In the margins of the major sedimentary basins in northern and western China,burnt rocks formed from the spontaneous combustion of coal seams are commonly found,resulting in special burnt rock landform. This landform is widely distributed in China,commonly with bright colore. However,its scientific and tourist values have been hardly focused on in literature. Few studies have involved the tourism development of such burnt rock landforms in China. Based on field investigations of outcrop sections,this study classifies these landforms into: burnt hilly landforms(including burnt red hilly landform,burnt colorful hilly landform and peak-covered landform of burnt rocks), erosional landform of burnt rocks(including gully landform,steep cliff landforms), collapse landform and loess-covering burnt rock landform according to the process of coal spontaneous combustion,landform genesis,spatial distribution and color of the burnt rocks. Among them,hilly and erosional landforms are commonly seen,while collapse landform mainly exists in areas where underground coal seams are burning. Loess-covering burnt rock landform formed with the Quaternary loess covering the burnt rocks. The formation of various burnt rock landforms is mainly controlled by such factors as coal seam thickness,stratum occurrence,tectonic movement,river erosion and paleoclimate. Burnt rock landforms should be given more attention due to its scientific value and tourism exploitation value. These burnt rock landforms have significant scientific and tourism development values and deserve appropriate attention.

The Eocene represents a critical interval for understanding the evolution of the global carbon cycle. During this period,Northeast China experienced significant fluctuations in atmospheric CO₂ concentrations,ranging from 454 to 1861 μmol/mol. While these variations underscore the region’s importance in carbon cycle research,current understanding of carbon cycling in terrestrial lake systems remains limited. Most studies have focused on modern lakes since the Pleistocene,leaving a notable gap in systematic research on carbon cycling in ancient lacustrine basins such as those of the Eocene. This study integrates multiple geochemical proxies with a quantitative carbon source-sink flux model to reconstruct organic carbon burial and carbon emissions in the Yilan paleo-lake basin during the Early Eocene Climatic Optimum(EECO)and the Middle Eocene Climatic Optimum(MECO)events. The findings reveal that the Yilan Basin exhibited peak primary productivity,organic carbon burial rates,and CO₂ emissions from fossil carbon oxidation during the EECO. Despite substantial carbon release during these events,the net carbon fixed via photosynthesis(reaching 241650 Mt during the EECO)and the resulting buried organic carbon(~4028 Mt during the EECO)significantly exceeded CO₂ emissions from fossil carbon oxidation(~1448 Mt during the EECO). Therefore,the Yilan Basin functioned as a net carbon sink in Northeast China during the EECO and MECO,serving as an important natural regulator of regional climate.

Shidao is the highest-altitude island in the South China Sea and a severely karst-affected area with weakly consolidated high beachrocks. It is also a challenging region for ecological protection and restoration engineering. This paper reports the findings of over a decade of field investigations,highlighting the Old Dragon Head(Laolongtou),Root Pipe Stone,and Wedge-shaped Prograding Stratification as the three top ecological landscapes and precious geological heritage resources in the Xisha Islands. The Laolongtou is the only naturally formed dragon-shaped stone in the world and a symbol of the military and civilian population’s dragon totem in the Xisha Islands. However,the rapid and destructive evolution of karstification caused by seven natural forces,including wave erosion,tidal erosion,wind erosion,high temperature,high humidity,high salinity,and freshwater leaching,as well as human activities,is alarming. Although this is an inevitable natural process,it is a tragedy for the top ecological landscapes. This paper briefly describes the characteristics of the seven natural forces of karstification and proposes the use of iron-aluminate cement-based materials with low alkalinity(pH value is 10~11),resistance to seawater corrosion,and increasing strength upon immersion(corrosion resistance coefficient>1),along with unique engineering techniques,to achieve the goal of external toughening and in-situ strengthening of the rock mass,ensuring the sustainable inheritance of the Laolongtou.

The Paleozoic plant terrestrialization(PPT)represents a pivotal point in the evolutionary history of life on Earth. This process not only reshaped surficial geomorphological landscapes but also exerted on others biotic evolution throughout the Phanerozoic. Until now,how benthic animals respond to PPT across different depositional environments,as well as their roles in the construction of benthic ecosystems,have remained insufficiently understood. Based on the compilation and synthesis of a global trace fossil dataset,this study establishes a time-depositional environment analytical framework. Within this framework,we systematically compare the evolutionary patterns of ichnodiversity,ichnodisparity,ichnotiering,and benthic ecosystem engineering across transitional coastal,fluvial,and lacustrine settings during the process of PPT. Furthermore,we quantitatively assess the behavioral responses of benthic animals to PPT. The results show that from the Cambrian to the Permian,the behavioral evolution of benthic animals exhibits pronounced time-limited and heterogeneity. During the Ordovician,benthic animals in transitional coastal environments had already begun to show initial responses to PPT,whereas those in fluvial and lacustrine environments display a clear temporal lag. This discrepancy is closely associated with the development of plant root systems,the progression of PPT,and subsequent forest expansion. Overall,with the progressive improvement of substrate stability and organic matter availability in both continental and transitional settings driven by terrestrial plants,benthic animals gradually expanded their ecospace utilization,accompanied by increased behavioral complexity and enhanced ecosystem engineering. In turn,benthic animals exerted a positive feedback on PPT through sediment reworking and the modulation of matter and energy fluxes. In addition to the influence of terrestrial vegetation,environmental factors such as climate change and tectonic activity,and sea-level fluctuations also played significant roles in shaping benthic evolutionary trajectories. This study provides a novel ichnological perspective for understanding Paleozoic ecosystem evolution and biotic-sediment interactions.

Tubiphytes is a taxonomically enigmatic organism with a broad geographic distribution and an extensive stratigraphic range,documented widely in reef facies from the Late Paleozoic to the Mesozoic,making its study of significant paleoecological importance. Abundant Tubiphytes fossils have been found in the Late Pennsylvanian strata of Guizhou Province,South China. Specifically,Tubiphytes-dominated bioherms are well-developed in the Gzhelian strata of the Houchang area,southern Guizhou,providing an excellent research object for investigating the palaeoecology of this enigmatic taxon. Palaeontological analyses indicate that Tubiphytes obscurus obscurus Maslov is the dominant species in the study area,and its microstructure and paleobiological characteristics indicates that this taxon functioned as an aggregate binder and encruster,involving symbiotic associations among foraminifera and microbial communities. Quantitative analyses show that in the Tubiphytes reefs of the study area,solitary Tubiphytes exhibit a symbiotic relationship with Archaeolithoporella and the colonial coral Ivanovia cf. manchurica,while massive Tubiphytes compete with organisms such as the colonial coral Ivanovia cf. manchurica and phylloid algae. Furthermore,Tubiphytes forms micro-encrusting communities with Archaeolithoporella, and—combined with successive generations of marine cement—contributes critically to the development of the reef’s microframework,thereby assuming a primary role in reef construction. These Tubiphytes-dominated micro-encrusting communities repeatedly formed reefs in environments lacking metazoans and constitute a key component of the expansive reef systems that flourished along the Paleo-Tethyan margin.

The Late Triassic Carnian Pluvial Episode(CPE,~234-232 Ma)is characterized by a sharp increase in global temperature and humidity,accompanied by significant changes in marine and terrestrial ecosystems,and is associated with the eruptions of the Wrangellia Large Igneous Province(LIP). Much of the current research on CPE has focused on marine strata with well-constrained stratigraphy,while research on the response processes of terrestrial ecosystems to CPE has been limited. Here,we review the status of terrestrial environmental,climatic,and plant changes during the CPE and explore its potential driving mechanisms. The evidence of multiple nearly synchronous negative carbon isotope excursions(CIEs),mercury(Hg)enrichment anomalies(peaks in the Hg/TOC ratio),and Hg isotopes provides direct evidence that the Wrangellia LIP was a driving factor for the significant changes in terrestrial environment,climate,and biology during the CPE. The eruption of the Wrangellia LIP released a large amount of CO₂,triggering global warming. This has led to enhanced atmospheric circulation and hydrological cycles,promoting increased global rainfall and a shift in climatic conditions from relatively warm and dry to relatively warm and humid. These conditions have resulted in the extensive development of terrestrial deltas and swamps,the rise of lake levels,the intensification of chemical weathering,the increase of hygrophytic plants and freshwater algae,and the re-emergence of global coal accumulation,as well as the origin and radiation of dinosaurs,coniferous plants,insects,crocodiles,turtles,and mammals. Terrestrial weathering,the expansion of surface water systems,and an increase in hygrophytic plants and freshwater algae have driven a significant rise in the amount of terrestrial organic carbon buried,contributing to the resurgence of global coal accumulation. The increase in the amount of organic carbon buried and the re-emergence of global coal accumulation have created negative feedback on the improvement in global atmospheric conditions. This can counteract the greenhouse effect caused by the release of greenhouse gases from the Wrangellia LIP,facilitate the gradual stabilization of the environment and climate during the CPE,and ultimately lead to the termination of the CPE. These results suggest that LIP can occur in multiple pulse forms and have a powerful ability to alter the carbon cycle,trigger environmental and climatic changes,and drive macroevolution of organisms. On the other hand,global coal accumulation plays a crucial role in climate stability.

The Devonian strata in the northern Guangdong Province are widely distributed and well-developed,with abundant fossil data. Through comprehensive stratigraphic comparisons and analyses of lithostratigraphy,biostratigraphy,sequence stratigraphy and event stratigraphy in the research area,and based on a measured section in the Nangang Village,Liannan County(four sedimentary facies,three biological zones and eight stratigraphic sequences),three distinct evolutionary stages of Devonian sedimentary paleogeography are recovered(Middle Devonian Givetian,Late Devonian Frasnian and Famennian). Under the opening and expansion of the Qinfang Trough,the northern Guangdong Province was gradually transgressed,forming a platform basin intertwined with a trough basin. It reached the largest ocean basin in the late Frasnian stage,and began to gradually recede during the Famennian stage. The paleogeographic feature affected the paleontological distribution and spatiotemporal migration,such that the transition from the coral-stromatoporoid reef community(Givetian),stromatoporoid reef community(Frasnian)and fungal-algae reef community(Famennian)was clear in the Nangang Village,Liannan County. According to Devonian regional paleogeographical characteristics,reef communities,tectonic and climatic background,the tectonic event was the dominant factor for the biological and geological environment,especially during the Late Devonian F-F event.

The Cretaceous period was characterized by numerous globally significant tectonic and climatic events that are well preserved in the Liupanshan Basin,where the exceptionally continuous and widely distributed Cretaceous strata,predominantly composed of fluvial-lacustrine deposits,host exquisitely preserved Lycoptera fossils,making this basin an ideal site for studying paleoclimatic and paleoenvironmental changes during the Cretaceous. Through an integrated approach combining sedimentology,stratigraphy,paleontology,and geochemistry,this study investigates the Liwaxia Formation in the Liupanshan Basin,employing organic carbon isotope(${\delta }^{13}{\mathrm{C}}_{\mathrm{o}\mathrm{r}\mathrm{g}}$)analysis,major and trace element geochemistry,and X-ray fluorescence(XRF)to examine the paleoclimate and paleoenvironment of Lycoptera-bearing intervals and to assess their relationship to global events. Geochemical results reveal three distinct ${\delta }^{13}{\mathrm{C}}_{\mathrm{o}\mathrm{r}\mathrm{g}}$ evolutionary stages: a significant negative excursion(from-30.21‰ to-27.19‰,amplitude 3.02‰)in intervals B3-B7,a sharp positive shift(from-28.05‰ to-24.13‰,amplitude 3.92‰)in intervals B11-B15,followed by an oscillatory positive trend in intervals B17-B25. The fossil-bearing horizons exhibit notable geochemical anomalies,including marked fluctuations in major elements(Ca,Mg)and trace elements(Sr,Th)relative to adjacent strata,while micro-XRF analysis of fish fossil bones reveals marked enrichments of heavy metals and toxic elements(Mn,Cr,As,S). These Lycoptera-bearing strata record lacustrine environmental conditions during the C3 stage of Oceanic Anoxic Event 1a(OAE1a),characterized by the diagnostic ${\delta }^{13}{\mathrm{C}}_{\mathrm{o}\mathrm{r}\mathrm{g}}$ negative excursion marking OAE1a onset and reflecting hot,arid,hypersaline,and anoxic conditions in the Liupanshan Basin. The mass mortality of Lycoptera likely resulted from the combined effects of persistent bottom-water anoxia caused by Early Cretaceous volcanic-induced greenhouse conditions and the toxicological impact of heavy metals and toxic elements enriched in volcanic ash. This research not only sheds light on the response mechanisms of the paleoclimate and paleoenvironment within the Liupanshan Basin to global events,but also provides crucial biogeochemical evidence and paleontological records essential for understanding the climatic and environmental evolution of Cretaceous terrestrial ecosystems and associated biological extinction events.

Ecological evolution varied significantly across different water depth during the Permian-Triassic mass extinction. Shallow-water carbonate platform environments,characterized by low ambient water depth,hosted the majority of benthic organisms and consequently exhibited heightened sensitivity to environmental changes. As such,they provide critical insights into marine ecosystem evolution under disaster scenarios. Although middle to deep-water settings have been extensively studied,research on shallow-marine environments remains limited. This paper focuses on the newly identified Panjiazhuang section,a shallow-water carbonate platform succession in the Changxing area of Zhejiang Province,and integrates sedimentological,paleontological,and isotopic geochemical analyses to reconstruct ecosystem evolution across the Permian-Triassic transition. In the Panjiazhuang section,a major extinction event is recorded at the top of the bioclastic limestone within the upper Permian Changxing Formation. This interval coincides with a distinct shift in microfacies—from foraminifera-and algae-rich bioclastic limestone to microbialite—indicating a rapid proliferation of cyanobacteria following the collapse of metazoan communities. Additionally,the inorganic carbon isotope exhibited a notable negative excursion during this time. The findings indicate that the ecosystem transition from bioclastic limestone to microbialite facies at the Paleozoic-Mesozoic boundary in the Panjiazhuang section represents a single-episode extinction process during the Permian-Triassic mass extinction event.

Paleoproterozoic stromatolites preserve structural features of microbial-environmental interactions,providing crucial biosedimentary records for deciphering the co-evolution of microbial communities and early environmental transitions. This study focuses on the branched columnar stromatolites from the basal Beidaxing Formation(~2.0 Ga)of the Hutuo Group in Wutai area,North China. Through macro-to-micro scale structural characterization,we elucidate their morphological features,controlling factors,and evolutionary significance. The results demonstrate that these stromatolites exhibit typical branched columnar structures,preserving well-defined alternating light-dark laminae(with light layers composed of microsparry or sparry dolomite and dark layers primarily of micritic dolomite), along with microclots and other microstructures. The alternating light-dark laminae reflect periodic microbial responses to environmental fluctuations,while the microclot structures originate from the synergistic interplay between microbial calcification and microbial mat degradation. Comprehensive analysis of both macroscopic morphological characteristics(including column inclination,diameter variations,and spatial distribution density)and sedimentological features(frequent scour surfaces,growth discontinuities,and abundant peloids)indicates their formation was governed by a dynamic equilibrium of key environmental factors: hydrodynamic conditions,growth space,light availability,and sediment input,etc. These stromatolites developed in moderate-to-high energy environments spanning the lower intertidal to shallow subtidal zones,characterized by low terrigenous input,moderate sedimentation rates,and frequent storm or tidal influences.

The formation of the “Conchostracan shale” layer at the top of the lower section of the Middle Jurassic Shaximiao Formation in the Sichuan Basin marks a major shift in the paleolake depositional environment and palaeogeography. This transition corresponds to the faunal succession of the Shulong-Emeilong fauna to the Mamenchisaurus fauna. Reconstructing the sedimentary and palaeogeographic transformation during this period is crucial for understanding the evolution of dinosaur faunas in the Sichuan Basin. Through the buried characteristics of Conchostracan fossil assemblages and whole-rock geochemical analyses,samples from the lower “Conchostracan Shale” layer,as well as the mudstone and siltstone samples from both the upper and lower sections of the Shaximiao Formation,were examined. The results indicate that Conchostracans thrived in warm,humid shallow lacustrine environments. A transition in sedimentary environments—from deltaic systems to shallow lacustrine,fluvial,and deltaic systems—occurred between the lower and upper sections of the Shaximiao Formation. Analysis of paleoclimate indices(CIA,CIW),redox indicators(δCe,V/Cr,U/Th,V/(V+Ni),V/Sc),and paleosalinity proxies(B/Ga,Sr/Ba)reveals a dynamic evolution of the paleoenvironment within the Shaximiao Formation. Palaeoclimatic conditions shifted from semi-humid and semi-arid to warm and humid,and later reverted back to semi-humid and semi-arid. Concurrently,the paleo-water environment experienced a transition from oxidizing and weakly reducing conditions to more reducing conditions,followed by a return to oxidizing and weakly reducing conditions. Paleosalinity remained predominantly freshwater throughout,with only localized,minor salinization observed in the upper sections. These findings suggest that during the late Middle Jurassic,the Sichuan Basin experienced significant precipitation,leading to the establishment of a warm and humid palaeoclimate and a reducing lake environment conducive to the extensive proliferation of Conchostracans. Subsequently,a shift toward drier climatic conditions likely drove the adaptive evolution of herbivorous dinosaur lineages,transitioning from the Shulong-Emeilong fauna to the Mamenchisaurus fauna.

Tectonic-sedimentary co-evolution in continental faulted lacustrine basins controls the development of source-reservoir systems and the processes of hydrocarbon accumulation and enrichment. Through meticulous analysis of core samples,drilling and logging data,and interpretation of high-resolution 3D seismic data,this study clarifies the sedimentary system characteristics and facies distribution patterns in the Chagan sag during the rift stage,revealing the co-evolution mechanism between tectonic activities and sediment filling. The research identifies two third-order sequences within the rift stage: (1)During the initial rifting phase(SQ1),the NE-trending Maoxi Fault and NW-trending Tula’ge Fault evolved from segmented activation to radial linkage,creating a highly compartmentalized rift framework. This structural pattern controlled the development of proximal,short-axis alluvial fan-fan delta systems,while intense fault displacement combined with warm-humid climates promoted the formation of semi-deep to deep lacustrine facies.(2)In the intensive rifting phase(SQ2),the NE-trending basin-controlling fault system dominated the sedimentary framework: volcanic activity during the first sub-member of the Suhongtu Formation occupied accommodation space,leading to widespread shallow lacustrine facies,while intra-rift volcanic topography fragmented braided river delta sand bodies. During the second sub-member,rapid volcanic accumulation outpaced subsidence,causing source depletion along the northern Maoxi Fault and southern Hule Fault segments,and redirecting sediment supply from the west to the northwest along the northern Hule Fault,thereby altering sandbody filling patterns. Coupling between high-displacement faults and humid climates during SQ1 controlled the development of major source rocks. Volcano-tectonic interactions during SQ2 modified sedimentary paleotopography,regulating reservoir sandbody distribution(e.g.,volcanic barriers fragmenting sand bodies;rapid accumulation triggering source system migration). Volcanic interlayers with stratified vesicles form effective reservoirs when connected to deep hydrocarbon sources via fault systems. The tectono-sedimentary synergistic evolution model established in this paper can provide guidance for reservoir prediction and exploration deployment in the study area,and also offer an analog model for the analysis of fault-depression basins with similar geological settings.

This paper investigates storm deposit characteristics in tidal flat environments of the Early Ordovician Yeli Formation in southern North China to elucidate their implications for palaeolatitude and palaeoclimate. Through comprehensive field sedimentological observations and carbonate microfacies analysis,five distinct microfacies were identified: intraclastic dolomite,quartz-bearing sandy dolomite,sandy dolomite,medium-crystalline dolomite,and fine-crystalline dolomite. These microfacies,combined with macroscopic sedimentary features,indicate an environmental transition from subtidal through intertidal to supratidal zones. Storm-generated sedimentary structures include scoured surfaces,storm gravel layers,graded bedding,massive bedding,hummocky cross-stratification,rip-up clasts,load and flame structures. Through systematic analysis of structure-environment relationships,six distinct storm deposition sequences were classified based on their formative hydrodynamics: subtidal vortex-dominated,subtidal combined vortex-wave,intertidal hybrid gravity flow-wave,intertidal debris flow,intertidal vortex-controlled,and supratidal tidal current sequences. The established depositional model demonstrates that storm flow dynamics primarily controlled the sequence architecture. The recorded increase in both storm frequency and intensity during the Early Ordovician corresponds to a climatic warming phase within the broader cooling trend. Regional synthesis indicates the eastern North China Block margin faced an open ocean at paleolatitudes of 15°~24°S. The research results not only deepen the understanding of the storm deposition sequence,but also provide key sedimentary data for the reconstruction of the Early Ordovician palaeoclimate and palaeogeography in southern North China.

The depositional environment in the Member 2 of Xujiahe Formation on eastern slope of Western Sichuan Depression has long been controversial. Using newly identified storm deposits as key evidence,this study aims to clarify the depositional environment of the in the Member 2 of Xujiahe Formation and the development characteristics of storm deposits in this area. Based on core observation,thin-section identification,grain-size analysis,and geochemical testing,the following conclusions are obtained: (1)Sedimentary structures such as bidirectional cross-bedding,wave-generated cross-bedding,and tidal bundles are widely developed in the in the Member 2 of Xujiahe Formation on the eastern slope of the western Sichuan Depression. Grain-size and geochemical data indicate that the study area was a high-energy environment characterized by periodic energy fluctuations,and that the water body was brackish to freshwater in nature. These features suggest a marine shoreline depositional environment,which can be further subdivided into four sedimentary subfacies: foreshore,upper shoreface,middle shoreface,and lower shoreface.(2)Typical storm-related sedimentary structures,including mud-clast layers,gutter casts,and hummocky cross-stratification,are developed in the foreshore to middle shoreface subfacies. At least nine episodes of storm deposition are vertically identified,and the sequences are dominated by incomplete A-B-C types,reflecting high-energy,high-frequency,and proximal storm depositional characteristics.(3)Against a regressive background,the storm-deposit development belt gradually migrated from shoreface to foreshore. The thickness of storm layers was relatively greater in the southwestern part during the early stage,but became thicker in the eastern part during the late stage,indicating a northeastward migration of the depositional center. The results demonstrate that the Xu 2 Member on the eastern slope of the western Sichuan Depression represents a storm-influenced marine shoreline depositional environment. Together with the paleogeographic framework of “deep in the west and shallow in the east,”these findings reveal a hydrocarbon accumulation element assemblage characterized by “provenance supply from the western depression,sand enrichment on the eastern slope,and sealing in the east,”thereby providing a geological basis for the selection of favorable exploration targets for tight sandstone in the area.

While gravity flow deposits have been identified in the Chang 7 member of the Yanchang Formation in the Wuqi area,northern Shaanxi Province,Ordos Basin,no such deposits have been reported in the Chang 8 and Chang 9 members. This study aims to comprehensively reveal the presence,types,and controlling effects of gravity flow deposits in the Chang 7-Chang 9 members on reservoir properties and oil-bearing potential.Through centimeter-scale core observations,grain-size analysis,and well-log interpretation of the Chang 7-Chang 9 members in the Wuqi area,an integrated analysis was conducted to determine the genetic types and characteristics of gravity flow sandstones. Gravity flow deposits are widely distributed in the Chang 7-Chang 9 members of the Wuqi area,dominated by turbidity current deposits,followed by sandy debris flow deposits,with additional gravity-driven slide-slip deposits. Multi-parameter identification criteria for gravity flow deposits in the Chang 7-Chang 9 members have been established: (1)Core structures: slide-slump deposits exhibit deformed and convolute bedding;sandy debris flows show thick massive bedding and mudstone clasts;turbidites display stacked,incomplete Bouma sequences. (2)Grain-size characteristics: sandy debris flows typically show “short-tailed” bimodal distributions(>95% saltation sub-population,steep slope;<5% suspension sub-population,gentle slope). Turbidites generally exhibit unimodal distributions. (3)C-M diagrams: C-M values parallel the C=M baseline,consistent with gravity flow deposition. Comparative analysis of reservoir properties,oil saturation,and well testing results demonstrates that sandy debris flow deposits significantly outper form turbidites. The widespread distribution of gravity flow deposits in the Chang 7-Chang 9 members holds substantial exploration significance. Sandy debris flows should be prioritized as prospective targets for tight oil exploration in the lower petroleum assemblage of the Yanchang Formation,followed by turbidite deposits.

Due to intense tectonic compression,the massive sandstone of the Bashijiqike Formation in the Cretaceous within the piedmont belt of the Kuqa Depression exhibit severe deformation,complex seismic imaging,and high ambiguity,resulting in limited methods and even fewer achievements in the detailed study of provenance transport pathway in the Keshen natural gas accumulation area. In response to this issue,a comprehensive study was conducted on the heavy mineral assemblages of over 400 sandstone samples from more than 40 wells in the Bashijiqike Formation of the Keshen area,as well as experimental analyses including sandstone clastic components and cathodoluminescence on over 600 samples from 26 wells. The results show that: (1)Zircon,tourmaline,garnet,and magnetite are consistently present as heavy minerals in the wells of this area. The presence and variations in the content of stable heavy minerals such as rutile,apatite,and titanite,along with unstable heavy minerals like epidote,chlorite,and mica,lead to differences in heavy mineral assemblages across well zones. Combined with the ZTR index,these variations can help determine the differences in sedimentary provenance pathways among the well zones. (2)The sedimentary source rocks of the thick sandstone mainly come from pre Carboniferous high-grade metamorphic rocks,low-grade metamorphic rocks,intermediate acidic igneous rocks,basic igneous rocks,and sedimentary rocks,which can be subdivided into nine heavy mineral combination zones from east to west. (3)Due to the control of the content of sandstone debris components by primitive sedimentation,the planar variation characteristics of the average content of potassium feldspar,plagioclase,and metamorphic rock debris in sandstone debris components indicate the existence of 5-7 source transport pathways. (4)Based on a comprehensive analysis of the characteristics of source pathways indicated by heavy mineral assemblages and sandstone debris components,it is believed that there were at least seven source transport pathways from east to west during the sedimentation period of the Bashijiqike Formation,among which Zone Ⅱ and Zone Ⅴ may have been channels with longer river extensions. The above understanding provides a basis for the analysis of large-scale sedimentary microfacies and favorable sand body distribution in the Keshen area,supporting the fine research and evaluation of gas reservoirs in this area.

The co-development of alluvial fans and aeolian deposits in arid regions is a common phenomenon. While wind reworking and redeposition on fan surfaces are widespread,research on their interactive sedimentation and detailed internal architecture characterization is relatively scarce. Based on modern remote sensing images and field outcrops,this study conducted detailed observations and dissection of the lithofacies,lithofacies associations,and planar distribution within the middle part of the modern Dunhuang alluvial fan. The study area primarily develops 9 lithofacies and 5 lithofacies associations,identifying two main sedimentary types: braided channel deposits and aeolian deposits. Among these,the large-scale cross-bedded sandstone lithofacies(St)and parallel-bedded sandstone lithofacies(Sp)represent typical aeolian deposits. The braided channels mainly develop 5 lithofacies associations: cross-bedded conglomerate facies-small-scale cross-bedded sandstone facies(Gt-Scs),clast-supported conglomerate facies-small-scale cross-bedded sandstone facies(Gcm-Scs),clast-supported conglomerate facies-massive sandstone facies(Gcm-Sm),lateral accretionary thin-bedded conglomerate facies-parallel-bedded sandstone facies(Gla-Sp),and clast-supported conglomerate facies-sandy conglomerate facies/pebbly sandstone facies(Gcm-Gs/Sg). Horizontally,the braided channels of the alluvial fan develop adjacent to the aeolian dunes. Vertically,aeolian sandstones and braided channel sandy conglomerates are interbedded,reflecting the alternating dominance of these two geological agents during different periods. Based on this,a depositional model controlled by cycles of dominant and subordinate agents on the lateral margins of the middle fan under an arid to semi-arid climatic background was established,characterized by “aeolian processes advance when fluvial activity retreats” and “fluvial processes advance when aeolian activity retreats”. During arid periods with prevailing monsoons,wind was the dominant geological agent,depositing thick large-scale cross-bedded and parallel-bedded sandstones. During wet periods with abundant rainfall and glacial meltwater,fluvial processes dominated the fan surface,resulting in braided channel features. This study enriches the depositional architectural models of alluvial fans and provides theoretical support for the genetic identification and hydrocarbon exploration of sandy conglomerate reservoirs within alluvial fans.

The Longmen Mountains region is one of the key areas for Devonian geological research in China. However,controversies persist concerning stratigraphic correlation and paleoenvironmental studies in this area. This study focuses on the Middle Devonian Guanwushan Formation and the Lower Carboniferous Zongchanggou Formation in the northwestern Sichuan Basin. Systematic field surveys of outcrop sections were conducted,complemented by thin-section petrographic analyses. A total of 210 carbonate rock samples were analyzed for carbon and oxygen isotope compositions. The results indicate that the middle part of the Guanwushan Formation in the northwestern Sichuan Basin was deposited under relatively higher paleosalinity and shallow-water conditions,representing a favorable stage for dolomite formation. The Guanwushan Formation exhibits conformable contacts with the overlying Shawozi Formation and the underlying Jinbaoshi Formation. The Devonian-Carboniferous boundary is marked by a regional unconformity,resulting in the absence of the upper Guanwushan Formation and the lower Zongchanggou Formation. Within the Guanwushan Formation,δ¹³C values range from -3.72‰ to 3.19‰(average: 0.61‰),while δ¹⁸O values vary between -7.30‰ to-1.11‰(average: -4.49‰). In the Zongchanggou Formation,δ¹³C values range from-4.47‰ to 2.08‰(average: -0.92‰),and δ¹⁸O values range from-5.83‰ to-0.64‰(average: -3.52‰). Paleoenvironmental reconstruction indicates that both the Guanwushan and Zongchanggou formations were deposited in typical marine settings. During deposition of the Guanwushan Formation,seawater temperatures ranged from 15 ℃ to 40 ℃,with an average of 25.32 ℃,suggesting a subtropical to tropical climate. In contrast,during deposition of the Zongchanggou Formation,seawater temperatures varied between 15 ℃ and 34 ℃,averaging 23.71 ℃,reflecting a temperate-tropical climate transition and revealing a cooling event across the Devonian-Carboniferous boundary. Furthermore,the multi-stage positive and negative excursions in δ¹³C were controlled by high-frequency sea-level fluctuations and periodic exposure of continental shelves,reflecting perturbations in the paleo-oceanic carbon cycle. The overall trends in carbon isotope variations across three measured outcrops in the study area show consistency and are broadly comparable to those documented in sections from Guangxi(China),France,and Germany,demonstrating their utility for global Devonian-Carboniferous stratigraphic correlation and subdivision. This study reveals the carbon isotope geochemical characteristics of the Devonian-Carboniferous strata in the northwestern Sichuan Basin,providing key evidence for regional isochronous stratigraphic correlation. It reconstructs the evolution of paleo-seawater temperatures and the mechanisms of carbon cycle fluctuations,identifies the favorable period for dolomite development,and holds significant implications for understanding paleoenvironmental evolution along the eastern Paleo-Tethyan margin and for hydrocarbon reservoir prediction.

This study investigates the shale of the upper sub-member of Member 4 of Shahejie Formation in the Minfeng subsag,Dongying sag,integrating core and thin-section observations with elemental geochemistry to reconstruct paleoenvironmental conditions. An innovative multi-method analytical framework was employed—including scanning electron microscopy coupled with cathodoluminescence(SEM-CL),focused ion beam-scanning electron microscopy(FIB-SEM),laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS),stable isotope(C,O,Sr)analysis,fluid inclusion microthermometry,and U-Pb geochronology—to systematically characterize diagenetic mineral evolution and elucidate the reservoir formation mechanism. Results indicate that deposition of the target interval occurred under an arid to semi-humid climate,within a fine-grained,brackish-deep lacustrine setting characterized by strong redox stratification. High-frequency vertical cyclicity is evident,reflecting a progressive facies transition from carbonate-rich mixed shale → mixed shale → feldspar-rich mixed shale. Total organic carbon(TOC)ranges predominantly between 1.8wt% and 6.0 wt%,with abundant organic matter accumulation attributed primarily to high sedimentation rates and robust terrigenous and/or endogenous organic input—rather than prolonged bottom-water anoxia alone. Granular calcite and fibrous calcite exhibit distinct geochemical signatures: divergent rare earth element(REE)patterns,contrasting δ¹³C and δ¹⁸O values,and significantly different U-Pb ages. Notably,columnar-to-fibrous calcite laminae oriented near-horizontally yield a broad U-Pb age spectrum(31.2±4.3 Ma to 25.1±4.2 Ma),spanning the full early-to-middle diagenetic interval. Illite comprises 80%~100% of the clay mineral assemblage;its formation is dominantly controlled by montmorillonite-to-illite transformation,while feldspar dissolution represents a major silica source for authigenic quartz precipitation. Authigenic quartz is ubiquitously observed within argillaceous laminae and calcite laminae. Under overpressured conditions,co-precipitation of authigenic quartz and recrystallized calcite effectively buffered porosity loss during cementation—thereby preserving critical pore space and facilitating subsequent pore enhancement via acidic fluid dissolution during later diagenesis. This interplay constitutes a key reservoir-quality preservation and improvement mechanism in deeply buried lacustrine shales.

The Qiongzhusi Formation in the Upper Yangtze Region is currently a key target for shale gas exploration. To reconstruct the sedimentary paleoenvironment of the Lower Cambrian Qiongzhusi Formation in southern Sichuan Basin,this study takes the Qiongzhusi Formation shales from Well A1 as the research object,and explores the weathering intensity,paleoclimatic characteristics,tectonic setting,and provenance features during their deposition through geochemical analyses of major elements,trace elements,and rare earth elements. The results reveal enrichment of TFe₂O₃,MgO,and K₂O,and depletion of SiO₂,Al₂O₃,and Na₂O in major elements. Among trace elements,Mo and Cd are strongly enriched,whereas Sr is significantly depleted. The REE distribution patterns are comparable to those of the upper continental crust,showing a right-inclined “V”shape with LREE enrichment,flat HREE trends,distinct LREE-HREE fractionation,and notable negative Eu anomalies. CIA values range from 48.16 to 69.36(average 64.03),and A-CN-K diagrams indicate moderate chemical weathering under a warm and humid climate. The Th/Sc-Zr/Sc plot suggests a first-cycle sedimentary origin for the shale,with no evidence for significant sedimentary recycling. Provenance diagrams(K₂O-Rb,TiO₂-Zr,Co/Th-La/Sc,and Th/Sc-Zr/Sc)consistently imply intermediate to acidic felsic igneous sources. Major element discrimination and REE abundances(ΣREE=136.51~297.68×10^-6,avg. 189.23×10^-6,higher than average continental crust)support a passive continental margin setting. Based on paleoclimatic conditions,provenance characteristics,and tectonic setting,it is inferred that the Lower Cambrian Qiongzhusi Formation shales in southern Sichuan were deposited in a passive continental margin under a warm,humid climate with moderate chemical weathering,predominantly sourced from intermediate-acidic felsic igneous rocks of the Kangdian-Yunnan craton with negligible hydrothermal influence.

The Pearl River Mouth Basin,a typical Cenozoic continental margin rift basin,derives its major hydrocarbon resources from the lacustrine source rocks of the Wenchang Formation in the Eocene. Divided by the central uplift,faulted and detached depressions have developed respectively in the northern and southern parts of the basin. There are significant differences in hydrocarbon distribution,and the causes of these differences remain unclear. In this study,technical methods including structural evolution analysis,sedimentary system reconstruction,and source-fault-sandbody association analysis were employed. It reveals the basin’s structural evolution law of “faulting first then detaching,faulting in the north and detachment in the south” and the sedimentary evolution characteristics of “terrestrial environment in the early stage and marine environment in the late stage,deltas in the north and fan deposites(fan delta,sublacustrine fan or submarine fans)in the south”. The different tectonic sedimentary evolution processes of the two types of depressions formed source-fault-sandbody associations,resulting in different petroleum accumulation patterns and enrichment laws. Differential source-fault-sandbody associations and petroleum accumulation patterns were established separately. Characterized by high quality lacustrine source rocks,steep faults and sandbodies near sediment provenance,faulted depressions were apt to generate oil-rich accumulation pattern. But for detached depressions featured by high quality lacustrine source rocks,fault block tilting adjusted faults and sandbodies far away from sediment provenance,gas-rich accumulation pattern with locally oil-rich was predominating. The study points out that hydrocarbons in faulted sags are enriched in the steep slope zone,uplifts in the depression-center and inner gentle slope zone,while those in detachment depressions are enriched in the gentle slope zone. This provides constructive suggestions for petroleum exploration.

The continuous discovery of giant hydrocarbon reservoirs in continental rift basins has highlighted bioclastic dolomite reservoirs as a promising new exploration frontier. This study integrates petrography,geochemistry,and in-situ isotopic techniques to investigate the genesis and pore evolution of bioclastic dolomite reservoirs in the Member 2 of Shahejie Formation in eastern Shijiutuo uplift of Bohai Bay Basin. The results reveal the following: (1)Three sets of bioclastic dolomite reservoirs are developed,and four types of replacive dolomites are identified—micritic envelope dolomite(ME),micritic-fine crystalline matrix dolomite(MD),early fibrous dolomite cement(CD₁),and late mosaic dolomite cement(CD₂). (2)Two dolomitization mechanisms are proposed: reflux and burial dolomitization,elucidating the genesis of different dolomite types. ME,MD,and early CD₁ formed under hypersaline reflux conditions in hot,semi-saline,lacustrine shallow shoals. (3)In the high-temperature,closed diagenetic environment of the shallow burial stage,organic acids generated from kerogen thermal decomposition promoted the dissolution-reprecipitation of MD and CD₁ to form CD₂. Concurrently,pore fluids rich in Mg²⁺ released by compaction,together with retained connate water,facilitated CD₂ cementation,filling intergranular pores. (4)During the synsedimentary stage,meteoric freshwater leaching selectively dissolved aragonite and high-Mg calcite,forming early secondary pores such as moldic and intrabioclastic cavities. In the middle to late burial stage,abundant organic acid production and hydrocarbon charging led to non-selective dissolution and microfracture development. However,reservoir space remains dominated by primary intergranular pores and early secondary pores. By coupling in-situ isotopic temperature reconstruction with multi-stage dolomitization mechanisms,this study refines previous models focused solely on reflux and mixing-zone dolomitization and provides a theoretical framework and predictive approach for reservoir quality enhancement and efficient hydrocarbon development in bioclastic dolomite reservoirs.

Shallow-water delta front sand bodies are widely developed and represent important hydrocarbon reservoirs with high exploration potential in continental basins. However,frequent migration and avulsion of distributary channels result in vertically stacked thin interbeds and laterally interwoven distributions,leading to complex architectural patterns. Under sparse well coverage,this complexity makes reservoir prediction highly challenging and less accurate. This study takes the Member 1 of Jurassic Shaximiao Formation in the Tianfu Gas Field,Sichuan Basin,as a case example,and proposes an intelligent prediction method for thin sand bodies by integrating multi-frequency seismic attribute automated machine learning(AutoML)with waveform indication inversion(WII). Laterally,optimized frequency-decomposed seismic data were used to automatically select key attributes and integrate multi-model learning,building nonlinear mappings that improved the correlation between seismic attributes and well-derived sand thickness from 0.64 to 0.82. This enabled quantitative prediction of sand bodies under sparse well control. Vertically,WII introduced facies-controlled constraints and used uranium-free gamma ray as the inversion target,allowing stable identification of sand bodies thicker than 10 m and reliable responses from thin layers of about 4 m,and establishing seismic response templates of architectural element assemblages. Based on these results,four types of architectural elements were identified: distributary channel,residual mouth bar,levee,and interdistributary bay. Furthermore,six stacking patterns including vertical superimposition and lateral accretion were summarized. The results also reveal that,under different depositional cycles,isolated narrow channels and compound wide channels show distinct spatial distributions and vertical stacking characteristics. In three dimensions,a spatial differentiation pattern was clarified,evolving from near-source net-like distributary channels to distal tongue-shaped and lobe-shaped mouth bars. Finally,a depositional architectural model of the shallow-water delta was established. This study achieves fine-scale multi-level architectural characterization under sparse well conditions and provides new insights and methods for efficient exploration and development of complex shallow-water delta reservoirs.

Characterizing Lower Paleozoic carbonate thermal reservoirs is essential for evaluating the geothermal resource potential of the eastern margin of the South North China Basin. Integrating findings from prior studies with newly acquired drilling,core,outcrop,and geochemical analytical data,this study systematically characterizes Cambrian and Ordovician thermal reservoirs,delineates their spatial distribution patterns and associated geothermal field attributes,and identifies prospective exploration targets. Key findings are as follows: (1)Lower Paleozoic carbonate thermal reservoirs in the study area are predominantly hosted in the Zhangxia Formation and overlying strata. Reservoir types include oolitic shoal,dolomitic,and karst reservoirs. Late-stage tectonic activity has significantly influenced the oolitic shoal and dolomitic reservoirs,promoting secondary karstification;consequently,well-developed karst reservoirs—predominantly Class II and III fractured systems—are widespread across the region.(2)Karst reservoir distribution exhibits clear structural control,with dominant NW-and NE-trending orientations. In shallow-buried settings,the top of the Cambrian reservoir ranges from 500 to 2500 m depth,whereas the Ordovician reservoir top lies between 100 and 2000 m. Corresponding top-reservoir temperatures range from 30 to 90 ℃.(3)A quantitative evaluation framework for karst reservoir favorability was established,incorporating three key parameters: burial depth,caprock geothermal gradient,and degree of karst development. Application of this framework identifies the western Shangqiu area of the Taikang Uplift as the most prospective zone for karst-hosted geothermal resources—providing a robust scientific basis for prioritizing future geothermal exploration and development efforts in the basin.

Coal accumulation is a crucial component of the global carbon cycle,facilitating the large-scale and long-term burial of atmospheric CO₂ on land. It is one of the primary factors leading to a decrease in atmospheric CO₂ concentration,which in turn causes a drop in global temperatures and can trigger the onset of an ice age. At the end of the Carboniferous period,a basin-wide coal accumulation event(Coal #8+9)occurred in the North China Basin,after which the globe entered the Early Permian P1 ice age. This suggests a potential causal link between the widespread coal accumulation in the NCB and the onset of the P1 ice age. To investigate this relationship,this study focuses on Coal #8+9 in the Ordos Basin. Spectral analysis was performed on its natural gamma ray logging curves to reconstruct the accumulation duration of Coal #8+9. Based on coal thickness,carbon content,and apparent density data,the carbon burial rate of the peatland was reconstructed. Using this rate and the estimated area of the Late Carboniferous peatland in the NCB,the annual carbon burial amount in the basin during that time was calculated. Subsequently,based on existing atmospheric data,the annual reduction in atmospheric CO₂ concentration resulting from this carbon burial was estimated,ultimately revealing the relationship between coal accumulation in the Late Carboniferous NCB and the onset of the P1 ice age. The results indicate that Milankovitch cycles of obliquity(35.5 kyr)and precession(21.7 kyr)were identified in Coal #8+9 of the North China Basin. The depositional duration is estimated to be between 98.31 kyr and 277.66 kyr,with an average of 188.20 kyr. The carbon burial rate of the peatland ranged from 42.41 to 78.87 g/·a, with an average of 59.21 g/m²·a. According to estimates of total atmospheric mass and CO₂ concentration,removing approximately 2.13 GtC from the atmosphere is required to lower the atmospheric CO₂ concentration by 1 μL/L. The annual carbon burial amount in the Late Carboniferous NCB was calculated to be between 3.82×10⁷ t and 7.01×10⁷ t,averaging 5.33×10⁷ t. This corresponds to an annual reduction in atmospheric CO₂ concentration of 1.79×10^-2~3.33×10^-2 μL/L,with an average of 2.51×10^-2 μL/L. The atmospheric CO₂ concentration before the end-Carboniferous coal accumulation was approximately 400 μL/L,while it was about 200 μL/L before the onset of the P1 ice age. Based on the average annual carbon burial rate of the NCB,it would take only about 8000 years to reduce atmospheric CO₂ by 200 μL/L,reaching the level associated with the P1 ice age inception. However,the average depositional duration of Coal #8+9 is 188.20 kyr,far exceeding the time required to reach the ice age threshold. Therefore,the massive carbon burial in the NCB could have led to a rapid decrease in atmospheric CO₂ concentration just before the onset of the P1 glaciation. The decoupling of ρCO₂ from continental silicate weathering,coupled with the rapid expansion of tropical rainforests and their repeated reorganization,indicates that the extensive coal accumulation in the NCB during the latest Carboniferous was the primary cause of the atmospheric CO₂ decline preceding the P1 ice age.