To improve the understanding of the relationship between silica source and organic matter accumulation,the origin of silica and its implications for organic matter enrichment in the Upper OrdovicianLower Silurian(O_(3...To improve the understanding of the relationship between silica source and organic matter accumulation,the origin of silica and its implications for organic matter enrichment in the Upper OrdovicianLower Silurian(O_(3)w-S_(1)l)black shale in western Hubei Province in the middle Yangtze area,were investigated through geochemical and petrological analyses.The results show that the O_(3)w-S_(1)l black shale is mainly composed of five lithofacies with varying graptolite abundance,total organic carbon(TOC),and silica contents.Biogenic silica and terrigenous siliciclastic input constitute the main silica sources in O_(3)w-S_(1)l black shale and they exhibit an upward inverse variation trend interpreted to be related to sea-level changes.Moreover,with the increase in biogenic silica content or decrease in terrigenous siliciclastic input,TOC values in black shale initially rise and then fall,which is different from originally expected simple linear relationship.We infer that organic matter enrichment and the distribution of silica from different origins are controlled by sea-level changes and variations in terrigenous input in a continental shelf with little hydrothermal influence.An environment with appropriate sea level and terrigenous input should be most favorable for organic matter accumulation,rather than one with excessive high sea level and less terrigenous input.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
基金financially supported by the Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education(China University of Geosciences)(Grant no.TPR-2021-13)the Science and technology research project of Hubei Provincial Department of Education(Grant no.Q20211304)+1 种基金the National Science and Technology Major Project of China(Grant no.2016ZX050340010022017ZX05035001-002)。
文摘To improve the understanding of the relationship between silica source and organic matter accumulation,the origin of silica and its implications for organic matter enrichment in the Upper OrdovicianLower Silurian(O_(3)w-S_(1)l)black shale in western Hubei Province in the middle Yangtze area,were investigated through geochemical and petrological analyses.The results show that the O_(3)w-S_(1)l black shale is mainly composed of five lithofacies with varying graptolite abundance,total organic carbon(TOC),and silica contents.Biogenic silica and terrigenous siliciclastic input constitute the main silica sources in O_(3)w-S_(1)l black shale and they exhibit an upward inverse variation trend interpreted to be related to sea-level changes.Moreover,with the increase in biogenic silica content or decrease in terrigenous siliciclastic input,TOC values in black shale initially rise and then fall,which is different from originally expected simple linear relationship.We infer that organic matter enrichment and the distribution of silica from different origins are controlled by sea-level changes and variations in terrigenous input in a continental shelf with little hydrothermal influence.An environment with appropriate sea level and terrigenous input should be most favorable for organic matter accumulation,rather than one with excessive high sea level and less terrigenous input.
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.
