Abstract:

Member Ⅲ-lower submember of Member Ⅱ in Shahejie Formation of Dongying Depression can be divided into Ⅲ third-order sequences on the basis of seismic data,lithology and electric characteristics etc.The bottom of sequence(SSI) corresponds to the lower submember of Member Ⅲ of Shahejie Formation,characterized by lowstand system tracts undeveloped,only lacustrine transgression system tracts and highstand system tracts developed,all of theses are controlled by the early tectonic subsidence and climate.Middle sequence(SSⅡ) represents the mid-submember sedimentation of Member Ⅲ in Shahejie Formation and has similar nature of the bottom sequence.SSI and SSⅡ are all T-R cyclic sedimentation.Top sequence(SSⅢ) representing sedimentation of the upper submember of Member Ⅲ-lower submember of Member Ⅱ in Shahejie Formation(forming Lowstand system tracts,water transgression system tracts and highstand system tracts) is a complete cycle.SSⅡ was formed under the conditions of tectonic activity relatively weak,climate relatively dry and water supply insufficiently.

Key words: Shahejie Formation:sequence contact, sequence, origin, Dongying depression