湖南保靖地区龙马溪组层序地层及沉积微相研究

A Study on Sequence Stratigraphy and Sedimentary Microfacies of Longmaxi Formation of Early Silurian in the Baojing Area,Hunan Province

通过钻井、测井结合野外露头分析,运用高分辨率层序地层学思路和方法,对湖南保靖地区龙马溪组进行层序地层划分及沉积微相研究。湖南保靖地区龙马溪组划分出三个中周期基准面旋回(sq1,sq2,sq3),组成一个长周期基准面旋回(SQ1),可以在研究区内良好对比。sq1的基准面上升半旋回为深水滞留盆地沉积,基准面下降半旋回为浊积扇网状水道沉积;sq2、sq3的基准面上升半旋回为浅水滞留盆地沉积,基准面下降半旋回为浊积扇扇中前缘席状砂沉积。从早到晚沉积盆地海平面逐渐下降,沉积中心向西北方向迁移。参考层序地层特征,结合本区页岩气地质条件,认为东南部甘溪-大坨地区为页岩气勘探有利区。

Through the analysis of drilling and logging data in combination of field outcrops,using the idea and method of high-resolution sequence stratigraphy,we have studied the sequence stratigraphic division and sedimentary microfacies of the Longmaxi Formation in Baojing County,Hunan Province. This set of strata was divided into three middle periodic base-level cycles（ sq1,sq2,sq3） which form a long-period base-level cycle（ SQ1） and can be well compared in the study area. The base-level rising upward half cycle of sq1 was the deposition of a deep-water reduction deposition basin,and the base-level descending half cycle of sq1 was turbidite braided channel sedimentation. The base-level rising of sq2 and sq3 was the deposition of a shallow water reduction basin,and the base-level descending half cycle of sq2 and sq3 was the sand deposition of a turbid leading edge.From early to late,the sea level of the basin gradually decreased,and the sedimentary center gradually migrated to northwest. Based on the stratigraphic characteristics of the sequence and the geological conditions of the shale gas in this area,it is considered that the Ganxi-Datuo are in the southeast of Baojing county is a favorable region for shale gas exploration.