AROMATIC HYDROCARBONS IN THE BILUO CO OIL SHALE OF THE SHUANGHU AREA, NORTHERN TIBETAN PLATEAU, AND THEIR IMPLICATIONS

Abstract

The organic-rich marine sediments commonly referred to as black shales were deposited in the Qiangtang basin, northern Tibet. Although achievements in the respective researches have been remarkable, the deposi- tional environment, source of organic matter, thermal maturity and bio- degradation, which played a significant role in the deposition of these sedi- ments during the Early Toarcian, are still topics of discussion. In this paper, the geochemical characteristics of aromatic hydrocarbons contained in bitumen B of oil shale samples from the Biluo Co section of the Shuanghu area, northern Tibet, are considered in detail. In the oil shale samples, 154 aromatic hydrocarbon compositions mainly falling into 12 aromatic hydrocarbon series were detected. Among them the phenanthrene series predominates, followed by the naphthalene series, each of the rest having a low abundance, and the aromatics distribution is represented by typical prepeaks. Various geochemical parameters of these aromatic hydro- carbons are calculated and used to deduce the depositional environment, as well as the origin and thermal maturity of the oil shale organic matter. The composition of organic matter and the relative abundance of aromatic hydrocarbons in the Biluo Co oil shale shows that these were mainly derived from lower marine organisms. At the same time, the relatively low abundance of 1,2,5-TMNr, 1,2,5,6-TeMNr, pimanthrene, biphenyl and other compounds, which are known to be diagnostic biomarkers of terraneous higher plants, is indicative of some higher plants input too. The high relative abundance of the DBT and 9-MP series suggests that the Biluo Co oil shale deposited in a