Abstract: In Shahejie ⅠMember in Qikou Depression, the massive “alcareous laminated mudstone”or “Bituminous rock”are discovered. However, by means of the optical microscope, the scanning electron microscope observation as well as the entire cock Xray diffraction analysis, it is identified most part of these “alcareous laminated mudstone”, “Bituminous rock”are composed by mudstone and coccolith limestone. The limestone geochemistry analysis, the mineralogy findings indicated that the forming of coccolith limestone were related with sea water, further compared with coccolith growth environment and the characteristic of its deposit in modern Black Sea, it is discovered the coccolith limestone of Shahejie ⅠMember in Qikou depression and even Bohai basin is similar to the coccolith limestone in the Black Sea. This indicate that at the communication period between Bohai Bay and sea, coccolith limestone in Qikou Depression is the result of blooms and deposition of coccolith when it entered the Bohai Basin from the open sea.

Key words: coccolith limestone, Shahejie ⅠMember, connection the sea and lake, Qikou Depression, Paleogene