四川盆地及其周缘地区寒武系洗象池群颗粒滩特征及分布

Characteristics and distribution of grain banks in the Cambrian Xixiangchi Group of Sichuan Basin and its adjacent areas

通过对野外露头剖面、钻井以及1︰200000区域地质调查等资料的综合研究,识别出四川盆地及其周缘地区寒武系洗象池群颗粒滩的岩石类型包括颗粒云岩、颗粒灰岩、细—中晶白云岩,颗粒类型主要为砂屑,次为鲕粒、砾屑以及少量生屑。发育潟湖—台内滩—潟湖、潟湖—台内滩—台坪、潮坪—潮缘滩—潮坪这3种向上变粗的沉积序列。单个旋回中的颗粒滩的厚度一般小于2.5m,垂向上多表现为频繁叠置的小规模薄型滩体,且横向规模小、可对比性差。平面上,颗粒滩主要分布在古隆起区和水下相对高地,整体为东北向分布。海平面升降和沉积能量的高低控制着颗粒滩发育规模,而构造条件决定了颗粒滩的横向连续性和平面分布。

Based on comprehensive research on field outcrops, wells and the regional survey in 1：200000 scale,the grain dolostone,grain limestone and fine- to mid-crystallized dolostone are found to constitute grain banks in the Cambrian Xixiangchi Group of Sichuan Basin and its adjacent areas.Sand-sized intraclast is the main type of intraclasts,and oolite,gravel-sized intraclast and minor bioclast follow in order.Three vertical sequences of upward-coarsening are identified,including lagoon-platform interior shoal-lagoon,lagoon-platform interior shoal-platform interior flat and tidal flat-tidal margin shoal-tidal flat.Each vertical cycle is commonly no more than 2. 5, m thick and thin banks are frequently superim-posed vertically in a relatively small scale,and the grain banks have small scale and bad continuity hori-zontally.The grain banks are mainly distributed on palaeo-uplifts and submarine highlands in the direction of northeast-southwest.Sea level fluctuation and sedimentary energy controlled the scale of grain banks, and the tectonic condition determined their lateral continuity and planar distribution.