摘要
The first set of Silurian marine red beds(FSRB)in South China exhibits distinct identification markers and spatial distribution.The origin of these red beds is intricately linked to the regional and global tectonic,paleo-oceanic,and paleoclimatic evolutionary processes.However,the scarcity of key fossils and the endemic characteristics of discovered taxa have posed challenges to intercontinental correlation and have led to divergent opinions regarding their age assignment,thereby impeding further in-depth research.Drawing upon fossil evidence from graptolites,conodonts,chitinozoans,brachiopods,and trilobites,this study comprehensively analyzes the age of the FSRB formed under varying paleogeographic conditions in South China.The findings reveal that the FSRB generally situated within the middle Aeronian to lower Telychian,Llandovery(ca.436–439 Ma),corresponding to the graptolite Lituigraptus convolutus Biozone(LM7),the Stimuloraptus sedgwickii Biozone(LM8),the Spirograptus guerichi Biozone(LM9),and the S.turriculatus Biozone(LM10).A notable diachronous pattern is observed for the base of the FSRB,becoming younger from east to west and from south to north.Specifically,the FSRB first emerged along the south margin of the Dabie Oldland during the middle Aeronian.Subsequently,they appeared progressively in the MiddleLower Yangtze/Jiangnan district during late Aeronian and in the Upper Yangtze region near the Aeronian/Telychian boundary.Finally,they occurred around the Chuanzhong Oldland during early Telychian.While the top boundary of the FSRB varies at different localities,it consistently lies below the middle Telychian strata containing the Xiushan Fauna.In the context of global oceanic oxidation in tropic seas,the dynamic spatiotemporal distribution of the FSRB in South China reflects a gradual retreat of anoxic and semi-anoxic waters from shallow seas towards the open ocean,replaced by oxygenated waters over a period of approximately 3 million years across the Aeronian/Telychian boundary.This process is closely associated with the continuous and rapid uplift of the seabed triggered by the northwestward expansion of the Cathaysian Oldland during the Kwangsian Orogeny.
基金
financially supported by the National Key Research and Development Program of China(Grant No.2022YFF0800200)
National Natural Science Foundation of China(Grant No.42372003)
Natural Science Foundation of Jiangsu Province(Grant No.BK20210992)。
