Evolution of the Lower Cambrian Oceanic Enviroment in China

Depositional environments for stratiform witherite deposits in the Lower Cambrian black shale sequence of the Yangtze Platform, southern Qinling region, SW China: Evidence from redox-sensitive trace element geochemistry

Authors:

Dao-Hui Pi, Shao-Yong Jiang, Li Luo, Jing-Hong Yang and Hong-Fei Ling

Abstracts:

Very large stratiform witherite mineralization occurs in Lower Cambrian black shales and siliceous rocks in the southern Qinling region of SW China. Two types of witherite ores are divided according to their colours, i.e., the white ores and the dark-gray ores. We analyzed a number of redox-sensitive trace elements in both the white and dark-gray ores from various witherite deposits. The redox-sensitive metal concentrations and the distribution of the two types of ores provide good evidence for their depositional redox conditions in the Early Cambrian ocean in the southern Qinling region. Our geochemical data suggest that both the dark-gray and white witherite ores may have been deposited in reducing environments, with the dark-gray ores deposited in an anoxic-euxinic environment, whereas the white ores deposited under a suboxic-anoxic condition.