川东北地区长兴组—飞仙关组沉积格局及成藏控制意义

川东北上二叠统长兴组—下三叠统飞仙关组总体为碳酸盐台地沉积,受古断裂的控制,宽广的台地被切割成台隆与台盆的沉积格局。受开江-梁平台盆的控制,长兴晚期—飞仙关早期在其两侧发育了较为对称的类似于威尔逊相模式的碳酸盐岩沉积体系,但陆棚相不甚发育,可能是台盆深度小、宽度窄、相变快引起的。由于期间经历了一次二级海平面的升降过程,使得长兴组广泛发育海侵生物礁,而飞仙关组发育海退型鲕粒滩,形成两类最为有利的储集相带。生物礁、鲕滩沉积相带在纵横向上不断迁移、抬升,主要发育于台盆的两侧,呈不连续环带状分布,明显受沉积相带控制。

Sedimentary framework of Changxing-Feixianguan Formations and its control on reservoiring in northeastern Sichuan basin

As a whole,the Upper Permian Changxing Formation-Lower Triassic Feixianguan Formation in northeastern Sichuan basin were deposited as carbonate platform.The extensive platform was cut into platform-highs and platform basins by fossil fractures.Being controlled by Kaijiang-Liangping platform-basin,relatively symmetrical carbonate sedimentary systems,similar to Wilson's facies pattern,were developed on both sides of the basin in late Changxing to early Feixianguan age,but shelf facies were poorly developed.It is possibly due to the shallow depth,narrow width and rapid facies change of the platform-basin.A second-order eustatic sea level change during this period resulted in the widely development of transgressive bioherm in Changxing Formation and regressive oolitic shoals in Feixianguan Formation,both of which would be the most favorable reservoir facies belts.The bioherm and oolitic shoal facies belts continuously migrated laterally and upraised vertically.They were mainly developed on both sides of the platform-basins and characterized by discontinuous zonary distribution,which were obviously controlled by sedimentary facies belts.