江西清江盆地临江组的沉积环境

Sedimentary environment analysis of the Linjiang Formation in the Qing-jiang basin, Jiangxi

临江组共分四个岩性段,地表剖面位于江西清江县临江镇南,仅出露三个岩性段,现按沉积序列,对三个含腹足类化石丰富的层段进行沉积环境讨论。1)临一段第2层 紫红色块状钙质粉砂质泥岩,普遍含钙质结核和团块,微层理发育,近顶部20cm层中含丰富的腹足类及口盖,腹足类多已破碎。主要为Valvata of.

Based on assemblage, paleoecology of gastropods and information function H (S), living conditions of gastropods in the Linjiang stage are known to be changed very rapidly.Analysis of 3 depositions shows that gastropods are mainly distributed in the shallow-water area of the Qingjiang basin.Generally speaking, fresh-water mollusks predominated in all the depositional period.When the temperature, water-depth, nutrition and salinity were favorable, the individuals and species were very high in number.The relationship between the gastropods and the depositional environment could be reflected by the H(S) value, high H(S) value showing a shallow lake deposition, and low H(S) an easily changeable environment, such as beach or littoral lake.There were many factors which influence the life of the gastropods.The water depth is the first one.When it was too deep or too shallow, the individuals decreased highly.The salinity was the second one.When much higher it may cause the individuals scarce, or even absent.Having analysed the change of depositional environment using the H(S), the paleoecology and lithological characters, the writer found the Qingjiang basin in the Linjiang stage was closed very rapidly and the lake entered its final stage.Four kinds of lithological facies (beach, littoral, sublittoral and deep lake) were investigated from the Linjiang Formation.On the basis of these four facies, one ideal pattern of sedimentary environment has been constructed (Fig.2).The history of lake evolution is discussed in detail in this paper also.