湖相重力流沉积特征及沉积模式

应用深水沉积学和地震沉积学的相关理论，通过岩心观察描述、钻测井资料分析及平面沉积相编图，对下刚果盆地A区块白垩系Pointe Indienne组深水重力流的类型、沉积特征、垂向沉积组合及沉积模式进行了探讨分析，指出该地区发育砂质碎屑流、泥质碎屑流、浊流及与重力流形成过程相关的滑动—滑塌沉积，并总结了该深水重力流的沉积模式。结果表明:砂质碎屑流沉积以块状层理细砂岩为主，含大型漂浮泥砾和泥岩撕裂屑；泥质碎屑流沉积以泥级碎屑为主，含有少量的暗色泥岩碎屑和砂质团块，见“泥包砾”结构；浊流沉积以发育完整或不完整的鲍马序列为特征；滑动—滑塌沉积具有明显的剪切滑移面，可见旋转火焰构造、砂岩扭曲杂乱分布及褶皱变形层；纵向上可识别出4种类型的重力流沉积垂向组合，以多期砂质碎屑流沉积叠置和砂质碎屑流沉积与浊流沉积叠置最为常见；研究区深水重力流沉积可分为上部扇、中部扇和外部扇3部分，上部扇以主水道沉积为主；中部扇以辫状水道和溢岸沉积为主，砂体厚度较大；外部扇以朵叶体沉积和薄层浊积岩为主，砂体厚度相对较薄。

Sedimentary Characteristics and Depositional Model of Lacustrine Gravity Flow Deposits:A case study of the Cretaceous Pointe Indienne Formation of Block A,Lower Congo Basin

Core observation， drilling and logging data analysis， mapping of sedimentary facies， and application of correlation theory were used in this investigation of the deep-water sedimentology and seismic sedimentology， gravity flow types， depositional characteristics and vertical sedimentary associations to develop a depositional model of the deep-water gravity flow deposits in the Cretaceous Pointe Indienne Formation of Block A， Lower Congo Basin. It was concluded that sandy debris flow， muddy debris flow， turbidity current and slide-slump deposits were developed in the study area. On this evidence， the depositional model consists of the following: flow deposits of sandy debris consisting mainly of massive bedded fine sandstone， but containing large floating mud gravel and torn mudstone debris； flow deposits of muddy debris， mainly of argillaceous clastics and containing a small amount of dark mudstone clastics and sandy mass， which have developed into an “argillaceous parcel” structure； turbidites characterized by a well-developed or incomplete Bouma sequence； and slide-slump deposits in which obvious shear slip planes， rotating flame structures， twisted and disordered distributions of sandstone and fold deformation were all observed. Analysis of the dynamics revealed four types of vertical sedimentary association in the gravity flow deposits. The two most common types are multi-stage superimposed sandy debris flows， and sandy debris flow superimposed upon turbidity flow. These are characterized by braided channel deposits and lobe body deposits. The deep-water gravity flow deposits in the study area occurred as an upper， middle and outer fan deposit. The upper fan consists mostly of main channel deposits characterized by slump deposits with deformed structures， and massive sandy debris flow deposits. The middle fan is mainly made up of braided channel deposits and overflow bank deposits characterized by massive sandy debris flows with floating mud gravel and relatively thick sand-bodies. The outer fan occurs mainly as lobe body deposits and thin turbidites in both complete and incomplete Bouma sequences， and with relatively thin sand-bodies.