Depositional environment and organic matter accumulation of the Lower Cambrian Shuijingtuo Formation in the middle Yangtze area, China

The organic-rich shale of the Lower Cambrian Shuijingtuo Formation in the Yangtze area is considered a high-quality source rock in South China. Geochemical proxies are used to reveal the formation and preservation conditions of the Shuijingtuo shale in Yichang in the middle Yangtze area. Geochemical proxies for paleoredox (U/Th, V/Cr, Ni/Co, and UEF versus MoEF), paleoproductivity (Ba/Al, Cu/Al, and Ni/Al), and terrigenous influx (Al and Ti) have been employed to interpret the mechanism of organic matter (OM) accumulation. The total organic carbon (TOC) contents of the Shuijingtuo shale is between 0.19 wt% and 4.77 wt% (with an average of 1.38 wt%). The shale can be divided into two intervals based on TOC content, the lower interval with high TOC (TOC >2 wt%) and the upper interval with low TOC (TOC