Turbidite Characteristics of Delta Front for the 3~(rd) Member of Shahejie Formation in Niuzhuang Sag, Jiyang Depression

Based on the comprehensive analysis of geological, well logging and seismic data, the turbidite characteristics of delta front in the 3~(rd) Member of Shahejie Formation in Niuzhuang sag are studied. The results show that there are two turbidity sedimentary types in this area, namely the sandy turbidite and muddy turbidite. The former has finer granularity and lower maturity of composition and texture, with characteristics of slumping redeposit and can be described by Bouma sequence, such as CDE, BCD and ABCD. Furthermore, the sandy turbidite can be classified into two subtypes: the turbidite sandbody with supplying channel and the turbidite sandbody without supplying channel. The former subtype has fan shaped distribution that can be further subdivided into five microfacies: inner-fan channel, middle-fan braided channel, space between middle-fan braided channel, middle-fan braided channel front and outer fan. The latter has slice and tongue shaped distribution and can be further subdivided into two microfacies: central section and marginal section. There are two subtypes of muddy turbidites developed in this area: graded straticule mudstone and inhomogeneous massive mudstone. The muddy turbidites can not be described in Bouma sequences, and their origins are of low-density turbidity currents. According to sedimentary characteristics of turbidity sediments, a integrated depositional mode of the delta and turbidites in this area are established. Meanwhile, the genesis of delta front turbidites and their significance in petroleum geology are discussed.