Abstract: During  Late Ordovician and Early Silurian, multiple layers of K-bentonite were deposited on  Yangtze block and surrounding areas, indicating frequent volcanic activity. Previous studies primarily focused on the chronology of the Ordovician-Silurian boundary. This study carried out a lithostratigraphic division of the Shimenkan section in Yongshan County, Yunnan Province, western edge of  Upper Yangtze, dividing it into the Jiancaogou Formation, Wufeng Formation, Longmaxi Formation Ⅰ, Longmaxi Formation Ⅱ and Xintan Formation. Eleven K-bentonite layers, each over 1 cm thick, were identified. Zircon U-Pb dating of K-bentonite at the boundaries of each formation yielded ages of (449.9±4.3) Ma for the base of Jiancaogou Formation, (443.8±1.0) Ma for the Wufeng and Longmaxi boundary, (438.5±3.5) Ma for the Longmaxi Formation Ⅰ  and Ⅱ  boundary, and (437.8±5.6) Ma for the top of the Xintan Formation. The trace elements characteristics of zircons suggest that  Late Ordovician-Early Silurian bentonites originated from a subduction-collision orogenic environment due to the convergence of  Cathaysian and Yangtze blocks. Additionally, the first layer of bentonites reflects the presence of residual ocean basins in South China, with its zircon U-Pb age (449.9±4.3) Ma marking the initial time of Guangxi movement on the western margin of  Upper Yangtze. However, there is no direct link between high-frequency volcanic activities with mass extinction events.

Key words: western margin of Upper Yangtze, K-bentonite, zircon U-Pb dating, zircon trace elements, mass extinction event