宜昌地区下寒武统沉积环境分析

宜昌地区早寒武世除天柱山期(南部和西部称岩家河期)岩性变化较大外,其他依次沉积了以黑色炭质页岩夹灰岩、细碎屑岩、石灰岩、白云岩等为主的岩性组合,反映了中扬子区岩性四分的特点。晚震旦世灯影末期区内是一个东高西低、东北高西南低的浅海沉积区。在此背景上,早寒武世早期(即天柱山期)遭受了短暂而快速海进之后,依次经历了浅海盆地边缘、斜坡带、浅海陆棚及潮坪等沉积环境的缓慢演化,显示了有规律的海退序列。在区内天柱山组、岩家河组及水井沱组等均首次发现了重力流沉积;在水井沱组下部炭质页岩所夹的薄层粉晶云岩中,首次发现了沉积型重晶石富集层。根据区内天柱山期为浅海斜坡带(岩家河期为浅海盆地边缘)、水井沱期为浅海盆地边缘至斜坡带等沉积环境判断。天柱山组(岩家河组)与水井沱组之问应为连续沉积、整合接触。图3表1参7

An Analysis of Lower Cambrian Depositional Environments in Yichang Region

With the exception that the rocks of Tianzhushan Stage varied from areas, four main types of rocks were deposited during the Early Cambrian Period of Yichang region, i. e. black shales interbedded with limestones, fine clastic rocks, limestones, and dolostones. This region was a shallow sea depositional area, with the northern and northeastern part shallower than the southern and southwestern part. After the rapid transgression at the beginning of the Early Cambrian Period, the depositional environment experienced an evolution regularly and slowly from the basin margin, slop shelf to the tidal flat, indicating a regressive sequence. Gravity flow deposits were found in Tianzhushan Formation. Yanjiahe Formation and Shuijingtuo Formation. Deposited barites were also found in Shuijingtuo Formation. On account of the depositional analysis. it is concluded that the Tianzhushan Formation and Shuijingtuo Formation were developed continuously and conformably.