桂北南丹巴平剖面早石炭亚纪盆地相烃源岩的地球生物学特征

Geobiological characteristics of basinal facies hydrocarbon source rocks of the Lower Carboniferous of Baping section in Nandan,northern Guangxi

早石炭亚纪冰川性海平面变化及黔桂盆地独特的古地理位置控制着盆地中的地球生物学过程,决定了生烃母质生物的生产力和有机质的保存条件,进而影响了盆地相烃源岩的形成与分布。通过对广西巴平剖面地球生物相分析,探讨下石炭亚系盆地相烃源岩形成的地球生物学过程,结果表明:汤粑沟期早期、旧司期中晚期生境型以Ⅵb(台间深海盆地生境相)为主,盆地中生产力水平较低,但盆地中水体较深,古氧相为厌氧相,有机质埋藏效率高,形成了下石炭亚系的优质烃源岩。汤粑沟中期生境型为Ⅵb,生产力水平低,古氧相为贫氧相—厌氧相,由于沉积速率过慢,发生了大量的Mn/Fe氧化还原反应,降低了有机质的埋藏效率,仅形成了一套非烃源岩。早旧司期及上司期生境型为Ⅳ1(范围为风暴浪基面至真光层下界面)、Ⅳ2(范围为真光层下界面至大陆架坡折处),生产力水平低—中,古氧相为准厌氧相—贫氧相,形成了一套非烃源岩—一般烃源岩。上司期末期—罗苏期生境型主要为Ⅲ2(范围为强光合作用面至风暴浪基面),局部为Ⅳ1,生产力水平中—高,古氧相为常氧相—贫氧相,有机质埋藏效率低,形成了一套非烃源岩—差烃源岩。

During the Early Carboniferous, glacio-eustasy and the palaeogeographic environment of Qiangui intra-platform basin played crucial roles in controlling the geobiological processes, the formation and distribution of basinal facies hydrocarbon source rocks. Analyses of biogeological facies from Baping section deposited in Qiangui basin in Guangxi, enable us to explore the geobiological processes of the formation of basinal facies hydrocarbon source rocks. The results show that： during the Early Tangbagouan and Middle-Late Jiusian, the Qiangui basin was mainly characterized by habitat type VIb, low productivity and anaerobic facies. A set of premium hydrocarbon source rocks formed during this period were attributed to the high burial efficiency of organic matter; during the Middle Tangbagouan, the Qiangui basin was characterized by habitat type Vib, low productivity and dysaerobic-anaerobic facies. A set of non-hydrocarbon source rocks were formed due to the slow sedimentation rate, abundant Mn/Fe redox reaction; during the Early Jiusian and Shangsian, the Qiangui basin was characterized IV, - IV 2, low-middle productivity and quasi-anaerobic-dysaerobic facies. A set of non-hydrocarbon source rocks-hydrocarbon source rocks were formed during this period; during the Late Shangsian and Luosu, the Qiangui basin was characterized by habitat type Ⅲ2-IV1, middle-high productivity and dysaeobic-aerobic facies. A set of non- hydrocarbon source rocks were formed by the low burial rate of organic matter.