Abstract: The contact relation was unclear within the Ordovician in Lunnan area of Tarim basin due to lack of related information. Recently, some direct proofs about the unconformity have been found by drilling and in-depth geologic study in this area, showing that there exist multiple unconformities within the Ordovician among Sangtamu formation, Lianglitag formation and Tumuxiuke formation, except for the conformity contact between Yijianfang formation and Tumuxiuke formation. There might be relatively long-term stratigraphic unconformities in successive fossil assemblage zones.

Key words: Tarim basin, Ordovician, stratigraphic unconformity, crust karst