Characteristics of Sedimentary Environment and  Filling  Model of the Lower Submember of the Fourth Member of Shahejie Formation,  Dongying Depression

Key words: 
• sedimentary environment /
• sedimentary model /
• gypsum salt beds /
• red beds /
• Dongying Depression

Abstract: The genetic type of sandbodies and sedimentary filling models were controlled by characteristics of sedimentary environment in sedimentary basin. According to the systematic sampling of argillaceous sediments of Es4x of Well Fengshen 2, Guan 112 and Liang 120 in Dongying Depression, whole rock Xray diffraction and macroelements and microelements were analyzed, based on which the paleoclimate indexs and paleosalinity indexs of Es4x of Dongying Depression were studied. It turned out that the paleoclimate index Rb/Sr was direct proportion to content of quartz and feldspar, element Cr and element P and inversely proportional to paleosalinity index content of carbonate and sulphate. The increasing ratio of Rb/Sr reflected relatively damp climate, while the increasing content of carbonate and sulphate reflected relatively arid climate. The characteristics of the climate of the period of Es4x of Dongying Depression were frequent damp climate alternate with arid climate. At the period of damp climate, the relative lake level rise and the salinity of lake water decline, while the relative lake level decline and the salinity of lake water rise at the period of arid climate. The characteristics of climate made the lake of Es4x of Dongying Depression have the character of high frequency oscillatory salt lake. Clastic sediments were the main deposits at the period of damp climate, including alluvial fan sediments, shallow water delta sediments, lakeshore beachbar sediments and nearshore subaqueous fan sediments, and the sag belt mainly deposited mudstone, lime mudstone, gypseous mudstone and a small quantity of argillaceous gypsum rock. At the period of arid climate, the deposition was mainly developed in sag belt and was characterised by gypsum and salt sediments, which have the evolutive sequence of gypseous mudstone, argillaceous gypsum rock, gypsum rock and salt rock upward and the zonal structure with lime mudstone, gypseous mudstone, argillaceous gypsum rock, gypsum rock and salt rock from the margin to the center of the lake in the plane.