The Sedimentologic Characteristics Of Beach And Bar In The Upper 4th Member Of Shahejie Formation (E₂²S₄^U), Zhuangxi Area Of Zhanhua Depression

On the basis of modern sedimentology and High-resolution Sequence Stratigraphy, also the comprehensive analysis of the cores, geophycial logs and modern sedimentary investigation, the sandy beach and bar complex in Upper 4th Member of Shahejie Formation,Zhuangxi Area,Zhanhua depression are studied.This paper studies the vertical evolution of the beach and bar sand developed in Paleogene of Zhanhua depression and the characteristics of sedimentary system distribution in Upper 4th Member of Shahejie Formation(E22S4U). The beach and bar sand developed in the early time of the fault stage or fault-sag transition stage, and grew in LST and TST in third-order sequence. At the Upper 4th Member depositional period, reef and clastic carbonate rock were developed in Sikou sag, clastic rocks were recognized in Zhuangxi area. The deposition of beach and bar sand was the combined result of the ancient terrain, depth, hydrodynamic conditions, coastline migration, paleoclimate conditions and the deposition supply system.In this study of beach bar strata, using cores, geophycial logs and seismic data, the Upper 4th Member of Shahejie Formation was divided into 5 fourth-order cycles and 22 fifth-order cycles. The frame structure was built up on the basis of the well correlations.The depositional model was established as a complex system developed on and around the underwater buried hill, based on the study of the beach and bar distribution. The beach and bar complex was reformed and transported by waves, and deposited on the on the top of and around the underwater buried hill at last,because of the lower water power and small scale of the basin. The development of the beach and bar was controlled by palaeotopographic, the sediments supply system and the landscape etc.The intensive study of Zhuang835 well area shows that beach and bar sand was buried mainly in both rising and falling hemicycle in cycleⅢand cycleⅡ, but the large scale bar dam was mainly developed in the rising hemicycle in cycleⅢand in the falling hemicycle in cycleⅡ2 andⅡ1. The sand body on the west side of the underwater hill is thinner and composed of beach sand. The sand on the center and east of the hill is mainly thick bar sand belts, which buried parallel to the south-north ancient terrain.The prediction research is based on the relationship analyzing between the position of overlop or denudation zone and the position of beach and bar sand. The main types of trap in study area are overlop stratigraphic traps, unconformity blocked traps, lithologic traps and construction–lithologic traps.