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.