Global occurrences of Steptoean Positive Carbon Isotope Excursion（SPICE） during Late Cambrian recorded a significant perturbation in marine carbon cycle, and might have had profound impacts on the biological evoluti...Global occurrences of Steptoean Positive Carbon Isotope Excursion（SPICE） during Late Cambrian recorded a significant perturbation in marine carbon cycle, and might have had profound impacts on the biological evolution. In previous studies, SPICE has been reported from the Jiangnan slope belt in South China. To evaluate the bathymetric extent of SPICE, we investigate the limestone samples from the upper Qingxi Formation in the Shaijiang Section in the Jiangnan Basin. Our results show the positive excursions for both carbonate carbon（δ^（13）C） and organic carbon（δ^（13）C_（org）） isotopes, as well as the concurrent positive shifts in sulfur isotopes of carbonate associated sulfate（CAS, δ^（34）S_（CAS）） and pyrite（δ^（34）S_（pyrite））, unequivocally indicating the presence of SPICE in the Jiangnan Basin. A 4‰ increase in δ^（13）C_（carb） of the Qingxi limestone implies the increase of the relative flux of organic carbon burial by a factor of two. Concurrent positive excursions in δ^（34）S_（CAS） and δ^（34）S_（pyrite） have been attributed to the enhanced pyrite burial in oceans with extremely low concentration and spatially heterogeneous isotopic composition of seawater sulfate. Here, we propose that the seawater sulfur isotopic heterogeneity can be generated by volatile organic sulfur compound（VOSC, such as methanethiol and dimethyl sulfide） formation in sulfidic continental margins that were widespread during SPICE. Emission of 32S-enriched VOSC in atmosphere, followed by lateral transportation and aerobic oxidation in atmosphere, and precipitation in open oceans result in a net flux of ^（32）S from continental margins to open oceans, elevating δ^（34）S of seawater sulfate in continental margins. A simple box model indicates that about 35% to 75% of seawater sulfate in continental margins needs to be transported to open oceans via VOSC formation.展开更多
The Middle-Upper Cambrian Xixiangchi Group in the Sichuan Basin is mainly a set of dolomites of platform facies.In the past,there was no effective way to determine the bottom boundary mark of the Upper Cambrian strata...The Middle-Upper Cambrian Xixiangchi Group in the Sichuan Basin is mainly a set of dolomites of platform facies.In the past,there was no effective way to determine the bottom boundary mark of the Upper Cambrian strata,so natural gas exploration of this horizon lagged behind.In this paper,it is revealed from the C and O isotopic profile of debris that in the middle of the Xixiangchi Group,there is a positive excursion event of carbon isotopes that can be correlated all over the world,so it can be used as an important mark to identify the Furongian Series(equivalent to the Upper Cambrian strata).Then,based on the characteristics of electric curves,the Furongian Series boundary mark was determined and its classification program was worked out preliminarily.It is shown that during the deposition of the Xixiangchi Group,it is a paleo-geomorphologically gentle-slope carbonate platform which is high in the east and low in the east,and a thinemoderate dolomite layer which is thin in the west and thick in the east is deposited.This layer is vertically divided into 4 intervals.Besides,the bottom boundary mark of the Furongian Series in the Sichuan Basin and its adjacent areas can be determined by combining the SPICE(Steptoean Positive Carbon Isotope Excursion)event of carbon isotopes with the characteristics of electric curves.Finally,the carbon isotope mark of the Furongian Series bottom boundary is the SPICE event corresponding to the positive excursion which is regionally correlated,the corresponding electrical mark is the GR small peak areas in the middle of the Xixiangchi group,and the corresponding lithologic symbol is the argillaceous dolomite.The research results are conducive to the further subdivision of the Xixiangchi Group in the Sichuan Basin and its adjacent areas and promoting the study on sedimentary evolution and reservoir distribution laws so that gas exploration in this series of strata can be speeded up.展开更多
The Lomagundi(-Jatuli)event,characterized by extremely high positive global inorganic carbon isotope excursion at about 2.2 billion years ago,is pivotal in investigating the causes and consequences of great oxygenatio...The Lomagundi(-Jatuli)event,characterized by extremely high positive global inorganic carbon isotope excursion at about 2.2 billion years ago,is pivotal in investigating the causes and consequences of great oxygenation event,inventory and sequestration of carbon on the Earth’s surface,evolution of life,and more profoundly tectonic control on Earth’s environment.However,the reasons that caused the isotopic excursion are not resolved yet.Herein,we report the discovery of meta-carbonate rocks with distinct positive carbon isotopic excursion from the Paleoproterozoic continental collision zone of the Kongling Complex,South China Craton.The δ^(13)C_(V-PDB) values for meta-carbonate rocks show positive values in the range from+5.5‰to+11.6‰,whereas the δ^(13)C_(V-PDB) values of associated graphite deposits range from-25.8‰to-9.5‰.Zircon U-Pb-Hf isotopes from zircon-bearing meta-carbonate sample yielded weighted average _(207)Pb/_(206)Pb age of 2001.3±9.5 Ma,with correspondingε_(Hf)(t)range from-7.05 to-3.16,comparable to the values of local 2.9–2.6 Ga basement rocks.Geochemical characteristics of meta-carbonate rocks,such as their rare earth element patterns and the trace element parameters of La,Ce,Eu,and Gd anomalies and Y/Ho ratio,suggest that the carbonate deposition took place in passive continental margin in association with large volumes of organic carbon.The extensive graphite deposits from Kongling Complex in South China Craton,their equivalents in the North China Craton and elsewhere across the globe prove that the burial of ^(12)C-enriched organic carbon has eventually resulted in the global enrichment of ^(13)C in the atmospheric CO_(2),which is recorded in the marine carbonate rocks.Isotopic mass balance estimates indicate that more than half of the organic carbon was buried during the oceanic closure.Hence,the observed global shift could be directly related to the continent collision event in greater China,thus resolving the long-standing paradox of the Lomagundi global positive carbon isotope excursion.Moreover,the present results suggest that orogenesis play a significant role in sequestration of carbon into the continental crust.展开更多
基金supported by the Natural Science Founddation of China (Nos.41272017,41322021)
文摘Global occurrences of Steptoean Positive Carbon Isotope Excursion（SPICE） during Late Cambrian recorded a significant perturbation in marine carbon cycle, and might have had profound impacts on the biological evolution. In previous studies, SPICE has been reported from the Jiangnan slope belt in South China. To evaluate the bathymetric extent of SPICE, we investigate the limestone samples from the upper Qingxi Formation in the Shaijiang Section in the Jiangnan Basin. Our results show the positive excursions for both carbonate carbon（δ^（13）C） and organic carbon（δ^（13）C_（org）） isotopes, as well as the concurrent positive shifts in sulfur isotopes of carbonate associated sulfate（CAS, δ^（34）S_（CAS）） and pyrite（δ^（34）S_（pyrite））, unequivocally indicating the presence of SPICE in the Jiangnan Basin. A 4‰ increase in δ^（13）C_（carb） of the Qingxi limestone implies the increase of the relative flux of organic carbon burial by a factor of two. Concurrent positive excursions in δ^（34）S_（CAS） and δ^（34）S_（pyrite） have been attributed to the enhanced pyrite burial in oceans with extremely low concentration and spatially heterogeneous isotopic composition of seawater sulfate. Here, we propose that the seawater sulfur isotopic heterogeneity can be generated by volatile organic sulfur compound（VOSC, such as methanethiol and dimethyl sulfide） formation in sulfidic continental margins that were widespread during SPICE. Emission of 32S-enriched VOSC in atmosphere, followed by lateral transportation and aerobic oxidation in atmosphere, and precipitation in open oceans result in a net flux of ^（32）S from continental margins to open oceans, elevating δ^（34）S of seawater sulfate in continental margins. A simple box model indicates that about 35% to 75% of seawater sulfate in continental margins needs to be transported to open oceans via VOSC formation.
基金Project supported by the National Major Science and Technology Project(No.2011ZX05004)PetroChina Southwest Oilfield Company Research Project“Xixiangchi stratigraphic division and sedimentary evolution rule research”(No.XNS14NH2015-002).
文摘The Middle-Upper Cambrian Xixiangchi Group in the Sichuan Basin is mainly a set of dolomites of platform facies.In the past,there was no effective way to determine the bottom boundary mark of the Upper Cambrian strata,so natural gas exploration of this horizon lagged behind.In this paper,it is revealed from the C and O isotopic profile of debris that in the middle of the Xixiangchi Group,there is a positive excursion event of carbon isotopes that can be correlated all over the world,so it can be used as an important mark to identify the Furongian Series(equivalent to the Upper Cambrian strata).Then,based on the characteristics of electric curves,the Furongian Series boundary mark was determined and its classification program was worked out preliminarily.It is shown that during the deposition of the Xixiangchi Group,it is a paleo-geomorphologically gentle-slope carbonate platform which is high in the east and low in the east,and a thinemoderate dolomite layer which is thin in the west and thick in the east is deposited.This layer is vertically divided into 4 intervals.Besides,the bottom boundary mark of the Furongian Series in the Sichuan Basin and its adjacent areas can be determined by combining the SPICE(Steptoean Positive Carbon Isotope Excursion)event of carbon isotopes with the characteristics of electric curves.Finally,the carbon isotope mark of the Furongian Series bottom boundary is the SPICE event corresponding to the positive excursion which is regionally correlated,the corresponding electrical mark is the GR small peak areas in the middle of the Xixiangchi group,and the corresponding lithologic symbol is the argillaceous dolomite.The research results are conducive to the further subdivision of the Xixiangchi Group in the Sichuan Basin and its adjacent areas and promoting the study on sedimentary evolution and reservoir distribution laws so that gas exploration in this series of strata can be speeded up.
基金financial support from National Natural Science Foundation of China(41802200)Natural Science Foundation of Hubei Province(2020CFB863)+5 种基金China Scholarship Council(201906415017)China University of Geosciences Wuhan(CUGQY1938)the partial support through JSPS KAKENHI Grant Numbers JP15H05831 and 20KK0081a PhD scholarship support from Niigata Universityfinancial support from National Natural Science Foundation of China(41520104003)China University of Geosciences Wuhan(CUGCJ1709)。
文摘The Lomagundi(-Jatuli)event,characterized by extremely high positive global inorganic carbon isotope excursion at about 2.2 billion years ago,is pivotal in investigating the causes and consequences of great oxygenation event,inventory and sequestration of carbon on the Earth’s surface,evolution of life,and more profoundly tectonic control on Earth’s environment.However,the reasons that caused the isotopic excursion are not resolved yet.Herein,we report the discovery of meta-carbonate rocks with distinct positive carbon isotopic excursion from the Paleoproterozoic continental collision zone of the Kongling Complex,South China Craton.The δ^(13)C_(V-PDB) values for meta-carbonate rocks show positive values in the range from+5.5‰to+11.6‰,whereas the δ^(13)C_(V-PDB) values of associated graphite deposits range from-25.8‰to-9.5‰.Zircon U-Pb-Hf isotopes from zircon-bearing meta-carbonate sample yielded weighted average _(207)Pb/_(206)Pb age of 2001.3±9.5 Ma,with correspondingε_(Hf)(t)range from-7.05 to-3.16,comparable to the values of local 2.9–2.6 Ga basement rocks.Geochemical characteristics of meta-carbonate rocks,such as their rare earth element patterns and the trace element parameters of La,Ce,Eu,and Gd anomalies and Y/Ho ratio,suggest that the carbonate deposition took place in passive continental margin in association with large volumes of organic carbon.The extensive graphite deposits from Kongling Complex in South China Craton,their equivalents in the North China Craton and elsewhere across the globe prove that the burial of ^(12)C-enriched organic carbon has eventually resulted in the global enrichment of ^(13)C in the atmospheric CO_(2),which is recorded in the marine carbonate rocks.Isotopic mass balance estimates indicate that more than half of the organic carbon was buried during the oceanic closure.Hence,the observed global shift could be directly related to the continent collision event in greater China,thus resolving the long-standing paradox of the Lomagundi global positive carbon isotope excursion.Moreover,the present results suggest that orogenesis play a significant role in sequestration of carbon into the continental crust.
