四川盆地广元地区大隆组有机质富集规律

Organic Matter Enrichment of Dalong Formation in Guangyuan Area of the Sichuan Basin

四川盆地西北广元地区上二叠统大隆组主要为碳酸盐岩、硅质岩和页岩互层沉积。对四川广元长江沟剖面进行精细解剖的结果表明，大隆组中有机碳质量分数为0．16%-14．6％，有机碳质量分数与岩性关系密切，高有机碳质量分数赋存于黑色页岩和纹层状灰岩中，其中碳酸盐岩的有机碳质量分数与纹层厚度呈反比，即纹层厚度越大有机碳质量分数越低。大隆组优质烃源岩位于大隆组中部岩段，岩性组合为黑色页岩和硅质岩互层，间夹薄层状灰岩或纹层状灰岩。微量元素分析结果显示有机质的富集明显受控于沉积阶段及早期成岩阶段的氧化还原条件。综合分析表明大隆组烃源岩有机质富集受晚二叠世沉积环境、氧化还原条件、生物生产力、深部热液流体的影响，其中厌氧、缺氧环境是大隆组烃源岩发育的主控因素，高生物产率是有机质富集的前提条件。

The Dalong Formation in Guangyuan area in northwestern Sichuan Basin is mainly composed of interbeds of carbonate rocks, siliceous rocks and shales. In this study, a Permian section in Changjianggou, Guangyuan area, has been analyzed in detail. The systematic sampling and measuring results indicate that the content of total organic carbon （TOC） ranging from 0.16% to 14.6% in the Upper Permian Dalong Formation is closely related with the host lithologies. High TOC occurs in black shale and laminated limestone. In carbonate rocks, TOC content shows a negative relationship with the thickness of massive bed, i.e. the bigger the bed thickness is, the smaller the TOC content. A good quality of hydrocarbon source rocks are developed in the middle part of the Dalong Formation, in which lithological association consists of interbeds of black shales and silica rocks interbedded with thin laminated limistones. The analysis of minor element reveals that organic matter richness is controlled by redox condition in deposition and early diagenesis stage. The results show that the main factors of organic matter enrichment in the Dalong Formation include depositional environments, redox conditions, organism productivity, and hot fluid activity in ocean bottom. Of them, anaerobic and anoxic environments and organism productivity are the most important for the organic matter enrichment in the Dalong Formation.