ZHANG Xiao, XU Gui-wen, DA Xue-juan, CHEN Lan*
（College of Petroleum and Natural Gas Engineering, Chongqing University of Science and Technology, Chongqing 401331, China）

Abstract: A set of black rock series with rich-organic matters and abundant fossils, developed in Jurassic strata of the Qiangtang Basin in Northern Tibet, China, have been paid more attention by various geologists. In this paper, the coccolith-bearing black shales at the Biluo Co section of the Shuanghu area in the Qiangtang Basin have been selected to study their organic and elemental geochemical characteristics. The results show that their total organic carbon (TOC) contents change from 2.84% to 3.71%, and their chloroform bitumen “A” vary from 0.18% to 0.29%. The organic matters belong to the type Ⅱ1, indicating that the organic matter was sourced from major plankton and minor terrestrial plants. Tmax values varying from 429 oC to 435 oC indicating that the rock series are in immature stage. Furthermore, the major elements such as Si, Al, Ca and so on for samples are relatively enriched, showing that the black rock series are dominantly sourced from the terrestrial clastic input. The characteristic ratios of V/Cr, U/Th, Ni/Co, and V/(Ni+V), enrichments of U and Mo, and features of no obvious Eu and Ce anomalies show that the black rock series were mainly deposited in a weakly reduced environment which is beneficial to the preservation of organic matters. This study indicates that the coccolith-bearing black rock series are relatively good hydrocarbon source rocks, which are well preserved, for further prospective exploration of oil and gas.

Keywords: Jurassic; black rock series; hydrocarbon source rocks; geochemical characteristics; Qiangtang Basin

ACTA MINERALOGICA SINICA Vol. 39, No.5, 2019, page 520-526