Huang Junping, Li Xiangbo, He Wenxiang, Wan Yanrong, Bao Hongping, Xu Yaohui, Wang Hongbo, Zhang Guisong, Wang Jing
Key Laboratory of Exploration Technologies for Oil and Gas Resources of Ministry of Education, College of Resources and Environment, Yangtze University, Wuhan 430100, PR China.
Research Institute of Petroleum Exploration & Development-Northwest, PetroChina, Lanzhou 730020, PR China.
ACS Omega. 2020 Apr 2;5(14):8001-8011. doi: 10.1021/acsomega.0c00077. eCollection 2020 Apr 14.
In this article, the lower Cambrian marine shale of the southern part of the Ordos basin is taken as an example to investigate the formation environment and development models of source rocks with high organic abundance in the ancient strata of the southern North China plate. The lower Cambrian shale source rocks had a thickness of 10-80 m, with high total organic carbon contents (an average of 2.68% and maximum of 9.39%) and favorable organic matter types-mainly sapropelinite macerals-and yet low S1, S2, and hydrogen index, which indicate that the source rocks have relatively high thermal maturity. Therefore, it is demonstrated that marine shale of the lower Cambrian proves to be excellent gas source rocks at the southern part of the Ordos basin and are presently distributed mainly in the south part of the North China plate. During the early Cambrian period, paleoproductivity was relatively high, as indicated by the rich C sterane contents, high sterane/hopane ratios, and high tricyclic terpane/hopane ratios in biomarkers and high P and Ba values in trace elements. The tectonic setting promoted the formation of highly abundant source rocks with favorable preservation conditions, as suggested by the relatively high V/Cr ratios and low Zr/Rb and Pr/Ph ratios. Thus, the paleoproductivity and preservation conditions were the main factors controlling the occurrence of highly abundant source rocks. The formation of highly abundant source rocks was under the joint effects of the tectonic setting and the undercompensation environments of the passive continental marginal slope of the Paleo-Qinling Ocean and deepwater bays. The paleo-geomorphologic troughs and/or fault depressions (because of tectonic movement) and deepwater bay environments together influenced the development scale of highly abundant source rocks, whereas the deepwater shelf environment of the continental marginal slope ensured the high quality of the source rocks.
本文以鄂尔多斯盆地南部下寒武统海相页岩为例，研究华北板块南部古地层中高有机丰度烃源岩的形成环境与发育模式。下寒武统页岩烃源岩厚度为10 - 80米，有机碳总量高（平均为2.68%，最高达9.39%），有机质类型良好——主要为腐泥质显微组分——但S1、S2和氢指数较低，这表明烃源岩具有较高的热成熟度。因此，证明鄂尔多斯盆地南部下寒武统海相页岩是优质气源岩，目前主要分布于华北板块南部。寒武纪早期，古生产力相对较高，生物标志物中丰富的C甾烷含量、高甾烷/藿烷比值和高三环萜烷/藿烷比值以及微量元素中高P和Ba值表明了这一点。构造背景促进了具有良好保存条件的高丰度烃源岩的形成，相对较高的V/Cr比值以及较低的Zr/Rb和Pr/Ph比值表明了这一点。因此，古生产力和保存条件是控制高丰度烃源岩形成的主要因素。高丰度烃源岩的形成是古秦岭洋被动大陆边缘斜坡和深水海湾的构造背景与欠补偿环境共同作用的结果。古地貌槽和/或断层坳陷（由于构造运动）以及深水海湾环境共同影响了高丰度烃源岩的发育规模，而大陆边缘斜坡的深水陆架环境确保了烃源岩的高质量。
