扬子板块西北缘晚奥陶-早志留世岩相古地理演化与烃源岩的关系

Relationship between Lithofacies Paleogeographic Evolution and Source Rocks of the Late Ordovicianearly Silurian in Northwestern Yangtze Plate

扬子地区晚奥陶-早志留世的五峰组和龙马溪组下段黑色炭质页岩是两套优质烃源岩,研究其沉积背景及其控制因素具有重要的理论和油气勘探意义。通过研究扬子板块西北缘野外露头和钻井资料,结合区域构造演化分析可知,晚奥陶世五峰组时期开始,扬子地区结束了碳酸盐沉积,进入黑色页岩沉积阶段。扬子西北缘五峰组-龙马溪组主体为局限的浅水陆棚沉积环境,但五峰组沉积于淹没台地阶段,龙马溪组沉积于陆棚继承阶段,其岩相的空间展布主要受川中隆起、汉南古陆及其他小的隆起带和水下隆的控制。这些发育在不同沉积背景下的烃源岩其有机质特征存在明显的差异性,可见岩相古地理对烃源岩的发育和分布具有重要的控制作用。

The Wufeng Formation and the black-shale of lower Longmaxi Formation (Late Ordovician-Early Silurian) were 2 sets of excellent source rocks in the Yangtze Area. It had an important theoretical and practical significance of oil and gas exploration for studying the depositional setting and controlling factors. According to the data from outcrops and well drilling along with the analysis of tectonic evaluation in the northwest Yangtze Area,It was proposed that from Wufeng Stage of late Ordovician,the lithofacies of Yangtze Area were changed from carbonates into the deposition of black shales. Wufeng and Longmaxi Formations of Northwestern Yangtze area were mainly a shallow shelf. Wufeng Formation was deposited when the platform was below sea level,while Longmaxi Formation was deposited on shelf inherited stage. The spatial distribution of lithofacies is controlled by central Sichuan uplift,Hannan old land and other smaller uplifts and subaqueous uplifts. These organic characteristics which are developed in different sedimentary source rocks have obvious difference,It can be seen that the lithofacies paleogeography controls the development and distribution of hydrocarbon source rocks.