Based on field geological survey,interpretation of seismic data and analysis of drilling and logging data,the evolution of geological structures,stratigraphic sedimentary filling sequence and sedimentary system around...Based on field geological survey,interpretation of seismic data and analysis of drilling and logging data,the evolution of geological structures,stratigraphic sedimentary filling sequence and sedimentary system around the Bogda Mountain were analyzed according to the idea of"structure controlling basin,basin controlling facies and facies controlling assemblages".The tectonic evolution of the basin around the Bogda Mountain can be divided into nine stages.The Middle-Late Permian–Middle-Late Triassic was the development stage of intracontinental rift,foreland basin and inland depression basin when lake,fan delta and braided river delta sedimentary facies developed.Early intracontinental rifting,late Permian tectonic uplift,and middle-late Triassic tectonic subsidence controlled the shape,type,subsidence rate and sedimentary system evolution of the basin.The Bogda Mountain area was the subsidence center and deposition center of the deep water lake basin in the Middle Permian with mainly deep-water deposition and local gravity flow deposition.This area had tectonic inversion in the Late Permian,when the Bogda Mountain uplifted to form a low bulge and a series of fan delta sand bodies.In the Middle-Late Triassic,subsidence occurred in the Bogda low uplift,characterized by extensive development of braided river delta deposits.展开更多
A new fossil insect taxon,Triasomaguviopsis jiyuanensis Zhang Q.et Zhang H.gen.et sp.nov.,is established based on a specimen from the Upper Member of the Tanzhuang Formation,Jiyuan Basin,western Henan Province,central...A new fossil insect taxon,Triasomaguviopsis jiyuanensis Zhang Q.et Zhang H.gen.et sp.nov.,is established based on a specimen from the Upper Member of the Tanzhuang Formation,Jiyuan Basin,western Henan Province,central China,and is assigned to the family Maguviopseidae of the superfamily Prosboloidea(Hemiptera,Cica domorpha).This new taxon ischaracterized by smaller granular tegmen,ScP+RA first forked near its mid-length,MP forked more toward apex of ScP+R with three terminals,and singular and sinuous CuA2.This new discovery extends the palaeogeographic distribution of Maguviopseidae to the Jiyuan Basin,increases diversity of this family and has the potential in biostratigraphic correlations.Insects from the Tanzhuang Formation may belong to the Tongchuan Entomofauna from the Ordos Basin,which has a close relationship with the Madygen Entomofauna from Kyrgyzstan.展开更多
Larger benthic foraminifera during the Eocene within the Tethyan realm played a crucial role in regional biostratigraphy.In the Middle East,particularly in Libya,Tunisia,and Egypt,nummulitids are key constituents of n...Larger benthic foraminifera during the Eocene within the Tethyan realm played a crucial role in regional biostratigraphy.In the Middle East,particularly in Libya,Tunisia,and Egypt,nummulitids are key constituents of nummulitic limestone reservoirs,making the taxonomic identification of this structurally complex group vital for biostratigraphic and petroleum applications.This review focuses on the genus Gaziryina of the nummulitids,clarifying its taxonomic status,biostratigraphic utility,and paleobiogeographic significance using biometric data from published literature.Previously misidentified as Nummulites pulchellus,Gaziryina species have been systematically reassessed based on biometric data from published literature.The findings confirm Gaziryina as a distinct genus comprising two species:Gaziryina basatinensis(late Lutetian-Bartonian,SBZ15-18a) and Gaziryina pulchellus(late Bartonian-Priabonian,SBZ18a/b-20).Morphological characters(test shape,size progression,chamber configuration,protoconch enlargement) and ontogenetic trends(tight to lax) indicate a phylogenetic transition where Gaziryina basatinensis evolved into Gaziryina pulchellus,consistent with Cope's rule.Paleobiogeographic reconstruction indicates a probable origin in the southern NeoTethys,likely the Western Desert of Egypt,with subsequent dispersal across the northern and southeastern Tethys.These findings confirm Gaziryina as a key biostratigraphic marker,necessitating further research on its evolution and biostratigraphic framework.展开更多
Stable carbon isotope ratio （δ13Ccarb） analysis has been widely applied to the study of the inter-conti- nental or global marine carbonate correlation. Large-scale Cambrian-Ordovician carbonate platforms were devel...Stable carbon isotope ratio （δ13Ccarb） analysis has been widely applied to the study of the inter-conti- nental or global marine carbonate correlation. Large-scale Cambrian-Ordovician carbonate platforms were developed in the Tarim Basin. But research on fluctuation character- istics and global correlation of δ13Ccarb is still weak. Based on conodont biostratigraphy and whole-rock δ13Ccarb data in the Tahe oil-gas field of the northern Tarim Basin, the global correlation and genesis of positive carbon isotope excursions in the Darriwilian--Early Katian was exam- ined. Three positive excursions were identified in the Tahe oil-gas field including the middle Darriwilian carbon iso- tope excursion （MDICE）, the Guttenberg carbon isotope excursion （GICE）, and a positive excursion within the Pygodus anserinus conodont zone which is named the Early Sandbian carbon isotope excursion （ESICE） in this paper. Furthermore, these positive excursions had no direct relation with sea level fluctuations. MDICE and GICE could be globally correlated. The Middle-Upper Ordovi- cian Saergan Formation source rocks of the Kalpin outcrops were in accordance with the geological time of MDICE and ESICE. GICE had close relationship with the source rock of the Lianglitag Formation in the basin.Massive organic carbon burial was an important factor controlling the genesis of these positive excursions.展开更多
The Middle-Upper Cambrian boundary is one of the current stratigraphical problems which remain openin the geological world, since there have been no universally acknowledged delimiting standard and stratotype.Acting o...The Middle-Upper Cambrian boundary is one of the current stratigraphical problems which remain openin the geological world, since there have been no universally acknowledged delimiting standard and stratotype.Acting on the instruction of Profs. Lu Yanhao and An Taixiang the author studied in details the Paibi Section,which is well exposed as a continuous sequence at an easily accessible locality. The Middle-Upper Cambrianboundary strata are composed of biocalcimicrosparite, indicating the sedimentary environment of anunderwater upheaval on the gentle slope along the frontal margin of the Yangtze carbonate platform. For the upper Middle and lower Upper Cambrian agnostid trilobite zones and conodont zones are erected,and a more accurate correlation between the trilobite and conodont sequences is established. Based on these,the Middle-Upper Cambrian boundary is drawn more reasonably and precisely than what was done before. Inshort, the section studied is superior to other known sections of Middle-Upper Cambrian. and it will probablybe an ideal candidate for the Middle-Upper Cambrian boundary stratotype.展开更多
Based on the analysis of the deformation styles in different tectonic belts of the MiddleUpper Yangtze region,as well as the dissection of typical hydrocarbon reservoirs,this study determined the controlling effects o...Based on the analysis of the deformation styles in different tectonic belts of the MiddleUpper Yangtze region,as well as the dissection of typical hydrocarbon reservoirs,this study determined the controlling effects of deformations on the hydrocarbon accumulations,obtaining the following results.The Middle-Upper Yangtze region experienced significant deformations during the Late Indosinian(T_(2)–T_(3)),the Middle Yanshanian(J_(3)–K_(1)),and the Himalayan,and five styles of tectonic deformations mainly occurred,namely superimposed deep burial,uplift,compressional thrusting,multi-layer decollement,and secondary deep burial.The distribution of hydrocarbon reservoirs in the piedmont thrust belts is controlled by the concealed structures on the footwall of the deep nappe.The gentle deformation area in central Sichuan experienced differential uplift,structural-lithologic hydrocarbon reservoirs were formed over a wide area.The eastern Sichuan-western Hunan and Hubei deformation area experienced Jura Mountains-type multi-layer detachment,compressional thrusting,and uplift.In relatively weakly folded and uplifted areas,conventional structural-lithologic hydrocarbon reservoirs have undergone adjustment and re-accumulation,and the shale gas resources are well preserved.In the strongly deformed areas,conventional hydrocarbon reservoirs were destroyed,while unconventional hydrocarbon reservoirs have been partially preserved.The marine strata in the Jianghan Basin experienced compression,thrusting,and denudation in the early stage and secondary deep burial in the late stage.Consequently,the unconventional gas resources have been partially preserved in these strata.Secondary hydrocarbon generation become favorable for conventional hydrocarbon accumulations in the marine strata.展开更多
The paleotectonic pattern,lithofacies paleogeographic features,sedimentary evolution and its controlling effects on hydrocarbon accumulation assemblages during the depositional period of the Sinian Dengying Formation ...The paleotectonic pattern,lithofacies paleogeographic features,sedimentary evolution and its controlling effects on hydrocarbon accumulation assemblages during the depositional period of the Sinian Dengying Formation in middle-upper Yangtze region were investigated based on outcrops,drilling,log and seismic data.The study shows that,(1)Affected by the breakup of the Rodinia supercontinent,the middle and upper Yangtze areas were in extensional tectonic environment during the depositional period of Dengying Formation.The carbonate platform was structurally differentiated.Intra-platform depressions controlled by syndepositional faults developed,forming a tectonic-paleogeographic pattern of"three platforms with two depressions".(2)During the depositional period of the first and second members of the Dengying Formation,rimmed platforms and intra-platform fault depressions developed in upper Yangtze area and isolated platform developed in middle Yangtze area,and there was the Xuanhan-Kaijiang ancient land block in eastern Sichuan.The depositional period of the third member of the Dengying Formation is the transformation period of tectonic-paleogeographic pattern,when a set of shallow water shelf sediment rich in mud was deposited due to transgression on the background of the eroded terrain formed in EpisodeⅠof Tongwan Movement.The sediment of the fourth member of the Dengying Formation inherited the paleogeographic pattern of the first and second members of the Dengying Formation in general,but the Deyang-Anyue intra-platform fault depression further expanded,and the middle Yangtze platform evolved into two separated platforms.(3)Tectonic-sedimentary differentiation and evolution of carbonate platform in the Sinian gave rise to two types of accumulation assemblages with wide distribution and great exploration potential,which are platform margin and intra-platform.展开更多
Most of the hinterland of the North China platform is devoid of Late Ordovician strata. The BaiyanhuaMountain section at Shetai Town is a standard section of the Upper Ordovician newly established in recentyears at th...Most of the hinterland of the North China platform is devoid of Late Ordovician strata. The BaiyanhuaMountain section at Shetai Town is a standard section of the Upper Ordovician newly established in recentyears at the northernmost margin of the platform. This establishment directly involved the determination of thenorth boundary of the platform and the understanding of its evolutionary Listory. The area is quite differentfrom the binterland of the platform in Middle Ordovician rock types and sedimentary environments, with theformer characterized by frequent slope deposits and the latter consisting almost entirely of platform deposits.The present paper focuses on the petrographic features and sedimentary ervironments of the Middle-UpperOrdovician strata in the area, providing further theoretical support to the establishment of the section and fil-ling the gap in this respect.展开更多
To address the discrepancies between well and seismic data in stratigraphic correlation of the Triassic Yanchang Formation in the Ordos Basin,NW China,traditional stratigraphic classification schemes,the latest 3D sei...To address the discrepancies between well and seismic data in stratigraphic correlation of the Triassic Yanchang Formation in the Ordos Basin,NW China,traditional stratigraphic classification schemes,the latest 3D seismic and drilling data,and reservoir sections are thoroughly investigated.Guided by the theory of sequence stratigraphy,the progradational sequence stratigraphic framework of the Yanchang Formation is systematically constructed to elucidate new deposition mechanisms in the depressed lacustrine basin,and it has been successfully applied to the exploration and development practices in the Qingcheng Oilfield.Key findings are obtained in three aspects.First,the seismic progradational reflections,marker tuff beds,and condensed sections of flooding surfaces in the Yanchang Formation are consistent and isochronous.Using flooding surface markers as a reference,a progradational sequence stratigraphic architecture is reconstructed for the middle-upper part of Yanchang Formation,and divided into seven clinoform units(CF1-CF7).Second,progradation predominantly occurs in semi-deep to deep lake environments,with the depositional center not always coinciding with the thickest strata.The lacustrine basin underwent an evolution of“oscillatory regression-progradational infilling-multi-phase superimposition”.Third,the case study of Qingcheng Oilfield reveals that the major pay zones consist of“isochronous but heterochronous”gravity-flow sandstone complexes.Guided by the progradational sequence stratigraphic architecture,horizontal well oil-layer penetration rates remain above 82%.The progradational sequence stratigraphic architecture and associated geological insights are more consistent with the sedimentary infilling mechanisms of large-scale continental depressed lacustrine basins and actual drilling results.The research results provide crucial theoretical and technical support for subsequent refined exploration and development of the Yanchang Formation,and are expected to offer a reference for research and production practice in similar continental lacustrine basins.展开更多
Taking the second member of the Xujiahe Formation of the Upper Triassic in the Xinchang structural belt as an example,based on data such as logging,production,seismic interpretation and test,a systematic analysis was ...Taking the second member of the Xujiahe Formation of the Upper Triassic in the Xinchang structural belt as an example,based on data such as logging,production,seismic interpretation and test,a systematic analysis was conducted on the structural characteristics and evolution,reservoir diagenesis and densification processes,and types and stages of faults/fractures,and revealing the multi-stage and multi-factor dynamic coupled enrichment mechanisms of tight gas reservoirs.(1)In the early Yanshan period,the paleo-structural traps were formed with low-medium maturity hydrocarbons accumulating in structural highs driven by buoyancy since reservoirs were not fully densified in this stage,demonstrating paleo-structure control on traps and early hydrocarbon accumulation.(2)In the middle-late Yanshan period,the source rocks became mature to generate and expel a large quantity of hydrocarbons.Grain size and type of sandstone controlled the time of reservoir densification,which restricted the scale of hydrocarbon charging,allowing for only a small-scale migration through sand bodies near the fault/fracture or less-densified matrix reservoirs.(3)During the Himalayan period,the source rocks reached overmaturity,and the residual oil cracking gas was efficiently transported along the late-stage faults/fractures.Wells with high production capacity were mainly located in Type I and II fault/fracture zones comprising the late-stage north-south trending fourth-order faults and the late-stage fractures.The productivity of the wells was controlled by the transformation of the late-stage faults/fractures.(4)The Xinchang structural belt underwent three stages of tectonic evolution,two stages of reservoir formation,and three stages of fault/fractures development.Hydrocarbons mainly accumulated in the paleo-structure highs.After reservoir densification and late fault/fracture adjustment,a complex gas-water distribution pattern was formed.Thus,it is summarized as the model of“near-source and low-abundance hydrocarbon charging in the early stage,and differential enrichment of natural gas under the joint control of fault-fold-fracture complex,high-quality reservoirs and structural highs in the late stage”.Faults/fractures with well-coupled fault-fold-fracture-pore are favorable exploration targets with high exploration effectiveness.展开更多
Based on recent advancements in shale oil exploration within the Ordos Basin,this study presents a comprehensive investigation of the paleoenvironment,lithofacies assemblages and distribution,depositional mechanisms,a...Based on recent advancements in shale oil exploration within the Ordos Basin,this study presents a comprehensive investigation of the paleoenvironment,lithofacies assemblages and distribution,depositional mechanisms,and reservoir characteristics of shale oil of fine-grained sediment deposition in continental freshwater lacustrine basins,with a focus on the Chang 7_(3) sub-member of Triassic Yanchang Formation.The research integrates a variety of exploration data,including field outcrops,drilling,logging,core samples,geochemical analyses,and flume simulation.The study indicates that:(1)The paleoenvironment of the Chang 7_(3) deposition is characterized by a warm and humid climate,frequent monsoon events,and a large water depth of freshwater lacustrine basin.The paleogeomorphology exhibits an asymmetrical pattern,with steep slopes in the southwest and gentle slopes in the northeast,which can be subdivided into microgeomorphological units,including depressions and ridges in lakebed,as well as ancient channels.(2)The Chang 7_(3) sub-member is characterized by a diverse array of fine-grained sediments,including very fine sandstone,siltstone,mudstone and tuff.These sediments are primarily distributed in thin interbedded and laminated arrangements vertically.The overall grain size of the sandstone predominantly falls below 62.5μm,with individual layer thicknesses of 0.05–0.64 m.The deposits contain intact plant fragments and display various sedimentary structure,such as wavy bedding,inverse-to-normal grading sequence,and climbing ripple bedding,which indicating a depositional origin associated with density flows.(3)Flume simulation experiments have successfully replicated the transport processes and sedimentary characteristics associated with density flows.The initial phase is characterized by a density-velocity differential,resulting in a thicker,coarser sediment layer at the flow front,while the upper layers are thinner and finer in grain size.During the mid-phase,sliding water effects cause the fluid front to rise and facilitate rapid forward transport.This process generates multiple“new fronts”,enabling the long-distance transport of fine-grained sandstones,such as siltstone and argillaceous siltstone,into the center of the lake basin.(4)A sedimentary model primarily controlled by hyperpynal flows was established for the southwestern part of the basin,highlighting that the frequent occurrence of flood events and the steep slope topography in this area are primary controlling factors for the development of hyperpynal flows.(5)Sandstone and mudstone in the Chang 7_(3) sub-member exhibit micro-and nano-scale pore-throat systems,shale oil is present in various lithologies,while the content of movable oil varies considerably,with sandstone exhibiting the highest content of movable oil.(6)The fine-grained sediment complexes formed by multiple episodes of sandstones and mudstones associated with density flow in the Chang 7_(3) formation exhibit characteristics of“overall oil-bearing with differential storage capacity”.The combination of mudstone with low total organic carbon content(TOC)and siltstone is identified as the most favorable exploration target at present.展开更多
The genesis and tectonic setting of Late Triassic volcanic rocks in the Ganzi–Litang ophiolitic mélange belt have long been a subject of contention.To elucidate these ambiguities,comprehensive petrological,geoch...The genesis and tectonic setting of Late Triassic volcanic rocks in the Ganzi–Litang ophiolitic mélange belt have long been a subject of contention.To elucidate these ambiguities,comprehensive petrological,geochemical,zircon U-Pb geochronological,and Sr-Nd isotopic analyses were conducted on the Luexigou basalts in the Litang area.This investigation has newly delineated a typical volcano-sedimentary sequence indicative of a mid-ocean ridge,with basalts dated to 215±3 Ma.These basalts exhibit geochemical characteristics akin to E-MORB,displaying relatively flat distribution patterns for rare earth elements and trace elements.They are notably depleted in high-field-strength elements(such as Nb and Ta),similar to volcanic arc basalts.展开更多
This study presents LA–ICP–MS U–Pb dating and whole-rock geochemical analyses of the Late Triassic Gangshan harzburgite in the Qingyuan area,with the aim of elucidating its petrogenesis and further constraining the...This study presents LA–ICP–MS U–Pb dating and whole-rock geochemical analyses of the Late Triassic Gangshan harzburgite in the Qingyuan area,with the aim of elucidating its petrogenesis and further constraining the early Mesozoic tectonic evolution of the eastern segment of the northern margin of the North China Block(NCB).Zircons from the harzburgites exhibit typical oscillatory growth zoning or striped absorp-tion in cathodoluminescence images.U–Pb analyses of zircons yield ages ranging from 2525 Ma to 225 Ma,with two youngest ages(225±7 Ma)indicating that the harzburgites were formed during Late Triassic.Geochemical analyses of the Gangshan harzburgites show that the rocks have low concentrations of SiO_(2)(42.38%–42.85%)and Al_(2)O_(3)(3.31%–3.33%),along with high concentrations of MgO(41.32%–41.76%),Cr(4856×10^(-6)–5191×10^(-6))and Ni(1942×10^(-6)–2041×10^(-6)).They also display low REE abundances(∑REE=4.38×10^(-6)–4.69×10^(-6))and flat REE patterns with low(La/Yb)_(N) ratios(1.24–1.56)and slightly po-sitive Eu anomalies(δEu=1.13–1.16).These features suggest that the Gangshan harzburgites are cumulates of basaltic magma derived from the depleted lithospheric mantle.Combined with previous studies,these Late Triassic mafic–ultramafic rocks,together with coeval granitoids in adjacent regions,constitute a typical bimodal association,suggesting that they formed in a post-orogenic extensional environment after the final closure of the Paleo-Asian Ocean.展开更多
The Qinling orogenic belt in central China underwent long-term tectonic evolution during an amalgamation between the North China and South China cratons.However,intense compressional deformation and uplift erosion res...The Qinling orogenic belt in central China underwent long-term tectonic evolution during an amalgamation between the North China and South China cratons.However,intense compressional deformation and uplift erosion resulted in the transformation and disappearance of much geological record from the Qinling orogenic belt,and the tectonic evolution of this belt remains poorly constrained during the Triassic.Located in the northernmost margin of the South China Craton,the Sichuan Basin preserves the complete Triassic sedimentary succession,and can provide significant information for understanding the Triassic tectonic evolution of the Qinling orogenic belt.We present detrital zircon U-Pb dating,trace element and in situ Lu-Hf isotope data for the Middle Triassic Leikoupo Formation and the Late Triassic Xujiahe Formation samples from the eastern Sichuan Basin,South China.The detrital zircon U-Pb ages of the Leikoupo Formation show seven age clusters of 280-242,350-300,500-400,1000-800,2000-1750,2100-2000 and 2600-2400 Ma,while those of the Xujiahe Formation show five age clusters of 300-200,500-350,1050-950,2000-1750 and 2600-2400 Ma.Combined with published paleocurrent and paleogeographic data,the sediments of the Leikoupo Formation are interpreted to be sourced from the North China Craton,Yangtze Craton and North Qinling orogenic belt,and the potential main source regions of the Xujiahe Formation included the South and North Qinling orogenic belts.Provenance analysis indicates that the North Qinling orogenic belt was in inherited uplift and coeval denudation in the Middle Triassic.The proportion of the detritus formed in the South Qinling orogenic belt increases gradually from the Leikoupo to Xujiahe formations.This significant provenance change indicates that rapid tectonic uplift and extensive denudation of the South Qinling orogenic belt occurred in the early Late Triassic,which is related to the collision between the North China and South China cratons during the Triassic.展开更多
There is significant debate concerning the tectonic characteristics and evolutionary understanding of the South China Block(SCB)during the Early Mesozoic.One of the key points of contention is the tectonic-magmatic ac...There is significant debate concerning the tectonic characteristics and evolutionary understanding of the South China Block(SCB)during the Early Mesozoic.One of the key points of contention is the tectonic-magmatic activity during the Triassic and its dynamic mechanisms.However,research on the detailed chronology and tectonic settings of granite plutons in key regions remains insuffi-cient,limiting the understanding of the tectonic-magmatic dynamic mechanisms in the interior of SCB during the Triassic.In this contribution,we present whole-rock major and trace elemental data,Sr-Nd isotope data,LA-ICP-MS zircon U-Pb age dating,and Lu-Hf isotope data for granites of Dashenshan pluton in the Xiangzhong,northwest part of SCB.The results indicate that the Dashenshan granite has an emplacement age of 208.4-212.5 Ma,characterized by high SiO_(2),Na_(2)O,and K_(2)O contents and low MgO and CaO.The Dashenshan granite is enriched in light rare-earth elements with a significant negative Eu anomaly(averageδEu=0.42).It is also enriched in Rb,K,and Th and shows pronounced depletion in Nb,Ta,and Ti,classifying it as peraluminous calc-alkaline granite,specifically of the I-type.The zircon ε_(Hf(t)) values range from−8.39 to−4.4,with an average of−5.82,and the Sr-Nd isotopes are relatively enriched[ε_(Nd)(t)=−9.31 to−6.8].Combining these geochemical characteristics,it is revealed that the Dashenshan granite was derived from the partial melting of middle to upper crustal metamorphic basement materials under medium-to low-temperature conditions,with possible minor contributions from mantle-derived materials.Furthermore,it underwent fractional crystallization,including plagioclase differentiation.By integrating the geochemical features and spatial distribution of Triassic granites in SCB,this study suggests that the regional tectonic evolution of SCB during the Triassic was primarily controlled by the collision of the SCB with the Indochina Block and the North China Block.In Xiangzhong,the tectonic setting transitioned from syn-collisional compression to post-collisional extension during the Late Triassic.The Dashenshan pluton formed in a post-collisional extensional setting,resulting from the decompression melting of middle-to-upper crustal rocks.The upwelling of the asthenosphere and upward heat transfer likely played a significant role in the formation of the Dashenshan granitic magma.展开更多
The recent discovery of natural gas within the fifth member of the Xujiahe Formation(T_(3)x_(5))in the Dongfeng area within the Sichuan Basin highlights the significant exploration potential of this member.However,the...The recent discovery of natural gas within the fifth member of the Xujiahe Formation(T_(3)x_(5))in the Dongfeng area within the Sichuan Basin highlights the significant exploration potential of this member.However,the unconvincing previous understanding of the sedimentary microfacies,combined with a total lack of studies on the sand body architecture and reservoir distribution,hampers the further exploration of this member.Using core data,log curves,and seismic data,along with sedimentary microfacies analysis,this study investigated the interfaces between the sand bodies of various scales in the Dongfeng area.Furthermore,this study explored the morphological characteristics,types,and stacking patterns of these sand bodies and determined the distributions of sand bodies and reservoirs in the area.The results indicate that the first sand group of the T_(3)x_(5) member(T_(3)x^(1)_(5))exhibits delta-front deposits,including subaqueous distributary channels,sheet sands,and interdistributary bays.Seven levels of sand body interfaces are identified in the T_(3)x^(1)_(5) sand group.Among them,the interfaces of the first and second levels were identified only in cores,those of the third and fourth levels were recog-nizable from cores combined with log curves,while those of the fifth,sixth,and seventh levels were distinguishable using seismic data.Three superimposed subaqueous distributary channel complexes are found in the Dongfeng area.Among them,complex 1 in the northwest exhibits the strongest water body energy,while complex 2 in the south displays the weakest.Complex 2 was formed earlier than com-plexes 1 and 3.Also,complex 1 is further subdivided into three vertically stacked subaqueous distrib-utary channels.The subdivision of sedimentary microfacies in the T_(3)x_(5) member reveals nine lithofacies types.Among them,stacked pancake-shaped,carbonaceous debris-bearing,massive,and cross-bedded medium-grained sandstones are considered favorable lithofacies.These four lithofacies types exhibit high porosity,as well as low natural gamma-ray(GR)values,low-to-medium deep investigate double lateral resistivity(RD),and high interval transit time(AC)on the log curves.Additionally,the reservoir distribution in the Dongfeng area was delineated based on the characterization of the favorable lith-ofacies.This study serves as a guide for future exploration and evaluation of the T_(3)x_(5) member in the Dongfeng area while also augmenting the methodologies for describing tight sandstone reservoirs.展开更多
The Yangtze Plate(YP)and the North China Plate(NCP)are key components of the East Asian continent,and their collision significantly influences the tectonic evolution of the eastern Asian continental margin.As the Sout...The Yangtze Plate(YP)and the North China Plate(NCP)are key components of the East Asian continent,and their collision significantly influences the tectonic evolution of the eastern Asian continental margin.As the South Yellow Sea is located at the convergence of these plates,it becomes a pivotal area for understanding the tectonic evolution of East Asia.The characteristics and provenance of clastic rocks of the Middle Permian-the Early Triassic were analyzed and the strata in the Central Uplift including the Qinglong Formation(T_(1)q)and Talung Formation(P_(3)d),consisting of various mudstones and sandstones,were anatomized.Results show that quartz and feldspar are the main diagenetic minerals,while illite and chlorite show signs of secondary alterations.Geochemical imprints indicate a gradual shift in provenance from ancient sedimentary and mafic igneous rocks to intermediate igneous rocks.In the meantime,the tectonic background transformed from continent to continental island arc from the Middle Permian to the Early Triassic.Therefore,we inferred that a soft collision between the North China Plate and the Yangtze Plate likely occurred during the Late Permian,resulted in intensified collision between two plates in the Early Triassic,and shaped the South Yellow Sea.This study provided valuable information on the timing of plate collisions in the South Yellow Sea.展开更多
The lamina(combination)types,reservoir characteristics and shale oil occurrence states of organic-rich shale in the Triassic Yanchang Formation Chang 73 sub-member in the Ordos Basin were systematically investigated t...The lamina(combination)types,reservoir characteristics and shale oil occurrence states of organic-rich shale in the Triassic Yanchang Formation Chang 73 sub-member in the Ordos Basin were systematically investigated to reveal the main controlling factors of shale oil occurrence under different lamina combinations.The differential enrichment mechanisms and patterns of shale oil were discussed using the shale oil micro-migration characterization and evaluation methods from the perspectives of relay hydrocarbon supply,stepwise migration,and multi-stage differentiation.The results are obtained in five aspects.First,Chang 73 shale mainly develops five types of lamina combination,i.e.non-laminated shale,sandy laminated shale,tuffaceous laminated shale,mixed laminated shale,and organic-rich laminated shale.Second,shales with different lamina combinations are obviously different in the reservoir space.Specifically,shales with sandy laminae and tuffaceous laminae have a large number of intergranular pores,dissolution pores and hydrocarbon generation-induced fractures.The multi-scale pore and fracture system constitutes the main place for liquid hydrocarbon occurrence.Third,the occurrence and distribution of shale oil in shale with different lamina combinations are jointly controlled by organic matter abundance,reservoir property,thermal evolution degree,mineral composition and laminae scale.The micro-nano-scale pore-fracture networks within shales containing rigid laminae,particularly sandy and tuffaceous laminations,primarily contain free-state light hydrocarbon components.In contrast,adsorption-phase heavy hydrocarbon components predominantly occupy surfaces of organic matter assemblages,clay mineral matrices,and framework mineral particulates.Fourth,there is obvious shale oil micro-migration between shales with different lamina combinations in Chang 73.Generally,such micro-migration is stepwise in a sequence of organic-rich laminated shale→tuffaceous laminated shale→mixed laminated shale→sandy lamiated shale→non-laminated shale.Fifth,the relay hydrocarbon supply of organic matter under the control of the spatial superposition of shales with various laminae,the stepwise migration via multi-scale pore and fracture network,and the multi-differentiation in shales with different lamina combinations under the control of organic-inorganic interactions fundamentally decide the differences of shale oil components between shales with different lamina combinations.展开更多
Wells CXD1 and CX2 have uncovered high-concentration potassium-and lithium-containing brines and substantial layers of halite-type polyhalite potash deposits within the 4th and 5th members of the Triassic Jialingjiang...Wells CXD1 and CX2 have uncovered high-concentration potassium-and lithium-containing brines and substantial layers of halite-type polyhalite potash deposits within the 4th and 5th members of the Triassic Jialingjiang Formation and the 1st Member of Leikoupo Formation(Jia 4 Member,Jia 5 Member,and Lei 1 Member)in the Puguang area,Sichuan Basin.These discoveries mark significant breakthroughs in the exploration of deep marine potassium and lithium resources within the Sichuan Basin.Utilizing the concept of“gas-potassium-lithium integrated exploration”and incorporating drilling,logging,seismic,and geochemical data,we have investigated the geological and enrichment conditions,as well as the metallogenic model of potassium-rich and lithium-rich brines and halite-type polyhalite.First,the sedimentary systems of gypsum-dolomite flats,salt lakes and evaporated flats were developed in Jia 4 Member,Jia 5 Member,and the 1st member of Leikoupo Formation(Lei 1 Member)in northeastern Sichuan Basin,forming three large-scale salt-gathering and potassium formation centers in Puguang,Tongnanba and Yuanba,and developing reservoirs with potassium-rich and lithium-rich brines,which are favorable for the deposition of potassium and lithium resources in both solid or liquid phases.Second,the soluble halite-type polyhalite has a large thickness and wide distribution,and the reservoir brine has a high content of K+and Li+.A solid-liquid superimposed“three-story structure”(with the lower thin-layer of brine reservoir in lower part of Jia 4 Member and Jia 5 Member,middle layer of halite-type polyhalite potash depositS,upper layer of potassium-rich and lithium-rich brine reservoir in Lei 1 Member)is formed.Third,the ternary enrichment and mineralization patterns for potassium and lithium resources were determined.Vertical superposition of polyhalite and green bean rocks is the mineral material basis of potassium-lithium resources featuring“dual-source replenishment and proximal-source release”,with primary seawater and gypsum dehydration as the main sources of deep brines,while multi-stage tectonic modification is the key to the enrichment of halite-type polyhalite and potassiumlithium brines.Fourth,the ore-forming process has gone through four stages:salt-gathering and potassium-lithium accumulation period,initial water-rock reaction period,transformation and aggregation period,and enrichment and finalization period.During this process,the halite-type polyhalite layer in Jia 4 Member and Jia 5 Member is the main target for potassium solution mining,while the brine layer in Lei 1 Member is the focus of comprehensive potassium-lithium exploration and development.展开更多
To clarify the mechanism of differential enrichment of intrasource shale oil,taking the third of seventh member of the Triassic Yanchang Formation(Chang 7_(3)submember for short)in the Ordos Basin,NW China as an examp...To clarify the mechanism of differential enrichment of intrasource shale oil,taking the third of seventh member of the Triassic Yanchang Formation(Chang 7_(3)submember for short)in the Ordos Basin,NW China as an example,we integrated high-resolution scanning electron microscopy(SEM),optical microscopy,laser Raman spectroscopy,rock pyrolysis,and organic solvent extraction experiments to identify solid bitumen of varying origins,obtain direct evidence of intrasource micro-migration of shale oil,and establish the coupling between the shale nano/micro-fabric and the oil generation,migration and accumulation.The Chang 7_(3)shale with rich alginite in laminae has the highest hydrocarbon generation potential but a low thermal transformation ratio.Frequent alternations of micron-scale argillaceous-felsic laminae enhance the hydrocarbon expulsion efficiency,yielding consistent aromaticity between in-situ and migrated solid bitumen.Mudstone laminae rich in terrestrial organic matter(OM)and clay minerals exhibit lower hydrocarbon generation threshold but stronger hydrocarbon retention capacity,with a certain amount of light oil/bitumen preserved to differentiate the chemical structure of in-situ versus migrated bitumen.Tuffaceous and sandy laminae contain abundant felsic minerals and migrated bitumen.Tuffaceous laminae develop high-angle microfractures under shale overpressure,facilitating oil charging into rigid mineral intergranular pores of sandy laminae.Fractionation during micro-migration progressively decreases the aromatization of solid bitumen from shale,through tuffaceous and mudstone,to sandy laminae,while increasing light hydrocarbon components and enhancing OM-hosted pore development.The intrasource micro-migration and enrichment of the Chang 7_(3)shale oil result from synergistic organic-inorganic diagenesis,with crude oil component fractionation being a key mechanism for forming sweet spots in laminated shale oil reservoirs.展开更多
基金Supported by the China Geological Survey Projects(DD20190106,DD20160203,DD20190090).
文摘Based on field geological survey,interpretation of seismic data and analysis of drilling and logging data,the evolution of geological structures,stratigraphic sedimentary filling sequence and sedimentary system around the Bogda Mountain were analyzed according to the idea of"structure controlling basin,basin controlling facies and facies controlling assemblages".The tectonic evolution of the basin around the Bogda Mountain can be divided into nine stages.The Middle-Late Permian–Middle-Late Triassic was the development stage of intracontinental rift,foreland basin and inland depression basin when lake,fan delta and braided river delta sedimentary facies developed.Early intracontinental rifting,late Permian tectonic uplift,and middle-late Triassic tectonic subsidence controlled the shape,type,subsidence rate and sedimentary system evolution of the basin.The Bogda Mountain area was the subsidence center and deposition center of the deep water lake basin in the Middle Permian with mainly deep-water deposition and local gravity flow deposition.This area had tectonic inversion in the Late Permian,when the Bogda Mountain uplifted to form a low bulge and a series of fan delta sand bodies.In the Middle-Late Triassic,subsidence occurred in the Bogda low uplift,characterized by extensive development of braided river delta deposits.
文摘A new fossil insect taxon,Triasomaguviopsis jiyuanensis Zhang Q.et Zhang H.gen.et sp.nov.,is established based on a specimen from the Upper Member of the Tanzhuang Formation,Jiyuan Basin,western Henan Province,central China,and is assigned to the family Maguviopseidae of the superfamily Prosboloidea(Hemiptera,Cica domorpha).This new taxon ischaracterized by smaller granular tegmen,ScP+RA first forked near its mid-length,MP forked more toward apex of ScP+R with three terminals,and singular and sinuous CuA2.This new discovery extends the palaeogeographic distribution of Maguviopseidae to the Jiyuan Basin,increases diversity of this family and has the potential in biostratigraphic correlations.Insects from the Tanzhuang Formation may belong to the Tongchuan Entomofauna from the Ordos Basin,which has a close relationship with the Madygen Entomofauna from Kyrgyzstan.
文摘Larger benthic foraminifera during the Eocene within the Tethyan realm played a crucial role in regional biostratigraphy.In the Middle East,particularly in Libya,Tunisia,and Egypt,nummulitids are key constituents of nummulitic limestone reservoirs,making the taxonomic identification of this structurally complex group vital for biostratigraphic and petroleum applications.This review focuses on the genus Gaziryina of the nummulitids,clarifying its taxonomic status,biostratigraphic utility,and paleobiogeographic significance using biometric data from published literature.Previously misidentified as Nummulites pulchellus,Gaziryina species have been systematically reassessed based on biometric data from published literature.The findings confirm Gaziryina as a distinct genus comprising two species:Gaziryina basatinensis(late Lutetian-Bartonian,SBZ15-18a) and Gaziryina pulchellus(late Bartonian-Priabonian,SBZ18a/b-20).Morphological characters(test shape,size progression,chamber configuration,protoconch enlargement) and ontogenetic trends(tight to lax) indicate a phylogenetic transition where Gaziryina basatinensis evolved into Gaziryina pulchellus,consistent with Cope's rule.Paleobiogeographic reconstruction indicates a probable origin in the southern NeoTethys,likely the Western Desert of Egypt,with subsequent dispersal across the northern and southeastern Tethys.These findings confirm Gaziryina as a key biostratigraphic marker,necessitating further research on its evolution and biostratigraphic framework.
基金supported by the National Key Scientific Project of China(No.2011ZX05005-0042016ZX05005-002)the National Basic Research Program of China(973 Program)(No.2012CB214806)
文摘Stable carbon isotope ratio （δ13Ccarb） analysis has been widely applied to the study of the inter-conti- nental or global marine carbonate correlation. Large-scale Cambrian-Ordovician carbonate platforms were developed in the Tarim Basin. But research on fluctuation character- istics and global correlation of δ13Ccarb is still weak. Based on conodont biostratigraphy and whole-rock δ13Ccarb data in the Tahe oil-gas field of the northern Tarim Basin, the global correlation and genesis of positive carbon isotope excursions in the Darriwilian--Early Katian was exam- ined. Three positive excursions were identified in the Tahe oil-gas field including the middle Darriwilian carbon iso- tope excursion （MDICE）, the Guttenberg carbon isotope excursion （GICE）, and a positive excursion within the Pygodus anserinus conodont zone which is named the Early Sandbian carbon isotope excursion （ESICE） in this paper. Furthermore, these positive excursions had no direct relation with sea level fluctuations. MDICE and GICE could be globally correlated. The Middle-Upper Ordovi- cian Saergan Formation source rocks of the Kalpin outcrops were in accordance with the geological time of MDICE and ESICE. GICE had close relationship with the source rock of the Lianglitag Formation in the basin.Massive organic carbon burial was an important factor controlling the genesis of these positive excursions.
文摘The Middle-Upper Cambrian boundary is one of the current stratigraphical problems which remain openin the geological world, since there have been no universally acknowledged delimiting standard and stratotype.Acting on the instruction of Profs. Lu Yanhao and An Taixiang the author studied in details the Paibi Section,which is well exposed as a continuous sequence at an easily accessible locality. The Middle-Upper Cambrianboundary strata are composed of biocalcimicrosparite, indicating the sedimentary environment of anunderwater upheaval on the gentle slope along the frontal margin of the Yangtze carbonate platform. For the upper Middle and lower Upper Cambrian agnostid trilobite zones and conodont zones are erected,and a more accurate correlation between the trilobite and conodont sequences is established. Based on these,the Middle-Upper Cambrian boundary is drawn more reasonably and precisely than what was done before. Inshort, the section studied is superior to other known sections of Middle-Upper Cambrian. and it will probablybe an ideal candidate for the Middle-Upper Cambrian boundary stratotype.
基金jointly funded by the National Natural Science Foundation(Nos.U19B6003,U20B6001,9175520021,42002137)Chinese Academy of Sciences(CAS)Strategic Leading Science&Technology Program(No.XDA14000000)。
文摘Based on the analysis of the deformation styles in different tectonic belts of the MiddleUpper Yangtze region,as well as the dissection of typical hydrocarbon reservoirs,this study determined the controlling effects of deformations on the hydrocarbon accumulations,obtaining the following results.The Middle-Upper Yangtze region experienced significant deformations during the Late Indosinian(T_(2)–T_(3)),the Middle Yanshanian(J_(3)–K_(1)),and the Himalayan,and five styles of tectonic deformations mainly occurred,namely superimposed deep burial,uplift,compressional thrusting,multi-layer decollement,and secondary deep burial.The distribution of hydrocarbon reservoirs in the piedmont thrust belts is controlled by the concealed structures on the footwall of the deep nappe.The gentle deformation area in central Sichuan experienced differential uplift,structural-lithologic hydrocarbon reservoirs were formed over a wide area.The eastern Sichuan-western Hunan and Hubei deformation area experienced Jura Mountains-type multi-layer detachment,compressional thrusting,and uplift.In relatively weakly folded and uplifted areas,conventional structural-lithologic hydrocarbon reservoirs have undergone adjustment and re-accumulation,and the shale gas resources are well preserved.In the strongly deformed areas,conventional hydrocarbon reservoirs were destroyed,while unconventional hydrocarbon reservoirs have been partially preserved.The marine strata in the Jianghan Basin experienced compression,thrusting,and denudation in the early stage and secondary deep burial in the late stage.Consequently,the unconventional gas resources have been partially preserved in these strata.Secondary hydrocarbon generation become favorable for conventional hydrocarbon accumulations in the marine strata.
基金Supported by the China National Science and Technology Major Project(2016ZX05004-001)
文摘The paleotectonic pattern,lithofacies paleogeographic features,sedimentary evolution and its controlling effects on hydrocarbon accumulation assemblages during the depositional period of the Sinian Dengying Formation in middle-upper Yangtze region were investigated based on outcrops,drilling,log and seismic data.The study shows that,(1)Affected by the breakup of the Rodinia supercontinent,the middle and upper Yangtze areas were in extensional tectonic environment during the depositional period of Dengying Formation.The carbonate platform was structurally differentiated.Intra-platform depressions controlled by syndepositional faults developed,forming a tectonic-paleogeographic pattern of"three platforms with two depressions".(2)During the depositional period of the first and second members of the Dengying Formation,rimmed platforms and intra-platform fault depressions developed in upper Yangtze area and isolated platform developed in middle Yangtze area,and there was the Xuanhan-Kaijiang ancient land block in eastern Sichuan.The depositional period of the third member of the Dengying Formation is the transformation period of tectonic-paleogeographic pattern,when a set of shallow water shelf sediment rich in mud was deposited due to transgression on the background of the eroded terrain formed in EpisodeⅠof Tongwan Movement.The sediment of the fourth member of the Dengying Formation inherited the paleogeographic pattern of the first and second members of the Dengying Formation in general,but the Deyang-Anyue intra-platform fault depression further expanded,and the middle Yangtze platform evolved into two separated platforms.(3)Tectonic-sedimentary differentiation and evolution of carbonate platform in the Sinian gave rise to two types of accumulation assemblages with wide distribution and great exploration potential,which are platform margin and intra-platform.
文摘Most of the hinterland of the North China platform is devoid of Late Ordovician strata. The BaiyanhuaMountain section at Shetai Town is a standard section of the Upper Ordovician newly established in recentyears at the northernmost margin of the platform. This establishment directly involved the determination of thenorth boundary of the platform and the understanding of its evolutionary Listory. The area is quite differentfrom the binterland of the platform in Middle Ordovician rock types and sedimentary environments, with theformer characterized by frequent slope deposits and the latter consisting almost entirely of platform deposits.The present paper focuses on the petrographic features and sedimentary ervironments of the Middle-UpperOrdovician strata in the area, providing further theoretical support to the establishment of the section and fil-ling the gap in this respect.
基金Supported by the National Science and Technology Major Project(2017ZX05001)CNPC Technology Project(2023YQX20111).
文摘To address the discrepancies between well and seismic data in stratigraphic correlation of the Triassic Yanchang Formation in the Ordos Basin,NW China,traditional stratigraphic classification schemes,the latest 3D seismic and drilling data,and reservoir sections are thoroughly investigated.Guided by the theory of sequence stratigraphy,the progradational sequence stratigraphic framework of the Yanchang Formation is systematically constructed to elucidate new deposition mechanisms in the depressed lacustrine basin,and it has been successfully applied to the exploration and development practices in the Qingcheng Oilfield.Key findings are obtained in three aspects.First,the seismic progradational reflections,marker tuff beds,and condensed sections of flooding surfaces in the Yanchang Formation are consistent and isochronous.Using flooding surface markers as a reference,a progradational sequence stratigraphic architecture is reconstructed for the middle-upper part of Yanchang Formation,and divided into seven clinoform units(CF1-CF7).Second,progradation predominantly occurs in semi-deep to deep lake environments,with the depositional center not always coinciding with the thickest strata.The lacustrine basin underwent an evolution of“oscillatory regression-progradational infilling-multi-phase superimposition”.Third,the case study of Qingcheng Oilfield reveals that the major pay zones consist of“isochronous but heterochronous”gravity-flow sandstone complexes.Guided by the progradational sequence stratigraphic architecture,horizontal well oil-layer penetration rates remain above 82%.The progradational sequence stratigraphic architecture and associated geological insights are more consistent with the sedimentary infilling mechanisms of large-scale continental depressed lacustrine basins and actual drilling results.The research results provide crucial theoretical and technical support for subsequent refined exploration and development of the Yanchang Formation,and are expected to offer a reference for research and production practice in similar continental lacustrine basins.
基金Supported by the National Natural Science Foundation of China(42302141).
文摘Taking the second member of the Xujiahe Formation of the Upper Triassic in the Xinchang structural belt as an example,based on data such as logging,production,seismic interpretation and test,a systematic analysis was conducted on the structural characteristics and evolution,reservoir diagenesis and densification processes,and types and stages of faults/fractures,and revealing the multi-stage and multi-factor dynamic coupled enrichment mechanisms of tight gas reservoirs.(1)In the early Yanshan period,the paleo-structural traps were formed with low-medium maturity hydrocarbons accumulating in structural highs driven by buoyancy since reservoirs were not fully densified in this stage,demonstrating paleo-structure control on traps and early hydrocarbon accumulation.(2)In the middle-late Yanshan period,the source rocks became mature to generate and expel a large quantity of hydrocarbons.Grain size and type of sandstone controlled the time of reservoir densification,which restricted the scale of hydrocarbon charging,allowing for only a small-scale migration through sand bodies near the fault/fracture or less-densified matrix reservoirs.(3)During the Himalayan period,the source rocks reached overmaturity,and the residual oil cracking gas was efficiently transported along the late-stage faults/fractures.Wells with high production capacity were mainly located in Type I and II fault/fracture zones comprising the late-stage north-south trending fourth-order faults and the late-stage fractures.The productivity of the wells was controlled by the transformation of the late-stage faults/fractures.(4)The Xinchang structural belt underwent three stages of tectonic evolution,two stages of reservoir formation,and three stages of fault/fractures development.Hydrocarbons mainly accumulated in the paleo-structure highs.After reservoir densification and late fault/fracture adjustment,a complex gas-water distribution pattern was formed.Thus,it is summarized as the model of“near-source and low-abundance hydrocarbon charging in the early stage,and differential enrichment of natural gas under the joint control of fault-fold-fracture complex,high-quality reservoirs and structural highs in the late stage”.Faults/fractures with well-coupled fault-fold-fracture-pore are favorable exploration targets with high exploration effectiveness.
基金Supported by the CNPC Major Science and Technology Project(2021DJ1806).
文摘Based on recent advancements in shale oil exploration within the Ordos Basin,this study presents a comprehensive investigation of the paleoenvironment,lithofacies assemblages and distribution,depositional mechanisms,and reservoir characteristics of shale oil of fine-grained sediment deposition in continental freshwater lacustrine basins,with a focus on the Chang 7_(3) sub-member of Triassic Yanchang Formation.The research integrates a variety of exploration data,including field outcrops,drilling,logging,core samples,geochemical analyses,and flume simulation.The study indicates that:(1)The paleoenvironment of the Chang 7_(3) deposition is characterized by a warm and humid climate,frequent monsoon events,and a large water depth of freshwater lacustrine basin.The paleogeomorphology exhibits an asymmetrical pattern,with steep slopes in the southwest and gentle slopes in the northeast,which can be subdivided into microgeomorphological units,including depressions and ridges in lakebed,as well as ancient channels.(2)The Chang 7_(3) sub-member is characterized by a diverse array of fine-grained sediments,including very fine sandstone,siltstone,mudstone and tuff.These sediments are primarily distributed in thin interbedded and laminated arrangements vertically.The overall grain size of the sandstone predominantly falls below 62.5μm,with individual layer thicknesses of 0.05–0.64 m.The deposits contain intact plant fragments and display various sedimentary structure,such as wavy bedding,inverse-to-normal grading sequence,and climbing ripple bedding,which indicating a depositional origin associated with density flows.(3)Flume simulation experiments have successfully replicated the transport processes and sedimentary characteristics associated with density flows.The initial phase is characterized by a density-velocity differential,resulting in a thicker,coarser sediment layer at the flow front,while the upper layers are thinner and finer in grain size.During the mid-phase,sliding water effects cause the fluid front to rise and facilitate rapid forward transport.This process generates multiple“new fronts”,enabling the long-distance transport of fine-grained sandstones,such as siltstone and argillaceous siltstone,into the center of the lake basin.(4)A sedimentary model primarily controlled by hyperpynal flows was established for the southwestern part of the basin,highlighting that the frequent occurrence of flood events and the steep slope topography in this area are primary controlling factors for the development of hyperpynal flows.(5)Sandstone and mudstone in the Chang 7_(3) sub-member exhibit micro-and nano-scale pore-throat systems,shale oil is present in various lithologies,while the content of movable oil varies considerably,with sandstone exhibiting the highest content of movable oil.(6)The fine-grained sediment complexes formed by multiple episodes of sandstones and mudstones associated with density flow in the Chang 7_(3) formation exhibit characteristics of“overall oil-bearing with differential storage capacity”.The combination of mudstone with low total organic carbon content(TOC)and siltstone is identified as the most favorable exploration target at present.
基金supported by the State Key Program of National Natural Science of China(Grant No.42230311)the China Geological Survey(Grant No.DD20243073).
文摘The genesis and tectonic setting of Late Triassic volcanic rocks in the Ganzi–Litang ophiolitic mélange belt have long been a subject of contention.To elucidate these ambiguities,comprehensive petrological,geochemical,zircon U-Pb geochronological,and Sr-Nd isotopic analyses were conducted on the Luexigou basalts in the Litang area.This investigation has newly delineated a typical volcano-sedimentary sequence indicative of a mid-ocean ridge,with basalts dated to 215±3 Ma.These basalts exhibit geochemical characteristics akin to E-MORB,displaying relatively flat distribution patterns for rare earth elements and trace elements.They are notably depleted in high-field-strength elements(such as Nb and Ta),similar to volcanic arc basalts.
基金Supported by projects of the National Natural Science Foundation of China(Nos.42372063,41722204).
文摘This study presents LA–ICP–MS U–Pb dating and whole-rock geochemical analyses of the Late Triassic Gangshan harzburgite in the Qingyuan area,with the aim of elucidating its petrogenesis and further constraining the early Mesozoic tectonic evolution of the eastern segment of the northern margin of the North China Block(NCB).Zircons from the harzburgites exhibit typical oscillatory growth zoning or striped absorp-tion in cathodoluminescence images.U–Pb analyses of zircons yield ages ranging from 2525 Ma to 225 Ma,with two youngest ages(225±7 Ma)indicating that the harzburgites were formed during Late Triassic.Geochemical analyses of the Gangshan harzburgites show that the rocks have low concentrations of SiO_(2)(42.38%–42.85%)and Al_(2)O_(3)(3.31%–3.33%),along with high concentrations of MgO(41.32%–41.76%),Cr(4856×10^(-6)–5191×10^(-6))and Ni(1942×10^(-6)–2041×10^(-6)).They also display low REE abundances(∑REE=4.38×10^(-6)–4.69×10^(-6))and flat REE patterns with low(La/Yb)_(N) ratios(1.24–1.56)and slightly po-sitive Eu anomalies(δEu=1.13–1.16).These features suggest that the Gangshan harzburgites are cumulates of basaltic magma derived from the depleted lithospheric mantle.Combined with previous studies,these Late Triassic mafic–ultramafic rocks,together with coeval granitoids in adjacent regions,constitute a typical bimodal association,suggesting that they formed in a post-orogenic extensional environment after the final closure of the Paleo-Asian Ocean.
基金supported by the National Key Research and Development Program of China(Grant No.2017YFC0602704)the National Natural Science Foundation of China(Grant No.U20B6001 and 91755211).
文摘The Qinling orogenic belt in central China underwent long-term tectonic evolution during an amalgamation between the North China and South China cratons.However,intense compressional deformation and uplift erosion resulted in the transformation and disappearance of much geological record from the Qinling orogenic belt,and the tectonic evolution of this belt remains poorly constrained during the Triassic.Located in the northernmost margin of the South China Craton,the Sichuan Basin preserves the complete Triassic sedimentary succession,and can provide significant information for understanding the Triassic tectonic evolution of the Qinling orogenic belt.We present detrital zircon U-Pb dating,trace element and in situ Lu-Hf isotope data for the Middle Triassic Leikoupo Formation and the Late Triassic Xujiahe Formation samples from the eastern Sichuan Basin,South China.The detrital zircon U-Pb ages of the Leikoupo Formation show seven age clusters of 280-242,350-300,500-400,1000-800,2000-1750,2100-2000 and 2600-2400 Ma,while those of the Xujiahe Formation show five age clusters of 300-200,500-350,1050-950,2000-1750 and 2600-2400 Ma.Combined with published paleocurrent and paleogeographic data,the sediments of the Leikoupo Formation are interpreted to be sourced from the North China Craton,Yangtze Craton and North Qinling orogenic belt,and the potential main source regions of the Xujiahe Formation included the South and North Qinling orogenic belts.Provenance analysis indicates that the North Qinling orogenic belt was in inherited uplift and coeval denudation in the Middle Triassic.The proportion of the detritus formed in the South Qinling orogenic belt increases gradually from the Leikoupo to Xujiahe formations.This significant provenance change indicates that rapid tectonic uplift and extensive denudation of the South Qinling orogenic belt occurred in the early Late Triassic,which is related to the collision between the North China and South China cratons during the Triassic.
基金supported financially by the Research Foundation of the Department of Natural Resources of Hunan Province(20230135DZ)the Provincial Natural Science Foundation of Hunan(2024JJ7080)+1 种基金the Scientific Research Fund of Hunan Provincial Education Department(23C0320)Hunan Provincial College Student Innovation and Entrepreneurship Training Project(S202311527014).
文摘There is significant debate concerning the tectonic characteristics and evolutionary understanding of the South China Block(SCB)during the Early Mesozoic.One of the key points of contention is the tectonic-magmatic activity during the Triassic and its dynamic mechanisms.However,research on the detailed chronology and tectonic settings of granite plutons in key regions remains insuffi-cient,limiting the understanding of the tectonic-magmatic dynamic mechanisms in the interior of SCB during the Triassic.In this contribution,we present whole-rock major and trace elemental data,Sr-Nd isotope data,LA-ICP-MS zircon U-Pb age dating,and Lu-Hf isotope data for granites of Dashenshan pluton in the Xiangzhong,northwest part of SCB.The results indicate that the Dashenshan granite has an emplacement age of 208.4-212.5 Ma,characterized by high SiO_(2),Na_(2)O,and K_(2)O contents and low MgO and CaO.The Dashenshan granite is enriched in light rare-earth elements with a significant negative Eu anomaly(averageδEu=0.42).It is also enriched in Rb,K,and Th and shows pronounced depletion in Nb,Ta,and Ti,classifying it as peraluminous calc-alkaline granite,specifically of the I-type.The zircon ε_(Hf(t)) values range from−8.39 to−4.4,with an average of−5.82,and the Sr-Nd isotopes are relatively enriched[ε_(Nd)(t)=−9.31 to−6.8].Combining these geochemical characteristics,it is revealed that the Dashenshan granite was derived from the partial melting of middle to upper crustal metamorphic basement materials under medium-to low-temperature conditions,with possible minor contributions from mantle-derived materials.Furthermore,it underwent fractional crystallization,including plagioclase differentiation.By integrating the geochemical features and spatial distribution of Triassic granites in SCB,this study suggests that the regional tectonic evolution of SCB during the Triassic was primarily controlled by the collision of the SCB with the Indochina Block and the North China Block.In Xiangzhong,the tectonic setting transitioned from syn-collisional compression to post-collisional extension during the Late Triassic.The Dashenshan pluton formed in a post-collisional extensional setting,resulting from the decompression melting of middle-to-upper crustal rocks.The upwelling of the asthenosphere and upward heat transfer likely played a significant role in the formation of the Dashenshan granitic magma.
基金funded by a SINOPEC project entitled Exploration Potential and Target Evaluation of Xujiahe Formation in the Northeastern Sichuan Basin(No.P23130).
文摘The recent discovery of natural gas within the fifth member of the Xujiahe Formation(T_(3)x_(5))in the Dongfeng area within the Sichuan Basin highlights the significant exploration potential of this member.However,the unconvincing previous understanding of the sedimentary microfacies,combined with a total lack of studies on the sand body architecture and reservoir distribution,hampers the further exploration of this member.Using core data,log curves,and seismic data,along with sedimentary microfacies analysis,this study investigated the interfaces between the sand bodies of various scales in the Dongfeng area.Furthermore,this study explored the morphological characteristics,types,and stacking patterns of these sand bodies and determined the distributions of sand bodies and reservoirs in the area.The results indicate that the first sand group of the T_(3)x_(5) member(T_(3)x^(1)_(5))exhibits delta-front deposits,including subaqueous distributary channels,sheet sands,and interdistributary bays.Seven levels of sand body interfaces are identified in the T_(3)x^(1)_(5) sand group.Among them,the interfaces of the first and second levels were identified only in cores,those of the third and fourth levels were recog-nizable from cores combined with log curves,while those of the fifth,sixth,and seventh levels were distinguishable using seismic data.Three superimposed subaqueous distributary channel complexes are found in the Dongfeng area.Among them,complex 1 in the northwest exhibits the strongest water body energy,while complex 2 in the south displays the weakest.Complex 2 was formed earlier than com-plexes 1 and 3.Also,complex 1 is further subdivided into three vertically stacked subaqueous distrib-utary channels.The subdivision of sedimentary microfacies in the T_(3)x_(5) member reveals nine lithofacies types.Among them,stacked pancake-shaped,carbonaceous debris-bearing,massive,and cross-bedded medium-grained sandstones are considered favorable lithofacies.These four lithofacies types exhibit high porosity,as well as low natural gamma-ray(GR)values,low-to-medium deep investigate double lateral resistivity(RD),and high interval transit time(AC)on the log curves.Additionally,the reservoir distribution in the Dongfeng area was delineated based on the characterization of the favorable lith-ofacies.This study serves as a guide for future exploration and evaluation of the T_(3)x_(5) member in the Dongfeng area while also augmenting the methodologies for describing tight sandstone reservoirs.
基金Supported by the National Natural Science Foundation of China(No.U 2344221)。
文摘The Yangtze Plate(YP)and the North China Plate(NCP)are key components of the East Asian continent,and their collision significantly influences the tectonic evolution of the eastern Asian continental margin.As the South Yellow Sea is located at the convergence of these plates,it becomes a pivotal area for understanding the tectonic evolution of East Asia.The characteristics and provenance of clastic rocks of the Middle Permian-the Early Triassic were analyzed and the strata in the Central Uplift including the Qinglong Formation(T_(1)q)and Talung Formation(P_(3)d),consisting of various mudstones and sandstones,were anatomized.Results show that quartz and feldspar are the main diagenetic minerals,while illite and chlorite show signs of secondary alterations.Geochemical imprints indicate a gradual shift in provenance from ancient sedimentary and mafic igneous rocks to intermediate igneous rocks.In the meantime,the tectonic background transformed from continent to continental island arc from the Middle Permian to the Early Triassic.Therefore,we inferred that a soft collision between the North China Plate and the Yangtze Plate likely occurred during the Late Permian,resulted in intensified collision between two plates in the Early Triassic,and shaped the South Yellow Sea.This study provided valuable information on the timing of plate collisions in the South Yellow Sea.
基金Supported by the National Natural Science Foundation of China(42302184)Innovation Group Project of Basic Research in Gansu Province,China(22JR5RA045)。
文摘The lamina(combination)types,reservoir characteristics and shale oil occurrence states of organic-rich shale in the Triassic Yanchang Formation Chang 73 sub-member in the Ordos Basin were systematically investigated to reveal the main controlling factors of shale oil occurrence under different lamina combinations.The differential enrichment mechanisms and patterns of shale oil were discussed using the shale oil micro-migration characterization and evaluation methods from the perspectives of relay hydrocarbon supply,stepwise migration,and multi-stage differentiation.The results are obtained in five aspects.First,Chang 73 shale mainly develops five types of lamina combination,i.e.non-laminated shale,sandy laminated shale,tuffaceous laminated shale,mixed laminated shale,and organic-rich laminated shale.Second,shales with different lamina combinations are obviously different in the reservoir space.Specifically,shales with sandy laminae and tuffaceous laminae have a large number of intergranular pores,dissolution pores and hydrocarbon generation-induced fractures.The multi-scale pore and fracture system constitutes the main place for liquid hydrocarbon occurrence.Third,the occurrence and distribution of shale oil in shale with different lamina combinations are jointly controlled by organic matter abundance,reservoir property,thermal evolution degree,mineral composition and laminae scale.The micro-nano-scale pore-fracture networks within shales containing rigid laminae,particularly sandy and tuffaceous laminations,primarily contain free-state light hydrocarbon components.In contrast,adsorption-phase heavy hydrocarbon components predominantly occupy surfaces of organic matter assemblages,clay mineral matrices,and framework mineral particulates.Fourth,there is obvious shale oil micro-migration between shales with different lamina combinations in Chang 73.Generally,such micro-migration is stepwise in a sequence of organic-rich laminated shale→tuffaceous laminated shale→mixed laminated shale→sandy lamiated shale→non-laminated shale.Fifth,the relay hydrocarbon supply of organic matter under the control of the spatial superposition of shales with various laminae,the stepwise migration via multi-scale pore and fracture network,and the multi-differentiation in shales with different lamina combinations under the control of organic-inorganic interactions fundamentally decide the differences of shale oil components between shales with different lamina combinations.
基金Supported by the National Research and Development Program(2017YFC0602804)Geological Bureau Program of Sichuan Province(SCDZ-KJXM202403).
文摘Wells CXD1 and CX2 have uncovered high-concentration potassium-and lithium-containing brines and substantial layers of halite-type polyhalite potash deposits within the 4th and 5th members of the Triassic Jialingjiang Formation and the 1st Member of Leikoupo Formation(Jia 4 Member,Jia 5 Member,and Lei 1 Member)in the Puguang area,Sichuan Basin.These discoveries mark significant breakthroughs in the exploration of deep marine potassium and lithium resources within the Sichuan Basin.Utilizing the concept of“gas-potassium-lithium integrated exploration”and incorporating drilling,logging,seismic,and geochemical data,we have investigated the geological and enrichment conditions,as well as the metallogenic model of potassium-rich and lithium-rich brines and halite-type polyhalite.First,the sedimentary systems of gypsum-dolomite flats,salt lakes and evaporated flats were developed in Jia 4 Member,Jia 5 Member,and the 1st member of Leikoupo Formation(Lei 1 Member)in northeastern Sichuan Basin,forming three large-scale salt-gathering and potassium formation centers in Puguang,Tongnanba and Yuanba,and developing reservoirs with potassium-rich and lithium-rich brines,which are favorable for the deposition of potassium and lithium resources in both solid or liquid phases.Second,the soluble halite-type polyhalite has a large thickness and wide distribution,and the reservoir brine has a high content of K+and Li+.A solid-liquid superimposed“three-story structure”(with the lower thin-layer of brine reservoir in lower part of Jia 4 Member and Jia 5 Member,middle layer of halite-type polyhalite potash depositS,upper layer of potassium-rich and lithium-rich brine reservoir in Lei 1 Member)is formed.Third,the ternary enrichment and mineralization patterns for potassium and lithium resources were determined.Vertical superposition of polyhalite and green bean rocks is the mineral material basis of potassium-lithium resources featuring“dual-source replenishment and proximal-source release”,with primary seawater and gypsum dehydration as the main sources of deep brines,while multi-stage tectonic modification is the key to the enrichment of halite-type polyhalite and potassiumlithium brines.Fourth,the ore-forming process has gone through four stages:salt-gathering and potassium-lithium accumulation period,initial water-rock reaction period,transformation and aggregation period,and enrichment and finalization period.During this process,the halite-type polyhalite layer in Jia 4 Member and Jia 5 Member is the main target for potassium solution mining,while the brine layer in Lei 1 Member is the focus of comprehensive potassium-lithium exploration and development.
基金Supported by the National Science and Technology Major Project(2024ZD1404901,2017ZX05035)Strategic Priority Research Program(Category B)of the Chinese Academy of Sciences(XDB10050100).
文摘To clarify the mechanism of differential enrichment of intrasource shale oil,taking the third of seventh member of the Triassic Yanchang Formation(Chang 7_(3)submember for short)in the Ordos Basin,NW China as an example,we integrated high-resolution scanning electron microscopy(SEM),optical microscopy,laser Raman spectroscopy,rock pyrolysis,and organic solvent extraction experiments to identify solid bitumen of varying origins,obtain direct evidence of intrasource micro-migration of shale oil,and establish the coupling between the shale nano/micro-fabric and the oil generation,migration and accumulation.The Chang 7_(3)shale with rich alginite in laminae has the highest hydrocarbon generation potential but a low thermal transformation ratio.Frequent alternations of micron-scale argillaceous-felsic laminae enhance the hydrocarbon expulsion efficiency,yielding consistent aromaticity between in-situ and migrated solid bitumen.Mudstone laminae rich in terrestrial organic matter(OM)and clay minerals exhibit lower hydrocarbon generation threshold but stronger hydrocarbon retention capacity,with a certain amount of light oil/bitumen preserved to differentiate the chemical structure of in-situ versus migrated bitumen.Tuffaceous and sandy laminae contain abundant felsic minerals and migrated bitumen.Tuffaceous laminae develop high-angle microfractures under shale overpressure,facilitating oil charging into rigid mineral intergranular pores of sandy laminae.Fractionation during micro-migration progressively decreases the aromatization of solid bitumen from shale,through tuffaceous and mudstone,to sandy laminae,while increasing light hydrocarbon components and enhancing OM-hosted pore development.The intrasource micro-migration and enrichment of the Chang 7_(3)shale oil result from synergistic organic-inorganic diagenesis,with crude oil component fractionation being a key mechanism for forming sweet spots in laminated shale oil reservoirs.
