四川盆地南江杨坝地区下寒武统烃源岩形成的地球生物学条件

Geobiological conditions for the formation of the Lower Cambrian source rocks in Yangba area of Nanjiang County in the Sichuan Basin

运用地球生物学方法评价烃源岩形成的条件,是对基于残余有机质分析的传统烃源岩评价方法的重要补充,对于高演化海相碳酸盐岩地区尤为重要。在实测野外露头剖面的基础上,通过系统分析四川盆地南江杨坝地区下寒武统各小层的沉积环境、古生物化石、岩石微量元素及总有机碳含量等特征,利用地球生物学基本原理,分析下寒武统烃源岩形成的生境型、海洋古生产力、古氧相及埋藏效率等条件。结果表明,筇竹寺组底部原始有机质数量多,发育于厌氧的沉积环境中,有机碳埋藏效率高,是优质烃源岩发育的有利层段。石龙洞组底部具备一般烃源岩发育的地球生物学条件。

Evaluating conditions of source rock development by geobiological approaches is an important supplement for the traditional evaluation method of source rocks based on analyses of remnant organic matter.This method is especially suitable for source rock evaluation in areas with highly-matured marine carbonate rocks.Our study is based on observation of outcrops and focused on a systematic analysis of the depositional environment,fossil organism,trace element data and total organic carbon in the Lower Cambrian of the Yangba area in Nanjiang County,Sichuan Basin.The forming conditions for the Lower Cambrian source rocks are recognized through a study on the habitat types,oceanic paleoproductivity,paleo-oxygenation facies and burial efficiency by using geobiolgical principles.The results show that the lower part of the Qiongzhusi Formation has the most favorable conditions for development of high-quality hydrocarbon source rocks as it has higher original organic content,anaerobic sedimentary environment and higher burial efficiency of organic carbon.In contrast,the lo-wer part of the Shilongdong Formation possesses basic geobiological conditions for development of ordinary source rocks.