Abstract: The triphibian chipping-rock sedimentary formation in Early Cenozoic in Adatan basin in western segment of east Kunlun Mt.was formerly considered to belong to "Low Tertiary".In the 1:25 ten thousands Kelangmiqiti sheet of regional geology survey for the first time in the chipping-rock construct,the freshwater Gastropoda fossils were found:Australorbis pseudoammonius huanghoensis Yu,Lymnea sp.According to the stratum contained fossils lithofacies characteristics and the breatheable epoch of the Gastropoda fo ssils,someone considered that the"Low Tertiary" in Adatan basin should belong to the Low Ganchaigou Group of Oligocene in Ancient Neoteric period.According to the analysis of the presence of that stratum and the Early Pleistocene Qigequan Formation unconformably covered,the once stronger scale apophysis was oncluded in Adatanba sin in Oligocene.