Abstract: The integration of geochemistry, palaeontology, sedimentary facies and palaeogeography, regional geology and global sea-level fluctuations shows that seawater encroachments did not occur in the oil-bearing basins in eastern China during Tertiary time. The presence of the "marine" Dinophyceae,foraminifera and calcareous ultramicrofossils are attributed to the salinized lakes and abundant nutrients. Dinophyceae is a kind of euryhaline organisms,and thus ubiquitous in ponds,lakes,rivers and seas,especially in brackish environments. This implies that caution should be exercised in the application of Dinophyceae as a facies fossil.