Non-uniform subsidence and its control on the temporal-spatial evolution of the black shale of the Early Silurian Longmaxi Formation in the western Yangtze Block, South China

The Ordovician-Silurian transition was a significant period when an obvious variation occurred worldwide in terms of tectonics, climate, oceans, paleontology, and sedimentology. Here we use stratigraphic forward modeling constrained by paleobiota, paleobathymetry, sedimentology, and geochemistry to study the tectonic subsidence history of the Early Silurian in the western Yangtze Block, South China. Numerical modeling suggests that the tectonic subsidence was not uniform during the deposition of the Early Silurian black shale of the Longmaxi Formation, with acceleration of tectonic subsidence during the later regression period. Furthermore, the subsidence rate at this time was at least three times that during the early transgression period. This acceleration resulted from the collision between the Yangtze Block and the southeastern Cathaysia Block, which affected the tectonic subsidence and the heterogeneity of the black shale. The results may provide quantitative implications for the reconstruction of the paleoenvironment, the evolution of paleobiota, the temporal-spatial distribution of the black shale, and the mechanism of block assemblage in South China.