The genetic type of siliceous minerals exerts differential controls on shale reservoir quality;however,current reservoir evaluation frameworks predominantly employ total quartz content as a proxy,neglecting the distinct reservoir effects associated with silica of different origins. This study systematically investigates the silica origin,genesis,and geological significance of Permian shales from the Wujiaping Formation Member 2(Wu-2 Member)and Maokou Formation Member 4(Mao-4 Member)in the Hongxing area,eastern Sichuan Basin,using an integrated approach combining scanning electron microscopy with energy-dispersive spectroscopy(SEM-EDS),X-ray diffraction(XRD),and major-trace element geochemistry. The key findings are as follows: (1)Both members contain detrital quartz and biogenic quartz-the latter encompassing structurally preserved(radiolarian fossils)and structurally recrystallized(microcrystalline quartz aggregates)varieties-while hydrothermal silica is absent. The Wu-2 Member is characterized by mixed detrital-biogenic silica(absolute detrital silica content: 21.7%;absolute biogenic silica content: 21.22%),whereas the Mao-4 Member is dominated by biogenic silica(absolute content 20.71%)with negligible detrital input(absolute content 3.34%).(2)Two contrasting silica enrichment models are proposed: a “superimposed enrichment model” for the Wu-2 Member,where deep-water shelf conditions sustained both substantial terrigenous supply and elevated bioproductivity;and a “carbonate dilution-controlled model” for the Mao-4 Member,where pervasive carbonate minerals accumulation overwhelmingly diluted siliceous components,passively elevating the relative proportion of biogenic silica.(3)Biogenic silica content serves as positive effects for evaluating organic matter enrichment,pore preservation,and reservoir fracability. Shifting the target window in the Hongxing area from carbon-rich,medium-silica lithofacies to carbon-rich,high-silica lithofacies increased daily test gas production from 11.67×10⁴ m³ to 26.64×10⁴ m³,demonstrating the pivotal role of biogenic silica content in engineering sweet-spot selection. A comprehensive evaluation framework integrating different genetic silica content and rock mechanical parameters is therefore recommended to guide precise layer selection and efficient development of Permian shale gas in the eastern Sichuan Basin.

The Early Cambrian sedimentary successions in northern and northwestern Sichuan Basin record critical information on the differential evolution of multiple provenance systems along the northwestern margin of the Yangtze Block. This study focuses on Lower Cambrian outcrop sections in the Guangyuan-Beichuan area(northwestern Sichuan)and the Nanjiang-Wangcang area(northern Sichuan). Through integrated sedimentological analyses including heavy mineral identification,lithic fragment composition statistics,cathodoluminescence (CL) imaging of detrital zircons,and palaeocurrent measurements,a systematic provenance tracing and palaeogeographic reconstruction were conducted. The results indicate that: (1)Three major source areas existed during the Early Cambrian in the study area—the Motianling,Pengguan,and Hannan provenances—which differ significantly in formation age,tectonic affinity,and parent rock lithology.(2)In northwestern Sichuan Basin,controlled by Palaeo-Tethyan subduction,the Motianling provenance continuously supplied felsic igneous and siliceous rock detritus,whereas the Pengguan provenance first emerged as a submarine high during the second member of the Qiongzhusi Formation and evolved into an exposed volcanic island arc by the Canglangpu stage,predominantly supplying mafic igneous(basaltic)detritus.(3)In northern Sichuan Basin,influenced by the Proto-Qinling Ocean,the Hannan provenance exhibited episodic evolution: during deposition of the Qiongzhusi Formation through the first member of the Canglangpu Formation(Xianfengdong Formation),it remained submerged and oolitic limestones developed in the northern Sichuan area;during the second member of the Canglangpu Formation(Yanwangbian Formation),it became subaerially exposed,forming alluvial fan-fan delta coarse clastic deposits.(4)By the late Canglangpu stage,all three source areas were exposed simultaneously,resulting in a palaeogeographic differentiation pattern characterized by sustained clastic infilling in northwestern Sichuan and a tripartite sedimentary response in northern Sichuan. This study provides new sedimentological evidence for multi-plate interactions along the northwestern margin of the Yangtze Block during the Early Cambrian.

The Qaidam Basin,on the northeastern margin of the Tibetan Plateau,preserves distinctive stratigraphic and sedimentary records of a complex basin-mountain system and multiple provenance sources. In the Dalangtan-Heibei sag of the northwestern basin,a thick Late Cenozoic gravel succession hosts a newly recognized gravel-type potash-bearing brine deposit. In this study,seven sandstone samples from different depths in boreholes CJ-2 and CJ-3 were analyzed for detrital zircon U-Pb geochronology,trace elements,and Lu-Hf isotopes. The detrital zircons are predominantly magmatic in origin,with Th/U ratios of 0.02-1.26 and REE patterns characterized by HREE enrichment,pronounced negative Eu anomalies,and positive Ce anomalies. U-Pb ages range from 213.9 to 3307 Ma and define four main age groups: 200-300 Ma,330-510 Ma,740-990 Ma,and 1.1-3.3 Ga. Provenance comparison shows that the Qigequan Formation in borehole CJ-2 was sourced mainly from the East Kunlun-Qimantagh,whereas that in borehole CJ-3 was influenced chiefly by the Altyn Tagh and the northern Qaidam margin. The Shizigou Formation shows stronger multi-source mixing: in borehole CJ-2 it records contributions from the East Kunlun-Qimantagh,northern Qaidam margin,South Qilian Mountains,and Altyn Tagh,whereas in borehole CJ-3 it was derived mainly from the East Kunlun-Qimantagh,with subordinate input from the Altyn Tagh and northern Qaidam margin. These inter-well provenance differences reflect the combined effects of lateral differentiation within the piedmont alluvial-proluvial fan system and intensified Late Cenozoic tectonic activity. The results can provide reliable age evidence for the rapid uplift of the Altun Mountains and the northern margin of the Tibetan Plateau,and offer new age constraints for exploring the gravel type potassium-bearing brine resources in the Dalangtan-Heibei sag of Qaidam Basin.

Coal-bearing tight sandstone reservoirs exhibit pronounced heterogeneity in lithologic associations,leading to substantial variability in reservoir quality. However,the diagenetic mechanisms governing this heterogeneity and the key geological controls on pore evolution remain inadequately constrained. This study focuses on the Lower-Middle Jurassic coal-bearing tight sandstone reservoirs in piedmont thrust belt of Southwestern Tarim Depression. Integrating core descriptions,thin-section petrographic analysis,and scanning electron microscopy(SEM)observations,we conducted a systematic comparative evaluation of reservoir characteristics across distinct lithologic associations. Based on coal seam distribution patterns and the architectural stacking of coal-sand-mud successions,three principal lithologic associations were delineated: Association A(braided delta plain),Association B(braided delta plain),and Association C(shore-shallow lacustrine to braided delta front). Diagenetic histories and pore-system attributes differ markedly among these associations. Association A experienced moderate mechanical compaction and pervasive early-stage calcite cementation sourced from primary depositional fluids;dissolution was limited,yielding a low total surface porosity of ~1.05%. In contrast,Associations B and C are strongly modulated by grain size,mud content,and critically humic acids leached from adjacent coal seams,resulting in intensified compaction. Late-stage ferroan dolomite and calcite cements in these associations correlate temporally and spatially with organic matter maturation. Moreover,organic acids generated during coal-measure hydrocarbon generation significantly enhanced the dissolution of feldspars and unstable volcanic lithic fragments,giving rise to well-developed intragranular dissolution pores and consistently higher total surface porosities(>2.0%). The palaeoenvironment of coal accumulation governs both the spatial configuration of coal seams and the lateral extent of lithologic associations. Associations A and B predominantly occur within the braided delta plain,where coal seams are thin and laterally discontinuous;Association C is confined to the shore-shallow lacustrine to braided delta front,characterized by moderately thick,laterally continuous coal seams. While initial depositional lithology and mineralogy exert foundational control on sandstone properties,the influence of coal seams on post-depositional diagenesis particularly through acid-driven inhibition of early carbonate cementation and promotion of feldspar/lithic dissolution during the mesodiagenetic stage is the dominant factor differentiating reservoir quality across associations.

The Zhujiang Formation(23-16 Ma) in Zhu Ⅲ Depression of Pearl River Mouth Basin developed during the rapid marine transgression in Early Miocene,documenting a critical depositional transition between the marine-continental transitional deposits of the Oligocene Zhuhai Formation and shallow-marine deposits of the Hanjiang Formation. However,sedimentary facies types,depositional evolution,and controlling factors during this transgression remain poorly constrained,limiting regional sedimentological interpretation and hydrocarbon exploration. This study integrates seismic,well-log,core,thin-section,and paleontological data to analyze sedimentary facies,depositional environments,and their controlling factors. Low foraminiferal abundance and diversity indicate a coastal sedimentary environment of the Member 2 of Zhujiang Formation,where as a gradual increase in abundance and diversity in the lower part of Member 1 reflects a shift to inner-shelf settings. Higher abundance and diversity of foraminifera in the upper part of Member 1 further indicate a transition to middle-outer shelf environments. Although water depth increased during the upper Member 1 deposition,strong sediment supply resulted in tidal-influenced deltaic systems prevailing in Member 2 and the lower part of Member 1. These deltas exhibit progradational patterns oriented from northwest to southeast,with distinct distributary-channel,mouth-bar,and interdistributary-bay microfacies. Abundant bioclasts and significant suspended mud indicate tidal rather than wave dominance,as wave dominated deposits typically show uniform grain size,good sorting,high rounding,and minimal mud content. Nevertheless,mouth bars exhibit evidence of both wave and tidal processes,highlighting complex hydrodynamic conditions. In the upper part of Member 1,depositional environment transitioned fully to middle-outer shelf settings characterized by tidal sand ridges and muddy shelf deposits dominated by silt and clay,reflecting significantly reduced sand input. The evolution of these sedimentary systems was primarily controlled by steadily rising sea levels,gradually decreasing sediment supply,and paleotopography,causing the depositional environment to shift from sand-rich deltaic systems to silt-and mud-dominated tidal sand-ridge and shelf-mud systems. Tidal sand ridges developed extensively but mainly occupied local paleotopographic highs. The findings provide insights into depositional evolution and controlling factors of the Zhujiang Formation around the Qionghai uplift,enhancing the understanding of sedimentary processes during rapid marine transgression.

As the most significant area for oil and gas exploration in the East China Sea Shelf Basin,the Xihu sag was characteried by a complex fault system during the Eocene. Investigating the “fault-sag”coupling process under multi-phase tectonic activity is crucial for palaeogeographic reconstruction and hydrocarbon exploration in this region. Based on high-resolution 3D seismic data,this study focuses on the characteristics of Eocene fault development in the western slope belt of the Xihu sag. It systematically analyzes the geometric patterns and activity history of the faults,and further investigates the “fault-sag”coupling process and its control on sedimentary systems. The results indicate that: (1)Controlled by basement structures,palaeo-uplifts,and the regional stress field,the Eocene fault system exhibits significant zonation and segmentation. The southern part of the western slope belt is characterized by single-fault and composite horst assemblages;the central part is dominated by various fault assemblages,including horst-graben and reverse fault terrace structures;while the northern part features homoclinal fault terraces and secondary horst-graben structures. (2)The Pinghu main fault,Hangzhou main fault,and Baoyunting-Wuyunting fault constitute the basin-controlling fault system. The intensity of fault activity peaked during the deposition of the lower Baoshi Member and gradually weakened throughout the depositional period of the Pinghu Formation. (3)The tectonic evolution of the basin was driven by variations in the subduction rate of the Pacific Plate. During the rifting stage,intense extensional tectonics formed a fault-controlled depositional framework,in which syn-sedimentary fault activity governed the migration and distribution of sedimentary centers. In the second rifting episode(Baoshi Formation depositional period),differential fault extension led to the development of multiple isolated sedimentary centers within the basin. During the fault-sag transition period(Pinghu Formation depositional period),the earlier palaeogeographic pattern of multiple uplifts and sags was transformed,as the isolated sedimentary centers merged and migrated southward. This study elucidates the dynamic response mechanism between faulting and sedimentation during the Eocene in the Xihu sag,providing a theoretical basis for further oil and gas exploration in the East China Sea Shelf Basin.

The study of source-to-sink systems plays a pivotal role in predicting sand-body distribution and lithologic trap configurations within rift basins. During the Paleogene,diverse palaeogeomorphological features developed along the eastern segment of the Shinan steep slope zone in the Bozhong sag—creating an ideal natural laboratory for investigating multiple source-to-sink system types. Nevertheless,research on temporal evolution of these systems remains limited,particularly due to the scarcity of quantitative analyses linking palaeogeomorphic architecture to sedimentary sand-body characteristics—a gap that significantly hinders the identification and prioritization of prospective exploration targets. Integrating 3D seismic data,core observations,and well-log interpretations,this study conducts a systematic characterization of Paleogene palaeogeomorphology and source-to-sink system architecture in the study area. We elucidate how sediment transport systems govern the spatial organization of depositional systems and establish stage-specific source-to-sink coupling models and palaeogeomorphology-controlled sediment dispersal frameworks. Our analysis identifies four principal sediment transport pathways: paleo-valleys,fault-controlled troughs,structural accommodation zones,and slope-break zones. Paleo-valleys are further classified into U-shaped,V-shaped,W-shaped,and composite morphologies;among these,U-shaped valleys exhibit the highest sediment transport efficiency,whereas V-and W-shaped variants demonstrate comparatively lower capacity. Fault-controlled troughs display asymmetric half-graben fill geometries,while structural accommodation zones develop in response to fault activity intensity—thereby regulating sediment entry points. Slope-break belts are subdivided into four categories: steep fault-terrace,gentle,fault-scarp,and intra-basin slope-break zones. A statistically robust positive correlation is observed between key palaeogeomorphic parameters—including catchment area of uplifted source regions,valley length,total valley distribution area,and valley count—and both the volume and lateral extent of associated sedimentary bodies. Finally,integrating transport distance from source and pathway type,we propose a two-tier(proximal vs. distal)classification scheme comprising five distinct subtypes,each supported by a corresponding source-to-sink coupling model.

The Triassic Yanchang Formation shale oil resources in the Ordos Basin hold significant development potential. Currently,horizontal well designs in the central lacustrine basin,established on the aggradational stratigraphic framework,are plagued by low sandstone encounter rates,creating a critical bottleneck for efficient development of shale oil. Taking the Longdong area of the Ordos Basin as an example,the internal subdivision scheme of the progradational strata was redefined using well logging and seismic data,establishing a unified isochronous progradational stratigraphic framework for the central lacustrine basin. Research has shown that under the combined influence of the collision between the Yangtze and North China blocks during the Indosinian Orogeny and the Carnian Pluvial Episode,the Yanchang Formation exhibits a three-layer architectural style characterized by aggradation-progradation-aggradation stratigraphic architecture. The original Chang 7 to Chang 3₂ members can be subdivided into 16 progradational sand groups,which prograde sequentially toward the central lacustrine basin. Among these,groups 1-3 exhibit sigmoid progradational filling patterns with low angle,groups 4-6 exhibit sigmoid progradational filling patterns with high angle,while groups 7-16 exhibit oblique-tangential progradational filling patterns. These research findings will provide crucial geological support for the deployment and design of horizontal wells in interbedded shale oil reservoirs in the central lacustrine basin area.

Based on field outcrops,microscopic observation and grain size analysis,this study investigates the sedimentary types,characteristics and evolution of the gravity flows in the Ordovician Yingtaogou Formation at the western margin of the Ordos Basin,and establishes a corresponding sedimentary model. The results show that: (1)Four deep-water sedimentary types are developed in the study area,namely debris flow deposits,high-density turbidity current deposits,low-density turbidity current deposits and deep-water autochthonous deposits. Debris flow deposits are mainly composed of calcirudite and develop massive bedding;high-density turbidity current deposits show inverse-to-normal grading sequence and develop Bouma-like sequence;low-density turbidity current deposits develop groove cast,flute mark and incomplete Bouma sequence;deep-water autochthonous deposits develop horizontal bedding.(2)Four types of gravity flow sedimentary microfacies are mainly developed in the study area,namely main channel deposits,channelized lobe deposits,sheet lobe deposits and distal lobe deposits. Main channel deposits are mainly debris flow deposits;channelized lobe deposits are composed of high-density turbidity current deposits superimposed on each other;sheet lobe deposits have high-density turbidity current deposits at the bottom and low-density turbidity current deposits at the top;distal lobe deposits mainly develop low-density turbidity current deposits.(3)The Yingtaogou Formation is divided into five evolutionary stages,from bottom to top: high sea level stage,low sea level stage,high sea level stage,low sea level stage and high sea level stage. In the high sea level stage,low-density turbidity currents and deep-water suspension deposits are mainly developed,while in the low sea level stage,debris flows,high-density turbidity currents and low-density turbidity currents are mainly developed.(4)The average porosity of sheet lobe deposits in the study area is about 6.61%,and the average permeability is about 6.02×10^-3 μm²,which is better than that of channelized lobe deposits and distal lobe deposits,and has good reservoir performance. The deep-water autochthonous deposits and sheet lobe deposits of the Yingtaogou Formation are superimposed,forming an ideal combination of source reservoir and covering rock with them. Therefore,the Ordovician gravity flow deposits at the western margin of the Ordos Basin are potential targets for the next oil and gas exploration.

Mianyang-Guang'an Trough in Sichuan Basin is an intra-platform depression developed within the Upper Yangtze Platform during the Late Permian to Early Triassic. This trough,with a water depth between fair-weather wave base and maximum storm wave base,transitions northward into slope facies. In Mianyang-Guang'an Trough,the Changxing Formation,deposited during the Late Permian,is characterized by numerous patch reefs/shoals with minimal dolomitization. By integrating petrographic analysis with Integrated Nonstationary Process Empirical Function Analysis(INPEFA),the Changxing Formation can be subdivided,in an ascending order,into the 1^st Member(SQ1-HST and SQ2-TST),lower part in the 2^nd Member(SQ2-HST),middle part in the 2^nd Member(SQ3),and upper part in the 2^nd Member(SQ4). The 1^st Member is mainly composed of micritic limestones intercalated with shales and mudstones,which constructed a ramp. The 2^nd Member,in contrast,is characterized by grainstones and framestones,which formed a rimmed platform. Mianyang-Guang'an Trough,which developed during the deposition of the 2^nd Member,comprises four subfacies,including shoals,reefs,inter-shoal zones and off-reef seafloor deposits. The shoals,which are commonly associated with HST in SQ2,SQ3 and SQ4,are mainly formed by skeletal grainstones,and characterized by low GR(29.3~34.6 API)and relatively low CNL values(13.3%~18.0%). The reefs,developed in the SQ4-TST,are formed of framestones and/or dolomitic framestones,and characterized by relatively low GR(34.0~37.3 API),and relatively high CNL values(19.0%~22.0%). The inter-shoal zones,developed in both HST and TST,consist of wackestones and packstones that are characterized by low CNL(9.9%~11.3%),low RT(33.1~37.3 Ω·m), low DEN(2.55~2.57 g/cm³),and low GR values(26.0~29.5 API). The off-reef seafloor deposits,which consist of intercalated micritic limestones,siltstones and mudstones,are commonly associated with the SQ2-HST,and characterized by serrated log curves. In terms of petrographic and stratigraphic characteristics,reefs and shoals developed in Mianyang-Guang'an Trough are comparable to those in the platform-interior facies,but distinct from those in the platform margins. The stratigraphic and sedimentary characteristics of the Changxing Formation in Mianyang-Guang'an Trough can provide a novel geological model for deciphering trough facies on the carbonate platforms,but also offer theoretical support for exploration in this region.