Objective To identify the next exploration direction， the main controlling factors and exploration potential of different types of shale oil enrichment in the Chang 7 member of the Ordos Basin are discussed. Methods In this study， the formation conditions and exploration potential of shale oil such as petrology， geochemical characteristics and reservoir capacity of the Chang 7 member shale were comprehensively studied using organic geochemistry， whole rock X-ray diffraction （XRD）， field emission scanning electron microscopy， and rock pyrolysis experiments. Results （1） The Chang 7₃ sub-member shale has high organic matter abundance， the best type， the highest maturity， and the greatest hydrocarbon generation potential. （2） The Chang 7 member shale is dominated by inorganic pores and fractures， with the largest proportion of micropores， and the shale reservoir capacity is stronger than that of mudstone. （3） The enrichment of shale oil in the Chang 7 member is controlled by five factors ： high-quality source rock， lithologic combination， fracture， mobility， and fracability. The distribution of high-quality source rocks controls the distribution range of shale oil， the lithology combination controls the hydrocarbon expulsion efficiency and the enrichment type of shale oil. The hydrocarbon expulsion efficiency of the source-reservoir interbedded type is the highest， which is conducive to the enrichment of sand bodies； the hydrocarbon expulsion efficiency of the thick source-thin reservoir type is the lowest， which is conducive to the in-situ retention and enrichment of shale oil. The two-sidedness of fractures controls the enrichment degree of shale oil. The development of fractures is conducive to the enrichment of sandstone interlayer shale oil， and the underdevelopment of fractures is conducive to the retention and enrichment of pure shale-type shale oil. The mobility and fracability of crude oil control the high yield of shale， and the mobility and brittleness index of shale crude oil are better than those of mudstone. Conclusions The Chang 7₃ sub-member in the Jiyuan area is a favorable exploration block for pure shale-type shale oil. The Zhengning and northern Shaanxi areas are favorable exploration blocks for sandstone-intercalated shale oil in the Chang 7₁ and Chang 7₂ sub-members. The Huachi area in Longdong is a favorable area for the exploration of both sandstone-intercalated and pure shale-type shale oil.

Significance The study of fine-grained sediment transport mechanisms is an important part of the “source-to-sink” system theory of fine-grained sediments， and it is significant for the restoration of sedimentary environments， understanding the distribution of fine-grained sediments and predicting the distribution of unconventional oil and gas resources. Due to the fine grain size， which makes them difficult to observe， and the diversity of transport modes， each transport mode corresponds to particular sedimentary structures. Therefore， research on the transport mechanisms of fine-grained sediments has progressed slowly. From a review of the existing research reported in China and elsewhere， it is evident that there is still a lack of sorting and summarizing research findings regarding the transport mechanisms of fine-grained sediments. Progress This study synthesizes current research， systematically sorts the transport modes and sedimentary characteristics of fine-grained sediments and classifies the transport modes of fine-grained sediments into three major categories： physical transport， chemical transport， and biological transport. Physical transport includes river water， atmosphere， bottom current， density underflow， and six types of gravity-flow transport. River water and atmospheric transport rely on the forces exerted by water flow and/or wind to overcome the gravitational force on fine-grained materials. These are mainly traction force and load force. Bottom current， density underflow， and gravity flow transport are triggered by tides， wind， earthquakes， floods， storms， volcanic eruptions and other means， with gravity being the main driving force. Clay minerals， dissolved organic carbon， carbonate minerals， iron minerals and others are transported as colloids or as true solutions. Dissolved substances are affected by environmental factors such as pH， Eh， temperature， pressure， and ion concentration or charge， and are transported by chemical means. Biological absorption and enrichment， environmental changes caused by biological activities and bioturbation all affect the formation and transport of fine-grained materials. ［Conclusion and Prospect］ Physical transport has diverse modes. With driving forces such as traction force， carrying capacity， and gravity， it can form a rich variety of sedimentary structures. Chemical transport mainly involves dissolved substances and is affected by environmental factors such as pH values and temperature. Biological transport influences the transport of fine-grained substances through absorption and enrichment， alteration of the environment， and bioturbation. In the future， attention should be focused on the interactions among the transport mechanisms of fine-grained sediments， the accuracy of identifying sedimentary structures should be improved， importance should be attached to simulation experiment research， and the quantitative analysis of chemical and biological effects should be strengthened， so as to enhance the understanding of the transport processes of fine-grained sediments and promote the development of the theory of fine-grained sedimentology.

Objective Tidal forces influence the form and scale of marine shelf deltas and the development and evolution of branch channels. The quantitative control mechanism of different amplitude tidal ranges on the dam body and branch channels of continental shelf deltas has garnered significant scientific interest. Methods In this study， a single factor control method was used to analyze the evolution of the key geologic bodies in the continental shelf delta under different tidal ranges using Delft3D hydrodynamic simulation software to establish four control groups： no， small， medium， and spring difference. Results The experimental results show that the down-cut depth and width of the branch channel decrease with the increase of the flow distance when there is no tidal effect. When tidal action is added， the number of distributary channels decreases with the increase of tidal range， but the down-cut degree and width of the distributary channels increase. The width-to-depth ratio of the branch channel ranges from 2-10 when there is no tidal action， and decreases to zero when there is a low tidal range. Under the influence of middle and spring tidal ranges， the width-to-depth ratio of the branch channel corresponds to 0-3 and 2-4， respectively. Conclusions The results show that tidal action is beneficial for increasing the broad-to-thickness ratio of sand bodies， and the delta morphology changes become more stable with the increase of tidal range. The number of branch channels in the delta under the influence of tides decreases significantly owing to the periodic influx and retreat of tides in the lateral direction. This promotes the formation of lateral channels and tidal channels. Under the influence of middle-spring difference， the lateral migration distance of the branch channel is shorter， the branch channel is more stable， and the dam body is more isolated， providing an important reference for reservoir configuration analysis of similar underground sediments.

Objective Significant advancements have been made in the research of sandy braided river deltas， but the sedimentary characteristics and evolution laws of sandy braided river deltas require further study， particularly the understanding of mouth bars and distributary sand bars. Methods Based on the underground reservoir data， this study used the Delft3D software to show the growth and evolution of a sandy braided river delta into a lake， summarizing its sedimentary characteristics and evolution laws. Results The evolution of a sandy braided river delta has three stages. In the early stage， the delta grows fastest， and the average diameter growth rate was greater than 6 m/step. Sediments are carried into the lake and quickly unloaded， forming a large flower-shaped mouth bar under the water. In the middle stage， the delta plain continues growing， and the delta front remains large， accounting for more than 50% of the delta area. Contiguous sand bodies are built. In the late stage， the delta grows slowly， the average diameter growth rate is maintained at 1m/step. The front area is small， less than 20% of the overall area. The delta plain has many distributary channels and ditches， leading to multiple paths for transforming the distributary sand bars. The delta front sand bars have different degrees of superposition and rhythm combination characteristics， and the distributary sand bars are built on the residual mouth bar. Conclusions A sedimentary model of a sandy braided river delta was established， providing reference for the genetic identification of distributary sand bar and mouth bar， and laying the foudation for advancing underground reservoir architecture research.

Objective Distributive fluvial systems （DFS） are widely developed in modern and ancient sedimentary strata and they are important hydrocarbon reservoirs. Multiple interacting DFS and evolving axial rivers may be developed in a narrow， shallow lacustrine basin with low accommodation. Methods Reproducing the deposition process through flume simulation experiments， this study used a high-precision three-dimensional （3D） scanner with a self-developed program to visual analyze the deposition area and clarify the stage-by-stage evolution characteristics of the DFS. Results （1） With the expansion of the DFS scale， the water flow on its surface gradually aggregates； the initial flow pattern is sheet flow， which then evolves into unrestricted and restricted flow； （2） as the basin can accommodate less space， the axial water flow in the basin gradually aggregates into an axial river， which has a destructive effect on the two sides of the DFS and constantly breaks， forming a large-scale fluvial deposition； （3） when multiple DFS are developed in a narrow， shallow lacustrine basin， the sedimentary sands are concentrated at the DFS near the source and downstream of the axial river， and the longer basin development time indicates a larger scale of fluvial deposition. Conclusions This study describes the developmental processes and sand body spreading patterns of multiple DFS and axial rivers developed in a narrow， shallow lacustrine basin with low accommodation and sufficient supply of material sources at the basin scale， providing theoretical support for oil and gas exploration and the study of distributive fluvial systems.

Objective Abundant ichnofossils present in the Eocene Pinghu Formation and Baoshi Formation in the Pingbei area， Xihu Sag. It is of practical significance for the division of sedimentary systems in the Xihu Sag to study the characteristics and distribution of its ichnofabrics and their indication of sedimentary environment. Methods Using core observations， the study identified ichnofossils and ichnofabrics in the Pingbei area. The IDIPA technique was employed to objectively quantify ichnofossil abundance and accurately determine both the bioturbation index and the ichnofabric index. By integrating these findings with ichnological indices， this study summarizes the characteristics of the planar distribution and vertical evolution of ichnofabric in the study area. Results （1） The study identified six ichnogenera of ichnofossils and divided them into four types of ichnofabrics： Planolites ichnofabric， Thalassinoides ichnofabric， Teichichnus ichnofabric and Beaconites ichnofabric. （2） The study area features a high landform in the northwest and a low landform in the southeast. Seawater invades from south to north， and the sedimentary environment transitions from a subtidal zone to an intertidal zone， and finally to a supratidal zone in the northwest where the highest terrain is located. The evolution pattern of the corresponding ichnofabrics follows the sequence Thalassinoides → Teichichnus → Planolites → Beaconites， consistent with regional sedimentary zoning and paleoclimate analysis. （3） From the Pinghu Formation to the Baoshi Formation in the study area， the study found an increase in the size， diversity and abundance of ichnofossils. The tiering transitioned from simple and shallow to complex and deep. The variety of organisms and the degree of bioturbation increased， and the biological habits evolved continuously， indicating that the sedimentary environment changed from anoxic to oxic. Conclusions Based on the characteristics of ichnofossils， ichnofabrics and sedimentary structures， the response relationship between the ichnofabrics and the sedimentary environment was established in the Pinghu Formation⁃Baoshi Formation in the Pingbei area. These findings provide new evidence for the changes in sedimentary environment from the perspective of ichnology in the Xihu Sag during the Eocene.

Significance Peat bogs play an important role in the global carbon cycle as a depositional carrier of paleo-wildfire events and paleoclimate information. By systematically sorting wildfires types in peat bogs and clarifying the academic terminology related to wildfire products such as charcoal， the carbon source and sink effects of wildfires in peat bogs were discussed. This information is useful for the study of the carbon cycle in deep time. Progress Wildfire product charcoal， approximately equivalent to the inertinite in coal， is a relatively stable carbon store of plant-incomplete combustion residues， which can provide a record of wildfire activities in geological history， from millennia to billions of years. Changes in charcoal material composition （e.g.， polysaccharides and lignin） and microstructure （e.g.， cell wall homogenization） can reflect the temperature range of paleo-wildfires. Wildfire types can be recovered and atmospheric oxygen content can be constrained using inertinite reflectance and content. The impacts of wildfires on the global carbon cycle include both short-term carbon source and long-term carbon sink effects. Wildfires lead to direct large carbon emissions and carbon release from deep peat burning. However， wildfire-driven persistent changes in soil microorganisms， aggregates， and organic matter can directly offset certain carbon losses， and charcoal provides a stable carbon store. Conclusions and Prospects Based on the carbon cycle model of peatland under normal burial conditions， the influence factors of wildfire， soil aggregates， fungi， and bacteria were introduced to propose a post-fire peatland carbon cycle model. Using the inertinite wildfire genesis and greenhouse gas emission models， and taking the carbon emission and carbon storage of wildfires in Early Cretaceous peat （coal-forming） bogs in Northeast China as an example， the results show that the long-term （million-year time scale） carbon sinks of forest vegetation growth and peatland are fully capable of neutralizing the short-term （year time scale） carbon source effect brought by wildfires. In the future， when evaluating the deep-time carbon cycle response to wildfires， it is necessary to consider the length of the time period and wildfire intensity， improving our understanding of climate change and environmental evolution caused by wildfire to promote the in-depth integration of deep-time and present-day climate change and carbon cycle research.

Objective The widespread siderites in the marine strata of the Toarcian Oceanic Anoxic Event （T-OAE） are believed to have resulted from a low sulfate concentration and increased terrestrial iron supply. Similar large amounts of siderite have also been reported in paleolakes in the same period. However， the mechanism of lacustrine siderite development and its connection with the T-OAE remain unexplored， but is crucial to a better comprehension of lacustrine biogeochemical cycling in the early Toarcian. Methods Mineralogical and carbon isotope geochemical analyses were performed on siderite samples from the lacustrine Anya section of the Ordos paleolake. The sources of iron and carbon， as well as the sedimentary environment， were investigated by integrating major and trace element data， which allowed exploration of the formation mechanism of siderites during the T-OAE period of climatic change. Results The coexistence of pyrites and siderites was observed by scanning electron microscopy （SEM）. The value of inorganic carbon isotopes （δ¹³C_carb） varies from -11.25‰ to +16.32‰， and the organic carbon isotope （δ¹³C_org） value ranges between -32.03‰ and +14.33‰. Light rare earth elements （REEs） are enriched and heavy REEs are depleted， with Eu anomalies ranging from 0.69 to 0.85. Conclusions The iron in the Anya siderites is derived from terrestrial inputs； the carbon included HCO₃^– produced by methanogenesis， as well as carbon released by organic matter decomposition and aerobic methane oxidation， either bacterially in the suboxic zone or archaeally below the oxic-anoxic interface immediately after methane production. The pore fluids during siderite formation were a suboxic to anoxic environment. During the T-OAE， intensified continental weathering and increased surface runoff transported abundant Fe²⁺ ions into basin lakes whose widespread anoxia， abundant organic matter and low sulfate concentrations created favorable conditions for extensive siderite deposition.

Objective The climate signals of the Danxia strata， a representative of Cretaceous continental red beds， offers key insights into red-bed sedimentation and Cretaceous geological events. Methods This study examined fine-grained clastic rocks in the Upper Cretaceous Danxia Basin， specifically the Second member and Fourth member of the Changba Formation and the Jinshiyan member of the Danxia Formation. Sedimentology， elemental and isotopic geochemistry were used to investigate the sedimentary environment and paleoclimate significance during key Upper Cretaceous stages （Cenomanian， Turonian， Campanian）. Results It was found that the fine-grained clastic rocks of these formations were deposited during a warm and humid climate phase， with suboxic to oxic water conditions. The water bodies were predominantly brackish， while localized high-salinity brackish and low-oxygen environments （e.g.， the Fourth member of the Changba Formation） were associated with lake shrinkage and climatic aridification. Water depth variations exhibit trends of initial contraction followed by expansion， gradual contraction， then initial expansion followed by contraction， which align with the changes in sedimentary facies and environment. Conclusions The Upper Cretaceous terrestrial sedimentary records of the Danxia Basin illustrate the climatic evolution of intermontane basins， shaped by global climate patterns of the Upper Cretaceous， as well as by significant influences from local topographic and geomorphic features.

Objective Research on the weathering process of the aggradation red earth in subtropical China has long been crucial for understanding the evolution of the Quaternary environment. However， a comprehensive know-ledge of the weathering environment of the aggradation red earth is hampered by the infrequent reporting of research on the weathering characteristics of the aggradation red earth at the spatial scale. Methods Based on a systematic analysis of the weathering characteristics of the aggradational red earth sections in southern China， this study focused on the Jinqu Basin， where non-zonal factors have a significant impact. The research primarily explored the chemical weathering characteristics and formation mechanisms of red earth within the basin， to deepen our understanding of the weathering features of aggradational red earth. Results （1） On a large scale， the weathering intensity of aggradational red earth in southern China is strongly correlated with hydrothermal conditions， with weathering intensifying as latitude decreases. However， the chemical weathering of red earth in certain locations or specific sections does not entirely conform to the latitudinal zonality in the mid-subtropical region between 25° N and 31° N， where aggradational red earth is widely spread. （2） The geochemical composition of aggradational red earth in the Jinqu Basin exhibits good consistency， with minimal differences in element enrichment or depletion among samples. However， there is regional variability in the degree of chemical weathering in the developmental stages of vermicular and typical red earth following the stagnation of vermicularization in the Jinqu Basin， compared with the chemical weathering characteristics of other aggradational red earth sections at the same latitude. （3） Influenced by a combination of factors such as provenance， topography， and local climate， the weathering characteristics of the aggradational red earth in the Jinqu Basin exhibit certain non-latitudinal zonal features. Conclusions The weathering characteristics of the aggradational red earth in southern China primarily follow a latitudinal zonal pattern under the large-scale monsoon evolution pattern. However， owing to the influence of non-zonal factors including topography， water， and differences in the geographic features of potential provenance， the chemical weathering of aggradational red earth also exhibits certain non-zonal characteristics within the mid-subtropical region between 25° N and 31° N. The relatively small and enclosed basin terrain of the Jinqu Basin， along with local microclimate conditions and contribution of bedrock weathering products to the red earth provenance， plays a significant role in interpreting the chemical weathering information of the red earth. Therefore， it is crucial to consider regional impacts while discussing the chemical weathering characteristics in different areas.