库车坳陷侏罗系砂岩碎屑组分及物源分析

An Analysis of Jurassic Sandstone Fragment Components and Their Provenance in Kuqa Depression

库车坳陷位于塔里木盆地的北部,其侏罗系发育良好,为一套陆相含煤沉积,可分为中、下部的煤系地层和上部的杂色碎屑沉积两部分。侏罗系包括阿合组、阳霞组、克孜勒努尔组、恰克马克组、齐古组和喀拉扎组。该区砂岩碎屑成分以石英为主,其次是长石及各种岩屑,有时含少量云母及绿泥石等碎屑矿物。砂岩结构不一,粗砂、中砂和细砂状结构均有,很少一部分为含砾结构。砂岩分选性以中等为主,少量分选好或分选差。砂粒的磨圆度各层位有所差异。本文对库车坳陷侏罗纪地层的砂岩进行了骨架矿物统计分析,通过碎屑岩矿物成分与结构的变化研究了库车坳陷侏罗系沉积岩石学特征,并应用Dickinson的分析理论及结果,对库车坳陷的碎屑岩进行物源与板块构造关系的分析与探讨,重点对库车河剖面的砂岩作了系统采样和测定,显微镜下观察了砂岩的碎屑组分,并对各组分采用点记法进行整个全视域薄片的砂岩的骨架矿物成分统计工作,根据碎屑组分特征与重矿物组合特征,结合区域构造、沉积古地貌及盆地演化史,对库车坳陷的物源进行了探讨。认为侏罗系下部的碎屑岩物源区以再旋回造山带为主,已经过一段时间的风化开始隆升,遭受强烈剥蚀,反映了前陆盆地形成时的早期旋回阶段的特征,来自三叠纪古前隆的物源较少,母岩以沉积岩为主;侏罗系中上?

Kuqa depression is located in the north of the Tarim basin. Its Jurassic strata comprising six groups are a set of continental coal-bearing sediments, which can be divided into the coal measure strata in the middle and lower part and the detrital sediments in the upper part. The fragment components are mainly quartz, feldspar and debris, together in a few places with a bit of mica and chlorite. The sandstone structures are different and the sorting is mainly of medium level. According to statistical analysis of sandstone fragment components, combined with a study of sedimentary characteristics based on variations of mineral compositions and structures, this paper has discussed the provenance of Kuqa depression in Jurassic. It is considered that the provenance of the lower part of Jurassic strata was mainly from the recycled orogenic belt, and rarely from Triassic forebulge,that the source rock was mainly sedimentary rock, and that the provenance of middle and upper part also mainly came from the recycled orogenic belt, with obvious material supply from forebulge. Besides, early sediments at the edge of the basin experienced current mechanic crush and reconstruction, and hence the quantity of mud boulder sediments increased. These sediments were controlled by two source areas, with source rocks being sedimentary rocks.