Characteristics and hydrocarbon significance of the source rocks of Lower Cambrian Niutitang Formation on the western side of the Xuefeng Mountain

Based on systematic observation, sampling and organic geochemical studies of Lower Cambrian Niutitang Formation source rocks on the western side of the Xuefeng Mountain area, this paper summarized such problems as source rocks distribution, organic matter types, the formation of source rocks and sedimentary environment, and the maturity of organic matter. Source rocks of Lower Cambrian Niutitang Formation are characterized by high organic carbon, low chloroform bitumen "A" and low hydrocarbon generation potential. The favorable source rocks are mainly distributed in Zunyi area of northern Guizhou, Tianzhu-Chengbu area of eastern Guizhou, Youyang-Mayang area of southeastern Chongqing-western Hunan and Xianfeng-Zhangjiajie area of western Hubei. Microscopic examination of kerogen reveals that organic matters are mainly sapropelinite(75%~93%) and saturated hydrocarbon/aromatic hydrocarbon(0.84%~27%, 5.77% on average), and the black shale organic matters are of type I. The values of Kerogen δ13Corg is relatively low, varying from -34.99‰ to -25.36‰, -31.80‰ on average, suggesting that the sedimenatry parent materials are mainly marine plankton and maritime bacteria, with marine algae being the source of part of the organic matter. In combination with Pr/ph analysis, the source rocks of Niutitang Formation were mainly formed in an anoxic and hypersaline environment. The bitumen reflectance values vary from 2.23% to 4.32%, 3.45% on average, and the vitrinite reflectance equivalent values vary from 1.84% to 3.23%, 2.43% on average, implying that most of the samples reached the overmature stage.