Geochemical characteristics of Permian event strata in western margin of Ordos Basin

It is of importance for gas prospecting that the section of Permian strata in the western margin of Ordos Basin has been systematically studied.Based on the research in terms of petrographyic,sedimentological and geochemical data,event layers which can be divided into two types have been discovered.These are volcanic event layer and regressive layer,which are developed in Taiyuan Formation respectively,one volcanic event layer in Shanxi Formation and three in Shihezi Formation.Major element,trace element and rare earth element data exhibit considerable variability.The results indicate that the event layers are better tools for regional stratigraphic division and correlation.