Sedimentary characteristics of the Lower Jurassic Baitianba Formation in western Sichuan foreland

The sedimentary facies and palaeogeography of the Lower Jurassic Baitianba Formation in western Sichuan foreland basin is explored on the basis of well logs,outcrops and cores in integration with regional geological data.The Lower Jurassic Baitianba Formation consists of four sedimentary facies,including the alluvial fan,meandering river,lacustrine delta and lacustrine facies.The alluvial fan facies may be subdivided into two subfacies: mid-fan and fan fringe subfacies.The meandering river facies may also be subdivided into two subfacies: channel and floodplain subfacies.The lacustrine delta facies include the delta plain and delta front subfacies.The lacustrine facies include the littoral-shallow lake and bathyal lake subfacies.The alluvial fans are widely developed in Qionglai,Anxian,Jiangyou,Wangcang and Nanjiang.The alluvial fans in Anxian extends eastwards,and graded into fluvial sandstone facies and delta facies in Jintang and Santai,and finally developed into lake facies,displaying the alluvial fan-river-delta-lake sedimentary model.