江汉—洞庭盆地下更新统地层划分与对比——“白沙井砾石层”再研究  

THE SUBDIVISION AND CORRELATION OF THE PLEISTOCENE IN THE JIANGHAN-DONGTING BASIN:RESTUDY ON THE “BAISHANJING GRAVEL LAYER”

作　　者：陈立德 邵长生 

机构地区：[1]武汉地质调查中心,湖北武汉430223

出　　处：《地层学杂志》2014年第2期208-219,共12页Journal of Stratigraphy

基　　金：中国地质调查局"长江中游城市群地质环境调查与区划综合研究(1212011140035)"资助

摘　　要：洞庭盆地周缘尤其是长沙一带"白沙井砾石层"和上覆"网纹红土"之间的接触关系存在分歧,由此产生了区内第四系更新统地层系统划分与对比的巨大差异。上世纪60年代以后,沈永欢、芮耀俊等将"白沙井砾石层"和"网纹红土"视为河流阶地二元结构的两个单元,并由此以阶地分析方法为理论基础,将长沙一带不同高程上分布的砾石层和网纹红土分别建立了诸多独立的岩石地层单位,并以其披覆的网纹红土为依据将其形成时代划为中更新世早期,并被广泛参考使用,由此造成了洞庭盆地内地层划分和对比的巨大困难。区域研究认为,江汉—洞庭盆地周缘发育一系列下更新统冲积扇或坡麓堆积,并向盆地内部倾向,这些冲积扇或坡麓堆积理应成为区内地层划分和对比的依据。长沙一带的砾石层是古湘江或其支流的冲积扇和在冲积扇基础上的辨状河流堆积,下游方向则发育湖泊三角洲沉积(汨罗组);网纹红土是在"白沙井砾石层"沉积并经剥蚀之后的堆积物,二者不是同时形成的,白沙井砾石层形成于早更新世(Q1),而上覆的网纹红土则形成于中更新世(Q2)。以阶地分析方法研究江汉—洞庭盆地下更新统应予以摒弃,而以阶地分析方法为基础建立的"洞井铺组"、"新开铺组"和"白沙井组",造成区内地层划分对比的混乱,应予以废止。建议将洞庭盆地周缘的下更新统砾石称之"常德组"和汨罗组(湖泊三角洲相),并将黄姑山组、陈家咀组、湖仙山组与下更新统汨罗组和"常德组"进行对比。洞庭盆地周缘的下更新统砾石层可与江汉平原周缘的下更新统云池组和阳逻组对比,马王堆组则与善溪窑组对比。The nature of the contact between the＂Baishajing gravel layer＂and the＂the reticulate red clay＂in the Dongting basin,especially in the Changsha area,is a matter of uncertainty.This uncertainty results in divergent opinions with regard to the stratigraphic subdivision and correlation of Pleistocene strata in the Jianghan-Dongting basin.In the 1960s,Shen Yonghuan,Rui YaoJun,and colleagues interpreted the＂Baishajing gravel layer＂and＂the reticulate red clay＂as two units in the dual structure of river terraces.Since then,the terrace analysis method has been widely used in the analysis of these strata,many lithostratigraphic units have been established at different elevations in the Changsha area,and the＂Baishajing gravel layer＂has been interpreted as middle Pleistocene in age.The many lithostratigraphic units make correlation in the Jianghan-Dongting basin difficult.Our regional mapping suggests that a series of alluvial fan or talus sediments were deposited and tilted toward the center of the Jianghan-Dongting basin in the Early Pleistocene.These alluvial fan or talus sediments should form the basis for stratigraphic subdivision and correlation in the area.In the Changsha area,the gravel layer represents alluvial fan or lake delta sediments deposits in the lower stream of the＂XiangJiang River＂and its tributaries.The reticulate red clay was deposited after the＂gravel layer＂was partially eroded.These two units were not deposited in the same time.The ＂Baishajing gravel layer＂ was deposited in the early Pleistocene（Q1）and the reticulate red clay in the middle Pleistocene（Q2）.The terrace analysis method should be discarded in the study of Pleistocene Series in the Jianghan-Dongting basin.The＂Dongjingpu Formation＂,＂Xingkaipu formation＂,and＂Baishajing formation＂,which were established using the terrace analysis method,should be abolished because they bring confusion in the stratigraphic classification and correlation in the area.In this paper,the gravel layer in the Dongtin

关 键 词：岩石地层 网纹红土 冲积扇 地层划分和对比 白沙井砾石层 第四系 江汉盆地 洞庭盆地 

分 类 号：P534.63[天文地球—第四纪地质学]