Organic matter accumulation in response to tectonism: New data from the Upper Permian Dalong Formation black shales in the Western Hubei Basin, South China and its implications for the end-Permian mass extinction

Redox conditions and primary productivity are proposed to be the major controls of organic matter accumulation in sediments. Studies on the impacts of tectonic processes on it are still limited. We took the Late Permian - Early Triassic Western Hubei Basin located in the north of the South China as an example. In black shales in the Dalong Formation, bottom water redox conditions and surface water productivity are constrained based on analysis of total organic carbon (TOC), geochemical (enrichment of Mo, U, Ni, Cd and Zn) and mineralogical characteristics. It shows the highest productivity in the lower Dalong Formation and the most intensively anoxic and restricted conditions in the middle Dalong Formation. The correlation of the sedimentary successions lying the two sides of the basin's boundary fault indicates a subsidence of the basement during the deposition of the lower - middle Dalong Formation, followed by the uplift during the deposition of the upper Dalong Formation. Integrated with the tectonic background of the basin, new data in this study support that: (1) the collision of South and North China plates controlled the paleoceanographic and hydrographic evolution of the Western Hubei Basin, as well as the organic matter accumulation in sediments; (2) the upwelling-induced high productivity and the good preservation in the anoxic environment jointly contributed to the organic matter enrichment in the lower Dalong Formation, while good preservation in anoxic environment is the major cause of the organic matter enrichment in the middle - upper Dalong Formation. This study indicates that tectonism can act as the ultimate driven mechanism for organic matter accumulation in black shales. Our data also supports that plate tectonism in related to the assembly of East Asian blocks with the main body of Pangea can also be treated as one of the ultimate driven mechanisms of the end-Permian mass extinction by creating a restricted anoxic Paleo-Tethys Ocean, which in return exerted a major disturbance to global seawater circulations.