The Ediacaran(Sinian) Doushantuo Formation in the central Guizhou Province represents a significant phosphorite metallogenic province hosting high-grade phosphate deposits in China. To elucidate the metallogenic geological conditions,deposit characteristics,and mineralization processes of the Doushantuo Formation phosphorites in the central Guizhou region, based on the principles of ore sedimentology and “Phosphate Factory”model,this study systematically investigates the phosphorite-bearing series through an integrated analysis of petrology,sedimentary facies and palaeogeography. Our research indicates that the primary phosphorites of the Doushantuo Formation in central Guizhou are dominated by intraclastic phosphorites(including sandy,gravelly,and silty intraclasts),with minor amounts of oolitic,peloidal,bioclastic,and stromatolitic phosphorites. The phosphorite ores are primarily characterized by phosphatic cement overgrowths and dolomitic cements in the pore,with subordinate clay matrix infillings. Secondary phosphorites include earthy to semi-earthy varieties,as well as brecciated and silicified phosphorites. Palaeogeographic studies reveal that the phosphorites mainly formed in an open beach environment along the northern and eastern margins of the central Guizhou Oldland,with localized development of stromatolitic phosphorites in tidal flat settings. The phosphorite horizons(Phosphorite-A and Phosphorite-B)are controlled by two transgressive-regressive cycles. The high-grade phosphorites in the Ediacaran(Sinian) Doushantuo Formation of central Guizhou underwent a three-stage mineralization process: initial phosphate precipitation,wave-winnowing concentration,and secondary leaching enrichment. Based on this framework,we propose an open-shoreline mineralization model for the Doushantuo phosphorites.

The first member of the Permian Maokou Formation in the Sichuan Basin,characterized by argillaceous carbonate rocks that exhibit both source and reservoir properties,making it a significant area for exploration. This study focuses on the development and characteristics of various pore types within these rocks. In this study,the qualitative and quantitative characterizations of pore types and their correlations and controlling factors were studied in detail. This was achieved through the measurement of porosity,X-ray diffraction analysis of whole-rock minerals,and total organic carbon(TOC)content analysis of 60 core samples from three wells in the southern Sichuan Basin. Additionally,qualitative observations were performed using argon ion polishing scanning electron microscopy on selected samples. Quantitative results indicate that samples from wells GS1 and JH1 are predominantly composed of organic-related pores,whereas samples from well TY1 exhibit substantial contributions from both clay mineral-related and organic-related pores. Statistical analysis reveals that when clay mineral content ranges between 15% and 50%,and TOC content exceeds 1%,the highest number of samples with porosity greater than 2% is observed. For marlstone with low clay mineral content(<10%),pore development is primarily controlled by TOC content and the degree of organic pore development. A clear positive correlation exists between porosity and TOC content,with a correlation coefficient as high as 0.87. As clay mineral content increases,the contribution of clay mineral-related pores to total porosity becomes more significant. Overall,the development of argillaceous carbonate reservoir space in the first member of the Maokou Formation is primarily influenced by clay mineral and TOC content. These findings have important implications for evaluating regional differences in reservoir development.

The Cambrian Longwangmiao Formation in the Gaoshti area of the Sichuan Basin is abundant in natural gas resources. However, studies on pore diversity among different beach bodies are still insufficient. Based on core observations and thin-section analysis,four distinct microfacies assemblages within the parasequences of the Longwangmiao Formation have been identified. These assemblages exhibit significant differences in diagenetic processes at various stages,particularly in the upper sections of each microfacies: (1)The sandstone shoal-oolitic shoal primarily develops intergranular dissolution pores due to meteoric freshwater dissolution,with porosity ranging from 2% to 6%.(2)The intershoal sea-sandstone shoal experiences both meteoric freshwater dissolution and dissolution during medium-deep burial stages, as well as extensive cementation,resulting in intergranular dissolution pores with porosity ranging from 1.5% to 5%.(3)The sandstone shoal-dolomite flat is influenced by meteoric freshwater dissolution,dissolution during medium-deep burial stages,and recrystallization,leading to the development of intergranular pores,intragranular dissolution pores,and intercrystalline dissolution pores with distinct pore size differentiation,exhibiting porosity ranging from 2% to 8%.(4)The medium-high energy sandstone shoal shows a strong correlation between burial dissolution intensity and late-stage cementation,resulting in intergranular dissolution pores with significant pore size variation,with porosity ranging from 1.4% to 5.8%. Therefore,the porosity of the four types of microfacies assemblages,ranked from highest to lowest,is as follows: sandstone shoal-dolomite flat (2%~8%),sandstone shoal-oolitic shoal (2%~6%),medium-high energy sandstone shoal (1.4%~5.8%),and intershoal sea-sandstone shoal (1.5%~5%). This study provides valuable insights into the types and evolutionary characteristics of secondary pores in rocks within the parasequences, which is crucial for evaluating the differences in various reservoir types.

Organic matter pores serve as the primary spaces for shale gas enrichment and accumulation,and their developmental characteristics are crucial for reservoir evaluation and selection. However,current research on the combinations,characteristics,and heterogeneity of mineral-organic matter pores remains relatively limited. This study focuses on the Longmaxi Formation and Wufeng Formation shales in the southern Sichuan Basin region,employing a suite of techniques including whole-rock X-ray diffraction analysis,argon ion polishing-scanning electron microscopy,electron micro-probe analysis,cathodoluminescence,and Image J image analysis. These methods are used to elucidate the relationships between minerals and organic matter,describe the structural characteristics of mineral-organic matter pore combinations,analyze the distribution patterns of these combinations across different lithofacies,and investigate the impact of their heterogeneous distribution on shale reservoir properties.The results reveal the following key findings: (1)Quartz,clay minerals,carbonate minerals,and pyrite exhibit multiple occurrence relationships with organic matter in shale,and a total of four categories comprising 12 types of mineral-organic matter pore combinations were identified;(2)The distribution of mineral-organic matter pore combinations varies among different lithofacies. Biogenic siliceous shale is predominantly characterized by quartz-organic matter pore combinations,with a relative content of 73.59%. Clay shale,feldspathic-calcareous siltstone,calcareous shale,and feldspathic siltstone are mainly dominated by clay mineral-organic matter pore combinations,with relative contents of 73.45%,55.45%,38.92%,and 53.66%,respectively. Calcareous siltstone is primarily characterized by carbonate mineral-organic matter pore combinations,with a relative content of 55.01%;(3)Organic matter encapsulated within quartz and clay minerals exhibits a flow structure,characterized by high organic matter content,large pore size,high porosity,and good pore connectivity. These pore types are the most favorable for reservoir development;(4)Biogenic siliceous shale is identified as the optimal shale gas reservoir,and its high gas content(3.53m³/t)aligns closely with the high relative abundance(33.71%)of favorable mineral-organic matter pore combinations. In conclusion,the distribution characteristics of mineral-organic matter pore combinations significantly influence the gas content of shale,and the relative content of favorable pore combinations is positively correlated with gas content. This finding holds substantial implications for the evaluation and selection of shale gas reservoirs.

To evaluate the shale oil exploration potential of the member 3 of the Paleogene Dongying Formation(Ed₃)in the Nanpu sag,this study investigates paleoclimate and paleoenvironmental variations and their impacts on organic matter accumulation through mineralogical and geochemical analyses of 21 shale samples. Results reveal strong heterogeneity in the Ed₃ shale,with TOC ranging from 0.30% to 2.66%,S₁+S₂ from 0.44 to 11.41mg/g,and HI from 57 to 466mg/g TOC,predominantly characterized by Type II kerogen at low to mature thermal maturity stages. Multiple geochemical proxies indicate that a semi-humid to semi-arid paleoclimate during the Ed₃ deposition influenced palaeoenvironmental fluctuations. From bottom to top,paleowater depth transitioned from shallow to deep and back to shallow,paleosalinity shifted from brackish to fresh and back to brackish,and redox conditions evolved from weakly oxidizing to weakly reducing and back to weakly oxidizing. These environmental fluctuations controlled differential organic matter accumulation. Under humid climates,high paleoproductivity and anoxic conditions in deeper waters promoted efficient organic matter burial and enrichment. Conversely,under arid climates,moderate paleoproductivity and oxic conditions in shallower waters resulted in lower organic matter burial and enrichment. The established model of organic-rich mudstone development provides a foundation for selecting favorable lacustrine shale oil exploration intervals.

The sedimentary environment and facies of the Cambrian Terreneuvian-Qiandongian Qiongzhusi Formation in central Yunnan Province are crucial for understanding the regional stratigraphic evolution. They hold significant implications for constraining the formation of phosphate deposits in the underlying Meishucun Formation,the development of shale gas reservoirs and preservation of the Chengjiang fauna within the Qiongzhusi Formation,and the recognition of depositional environments in the overlying Canglangpu Formation. This study focuses on analyzing sedimentary structures and paleocurrent patterns from the Erjie field profile in the Jinning area,central Yunnan Province,based on detailed field observations. The findings indicate that: (1)The Qiongzhusi Formation in the Jinning area exhibits characteristics of ponded turbidity current deposits,such as repeated Bouma sequences A,recurrent parallel beddings,and relatively thick mudstone caps. (2)Contourite are ubiquitous,associated with bidirectional and unidirectional cross-bedding as well as wave-ripple lamination. (3)Paleocurrent data reveal six dominant and subdominant orientations,forming three nearly opposite pairs: 50° vs. 213°,111° vs. 292°,and 171° vs. 341°;and(4)rose diagrams of paleocurrents from individual bidirectional cross-beds display marked asymmetry. Through comprehensive analysis of sedimentary environments,paleogeography,and interactions of sedimentary flows,it is suggested that the Qiongzhusi Formation was likely deposited in a deep-water ponded basin characterized by widespread contour current deposits,as well as internal-wave and internal-tidal deposits induced by deep-water contour currents.

The structural and sequential complexity and variability of microbialites result in multiple interpretations of their depositional environments. This study focuses on the 6th to 10th sub-members of the fifth member of the Ordovician Majiagou Formation(Ma5_6-10 sub-member)in the central-eastern Ordos Basin as an example. Based on systematic core and thin-section analyses,this paper presents a detailed characterization of microbialite sequences under varying sea-level conditions,aiming to reduce uncertainties in sedimentary environment interpretation. The results show that: (1)Three types of microbial carbonates,including stromatolites,thrombolites and microbial-bonded granular dolomite,are developed in the study area,forming two major categories and six types of microbialite sedimentary sequences. (2)During a fourth-order sea-level fall,interactions among the concavo-convex paleogeomorphologic pattern,gradual differentiation of seawater salinity,and energy control the formation of diverse microbialite sequences. These sequences exhibit complex lithologic correlations composed of four upward-shallowing fifth-order(meter-scale)cycles: lagoon-tidal flat,lagoon-microbial mound-tidal flat,lagoon-microbial mound and lagoon-microbial mound-evaporite evaporative lagoon/tidal flat. (3)Under a fourth-order sea-level rise,microbialite sequences and lithological assemblages are relatively simple,comprising two fifth-order cycles: microbial mound and intermound sea-microbial mound. The higher accommodation space during this phase contributes to the thicker single-cycle deposition. These findings reveal the construction patterns and controlling factors of microbialite sequences under varying sea level changes,providing a foundation for the subsequent inversion of different geomorphologic units and the sedimentary environmental evolution through the analysis of microbialite sequence structures.

The southern Fuxin Uplift Belt in the Songliao Basin hosts a shallow-water meandering river delta sedimentary system within the Fuyu oil layer,holding significant hydrocarbon exploration potential. This study establishes a high-resolution sequence stratigraphic framework for the Fuyu oil layer through integrated application of INPEFA technique and chromaticity indices,integrated with core descriptions,well logs,and petrological analyses. Sedimentary facies types were identified through petrological characteristics,sandbody genetic sequences,and well-log facies,enabling systematic analysis of spatiotemporal evolution patterns of deltaic sandbodies within the sequence framework. Results indicate that the Fuyu oil layer formed during a transgressive background with high-frequency base-level fluctuations,comprising four fourth-order sequences (medium-term cycles MSC1-MSC4) and 13 fifth-order sequences (short-term cycles SSC1-SSC13). SSC1-SSC6 exhibited regressive tendencies with high-frequency base-level oscillations,during which delta plain distributary channels evolved from high-sinuosity narrow ribbons to stable anastomosing networks,forming multi-phase vertically stacked channel complexes. SSC7-SSC12 transitioned to transgressive dominance,with delta plains gradually transforming into delta outer front environments where subaqueous distributary channels exhibited lateral accretion and isolated thin ribbons,accompanied by well-developed mouth bars. SSC13 returned to regression,characterized by continuously distributed subaqueous distributary channels and sheet sands. The study reveals that high-frequency base-level fluctuations controlled vertical evolution and planar distribution of shallow-water delta sandbodies. Multi-phase stacking of channel sandbodies driven by base-level oscillations,together with the high continuity and spatial connectivity of distributary channels,jointly governed the formation of thick,sand-rich reservoirs. This research provides novel geological insights for predicting hydrocarbon reservoirs in shallow-water meandering river deltas,offering practical guidance for exploration and development of the Fuyu oil layer in the Songliao Basin.

The black shale of the Wufeng and Longmaxi formations in the southern Sichuan region is a primary target for shale gas exploration. This study investigates the lithofacies characteristics,sedimentary environment evolution,and depositional processes of the Wufeng and Longmaxi formations shale using core and thin-section observations,2D XRF elemental scanning,scanning electron microscopy(SEM),micro-area QEMSCAN analysis,whole-rock XRD,and geochemical analysis. The results indicate the following: (1)Based on a multi-element lithofacies classification scheme that considers “TOC content-mineral content-genesis-sedimentary structure”,the Wufeng and Longmaxi formations shale is categorized into eight lithofacies types: high-TOC massive biosiliceous shale,extremely high-TOC thin-laminated biosiliceous shale,high-TOC very thin-laminated bio-detrital siliceous shale,medium-TOC laminated detrital siliceous shale,high-TOC laminated chemo-bio-calcareous-siliceous mixed shale,high-TOC very thin-laminated bio-detrital siliceous-argillaceous mixed shale,medium-TOC laminated detrital siliceous-argillaceous mixed shale,and medium-TOC laminated detrital ternary mixed shale. The lithofacies characteristics,vertical distribution,and spatial distribution of these lithofacies were thoroughly characterized. (2)The sedimentary environment evolved through five stages from bottom to top. The paleoclimate transitioned from warm and humid at the base of the Wufeng Formation to dry and hot in the middle,then to dry and cold at the top,followed by warm and humid in the lower Longmaxi Formation, leading to warm and wet conditions in the middle-upper Longmaxi Formation. Two large-scale marine transgressions occurred in the lower Wufeng Formation and the lower Longmaxi Formation,resulting in sea-level rise. During periods of high sea levels,the water body exhibited weak confinement,strong reducibility,low salinity,and high paleoproductivity. A glacial event at the top of the Wufeng Formation caused a drop in sea-level,leading to strong water confinement,weak reducibility,high salinity,and low paleoproductivity. (3)High-frequency changes in the sedimentary environment significantly influenced shale lithofacies development and organic matter enrichment. The organic matter content of different lithofacies shows a strong positive correlation with paleoproductivity and water reducibility. Extremely high-TOC thin-laminated biosiliceous shale and high-TOC very thin-laminated bio-detrital siliceous shale were predominantly deposited during periods of high paleoproductivity and strong water reducibility. These findings not only enhance the understanding of organic matter enrichment and shale sedimentation,but also provide a theoretical basis for predicting favorable layers for exploration and development in the southern Sichuan Basin in the future.

The Nanyang sag,a typical continental rift freshwater lake basin in eastern China,encompasses the Niusanmen sub-sag as its southeastern secondary sag,where thick-layered fine-grained sedimentary rocks developed within the Paleogene Hetaoyuan Formation. The Hetaoyuan Formation is stratigraphically divided into three members from top to bottom: Member 1(H₁),Member 2(H₂),and Member 3(H₃). Through integrated experimental analyses including thin-section petrography,scanning electron microscopy,mineral composition characterization,and geochemical parameter determination of core samples,this study systematically identifies lithofacies types of fine-grained sedimentary rocks,reconstructs the sedimentary environment of the Hetaoyuan Formation,and establishes four distinct evolutionary stages(A,B,C,D). The investigation provides critical insights into the depositional evolution and environmental dynamics of this lacustrine succession within the rift basin setting. The results indicate: (1)The depositional environment of the He Member 2 Submember Ⅲ to He Member 3 Submember Ⅰ was primarily semi-deep to deep lake,with overall low paleosalinity,exhibiting characteristics of freshwater to brackish water,and relatively stable climatic conditions indicative of a humid paleoclimate. (2)Based on mineral composition,sedimentary structures,and grain size characteristics,the fine-grained sedimentary rocks of the He Member 2 Submember Ⅲ to He Member 3 Submember Ⅰ can be classified into nine lithofacies,among which laminated mixed shale and laminated feldspathic shale are the most developed. (3)Terrestrial input and paleoproductivity have a significant impact on the vertical variation of lithofacies,with the content of dolomite primarily influenced by water salinity. Stable climatic conditions,deeper water environments,and abundant terrestrial input are conducive to the development of mixed laminated fine-grained sedimentary rocks. Spatially,the semi-deep to deep lake areas are mainly developed around the periphery of the central depression belt’s Niusanmen sub-depression,with mixed shale being the predominant lithofacies;vertically,mixed shale is developed in all stages,with stage A and stage C paleoenvironments being favorable for the enrichment of organic matter in source rocks,making them promising areas for shale oil exploration.

The Qaidam Basin,situated at the intersection of the Palaeo-Asian and Tethys-Himalaya tectonic domains,exhibits a unique basin-mountain structural pattern. Its well-developed Cenozoic strata preserve continuous sedimentary records spanning from the early Cenozoic to the Quaternary period. Late Pleistocene sediments comprise four lithofacies types: gravel,sand,clay,and evaporite layers. Gravel and sand layers dominate the basin’s margins(1 to 45m thick),while clay and evaporite layers(150 and 300m thick)prevail in the basin center. Based on lithological,biological,climatic,event,and age classification and correlation,the late Pleistocene strata are subdivided into five genetic sedimentary types: diluvial,alluvial,fluvial,lacustrine,and chemical deposition. Through comprehensive analysis of 56 boreholes and outcrop profiles,the late Pleistocene sedimentary facies of the Qaidam Basin have been thoroughly studied. The results indicate five distinct sedimentary facies types: alluvial fan,braided river,lacustrine delta,freshwater lake,and saline lake. Braided river facies are primarily distributed in areas such as Alar,Utumeiren,Dagele,Xialiha,and Huaitoutala. Similarly,significant changes in braided river or river delta facies are observed along the northern margin of the basin,while minimal changes occur along the southern margin. Triggered by the Gonghe Movement,the unified Qaidam paleolake disintegrated into multiple isolated small lake basins. In these isolated basins,such as Dalangtan,Chahan Slatu,Kunteyi,and Mahai,rapid brine concentration led to the deposition of shore-shallow saline lake subfacies. The Yiliping area also exhibits shore-shallow saline lake subfacies,whereas the main bodies of the Qarhan and Da Qaidam areas maintained freshwater and brackish lacustrine environments. Gahai Lake,Keluk Lake,and Tuosu Lake formed a unified freshwater lake system.

During the exploitation of deep coal resources,the North China Coalfield faces severe threats from karst water inrush disaster originating from the Lower Paleozoic aquifer. Investigating the development characteristics and evolution processes of karst in outcrops provides critical insights into mechanisms such as water storage,water conductivity,and water inrush during coal mining in karst regions covered by Quaternary unconsolidated deposits. This research also offers practical guidance for the prevention of karst water rush hazards. Taking the Shungeng Mountain area in Huainan-located at the southern margin of the North China Coalfield as the study area,this work systematically investigates the types and characteristics of Lower Paleozoic karst through field geological survey,geological profile survey,macro-and micro-structural analysis of karst breccias,and genetic evolution studies,all integrated with the region’s sedimentary and tectonic history. The results show that the Lower Paleozoic karst can be divided into three types based on development timing: sedimentary karst,epigenetic karst and modern karst. Sedimentary karst,characterized by syngenetic karst breccia,was formed during sedimentary discontinuities and was closely related to paleo-atmospheric precipitation,marine transgressions and regressions and dissolution. Epigenetic karst is marked by the interlayer karst breccia developed after diagenesis,and the karst breccia formed by Yanshan stretching movement. The interlayer palaeokarst was formed during the crustal uplift of the Early Ordovician,and was formed by the collapse and consolidation of the karst between the layers of strata due to long-term weathering-erosion and the action of groundwater flow. The tectonic breccia karst occurred in the Lower Paleozoic internal strata,due to the multi-stage tensile structure,which formed in the fracture zone,and was filled with the multi-stage crystallization of calcite,impregnated with iron. The modern karst is marked by the dissolved channel and karst collapse,which develops in the plane tension fissures,faults or intersection of both,and is caused by long-term atmospheric precipitation and infiltration,gravity collapse or subsurface erosion.

The distribution of the Asian drainage network has undergone a complex evolution due to the Cenozoic uplift of the Tibetan Plateau. As a critical transport channel located northwest of the South China Sea,the Red River plays a pivotal role in the source-to-sink sedimentary system of the South China Basin. Therefore,reconstructing its evolutionary history is essential for understanding regional paleogeographic patterns. In this study,detrital zircon U-Pb chronology was employed to analyze sediments from the Red River system. The results reveal six major age groups: Himalayan orogeny(30-40 Ma),Indosinian orogeny(240-260 Ma),Caledonian orogeny(440-460 Ma),Jinningian orogeny(750-1000 Ma),Lüliangian orogeny(1700-2000 Ma),and the Ancient Crust Growth Period(2300-3000 Ma). These findings indicate that the southwestern Yangtze Craton(Ailao Shan and Day Nui Con Voi Belts)and the northern IndoChina Block are the primary sources of the Red River sediments. Furthermore,it is proposed that during the Early Miocene,the modern Red River was initially a minor river in northern Vietnam. Subsequently,with the continuous uplift of the Yunnan-Guizhou Plateau in the southeastern part of the Tibetan Plateau,the Red River experienced headward erosion along the Ailao Shan-Red River strike-slip fault zone during the Neogene. By the Pleistocene,sediments transported by the modern Red River had covered the entire Yinggehai Basin.

The Greenland Interstadial 8(GIS-8)event during Marine Isotope Stage 3(MIS3)is characterized by significant warming at northern high latitudes. However,relatively few high-resolution geological records have been used to reveal its detailed structure and global response. In this study,nine high-precision ²³⁰Th ages and 442 oxygen isotope(δ¹⁸O)data were measured from a stalagmite(XY2-10) collected from Xianyun Cave in Fujian Province. These data enable us to reconstruct the evolution of the East Asian Summer Monsoon(EASM)intensity with an average temporal resolution of 5 years over the period of 38.20-36.10ka B.P.(Before Present,“Present”refers to 1950 AD),which covers the Chinese Interstadial 8(CIS-8)event. The δ¹⁸O time series exhibit a stable negative characteristic during the CIS-8 period,consistent with the trends observed in δ¹⁸O records from other stalagmites in the Chinese monsoon region,such as those from Hulu Cave,Yongxing Cave,and Xiaobailong Cave. However,the strengthening trend in summer monsoon intensity recorded by the stalagmite in Xianyun Cave during CIS-8 contrasts with the cooling trend evident in the Greenland ice core δ¹⁸O record. The analysis suggests that during CIS-8,enhanced cooling in Antarctica strengthened the Mascarene High and the transequatorial flow in the Southern Hemisphere,resulting in an overall stronger EASM in southern China, as reflected in the stalagmite δ¹⁸O records. Our sub-decadal resolution record also identifies 21 centennial- to interdecadal-scale summer monsoon enhancement events within the CIS-8 interval. These events correlate well with corresponding events in the Greenland NEEM(Northern Greenland Eemian Ice Drilling)ice-core δ¹⁸O record and the core albedo record from the Arabian Sea Basin. This correlation indicates that the EASM enhancement(weakening),warming(cooling)of northern high latitudes,and northward(southward)shift of the Intertropical Convergence Zone(ITCZ)are strongly linked on centennial- to interdecadal-scales. These connections are likely driven by rapid air-sea coupling mechanism,which is influenced by changes in the Atlantic Meridional Overturning Circulation(AMOC) in the North Atlantic.

The exploration and development potential of shale oil in the Jurassic Lianggaoshan Formation of the Sichuan Basin is enormous. Understanding the depositional and evolutionary patterns of mudstone has become increasingly urgent,and astronomical forcing is an important mechanism driving mudstone deposition and evolution. In this study,the natural Gamma Ray logging curve was selected as a proxy for paleoclimate,and a cyclostratigraphic analysis of the Lower Liang 2 Submember in the Fuxing area of the Sichuan Basin was conducted to establish a high-frequency sequence stratigraphic framework and explore the spatial and temporal distribution patterns of mudstone lithofacies within the sequence pattern. The following results were obtained: (1)Multiple astronomical cycles of 405ka,128ka,43ka,and 21ka were identified in the Lower Liang 2 Submember,corresponding to the fourth and fifth-order sequences. High and low-eccentricity cycles were used to achieve high-precision stratigraphic subdivision and correlation. (2)Combining the palaeoenvironmental parameters of elemental geochemistry with the trend analysis of Total Organic Carbon(TOC),we have demonstrated the close relationship between palaeoclimate,terrestrial input conditions,TOC,and astronomical cycles. This study has elucidated the significant control exerted by long-and short-eccentricity cycles on lithofacies development and their combinations. Eccentricity emerges as a crucial factor governing climate evolution and lithofacies spatial distribution. The Long Eccentricity is a key factor in controlling climate evolution,organic matter enrichment,and the spatial distribution of lithofacies,while the Short Eccentricity plays a role in local regulation. (3)Based on the astronomical response of lithofacies and lithofacies combinations,we have summarized the climate and sedimentary cyclicity patterns primarily controlled by Eccentricity. During periods of high Eccentricity,intensified insolation,precipitation,and river runoff lead to lake expansion,with deepwater laminated mudstone rich in organic matter forming in the basin center. Conversely,during periods of Low Eccentricity,the climate becomes arid,monsoons weaken,and weathering intensifies,resulting in severe river incision and the development of large-scale deltaic sand bodies on basin slopes. Turbidite sandstones mainly form in the downslope and deepwater areas. This research is of great significance for understanding the origin of organic-rich mudstones and predicting high-quality mudstone reservoirs.

This study focuses on the control of astronomical orbital forcing climate change on sea level and sedimentation rate during the Oligocene in the northern South China Sea,which in turn affects the generation and preservation of organic matter. Using natural gamma logging data from drilling Wells L9,C6,and Y9 in the study area,together with Palynology,foraminiferal,and organic matter data,cyclostratigraphic analyses are applied to reveal the control mechanism of astronomical orbital cycles on hydrocarbon source rock development. The 2.4Ma ultra-long eccentricity and 1.2Ma long obliquity cycles were identified in the northern part of the South China Sea. During high-eccentricity and high-obliquity phases,the climate was warm and humid,sea level was relatively high,biological productivity increased,and the depositional environment became more reducing,all of which favored the accumulation and preservation of organic matter. Under these conditions,the abundance of organic matter ranged from 1.5% to 4%,with amorphous organic matter content increasing by 14.2%. In contrast,during low-eccentricity and low-obliquity phases,the climate was cold and arid,sea level was low,biological productivity decreased,and the depositional environment became more oxidizing. In this case,the organic matter abundance ranged from 0.3% to 1.5%,with vitrinite-rich(coaly)components accounting for 66.4% to 95.1%. Furthermore,it was found that when the sedimentation rate was less than 9cm/ka,the organic matter abundance could reach~3.5%,whereas at rates greater than 12cm/ka,the abundance decreased to 0.3%~0.7%. On this basis,a depositional model for Oligocene marine hydrocarbon source rocks in the northern South China Sea under astronomical forcing was established,providing insights into the spatial and temporal distribution of high-quality source rocks and offering a scientific reference for future deep-time and deep-Earth hydrocarbon exploration.