The Late Permian to Early Triassic marked a pivotal phase in paleoenvironmental and tectonic shifts.The Kaijiang-Liangping intracratonic sag,a tectonic geomorphology formed by Emei taphrogenesis in the Sichuan Basin,i...The Late Permian to Early Triassic marked a pivotal phase in paleoenvironmental and tectonic shifts.The Kaijiang-Liangping intracratonic sag,a tectonic geomorphology formed by Emei taphrogenesis in the Sichuan Basin,is situated within a clear water carbonate platform.Under these conditions,the black shales of the Dalong Formation in the sag have ultrahigh organic matter content.However,the mechanism by which these conditions control the accumulation of such organic matter remains unclear.Petrological and geochemical analyses of well DY-1H revealed four distinct units within the Dalong Formation:A,B,C,and D,with average total organic carbon contents of 3.00%,9.59%,4.57%,and 0.27%,respectively.The kerogen maceral,carbon isotope,and pyrolysis results show that the organic matter mainly comprises Type Ⅱ_(2) kerogen.Benthic plants growing in clear water may be the primary source of this kerogen.Shallow water,suboxic conditions,strong volcanism,and high productivity characterize Unit A.Unit B features restricted ocean circulation,anoxic conditions,weak upwelling,moderate volcanism,and high productivity.Unit C is characterized by anoxic conditions,strong upwelling,weak volcanism,and moderate productivity.Oxic conditions and low productivity define Unit D.These findings challenge traditional models that struggle to explain the accumulation of ultrahigh organic matter in Unit A under suboxic conditions,Unit C under moderate productivity,and Unit B with abnormally high organic matter content.The flourishing of benthic plants,a considerable source of Type Ⅱ_(2) kerogen that resists decomposition and favors preservation,is the dominant factor controlling the ultrahigh organic matter accumulation of black shales in Units A,B,and C under clear water conditions.Oxidized bottom waters and decreased benthic plant growth were crucial to the sharp decline in organic matter.展开更多
Craton basins are the main sites where marine carbonate oil and gas reservoirs develop in China.However,the previous studies scarcely focused on the controlling effects of tectonic differentiation on the formation of ...Craton basins are the main sites where marine carbonate oil and gas reservoirs develop in China.However,the previous studies scarcely focused on the controlling effects of tectonic differentiation on the formation of large oil and gas fields in the ancient craton basins.In such circumstances,it is difficult to evaluate and select the favorable zones for exploring carbonate oil and gas.In this paper,based on the research results of the SinianeTriassic prototype basin and lithofacies paleogeography of the Sichuan Basin,the tectonic differentiation pattern of craton basins and its controls on the accumulation elements and the distribution of hydrocarbons were analyzed with reference to the concept that structures control the sedimentation and distribution of oil and gas.The study reveals the results in three aspects.First,the intra-cratonic graben controls the high-quality source rocks and the hydrocarbon generation center,which forms good source-reservoir assemblage with the highquality reservoir in the platform margin at the flank,showing excellent near-source accumulation conditions.Second,the three types of paleo-uplifts(i.e.differential denudation,syn-sedimentary,and folding)and the deep-large faults developed in the craton are favorable for the formation and distribution of large-scale carbonate reservoirs.Third,the superimposed areas with tectonic differentiation in multiple periods and multiple types are favorable for forming large oil and gas fields.It is concluded that the marine carbonate rocks show a huge oil and gas exploration potential in the Sichuan Basin.Attention should be paid to the new exploration targets of natural gas,such as the Sinian Dengying Fm.in the platform margin at the east flank of DeyangeAnyue graben,the Lower Cambrian Longwangmiao Fm.on the slope of paleo-uplift in central Sichuan Basin,and the Middle Permian Maokou Fm.in centralewest Sichuan Basin,where oil and gas accumulation conditions are favorable.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.U2344209,U42230310,U42207293)Natural Science Foundation of Sichuan Province,China(Grant No.2023NSFSC0262).
文摘The Late Permian to Early Triassic marked a pivotal phase in paleoenvironmental and tectonic shifts.The Kaijiang-Liangping intracratonic sag,a tectonic geomorphology formed by Emei taphrogenesis in the Sichuan Basin,is situated within a clear water carbonate platform.Under these conditions,the black shales of the Dalong Formation in the sag have ultrahigh organic matter content.However,the mechanism by which these conditions control the accumulation of such organic matter remains unclear.Petrological and geochemical analyses of well DY-1H revealed four distinct units within the Dalong Formation:A,B,C,and D,with average total organic carbon contents of 3.00%,9.59%,4.57%,and 0.27%,respectively.The kerogen maceral,carbon isotope,and pyrolysis results show that the organic matter mainly comprises Type Ⅱ_(2) kerogen.Benthic plants growing in clear water may be the primary source of this kerogen.Shallow water,suboxic conditions,strong volcanism,and high productivity characterize Unit A.Unit B features restricted ocean circulation,anoxic conditions,weak upwelling,moderate volcanism,and high productivity.Unit C is characterized by anoxic conditions,strong upwelling,weak volcanism,and moderate productivity.Oxic conditions and low productivity define Unit D.These findings challenge traditional models that struggle to explain the accumulation of ultrahigh organic matter in Unit A under suboxic conditions,Unit C under moderate productivity,and Unit B with abnormally high organic matter content.The flourishing of benthic plants,a considerable source of Type Ⅱ_(2) kerogen that resists decomposition and favors preservation,is the dominant factor controlling the ultrahigh organic matter accumulation of black shales in Units A,B,and C under clear water conditions.Oxidized bottom waters and decreased benthic plant growth were crucial to the sharp decline in organic matter.
文摘Craton basins are the main sites where marine carbonate oil and gas reservoirs develop in China.However,the previous studies scarcely focused on the controlling effects of tectonic differentiation on the formation of large oil and gas fields in the ancient craton basins.In such circumstances,it is difficult to evaluate and select the favorable zones for exploring carbonate oil and gas.In this paper,based on the research results of the SinianeTriassic prototype basin and lithofacies paleogeography of the Sichuan Basin,the tectonic differentiation pattern of craton basins and its controls on the accumulation elements and the distribution of hydrocarbons were analyzed with reference to the concept that structures control the sedimentation and distribution of oil and gas.The study reveals the results in three aspects.First,the intra-cratonic graben controls the high-quality source rocks and the hydrocarbon generation center,which forms good source-reservoir assemblage with the highquality reservoir in the platform margin at the flank,showing excellent near-source accumulation conditions.Second,the three types of paleo-uplifts(i.e.differential denudation,syn-sedimentary,and folding)and the deep-large faults developed in the craton are favorable for the formation and distribution of large-scale carbonate reservoirs.Third,the superimposed areas with tectonic differentiation in multiple periods and multiple types are favorable for forming large oil and gas fields.It is concluded that the marine carbonate rocks show a huge oil and gas exploration potential in the Sichuan Basin.Attention should be paid to the new exploration targets of natural gas,such as the Sinian Dengying Fm.in the platform margin at the east flank of DeyangeAnyue graben,the Lower Cambrian Longwangmiao Fm.on the slope of paleo-uplift in central Sichuan Basin,and the Middle Permian Maokou Fm.in centralewest Sichuan Basin,where oil and gas accumulation conditions are favorable.
