Environmental Effects on Differential Organic Matter Enrichment of the Lower Cambrian Shale, Tarim Basin, NW China

Abstract

The early Cambrian shale is of an important petroleum source rock on the Earth. Due to few drilling data and poor seismic data, the organic matter enrichment of the Lower Cambrian shale is still an enigma in the Tarim Basin. Total organic carbon (TOC), major and trace element data of shale samples from five boreholes were experimented to decipher the mechanism of the organic matter enrichment in the early Cambrian shales. The results show that the shales deposited in the western restricted intraplatform have much higher TOC contents (3.2%–19.8%, on average 11.0%) than those from the eastern basin (2.2%–10.2%, on average 4.5%). The paleoproductivity proxies (Ba, Ba/Al, P/Al) in the western restricted platform are much higher than those in the eastern basin. The trace element indicators such as V/Cr, Ni/Co, Mo‐TOC and MoEF‐UEF suggest an anoxic environment across the basin, but a more restricted environment in the western intraplatform. It is concluded that the paleoproductivity rather than anoxic condition and hydrothermal activity have resulted in the differentiation of the organic matter enrichment from the western intraplatform to eastern basin in the early Cambrian shales, and restricted environment is favorable for paleoproductivity and preservation of organic matter.

Carbon Isotope Stratigraphy of the Cambrian System in the Eastern Tarim Basin, China

“…The Middle Oldland of the Tarim Block gradually submerged to form a large-scale platform named the West Platform . Between the West Platform and the Luoxi Platform, there was a depression named the East Depression (Zhao et al, 2011) (Fig. 2d).…”