crude n-alkane carbon isotope （δ¹³C_alkane） in the three categories,   Methods  in this study the composition of δ¹³C_alkane in 17 Ordovician crude oil samples from the northern Tahe oilfield, combined with relevant organic geochemical parameters, were examined for depositional environment, maturity and biodegradation.   [Results and conclusions]  The differences in physical properties allows the crude oils in Tahe to be categorized as heavy, medium and light crude oils. The δ¹³C_alkane value is between 37‰ and -31‰. It has the properties of marine crude oil, indicating that the composition and distribution of δ¹³C_alkane are by the depositional environment and the type of parent material. Maturity gradually increases from heavy to medium to light crude oil, in turn leading to heavier δ¹³C_alkane values, which is significantly higher in the lowcarbon-number part of the heavy crude oil. The heavy crude oil has been more strongly biodegraded than the medium and light crude oil, indicating that the degree of biodegradation is the main factor affecting the positive bias of δ¹³C₁₄ to δ¹³C₁₉ values of the medium- and low molecular weight n-alkanes in heavy crude oil.

Objective      Biodegraded crude oil is commonly found in poriferous basins globally. Biodegradation will have a profound impact on the physical properties and group components of crude oil, resulting in an increase in the oil density and viscosity, an enrichment in the non-hydrocarbon, asphaltene, sulfur metallic ion content and acid value. In recent years, the Mesozoic （Jurassic and Cretaceous） oil-bearing sandstone reservoirs in the east margin of the Chepaizi uplift have attracted much more attention due to the discovery of large quantities of crude oil, but their severe biodegradation restricts the exploration process. In order to clarify the biodegradation level of Mesozoic crude oil in the east margin of the Chepaizi uplift, the saturated hydrocarbon and the aromatic hydrocarbon fractions extracted from the reservoir samples from 10 wells in the Mesozoic east margin of Chepaezi uplift were analyzed by gas chromatography-mass spectrometry （GC-MS）, and molecular biomarkers strongly resistant to biodegradation were investigated.       Methods      Cluster analysis, a statistical method, is an effective tool to classify studied samples into different groups by their similarity distances which were calculated from the different variables investigated. Allowing for the severe oil alteration, the following nine biomarker parameters related to tricyclic terpenes （TT）, tetracyclic terpenes （Tet） and triaromatic steranes （TAS） with strong biodegradation resistance were selected： （C₁₉TT + C₂₀TT）/ （C₂₃TT + C₂₄TT）, C₁₉TT/C₂₃TT, C₂₃TT/C₂₁TT, C₂₂TT/C₂₁TT, C₂₄TT/C₂₃TT, ETR, C₂₄ Tet/C₂₆TT, C₂₇ TAS/C₂₈TAS （20R）, C₂₆TAS/C₂₈TAS （20S）. Cluster analysis （HCA） was performed to classify the Mesozoic crude oil populations. On this basis, the biodegradation level of Mesozoic crude oil was qualitatively evaluated according to the PM （Peters and Moldowan） method and descriptive terms. Then, following the academic theory of Manco scale, eight compounds with different sensitivities to microbial degradation, which characterize progressive bioresistance, were selected. Variables was assigned for them to optimize the quantitative evaluation scale of Manco method. The parametric vectors of the eight compounds generally covered the whole degradation level （PM0 ~ PM10）, including （1） n-alkanes （m/z 85）； （2） naphthalene and alkyl naphthalene （m/z 128, 142, 156, 170, 184, 198）； （3） alkyl dibenzothiophene （m/z 198, 212, 226）； （4） C_0-3 phenanthrene （m/z 178, 192, 206, 220）； （5） pentacyclic triterpenes （m/z 191, 177, 205）； （6） sterane （m/z 217, 218, 259）； （7） tricyclic terpenoids （m/z 191, 177）； and （8） triaromatic steroids （m/z 231, 245）. MN₁ （Manco Number 1） and MN₂ （Manco Number 2） were calculated by the formulas, and the correlation between them and crude oil properties was analyzed.       Results and Discussions      The result shows that the Mesozoic crude oil is a typical heavy oil with high density and high viscosity, especially the viscosity of crude oil shows an order of magnitude change, which essentially reflects the alteration effect of microbial degradation. The oil density showed roughly positive correlation with the viscosity and the NSO （resin + asphaltene） fraction content, and negative correlation with the burial depth. Progressive biodegradation of crude oils may be responsible. The results of cluster analysis shows that the Mesozoic crude oil in the eastern Chepaizi uplift can be divided into four oil populations, i.e., I, II, III and IV. According to the difference of crude oil degradation level, different crude oil groups can be subdivided into different families. For example, group I crude oil is subdivided into family I₁ crude oil （well P1, 781.5 m and 721.5 m） with a biodegradation level of PM7 （heavy） and family I₂ crude oil （wells P607 and P624） with a biodegradation level of PM8 （very heavy）. Group II is subdivided into family II₁ crude oil （well P1, 748.5 m and 751.2 m） with a biodegradation level of PM7 （heavy） and family II₂ crude oil （wells P60 and P604） with a biodegradation level of PM9 （very heavy）. Group III is subdivided into family III₁ crude oil （wells P629, P68, and P606） with a biodegradation level of PM9 （very heavy） and family III₂ crude oil （well P646） with a biodegradation level of PM9+ （severe）. Group IV includes well P1（756.8 m, 757 m, 761.6 m, and 766.5 m） and well P609, and the biodegradation level of group IV is PM8 （very heavy）. Qualitative evaluation result by the PM method shows that the degradation level of Mesozoic crude oil can reach PM7-PM9+. The MN₁ value obtained by the optimized Manco method ranges from 19 693 to 215 623； the MN₂ value obtained by the optimized Manco method ranges from 768 to 954. For a single oil population, the values of MN₁ and MN₂ increased with the biodegradation level. In addition, the Manco number shows a good positive correlation with oil density, viscosity, non-hydrocarbon and asphaltene content, and a good negative correlation with total hydrocarbon content. The exception is the oil from well P646, which has a higher level of biodegradation than well P606 but shows a lower viscosity. Factually, there is not a simple relationship between the oil viscosity and the Manco number. Processes other than biodegradation, i.e., secondary oil charge, water washing, mixing of multiple maturity oil charges, and loss of light ends from heavy oils could produce variations in oil viscosity and density. The two episodes of oil charging, early biodegraded oils mixed with the later remigration of preexisting oils due to the structural adjustment, yet the same oil origin in the Chepaizi uplift maybe responsible for this case. In addition, differences in preservation conditions due to changes in burial depth can be one of the factors affecting biodegradation.       Conclusions      The optimized Manco method successfully distinguishes the oil-bearing reservoir samples with biodegradation level in PM7-PM9+, which is consistent with the PM result, that is, the biodegradation level of family Ⅰ₁, family Ⅱ₁, family Ⅰ₂, group Ⅳ, family Ⅱ₂, family Ⅲ₁, family Ⅲ₂ successively increases. In addition, the optimized Manco method provides a more detailed classification than the PM method, because it can clearly distinguish crude oil with the same PM level but different crude oil physical properties. This way, the differences in the biodegradation of oil-bearing reservoir samples can be clearly shown. The combination of qualitative evaluation by the PM method and quantitative evaluation by the optimized Manco method can reveal the difference in crude oil physical properties, which plays a guiding role for oil and gas exploration in this area.

Objective  Coal-measure source rocks in Ordos Basin are developed, and the content of tricyclic terpane in saturated hydrocarbons is rich. However, the distribution patterns of tricyclic terpane show important differences in the study area. Therefore, it is of great significance to explore the main controlling factors for these differences.   Methods  Saturated hydrocarbons of 26 coal-measure source rock samples in the Upper Paleozoic of the Ordos Basin were analyzed in detail by gas chromatography and chromatography⁃mass spectrometry.   Results and Discussions  According to the distribution characteristics of tricyclic terpanes （TTs）, the source rock samples in the study area were divided into three types of distribution patterns. The C₁₉TT is the main peak of the type I source rock, and the content of C₁₉TT, C₂₀TT and C₂₁TT gradually decreases. At the same time, the Pr/Ph ratio is high, and the ratio distribution range is between 1.19 and 3.84, with an average value of 2.99. The content of C₂₄ tetracyclic terpane is also rich in this type of sample. The ratio distribution range of C₂₄ tetracyclic terpane/C₂₆ tricyclic terpane is between 2.39 and 32.54, with an average value of 9.80. Both C₂₈ tricyclic terpane and C₂₉ tricyclic terpane are absent. This kind of sample is mainly humic coal and carbonaceous mudstone, revealing the characteristics of a lacustrine facies sedimentary environment. By contrast, the tricyclic terpanes of type II source rocks are dominated by C₂₃TT, and the content of C₁₉TT, C₂₀TT and C₂₁TT gradually increases, whereas the Pr/Ph ratio is low and the ratio distribution range is mainly within the range of 0.34 and 0.90, with an average value of 0.61. The content of C₂₄ tetracyclic terpane is not abundant, and the ratio distribution range of C₂₄ tetracyclic terpane/C₂₆ tricyclic terpane is mainly between 0.42 and 0.77, with an average value of 0.54. Both the C₂₈ tricyclic terpane and C₂₉ tricyclic terpane are abundant. In addition to coal-measure mudstone, humic coal and carbonaceous mudstone are present in these samples, and their sedimentary environment is quite different from that of type I source rocks. The distribution of tricyclic terpanes in type III source rocks is in the middle of the type I and type II source rocks. The main peak carbon of tricyclic terpane is C₂₃TT, whereas the relative content of C₁₉TT, C₂₀TT and C₂₁TT decreases in turn with a stepwise distribution. In addition, the Pr/Ph ratio is 2.07 and the C₂₄ tetracyclic terpane/C₂₆ tricyclic terpane is 3.53, both of which are between the type I and type II source rocks.   Conclusions  The results reveal that with an increase of the thermal evolution degree of source rocks, the total amount of tricyclic terpanes shows a gradually increasing trend, although the distribution patterns of tricyclic terpanes in different types of source rocks have not changed significantly. To put it another way, the different distribution patterns of tricyclic terpanes in coal-measure source rocks in the study area are less affected by the thermal evolution degree of organic matter. Rather, they are mainly controlled by the sedimentary environment and parent material type.

  Objective   Exploration of Permian sandstone in southern Dagang shows high-yield oil, but the reservoir characteristics and genetic mechanisms remain uncertain.   Methods   Core observations, thin-section identifications, cathodoluminescence analysis, scanning electron microscopy, fluid inclusion analysis, carbon and oxygen isotopic composition analysis, electron probe microanalysis, and in-situ laser ablation, coupled with the consideration of burial evolution history and hydrocarbon charging history, were used in this investigation into the deep-seated sandstone reservoirs in the Wangguantun and Wumaying regions of the southern Dagang exploration area.   Results and Discussions   It was found that the Permian sandstone in the southern Dagang region has a high compositional maturity, predominantly characterized by quartz sandstone and sublithic sandstone. The storage spaces in high-quality reservoirs consist primarily of secondary intergranular pores and intercrystalline micropores in kaolinite. Influenced by tectonic movements, the reservoirs have undergone early open-system atmospheric-water leaching and dissolution, followed by late closed-system acid dissolution resulting from hydrocarbon source rock interactions. A range of factors influenced the development of high-quality reservoirs, with the high compositionally mature medium-to-coarse sandstones being the basic material. Early strata uplift and erosion, which led to significant secondary porosity from atmospheric fresh-water leaching, were critical factors. Early hydrocarbon charging inhibited by cementation processes favored the preservation of secondary porosity.   Conclusions   Reservoirs in the slope and depression zone that were formed in an area of atmospheric water leaching are appropriate exploration targets. This model is also relevant for pre-drilling prediction of Permian reservoirs in other regions of the Bohai Bay Basin.

Objective    The tight glutenite reservoir of the Shahezi Formation in the Xujiazi Fault Depression has great potential for natural gas exploration and is expected to become the key replacement field of deep volcanic gas reservoir exploration in Daqing oilfield.     Methods    The distribution of sedimentary facies and evolution models of the Shahezi Formation in the Xujiaweizi Fault Depression were studied using comprehensive core, logging, and seismic data.     [Results and Conclusions]    The results show that there are braided river delta, fan delta, far shore turbidite fan with supply channel, near shore subaqueous fan, slump turbidite fan in front of fan delta, shallow lake-semi-deep lake, and deep lake deposits in the Shahezi Formation of the Xujiaweizi Fault Depression. The gentle slope belt on the east side of the Anda, Xudong, and Zhaozhou Depressions received the detritus from the Zhaodong-Chaoyanggou basement paleo-uplift and developed braided river delta deposits； locally developed lacustrine turbidite fan deposits were formed by distant source supply channels. The western steep slope belts such as the Anda-Xudong, Xuxi, and Zhaozhou Depressions received coarse debris from the Central fault uplift area and developed a fan delta depositional system, which was characterized by near source and short flow. Nearshore subaqueous fan depositions were locally developed, and due to the instability of fan delta depositional bodies developed on the edge of lake basin, slump turbidite fan depositions were formed in front of fan delta depositional bodies.