阿干镇煤田中侏罗统下部砂体沉积环境的初步研究

A Preliminary Study of Sedimentary Environment on Sand Bodies of Lower Aganzhen Group,Middle Jurassic Series,Aganzhen Coal Basin,Lanzhou,Gansu

Aganzhen coal basin is a coalbearing strata of middle Jurassic series.The base of it is composed of basal conglomerate and sandbodies.The result of grainsize analysis to the sand-bodies with ninetysevensamples indicates that it is a sediments of fluvial facies,composed of boththe lag deposit and point bar deposit facies.This is a meandering streamof intermontane basin growth.After the sediments of fluvial facies,the terrain tended to plain.Onthe basis of this condition,the marshland developed and then under theconditions of the climate,warm and damp,formed the sediments of thethicker coal bed.Afterwards the climate turned dry and hot,so develo-ped the shallow lake deposit.To make a comprehensive survey of the coal-bearing strata,we con-sider it as a half cyclothem structure with the characteristics of the gra-insize from coarse to fine and the kinetic energy of flowing water tend-ing to become small and stable.