济阳坳陷牛庄洼陷沙三段三角洲前缘浊积岩特征

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

根据地质、测井、地震资料的综合分析 ,对济阳坳陷牛庄洼陷沙河街组三段三角洲前缘的浊积岩特征进行了研究。结果表明 ,该区存在砂质浊积岩体和细粒浊积岩体两种浊流沉积物。其中砂质浊积岩体粒度较细、结构成熟度和成分成熟度较低 ,结构和构造均反映了砂体具有滑塌再沉积的特点 ,可用Bouma序列来描述 ,常发育CDE ,BCD ,ABCD型浊流组合。砂质浊积岩体可进一步划为有根式和无根式两类。有根式砂体常呈扇形 ,可分为内扇槽道、中扇辫状水道、水道间、水道前缘和外扇无水道五种微相 ;无根式砂体常呈片状、舌状 ,可分为中心微相和边缘微相两个相带。细粒浊积岩属于低密度流的产物 ,不能用Bouma序列来解释 ,主要发育递变纹层泥岩和不均匀的块状泥岩两种细粒浊积岩。根据两类沉积物的沉积特征 ,建立了该区三角洲 -浊积岩体综合沉积模式。

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.