THE RESEARCH OF SEDIMENTARY CHARACTERISTICS IN THE LOWER YOUSHASHAN FORMATION,NEOGENE OF WUNAN AREA,SOUTHWESTERN QAIDAM BASIN

The Paleogene sedimentary characteristics from the lower Youshashan formation, Neogene of Wunan area have been studied by core observation, thin section identification, grain size analysis and log interpretation.The lower Youshashan formation of Wunan area can be divided into five formations. The first and second formations belong to flooded-lake gravity currents depositional system, mainly develop flooded-lake facies, and it is divided into lake subfacies, channel subfacies and sands subfacies. The third, forth and fifth formations is shadow lake-deltaic depositional system, mainly develop shadow lake delta facies. In the region of interest, shadow lake delta facies develops both delta plain and delta front facies. Through researched sedimentary facies, sub-facies and micro-facies, summarized the characteristic, recognized the evolution feature of sedimentary facies and sandbody distribution rules, it possesses guiding sense to the sandbody prediction and the calculation of reserves in the future.