Lithofacies Palaeogeography of the Qingxudong Epoch,Duyun Stage,Cambrian Period and its Relationship to Lead-Zinc Deposits in Western Hunan and Eastern Guizhou Province

Based on two types of facies-changing surfaces and two types of diachrononisrns in stratigraphic records,and combining with the sedimentary characteristics and lateral facies distribution of more than ten typical Cambrian profiles in the upper Yangtze region,the lithofacies palaeogeography of the Qingxudong epoch,Duyun stage,Cambrian Period has been studied with the isochronal dominant facies method and a stratigraphic map is prepared.The paleogeography in the study area is characterized by high in the west and low in the east,deep water in the south and shallow water in the north.The sediments overlapped from NW to SE,and exhibit diachrononism with increasing depth.The differences of the lithology,thickness,color and sedimentary facies are due to the sedimentary facies change and diachrononism.Vertically,the stratigraphic succession from the dolomite member and the limestone member of the Qingxudong Formation makes up of a large-scale upward-shoaling sedimentary facies succession and demonstrates a growth process of a ramp carbonate platform.Horizontally,the principal lithofacies palaeogeographic units in the upper Yangtze region,i.e.,carbonate tidal flat,shallow ramp facies,middle ramp facies,deep ramp facies,shallow shelf facie,and deep shelf facies as well as basin facies from the northern to the southern have been described.The lithofacies palaeography exerts a key control on the stratabound-type lead-zinc deposits,which are distributed in the middle-and shallow ramp facies of the restricted platform,and the assemblage making up of turbidite and micrite mounds(algal bioherm) and rudstone is a well developed succession for lead-zinc deposits.