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
Using data from tens of measured and observed outcrop successions,thin rock slices and sample analyses,we comprehensively studied the Cambrian sedimentary environments and evolutionary characteristics in the north mar...Using data from tens of measured and observed outcrop successions,thin rock slices and sample analyses,we comprehensively studied the Cambrian sedimentary environments and evolutionary characteristics in the north margin of the Middle-Upper Yangtze Plate.During the Cambrian,platform,slope,and deep sea basin environments were developed in the study area.On the platform,both clastic rocks and carbonate rocks were deposited.Clastic rocks mainly occur in the Lower Cambrian,and were deposited in marine shore and shelf environments.Carbonate rocks are dominant in the Middle and Upper Cambrian,and were deposited in the open platform,restricted platform,tidal flat,beach,and reef environments.Carbonate gravity flow deposits were developed on the slope.In the basin,mainly black shales and chert beds were deposited.The Cambrian represents one large transgression-regression cycle,and maximum transgression occurred in the Qiongzhusi Age of the Early Cambrian.Tectonics and sea level fluctuations had important impacts on sedimentary environments.The Chengkou-Fangxian-Xiangfan Fracture controlled the position of the platform,slope and basin,as well as the silica supply for chert deposition in basin.Sea level fluctuations controlled types of sediments and sedimentary facies on the platform.In the study area,there are good reservoir rocks,including dolomites,grainstones,debris flow deposits,sandstones,and conglomerates;there are good source rocks,including black shales,dark micrites,and chert beds;and there are also good reservoir-source rock assemblages.The hydrocarbon potential of the study area is great.展开更多
Salinity is a crucial property of water body and is essential for the restoration of paleoecology and paleoenvironment.However,the theoretical method of application of elemental geochemical proxies to paleosalinity re...Salinity is a crucial property of water body and is essential for the restoration of paleoecology and paleoenvironment.However,the theoretical method of application of elemental geochemical proxies to paleosalinity reconstruction is still underdeveloped.Moreover,accurate determination and reconstruction of paleosalinity and its variation in an offshore lacustrine basin have been extremely challenging thus far.This study presents detailed elemental geochemical investigations from the Zhanhua Sag in the southern Bohai Bay Basin to reconstruct the salinity variation in the Paleogene Eocene Shahejie Formation(50.8-33.9 Ma).Based on the variation of strontium barium ratio(Sr/Ba)and boron gallium ratio(B/Ga),we determined three typical salinity types of water body:salty water(Sr/Ba>0.5,B/Ga>6),brackish water(0.2<Sr/Ba<0.5,3<B/Ga<6),and fresh water(Sr/Ba<0.2,B/Ga<3),after eliminating carbonate-sourced strontium(Sr).The salinity values following Couch’s paleosalinometer r anged from 3.1 to 11.9,reflecting the overall characteristics of oligohaline(0.5<salinity value<5)to mesohaline(5<salinity value<18)brackish water.All proxies yielded similar trends in paleosalinity variation,demonstrating a clear trend of rising and then declining from 50.8 Ma to 33.9 Ma.We considered that the B/Ga ratio had the highest reliability and resolution in determining the salinity types of water body in the study area.The environmental factors causing paleosalinity variation were also thoroughly analysed based on the temporal relationship among the salinity types of watermasses,paleoclimate characteristics from pollen records,and marine transgression events from marine fossils.Our research established a model of paleoclimatic and eustatic mechanisms to explain paleosalinity variation,providing reasonable and integral driving forces for the salinity variation of all offshore lacustrine basins.展开更多
The Upper Ordovician Wufeng-Lower Silurian Longmaxi and the Lower Cambrian Qiongzhusi shales are the major targets for shale gas exploration and development in China.Although the two organic-rich shales share similar ...The Upper Ordovician Wufeng-Lower Silurian Longmaxi and the Lower Cambrian Qiongzhusi shales are the major targets for shale gas exploration and development in China.Although the two organic-rich shales share similar distribution ranges and thicknesses,they exhibit substantially different exploration and development results.This work analyzed the nanopore structures of the shale reservoirs in this region.Pore development of 51 shale samples collected from various formations and locations was compared using the petromineralogical,geochemical,structural geological and reservoir geological methods.The results indicate that the reservoir space in these shales is dominated by organic pores and the total pore volume of micropores,mesopores,macropores in different tectonic areas and formations show different trends with the increase of TOC.It is suggested that organic pores of shale can be well preserved in areas with simple structure and suitable preservation conditions,and the shale with smaller maximum ancient burial depth and later hydrocarbongeneration-end-time is also more conducive to pore preservation.Organic pore evolution models are established,and they are as follows:①Organic matter pore development stage,②Early stage of organic matter pore destruction,and③late stage of organic matter pore destruction.The areas conducive to pore development are favorable for shale gas development.Research results can effectively guide the optimization and evaluation of favorable areas of shale gas.展开更多
In recent years, a considerable amount of microscopic spherules have been found in concentrates recovered from some stratabound gold deposits occurring in Middle-Upper Triassic turbidite series in northwestern Sichuan...In recent years, a considerable amount of microscopic spherules have been found in concentrates recovered from some stratabound gold deposits occurring in Middle-Upper Triassic turbidite series in northwestern Sichuan. Study indicates that these spherules are cosmic dust. It is the first time that cosmic dust of extraterrestrial origin has been found in hydrothermal gold deposits in China.The spherules are steel-grey in colour and show metallic luster. Their grain size is commonly less than 100 μm. According to their composition, they belong to chromium-rich iron cosmic dust. The spherules have complex and diverse microscopic structures and textures, i.e. they show a very distinct Widmanstaten structure.The variation of cosmic dust content in gold deposits exhibits a positive correlation with the mineralization intensities and hydrothermal alteration. Such a relation indicates that the ore sub- stances may transport not only mechanically but also may chemically in hydrothermal solutions.展开更多
The author dwells on palynological characteristics of Middle and Upper Jurassic continental deposits in Transbaikalye within the Chita region adjacent to the territory of China. The paper contains descriptions of thre...The author dwells on palynological characteristics of Middle and Upper Jurassic continental deposits in Transbaikalye within the Chita region adjacent to the territory of China. The paper contains descriptions of three sets of spores and pollen taken from Shadoronsk and one set from Undino-Dainsk biostratigraphic horizons. It also provides comparison characteristics of palynocomplexes that belong to Middle and Upper Jurassic deposits in East Transbaikalye with coeval complexes in Siberia and Kazakhstan and provides geological sequence of their formation.展开更多
Upwelling currents play a crucial role in the enrichment of organic matter,yet the mechanisms driving this process remain incompletely understood due to methodological and data resolution limitations.In this paper,we ...Upwelling currents play a crucial role in the enrichment of organic matter,yet the mechanisms driving this process remain incompletely understood due to methodological and data resolution limitations.In this paper,we employ a combination of biostratigraphic classification,qualitative methods,and quantitative methods to systematically analyze the sedimentological and geochemical characteristics of the Lower Silurian Longmaxi Formation in the northern Chongqing-western Hubei area,southern China.The relationship between the upwelling currents and organic matter enrichment in the shale of the Longmaxi Formation is investigated.Results indicate that the upwelling currents in the study area were primarily influenced by the foreland flexure process.From the Rhuddanian(flexure-sedimentation stage)to the Aeronian(flexure-migration stage),the more intense tectonic activity led to gradual opening of the barrier between the South Qinling Ocean and the Yangtze Platform,resulting in an increase in the influx of the oceanic current.The upwelling currents significantly contributed to the organic matter production,albeit without substantially affecting the preservation conditions.Throughout the succession of the Longmaxi Formation,the organic matter content decreased gradually from the passive continental margin to the foreland flexural stagnant basin,which was mainly due to deterioration of the preservation conditions as a result of sea level fall and increased terrigenous input.Despite the increase in the upwelling currents,they did not decisively control the organic matter enrichment.Spatially,during the Rhuddanian to Aeronian period,the organic matter content decreased similarly from the passive continental margin to the foreland flexural stagnant basin,influenced by reduced organic matter production caused by weakening of the upwelling currents and the worsening preservation conditions caused by sea-level fall.The terrigenous input had a relatively minor impact.The results of this study provide new insights into the role of upwelling currents in the organic matter enrichment within the Longmaxi Formation,overcoming previous methodological and resolution barriers.展开更多
Figuring out whether the sedimentary provenance regions of the thick deep-water turbidite systems deposited during Middle–Upper Ordovician in South Quruqtagh are the intracontinental uplifts or the peripheral orogeni...Figuring out whether the sedimentary provenance regions of the thick deep-water turbidite systems deposited during Middle–Upper Ordovician in South Quruqtagh are the intracontinental uplifts or the peripheral orogenic belts is of great significance for us to understand the tectono-sedimentary nature of the northeastern Tarim Basin and basin-range coupling processes in the middle Paleozoic.This paper reports the in situ LA-ICP-MS U–Pb ages and Hf isotope data on detrital zircons from two Middle–Upper Ordovician sandstone samples which were collected from the Charchag Formation and the Zatupo Formation in South Quruqtagh,respectively.The results show that the studied two samples have extremely similar U–Pb age patterns and Hf isotopic compositions,reflecting multiphase tectonothermal events with age groups of 527–694,713–870 Ma(peaking at 760 Ma),904–1,090,1,787–2,094 Ma(peaking at 1,975 Ma)and 2,419–2,517 Ma.Combining previous studies,the presence of age groups of 713–1,090 and1,787–2,094 Ma,respectively,demonstrates that Tarim had ever been a part of Rodinia and Columbia supercontinent.Moreover,98%of 713–870 Ma detrital zircons are characterized by negative e Hf(t)values ranging from-38.07 to-0.61,which are highly consistent with those of Neoproterozoic granites from the Quruqtagh area.No Early Paleozoic ages(*470–500 Ma)signifying subduction or collision events in Altyn Tagh were detected in the two samples,indicating that the Middle–Late Ordovician sediments in South Quruqtagh and northern Mangar depression were mainly derived from intracontinental uplifts,i.e.,the North Quruqtagh uplift or the Tabei paleo-uplift,rather than the Altyn Tagh.In conjunction with regional sedimentary-tectonic background and previous studies,we proposed preliminarily that the northeastern Tarim remained as a passive continental margin in Late Ordovician and changed into an active-continental margin in Silurian due to the southward subduction of the South-Tianshan Ocean.展开更多
Earth’s ecosystems and human activities are threatened by a broad spectrum of hazards of major importance for the safety of ground infrastructures,space systems and space flight:solar activity,earthquakes,atmospheric...Earth’s ecosystems and human activities are threatened by a broad spectrum of hazards of major importance for the safety of ground infrastructures,space systems and space flight:solar activity,earthquakes,atmospheric and climatic disturbances,changes in the geomagnetic field,fluctuations of the global electric circuit.Monitoring and understanding these major hazards to better predict and mitigate their effects is one of the greatest scientific and operational challenges of the 21st century.Though diverse,these hazards share one feature in common:they all leave their characteristic imprints on a critical layer of the Earth’s environment:its ionosphere,middle and upper atmosphere(IMUA).The objective of the International Meridian Circle Program(IMCP),a major international program led by the Chines Academy of Sciences(CAS),is to deploy,integrate and operate a global network of research and monitoring instruments to use the IMUA as a screen on which to detect these imprints.In this article,we first show that the geometry required for the IMCP global observation system leads to a deployment of instruments in priority along the 120°E-60°W great meridian circle,which will cover in an optimal way both the dominant geographic and geomagnetic latitude variations,possibly complemented by a second Great Circle along the 30°E-150°W meridians to capture longitude variations.Then,starting from the Chinese Meridian Project(CMP)network and using it as a template,we give a preliminary and promising description of the instruments to be integrated and deployed along the 120°E-60°W great circle running across China,Australia and the Americas.展开更多
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 China Petroleum Chemical Industry Co.,LTD (Grant No.YPH08015)
文摘Using data from tens of measured and observed outcrop successions,thin rock slices and sample analyses,we comprehensively studied the Cambrian sedimentary environments and evolutionary characteristics in the north margin of the Middle-Upper Yangtze Plate.During the Cambrian,platform,slope,and deep sea basin environments were developed in the study area.On the platform,both clastic rocks and carbonate rocks were deposited.Clastic rocks mainly occur in the Lower Cambrian,and were deposited in marine shore and shelf environments.Carbonate rocks are dominant in the Middle and Upper Cambrian,and were deposited in the open platform,restricted platform,tidal flat,beach,and reef environments.Carbonate gravity flow deposits were developed on the slope.In the basin,mainly black shales and chert beds were deposited.The Cambrian represents one large transgression-regression cycle,and maximum transgression occurred in the Qiongzhusi Age of the Early Cambrian.Tectonics and sea level fluctuations had important impacts on sedimentary environments.The Chengkou-Fangxian-Xiangfan Fracture controlled the position of the platform,slope and basin,as well as the silica supply for chert deposition in basin.Sea level fluctuations controlled types of sediments and sedimentary facies on the platform.In the study area,there are good reservoir rocks,including dolomites,grainstones,debris flow deposits,sandstones,and conglomerates;there are good source rocks,including black shales,dark micrites,and chert beds;and there are also good reservoir-source rock assemblages.The hydrocarbon potential of the study area is great.
基金Supported by the National Natural Science Foundation of China(No.42272110)。
文摘Salinity is a crucial property of water body and is essential for the restoration of paleoecology and paleoenvironment.However,the theoretical method of application of elemental geochemical proxies to paleosalinity reconstruction is still underdeveloped.Moreover,accurate determination and reconstruction of paleosalinity and its variation in an offshore lacustrine basin have been extremely challenging thus far.This study presents detailed elemental geochemical investigations from the Zhanhua Sag in the southern Bohai Bay Basin to reconstruct the salinity variation in the Paleogene Eocene Shahejie Formation(50.8-33.9 Ma).Based on the variation of strontium barium ratio(Sr/Ba)and boron gallium ratio(B/Ga),we determined three typical salinity types of water body:salty water(Sr/Ba>0.5,B/Ga>6),brackish water(0.2<Sr/Ba<0.5,3<B/Ga<6),and fresh water(Sr/Ba<0.2,B/Ga<3),after eliminating carbonate-sourced strontium(Sr).The salinity values following Couch’s paleosalinometer r anged from 3.1 to 11.9,reflecting the overall characteristics of oligohaline(0.5<salinity value<5)to mesohaline(5<salinity value<18)brackish water.All proxies yielded similar trends in paleosalinity variation,demonstrating a clear trend of rising and then declining from 50.8 Ma to 33.9 Ma.We considered that the B/Ga ratio had the highest reliability and resolution in determining the salinity types of water body in the study area.The environmental factors causing paleosalinity variation were also thoroughly analysed based on the temporal relationship among the salinity types of watermasses,paleoclimate characteristics from pollen records,and marine transgression events from marine fossils.Our research established a model of paleoclimatic and eustatic mechanisms to explain paleosalinity variation,providing reasonable and integral driving forces for the salinity variation of all offshore lacustrine basins.
基金supported by the National Science and Technology Major Project(Grant No.2017ZX05035)
文摘The Upper Ordovician Wufeng-Lower Silurian Longmaxi and the Lower Cambrian Qiongzhusi shales are the major targets for shale gas exploration and development in China.Although the two organic-rich shales share similar distribution ranges and thicknesses,they exhibit substantially different exploration and development results.This work analyzed the nanopore structures of the shale reservoirs in this region.Pore development of 51 shale samples collected from various formations and locations was compared using the petromineralogical,geochemical,structural geological and reservoir geological methods.The results indicate that the reservoir space in these shales is dominated by organic pores and the total pore volume of micropores,mesopores,macropores in different tectonic areas and formations show different trends with the increase of TOC.It is suggested that organic pores of shale can be well preserved in areas with simple structure and suitable preservation conditions,and the shale with smaller maximum ancient burial depth and later hydrocarbongeneration-end-time is also more conducive to pore preservation.Organic pore evolution models are established,and they are as follows:①Organic matter pore development stage,②Early stage of organic matter pore destruction,and③late stage of organic matter pore destruction.The areas conducive to pore development are favorable for shale gas development.Research results can effectively guide the optimization and evaluation of favorable areas of shale gas.
基金This study was supported by National Natural Science Foundation of China Grant 4880099
文摘In recent years, a considerable amount of microscopic spherules have been found in concentrates recovered from some stratabound gold deposits occurring in Middle-Upper Triassic turbidite series in northwestern Sichuan. Study indicates that these spherules are cosmic dust. It is the first time that cosmic dust of extraterrestrial origin has been found in hydrothermal gold deposits in China.The spherules are steel-grey in colour and show metallic luster. Their grain size is commonly less than 100 μm. According to their composition, they belong to chromium-rich iron cosmic dust. The spherules have complex and diverse microscopic structures and textures, i.e. they show a very distinct Widmanstaten structure.The variation of cosmic dust content in gold deposits exhibits a positive correlation with the mineralization intensities and hydrothermal alteration. Such a relation indicates that the ore sub- stances may transport not only mechanically but also may chemically in hydrothermal solutions.
文摘The author dwells on palynological characteristics of Middle and Upper Jurassic continental deposits in Transbaikalye within the Chita region adjacent to the territory of China. The paper contains descriptions of three sets of spores and pollen taken from Shadoronsk and one set from Undino-Dainsk biostratigraphic horizons. It also provides comparison characteristics of palynocomplexes that belong to Middle and Upper Jurassic deposits in East Transbaikalye with coeval complexes in Siberia and Kazakhstan and provides geological sequence of their formation.
基金supported by the Hubei Province Natural Science Geological Innovation Development Joint Funding Project (2024AFD388)。
文摘Upwelling currents play a crucial role in the enrichment of organic matter,yet the mechanisms driving this process remain incompletely understood due to methodological and data resolution limitations.In this paper,we employ a combination of biostratigraphic classification,qualitative methods,and quantitative methods to systematically analyze the sedimentological and geochemical characteristics of the Lower Silurian Longmaxi Formation in the northern Chongqing-western Hubei area,southern China.The relationship between the upwelling currents and organic matter enrichment in the shale of the Longmaxi Formation is investigated.Results indicate that the upwelling currents in the study area were primarily influenced by the foreland flexure process.From the Rhuddanian(flexure-sedimentation stage)to the Aeronian(flexure-migration stage),the more intense tectonic activity led to gradual opening of the barrier between the South Qinling Ocean and the Yangtze Platform,resulting in an increase in the influx of the oceanic current.The upwelling currents significantly contributed to the organic matter production,albeit without substantially affecting the preservation conditions.Throughout the succession of the Longmaxi Formation,the organic matter content decreased gradually from the passive continental margin to the foreland flexural stagnant basin,which was mainly due to deterioration of the preservation conditions as a result of sea level fall and increased terrigenous input.Despite the increase in the upwelling currents,they did not decisively control the organic matter enrichment.Spatially,during the Rhuddanian to Aeronian period,the organic matter content decreased similarly from the passive continental margin to the foreland flexural stagnant basin,influenced by reduced organic matter production caused by weakening of the upwelling currents and the worsening preservation conditions caused by sea-level fall.The terrigenous input had a relatively minor impact.The results of this study provide new insights into the role of upwelling currents in the organic matter enrichment within the Longmaxi Formation,overcoming previous methodological and resolution barriers.
基金supported by the National Natural Science Foundation of China(41172096)the National Science and Technology Major Project of China(2011ZX05008-003)
文摘Figuring out whether the sedimentary provenance regions of the thick deep-water turbidite systems deposited during Middle–Upper Ordovician in South Quruqtagh are the intracontinental uplifts or the peripheral orogenic belts is of great significance for us to understand the tectono-sedimentary nature of the northeastern Tarim Basin and basin-range coupling processes in the middle Paleozoic.This paper reports the in situ LA-ICP-MS U–Pb ages and Hf isotope data on detrital zircons from two Middle–Upper Ordovician sandstone samples which were collected from the Charchag Formation and the Zatupo Formation in South Quruqtagh,respectively.The results show that the studied two samples have extremely similar U–Pb age patterns and Hf isotopic compositions,reflecting multiphase tectonothermal events with age groups of 527–694,713–870 Ma(peaking at 760 Ma),904–1,090,1,787–2,094 Ma(peaking at 1,975 Ma)and 2,419–2,517 Ma.Combining previous studies,the presence of age groups of 713–1,090 and1,787–2,094 Ma,respectively,demonstrates that Tarim had ever been a part of Rodinia and Columbia supercontinent.Moreover,98%of 713–870 Ma detrital zircons are characterized by negative e Hf(t)values ranging from-38.07 to-0.61,which are highly consistent with those of Neoproterozoic granites from the Quruqtagh area.No Early Paleozoic ages(*470–500 Ma)signifying subduction or collision events in Altyn Tagh were detected in the two samples,indicating that the Middle–Late Ordovician sediments in South Quruqtagh and northern Mangar depression were mainly derived from intracontinental uplifts,i.e.,the North Quruqtagh uplift or the Tabei paleo-uplift,rather than the Altyn Tagh.In conjunction with regional sedimentary-tectonic background and previous studies,we proposed preliminarily that the northeastern Tarim remained as a passive continental margin in Late Ordovician and changed into an active-continental margin in Silurian due to the southward subduction of the South-Tianshan Ocean.
基金This work was supported by the International PartnershipProgram of Chinese Academy of Sciences(Grant No.183311KYSB20200003)the Beijing Municipal Science and Technology Commission(Grant No.Z181100002918001).
文摘Earth’s ecosystems and human activities are threatened by a broad spectrum of hazards of major importance for the safety of ground infrastructures,space systems and space flight:solar activity,earthquakes,atmospheric and climatic disturbances,changes in the geomagnetic field,fluctuations of the global electric circuit.Monitoring and understanding these major hazards to better predict and mitigate their effects is one of the greatest scientific and operational challenges of the 21st century.Though diverse,these hazards share one feature in common:they all leave their characteristic imprints on a critical layer of the Earth’s environment:its ionosphere,middle and upper atmosphere(IMUA).The objective of the International Meridian Circle Program(IMCP),a major international program led by the Chines Academy of Sciences(CAS),is to deploy,integrate and operate a global network of research and monitoring instruments to use the IMUA as a screen on which to detect these imprints.In this article,we first show that the geometry required for the IMCP global observation system leads to a deployment of instruments in priority along the 120°E-60°W great meridian circle,which will cover in an optimal way both the dominant geographic and geomagnetic latitude variations,possibly complemented by a second Great Circle along the 30°E-150°W meridians to capture longitude variations.Then,starting from the Chinese Meridian Project(CMP)network and using it as a template,we give a preliminary and promising description of the instruments to be integrated and deployed along the 120°E-60°W great circle running across China,Australia and the Americas.
