Since 1985, samples with a total weight of more than 14,000 kg, mainly from three key sections in western and northwestern Hunan, South China, have been processed for conodonts. In strata older than the late Late Camb...Since 1985, samples with a total weight of more than 14,000 kg, mainly from three key sections in western and northwestern Hunan, South China, have been processed for conodonts. In strata older than the late Late Cambrian paraconodonts have proved useful for stratigraphic subdivision and correlation. Thirteen conodont zones are proposed in the Middle Cambrian through lowermost Ordovician. The correlation between these zones and those of North China, western U. S.A., western Newfoundland, Canada, and Iran is discussed. In ascending order, these 13 zones are as follows: The Gapparodus bisulcatus-Westergaardodina brevidens Zone, Shandongodus priscus-Hunanognathus tricuspidatus Zone, Westergaardodina quadrata Zone, Westergaardodina matsushitai-W. grandidens Zone, Westergaardodina lui-W. am Zone, Westergaardodina cf. calix-Prooneotodus rotundatus Zone, Proconodontus tenuiserratus Zone, Proconodontus Zone, Eoconodontus Zone, Cordylodus proavus Zone, Cordylodus intermedius Zone, Cordylodus lindstromi Zone, and Cordylodus angulatus Zone (lower part). The Westergaardodina lui-W. ani and Westergaardodina cf. calix-Prooneotodus rotundatus Zones replace the Westergaardodina proligula and Westergaardodina cf. behrae-Prooneotodus rotundatus Zones, respectively, in the lowermost Upper Cambrian. Two new species (Westergaardodina Iui and Westergaardodina ani) and one conditionally identified species (Westergaardodina cf. calix) are described.展开更多
The Tarim Basin is located in northwestern China and is the biggest basin in China with huge oil and gas resources. Especially the Lower to Middle Cambrian and Middle to Upper Ordovician possess the major marine sourc...The Tarim Basin is located in northwestern China and is the biggest basin in China with huge oil and gas resources. Especially the Lower to Middle Cambrian and Middle to Upper Ordovician possess the major marine source rocks in the Tarim Basin and have large shale gas resource potential. The Cambrian–Ordovician shales were mainly deposited in basin–slope facies with thicknesses between 30–180 m. For shales buried shallower than 4500 m, there is high organic matter abundance with TOC（total organic carbon） mainly between 1.0% and 6.0%, favorable organic matter of Type I and Type II, and high thermal maturity with RoE as 1.3%–2.75%. The mineral composition of these Cambrian–Ordovician shale samples is mainly quartz and carbonate minerals while the clay minerals content is mostly lower than 30%, because these samples include siliceous and calcareous shale and marlstone. The Cambrian and Ordovician shales are compacted with mean porosity of 4% and 3%, permeability of 0.0003×10^（-3）–0.09×10^（-3） μm^2 and 0.0002×10^（-3）–0.11×10^（-3） μm^2, and density of 2.30 g/m^3 and 2.55 g/m^3, respectively. The pores in the shale samples show good connectivity and are mainly mesopore in size. Different genetic types of pores can be observed such as intercrystal, intergranular, dissolved, organic matter and shrinkage joint. The reservoir bed properties are controlled by mineral composition and diagenesis. The maximum adsorption amount to methane of these shales is 1.15–7.36 cm^3/g, with main affecting factors being organic matter abundance, porosity and thermal maturity. The accumulation characteristics of natural gas within these shales are jointly controlled by sedimentation, diagenesis, hydrocarbon generation conditions, reservoir bed properties and the occurrence process of natural gas. The natural gas underwent short-distance migration and accumulation, in-place accumulation in the early stage, and adjustment and modification in the later stage. Finally, the Yulin（well Y1） and Tazhong（well T1） areas are identified as the targets for shale gas exploration in the Tarim Basin.展开更多
Late Cambrian to Early Ordovician sedimentary rocks in the western Tarim Basin, Northwest China, are composed of shallow-marine platform carbonates. The Keping Uplift is located in the northwest region of this basin. ...Late Cambrian to Early Ordovician sedimentary rocks in the western Tarim Basin, Northwest China, are composed of shallow-marine platform carbonates. The Keping Uplift is located in the northwest region of this basin. On the basis of petrographic and geochemical features, four matrix replacement dolomites and one type of cement dolomite are identified. Matrix replacement dolomites include （1） micritic dolomites （MD1）; （2） fine-coarse euhedral floating dolomites （MD2）; （3） fine-coarse euhedral dolomites （MD3）; and （4） medium-very coarse anhedral mosaic dolomites （MD4）. Dolomite cement occurs in minor amounts as coarse saddle dolomite cement （CD1） that mostly fills vugs and fractures in the matrix dolomites. These matrix dolomites have δ18O values of ？9.7‰ to ？3.0‰ VPDB （Vienna Pee Dee Belemnite）; δ13C values of ？0.8‰ to 3.5‰ VPDB; 87Sr/86Sr ratios of 0.708516 to 0.709643; Sr concentrations of 50 to 257 ppm; Fe contents of 425 to 16878 ppm; and Mn contents of 28 to 144 ppm. Petrographic and geochemical data suggest that the matrix replacement dolomites were likely formed by normal and evaporative seawater in early stages prior to chemical compaction at shallow burial depths. Compared with matrix dolomites, dolomite cement yields lower δ18O values （？12.9‰ to ？9.1‰ VPDB）; slightly lower δ13C values （？1.6‰-0.6‰ VPDB）; higher 87Sr/86Sr ratios （0.709165-0.709764）; and high homogenization temperature （Th） values （98°C-225°C） and salinities （6 wt%-24 wt% NaCl equivalent）. Limited data from dolomite cement shows a low Sr concentration （58.6 ppm） and high Fe and Mn contents （1233 and 1250 ppm, respectively）. These data imply that the dolomite cement precipitated from higher temperature hydrothermal salinity fluids. These fluids could be related to widespread igneous activities in the Tarim Basin occurring during Permian time when the host dolostones were deeply buried. Faults likely acted as important conduits that channeled dolomitizing fluids from the underlying strata into the basal carbonates, leading to intense dolomitization. Therefore, dolomitization, in the Keping Uplift area is likely related to evaporated seawater via seepage reflux in addition to burial processes and hydrothermal fluids.展开更多
Going deep has been the strategy for the sustainable development of the Tahe Oilfield.Following the TS1 well in block 1,which revealed excellent combinations of hydrocarbon generation,migration and accumulation in the...Going deep has been the strategy for the sustainable development of the Tahe Oilfield.Following the TS1 well in block 1,which revealed excellent combinations of hydrocarbon generation,migration and accumulation in the deeper parts of the Tarim Basin,the TS2 well was drilled to learn more about the prospectivity in the deeper parts of the main blocks of the Tahe Oilfield.Seventeen core samples were collected to perform fluid inclusion studies,including petrography,fluorescence microspectrometry,and microthermometry.The results show that the deeper parts of the Tahe Oilfield have a good hydrocarbon potential.The Cambrian source rocks can supply sufficient oil for not only the Cambrian reservoirs,but also for the Lower Ordovician reservoirs.The CambrianOrdovician carbonates reservoirs experienced at least three oil charging events and one late gas charging event.Oil accumulations formed in the early stage of basin evolution were likely destroyed in the late stage with deep burial,tectonic movements,or invasion of hydrothermal fluids.Therefore,the deep hydrocarbon exploration of the Tahe Oilfield,even the whole Tarim Basin,should focus on gas accumulations,although oil accumulations,especially in Cambrian reservoirs,cannot be neglected.展开更多
In Korea, trilobites are among the most intensively studied fossil groups in the past century and provide invaluable information about lower Paleozoic stratigraphy, paleogeography, and tectonics of the Korean Peninsul...In Korea, trilobites are among the most intensively studied fossil groups in the past century and provide invaluable information about lower Paleozoic stratigraphy, paleogeography, and tectonics of the Korean Peninsula. Trilobites occur in the lower Paleozoic Joseon Supergroup of the Taebaeksan Basin which was part of the Sino-Korean Craton in the Paleozoic. The Joseon Supergroup is divided into the Taebaek, Yeongwol, and Mungyeong groups. The Taebaek and Yeongwol groups are richly fossiliferous, while the Mungyeong Group is poorly fossiliferous. Contrasting trilobite faunal contents of the Taebaek and Yeongwol groups resulted in two separate biostratigraphic schemes for the Cambrian–Ordovician of the Taebaeksan Basin. A total of 22 biozones or fossiliferous horizons were recognized in the Taebaek Group; 19 zones were established in the Yeongwol Group; and four biozones were known from the Mungyeong Group. These trilobite biozones of the Taebaeksan Basin indicate the Joseon Supergroup ranges in age from the Cambrian Series 2 to Middle Ordovician and can be correlated well with the formations of North China, South China, and Australia.展开更多
The Cambrian of the North China platform consists chiefly of shallow water deposits and shows the sedimentary characters of an epicontinental sea basin. Controlled mainly by global sea level changes and sedimentary in...The Cambrian of the North China platform consists chiefly of shallow water deposits and shows the sedimentary characters of an epicontinental sea basin. Controlled mainly by global sea level changes and sedimentary influx, the depositional sequences all exhibit as composite sequences. From bottom upward, 14 sequences (3rd order) are recognized, which may be grouped into 5 sequence sets and further into 2 mesosequences (2nd order). It is suggested herein that the Cambrian/Ordovician boundary may better be set at the MFS (maximum flooding surface) of the sequence OSq1, above which the conodont Cordylodus lindstroemi occurs. This position is about 40 m above the traditional Cambrian/Ordovician boundary and is within the Yeli Formation.展开更多
基金This study was supported by the National Natural Science Foundation of China(Grants 4037200140072007+3 种基金49772083 to Dong Xiping)by the Laboratory of Paleobiology and Stratigraphy,Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences(Grant 023106 to Dong Xiping)by the Research Fund for Doctoral Program of High Education(Grant 2000000127 to Dong Xiping)by a travel grant from the Ohio State University(to Stig M.Bergstrom).
文摘Since 1985, samples with a total weight of more than 14,000 kg, mainly from three key sections in western and northwestern Hunan, South China, have been processed for conodonts. In strata older than the late Late Cambrian paraconodonts have proved useful for stratigraphic subdivision and correlation. Thirteen conodont zones are proposed in the Middle Cambrian through lowermost Ordovician. The correlation between these zones and those of North China, western U. S.A., western Newfoundland, Canada, and Iran is discussed. In ascending order, these 13 zones are as follows: The Gapparodus bisulcatus-Westergaardodina brevidens Zone, Shandongodus priscus-Hunanognathus tricuspidatus Zone, Westergaardodina quadrata Zone, Westergaardodina matsushitai-W. grandidens Zone, Westergaardodina lui-W. am Zone, Westergaardodina cf. calix-Prooneotodus rotundatus Zone, Proconodontus tenuiserratus Zone, Proconodontus Zone, Eoconodontus Zone, Cordylodus proavus Zone, Cordylodus intermedius Zone, Cordylodus lindstromi Zone, and Cordylodus angulatus Zone (lower part). The Westergaardodina lui-W. ani and Westergaardodina cf. calix-Prooneotodus rotundatus Zones replace the Westergaardodina proligula and Westergaardodina cf. behrae-Prooneotodus rotundatus Zones, respectively, in the lowermost Upper Cambrian. Two new species (Westergaardodina Iui and Westergaardodina ani) and one conditionally identified species (Westergaardodina cf. calix) are described.
基金financially supported by the National Key Project of Science and Technology for Development of Key Techniques for Shale Gas Exploration and Development(Grant No.2011ZX05018)the State Key Laboratory of Petroleum Resources and Prospecting(No.prp2009-02)of China University of Petroleum(Beijing)
文摘The Tarim Basin is located in northwestern China and is the biggest basin in China with huge oil and gas resources. Especially the Lower to Middle Cambrian and Middle to Upper Ordovician possess the major marine source rocks in the Tarim Basin and have large shale gas resource potential. The Cambrian–Ordovician shales were mainly deposited in basin–slope facies with thicknesses between 30–180 m. For shales buried shallower than 4500 m, there is high organic matter abundance with TOC（total organic carbon） mainly between 1.0% and 6.0%, favorable organic matter of Type I and Type II, and high thermal maturity with RoE as 1.3%–2.75%. The mineral composition of these Cambrian–Ordovician shale samples is mainly quartz and carbonate minerals while the clay minerals content is mostly lower than 30%, because these samples include siliceous and calcareous shale and marlstone. The Cambrian and Ordovician shales are compacted with mean porosity of 4% and 3%, permeability of 0.0003×10^（-3）–0.09×10^（-3） μm^2 and 0.0002×10^（-3）–0.11×10^（-3） μm^2, and density of 2.30 g/m^3 and 2.55 g/m^3, respectively. The pores in the shale samples show good connectivity and are mainly mesopore in size. Different genetic types of pores can be observed such as intercrystal, intergranular, dissolved, organic matter and shrinkage joint. The reservoir bed properties are controlled by mineral composition and diagenesis. The maximum adsorption amount to methane of these shales is 1.15–7.36 cm^3/g, with main affecting factors being organic matter abundance, porosity and thermal maturity. The accumulation characteristics of natural gas within these shales are jointly controlled by sedimentation, diagenesis, hydrocarbon generation conditions, reservoir bed properties and the occurrence process of natural gas. The natural gas underwent short-distance migration and accumulation, in-place accumulation in the early stage, and adjustment and modification in the later stage. Finally, the Yulin（well Y1） and Tazhong（well T1） areas are identified as the targets for shale gas exploration in the Tarim Basin.
基金in part provided by Petro China(Grant No.09HT10500000068)Sinopec(Grant No.G5800-07-ZS-WX032)the State Key Lab of Oil/Gas Reservoir Geology and Exploitation at CDUT(Grant No.PLC200801)to H.Qing
文摘Late Cambrian to Early Ordovician sedimentary rocks in the western Tarim Basin, Northwest China, are composed of shallow-marine platform carbonates. The Keping Uplift is located in the northwest region of this basin. On the basis of petrographic and geochemical features, four matrix replacement dolomites and one type of cement dolomite are identified. Matrix replacement dolomites include （1） micritic dolomites （MD1）; （2） fine-coarse euhedral floating dolomites （MD2）; （3） fine-coarse euhedral dolomites （MD3）; and （4） medium-very coarse anhedral mosaic dolomites （MD4）. Dolomite cement occurs in minor amounts as coarse saddle dolomite cement （CD1） that mostly fills vugs and fractures in the matrix dolomites. These matrix dolomites have δ18O values of ？9.7‰ to ？3.0‰ VPDB （Vienna Pee Dee Belemnite）; δ13C values of ？0.8‰ to 3.5‰ VPDB; 87Sr/86Sr ratios of 0.708516 to 0.709643; Sr concentrations of 50 to 257 ppm; Fe contents of 425 to 16878 ppm; and Mn contents of 28 to 144 ppm. Petrographic and geochemical data suggest that the matrix replacement dolomites were likely formed by normal and evaporative seawater in early stages prior to chemical compaction at shallow burial depths. Compared with matrix dolomites, dolomite cement yields lower δ18O values （？12.9‰ to ？9.1‰ VPDB）; slightly lower δ13C values （？1.6‰-0.6‰ VPDB）; higher 87Sr/86Sr ratios （0.709165-0.709764）; and high homogenization temperature （Th） values （98°C-225°C） and salinities （6 wt%-24 wt% NaCl equivalent）. Limited data from dolomite cement shows a low Sr concentration （58.6 ppm） and high Fe and Mn contents （1233 and 1250 ppm, respectively）. These data imply that the dolomite cement precipitated from higher temperature hydrothermal salinity fluids. These fluids could be related to widespread igneous activities in the Tarim Basin occurring during Permian time when the host dolostones were deeply buried. Faults likely acted as important conduits that channeled dolomitizing fluids from the underlying strata into the basal carbonates, leading to intense dolomitization. Therefore, dolomitization, in the Keping Uplift area is likely related to evaporated seawater via seepage reflux in addition to burial processes and hydrothermal fluids.
基金supported by National Basic Research Program of China(Grant No.2012CB214804)the Fundamental Research Funds for the Central Universities, China University of Geosciences(Wuhan)(Grant No. cug130104)
文摘Going deep has been the strategy for the sustainable development of the Tahe Oilfield.Following the TS1 well in block 1,which revealed excellent combinations of hydrocarbon generation,migration and accumulation in the deeper parts of the Tarim Basin,the TS2 well was drilled to learn more about the prospectivity in the deeper parts of the main blocks of the Tahe Oilfield.Seventeen core samples were collected to perform fluid inclusion studies,including petrography,fluorescence microspectrometry,and microthermometry.The results show that the deeper parts of the Tahe Oilfield have a good hydrocarbon potential.The Cambrian source rocks can supply sufficient oil for not only the Cambrian reservoirs,but also for the Lower Ordovician reservoirs.The CambrianOrdovician carbonates reservoirs experienced at least three oil charging events and one late gas charging event.Oil accumulations formed in the early stage of basin evolution were likely destroyed in the late stage with deep burial,tectonic movements,or invasion of hydrothermal fluids.Therefore,the deep hydrocarbon exploration of the Tahe Oilfield,even the whole Tarim Basin,should focus on gas accumulations,although oil accumulations,especially in Cambrian reservoirs,cannot be neglected.
基金supported by a grant from the National Research Foundation of Korea(Grant No.NRF-2014R1A1A2002851)
文摘In Korea, trilobites are among the most intensively studied fossil groups in the past century and provide invaluable information about lower Paleozoic stratigraphy, paleogeography, and tectonics of the Korean Peninsula. Trilobites occur in the lower Paleozoic Joseon Supergroup of the Taebaeksan Basin which was part of the Sino-Korean Craton in the Paleozoic. The Joseon Supergroup is divided into the Taebaek, Yeongwol, and Mungyeong groups. The Taebaek and Yeongwol groups are richly fossiliferous, while the Mungyeong Group is poorly fossiliferous. Contrasting trilobite faunal contents of the Taebaek and Yeongwol groups resulted in two separate biostratigraphic schemes for the Cambrian–Ordovician of the Taebaeksan Basin. A total of 22 biozones or fossiliferous horizons were recognized in the Taebaek Group; 19 zones were established in the Yeongwol Group; and four biozones were known from the Mungyeong Group. These trilobite biozones of the Taebaeksan Basin indicate the Joseon Supergroup ranges in age from the Cambrian Series 2 to Middle Ordovician and can be correlated well with the formations of North China, South China, and Australia.
文摘The Cambrian of the North China platform consists chiefly of shallow water deposits and shows the sedimentary characters of an epicontinental sea basin. Controlled mainly by global sea level changes and sedimentary influx, the depositional sequences all exhibit as composite sequences. From bottom upward, 14 sequences (3rd order) are recognized, which may be grouped into 5 sequence sets and further into 2 mesosequences (2nd order). It is suggested herein that the Cambrian/Ordovician boundary may better be set at the MFS (maximum flooding surface) of the sequence OSq1, above which the conodont Cordylodus lindstroemi occurs. This position is about 40 m above the traditional Cambrian/Ordovician boundary and is within the Yeli Formation.
