江西省区域地层研究新进展

江西省区域地层类型丰富,在《江西省区域地质志》的编写过程中,某些段代的研究有较明显的进展。现把这一新情况、新认识、新问题,扼要地作一介绍,供同志们研讨。江西省区地跨扬子区和华南区各一部分,系地质界颇为关注的地区。各时代地层分布普遍,发育较全,类型较多,是研究地层、古生物及沉积古地理的良好地区。区内晚前寒武纪地层包括了中元古界和上元古界。前者主要出露于省区北部,由一套厚逾万米的火山—沉积型的类复理石建造组成,构成九岭山和嶂公山二复式背斜的主体,称双桥山群。该群进一步划分为上、下两个亚群和四个岩组,其中产有以 Protoleiosphae-

NEW ADVANCES IN THE STUDY OF THE REGIONAL STRATIGRAPHY OF JIANGXI PROVINCE

A relatively complete sequence of strata is present in Jiangxi;it includes quite a lot of stratigraphic units.The Shuangqiaoshan Group of the middle Proterozoic is a series of metamorphic rocks.The upper Proterozoic and early Paleozoic strata are mainly represented by covers in northern Jiangxi,as is the case in the Yangtze region and the Central China-Southwest China region;they are not complete in the central-southern part of the province,the Silurian being absent.Of these strata the Ordovician strata are all of graptolitic facies,and may be divided into three series,six formations and nineteen graptolite zones. The late Paleozoic strata consist entirely of platform-type sediments,mainly of marine facies.The Devonian strata in western Jiangxi grade from marine to continental facies eastwards and northwards.The two kinds of facies are represented by Protolepidodendron schar yanum-Barrandeina dusleiana Yunnanella and Leptophoeum rhombicum fossil assemblages,respectively.The lower Carboniferous varies relatively greatly in facies,whose depositional fea- tures are similar to those of the Devonian.The upper Carboniferous shows a stable facies type,represented mainly by carbonate sediments.The zoning of the fusu- linid assemblages that it contains can be correlated with the division of large regions.From north to south the Permian sedimentary formations exhibit distinct transitional features.South of the lint of Qianshan-Shangyao,the Maok- ouian sediments have changed into coal-bearing terrigenous clastic rocks,refer- red to as the Anzhou Formation.It contains cephalopods such as Paragast- rioceras,Altudoceras,Mexicoceras and Waagenoceras. The Meso-Cenozoic strata are particularly complex.The early Triassic sediments consist mainly of marine carbonates,called the Daye Group; the middle series is mainly made up of a clastic formation;the upper series is represented by paralic coal-bearing sediments,i.e.the Anyuan Formation. The Jurassic is characterized by the presence of continental sediments.Its lower series is mainly of fluvial facies,called the Linshan Formation; the middle series is of limited distribution;the upper series comprises a volcanic-sedimentary formation.The lower Cretaceous is named the“Huoba Group”,which is characterized by occurrence of T.P.N.pelecypod assemb- lages.The upper series is called the Gongzhou Formation and the Nanxiong Group.The latter contains a great quantity of ooliths,so its stratigraphic horizon is ascertained.The lower Tertiary is mainly distributed in the Wuning,Qingjiang and Chijiang basins.The most important fossils are those of mammals,e.g.Coryphodon,Bemalambda,Archaeolambda and Phenaceras lacustrio.The upper Tertiary is only found in the Guangchang and Ji’an basins,which is composed of a set of not firmly consolidated rocks.The Quaternary is repre- sented by till accumulations in the Lushan area,which may be classified into sediments of the Poyang,Dagu and Lushan ice ages.The sediments that are of the widest distribution iu the province include fluvial and lacustrine accumulations.