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LI Xin-wei, LI Chao, ZHOU Li-min, ZHAO Hong. Accurate Determination of the Age of the Carbonaceous Mudstone of the Ordovician-Silurian Boundary in Zheng'an County, Guizhou Province by Re-Os Isotope Dating Method and Its Application in Paleoenvironmental Inversion[J]. Rock and Mineral Analysis, 2020, 39(2): 251-261. DOI: 10.15898/j.cnki.11-2131/td.201907310116
Citation: LI Xin-wei, LI Chao, ZHOU Li-min, ZHAO Hong. Accurate Determination of the Age of the Carbonaceous Mudstone of the Ordovician-Silurian Boundary in Zheng'an County, Guizhou Province by Re-Os Isotope Dating Method and Its Application in Paleoenvironmental Inversion[J]. Rock and Mineral Analysis, 2020, 39(2): 251-261. DOI: 10.15898/j.cnki.11-2131/td.201907310116
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Accurate Determination of the Age of the Carbonaceous Mudstone of the Ordovician-Silurian Boundary in Zheng'an County, Guizhou Province by Re-Os Isotope Dating Method and Its Application in Paleoenvironmental Inversion

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  • BACKGROUNDOrganic-rich sedimentary rocks of the Wufeng-Longmaxi Formation are widely developed in the Ordovician-Silurian boundary of the Upper Yangtze platform in China, which is rich in shale gas resources. Using the Re-Os isotope system to study this set of sedimentary formations, not only can the precise age of the formation be obtained, but also the sedimentary environment of this period based on the enrichment mechanism of Re and Os elements can be inferred. This provides a more reasonable explanation for the trigger mechanism of the second large-scale biological extinction event in Earth's history.OBJECTIVESTo accurately constrain the age of carbonaceous mudstone and infer the conditions of the paleoenvironment.METHODSThe 11 carbonaceous mudstone samples from dirll core of Banzhu No.1, Zheng'an County, Guizhou Province were studied. These dirll core samples were continuous across the boundary of the Ordovician Wufeng Formation-Silurian Longmaxi Formation. Through the high precision Re-Os isotopic dating of the 11 samples, the Ordovician-Silurian boundary stratigraphic age was obtained.RESULTSThe Re-Os isotope age was calculated to be 443.68±6.24Ma2σ, n=7, (187Os/188Os)i=0.699±0.019, MSWD=0.55. The results were highly consistent with the age (443.7±1.5Ma) published by the International Commission on Stratigraphy, which provided a direct and accurate age basis for the Ordovician-Silurian boundary. Os isotope characteristics showed that amounts of terrigenous detrital were involved in the diagenesis, the occurrence of multi-stage volcanic activities and the transition from glacial period to interglacial period. The Re-Os isotopic features of the continuous sedimentary strata reflected that the sedimentary environment of the Ordovician Wufeng Formation-Silurian Longmaxi Formation had undergone the change of oxygen enrichment-oxygen enrichment-rich oxygen enrichment in this study area.CONCLUSIONSHirnantian glaciation events and volcanic eruption caused biological extinction and together promoted organic matter enrichment, providing hydrocarbon generation potential for the Wufeng Formation-Longmaxi Formation organic-rich sedimentary rocks.

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