Paleodepositional conditions and organic matter accumulation mechanisms in the Upper Ordovician-lower Silurian Wufeng-Longmaxi shales, Middle Yangtze region, South China

The deposition of black shales has been widely attributed to primary productivity, preservation controlled by redox conditions, and detrital dilution controlled by sedimentation rates. It is difficult to distinguish the relative importance of productivity and redox conditions in organic matter accumulation. On the Upper Ordovician-Lower Silurian Wufeng-Longmaxi black shales, we combined petrographic features, major and trace elemental proxies, and organic carbon isotopic analysis to determine the relative importance of productivity versus anoxia on organic matter accumulation and the evolution of factors controlling organic matter accumulation across the Ordovician-Silurian boundary in the Middle Yangtze region. Our research also sheds light on the temporal variations in redox conditions that caused the Late Ordovician mass extinction.