Abstract: There have not been an unified classification and correlation of Late Ordovician strata in Lunnan area of Tarim basin. This paper pre-sents original meaning and evolution of Sangtamu formation, based on which and principles about formation definition and its classification giv-en by A Guide Book of China's Geologic Positions, redefined the meaning of Sangtamu formation, and makes clasification and correlation of Late Ordovician biostrata in Lunnan area, including Sangtamu formation of Upper Ordovician. Study indicates that the era of Sangtamu forma-tion should be proper in Late Baota epoch to W ufeng epoch, which will be as a new guide for in-depth study of Lunnan 's stratigraphic classfica-tion and correlation.

Key words: Tarim basin, Lunnan area, Upper Ordovician, stratigraphic classification, stratigraphic correlation