EVOLUTION OF BASE-LEVEL CYCLES AND LITHOLOGIC TRAPS OF THE SHA-3 MEMBER IN THE CENTRAL SAG OF THE DONGYING DEPRESSION, THE BOHAIWAN BASIN

Based on study of drilling data and seismic data, the high-resolution sequence stratigraphical framework of Sha-3 member in the central sag of Dongying depression has been established. The middle member of Sha-3 can be divided into one long-term and six short-term of base level cycles. In accordance with the characteristics of the base levels and the forming mechanism of the sandbody, the lithologic traps can be divided into three types: slump turbidite trap, slope-moving turbidity fan trap and sublacustrine fan trap. The formation of traps was related to the evolution of base levels. The sub-lacustrine fan and slope-moving turbidity fan which consisted of the main reservoirs were formed during rising stage of the base level, and the slump turbidite was formed during the falling of base level.