南海北部陆坡区新近系沉积体系特征与天然气水合物分布的关系

Characteristics of Neogene depositional systems on the northern continental slope of the South China Sea and their relationships with gas hydrate

南海北部陆坡区新生界含有丰富的油气资源和各种矿产资源,对其沉积体系的分析可以指导资源勘探和开发。笔者在对南海北部陆坡区的西沙海槽和东沙海域的地震剖面解释与研究的基础上,依据“外部形态+内部属性”的分类原则,在中新世以来的沉积层中共识别出8种典型的地震相:席状平行相、席状波形相、席状空白相、席状杂乱相、席状前积相、帚状前积相、透镜状前积相和丘状杂乱相。结合地震相分析,在南海北部陆坡区识别出6种典型的沉积体系:三角洲体系、等深流、低位扇、滑塌块体、浊积扇和扇三角洲体系;其中等深流、滑塌块体和各种扇体的前缘与BSR分布的吻合率最高,是最有利于天然气水合物聚集成矿的相带。

The Cenozoic on the northern continental slope of the South China Sea contains abundant petroleum and other mineral resources, so an analysis of its depositional systems can help geologists to guide resource exploration and exploitation. On the basis of the interpretation and study of seismic sections in the Xisha trough and Dongsha sea area on the northern slope of the South China Sea and in light of the seismic facies classification principle of external geometric shape plus internal reflector configuration, eight typical seismic facies are recognized in sedimentary beds since the Miocene; they are： sheet-parallel, sheet-wavy, sheet-blank, sheet-chaotic, sheet-foreset, brush-shaped foreset, lenticular foreset and mound-chaotic facies. On that basis, six depositional systems are recognized on the northern slope of the South China Sea; they are： delta, contourite,submarine fan or slope fan, slump block, turbidite fan and fan-delta. Of these, the distribution of the contourite,slump block and fronts of deltas or fans is highly consistent with the distribution of BSR, and thus they are the most favorable facies for gas hydrate accumulation.