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
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 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
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
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
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
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
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
1.Objectives,A nearly E-W trending Early Mesozoic alkaline and mafic rock belt is exposed on the northern margin of the North China Craton(NCC),and geochemistry and isotope studies indicate that the magmas were origin...1.Objectives,A nearly E-W trending Early Mesozoic alkaline and mafic rock belt is exposed on the northern margin of the North China Craton(NCC),and geochemistry and isotope studies indicate that the magmas were originated from the depleted lithospheric mantle,implying the thinning and destruction of the lithosphere in the northern margin and eastern of the NCC(Zhang SH et al.,2012).The Alxa Block is located in the westernmost part of the NCC,which plays a significant part in understanding the tectonic evolution of the NCC.This paper mainly reports a firstly discovered 217 Ma gabbro from the Yabulai district in the western Alxa Block,where widely exposes Late Paleozoic intermediate-acid intrusive rocks and volcanic rocks(Liu Q et al.,2017).展开更多
The late Palaeozoic tectonic magmatism in the north-ern Qaidam tectonic belt(NQTB)related to the Palaeo-Tethys Ocean has become a critical issue.We performed a detailed geochronological and geochemical study of Lenghu...The late Palaeozoic tectonic magmatism in the north-ern Qaidam tectonic belt(NQTB)related to the Palaeo-Tethys Ocean has become a critical issue.We performed a detailed geochronological and geochemical study of Lenghu(LH)granitic rocks in the western NQTB.LA-ICP-MS U-Pb dating of zircons from LH granitic rocks yields emplacement ages of 253±4 Ma and 264±4 Ma,indicating a two-stage emplacement process.Geochemi-cal analyses show that the LH granitic rocks have low ACNK values and are enriched in LILEs(Rb,Th,Ba)and depleted in HFSEs(Sr,Nd,and Ta).The samples are enriched in LREEs(LREE/HREE=1.5-7.3).Values of(La/Yb)N range between 0.9 and 6.5,and all samples show negative Eu anomalies(δEu=0.2-0.6),with typical characteristics of island arc magmatism.The LH granitic rocks haveεHf(t)values of-3.7 to+8.0 and yield a TCDM age of 1.51-0.78 Ga.The data suggest that the LH granitic rocks were derived from partial melting of Proterozoic crust-related mafic to intermediate rocks with significant crust-mantle interac-tions.The results,combined with regional magmatic informa-tion,indicate that the Late Permian-early Triassic magmatism in western NQTB were controlled by subduction rollback-retraction of South Kunlun Oceanic plate under the Kun-lun-Qaidam Block.展开更多
The Triassic granitoids in Central Tianshan play a key role in determining the petrogenesis and tectonic evolution on the southern margin of the Central Asian orogenic belt.In this study,we present SHRIMP zircon U-Pb ...The Triassic granitoids in Central Tianshan play a key role in determining the petrogenesis and tectonic evolution on the southern margin of the Central Asian orogenic belt.In this study,we present SHRIMP zircon U-Pb ages,Hf isotopic and geochemical data on the Xingxingxia biotite granite,amazonite granite and granitic pegmatite in Central Tianshan,NW China.Zircon U-Pb dating yielded formation ages of 242 Ma for the biotite granite and 240 Ma for the amazonite granite.These granitoid rocks have high K_(2)O with low MgO and CaO contents.They are enriched in Nb,Ta,Hf and Y,while being depleted in Ba and Sr,showing flat HREE patterns and negative Eu anomalies.They have typical A-type granite geochemical signatures with high Ga/A_(1)(8–13)and TFeO/(TFeO+MgO)ratios,showing an A_(2) affinity for biotite granite and an A_(1) affinity for amazonite granite and granitic pegmatite.Zircon ε_(Hf)(t)values of the granitoids are 0.45–2.66,with Hf model ages of 0.99–1.17 Ga.This suggests that these A-type granites originated from partial melting of the lower crust.We propose that Xingxingxia Triassic A-type granites formed under lithospheric extension from post-orogenic to anorogenic intraplate settings and NE-trending regional strike-slip fault-controlled magma emplacement in the upper crust.展开更多
The Tianshan range,a Paleozoic orogenic belt in Central Asia,has undergone multiple phases of tectonic activities characterized by the N-S compression after the early Mesozoic,including the far-field effects of the Ce...The Tianshan range,a Paleozoic orogenic belt in Central Asia,has undergone multiple phases of tectonic activities characterized by the N-S compression after the early Mesozoic,including the far-field effects of the Cenozoic Indian-Asian collision.However,there are limited reports on the tectonic deformation and initiation of Triassic intracontinental deformation in the Tianshan range.Understanding this structural context is crucial for interpreting the early intracontinental deformation history of the Eurasian continent during the early Mesozoic.Growth strata and syn-tectonic sediments provide a rich source of information on tectonic activities and have been extensively used in the studies of orogenic belts.Based on detail fieldwork conducted in this study,the middle-late Triassic Kelamayi Formation of the northern Kuqa Depression in the southern Tianshan fold-thrust belt has been identified as the typical syn-tectonic growth strata.The youngest detrital zircon component in two lithic sandstone samples from the bottom and top of the Kelamayi growth strata yielded U-Pb ages of 223.4±3.1 and 215.5±2.9 Ma,respectively,indicating that the maximum depositional age of the bottom and top of the Kelamayi growth strata is 226-220 and 218-212 Ma.The geochronological distribution of detrital samples from the Early-Middle Triassic and Late Triassic revealed abrupt changes,suggesting a new source supply resulting from tectonic activation in the Tianshan range.The coupling relationship between the syn-tectonic sedimentation of the Kelamayi Formation and the South Tianshan fold-thrust system provides robust evidence that the Triassic intracontinental deformation of the South Tianshan range began at approximately 226-220 Ma(during the Late Triassic)and ended at approximately 218-212 Ma.These findings provide crucial constraints for understanding the intraplate deformation in the Tianshan range during the Triassic.展开更多
The Songliao Basin(SLB)covers an area of approximately 260,000 km2in northeastern Asia and preserves a continuous and complete Cretaceous terrestrial record(Wang et al.,2021).The region is the most important petrolife...The Songliao Basin(SLB)covers an area of approximately 260,000 km2in northeastern Asia and preserves a continuous and complete Cretaceous terrestrial record(Wang et al.,2021).The region is the most important petroliferous sedimentary basin in China because of its continual annual oil and gas equivalent production of tens of millions of tons(ca.220–440 million barrels per year)since 1959.The SLB was previously thought to have developed on Hercynian basement and accumulated continuous sedimentary deposits during the Late Jurassic and Cretaceous(Wan et al.,2013;Wang et al.,2016).展开更多
In this study,zircon U-Pb dating of volcanic rocks from the Zhongba ophiolite of the Yarlung Zangbo Suture Zone(YZSZ)in southern Xizang(Tibet)yielded an age of 247±3 Ma.According to whole rock geochemical and Sr-...In this study,zircon U-Pb dating of volcanic rocks from the Zhongba ophiolite of the Yarlung Zangbo Suture Zone(YZSZ)in southern Xizang(Tibet)yielded an age of 247±3 Ma.According to whole rock geochemical and Sr-NdPb isotopic data,the Early Triassic samples could be divided into two groups:Group 1 with P-MORB affinity,showing initial^(87)Sr/^(86)Sr ratios of 0.70253–0.70602,ε_(Nd)(t)values of 4.2–5.3,(^(206)Pb/^(204)Pb)_(t)ratios of 16.353–18.222,(^(207)Pb/^(204)Pb)_(t)ratios of 15.454–15.564,and(^(208)Pb/^(204)Pb)_(t)ratios of 35.665–38.136;Group 2 with OIB affinity,showing initial^(87)Sr/^(86)Sr ratios of 0.70249–0.70513,ε_(Nd)(t)values of 4.4–4.9,(^(206)Pb/^(204)Pb)_(t)ratios of 17.140–18.328,(^(207)Pb/^(204)Pb)_(t)ratios of 15.491–15.575,and(^(208)Pb/^(204)Pb)_(t)ratios of 36.051–38.247.Group 2 rocks formed by partial melting of the mantle source enriched by a former plume,and assimilated continental crustal material during melt ascension.The formation of Group 1 rocks corresponds to the mixing of OIB melts,with the same components as Group 2 and N-MORBs.The Zhongba Early Triassic rocks belong to the continental margin type ophiolite and formed in the continental–oceanic transition zone during the initial opening of the Neo-Tethys in southern Xizang(Tibet).展开更多
To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Memb...To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Member)in the Ordos Basin,thin sections,scanning electron microscopy,energy spectrum analysis,X-ray diffraction whole rock analysis,and dissolution experiments are employed in this study to investigate the characteristics and control factors of feldspar dissolution pores.The results show that:(1)Three types of diagenetic processes are observed in the feldspar of Chang 7 sandstone in the study area:secondary overgrowth of feldspar,replacement by clay and calcite,and dissolution of detrital feldspar.(2)The feldspar dissolution of Chang 7 tight sandstone is caused by organic acid,and is further affected by the type of feldspar,the degree of early feldspar alteration,and the buffering effect of mica debris on organic acid.(3)Feldspars have varying degrees of dissolution.Potassium feldspar is more susceptible to dissolution than plagioclase.Among potassium feldspar,orthoclase is more soluble than microcline,and unaltered feldspar is more soluble than early kaolinized or sericitized feldspar.(4)The dissolution experiment demonstrated that the presence of mica can hinder the dissolution of feldspar.Mica of the same mass has a significantly stronger capacity to consume organic acids than feldspar.(5)Dissolution pores in feldspar of Chang 7 Member are more abundant in areas with low mica content,and they improve the reservoir physical properties,while in areas with high mica content,the number of feldspar dissolution pores decreases significantly.展开更多
Perleididae is a group of stem neopterygian fishes known only from the Triassic.Here,we report the discovery of a new perleidid,Teffichthys wui sp.nov.,based on six well-preserved specimens from the late Smithian(Olen...Perleididae is a group of stem neopterygian fishes known only from the Triassic.Here,we report the discovery of a new perleidid,Teffichthys wui sp.nov.,based on six well-preserved specimens from the late Smithian(Olenekian,Early Triassic)marine deposits of Jurong,Jiangsu and Chaohu,Anhui,China.This new discovery documents the third and youngest species of Teffichthys,which is slightly younger than the Dienerian(Induan)T.elegans from Guizhou and the early Smithian T.madagascariensis from Madagascar.The new species shows diagnostic features of Teffichthys(presence of a spiracular,38-41 lateral line scales,and no more than three epaxial rays in the caudal fin)but differs from T.madagascariensis and T.elegans in some autapomorphies(e.g.,a horizontal opercle/subopercle contact and smooth scales with a nearly straight posterior margin).The diagnostic features for the genus Teffichthys and the family Perleididae are emended based on detailed comparisons of the new taxon with other perleidids.The phylogenetic relationships of perleidids with other stem neopterygians are discussed using a cladistic approach,and the results provide new insights into the phylogeny and classification of main stem neopterygian clades.展开更多
Conodonts,as a biotic group,next to ammonoids,pollen and spores,crustaceans and vertebrates,provide proxy clues for environment and age assessments of the rocks in which they occur.Conodonts are widely used for Triass...Conodonts,as a biotic group,next to ammonoids,pollen and spores,crustaceans and vertebrates,provide proxy clues for environment and age assessments of the rocks in which they occur.Conodonts are widely used for Triassic marine biostratigraphy.However,there are various discussions about their multielement taxonomy and evolutionary lineages(e.g.,generation,speciation).Although first studies reported that most Triassic conodont species were unimembrate,studies carried out in the following years maintained that all Triassic conodonts were multimembrate.Although statistical reconstructions of a number of Triassic apparatuses were attempted,the discovery of fused clusters and natural assemblages has subsequently demonstrated that Triassic conodonts are indeed multimembrate,and all of the elements exist together in the same apparatus.The present paper aims to clarify the evolutionary relationship and array of some Lower Triassic conodonts.Columbitella dagisi n.sp.is described.展开更多
The West Qinling Orogen(WQO)is located in the western part of the Qinling Orogen and in the transition zone of Qilian Orogen,Songpan-Garze Orogen and Yangtze Block,and also the key position of Triassic collision oroge...The West Qinling Orogen(WQO)is located in the western part of the Qinling Orogen and in the transition zone of Qilian Orogen,Songpan-Garze Orogen and Yangtze Block,and also the key position of Triassic collision orogenic event.The study of the Early Triassic strata in the WQO is contributed to analyze the closure process of the paleo-Tethys.We conducted LA-ICP-MS U-Pb dating studies on detrital zircons to determine the provenance,depositional age,and tectonic setting of the Early Triassic Longwuhe Formation in the Lintan area of the WQO.The results show that the majority of the detrital zircons in the Longwuhe Formation are mainly magmatic origin and have characteristic of crust source zircon.The lowest limit of sedimentation of the Longwuhe Formation is constrained to the Early Triassic,with the youngest detrital zircon age of 253±3 Ma.The ages can be divided into five age groups:3346–1636 Ma,with two peak ages of ca.2495 and ca.1885 Ma;1585–1010 Ma,with a peak age at ca.1084 Ma;992–554 Ma,with a peak age at ca.939 Ma;521–421 Ma,with a peak age at ca.445 Ma;418–253 Ma,with a peak age at ca.280 Ma.Apparently,the sources of the Longwuhe Formation include the northern margin of the WQO,the Qilian Orogen(QLO)and the basement of the southern margin of the North China Block(NCB),of which the ancient basement of the southern margin of the NCB is the main source area of the Longwuhe Formation.Combined with previous studies,we propose that the Longwuhe Formation was formed in a fore-arc basin,which is related to the closure of the A’nyemaqen-Mianlüe Ocean from the Early Permian to Early–Middle Triassic due to the northward subduction-collision of the Yangtze Block(YZB).This also indicates that the A’nyemaqen-Mianlüe Ocean has flat subduction characteristics.展开更多
The Curvicubitidae is a Triassic cicada family with some taxa systematically debatable.Here a new curvicubitid species,Beaconiella tongchuanensis sp.nov.,is established from the Middle Triassic Tongchuan Entomofauna i...The Curvicubitidae is a Triassic cicada family with some taxa systematically debatable.Here a new curvicubitid species,Beaconiella tongchuanensis sp.nov.,is established from the Middle Triassic Tongchuan Entomofauna in NW China.Restudy of the two Australian species of Beaconiella Evans,1963(B.fennahi and B.multivenata)confirms that they are different species and first reveals the hindwing venation of B.multivenata.A detailed restudy of Curvicubitus triassicus Hong,1984 confirms the treatment of Curvicubitus as a junior synonym of Beaconiella.A key to all the six species of Beaconiella in Curvicubitidae is first given.Although reported from only three sites,the family Curvicubitidae potentially was globally distributed during the Middle-Late Triassic,implying that this family probably originated as early as the Early Triassic or even the Permian.展开更多
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 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 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 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 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(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 National Key Research and Development Project of the Ministry of Science and Technology of China(Grant No.2017YFC0601301)the Basic Scientific Research Fund of the Institute of Geology,Chinese Academy of Geological Sciences(No.J2103)+1 种基金the National Natural Science Foundation of China(Grant No.41572190,41972224)the China Geological Survey(Grants No.DD2019004).
文摘1.Objectives,A nearly E-W trending Early Mesozoic alkaline and mafic rock belt is exposed on the northern margin of the North China Craton(NCC),and geochemistry and isotope studies indicate that the magmas were originated from the depleted lithospheric mantle,implying the thinning and destruction of the lithosphere in the northern margin and eastern of the NCC(Zhang SH et al.,2012).The Alxa Block is located in the westernmost part of the NCC,which plays a significant part in understanding the tectonic evolution of the NCC.This paper mainly reports a firstly discovered 217 Ma gabbro from the Yabulai district in the western Alxa Block,where widely exposes Late Paleozoic intermediate-acid intrusive rocks and volcanic rocks(Liu Q et al.,2017).
基金supported by the National Natural Science Foundation of China(No.41702204)the China Geology Survey(grant number DD20189614)the Basic Science Founda-tion of the Institute of Geomechanics(grant DZLXJK202004).
文摘The late Palaeozoic tectonic magmatism in the north-ern Qaidam tectonic belt(NQTB)related to the Palaeo-Tethys Ocean has become a critical issue.We performed a detailed geochronological and geochemical study of Lenghu(LH)granitic rocks in the western NQTB.LA-ICP-MS U-Pb dating of zircons from LH granitic rocks yields emplacement ages of 253±4 Ma and 264±4 Ma,indicating a two-stage emplacement process.Geochemi-cal analyses show that the LH granitic rocks have low ACNK values and are enriched in LILEs(Rb,Th,Ba)and depleted in HFSEs(Sr,Nd,and Ta).The samples are enriched in LREEs(LREE/HREE=1.5-7.3).Values of(La/Yb)N range between 0.9 and 6.5,and all samples show negative Eu anomalies(δEu=0.2-0.6),with typical characteristics of island arc magmatism.The LH granitic rocks haveεHf(t)values of-3.7 to+8.0 and yield a TCDM age of 1.51-0.78 Ga.The data suggest that the LH granitic rocks were derived from partial melting of Proterozoic crust-related mafic to intermediate rocks with significant crust-mantle interac-tions.The results,combined with regional magmatic informa-tion,indicate that the Late Permian-early Triassic magmatism in western NQTB were controlled by subduction rollback-retraction of South Kunlun Oceanic plate under the Kun-lun-Qaidam Block.
文摘The Triassic granitoids in Central Tianshan play a key role in determining the petrogenesis and tectonic evolution on the southern margin of the Central Asian orogenic belt.In this study,we present SHRIMP zircon U-Pb ages,Hf isotopic and geochemical data on the Xingxingxia biotite granite,amazonite granite and granitic pegmatite in Central Tianshan,NW China.Zircon U-Pb dating yielded formation ages of 242 Ma for the biotite granite and 240 Ma for the amazonite granite.These granitoid rocks have high K_(2)O with low MgO and CaO contents.They are enriched in Nb,Ta,Hf and Y,while being depleted in Ba and Sr,showing flat HREE patterns and negative Eu anomalies.They have typical A-type granite geochemical signatures with high Ga/A_(1)(8–13)and TFeO/(TFeO+MgO)ratios,showing an A_(2) affinity for biotite granite and an A_(1) affinity for amazonite granite and granitic pegmatite.Zircon ε_(Hf)(t)values of the granitoids are 0.45–2.66,with Hf model ages of 0.99–1.17 Ga.This suggests that these A-type granites originated from partial melting of the lower crust.We propose that Xingxingxia Triassic A-type granites formed under lithospheric extension from post-orogenic to anorogenic intraplate settings and NE-trending regional strike-slip fault-controlled magma emplacement in the upper crust.
基金supported by the National Key Research and Development Project(Grant No.2018YFC0603700)research grants from the China Geological Survey(Grant Nos.DD20230408,DD20190011,DD20191011 and DD20221824)+1 种基金the Fundamental Research Funds from the Chinese Academy of Geological Sciences(Grant No.JKY202011)the Key Laboratory of Airborne Geophysics and Remote Sensing Geology Ministry of Natural Resources(Grant No.2023YFL23)。
文摘The Tianshan range,a Paleozoic orogenic belt in Central Asia,has undergone multiple phases of tectonic activities characterized by the N-S compression after the early Mesozoic,including the far-field effects of the Cenozoic Indian-Asian collision.However,there are limited reports on the tectonic deformation and initiation of Triassic intracontinental deformation in the Tianshan range.Understanding this structural context is crucial for interpreting the early intracontinental deformation history of the Eurasian continent during the early Mesozoic.Growth strata and syn-tectonic sediments provide a rich source of information on tectonic activities and have been extensively used in the studies of orogenic belts.Based on detail fieldwork conducted in this study,the middle-late Triassic Kelamayi Formation of the northern Kuqa Depression in the southern Tianshan fold-thrust belt has been identified as the typical syn-tectonic growth strata.The youngest detrital zircon component in two lithic sandstone samples from the bottom and top of the Kelamayi growth strata yielded U-Pb ages of 223.4±3.1 and 215.5±2.9 Ma,respectively,indicating that the maximum depositional age of the bottom and top of the Kelamayi growth strata is 226-220 and 218-212 Ma.The geochronological distribution of detrital samples from the Early-Middle Triassic and Late Triassic revealed abrupt changes,suggesting a new source supply resulting from tectonic activation in the Tianshan range.The coupling relationship between the syn-tectonic sedimentation of the Kelamayi Formation and the South Tianshan fold-thrust system provides robust evidence that the Triassic intracontinental deformation of the South Tianshan range began at approximately 226-220 Ma(during the Late Triassic)and ended at approximately 218-212 Ma.These findings provide crucial constraints for understanding the intraplate deformation in the Tianshan range during the Triassic.
基金supports from the International Continental Scientific Drilling Programfunded by the National Natural Science Foundation of China(Grant Nos.41790453,41472304,42102129,42102135 and 41972313)+2 种基金Natural Science Foundation of Jilin Province(Grant No.20170101001JC)the National Key Research&Development Program of China(Grant No.2019YFC0605402)China Geological Survey(Grant No.DD20189702)。
文摘The Songliao Basin(SLB)covers an area of approximately 260,000 km2in northeastern Asia and preserves a continuous and complete Cretaceous terrestrial record(Wang et al.,2021).The region is the most important petroliferous sedimentary basin in China because of its continual annual oil and gas equivalent production of tens of millions of tons(ca.220–440 million barrels per year)since 1959.The SLB was previously thought to have developed on Hercynian basement and accumulated continuous sedimentary deposits during the Late Jurassic and Cretaceous(Wan et al.,2013;Wang et al.,2016).
基金the National Natural Science Foundation of China(Grant Nos.91955206,41603038)Second Tibetan Plateau Scientific Expedition and Research program(Grant No.2019QZKK0803)+2 种基金Scientific Research Foundation for Advanced ScholarsWest Yunnan University of Applied Sciences(Grant No.2022RCKY0004)Yunnan Fundamental Research Projects(Grant No.202301AT070012).
文摘In this study,zircon U-Pb dating of volcanic rocks from the Zhongba ophiolite of the Yarlung Zangbo Suture Zone(YZSZ)in southern Xizang(Tibet)yielded an age of 247±3 Ma.According to whole rock geochemical and Sr-NdPb isotopic data,the Early Triassic samples could be divided into two groups:Group 1 with P-MORB affinity,showing initial^(87)Sr/^(86)Sr ratios of 0.70253–0.70602,ε_(Nd)(t)values of 4.2–5.3,(^(206)Pb/^(204)Pb)_(t)ratios of 16.353–18.222,(^(207)Pb/^(204)Pb)_(t)ratios of 15.454–15.564,and(^(208)Pb/^(204)Pb)_(t)ratios of 35.665–38.136;Group 2 with OIB affinity,showing initial^(87)Sr/^(86)Sr ratios of 0.70249–0.70513,ε_(Nd)(t)values of 4.4–4.9,(^(206)Pb/^(204)Pb)_(t)ratios of 17.140–18.328,(^(207)Pb/^(204)Pb)_(t)ratios of 15.491–15.575,and(^(208)Pb/^(204)Pb)_(t)ratios of 36.051–38.247.Group 2 rocks formed by partial melting of the mantle source enriched by a former plume,and assimilated continental crustal material during melt ascension.The formation of Group 1 rocks corresponds to the mixing of OIB melts,with the same components as Group 2 and N-MORBs.The Zhongba Early Triassic rocks belong to the continental margin type ophiolite and formed in the continental–oceanic transition zone during the initial opening of the Neo-Tethys in southern Xizang(Tibet).
基金Supported by the National Natural Science Foundation of China(42202176)CNPC-Southwest University of Petroleum Innovation Consortium Cooperation Project(2020CX050103).
文摘To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Member)in the Ordos Basin,thin sections,scanning electron microscopy,energy spectrum analysis,X-ray diffraction whole rock analysis,and dissolution experiments are employed in this study to investigate the characteristics and control factors of feldspar dissolution pores.The results show that:(1)Three types of diagenetic processes are observed in the feldspar of Chang 7 sandstone in the study area:secondary overgrowth of feldspar,replacement by clay and calcite,and dissolution of detrital feldspar.(2)The feldspar dissolution of Chang 7 tight sandstone is caused by organic acid,and is further affected by the type of feldspar,the degree of early feldspar alteration,and the buffering effect of mica debris on organic acid.(3)Feldspars have varying degrees of dissolution.Potassium feldspar is more susceptible to dissolution than plagioclase.Among potassium feldspar,orthoclase is more soluble than microcline,and unaltered feldspar is more soluble than early kaolinized or sericitized feldspar.(4)The dissolution experiment demonstrated that the presence of mica can hinder the dissolution of feldspar.Mica of the same mass has a significantly stronger capacity to consume organic acids than feldspar.(5)Dissolution pores in feldspar of Chang 7 Member are more abundant in areas with low mica content,and they improve the reservoir physical properties,while in areas with high mica content,the number of feldspar dissolution pores decreases significantly.
文摘Perleididae is a group of stem neopterygian fishes known only from the Triassic.Here,we report the discovery of a new perleidid,Teffichthys wui sp.nov.,based on six well-preserved specimens from the late Smithian(Olenekian,Early Triassic)marine deposits of Jurong,Jiangsu and Chaohu,Anhui,China.This new discovery documents the third and youngest species of Teffichthys,which is slightly younger than the Dienerian(Induan)T.elegans from Guizhou and the early Smithian T.madagascariensis from Madagascar.The new species shows diagnostic features of Teffichthys(presence of a spiracular,38-41 lateral line scales,and no more than three epaxial rays in the caudal fin)but differs from T.madagascariensis and T.elegans in some autapomorphies(e.g.,a horizontal opercle/subopercle contact and smooth scales with a nearly straight posterior margin).The diagnostic features for the genus Teffichthys and the family Perleididae are emended based on detailed comparisons of the new taxon with other perleidids.The phylogenetic relationships of perleidids with other stem neopterygians are discussed using a cladistic approach,and the results provide new insights into the phylogeny and classification of main stem neopterygian clades.
文摘Conodonts,as a biotic group,next to ammonoids,pollen and spores,crustaceans and vertebrates,provide proxy clues for environment and age assessments of the rocks in which they occur.Conodonts are widely used for Triassic marine biostratigraphy.However,there are various discussions about their multielement taxonomy and evolutionary lineages(e.g.,generation,speciation).Although first studies reported that most Triassic conodont species were unimembrate,studies carried out in the following years maintained that all Triassic conodonts were multimembrate.Although statistical reconstructions of a number of Triassic apparatuses were attempted,the discovery of fused clusters and natural assemblages has subsequently demonstrated that Triassic conodonts are indeed multimembrate,and all of the elements exist together in the same apparatus.The present paper aims to clarify the evolutionary relationship and array of some Lower Triassic conodonts.Columbitella dagisi n.sp.is described.
基金supported financially by the National Nature Sciences Foundation of China(Nos.41872235,42172236,41872233,42072267,41802234,41602229 and 41502191)China Scholarship Council(No.201806565026)+3 种基金Natural Science Basic Research Plan in Shaanxi Province of China(Nos.2019JM-312,2019JQ-090 and 2019JQ-209)China Geological Survey(Nos.12120114041201 and DD2016007901)China Postdoctoral Science Foundation(No.2016M592726)the Fundamental Research Funds for the Central Universities of China(Nos.300102270202,300103120009,202110710062,300103183081,300104282717,300102279204 and 201810710233).
文摘The West Qinling Orogen(WQO)is located in the western part of the Qinling Orogen and in the transition zone of Qilian Orogen,Songpan-Garze Orogen and Yangtze Block,and also the key position of Triassic collision orogenic event.The study of the Early Triassic strata in the WQO is contributed to analyze the closure process of the paleo-Tethys.We conducted LA-ICP-MS U-Pb dating studies on detrital zircons to determine the provenance,depositional age,and tectonic setting of the Early Triassic Longwuhe Formation in the Lintan area of the WQO.The results show that the majority of the detrital zircons in the Longwuhe Formation are mainly magmatic origin and have characteristic of crust source zircon.The lowest limit of sedimentation of the Longwuhe Formation is constrained to the Early Triassic,with the youngest detrital zircon age of 253±3 Ma.The ages can be divided into five age groups:3346–1636 Ma,with two peak ages of ca.2495 and ca.1885 Ma;1585–1010 Ma,with a peak age at ca.1084 Ma;992–554 Ma,with a peak age at ca.939 Ma;521–421 Ma,with a peak age at ca.445 Ma;418–253 Ma,with a peak age at ca.280 Ma.Apparently,the sources of the Longwuhe Formation include the northern margin of the WQO,the Qilian Orogen(QLO)and the basement of the southern margin of the North China Block(NCB),of which the ancient basement of the southern margin of the NCB is the main source area of the Longwuhe Formation.Combined with previous studies,we propose that the Longwuhe Formation was formed in a fore-arc basin,which is related to the closure of the A’nyemaqen-Mianlüe Ocean from the Early Permian to Early–Middle Triassic due to the northward subduction-collision of the Yangtze Block(YZB).This also indicates that the A’nyemaqen-Mianlüe Ocean has flat subduction characteristics.
基金supported by the National Natural Science Foundation of China(42293280)the Fundamental Research Funds for the Liaoning Universities and Shenyang Normal University(BS202209).
文摘The Curvicubitidae is a Triassic cicada family with some taxa systematically debatable.Here a new curvicubitid species,Beaconiella tongchuanensis sp.nov.,is established from the Middle Triassic Tongchuan Entomofauna in NW China.Restudy of the two Australian species of Beaconiella Evans,1963(B.fennahi and B.multivenata)confirms that they are different species and first reveals the hindwing venation of B.multivenata.A detailed restudy of Curvicubitus triassicus Hong,1984 confirms the treatment of Curvicubitus as a junior synonym of Beaconiella.A key to all the six species of Beaconiella in Curvicubitidae is first given.Although reported from only three sites,the family Curvicubitidae potentially was globally distributed during the Middle-Late Triassic,implying that this family probably originated as early as the Early Triassic or even the Permian.
