The Late Paleozoic Ice Age across Carboniferous and Permian had a significant impact on the Kungurian （Upper Cisuralian series of Permian） Chihsia Formation in South China. This re- suited in a unique interval with ...The Late Paleozoic Ice Age across Carboniferous and Permian had a significant impact on the Kungurian （Upper Cisuralian series of Permian） Chihsia Formation in South China. This re- suited in a unique interval with features such as the lack of reef in Chihsian limestone, widespread stinkstone and nodular/bedded chert. The Chihsia limestone （Kungurian stage） deposited during a time of cooling was resulted from oceanic upwelling. Here we present evidence for this upwelling using sev- eral geochemical analyses： bulk organic carbon isotope, biomarker molecular geochemical data, and authigenic silica of the stinkstone member in the lower Chihsia Formation of the Kuangurian stage from the Enshi Section in western Hubei Province, South China. The lower part of the stinkstone member shows a rapid organic carbon isotope excursion with a -3%o shift triggered by the upwelling of 13C-depleted bottom water. The concurrent rapid increasing of authigenic silica content resulted from the enhanced supply of dissolved silica in the upwelling water mass. This upwelling at the Enshi Section also led to relative high TOC content, accounting for the widespread stinkstone in the lower Chihsia Formation during the Kungurian stage in Permian.展开更多
Highly-mature carbonate source rock is essential to the exploration of oil and gas in southern China. In this study, the carbonate strata in the relatively well-developed Lower Permian Chihsia Formation (located in Ch...Highly-mature carbonate source rock is essential to the exploration of oil and gas in southern China. In this study, the carbonate strata in the relatively well-developed Lower Permian Chihsia Formation (located in Chaohu, Lower Yangtze) were targeted, and the formation and influencing factors of source rock were discussed based on paleoenvironment reconstruction using comprehensive sedimentology, palynofacies, and organic geochemistry data. The results demonstrate that the Chihsia Formation is oxygen-deficient biogenic carbonate sediments, with marked variations in the organic and inorganic components, formed during a period of Permian transgression. The formation of source rock is the combined result of high bioproductivity and oxygen-deficient environment generated by transgression and oxygenation events which frequently occurred during transgression periods. Source rock was affected by self-dilution effects and diagenesis, causing its heterogeneous distribution in many intervals. Source rock is over 40 m thick, and can be identified based on its different organic, biological, and mineral composition characteristics. The carbonate rock appears to require no specific clay content in order to become a source rock. The combination of sedimentology, palynofacies, and organic geochemistry has provided an effective means for evaluating and predicting high-maturity carbonate source rock in the region.展开更多
Bedding-parallel fibrous veins occurring as lenticular to flattened intercalations were found in the organic-rich marlstone/calcareous shale of the upper Lower Permian Chihsia Formation in western Hubei Province,South...Bedding-parallel fibrous veins occurring as lenticular to flattened intercalations were found in the organic-rich marlstone/calcareous shale of the upper Lower Permian Chihsia Formation in western Hubei Province,South China. They dominantly consist of fibrous calcite crystals with smooth and tight boundaries, forming fencelike inward, syntaxial growth clusters toward the vein center along which a median suture line generally occurs.Petrographic evidence indicates that these veins may form at relatively shallow burial depth, where fluid overpressures would have incrementally created the bed-parallel vein space, resulting in displacive growth of fibrous calcite.On the other hand, the C, O and S isotopic data across the vein reveal slightly depleted d13Ccarbvalues(-3.32 % to +0.19 % VPDB) and moderately depleted d18Ocarbvalues(-9.6 % to-7.3 % VPDB) with respect to those of coeval seawaters and slightly heavier d34Spyritevalues(-7.88 % CDT) with respect to those of ambient rocks.Stable isotope evidence consistently suggests significant contribution of bacterial sulfate reduction(BSR) to the formation of the fibrous calcite cements in the vein. The BSR could have been intensive with the availabilities of residual sulfate and abundant organic matters in theChihsia sediments during shallow burial, increasing the alkalinity of pore waters and further promoting carbonate precipitation. Thus, the bedding-parallel fibrous calcite vein in the upper Lower Permian Chihsia Formation is an important time-specific petrographic capsule, providing clues for understanding the diagenetic process in organicrich sediments.展开更多
The Chihsia Formation is one of the four sets of regional marine hydrocarbon source rocks from South China.In the past two decades,detailed geochemical and sedimentological studies have been carried out to investigate...The Chihsia Formation is one of the four sets of regional marine hydrocarbon source rocks from South China.In the past two decades,detailed geochemical and sedimentological studies have been carried out to investigate its origination,which have demonstrated that the high primary productivity plays a primary role in the deposition of sediments enriched in the organic matter.However,the mechanism of this high productivity and the path of the deposition and burial of the organic matter have always been a mystery.Based on the previous studies on the Shangsi Section in Guangyuan City,Sichuan Province,we proposed that the development of the equatorial upwelling due to the sea level rise is responsible for the relatively high productivity in the Chihsia Formation.The sea waters with high nutrient were transported by the sub-surface currents along the equator.High organic carbon flux was deposited on the deeper shelf,and then decomposed by bacteria,leading to the occurrence of anaerobic respiration.The metabolism of the microorganisms consumed the dissolved oxygen in waters,which was in favor of the preservation of the organic matter.This suggested geobiological model integrating with paleoclimatology,paleoceanography and geomicrobiology will help us to understand the causes of this particular sedimentary sequence.展开更多
基金supported by the National Natural Science Foundation of China (No. 41302021)the Science and Technology Research Project of Jiangxi Province Education Department (No. GJJ13452)+1 种基金Research by Hao Yu is supported by the National Natural Science Foundation of China (No. 41290260)the Ministry of Education of China (No. 20120001110052)
文摘The Late Paleozoic Ice Age across Carboniferous and Permian had a significant impact on the Kungurian （Upper Cisuralian series of Permian） Chihsia Formation in South China. This re- suited in a unique interval with features such as the lack of reef in Chihsian limestone, widespread stinkstone and nodular/bedded chert. The Chihsia limestone （Kungurian stage） deposited during a time of cooling was resulted from oceanic upwelling. Here we present evidence for this upwelling using sev- eral geochemical analyses： bulk organic carbon isotope, biomarker molecular geochemical data, and authigenic silica of the stinkstone member in the lower Chihsia Formation of the Kuangurian stage from the Enshi Section in western Hubei Province, South China. The lower part of the stinkstone member shows a rapid organic carbon isotope excursion with a -3%o shift triggered by the upwelling of 13C-depleted bottom water. The concurrent rapid increasing of authigenic silica content resulted from the enhanced supply of dissolved silica in the upwelling water mass. This upwelling at the Enshi Section also led to relative high TOC content, accounting for the widespread stinkstone in the lower Chihsia Formation during the Kungurian stage in Permian.
基金supported by the National Natural Science Foundation of China (Grant No. 40872089)Science and Technology Office Fund of China Petroleum & Chemical Co., Ltd. (Grant No. G080007ZS188)the National Oil and Gas Special Fund (Grant No. 2008ZX05023-003)
文摘Highly-mature carbonate source rock is essential to the exploration of oil and gas in southern China. In this study, the carbonate strata in the relatively well-developed Lower Permian Chihsia Formation (located in Chaohu, Lower Yangtze) were targeted, and the formation and influencing factors of source rock were discussed based on paleoenvironment reconstruction using comprehensive sedimentology, palynofacies, and organic geochemistry data. The results demonstrate that the Chihsia Formation is oxygen-deficient biogenic carbonate sediments, with marked variations in the organic and inorganic components, formed during a period of Permian transgression. The formation of source rock is the combined result of high bioproductivity and oxygen-deficient environment generated by transgression and oxygenation events which frequently occurred during transgression periods. Source rock was affected by self-dilution effects and diagenesis, causing its heterogeneous distribution in many intervals. Source rock is over 40 m thick, and can be identified based on its different organic, biological, and mineral composition characteristics. The carbonate rock appears to require no specific clay content in order to become a source rock. The combination of sedimentology, palynofacies, and organic geochemistry has provided an effective means for evaluating and predicting high-maturity carbonate source rock in the region.
基金supported by the National Natural Science Foundation of China(40839907,41302021 and41203030)
文摘Bedding-parallel fibrous veins occurring as lenticular to flattened intercalations were found in the organic-rich marlstone/calcareous shale of the upper Lower Permian Chihsia Formation in western Hubei Province,South China. They dominantly consist of fibrous calcite crystals with smooth and tight boundaries, forming fencelike inward, syntaxial growth clusters toward the vein center along which a median suture line generally occurs.Petrographic evidence indicates that these veins may form at relatively shallow burial depth, where fluid overpressures would have incrementally created the bed-parallel vein space, resulting in displacive growth of fibrous calcite.On the other hand, the C, O and S isotopic data across the vein reveal slightly depleted d13Ccarbvalues(-3.32 % to +0.19 % VPDB) and moderately depleted d18Ocarbvalues(-9.6 % to-7.3 % VPDB) with respect to those of coeval seawaters and slightly heavier d34Spyritevalues(-7.88 % CDT) with respect to those of ambient rocks.Stable isotope evidence consistently suggests significant contribution of bacterial sulfate reduction(BSR) to the formation of the fibrous calcite cements in the vein. The BSR could have been intensive with the availabilities of residual sulfate and abundant organic matters in theChihsia sediments during shallow burial, increasing the alkalinity of pore waters and further promoting carbonate precipitation. Thus, the bedding-parallel fibrous calcite vein in the upper Lower Permian Chihsia Formation is an important time-specific petrographic capsule, providing clues for understanding the diagenetic process in organicrich sediments.
基金supported by National Basic Research Program of China (Grant No. 2011CB808800)National Natural Science Foundation of China (Grant No. 41072078)
文摘The Chihsia Formation is one of the four sets of regional marine hydrocarbon source rocks from South China.In the past two decades,detailed geochemical and sedimentological studies have been carried out to investigate its origination,which have demonstrated that the high primary productivity plays a primary role in the deposition of sediments enriched in the organic matter.However,the mechanism of this high productivity and the path of the deposition and burial of the organic matter have always been a mystery.Based on the previous studies on the Shangsi Section in Guangyuan City,Sichuan Province,we proposed that the development of the equatorial upwelling due to the sea level rise is responsible for the relatively high productivity in the Chihsia Formation.The sea waters with high nutrient were transported by the sub-surface currents along the equator.High organic carbon flux was deposited on the deeper shelf,and then decomposed by bacteria,leading to the occurrence of anaerobic respiration.The metabolism of the microorganisms consumed the dissolved oxygen in waters,which was in favor of the preservation of the organic matter.This suggested geobiological model integrating with paleoclimatology,paleoceanography and geomicrobiology will help us to understand the causes of this particular sedimentary sequence.
