Geochemical and palynological investigation of the Shengli River marine oil shale (China): Implications for paleoenvironment and paleoclimate

The Shengli River oil shale, located in the North Qiangtang depression, northern Tibet plateau, represents a potential large marine oil shale resource in China. A geochemical and palynological investigation of the oil shale was performed to reconstruct paleoenvironment and paleoclimate during deposition. The total organic carbon (TOC) contents (15.05%-20.34%) and S-2 values (103.27-129.12 mg HC/mg rock) of oil shale samples are high, and the organic matter consists mainly of type II kerogen. The thermal maturity assessed from PI (0.033-0.036) and T-max (433-436) shows an immature to early Mature stage of the organic matter. Analyzed oil shale samples from the Shengli River area are characterized by a dominance of low carbon number molecular compositions with high C-21(-)/C-21(+) (2.10-2.83), low Pr/Ph (0.63-0.75) and high concentrations of C-27 sterane and homohopanes (C-31-C-35), indicating reducing environments, highly saline conditions, and a prevalent contribution of algae to organic matter accumulation. The analyzed oil shale samples have an uncommonly heavy C isotopic composition, ranging in delta C-13 values of bulk organic matter from -20.79 parts per thousand to -21.78 parts per thousand. The enrichment in C-13 is mainly attributed to the high productivity of algae rather than solely the result of hypersalinity. Composition of palynofloras from oil shale samples suggests that the climate of the Qiangtang basin region during the deposition of oil shales was warm and humid or sub-humid. (C) 2009 Elsevier B.V. All rights reserved.