A Preliminary Study of Sedimentary Facies,Palaeogeograpgy and Mineralization Regularity in Shanxi during the Early Benxian(the Fe-Al-Bearing Rock Members)of Middle Carboniferous Times

This paper deals with sedimentary facies and palaeogeography in Shanxi during the early Benxian of Middle Carboniferous times in light of the criteria for recognition of sedimentary facies such as sedimentary structures. fossil assemblages, trace elements and isotopic data. During the period, oldland and islands were confined to the southern and northern ends of Shanxi, respectively, whereas the central part of it was generally occupied by the barriered tidal flat-lagoon system which may be divided into twelve lagoon districts and five swamp districts. The mineralization regularity has also been discussed in terms of sedimentary facies and palaeogeography. Bauxite, iron and pyrite deposits are all associated with ancient lagoons. Pyrite deposits tend to occur in the central facies of the lagoons, whereas iron deposits in the marginal facies. Bauxite deposits are dominantly related to the lagoon beach facies. For example, the rough bauxite ores often lie in the lower part of the subtidal zone; the clastic and oolitic bauxite ores in the upper part of the subtidal zone and intertidal zone, and the compact massive ores in the supratidal zone and swamp facies.