CHARACTERISTICS OF THE PERMIAN STRATA IN SHANXI AND THEIR LAWS OF VARIATION

Take for example a type section in the Western Mountain in Taiyuan, Shanxi,this paper discusses in more detail the lithologies,grain size of clastic rocks,ore potentiality,key beds,stratigraphic hues and thickness of various formations and members of the Permian in Shanxi.The laws of vertical and lateral variation of three Permian formations are developed through a comprehensive analysis. The lower Shiheze Formation of the Lower Permian in Shanxi is represented by a sequence of dominantly fluvio—lacustrine deposits with swampy deposits. The main lithologies consist of yellowish green, grayish green, yellowish gray,apricot yellow and purple sandstones,conglomerates,shales and mudstones of various grain sizes,intercalated with coal stringers or carbonaceous shales,with manganiferous iron ore in the upper member. The upper Shihezi Formation of the Upper Permian is marked by a sequence of dominantly fluvio-lacustrine deposits with lesser swampy and marine deposits.The main lithologies include yellowish green,apricot yellow,grayish white,purple,blucish gray and variegated sandstones,mudstones and shales, intercalated with manganiferous iron ore and coal seams and stringer,with 1--5 chert 1ayers（bands or nodules）in mudstones at the top. The Shiqianfeng Formation of the Upper Permian is represented by a purple sequence of strata composed of fluviolacustrine clastic rocks, clay rocks,carbonate rocks and minor evaporites（gypsum）,of which arkose makes up more than 80％ of the clastic rocks. The vertical variation of the three above-mentioned formations are gradual.From below upwards,the compositional maturity and textural maturity of sandstones become high gradually, argillaceous rocks become more and more; foliation becomes less and less developed; the hues of the str ta change from yellowish gree to yellowish green,purple and variegated to purple and brick red;plant fossils become less and less;and the interbeds change from coal and a small amount of manganiferous iron ore to chert and manganifous iron ore to limestone and gypsum,all this shows that from the Early Permian to Late Permian the climatic and oxidizing—reducing conditions in Shanxi changed from humid—warm and weakly oxidizing and reducing one to semi—humid,-warm and -arid and oxidizing one to hot, arid and strongly oxidizing one. Laterally,from north to south, the level of occurrence of coal, marine rocks,plant fossils,manganiferous iron ore, chert and carbonate rocks beomes higher and higher and purple rocks are better developed in the north than in the south of Shanxi,_<sub><sub><sub>this shows that the northern part of Shanxi uplifted slowly,that the lacustrine deposits become more developed southwards and that the dry climate of the northern hemisphere affected Shanxi from northwest and spread southward s gradually during the late part of the Early Permian.