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The study area includes the Bohai basin of north China and Dongtai basin of east China. Regional cycles of sea level change during the Tertiary in the Bohai basin correlate fairly well with global cycles, but differ from those in the Dongtai basin where the lowest sea level occurred at the end of the Eocene. The paleogene sediments, which were previously considered to be of continental origin, are now shown to be marine deposits because of the presence of abundant nannoplankton. This reinterpretation of the Paleogene indicates that transgression had taken place in these areas at that time, and that the closure of the paleosea between the North China and South China plates was delayed for a long time. Fan-delta and turbidite facies occur in anticlines of different dimensio s, some of which form traps for oil and gas accumulations. Abnormal formation pressures occur in Eocene shale sections and contributed to the formation of shale diapirs, growth faults, and some large-scale gravitational slide blocks. The slide blocks are the most important structural features of the region.
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