Effect of Primary Production, Dilution and Preservation on Organic Matter Accumulation for the Lower Cambrian Shale

Abstract

In order to investigate the influence of primary production, dilution and preservation on organic matter accumulation, geochemical data and geochemical proxies of primary production, clastic influx and redox conditions were presented from the Cambrian Niutitang Formation organic-rich shales. The primary production proxies (TOC, Mo, P, Ba and Babio) and redox proxies (Ni/Co, V/Cr, U/Al and Th/U) suggest that the black organic-rich shales of the Niutitang Formation are deposited in anoxic/euxinic condition with high primary production. The pyrite of the Niutitang Formation is composed of spherical framboids, indicating that the anoxic bottom water could not prevail before organic matter degradation during the Niutitang Formation deposition. High primary production enhances organic carbon flux into chemocline layer and bottom water, leading to the anoxic bottom water from oxygen consumption by microorganisms and organic matter degradation. The anoxic bottom water in turn is beneficial to preservation of organic matter. In addition, Ti/Al ratios correlate well with TOC contents through the Niutitang Formation, indicating that clastic inputs enhance the burial rate for preventing organic matter from degradation during Niutitang Formation deposition. Therefore, the accumulation of organic matter in the Niutitang Formation is mainly influenced by primary production rather than the redox conditions in bottom water.