Shahejie Fm

Bohai Bay region. The naming section of the first to third members is located in Hua No. 7 well at Shahejie Township, Shanghe County, Shandong, and that of the fourth member is in Dongfeng No. 2 well. Named by the North China Petroleum Exploration Bureau, Ministry of Petroleum in the late 1950s and formally used by Jia Zhonghui, Ma Zaitian, Shuai Defu et al. in the “Report on the Comprehensive Study of Petroleum Geology of the North China Plain”.

A sequence of dark-colored sandy mudstone composed mainly of gray and dark gray mudstone, with a thickness of >2000 m. In ascending order the formation is divided into four members: Fourth member is marked by red mudstone in the lower part, bluish gray mudstone with gypsum-halite in the middle part and gray mudstone with organic limestone in the upper part. Third member is dark gray and gray mudstone with sandstone, the base of which contains oil shale. Second member is alternating variegated sandy mudstone. First member is gray mudstone with oil shale, organic limestone and dolomite.

The formation contains rich fossils of various groups. Freshwater and brackish forms occur together and endemic genera and species appear in large quantities, of which ostracods, gastropods, charophytes, sporopollen and fishes are of great significance for stratigraphic correlation and analysis of sedimentary environment. Ostracods in the fourth member are represented by the Austrocypris-Cyprinotus assemblage, gastropods are the Sinoplanorbis-Lymnaea assemblage, charophytes are the Gyrogona-Obtusochara assemblage and sporopollen is the Ephedripites-Ulmoideipites-Pinaceae assemblage. In the third member, ostracods are the Huabeinia chinensis assemblage, gastropods are the Liratina tuozhuangensis assemblage, charophytes are the Shandongochara decorosa assemblage and sporopollen is the Quercoidites-Ulmipollenites assemblage. In the third and fourth members, fishes are Diplomystus shengliensis, Knightia bohaiensis, Tungtingichthys eocanus and Clupeidae, and in addition, Eocene anthracotheres have been found in strata possibly equivalent to the third member of the formation in the Liaohe oilfield. In the second member, ostracods are the Camarocypris elliptica assemblage and Cyprinidae, gastropods are the Tulotomoides-Trunctus assemblage, charophytes are the Charites producta assemblage and sporopollen is the Ephedripites-Rutaceoipollis assemblage. In the first member, there are the ostracod Phacocypris huiminensis assemblage, the gastropod Bohaispira-Gangetia assemblage, the fish Wangia yihezhuangensis and Serenade, and the sporopollen Quercoidites-Liquidambar-Pollenites assemblage. Besides the aforesaid fossils, the formation also yields algae, foraminifera and echinoids.

As the eco-environment changed frequently, the biotas in various members of the formation have their own features and show a certain regional features, and most genera and species are of endemic types. Take the fourth member for example. Its middle and lower parts are continental deposits. In the biotas, species such as the ostracods Cyprinotus igneus, C. cangzhouensis, C. wangquantunensis and Eucypsis spp. are all common elements in freshwater and low-salinity water areas in China and abroad, whereas from the upper part of the fourth member to the first member there appear some offshore lake brackish faunas, of which large numbers are new genera and species, e.g. Huabeinia, Camarocypsis, Guangbeinia and Chinocythere, as well as the gastropods Bohaispiridae and fishes of the brackish orders Clupeomorpha and Perca. Moreover, the sporopollen assemblage also contains a certain quantity of tropical and subtropical elements.

According to the lithology and biotas, this formation is mainly a sequence of fluvio-lacustrine and paralic deposits.