Impacts of major geologic events on sedimentary paleoenvironments and organic matter enrichment of shales during the Ordovician-Silurian boundary:A case study of shales of Wufeng-Longmaxi Formation in Middle and Upper Yangtze regions
Major geological events,such as volcanisms,Hirnantian glaciation,sea level fluctuations,and mass extinctions,occurred with a significant impact on the paleoceanic environment during the geological period of the Ordovician/Silurian boundary.In this study,the shales of Wufeng-Longmaxi Formation in the Middle and Upper Yangtze regions were taken as the main objects of study,and the influence mechanism of different geological events on the paleo-sedimentary environment and the organic matter enrichment of the shales was investigated through the geochemistry characterization.The analysis results showed that the nutrients released from the appropriate amount of volcanic ash input to the ocean by volcanic activity would cause the rapid flourishing of marine organisms,the elevation of the pale ocean productivity guarantees the source of organic matter,and the anoxic environment at the bottom of the ocean caused by the volcanic activity is conducive to the preservation of the buried organic matter.Intense volcanic activity produces toxic substances that will be a threat to the biological survival environment.In addition,the aerosols formed in the atmosphere by volcanic ash can cause solar radiation not to reach the surface,causing a drop in temperature.The biological extinction event at the end of the Ordovician Period occurred under the combined effect of the Hirnantian glaciation and volcanic activity,with a large accumulation of organic matter.
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