The Jiujialu Formation of the Lower Carboniferous in central Guizhou Province represents a significant bauxite-bearing stratigraphic unit in the region. This study aims to clarify the metallogenic geological setting and the dominant ore-forming processes of the bauxite deposits within the Jiujialu Formation in central Guizhou Province. Based on the theoretical framework of metallogenic sedimentology and supported by quantitative palaeogeographic reconstruction,the study employs an integrated approach combining petrology,sedimentology,and sedimentary geochemistry of the ore-bearing deposit to reconstruct the palaeoenvironment and explore the mechanisms of bauxite formation. The findings indicate that during the Early Carboniferous,central Guizhou Province was characterized by a nearshore karst peneplain depositional setting. The aluminous strata developed within a closed,karst-depression-controlled lacustrine-marsh wetland environment. The basal iron-rich section of the Jiujialu Formation represents Fe-enriched interval formed from relict slope deposits of ancient weathering crusts. The overlying clay-rich interval comprises dark clay rocks formed in transitional facies influenced by marine transgression or inundation. The middle aluminous section shows a regular vertical succession of lithofacies,including layered claystone,massive bauxite or bauxitic rock,pisolitic bauxite,clastic bauxite,and porous bauxite. This lithofacies assemblage reflects a metallogenic process combining both wetland sedimentation and subaerial leaching under subaerial exposure conditions. The deposition of Al-rich source rocks was followed by desiccation of the lacustrine-wetland system and the formation of a vadose leaching sequence under the influence of fluctuating groundwater levels. Based on these results,a metallogenic model for the bauxite deposits of the Jiujialu Formation in the Lower Carboniferous of central Guizhou Province is proposed.

The source-to-sink system(S2S)refers to the complete process of sediment erosion,transport,and deposition,in which sediments are generated from erosional landscapes,transported through routing systems,and ultimately deposited within depositional environments. Research on S2S not only advances our comprehensive understanding of Earth surface dynamics and their evolution,but also provides a geological basis and predictive models for identifying favorable sandbody distributions and guiding sedimentary mineral exploration and development. Based on a review of the history of S2S studies,this work highlights current research frontiers,including integrated perspectives on modern S2S systems,deep-time S2S systems and palaeogeographic reconstruction,characterization of S2S processes coupled with geomorphic-sedimentary evolution modeling,and applications of S2S theory in energy geology. Significant progress has been achieved in several aspects,such as classification of S2S systems and characterization of their main types,source-area attributes and sediment supply,sediment transport processes and signal propagation along routing systems,depositional processes(sandbody dispersal systems)and their controlling factors,quantitative characterization of S2S components(e.g.,the BQART model),and prediction of sandbody distribution. Finally,future research should place greater emphasis on the quantitative characterization of sediment transport and signal propagation of routing system,as well as predictive approaches for sandbody distribution.

Coal facies,referring to the sedimentary facies of coal,denote the original genetic type of coal,which is determined by the type of ancient peat swamp. After more than 70 years of development,coal facies research has achieved significant progress,with successive establishment of genetic parameters such as the Tissue Preservation Index(TPI),Gelification Index(GI),Groundwater Influence Index(GWI),and Vegetation Index(Ⅵ). Diessel classified coal facies types into dry forest swamp,wet forest swamp,marsh,and fen,using TPI-GI discrimination diagram. Chinese scholars have summarized the coal facies characteristics of major coal-accumulating periods in China: the Carboniferous-Permian coals in the North China coal-accumulating area are dominated by transition marsh-wet forest swamp facies;the Late Permian coals in the South China coal-accumulating area are mainly composed of transition marsh facies;the Early-Middle Jurassic coals in the Northwest China coal-accumulating area are characterized by the dominance of wet forest swamp-dry forest swamp facies;and the Early Cretaceous coals in the Northeast China coal-accumulating area are dominated by wet forest swamp facies. These characteristics reflect that significant differences exist in the types of coal-forming swamps,coal-forming plants,and paleoclimatic conditions across different coal-accumulating periods. With the discovery of unconventional resources such as deep coalbed methane and critical metals in coal-bearing series,the application of coal facies in the development of these resources has regained attention. Coal formed in different mires exhibit inherent differences in coal petrological and quality characteristics,and thus,the coal facies analysis can be applied to the evaluation of coal hydrocarbon generation potential,reservoir physical property analysis,and prediction of coal-associated resources. In recent years,with the deepening research on the sedimentary environment of coal-bearing series,mire evolution,and paleowildfire events,the rationality of using coal facies parameters such as TPI and GI as indicators for the sedimentary environment of coal-bearing series and coal has been questioned to a certain extent. The rationalization and standardized use of coal facies parameters urgently require discussion and resolution. For the sustainable development of coal facies research,future efforts should be focused on advancing the basic theories of coal facies analysis-especially the research on the genesis of macerals and modern peat mire environments and strengthening the application of coal facies analysis in practical production to better promote the utilization of mineral resources in coal-bearing series.

The global technically recoverable resources of shale oil are estimated at approximately 251.2 billion metric tons,derived from 157 organic-rich shale units across 116 basins. Internationally,shale oil exploration has largely focused on marine shale successions,whereas in China,lacustrine shales represent the primary target. The assessment of shale oil enrichment intervals is fundamentally governed by lithofacies palaeogeography. Lithofacies palaeogeographic reconstruction of lacustrine shale strata relies on quantitative datasets derived from outcrop,core,and geophysical analyses. Critical aspects of such reconstructions include considerations of temporal and spatial scales,single-factor analysis,and the application of conceptual depositional models. Recent progress in the study of shale laminae offers valuable single factors and diagnostic methods for interpreting depositional environments in palaeogeographic studies. Significant variations in reservoir properties and shale oil occurrence are observed among different lamina types. Consequently,palaeogeographic mapping based on lamina combinations and shale microfacies analysis represents an emerging research trend. Future research should aim to address the heterogeneous characteristics of lithofacies and organic matter distribution in lacustrine shale strata. Future studies should aim to resolve the heterogeneous distribution of lithofacies and organic matter in lacustrine shales,with priority given to: (1)delineating the spatial architecture of organic-rich shales within high-resolution chronostratigraphic frameworks,(2)characterizing mineral-organic composite structures,(3)establishing standardized microfacies classifications,and(4)developing depositional process simulations integrated with intelligent mapping techniques. An integrated approach combining modern sedimentological observations,sedimentary process simulations(both physical and numerical),organic petrology,and biomarker analysis is essential to reassess the sedimentary microfacies and organic enrichment mechanisms in lacustrine shale strata. This will facilitate the development of revised depositional models that accurately reflect the transport-deposition dynamics of fine-grained sediments,palaeotopographic constraints,and bioevolutionary context. By combining “inversion” and “forward modeling” methods and lever aging artificial intelligence technology,and incorporating key sweet-spot evaluation parameters,it is possible to quantitatively predict and intelligently map the spatiotemporal distribution of different lamina combinations. This methodology will allow for precise lithofacies palaeogeographic characterization of lacustrine shale strata and provide scientific guidance for the optimization of shale oil enrichment areas/layers.

The Earth’s evolutionary history has witnessed six major glaciations or glacial events,among which the earliest is believed to be the Pongola glaciation in South Africa,occurring approximately 2.9 billion years ago. A number of papers have been published on the last five major glaciations,yet understanding of the Pongola glacier remains limited. This raises key questions: did glaciation exist in the Archean,and how to identify it?By analyzing the characteristics of diamictites in the Mozaan Group(2.9 Ga)of the Pongola Supergroup in the Kaapvaal Craton,South Africa,this study summarizes the diagnostic markers of glacial deposits,and discusses whether the diamictites of the Archean Pongola Supergroup are glacial origin. Meanwhile,it aims to draw more attention from peers to the establishment and development of glacial sedimentology:a subdiscipline of event sedimentology in China. The Mesoarchean Pongola Supergroup is primarily distributed in the southeastern part of the Kaapvaal Craton and can be further divided into two groups: the Nsuze Group and the Mozaan Group. Petrological,sedimentological,and major/trace element geochemical analyses of the Mozaan Group diamictites support the interpretation of glacial origin. The Mozaan Group diamictites generally exhibit the following characteristics: (1)relatively thin thickness(<50 m);(2)massive mixed accumulation;(3)poor sorting and roundness of gravels;(4)gravels of varying particle sizes and compositions “floating” in a fine-grained matrix;(5)gravels with multiple sets of striations and polished surfaces;(6)quartz grains show elongation or deformation with silt-sized grains distributed around sandy grains in thin sections(referred to as a “nebular structure”);(7)dropstones developed in varves. Geochemical studies of elements reveal the following: the data points of Mozaan Group diamictites show a restricted distribution in the SiO₂/Al₂O₃ diagram,which is significantly different from the typical linear negative correlation observed in modern and ancient sediments that have undergone significant weathering and sorting;The distribution range of TiO₂/Al₂O₃ is also narrow,and the major element compositions are similar;The matrix of the diamictites is rich in total iron(Fe₂O₃(T))and shows a marked depletion of calcium(Ca)and sodium(Na). The mathematical inversion of measured δ¹⁸O and δ¹⁷O values in the diamictite and the underlying shale yields δ¹⁸O values of weathering water consistent with the isotopic characteristics of modern polar meteoric water,indicating cold climatic conditions. In addition,indicators such as the Chemical Index of Alteration(CIA)suggest that the Mozaan Group diamictites have barely experienced diagenetic alteration or chemical weathering,thus well representing the characteristics of their provenance. Therefore,the following glacial depositional model is proposed based on the above findings: during periods of low sea level,glaciers advanced along valleys toward the continental shelf. The till(glacial sediment)consisted of not only basal till,lateral till,and rock flour produced by glacial abrasion of the bedrock,but also rounded quartz grains mixed from shelf sands and fine-grained weathered materials derived from ferruginous mud. Some diamictites originated from the direct deposition of glacial sediments in periglacial zones and subsequent modification,characterized by a sharp contact between the diamictites and the underlying bedrock,with deformed layers present beneath parts of the diamictites. Another part of the thick diamictite layers,indicated by dropstones in the upper part,was transported by ice rafts to ice-distal glaciomarine environments.

The Eocene submarine fan channel system in the Rovuma Basin,East Africa,constitutes a significant case study for investigating the interaction between deep-water gravity flows and bottom currents. To address key scientific questions concerning the genetic types of individual channels and their distribution following differential reworking by bottom currents,this study systematically examines the genetic classification,spatial distribution,and mechanisms of bottom-current modification of single-channel systems in the lower Eocene strata of the region. Integrated analysis is based on core samples,well logging data,3D seismic datasets,and experimental results. The findings reveal the following: (1)The deep-water channel depositional system comprises four genetically distinct lithofacies—debris flow,turbidity current,bottom-current reworked,and hemipelagic drape deposits—which are further classified into 17 subtypes. Based on the relative abundance of gravity flow-related lithofacies,two primary types of single-channel systems are identified: debris flow-dominated fill channels and high-density turbidity current-dominated fill channels.(2)Debris flow-dominated fill channels are characterized by low width-to-depth ratios,sinuous geometries,and poorly developed levees. In contrast,high-density turbidity current-dominated fill channels exhibit straight to moderately sinuous morphologies,significantly higher width-to-depth ratios,and more pronounced levee development and thickness. Under the influence of bottom currents,both channel types display asymmetric cross-sectional profiles and lateral migration opposite to the direction of bottom-current flow. However,the high-density turbidity current-dominated channels exhibit greater asymmetry and more intense migration behavior.(3)Mechanistically,due to the high shear strength of debris flows,bottom-current reworking occurs primarily through “in-situ winnowing,” resulting in lenticular lithofacies containing internal traction structures. These channels show weak levee-channel asymmetry(average asymmetry index ≈1.35)and limited lateral migration(average migration index ≈0.65). Conversely,high-density turbidity currents,which possess lower shear strength,undergo “bulk reworking” of fine-grained suspended sediments by bottom currents. This process promotes the development of downcurrent-side lateral accretion deposits,leading to enhanced levee-channel asymmetry(average asymmetry index ≈2.5),increased confinement along the northern channel margins,and more pronounced migration against the bottom-current direction(average migration index ≈0.8). This study elucidates the differential response mechanisms of genetically distinct channel types to bottom-current interactions,offering critical insights for high-resolution characterization and targeted exploration of deep-water reservoirs.

The Triassic Lower Karamay Formation(T₂k₁)represents the primary target for petroleum exploration in the Xia 77 area,located on the northwest margin of Junggar Basin. Integrating data from drilling,core observations,well logging,and associated analytical experiments,this study applies fundamental principles of sedimentology to analyze the sedimentary facies architecture and evolutionary characteristics of the T₂k₁. The findings reveal the following: (1)The formation was deposited within a shallow-water fan delta system,which is subdivided into two main subfacies: the fan delta plain and the fan delta front. The fan delta front can be further classified into inner and outer front subfacies.(2)Within the fan delta plain,three gravity flow-dominated microfacies were identified: braided channels,floodplains,and debris flows. In the fan delta inner front,two traction flow-dominated microfacies are recognized—subaqueous distributary channels and subaqueous distributary bays. The fan delta outer front is characterized by three traction flow-induced microfacies: subaqueous distributary channels,subaqueous distributary bays,and mouth bars.(3)During the depositional period of the Lower Karamay Formation,the lake basin underwent a gradual deepening,transitioning from shallow to deeper water conditions. This hydrodynamic shift resulted in a regressive sedimentary sequence in response to overall lake transgression. Laterally,the progradational-to-retrogradational evolution of the system led to a northeastward backstepping of the fan delta plain,inner front,and outer front subfacies.

Following the discovery of the Anyue extra-large gas field in central Sichuan,significant exploration breakthroughs have been achieved in Member 2 of Dengying Formation in the Penglai area of northern Sichuan Basin in recent years. However,the exploration and development of this region remain constrained due to the complex microfacies types,considerable burial depth and strong heterogeneity of microbial mounds and shoals within the Dengying Formation. Based on core data from Well Wang-1C—a fully cored scientific exploration well located in northern Sichuan Basin—this study systematically investigates the microfacies types,sedimentary evolution,and reservoir characteristics of microbial mounds-bank complex in the Member 2 of Dengying Formation. The main findings are as follows: (1)Four primary dolomite lithofacies are identified in the Member 2 of Dengying Formation at Well Wang-1C: microbial dolomite,granular dolomite,crystalline dolomite,and dolomite breccia. Among these,laminated stromatolite dolomite,thrombolite dolomite,botryoidal dolomite,and mud-crystalline dolomite are the most developed. (2)Member 2 is predominantly composed of restricted platform deposits,with key microfacies including basal mound,core mound,mound crest,grain bank,and subtidal flat. (3)Three distinct microfacies assemblages can be recognized within the microbial mound-bank system: (Ⅰ)subtidal flat-basal mound-core mound,(Ⅱ)subtidal flat-grain dolomite bank,and(Ⅲ)subtidal flat-basal mound-core mound-grain dolomite bank. Each assemblage exhibits a substantial thickness,typically ranging from 25 to 50 m. (4)Reservoir spaces in the microbial mound-bank complex include primary pores and secondary dissolution pores. Reservoir development is primarily controlled by microfacies distribution,high-frequency sea-level fluctuations,and diagenetic processes. Notably,the microbial mound-core and mound-crest facies exhibit the most favorable reservoir properties,followed by granular shoal facies,whereas the subtidal flat facies displays the poorest physical characteristics. The above results can provide geological theoretical basis for the prediction of the distribution of ultra-deep microbial mound and flat reservoirs,and the exploration and development of natural gas in the northern Sichuan Basin.

During the Ordovician-Silurian transition,the southern Sichuan Basin experienced the superposition of global and regional geological events,resulting in the complexity of its underwater topography. This complexity led to the variation of the environment during the deposition period of the Longmaxi Formation shale in this area,which in turn controlled the development of shale lithofacies. This study takes the Longmaxi Formation shale in Changning area of southern Sichuan Basin as the research object. Based on drilling wells,seismic data and various analytical test data,the underwater topography and lithofacies development characteristics during the depositional period of the Longmaxi Formation in this area were studied. The results show that: (1)The underwater topography during the depositional period of the Longmaxi Formation in Changning area has a pattern of alternating high land and depression,which can be further divided into underwater high land,slope area and depression;(2)The lithofacies types of the Longmaxi Formation shale in Changning area are diverse and the reservoir differences are obvious. The shale lithofacies have obvious “storage and gas content control” characteristics. Among them,the mixed siliceous shale lithofacies(S-2)and the calcareous siliceous shale lithofacies(S-3)are the dominant lithofacies of the Longmaxi Formation shale in Changning area,which have the “three highs”(high TOC,high porosity and high total gas content)characteristics;(3)The underwater topography pattern has an obvious differential control effect on the development of shale lithofacies. The underwater high land is mainly occupied by mixed shale lithofacies association(M)and siliceous shale lithofacies association(S),the slope area is dominated by siliceous shale lithofacies association(S),and the depression is mainly composed of mixed shale lithofacies association(M)and siliceous shale lithofacies association(S). The mixed siliceous shale lithofacies(S-2),the best lithofacies with high TOC,high gas content and high porosity,is mainly distributed in the slope area and the area close to the underwater high land. This study is of great significance for revealing the distribution law of shale lithofacies and predicting the planar distribution of favorable shale lithofacies.

Recently,mixed sedimentation involving clastic,carbonate,and evaporite components has been identified at the base of the Majiagou Formation in the Ordos Basin,offering significant insights into the tectonic-palaeogeographic framework during its early depositional phase. This study systematically examines macroscopic and microscopic petrological features,along with representative depositional sequences,to reconstruct the depositional environment. Integrated geochemical analyses were conducted to investigate the genetic mechanisms,geological significance,and elemental behavior associated with this mixed sedimentary system. Key findings include: (1)The mixed sedimentary assemblage comprises three primary lithological components—clastic rocks,carbonate rocks,and anhydrite.(2)Sedimentary structures indicative of tidal flat environments,including scour surfaces,normal grading,transitional bedding,and brecciated anhydrite,were observed and used to define four subfacies: tidal-dominated channels(F1),muddy/arenaceous dolomitic flat(F2),gypsum-bearing dolomitic flat(F3),and supratidal sabkha(F4).(3)Geochemical data reveal distinct elemental partitioning during sedimentation,with vertical variations reflecting fluctuating terrestrial input driven by sea-level changes. Laterally,rare earth elements exhibit greater mobility compared to terrigenous elements,suggesting longer transport distances. The results indicate that the mixed sedimentation originated from reworking of sandstones derived from the exposed Changcheng System within the central Wushen Banner-Jingbian palaeouplift,triggered by marine transgression during the early stage of Majiagou deposition. This unit thus serves as critical evidence for the existence and persistence of the Wushen Banner-Jingbian palaeouplift during the O₁m₁ to O₁m₂ intervals,which played a critical role in facilitating regional uplift and ensuring sustained supply of terrigenous clastics throughout this period.

The Taiyuan Formation of Ordos Basin is a mixed depositional system of coal-bearing paralic facies developed under an epicontinental sea setting. Current inconsistencies in the understanding of its mixed depositional system,as well as unclear mixed characteristics and controlling factors,have constrained the exploration and evaluation of high-quality reservoirs such as tight limestones and tight sandstones. Based on systematic observations of cores,thin sections,and outcrops of the Taiyuan Formation in the eastern basin,combined with well logging and mud logging data,this study conducted an in-depth analysis of the cyclicity,lithofacies,and lithological characteristics of the Taiyuan Formation. Through a systematic examination of multiscale mixed depositional features and patterns,the main controlling factors and formation processes were clarified,and a mixed depositional model was established. The Taiyuan Formation in the study area constitutes a relatively complete third-order sequence,which can be subdivided into five fourth-order sequences,recording a relatively full transgressive-regressive cycle. The fourth-order sequences exhibit a binary structure of transgressive and highstand systems tracts. The transgressive systems tract is dominated by carbonate platform deposits,with local development of deltaic and barrier sandbar sand bodies,while the highstand systems tract is primarily composed of tidal flat and lagoon deposits. The Taiyuan Formation exhibits mixed deposition at three scales: Cyclic mixing at the macro-scale,primarily controlled by high-frequency sea-level fluctuations and their amplitudes,reflects the influence of temporal periodic changes on mixed stacking patterns;Contemporaneous heterotopic facies mixing at the meso-scale,governed by terrigenous clastic supply,carbonate productivity,and depositional topography,highlights the constraints of spatial environmental variations on the distribution of endogenic and exogenic sediments;and Component mixing at the micro-scale,mainly regulated by terrigenous clastic input,hydrodynamic conditions,and physicochemical factors,reflects the control on the distribution of mixed sedimentary components. The mixed deposition in the Taiyuan Formation is characterized by multiscale development,multi-factor synergy,and dynamic evolution of depositional environments.

Lacustrine deep-water gravity flow sedimentary sand bodies are the crucial targets for oil and gas development. Investigating the depositional characteristics of gravity flow sand bodies at the development scale can complement gravity flow depositional models and provide a basis for efficient exploitation of gravity flow reservoir. Based on cores,well logging and other data,this study examines the depositional characteristics,microfacies classification,and distribution of the Chang 7₁ gravity flow in Heshuinan area of the Ordos Basin at the development scale. We compare the reservoir characteristics between the different microfacies and summarizes the gravity flow depositional model. The results show the presence of six lithofacies types and six lithofacies combinations of the Chang 7₁,including Massive-bedded fine sandstone(Sm),Massive-bedded fine sandstone with mud pebbles and mudstone rip-up clasts(Smm),Normally graded-bedding fine sandstone(Sn),Parallel-bedded muddy siltstone(MSp),Lenticular-bedded silty mudstone(MSl),Massive-like mudstone(Mm). This study subdivides the unconfined channel area into four sedimentary microfacies: main channel,channel margin,overflow bank,mud faice of semi-deep to deep lake mud. The main channel is predominantly formed by sandy debris flow deposits,exhibiting good reservoir properties,mainly consisting of Sm-Mm(MSl)-Sm and Sm-Smm lithofacies combinations. The channel margin is mostly formed by the hybrid flow deposits,exhibiting moderate reservoir properties,primarily developing MSp-Sm and Sn-Sm(Smm)lithofacies combinations. The overflow bank is mainly formed by the turbidity current deposits,with the poorest reservoir properties,dominated by Sn-MSp and Sn-Mm(MSl)lithofacies combinations. The Chang 7₁ gravity flow in the Heshuinan area underwent three evolutionary stages: sandy debris flow,hybrid flow,turbidity current. The gentle topography and complex fluid evolution result in significant lateral facies variations perpendicular to the sediment source direction. During the same period,three main sedimentary facies developed: main channel,channel margin,and overflow bank. Gravity flow depositional characteristics,and sedimentary patterns are investigated in small-scale in this study,providing the theoretical guidance for effective exploitation of gravity flow hydrocarbon reservoir.

The Middle Jurassic black rock series in the Qiangtang Basin serve as significant hydrocarbon source rocks due to their high organic matter contents. The Biluo Co section was chosen as the research target. Based on paleontological stratigraphy and by analyzing the total organic carbon(TOC)contents as well as variations in carbon and oxygen isotopes,this study discussed the spatio-temporal distribution patterns of carbon and oxygen isotopes from the black rock series of the Bathonian-Callovian stages(Middle Jurassic),and the characteristics of the paleoenvironment and paleoclimate during this period. Results show that the TOC contents range from 0 to 1.5%,δ¹³C_org,δ¹³C_carb and δ¹⁸O values vary between-24‰ and-26‰,-4.819‰ and 2.323‰(mean values of-0.659‰),-13.96‰ and 0.66‰(mean values of-7.37‰),respectively. According to the global carbon isotope correlations,the negative inorganic carbon excursions in the early Bathonian is associated with the enhanced terrigenous input triggered by the Early-Middle Jurassic regression event. The positive shifts of δ¹³C_carb from the Middle-Late Bathonian to the Early Callovian correspond to the event of a substantial surge in marine primary productivity. During the Callovian-Early Oxfordian,a widespread positive carbon isotopes anomalies and high TOC contents of shales occurred in regions such as the Qiangtang Basin,Saudi Arabia,Paris Basin,and Polish Carpathians,which shows that the organic-rich black rock series are closely related to large-scale marine transgressions and primarily driven by the increase in the burial flux of organic matters under the backdrop of global sea-level rise. Moreover,paleontological and petrological characteristics,and redox-sensitive proxies(e.g.,V/(V+Ni),V/Cr,Ni/Co ratios) suggest that the black rock series deposited in a relatively reducing sedimentary environments. This study highlights that the carbon and oxygen isotopes of Middle Jurassic black rock series have the global distribution patterns influenced by multiple factors,including redox conditions,sea-level fluctuations, burial dynamics of organic matters, and so on.

A large-scale marine regression occurred during the depositional period of the Middle Jurassic Xiali Formation in the North Qiangtang Depression,accompanied by the widespread deposition of gypsum-bearing clastic sediments. Based on integrated petrological characteristics and elemental geochemical analyses of clastic rocks from the Xiali Formation in the Shenglihexi section and Well QK-1,we systematically analyzed the intensity of chemical weathering,provenance characteristics,and tectonic setting of these sediments,which is critical for understanding the evolutionary history and evaporite response of the Jurassic basin system. The results indicate that the Chemical Index of Alteration(CIA)values of these clastic rocks are significantly influenced by grain size and sediment sorting,but minimally affected by sedimentary recycling;thus,the CIA values of mudstone samples reflect the intensity of chemical weathering in the source region. Mudstones from the Xiali Formation in Well QK-1 exhibit considerable variation in CIA values(60-77),with negligible influence from potassium metasomatism,indicating that the source area underwent generally moderate to weak chemical weathering. In contrast,mudstones from the Shenglihexi section show significant effects of potassium metasomatism;after correction for this influence(CIAcorr),their values range from 80 to 85,suggesting intense chemical weathering in the corresponding source region. Discriminant diagrams based on La/Th vs. Hf,Co/Th vs. La/Sc,La/Yb vs. 􀰐REE,and A-CN-K plots,along with pronounced negative Eu anomalies,collectively indicate a predominantly felsic rock provenance for these clastic deposits. Clastic sediments from the western and central segments of the North Qiangtang Depression were deposited in a continental collision setting,whereas those from the eastern segment were formed in an arc-related tectonic environment. This interpretation aligns well with the established tectonic framework of the North Qiangtang Depression during the Middle Jurassic. During this period,the central and western regions functioned as a weakly magmatic intracontinental foreland basin,while the eastern region likely developed as a back-arc foreland basin,induced by southward subduction of the Bangonghu-Nujiang Tethys Ocean. Multiple transgressive-regressive cycles,combined with a relatively arid palaeoclimate and restricted paleogeographic conditions in the North Qiangtang Depression during the Early to Middle Jurassic,may have created favorable conditions for the formation of extensive gypsum-rich evaporites within the Xiali Formation.

During the Early Cambrian,organic-rich shales of the Liuchapo Formation and Niutitang Formation developed in northwestern Hunan,exhibiting good shale gas exploration potential. To address the issues of insufficient precision in Early Cambrian stratigraphic correlation and unclear mechanisms of carbon isotope evolution,this study systematically collected 133 carbonate rock samples from the drilling core of the Well Xiangzhangdi-1 (with a well depth of 2018.25 m and a core recovery rate of 98%). Analyses were conducted on the evolution trends of carbon and oxygen isotopes( {{\delta }^1}^3C, {{\delta }^1}^8O),as well as studies on shift events and stratigraphic correlation. Five negative {{\delta }^1}^3C anomalies(with amplitudes up to 12.1‰)and three positive anomaly events(with amplitudes approaching 9‰)were identified in the Early Cambrian slope facies area of northwestern Hunan,revealing their synchrony with global carbon cycle events such as BACE and ZHUCE. The results show that the Ediacaran-Cambrian boundary(BACE event)corresponds to the peak of negative {{\delta }^1}^3C shift(-9.8‰),consistent with records from Siberia,Morocco,and the South China platform facies. Positive shift events(ZHUCE,CARE)are coupled with intervals of high organic matter abundance(with TOC peak values reaching 10.5%),indicating that enhanced carbon burial driven by biological prosperity is the main controlling factor for positive {{\delta }^1}^3C shifts. This study establishes a carbon isotope stratigraphic framework for Early Cambrian boreholes in the South China slope facies,providing a chemostratigraphic basis for regional shale gas sweet spot prediction.

A massive Tertiary salt deposit containing 10 billion tons has been identified in the Huanggang buried sag of southwestern Shandong Province. This deposit is a rare super-large rock salt deposit in eastern China. To investigate the material sources and depositional environment of this salt formation,we conducted a comprehensive analysis of salt mineral assemblages,stratigraphic distributions,and 87Sr/86Sr isotopic compositions in halite and anhydrite from a 520-meter core(Borehole YZK-3)situated at the basin margin. Among the salt minerals,carbonate minerals mainly contained calcite,dolomite,ankerite and minor aragonite. Sulfate minerals contained anhydrite,with minor gypsum and celestite. Chloride minerals were composed of only halite. Based on their distribution and genesis,the paleolake evolution during the Middle-Late Eocene to Oligocene progressed through five distinct stages: freshwater→brackish→saline→brackish→freshwater lake systems. The⁸⁷Sr/⁸⁶Sr ratios measured in halite and anhydrite(0.711227-0.71177)significantly exceed contemporaneous seawater values. This isotopic disparity,combined with existing hydrothermal research data,demonstrates the absence of marine influences in the brine system.Substantial contributions from deep hydrothermal fluids mixed with meteoric waters was an important source of salt material.

The braided river delta sandbodies containing coal developed in the Lower Jurassic in the piedmont southwestern Tarim Basin,the overall exploration level is relatively low,with significant differences in the properties of source rocks and reservoir characteristics in different regions,which in turn restricts the oil and gas exploration process. This article takes the sandy reservoirs of the Lower Jurassic in the Fusha and Aketao regions as examples,and fully utilizes various rock and mineral testing and analysis methods to analyze the differences in the properties of the parent rock and reservoirs. The results show that the source rocks in the Fusha area are mainly Early Proterozoic metamorphic rocks. The reservoir exhibits characteristics of “poor feldspar and rich metamorphic rock debris”(Q_57.3F_4.8R_37.9),and the high content of plastic debris leads to strong burial compaction in the later stage,with a compaction reduction of up to 20.11%. Late cementation and dissolution were weak. The reservoir space is a small amount of residual primary pores,and the current porosity is only 8.98%. Aketao area is the Late Paleozoic-Triassic extrusive rock,and the reservoir exhibits the characteristics of “rich feldspar and extrusive rock debris”(Q_33.2F_17.5R_49.3). The Compaction is weak,and the early cementation is strong,The high content of soluble components and the influence of organic acids lead to strong dissolution,with a dissolution pore increase of 4.03%. The development of intergranular and intragranular dissolution pores improves the reservoir quality,and the current porosity is 12.95%. Comprehensive research suggests that the properties of the parent rock lead to differences in the petrological characteristics,diagenetic intensity,diagenetic evolution sequence,reservoir space types,and pore evolution processes of the Lower Jurassic sandstone reservoirs in the piedmont southwestern Tarim Basin. This study provides theoretical support for the prediction of high-quality sandstone reservoirs in the Jurassic period in the piedmont southwestern Tarim Basin.

In order to reveal the driving mechanism of sea level changes in the North China Basin in the low latitudes of the Late Carboniferous. Taking Benxi-Taiyuan Formations in Liujiang Coalfield of North China Basin as an example,the restoration of sea level change in low latitude area and its relationship with glacier cycle in high latitude area are studied. The results show that: (1)Three sedimentary systems of coastal plain river-lake,littoral zone and shallow sea are identified in the target strata of the study area. The changes of sedimentary environment record two secondorder transgression-regression cycles(Bashkir-Middle Moscow period and Late Moscow-Early Assel period)and four third-order transgression-regression cycles(Early Bashkir period,Middle Bashkir-Early Moscow period,Late Moscow period and Late Moscow-Assel period). (2)The highlatitude glacial and interglacial periods correspond to the second-order relative high sea level and low sea level periods in the study area,respectively,indicating that the high-latitude glacial cycle is the main controlling factor of the second-order sea level change in the late Carboniferous low-latitude North China Basin. (3)The coal-organic-rich mudstone and bauxite developed during the glacial period,indicating the falling sea level and temperature during the glacial period,which is conducive to the exposure of sedimentary interfaces,swamping,and the generation and preservation of organicmatter in the epicontinental sea basin. At the same time,the decline of sea level during the glacial period also caused the prevalence of dry-wet alternate flood plain environment. In this environment,terrigenous clastic sediments are reweathered and leached,which promotes the formation of bauxite mudstone or bauxite. This study deepens our understanding of the driving mechanism of sea level change and the accumulation of sedimentary minerals such as coal and bauxite in the late Carboniferous North China Basin.

To investigate the feasibility of compressed carbon dioxide(CO₂)energy storage in deep aquifers of the Hengyang Basin,this study focuses on the Honghuatao Formation sandstone reservoir within the Cretaceous paleo-desert aeolian sedimentary strata. By integrating petrological characterization experiments with site-scale numerical simulations,the carbon sequestration and energy storage potential of the reservoir were systematically evaluated. Petrographic thin-section analysis,scanning electron microscopy(SEM),and porosity-permeability tests reveal that the Honghuatao Formation sandstone is predominantly composed of medium-to fine-grained feldspathic quartz sandstone with pervasive calcareous cementation. The reservoir exhibits low porosity and permeability,characteristic of tight sandstone. The overlying mudstone caprock,with negligible porosity and stable regional distribution,forms an effective reservoir-seal combination.A three-dimensional numerical model of the compressed CO₂ energy storage system was established based on experimental data. Simulation results indicate that under a reservoir permeability of 15×10^-3 μm^-2,60-day cyclic injection-withdrawal operations induce pressure fluctuations≤0.5 MPa,with energy round-trip efficiency exceeding 99.98%. Additionally,low-temperature CO₂ injection triggers localized temperature reduction(up to 5 ℃),pore pressure accumulation(maximum 1.27 MPa),partial effective stress reduction,and significant vertical displacement in the reservoir. The study demonstrates that the Honghuatao Formation sandstone holds potential for CO₂ storage and energy storage. However,its low permeability limits injection-withdrawal capacity,necessitating acidification or hydraulic fracturing modifications to enhance pore-permeability properties for scalable applications. This research provides theoretical insights into the utilization of paleo-desert aeolian sandstone for subsurface energy storage and the advancement of low-carbon energy technologies.

The Permian Shanxi Formation in the Yan’an Gas Field of the Ordos Basin contains tight sandstone gas reservoirs within a shallow delta front. However,predicting sandbody distribution is challenging due to strong reservoir heterogeneity,large well spacing,and the signal-attenuating effects of the Quaternary loess plateau. As a result,the distribution patterns of effective gas-bearing reservoirs remain poorly understood. Using the S2³ submember of the Shanxi Formation in the Gaojiahe area of the central Yan’an Gas Field as a case study,this research proposes an intelligent sandbody prediction method based on an adaptive weighting strategy. This approach integrates the relationship between amplitude-frequency characteristics and tuned thickness into an attention mechanism,establishing an adaptive weighting framework for multi-band seismic attributes. The weighting strategy prioritizes high-frequency attributes for identifying thin layers and low-frequency attributes for thick layers,effectively addressing sandbody prediction challenges in the presence of low-quality seismic data. Compared with existing methods,the proposed approach yields the most accurate sandbody thickness predictions across various ratios of learning wells to blind wells. For example,in a test involving 45 learning wells and 63 blind wells,the correlation coefficient(R) between predicted and actual sandbody thickness reached 0.85. Prediction results indicate that the S2³ submember in the Gaojiahe area develops wide,banded sand bodies deposited in a shallow-water delta-front environment. Thick,coarse-grained sediments in the main distributary channels,along with the main body and inner edge of the mouth bar,are confined within the palaeo-geomorphological low of the main valley. Due to wave scouring,these intervals exhibit high quartz content and represent the principal effective gas reservoirs.

As the exploration and development of shale gas continue to deepen,the accurate and efficient division and prediction of lithofacies have become key factors in evaluating the quality of shale gas reservoirs. Traditional lithofacies logging identification methods are limited by their strong subjectivity,inability to handle large-scale datasets,and difficulty in effectively capturing the complex nonlinear relationships in the data. This study takes the Lower Cambrian Qiongzhusi Formation shale gas reservoir in the Sichuan Basin as an example. It utilizes precise data from rock core testing and logging curves to establish a lithofacies-labeled dataset. A novel ensemble learning(Voting)model is proposed,integrating traditional machine learning models(Decision Tree,Support Vector Machine(SVM),and K-Nearest Neighbors(KNN))and a deep learning model(1D Convolutional Neural Network,1D-CNN)for lithofacies classification and prediction. The study also compares the predictive performance of traditional machine learning and deep learning models with that of the ensemble learning model,assessing its application potential in complex shale lithofacies prediction. The results indicate that the ensemble learning(Voting)model achieves the highest lithofacies prediction accuracy of 94.0%,significantly outperforming individual base learners(Decision Tree,KNN,SVM,and 1D-CNN). The proposed ensemble learning method effectively overcomes the recognition bias caused by sample imbalance in traditional classification algorithms by leveraging the strengths of the four base learner models. This improvement enhances the ability to identify lithofacies with limited samples,providing technical support for the high-precision reconstruction of logging-based lithofacies profiles and sweet spot prediction in the deeply buried,over-mature Qiongzhusi Formation shale gas reservoirs in the Sichuan Basin.

In recent years,machine learning has shown significant advantages in reservoir parameter evaluation based on well logs. However,due to the limited size of core samples,the generalization ability of these models is often not guaranteed. In this study,more than 100 sets of high-pressure mercury injection data and seven types of well logs were collected from the Triassic Yanchang Formation in the Jiyuan area of the Ordos Basin. The study systematically compares the performance of TabPFN and seven other common machine learning methods under small data conditions. The SHAP interpretability analysis is also used to understand the model’s decision-making mechanisms. The results show: (1)The average permeability of the Yanchang Formation sandstone reservoir in the study area is 0.39×10^-3 μm²,which is typical of low- to ultra-low permeability reservoirs. These reservoirs have small pore throat radii and complex pore structures. The first principal component explains 65.00% of the total variance of the pore structure parameters. Combined with production data and mechanism analysis,it is considered an appropriate target variable for characterizing pore structure. (2)The TabPFN model performs excellently in small-data environments,achieving R² values of 0.81 and 0.87 in the validation and blind well test sets,respectively. Its high performance without parameter tuning demonstrates its outstanding applicability. (3)According to feature importance ranking,density log,sedimentary facies,acoustic log,geological layering,and deep resistivity are the top five features. Sedimentary facies and geological layering make greater contributions in extreme pore structure intervals,highlighting the critical role of discrete geological variables in improving model performance. This study provides an effective data-driven case for characterizing the pore structure of low-permeability sandstone reservoirs under small data conditions.

The sepiolite-containing succession in the Member 1 of the Middle Permian Maokou Formation in the Sichuan Basin exhibit self-generation and self-accumulation characteristics,positioning them as a promising new frontier for the exploration of unconventional gas reservoirs. However,the identification and predictive distribution of these strata are still underdeveloped. This study utilizes core samples,thin sections,X-ray diffraction(XRD)analysis,well logging,and mud logging data,performing sensitivity analysis to select six key well log curves: CNL,DEN,GR,RT,RXO,and AC. The SMOTE algorithm is employed to address feature imbalance. The workflow for predicting sepiolite-containing succession based on multi-gradient boosting algorithms is as follows: (1)The CatBoost algorithm is used for binary classification to determine the presence of sepiolite;(2)CatBoost performs multi-class classification to categorize the morphology of sepiolite-containing succession;(3)XGBoost is applied for regression analysis to predict the talc content in the sepiolite-containing succession;(4)The effective thickness of sepiolite-containing succession is identified based on talc content. The sepiolite-containing succession in the Member 1 of Maokou Formation primarily exhibit three morphologies: spotty,lenticular,and layered. Prediction results indicate that spotty talc is mainly developed in the northern and central southern regions of Sichuan Basin,with thickness increasing toward the northeast;lenticular talc is predominantly distributed in the western Sichuan region;and layered talc is mainly found in north western,central and southern Sichuan Basin. Overall,the sepiolite-containing succession in the Member 1 of Maokou Formation show a distribution pattern of‘thicker in the northeast,thinner in the southwest.’The Tongjiang-Changshou intracratonic sag area and the Hechuan-Weiyuan-Luzhou region serve as the sedimentary centers for the effective thickness of sepiolite-containing succession,providing a basis for future exploration and deployment in these areas.

This research uses the basic end-member modeling algorithm,non-parametric estimation decomposition algorithm,and grain size-standard deviation method to evaluate the grain-size data of the Holocene sediments from core SE3 in the Hangzhou Bay area,in order to investigate the vertical distribution pattern of different grain-size end-members and their coupling relationship with environmental evolution. Results show that the basic end-member modeling algorithm acts as the best method in decomposing grain-size end-member in comparison with the other two methods. Five grain-size end-members were identified in the study area by the basic end-member modeling algorithm: EM1(clay and silt),EM2(coarse silt and very coarse silt),EM3(very coarse silt,very fine sand and fine sand),EM4(fine sand and medium sand)and EM5(medium sand and coarse sand). Their vertical distribution patterns are controlled by the evolution of sea level,depositional environment,and dynamic process. The coarse-grained end-members EM5 and EM4,representing bed load,are primarily supplied by the Qiantang River and distributed in the amalgamated fluvial channel,floodplain,and paleo-estuarine deposits. As sea levels rising,the content of proximal EM5 decreases upwards,while the content of relatively distal EM4 increases. The fine-grained end-members EM2 and EM1,representing suspended load,are distributed in the offshore shallow marine and present-day estuary stratigraphic units;they are mainly derived from the Changjiang by a combination of alongshore and tidal currents in a high sea-level setting. EM3,representing bed load with a normal distribution of grain size,is primarily distributed in the present-day estuary deposits,and probably represents the sediment transported and sorted by tidal currents and storm surges. This study sheds a new light in reconstructing the evolution history of sea level,environment,and source-to-sink processes in estuarine areas by using sensitive grain-size end-member algorithm analysis.

The Taohe River Basin is a key origin of prehistoric cultures in western China,with a clearly defined cultural evolution trajectory,making it an ideal area for studying prehistoric human activities. Based on a comprehensive collection of archaeological site data,this study uses methods such as site analysis,tomb excavations,and grid reconstruction models to reconstruct the settlement patterns,populations,and cultivated lands during five cultural phases in the basin: Yangshao,Majiayao,Qijia,Xindian,and Siwa. The analysis indicates: (1)Prehistoric settlements in this region expanded from the source of the Wei River to the Taohe River Basin,reaching their peak during the Majiayao and Qijia cultures(5.4~3.6 ka BP),and then gradually contracted and diversified after 3.4 ka BP,with corresponding changes in population and cultivated land. (2)The changes in prehistoric cultivated land in this region were significantly influenced by climatic changes. During the Yangshao to Qijia cultural period,he climate was relatively warm and moist,fostering agricultural development,which led to an increase in settlements and population. After 3.6 ka BP,as the climate shifted to cooler and drier conditions,production modes diversified;the lower-altitude northern areas continued to focus on agriculture,while the higher-altitude southern areas developed a mixed farming-pastoral economy.