Abstract: In Sept.,1984, Well Shacan No.2 was drilled in Tabei uplift by Northwest Petroleum Bureau,SinoPec, and the onshore marine oil and gas of Paleozoic was discovered firstly in China. The important discovery creates a new domain for hydrocarbon prospecting. Particularly since "the Ninth-Five Year Plan",Tahe oilfield has been discovered and proved followed by strengthening the exploralory efforts of Paleozoic, gaining a major progression, and establishing an onshore marine petroleum-generating theory of Paleozoic in China. Based on these,profound studies of Ordovician karst and reservoir body are made, revealing basic characteristics of Tahe big oilfield.

Key words: Tarim basin, Paleozoic, Marine facies, oil and gas exploration