Development mode and distribution characteristics of biolimestone of the Shahejie1 Formation in the Changdi Area of the Zhanhua Sag

Abstract

Using core, drilling, logging and seismic data, the development and sedimentary evolution of biolimestone of the first member of Shahejie Formation of Zhanhua Sag were researched. The first member of Shahejie Formation Changdi Area is defined as a third-order sequence, and the biolimestone developed in the first member of Shahejie Formation was divided into three fourth-order sequences. The lacustrine transgressive system tract and the lacustrine regressive system tract, where the biolimestone both developed were also identified. The development of biolimestone is influenced by paleoclimate, relative paleowater depth and paleogeomorphology. There are three types of paleo water depth variation in the Member of Shahejie Formation, namely the water withdrawal, the high position water and the low position water. Through paleogeomorphology restoration, it is clear that the biolimestone in the first member of Shahejie Formation is mainly distributed in the southeast and eastern slope trough, and then it is determined that there are two development modes in the study area, which are the biolimestone developed in gentle slope and the biolimestone developed in trough. Due to the periodic change of the lake level, the distribution of the biolimestone in the first member of Shahejie Formation also changed correspondingly. The biolimestone is thicker around the uplift and thinner along the gentle slope direction, and its belt-like distribution is parallel to the periphery of the buried hill.