鄂西地区茅口组重力流沉积特征及古地理意义

Gravity Flow Sedimentary Characteristics and Environmental Significance in Maokou Formation,Western Hubei Area

通过对鄂西地区中二叠统详细的野外剖面测量及沉积微相分析,发现鄂西地区中二叠统茅口组发育重力流沉积,沉积类型多样,发育于碳酸盐岩斜坡沉积环境中,自上而下分为滑塌沉积、碎屑流沉积、颗粒流沉积。滑塌沉积主要发育于湖南慈利江垭剖面,颗粒流与碎屑流发育于湖北长阳资丘剖面。滑塌沉积物主要由杂乱堆积的棱角状—次棱角状砾屑灰岩组成,分选不好,颗粒支撑,为台地边缘短距离滑塌形成;碎屑流沉积物由砾屑灰岩、砂砾屑灰岩、生物碎屑泥晶灰岩组成,砾石略呈定向排列,呈次棱角状—次圆状,砾石逐渐减少;颗粒流沉积物由砂砾屑灰岩、颗粒状灰泥灰岩组成,见粒序层及波状层理,发育2～3个旋回。研究区重力流沉积的发育受控于构造演化,其时空分布的特征与该区中二叠世台—盆沉积的格局相吻合,对于研究区的二叠纪沉积演化研究有一定意义。

By use of strata study on the field outcrops and microfacies analysis indoor,types of gravity-flow deposits have been found in Maokou Formation Middle Permian,western Hubei province,which developed in carbonate slope depositional environment,from top to bottom slump deposits,debris flow deposits,particle flow deposits have been regonized,slump deposits developed in the Cili Jiang Ya section,Hunan province,particle flow and debris flow developed in the Ziqiu section Changyang country.Slump sediments is composed of the clutter angular-subangular calcirudite,poor sorting,grain-supported,short-range slump slided off from the platform margin;debris flow deposits formed of the calcirudite,gravel limestone,bioclastic micritic limestone,gravel is slightly alignment and sub-angular,sub rounded,gravel gradually reduced from bottom to top;particle flow is composed of the gravel limestone sediments,wackstone with miliolids,which developed 2 to 3 cycles and graded layer and wavy bedding.Gravity flow deposits in the study area controlled by the tectonic evolution,the characteristics of its spatial and temporal distribution of the area in the middle Permian is consistent with platform-basin deposition pattern,and it has certain significance for the Permian sedimentary evolution in the study area.