四川盆地二叠纪-三叠纪开江-梁平陆棚形成演化与礁滩发育

Formation and evolution of Permian-Triassic Kaijiang-Liangping shelf and development of reef-shoal reservoirs in Sichuan Basin,China

四川盆地北部开江-梁平陆棚的形成与峨眉"地裂运动"有关。通过对野外露头、钻探资料及地震资料系统分析,其发展和消亡过程对区内上二叠统吴家坪组-下三叠统飞仙关组沉积相的演化有着明显的控制作用,决定了生物礁和鲕粒滩的分布,从而也决定了礁、滩气藏的类型、规模及分布。上二叠统吴家坪组为碳酸盐岩缓坡沉积,至长兴期,受拉张作用进一步加剧影响,陆棚相区进一步下沉,陆棚边缘的生物礁及高能滩集中快速生长,沉积模式由碳酸盐缓坡演化为镶边台地沉积。随着台地的不断增生,鲕粒滩分布区不断向东往陆棚一侧迁移,发育层位从台地向陆棚亦逐渐抬升,开江-梁平陆棚逐渐萎缩并最终消亡。

The Kaijiang-Liangping shelf in the north of Sichuan Basin was formed by the Emei Mantle Plume event during Permian to Triassic periods.Through analysing the outcrops,drilling data and seismic data,it is found that its formation,evolution and extinction have exerted clear controls on the sedimentary facies of the Wujiaping Formation-Feixianguan Formation and the distribution of the reef and oolitic shoal carbonate rocks.Thereby,the shelf controls the type,scale and distribution of the reef-shoal gas pools.During the Late Permian Wujiaping period,carbonate rocks were deposited in a carbonate rock ramp.Then,due to the sink of the shelf caused by the regional stretching,the Changxing Formation was characterized by the rapid growth of reefs and high-energy shoals.These reef and shoal carbonate rocks composed a platform margin and a rimmed platform formed.With the growth of the platform,oolitic beach migrated from the west to the east of the shelf.The shelf finally shrivelled and disappeared.