Characteristics and Geological Significance of the Paleogene Microfossil Assemblages in the Liaoxi Sag,Bohai Bay Basin
The deep-water environment in lakes of the middle and late Paleogene in the Liaoxi sag,Bohai Bay Basin,formed a special group of paleontological fossils.In this study,we characterized the microfossil assem-blages through investigating the paleontological drilling data in this study area.Five fossil assemblages of pollen algae and five mesomorphic fossil assemblages were established.In the western and northwestern Shahejie For-mation,distinct near trapezoidal mesomorph fossils Candona sagmaformis,C.postabscissa,and membrane tube algae fossils Hystrichosphaeridium tubiferidium tubiferi and Membranilarnacia originally formed in deep-water were observed.Moreover,mesomorph fossils Tianjinia fiulgida,Bohaicythere sp,Parabohainia elliptica,and others formed in deep-water were widely observed in Dongying Formation.These fossil signatures indicate that the range of sedimentary center in deep water expanded gradually from Shahejie Formation to Dongying Forma-tion,and it connected with the sedimentary centers of the Liaozhong depression in the end.Meanwhile,compar-ison study of a large number of paleontological fossils and their rock lithology,we concluded that the Liaoxi sag and the low convex zone of Liaoxi sag had a large range of sedimentary breaks when deposited in the second sec-tion of Shahejie Formation.Also,the upper subsection of the third section of Shahejie Formation is widely de-veloped.This study provides a strong evidence for the division and comparison of the Paleogene strata in this re-gion,and meanwhile this study enriched the relevant studies on sedimentary environment.
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