Abstract: In Tazhong-88 Well, the conodont fossils in the late of Middle Ordovician and the early of Late Ordovician slope facies have been found for the first time. The seismic and logging data indicate that there exists Tumuxiuke formation of Upper Ordovician and Yijianfang formation of Middle Ordovician in Tazhong-88 Well. The existence of these strata in Tazhong low swell becomes possible for the stratigraphic correlation of Ordovician and the analyses of regional structure and sedimentary environment among Tazhong, Lunnan and Yingmaili areas.

Key words: Tazhong area, conodont, Ordovician, Yijianfang formation, Tumuxiuke formation