| Summary: | The Shadongnan structural zone in the western Bohai Sea area is located in the transitional position from the Shaleitian uplift to the Sha'nan sag. Due to the influence of various factors such as inherited uplift, syn-depositional faults and ancient valleys in different periods, the development of sedimentary facies is relatively complex, restricting the further oil and gas exploration and development. We restored the ancient landform of each three-level sequence in the Dongying formation in the sedimentary period using the strata thickness method, identifying uplifts, slopes, ancient valleys, fault troughs, and shallow and deep sub-sags in the study area. Meanwhile, there are two kinds of ancient landform in the Shadongnan structural zone bounded by the NNE-trending transform fault, with the valley-paleoslope-fault slope-break in the west and the valley-multistage fault slope-break in the east. The former is composed of eroded valleys, buried hill slopes and early syn-depositional faults, while the latter eroded valleys and two or three syn-depositional faults with the same direction and different periods. Our study showed that the valleys located at the edge of the uplifts were the source channels in the early stage and filled with sediments in the late stage. The distribution and filling of the sedimentary system of the valley-paleoslope-fault slope-break were mainly controlled by the ancient slope-fault slopes, and the syn-depositional faults controlling the fault slopes were relatively active in the Shahejie formation and controlled the deposition and filling of the lowstand fans and turbidite fans. By the SQ-Ed3 period, the fault activities gradually weakened, and the fault slope-break distinct the fan delta plain and front in SQ-Ed3 from the deposition of the braided river delta front and shallow lake in SQ-Ed2d and SQ-Ed2u. The Shadongnan No.1 syn-depositional fault with the valley-multistage fault slope-break, which was developed and activated in SQ-Ed3, controlled the formation of the deep sub-sags and the development of the small fan deltas under the first slope break. The Sha'nan syn-depositional fault both formed and activated in SQ-Ed2d was acted as the second slope break separating the bulges and slopes, and controlled the depositional filling of the small fan delta in SQ-Ed2d.
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