Abstract
Based on the comparison between the sedimentary rate of the Guanyinqiao Member and modern deep sea, as well as the analysis of paleoecology, biopalaeogeographic features, sea level changes and comprehensive sedimentary characteristics, it is demonstrated by the authors that the Guanyinqiao Member in the Yangtze area is formed in the deep sea environment and belongs to contourite facies. The relationship between the events and the mass extinction at the turn of Ordovician-Silurian is discussed. The authors believe that the high-frequency volcanic events, which are widely developed at that time, may be the main and direct cause of the extinction. The coupling effects of volcanic events, iridium and carbon isotope abnormities and the initial hypoxia events in the early Silurian may be the main cause of the extinction of the Hirnantia-Dalmanitina fauna.
Highlights
Since the foundation of the term of Wufeng Shale Member by Sun Yunzhu in 1931, Chinese geologists have debated the sedimentary environment in this area for over 40 years
Based on the comparison between the sedimentary rate of the Guanyinqiao Member and modern deep sea, as well as the analysis of paleoecology, biopalaeogeographic features, sea level changes and comprehensive sedimentary characteristics, it is demonstrated by the authors that the Guanyinqiao Member in the Yangtze area is formed in the deep sea environment and belongs to contourite facies
Some geologists think that Wufeng Shale Member was formed in the epicontinental sea of continental shelf [1]-[10], and others are in favor of the view of the deep-sea environment [11] [12] [13]
Summary
Since the foundation of the term of Wufeng Shale Member by Sun Yunzhu in 1931, Chinese geologists have debated the sedimentary environment in this area for over 40 years. Some geologists think that Wufeng Shale Member was formed in the epicontinental sea of continental shelf [1]-[10], and others are in favor of the view of the deep-sea environment [11] [12] [13]. The Yangtze region starts from the west of Kangdian ancient land. In the early Ordovician, Yangtze region was a stable platform, except for the western Kangdian ancient land, southeastern Jiangnan ancient land and northern Huaiyang ancient land. Since the beginning of the middle Ordovician, the sea level in the Yangtze area has been rising, the nodular limestone of shelf and the cracked limestones of deep shelf formed. In the late stage of Ordovician, deep water shale deposits formed due to the maximum rise of the sea level
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