黔中隆起震旦系灯影组高热演化沥青地球化学特征及差异分析

Geochemical Characteristics and Differences of Highly Matured Bitumen in the Sinian Dengying Formation

黔中隆起地区震旦系灯影组白云岩的溶蚀孔洞、构造裂缝等储集空间中发现有白云石、石英和黑色炭质沥青的充填,其中沥青的形成晚于白云石但早于石英。研究采集了贵州开阳县双流镇白马洞新桥剖面(双流白马)和金沙县岩孔镇箐口村剖面(金沙岩孔)2处沥青样品。沥青样品都具有较高的热演化程度,扫描电镜下呈块状或小球状;根据碳同位素组成,认为沥青来源于下寒武统烃源岩。但2处沥青又具有显著的差异。双流白马沥青与金沙岩孔沥青相比,具有较低的热演化程度,2处沥青反射率平均值分别为4.30%和5.17%;具有相对较高的N、O、S含量和相对较高的H/C值以及相对较轻的碳同位素组成。流体包裹体测温和沥青反射率表明2处埋藏热演化过程的差异导致了沥青在元素组成和同位素组成上的差异。

There is large amount of reservoir space including dissolution pores and tectonic fractures in the dolostone from the Sinian Dengying Formation in the central Guizhou uplift, which were filled with many dolomites, quartz and black bitumen. Based on the relationship, the formation of bitumen is later than that of dolomites but earlier than quartz. In this study, two groups of bitumen were sampled in Baima and Yankong outcrops, respectively. The Baima outcrop is located in Shuangliu town of Kaiyang county, Guizhou province, and the Yankong outcrop is in Yankong town of Jinsha county, Guizhou province. Both groups of bitumen have relatively high thermal maturity, and they are cubic or spherical under scanning electronic microscope. According to carbon isotopic compositions, bit- umen is expected to be from the Lower Cambrian source rocks. There are remarkable differences between the two groups. Compared with those in Yankong outcrop, bitumen in Baima outcrop has relatively lower thermal maturity, higher in N,O and S contents and H/C ratios,and lighter in carbon isotopic compositions. The average Rb values for Baima and Yankong bitumen are 4.30% and 5.17%,respectively. Homogenization temperatures of fluid inclusions and Rb values indicate that bitumen of these two groups has experimented different burial-thermal evolution processes. The different processes cause the differences in element and isotopic compositions of bitumen from different locations. Such researches would be significant for further studies on genesis and sources of natural gas in the central Guizhou uplift.