Abstract：According to 1∶200000 and 1∶50000 regional geological maps, the strata over the Ordovician Majiagou Formation along Dajiakou and Nantai profiles were assigned to the Liujiagou Formation. In this paper the authors performed lithostratigraphic correlation and dating of detrital zircons, and proposed that the strata above the surface of unconformity are Benxi Formation instead of Liujiagou Formation, as evidenced by the similar lithofacies associations, gravel compositions and age spectra of detrital zircons from Dajikou, Nantai and Shanwanzi profiles.