摘要
根据大量野外观察和室内分析结果，较详细论述了江西修水地区第四系网纹红土的地貌地层、岩石地层、磁性地层和年代地层等方面的特征，并在此基础上，就有关网纹红土的形成时代、成因以及与黄土的对比等问题进行了讨论，提出１）网纹红土可分为强网纹化红土和弱网纹化红土两个岩性段，每个岩性段又由若干个密集网纹层与稀疏网纹层构成；网纹红土与下伏红色砾石层属同期产物；２）网纹红土中的密集网纹层的地质意义相当于北方黄土中的古土壤；３）网纹红土形成于早更新世末（约０．９ＭａＢ．Ｐ．）至晚更新世初（约０．１ＭａＢ．Ｐ．）；４）网纹红土发育于湿热气候条件下，地下水埋深浅，地表低洼、排水不畅的环境。
The Laiyang Formation,about 2300m thick and named after Laiyang city,is composed of Late Mesozoic well developed and widespread continental sediments,and ascendingly divided into six members:Xiaoxianzhuang,Zhifengzhuang,Maershan,Shuinan,Longwanzhuang and Qugezhuang Members.Nonmarine sediments prevail in the Laiyang Formation,in which two cycles are recongnized with the Xiaoxianzhuang Member forming the lower cycle,and the remaining five members forming the upper one. For a long time the geological age of the Laiyang Formation has been a controversial subject.Some regard it to be Early Cretaceous in age,and others consider it to be Late Jurassic,mainly based on fish fossils.The purpose of the present work is to discuss the fossils from the Laiyang Formtion and on the geological age of this Formation.The Shuinan Member is characterized by interbedded grayish dark and gray shales,shaly dolomite,doloclaystone,dololutite and siltstones and contains abundant fossils such as insects,fish,plants,conchostracans,and gastropods,which are considered to be Early Cretaceous in age by many geologists.Various kinds of fossils obtained from the Qugezhuang Member,with bivalves and ostracods being the dominant.The age of these fossils are believed to be Early Cretaceous,too. The Laiyang Formation is considered by the presents authors to be Late Jurassic to Early Cretaceous in age.The strata from the Shuinan to Qugezhuang Members are Early Cretaceous in age.The Early Cretaceous biotas were found in these Members.The beds underlying the Shuinan Member,from the Xiaoxianzhuang to Maershan Members contain no same fossils as mentioned above and the only identifiable fossils are conchostracans.These strata may be Late Jurassic.A Late Jurassic age may be suggested on the basis of the activities of the Yi Shu faults.At least,part of the Laiyang Formation is belived to be deposited during Late Jurassic time,because it is the oldest sediments of the Mesozoic found in the Laiyang Basin and the Jiaolai Depression.This opinion is also supported by the evidence from sedimentation rate.
出处
《地层学杂志》
CSCD
北大核心
1997年第3期226-232,共7页
Journal of Stratigraphy
基金
国家科委预研究项目
关键词
网纹红土
第四系
地层学
江西
修水地区
Shandong, Laiyang Formation, basin evolution, palaeontological biota, Early Cretaceous, Late Jurassic
