Palaeogeographic units on the Earth’s surface exhibit a hierarchical structure,however,their connotations,research significance,reconstruction scales,and methodologies remain unclear,hindering the coordinated development of palaeogeography. Each palaeogeographic unit is a palaeogeographic unit with specific climatic,hydrological,and ecological characteristics. Based on the relative size and formation of landforms,palaeogeographic units are divided into three levels: large,medium,and small,correspondingly classifying palaeogeographic research scales into three levels. Large-scale palaeogeographic research investigates the spatiotemporal distribution and multi-sphere interactions of large-scale palaeogeographic units(oceans,continents,and large-scale geomorphic undulations within them)over millions to tens of millions of years. This research is conducted globally and across tectonic plates(or basins),aiming to predict habitable Earth and prospective areas for mineral resources. Medium-scale palaeogeographic research focuses on the characteristics,distribution,evolution,and associated surface processes of medium-scale palaeogeographic units(geomorphic units between large-scale geomorphic undulations and sub-environments)within a large geomorphic unit(such as a basin). It operates on timescales of hundreds of thousands of years and serves to predict habitable region and guide mineral resource exploration. Small-scale palaeogeographic research examines the characteristics,distribution,changes,and corresponding small-scale surface processes of sub-/micro-environments within a sedimentary system. This research covers timescales of tens to hundreds of thousands of years and aims to predict human habitable locality and to evaluate and develop mineral resources. Future palaeogeography should further develop multi-information quantitative interpretation methods for multi-scale palaeogeographic parameters,innovate intelligent reconstruction technologies of multi-scale palaeogeography,deepen the understanding of the formation mechanisms across different scales,establish models that explain how palaeogeography controls mineral resource distribution at various scales,and enhance collaborative research on multi-scale palaeogeography.

The transitional zone between land and sea is an area where rivers,waves and tides act together,and the interwoven hydrodynamic forces shape the sand body morphology and palaeogeographic pattern. This paper takes the Main-M1 member and LU sub-member of the oil and gas-rich Napo Formation in the Oriente Basin of Ecuador as an example. By using core,logging and mud logging data,the sequence framework is established. Provenance was constrained using heavy-mineral assemblages and detrital zircon U-Pb geochronology,while pre-depositional palaeogeomorphology was restored using residual-thickness and imprint methods. The study shows that the Napo Formation can be divided into one second-order sequence and five third-order sequences. The Main-M1 member and LU sub-member are both in the lowstand systems tract of their respective third-order sequences. The provenance mainly comes from the eastern and southeastern Amazon Craton,and the palaeogeomorphology is generally a single inclined slope with the east high and the west low. The LU sub-member is an intertidal delta system controlled by rivers and tides as a whole,with a delta plain in the east and a delta front in the west. The Main-M1 member has evolved into a mixed system of east tidal delta,west wave-controlled shallow marine shelf and coastal current interwoven transformation. The Napo Formation records the evolution process from the river-tide inter-control to the river-wave-tide ternary mixed system,indicating that under the constraints of tectonic subsidence and provenance conditions,the interwoven hydrodynamic forces are the key factors controlling the distribution of sand bodies and palaeogeographic patterns in the transitional zone between land and sea in the foreland basin. This has reference significance for the palaeogeographic restoration of similar transitional zones between land and sea in foreland basins.

The classification of microbialites constitutes a fundamental basis for investigating their origin and distribution. Owing to ambiguities in the definition of microbialites,these rocks are,in essence,predominantly bacterial in origin. Consequently,the term “bacterialite” is considered more precise than “microbialite” when referring to sedimentary rocks formed through bacterial activity. Bacterialites may be recognized as an independent category within the conventional classification of carbonate rocks,positioned alongside reef carbonates. Based on mineral composition,bacterialites can be divided into seven primary types: bacterial carbonates,siliceous,ferrous,phosphate,saline,bauxitic,and clastic bacterialites,each of which allows for further subdivision. Taking bacterial limestones as a representative example,they are classified according to macrostructural features into thrombolites,stromatolites,coatites,and leiolites. Thrombolites are subdivided into framework-bearing and non-framework types. Framework thrombolites can be further categorized into sparry,micritic-sparry,and micritic types,reflecting a progressive decrease in hydrodynamic energy and a corresponding increase in water depth from sparry to micritic forms. Stromatolites are classified based on lamination clarity into lamination-clear and lamination-obscure types;the former typically form in intertidal to supratidal(subaerial)environments,while the latter occur in subtidal(subaqueous)settings. Additionally,stromatolites are categorized morphologically into columnar,wavy,planar laminar,domal,conical,and wall-like forms,with each morphotype further differentiated by size. Coatites are similarly classified according to the distinctness of concentric lamination into lamination-clear and lamination-obscure types,which correspond to intertidal and subtidal depositional environments,respectively. They may also be subdivided based on size into oncolites and bacterial oolites. Leiolites are classified into microcrystalline and granular varieties. This classification system presents several innovative aspects: (1)mineral composition is introduced as the principal criterion for defining major bacterialite categories;(2)the nomenclature is revised by replacing “microbialite” with the more accurate term “bacterialite”;(3)the texture-based classification of framework thrombolites provides enhanced environmental interpretation;(4)stromatolites are classified both by lamination clarity—indicative of depositional conditions—and by morphology and size;(5)coatites are systematically categorized according to the degree of concentric lamination,which serves as an environmental indicator;and(6)a formal classification of leiolites is proposed,accompanied by clearly defined diagnostic criteria.

This study focuses on sandstone “concretions” in the Cretaceous Qingshuihe Formation at the Hongshanhu Section. It systematically investigates the lithological characteristics of concretion-bearing strata,as well as the external morphology,internal structure,material composition,formation environment and genesis of the concretions. The Cretaceous Qingshuihe Formation at the Hongshanhu Section mainly develops a set of shallow-water delta facies sandstones with large-scale cross-bedding. Spherical,hemispherical,ellipsoidal,and other shaped sandstone “concretions” are widely distributed in the bottom sandstones of distributary channels of different stages. Currently,there are three viewpoints on the genesis of these concretions: (1)spherical weathering genesis;(2)diagenetic genesis;(3)intraclast genesis. To clarify their genesis,this paper systematically studies the macro occurrence,microtexture,material composition of the concretions,and their genetic relationship with host sandstones through field geological section measurement and petrographic thin section observation. The results show that the concretions are not intraclasts,but products of “concretionary” diagenetic cementation of sandstones during the syngenetic-diagenetic stage,followed by differential weathering after uplift to the surface. Carbonized plant detritus is commonly developed in the center of the “concretions”,with ferruginous calcite and calcite cement zonations sequentially formed outward around the plant detritus. The bedding structure of the “concretions” is consistent with that of the host sandstones without later tectonic disturbance. Due to dense cementation,the sandstone “concretions” have significantly stronger weathering resistance than the surrounding uncemented or weakly cemented sandstones,presenting spherical,hemispherical,ellipsoidal,and other irregular shapes after epigenetic weathering. Combined with the analysis of regional sedimentary background and diagenetic environment,it is believed that the formation of such diagenetic “concretions” indicates strong hydrodynamic forces in distributary channels,abundant organic matter input during the shallow-water delta deposition of the Qingshuihe Formation,and weakly alkaline-neutral pore water medium during the early diagenetic stage,which provided favorable chemical conditions for cement precipitation. The research results not only clarify the controversy over the genesis of sandstone “concretions” in the Qingshuihe Formation,but also provide key geological evidence for the restoration of the Cretaceous shoreline shallow-water delta sedimentary environment and the study of diagenetic evolution in the Junggar Basin,and have reference value for the heterogeneity research of oil and gas reservoirs and oil and gas development.

Based on a systematic review of the evolution from macroscopic qualitative description to high-precision quantitative analysis of the Permian lithofacies palaeogeography in southern China,this study focuses on the rock evolution characteristics and formation mechanisms centered on the dolomite of the Qixia Formation-Maokou Formation and the siliceous rocks of the Gufeng Formation、Dalong Formation. The study emphasizes that the spatiotemporal distribution of lithofacies profoundly reflects the control of tectonics,especially the dynamic background driven by scissor-like collision and the distal effect of mantle plumes,which determine the spatiotemporal evolution of the sedimentary pattern and the characteristics of the platform-basin differentiation. In response to the current bottleneck problem in the delimitation of facies belts,this study proposes that the spatiotemporal constraints should be strengthened by relying on palaeobiogeographic similarity indicators,and combined with big data and artificial intelligence technologies,to promote the transformation from static map drawing to dynamic process prediction,aiming to provide more rigorous petrological evidence and evolution models for the evaluation of “sweet spots” in unconventional oil and gas exploration.

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.

This study reconstructs the tectonic evolution and lithofacies palaeogeographic development of North Africa from the Cambrian to the Devonian through an integrated analysis of seismic,well-log,and core data. Emphasis is placed on evaluating how major tectonic events—interacting with eustatic sea-level fluctuations and climatic shifts—controlled sedimentary processes and basin architecture in the region. Results indicate that during the Cambrian-Ordovician,a depression basin dominated the western craton margin of the Tethys domain;progressive climatic cooling and continental glaciation led to the transition from braided fluvial systems to glaciogenic deposits. In the Silurian,rifting associated with the initial opening of the Paleo-Tethys Ocean triggered widespread marine transgression,resulting in the deposition of organic-rich shales in the Lower Silurian. Subsequent late Silurian regression facilitated the development of deltaic and fluvial systems. During the Devonian,the Hercynian orogeny profoundly reconfigured regional basin geometry,establishing a passive continental margin. Fluvial(braided and meandering)systems were progressively replaced by deltaic and shallow-marine environments;persistent bottom-water anoxia in the Late Devonian favored the accumulation and preservation of high-quality source rocks. Collectively,this work elucidates the synergistic controls exerted by tectonics,eustasy,and climate on the paleogeographic evolution of North Africa,identifies prospective hydrocarbon reservoir fairways,and provides a robust geological framework to guide future petroleum exploration.

The lacustrine carbonates of the Lower Cretaceous Barra Velha(BVE)Formation are important pre-salt oil and gas reservoirs in the deep-water Santos Basin in eastern Brazil,and their unique rock fabric characteristics have become the focus of academic attention. Over the past decade,numerous studies have been published on the fabric and genesis of these carbonates,yet controversies persist. Existing researches indicate that the in-situ carbonates of the BVE Formation mainly consist of calcite shrubs,calcite spherulites,and magnesium-rich clay minerals. There are opposing views on the genesis of the sedimentary fabric,whether it is microbial or chemical in origin,and correspondingly different classification schemes for the rocks. The deposition models also vary,including microbial deposition,chemical deposition,and travertine deposition. Since no obvious biological structures/substances have been identified so far,and the shrubs and spherulites exhibit fibrous crystal structures,an increasing number of studies support the view that chemical precipitation is the dominant process. However,it remains difficult to determine whether microbial and/or hydrothermal activity was involved. The comprehensive investigation of paleontological,autogenetic clay minerals and C-O-Sr isotopes shows that the sedimentary environment of BVE carbonates is a lake with high salt,high alkali and high evaporation,but the water temperature,water depth,material sources such as Mg-Si-Ca,carbonate formation stage or sedimentary and diagenetic superposition process and effect are still unclear. Based on the review of the relevant research progress,it is suggested that future studies should start from environmental medium parameters,material sources,and the origin of the main components,and carry out matched high-precision micro-fabric and in-situ major and trace elements,isotope analyses,as well as supporting experiments and numerical simulation,combined with modern investigation,macroscopic rock distribution,and dynamic system information on basin paleostructure and paleoclimate evolution,to unravel the enigma of the genesis of these carbonates together.

The Neoproterozoic represents a critical interval in the evolution of the Earth surface system,during which oceans transitioned from low-oxygen,microbially dominated conditions to a stratified and progressively oxygenated state,accompanied by profound reorganization of seawater chemistry and carbonate depositional systems. Marine dolomite cements,owing to their synsedimentary to early diagenetic modes of formation,have been widely used to reconstruct Neoproterozoic seawater chemistry;however,their formation mechanisms and principal controlling factors remain debated. This study synthesizes petrographic observations together with multiple geochemical proxies,including C,O,Sr,Mo,U,and Mg isotopes,from globally representative Neoproterozoic carbonate successions,to systematically evaluate the petrographic characteristics and paleoenvironmental significance of marine dolomite cements. The stratigraphic comparisons indicate that,despite regional variations in cement morphologies and isotopic compositions,the timing of dolomite precipitation and associated genetic patterns are broadly comparable,suggesting a dominant control by a common global seawater chemical background. Multi-isotopic records further demonstrate that Neoproterozoic seawater chemistry did not remain in a long-term steady state,but evolved dynamically in response to tectonic reorganization,glacial-interglacial oscillations,and variations in continental weathering fluxes. The widespread occurrence of dolomite therefore does not reflect a single,persistently existing “dolomite sea,”but instead records the episodic emergence of favorable chemical conditions during different tectonic-climatic stages. Dolomite precipitation windows are inferred to have been opened under a relatively elevated Mg/Ca background,when low sulfate concentrations,high alkalinity,and appropriate redox conditions acted in concert. Neoproterozoic tectonic-climatic processes modulated seawater end-member inputs and material cycling,allowing such precipitation windows to recur at the global scale and thereby accounting for the anomalous abundance of marine dolomite during this interval. This study systematically clarified the key controlling mechanisms of Neoproterozoic marine dolomite formation from a multi-scale and multi-isotope perspective,providing important constraints for reconstructing the chemical evolution of ancient oceans and understanding the co-evolution of the Earth’s surface system in deep time.

The diagenetic sequence and pore evolution of ancient carbonate rocks in deep or ultra-deep burial depth is one of the hot topical in reservoir evolution. Based on analysis of the petrographic, geochemical, and U-Pb dating of diagenesis minerals of the Dengying Formation at Chuanshen 1(CS1), Jinshi 1(JS1) and other wells, the authors has adopted the comparative methods, in which compare the matrix dolomites with different dolomite cements, as well as the other diagenetic minerals, occurred in cement or fillings in vugs & fractures with regard to the data of carbon, oxygen, and strontium isotopes, homogenization temperatures, U-Pb dating of dolomites and calcites, either in the Dengying Formation of Ediacaran, or Xianrendong Formation of the Early Cambrian, or Maokou Formation of Middle Permian. The diagenetic sequence has been reasonable modified: fibrous or fibrous growth→column fibrous or foliated or blade(length-fast cement) or dogtooth shaped→coarser fibrous or bundle shaped of marine cementation and bundle shaped cement or fasicular or radial dolomite cements. i.s botryoids or comb shell shaped or primary dolomite biomorphs of nanoscale spheroids→micro-stalactitic or vadose silt of meteoric cementation→cryptocrystalline or microcrystalline quartz(1^st)→fluorapatite, barite and fluorite(1^st)→semi-automorphic micro-crystalline dolomite→fine crystalline dolomite→fine and medium crystalline quartz(2^nd) or medium to coarse dolomite→Saddle dolomite(1^st)→medium to coarse crystalline calcite(1^st)→hydrocarbon discharge(episodes)→fluorite(continuous dissolution. 2^nd or 3^rd)+coarse calcite(2^nd)→coarse quartz(3^rd)+Galena+Sphalerite+Pyrite+Fluorite(4^th)+coarse calcite(3^rd)+coarse crystalline dolomite(or Saddle dolomite(2^nd)→pyrobitumens(pyrolysis or TSR, methane)→coarse calcite(4^th)+quartz(4^th); and the medium to coarse dolomite in some of the fractures or cavities is of early hot fluid dolomite origin, with relatively low ${\delta }^{13}{\mathrm{C}}_{\mathrm{P}\mathrm{D}\mathrm{B}}$(-1.78‰~-1.69‰) and ${\delta }^{18}{\mathrm{O}}_{\mathrm{P}\mathrm{D}\mathrm{B}}$(-9.28‰~-9.32‰) and moderate. homogenization temperatures(Th=130.9 ℃, 135.3 ℃, 116.6 ℃) and salinity(12.63wt% NaCl); the U-Pb Concordia Age of dolomite(D_Ⅱ-Ⅲ)is between 474.0±74.0 Ma to 482.0±56.0 Ma, By integrating analyses of burial history, the geological-time of dolomite(D_Ⅱ-Ⅲ) is mostly like to occur in the late Ediacaran to Cambrian(No later than Early Ordovician). The weak extension during the late Ediacaran to Cambrian period, interval by multiple episodes of tectonic compression and exhumation, provided the conditions for the meteoric water percolated downward along the faults or fractures, heated by deep circulation as well as mixing with formation water, lead to precipitate of dolomite. The diagenesis effect on pore evolution display that the early dolomite cementation developed in hot fluid had a smaller proportion and had little effect on pore reduction, in compared with diagenesis such as large-scale marine cementation, strong silicification, compaction, and dedolomitization.

The sedimentary environment of the Pinghu Formation in the BW area of the Xihu sag has long been controversial. In this study,19 mudstone samples were collected and analyzed for trace elements and rare earth elements(REEs)using two methods: conventional whole-rock total digestion and selective acetic acid extraction. Based on the geochemical data obtained,multiple proxies were integrated to systematically analyze the redox conditions,paleoclimatic characteristics,and paleosalinity evolution during the depositional period of the Pinghu Formation. The results show that: (1)Element concentrations obtained via acetic acid extraction are significantly lower than those from whole-rock digestion,but both methods reveal consistent elemental distribution patterns. Moreover,the acetic acid extraction method is proven to be more effective than conventional whole-rock digestion when applying specific elemental proxies to identify sedimentary environments,especially for distinguishing terrestrial and marine facies.(2)The redox conditions during the depositional period of the Pinghu Formation were predominantly suboxic to oxic,indicating a relatively oxidizing environment;paleoclimate and paleosalinity evolved concurrently,characterized by an initial warm and humid freshwater setting,which shifted to an arid and saline environment by the end of the early stage. This was followed by a transition to a warm and humid brackish setting in the middle stage,a return to arid and saline conditions by the mid-stage,and finally a return to a warm and humid freshwater environment in the late stage. In light of the sedimentary context of the study area,the synchronous variations in paleoclimate and paleosalinity are interpreted as recording four successive changes,collectively indicating at least two major marine transgressions during the depositional period of the Pinghu Formation. The above results have significant scientific guiding significance and application value for deepening oil and gas exploration in the Xihu sag of the East China Sea Shelf Basin.

Karstified carbonate geothermal reservoirs,characterized by high porosity-permeability and substantial development potential,represent a key target in deep geothermal exploration. The thick and strongly karstified Middle-Upper Cambrian carbonates of the Yuncheng Basin provide an ideal setting for investigating the genesis of deep karst reservoirs;however,the controlling mechanisms of reservoir development under multiphase tectonic-karst overprinting remain insufficiently constrained. In this study,outcrop observations,seismic data,cores,wireline logs,and casting thin sections,integrated with regional tectonic evolution and paleogeomorphic reconstruction,are used to systematically investigate lithologic and reservoir characteristics,diagenetic processes,karst types,and karstification stages of the Middle-Upper Cambrian carbonate succession. The results indicate that: (1)dominant lithologies include oolitic limestone,bioclastic limestone,stromatolitic and argillaceous limestone,and micro-to fine-crystalline dolostone,with reservoir space mainly comprising selective dissolution pores,bedding-parallel dissolution belts,and structural fractures;(2)three genetic categories of karstification and five major evolutionary stages are recognized,controlled by multiphase tectonic uplift,among which large exposure surfaces formed during the Huaiyuan,Late Caledonian,and Yanshanian events served as key loci for epigenetic karstification;(3)the karst reservoir initiated by synsedimentary to early diagenetic dissolution,significantly enlarged through three phases of superimposed epigenetic karstification,and was further modified by fracture-controlled burial dissolution,ultimately forming a composite system characterized by high porosity and strong connectivity. These results clarify the formation mechanisms of the Middle-Upper Cambrian karst geothermal reservoir in the Yuncheng Basin under multiphase karstification and tectonic evolution,and provide a robust theoretical basis for the prediction and evaluation of carbonate geothermal system. The findings also have important implications for geothermal exploration in North China and in analogous fault-depression basins.

The Kuqa Depression hosts extensively distributed Mesozoic coal-bearing strata,characterized by substantial coal seam thickness and relatively abundant deep coalbed methane(CBM)resources. This study focuses on the Jurassic Kezilenuer Formation coal-bearing strata of the Kuqa Depression. Relative to shallow CBM reservoirs,deep coal seams exhibit markedly complex geological characteristics—including well-developed partings,heterogeneous coal matrix structure,and coexistence of adsorbed and free gas phases—posing significant challenges for reliable logging-based gas content evaluation. Integrating core observations from deep coal intervals in the study area with conventional logging,borehole imaging,and nuclear magnetic resonance(NMR)logging data,this work systematically investigates the geological characteristics of deep coal rocks and develops a robust methodology for quantifying their gas content. Deep Jurassic coal rocks in the Kuqa Depression consistently display low natural gamma radiation,low bulk density,high electrical resistivity,high neutron porosity,and large acoustic transit time—distinctive petrophysical signatures corroborated by imaging logs,which reveal bright blocky and speckled textures. Macroscopically,coal seams of the Kezilenuer Formation are predominantly semi-bright to semi-dull,classified as medium-fixed-carbon,high-volatile,medium-low-ash,and ultra-low-moisture coals. Coal seams No.2 and No.3 within Member 4 of the Kezilenuer Formation represent the principal target intervals,with average thicknesses of 4.5 m and 6.2 m,respectively,and mean burial depths exceeding 4000 m. Imaging log analysis indicates that these deep coal rocks largely retain primary(undisturbed)structural integrity. Leveraging empirical correlations established between laboratory-measured gas composition/contents and corresponding logging response parameters,a region-specific logging evaluation model was developed for estimating both compositional parameters and total gas content in deep coal rocks. Calculated total gas contents range from 5.95 to 10.95 m³/t(mean: 9.5 m³/t),comprising an average adsorbed gas content of 7.12 m³/t and an average free gas content of 2.38 m³/t. Complementary analysis using the T₁-T₂ cross-plot derived from NMR logging further reveals that higher gas content is preferentially associated with intervals exhibiting elevated resistivity,higher fixed carbon content,and structurally stable coal matrices. Synthesizing coal seam identification,maceral and industrial component analyses,and quantitative gas content estimation,this study establishes an integrated evaluation framework—combining conventional logs,borehole imaging,and 2D NMR logging—for jointly assessing deep coalbed methane and shale gas potential,thereby supporting resource assessment,reserve estimation,and exploration decision-making.

Significant breakthroughs have been achieved in the Ordovician ultra-deep fault-controlled carbonate reservoirs in the Fuman area,Tarim Basin in recent years. This area is rich in oil and gas resources and has tremendous exploration potential,being one of the largest ultra-deep oilfields established in China at present. Nevertheless,the Fuman area has a deep burial depth and has undergone multiple tectonic evolution stages,leading to complex reservoir spaces and extremely strong heterogeneity. Thus,it is urgently necessary to clarify the characteristics of the reservoir spaces in the Yijianfang Formation of the study area and determine the types of reservoirs,establishing a logging identification method for reservoirs in a single well. Relying on geological data such as cores and thin sections,the petrological and reservoir space characteristics of the Yijianfang Formation were clarified,and four types of reservoirs were summarized: vug type,fracture type,fracture-vug type,and cave-type. With the aid of conventional logging and image logging data,the logging response characteristic chart of “conventional+imaging+pattern” was established. According to the image logging characteristics of different types of reservoirs,the technique of vug, cave and fracture stripping was utilized to achieve the identification of reservoirs in a single well and clarify the scale and physical property differences. The results indicate that the cave type reservoirs have a large scale and excellent physical properties,contributing mainly to oil and gas productivity. The fracture-vug type reservoirs have a medium scale and physical properties,serving as both an oil and gas migration channel and a storage space. The fracture type and vug type reservoirs have relatively poor scale and physical properties. Therefore,the cave type reservoirs are high-quality reservoirs in the study area and also the focus of current exploration and development. The research results provide a solution approach and technical support for the identifying Ordovician ultra-deep fault-controlled carbonate reservoirs in the Fuman area.