Origin of Salt and Gypsum Rock in the ThirdMember of Shahejie Formation of Lower Tertiary in Dongpu Depression

Key words: 
• origin of salt and gyp sum rock /
• lake level change /
• lowstand sandbody

Abstract: The column of salt and gyp sum rock that are interbeded with black mudstone are developed in 3^rd - 4^thsub-member of Shaheje Formation of Lower Tertiary in Dongpu Dep ression. The black mud-stone was deposited in deep water, and the salt and gyp sum have been considered to be deposited in deepwater, too. In recently study, much mark of shallow water origin and evaporation are found, so the salt and gyp sum rock is considered of evaporation origin in Shallow water. That the black mudstone deposited in deep water interbedded with salt and gyp sum deposited in shallow water shows that during the sedimentation of 3^th and 4^th sub-member, the lake 1evel changes frequently.And it is because of the frequently change of lake 1evel, lowstand sandbodywas deposited in the sedimentation center in the direction of main sediments source, and the lowstand sandbody are the main reservoir of lithic oil pool