Bohai Bay basin province is a major Cenozoic rift basin, which includs 3 geographical units, namely, northern North China Plain, sea area of Bohai Bay and Xialiaohe Plain. The data of petroleum exploration have clearly indicated that the architecture of the basin can be divided into 3 tectonic levels. The lower level, the basement of basin which consists of pre-Eogene formation, is dissected by a great number of basement faults (mostly normal faults), and have constructed a series of half-grabens (or grabens) and half-horsts (or horsts). The middle level, which consists of Eogene filling up in the half-grabens and grabens, is involved in the deformation of basement structure and result in many cover faults, the upper level, which consists of Neogene and Quaternary, is not involved in the deformation of basement structure, and overlies as a blanket upon the whole basin province including both grabens and horsts so that the whole Bohai Bay basin province forms a united major depression.
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