Characteristics of sedimentary geochemistry and evolution of platform of the Lianglitag Formation carbonate, Upper Ordovician in Tahe Oilfield

The Upper Ordovician Lianglitag Formation, Tahe Oilfield, mainly consists of micrite, nodular limestone in the lower member and oolitic limestone, bioclastic limestone, calcarenite, calcirudite in the upper member, which constitutes a shallowing upward sedimentary sequence. Based on sequence stratigraphy research, the Lianglitag Formation is a integral three-order sequence, which is composed by two systems tracts. By means of detail investigation in petrographic and geochemical characteristics of stratigraphic units in every systems tract, the palaeogeographic and sedimentary facies distribution are recognized. There are three kinds of facies belts during upper Ordovician in Tahe Oilfield: platform, platform margin and slope facies, which is approximately east-west strike and distribute orderly from north to south in the plane. Analysis of trace elements and rare earth elements further support and improve the analysis of sedimentary facies. The content of V " Ni and Cr trace elements shows a overall increasin