Identification and Formation Mechanism of Fans Developed in 1^st Member of Shahejie and Dongying Formations, Gaoliu and No.4 Tectonic Belt, Nanpu Sag

The identification of fans under the para-sequence framework helps to reveal the sedimentary filling history of continental rift basins, the relationship between sediment and tectonic activities, and to guide the further exploration for oil field. Cores, logging data, and seismic data are used to study the evolution process, shapes, internal architecture, and formation mechanism of fans. Fans are mainly developed in midwestern Gaoliu tectonic belt in 1^st member of Shahejie Formation, and expand to No. 4 tectonic belt in Dongying Formation. The fans can be classified into 4 types based on shapes and internal architectures:(1) the fans are wide in delta plain, and gradually narrow down in delta front, channels are well developed with multi-branches in delta plain, mouth bars are deposited close to delta plain, and this type of fans is developed when the faulting rate of boundary faults is higher than subsidence rate in the lake; (2) the fans are narrow in delta plain, and gradually widen in delta front, the channels show limited branches in delta plain, the amount of mouth bars are large, but each mouth bar shows a small coverage area, and this type of fans is developed when the reverse drag anticlines appear; (3) the fans are elongated, the channels show limited branches in delta plain, the subaqueous channels are unstable, the mouth bars are large in quantity and total coverage area, and this type of fans is developed when the faulting rate of boundary faults is lower than the subsidence rate in the lake; (4) the fans are bird-foot shaped, channels are stable in delta plain, subaqueous channels show large amount of branches, the amount of mouth bars are small, but each mouth bar shows a large coverage area, and this type of fans is developed when the faulting rate of boundary faults is approximately equal with the subsidence rate in lake.