As one of the core dynamic mechanisms for the transport of fine-grained sediments in the deep-water environment of continental lacustrine basins,the meticulous characterization and genetic analysis of the sedimentary sequences of fine-grained turbidite deposits constitute a key entry point for revealing the shale oil accumulation mechanism and improving the classification system of shale oil types. Taking the Member 1 of the Upper Cretaceous Qingshankou Formation in the Changling sag of the Songliao Basin as the research object,a total of nine sedimentary units have been identified based on the data from three full-core drilling wells,and the Markov chain method was adopted to analyze the turbidite sedimentary sequences,which reveals the transition laws of turbidite events from initiation,high-energy transportation to terminal attenuation in the prodelta-semi-deep lake-deep lake sedimentary environments. Based on the actual geological data of the study area,the sedimentary characteristics of fine-grained turbidite currents in continental lacustrine basins were characterized,and a sedimentary sequence model for fine-grained turbidite deposits in continental lacustrine basins is established,among which the fine-grained turbidite deposits are composed of Units T₁ to T₇ that clearly reflect the high-energy to low-energy sedimentary evolution laws of turbidites. Synthesizing such parameters as lithologic assemblages,sedimentary structures and sand-to-shale ratio,a classification scheme for shale oil types in the study area is proposed. The characteristics of different shale oil types are significantly controlled by the fine-grained turbidite deposits: the interbedded type is governed by proximal turbidite deposits,with sandstone and siltstone interbeds providing high-quality reservoir spaces for shale oil;the laminated type is associated with distal turbidite deposits,dominated by high-frequency thin-bedded silty mudstones and shales and possessing favorable reservoir physical properties and brittleness;the massive type is related to the combined effects of terminal turbidite deposits and lacustrine still-water deposits in the lacustrine basin,with relatively poor reservoir physical properties and brittleness.

As a super basin,the Ordos Basin currently lacks a unified understanding of its Paleozoic-early Mesozoic tectono-sedimentary evolutionary stages and key basin prototypes. This study systematically examines the tectono-sedimentary evolution of the Hinggan-Mongolian and Qin-Qi orogenic belts,regional unconformities and distribution of Paleozoic formations within the basin,stratigraphic genesis and distribution of volcanic tuff events,and sedimentary filling characteristics from the Paleozoic to Middle Triassic. The tectono-sedimentary evolution of the Ordos Basin is divided into eight stages in this periods. During the Cambrian and Early-Middle Ordovician periods,three types of basin prototypes coexisted: passive continental margin subsidence along the southwestern margin,northwest margin graben,and intra-cratonic subsidence in the central-eastern region. The Late Ordovician had coexistence of two basin prototypes: post-arc rift along the southwestern margin and northwest margin graben. The Late Carboniferous-Early Permian witnessed coexistence of two basin prototypes: intra-cratonic subsidence and post-arc rift along the northwest margin. Following mid-Permian land-building movements, intra-cratonic subsidence and Baotou foreland basin developed during the Late Permian-Middle Triassic. Based on the development and distribution of basin prototypes from the Cambrian to Middle Triassic,their superimposed relationships,and the oil and gas geological conditions they control,combined with recent exploration progress,this study proposes that the Lower Paleozoic formations along the southern margin,sub-salt formations in the central-eastern region,Upper Ordovician shale oil and gas along the western margin,and multi-type natural gas in the Upper Paleozoic constitute the oil and gas succession zones of the Ordos super basin.

Marine red beds(MRBs)have attracted considerable attention due to their distinctive coloration,complex formation mechanisms,diverse sedimentary types,and valuable information regarding palaeo-oceanography,palaeoclimate,and even biological evolution. However,there are obvious bias in geological time and regional research and knowledge on MRBs,with particular focus concentrated on Precambrian,Early Paleozoic,Early Triassic,and Jurassic-Cretaceous MRBs. The late Silurian to Early Devonian represents a critical interval of global palaeogeographical reorganization,atmospheric compositional changes,and ecosystem transformation,yet MRBs from this period have received limited attention. Northern Xinjiang is one of the regions with relatively continuous late Silurian to Early Devonian strata in China. Based on previous research data,combined with our extensive regional investigations in recent years,newly acquired fossils dominated by conodonts,and sedimentary facies markers,this paper preliminary identifies the spatiotemporal distribution,lithological and biological assemblage characteristics of MRBs in the study area,and then makes comparisons with other contemporaneous MRBs in China. On this basis,the prospects for the study of MRBs in the late Silurian-Early Devonian are proposed. On the premise of establishing a high-precision biochronostratigraphical framework,a global database of MRBs at the late Silurian-Early Devonian is established to identify the distribution and characteristics of MRBs at this interval,and to carry out comprehensive comparison,then to explore the relationships between MRBs and important bio-environmental events in the period. It will contribute to a more comprehensive,systematic and in-depth understanding of the characteristics of the Earth’s multi-geosphere transformation and their coupling relationships during the late Silurian-Early Devonian.

For the problem of unclear evolutionary process of deep-water gravity flow deposition in the first member of Ordovician Lashizhong Formation in northwestern margin of Ordos Basin,the characteristics and evolution are studied on the basis of outcrop data,microscopic observation and grain size analysis,and finally the sedimentary modles are established. The results show that: (1)five lithofacies are developed in the study area,corresponding to horizontal bedding shale facies(F1),massive bedding calcirudite facies(F2),graded bedding fine sandstone facies(F3),parallel bedding fine sandstone to siltstone facies(F4)and small-scale cross-bedding siltstone facies(F5);(2)four deep-water depositional types are identified according to the shapes and stacking styles of sandstones: complex channels deposition,migrating channels depositon,proximal lobes deposition and distal lobes deposition;(3)complex channels,lobes,migrating channels and lobes are developed vertically in sequence;and(4)gravity flow deposition can be divided into two stages. In the first stage,the energy of gravity flow is high,forming the complex channel;With energy attenuation,small-scale lobes are developed. When in the second stage,the gravity flow erupts,which the energy is lower than the gravity flow in the first stage,and migrating channel is developed. As the energy of gravity flow continues to wane,deposition becomes dominant,resulting in a vertical transition form channels to lobes,with proximal lobes and distal lobes sequentially are developing in the depositional system. This study can improve the understanding of the sedimentary evolution law of gravity flow and is helpful to deep-water oil and gas exploration.

The frequently dynamic changes in the mixed fine-grained sedimentary environment of shale oil in saline lacustrine basins exert a decisive controlling influence on organic matter enrichment,source rock development,and the distribution of sweet spots. This study focuses on the Lucaogou Formation in the Jimusar sag,Junggar Basin and the Member 2 of Funing Formation in the Gaoyou sag,Subei Basin,both typical saline lacustrine basins. Through systematic integrated methods of petrology and organic-inorganic geochemistry,a comparative investigation was conducted from the perspective of lithofacies sedimentary genesis. The results indicate that there are significant differences in the lithofacies types and their sedimentary genesis between the Lucaogou Formation and the Member 2 of Funing Formation. The four main lithofacies types in the Lucaogou Formation developed in a relatively cold,arid,and saline water-mass environment. They are controlled by a composite model of “saline deep-water for preservation and less saline shallow-water with high productivity”. The mudstones exhibit high productivity and the best hydrocarbon generation potential,while carbonate rocks and siltstones represent high-quality sweet spots. The palaeoenvironment undergoes abrupt changes,resulting in the formation of the shale interbedded/intercalated with sand. In contrast,the Member 2 of the Funing Formation formed in a warm and humid climate,developed six main lithofacies types under a composite model of “saline shallow-water for preservation and less saline deep-water with high productivity”. The felsic-clay mixed shale and clay-bearing felsic shale,which exhibit the highest TOC content,developed in less saline deep-water environments. The combination of favorable preservation conditions and high productivity jointly enhances their superior hydrocarbon generation potential. Unlike the source-reservoir separated sweet spots in the Lucaogou Formation,the sedimentary facies in the Member 2 of Funing Formation exhibit gradual transitions,with various lithofacies possessing both hydrocarbon generation and reservoir capacities,forming a integrated source rock-reservoir,namely mixed shale type of sweet spots. This study emphasizes the differential palaeoenvironments of various lithofacies formed under the dynamic saline lacustrine basins,which is expected to provide scientific references for predicting and evaluating the distribution of sweet spots in shale oil exploration and development.

The formation of organic matter reflects the integrated physical,chemical,and biological responses to key global and regional geological events occurring across the lithosphere,hydrosphere,atmosphere,and biosphere. Organic-rich shales of Paleogene-Eocene age in terrestrial lake basins of eastern China are characterized by extensive lateral distribution,high total organic carbon(TOC)content,and considerable stratigraphic thickness—making them ideal archives for investigating the controls on organic-rich shale deposition under multi-sphere interactions. This study focuses on the Middle Eocene Shahejie Formation in the Jiyang Depression(Bohai Bay Basin)and integrates geochemical proxies—including TOC and total sulfur(TS)concentrations,organic carbon isotopic composition( {\delta }^{13} C_{org}),iron speciation,and pyrite sulfur isotopes( {\delta }^{34} S_{pyr})—with regional stratigraphic data from eastern China basins. Our findings indicate that TOC values in the Shahejie Formation range from 1 wt% to 10 wt%,with most samples exhibiting a TOC/TS ratio>2,a highly reactive iron to total iron ratio>0.38,and a pyrite iron(Fe_Py)to Fe_HR ratio<0.6. These geochemical signatures suggest that organic shale accumulation was primarily driven by elevated primary productivity under warm-humid paleoclimatic conditions,further modulated by co-occurring tectono-volcanic processes—including volcanic input,hydrothermal fluid influx,and episodic marine incursions. Comparative analysis across eastern China basins reveals that widespread Middle Eocene organic carbon burial was ultimately governed by deep-Earth-driven geological events that facilitated cross-sphere exchange of mass and energy. Although volcanic,hydrothermal,and marine inputs may have introduced additional sulfate,bacterial sulfate reduction efficiently depleted the sulfate reservoir,establishing ferruginous(anoxic,non-sulfidic)bottom-water conditions conducive to the preservation of organic matter.

To investigate the pore structure characteristics of the shale oil reservoir in the Jurassic Da’anzhai Member in Longgang area,northern Sichuan Basin,a systematic analysis of pore features and their controlling factors in the Da’anzhai shale was conducted using organic carbon analysis,field emission scanning electron microscopy(FE-SEM),X-ray diffraction(XRD),nitrogen adsorption,and nuclear magnetic resonance(NMR)experiments. The results indicate that: (1)The pore types in the Da’anzhai shale oil reservoir are dominated by clay mineral intercrystalline pores,followed by calcite intercrystalline pores,quartz intercrystalline pores,with minor organic matter pores and pyrite intercrystalline pores. (2)Clay content controls the pore volume and specific surface area of the shale,while organic matter content has minimal influence on porosity. (3)Calcite intercrystalline pores primarily contribute to larger pores but are limited in number and volume. Microscopically,these pores are mainly found within biogenic shells,with the shell edges being dense and non-porous. The low degree of asphalt filling and poor connectivity are notable. The development of calcite intercrystalline pores is controlled by shell recrystallization,with larger shells being more prone to recrystallization and forming intercrystalline porosity. (4)Authigenic quartz intercrystalline pores are distributed along shell edges,exhibiting better connectivity than calcite intercrystalline pores. These pores formed earlier than the hydrocarbon generation stage of organic matter and are often filled with hydrocarbons,contributing significantly to effective storage space. Their development is controlled by the degree of silicification of shells,with larger shells more susceptible to replacement,forming quartz intercrystalline pores. (5)The mixing of clay and shells results in a distinct “binary” structure in the reservoir space: clay-rich areas are characterized by pores with high specific surface area,small pore size,and good adsorption capacity,while shell-rich areas are dominated by pores with low specific surface area,large pore size,but limited connectivity.

Authigenic kaolinite is developed in the tight sandstone reservoirs at the bottom of Xu 4 Member in the Qiongxi-Baimamiao area of southwestern Sichuan Basin. To investigate its formation and preservation mechanisms and their relationship with high-quality reservoir distribution,we conducted a comprehensive study integrating petrophysical analysis,rock thin sections,scanning electron microscopy(SEM),fluid inclusion analysis,cathodoluminescence(CL),and in-situ micro-scale carbon-oxygen isotope analysis. This research focuses on analyzing the microcharacteristics,formation stages,formation and preservation mechanisms of authigenic kaolinite,and its impact on reservoir quality of the Xu 4 Member tight sandstones. The study reveals that the tight sandstone reservoirs of Xu 4 Member are predominantly composed of lithic sandstones,and the reservoir space is dominated by intragranular dissolution pores,with lithic intragranular dissolution pores being the most prevalent type. Authigenic kaolinite in the reservoirs predominantly exhibits “worm”and “accordion”shapes,filling intergranular pores and intragranular dissolution pores. The reservoir contains two distinct stages of authigenic kaolinite formation,both derived from the dissolution of aluminosilicate lithics and feldspars within the reservoir. The early-stage dissolution was facilitated by humic acids sourced from adjacent coal-bearing strata,while the late-stage dissolution resulted from organic acids generated through decarboxylation of mature organic matter in mudstones. The potassium feldspar content in the sandstone reservoir of the Xu 4 Member is relatively low,providing only a minimal amount of K⁺. When late-stage organic acids are charged,the formation temperature is relatively low. As diagenesis progresses,the organic acids are gradually consumed. Meanwhile,a significant amount of Fe²⁺ and Mg²⁺ from mudstone participate in the precipitation of ankerite and are thus depleted. Consequently,the concentrations of K⁺,Fe²⁺,and Mg²⁺ in the diagenetic fluids are insufficient to facilitate large-scale illitization and chloritization of authigenic kaolinite. The formation temperature and the organic acid concentration can not simultaneously meet the conditions necessary for the transformation of authigenic kaolinite to dickite. As a result,authigenic kaolinite has not been able to convert in significant quantities into illite,chlorite,and dickite,and has been preserved to this day. Therefore,sandstones formed under high-energy hydrodynamic conditions with coarser grain sizes and better sorting exhibit stronger dissolution,resulting in developed authigenic kaolinite and superior reservoir properties. Research indicates that the unique preservation mechanism of authigenic kaolinite in Xu 4 Member has partly maintained reservoir porosity and permeability. Moreover,authigenic kaolinite content can reflect the intensity of dissolution,further indicating the quality of reservoir properties. Consequently,kaolinite content can be used as a reliable marker for identifying high-quality tight sandstone reservoirs in Xu 4 Member of the Qiongxi-Baimamiao area,southwestern Sichuan Basin.

Submarine fans commonly accumulate on a large scale within continental slope minibasins,where their architectural evolution is predominantly governed by paleotopographic configuration. In settings influenced by dip-oriented synsedimentary normal faults,such minibasins frequently host laterally elongated fault-controlled troughs,which are associated with longitudinally distributed,multi-tiered slope breaks. Although these multi-step slope breaks exert first-order control on the spatial distribution,internal architecture,and stacking patterns of submarine fan reservoirs,the underlying geomorphic and dynamic mechanisms remain inadequately constrained. This study focuses on the Upper Jurassic B4 reservoir in the X Oilfield(North Sea,UK),integrating high-resolution well-log data and 3D seismic interpretation to reconstruct paleobathymetry and decipher reservoir-scale architectural heterogeneity. Our analysis reveals that the submarine fan developed within a structurally confined slope fault trough,characterized by: (i)a western primary upper slope with an average gradient of~7.5°;(ii)three distinct,longitudinally aligned deepwater slope breaks;(iii)a pronounced gradient differential of 6.3° across the primary slope break,contrasting with sub-3° differentials across the secondary and tertiary breaks. Critically,the longitudinal multi-step slope breaks dictate both planform architectural organization and temporal migration-stacking behavior of fan elements. Elevated sediment supply coupled with steep upper-slope gradients promotes high-velocity,supercritical turbidity currents(Froude numbers>1),resulting in proximal bypass dominance—wherein sediment largely bypasses the primary lower slope. The large gradient differential at the primary break enhances flow confinement and sand-body thickness through hydraulic jump-induced deposition. In contrast,reduced gradient differentials across downstream(secondary-tertiary)slope segments decelerate flows,fostering the development of multibranched avulsion channels,levee-channel complexes,and distributary lobes on the lower slopes. As successive lower-slope tiers become progressively filled and aggraded,lobe deposition preferentially shifts toward lower-tier slopes possessing greater accommodation space,producing retrogradational stacking geometries. Furthermore,enhanced lateral confinement—imposed by adjacent fault-bounded margins—deflects lobe progradation trajectories and modifies lobe morphology from classic lobate to elongate,tongue-shaped forms.

Slope microbasin is an important sedimentary site of deep-sea fan,which has huge oil and gas resources and research value,but the research of deep-water sedimentary system in microbasin is relatively weak. Therefore,this paper takes a mud diapir micro-basin in the continental slope area of Niger Delta basin in West Africa as the research object. Based on shallow 3D seismic data and RGB frequency division attribute fusion technology,this paper analyzes the structural characteristics of the deep-water sedimentary system in the microbasin,and reveals the relevant evolutionary control factors and formation process. The results show that the deep-water sedimentary system in the microbasin develops in the sequence of Mass-transport deposition,submarine channel deposition and submarine lobe deposition,in which the submarine lobe occupies the dominant position in the microbasin deposition. By using seismic section and plane RGB frequency division attribute analysis,the lobes developed in the microbasin were divided into two hierarchical orders: composite lobe and single lobe. At different stages,single lobe exhibits has two stack patterns in radial direction,which are progradation and retrogradation,and lateral migration in transverse direction. The distribution and stack patterns of these sedimentary units reflect the influence of the initial topography of the micro basin and the fluctuation of the early sedimentary bodies on the late sedimentary logistics. In addition,the evolution of the depositional system in the micro basin has mainly gone through four stages: the filling of the original topography by the initial sediments,the regulation and restriction of the topography and geomorphology on the sedimentary flow,the compensation and superposition of secondary lobes in different stages,and the channel erosion after the filling of the micro basin. The single lobe superimposed stack pattern in different stages and sedimentary evolution stages have a great impact on the physical properties and connectivity of deep-water lobe reservoirs. This study has a certain reference value for the efficient development of lobe reservoirs in micro basins.