神狐海域海底峡谷群脊部细粒浊积体分布范围及意义

利用广州海洋地质调查局在南海北部神狐钻探区采集的高分辨率地震数据，结合2007年第一次水合物钻探航次(GMGS01)获取的岩心资料，从宏观地震反射结构、微观岩心粒度特征两个方面对GMGS01区块内残留在峡谷群脊部的细粒浊积体进行特征识别和刻画。研究结果显示，似海底反射(bottom simulating reflectors，BSR)之上存在着2套特征不同的沉积单元，位于下部的沉积单元1表现为薄层杂乱透镜状的地震反射特征，对应于粒度C-M图版中与C=M基线近似平行的含水合物层段的样品，被解释为峡谷群脊部的细粒浊积体。选取穿过神狐海域峡谷群中第16条海底峡谷的8条测线为研究对象，能够揭示沉积单元1(细粒浊积体)自北向南的空间变化特征，从而进行分布范围的确定。神狐海域沉积过程分析表明，峡谷群脊部的细粒浊积体是北部小型水道侵蚀下伏沉积物并发生再搬运和再沉积的结果。利用区域性覆盖的二维地震资料，本次研究确定了小型水道的北部侵蚀边界。综合GMGS01区块细粒浊积体的地震反射特征、穿过神狐海域东部第16号海底峡谷自北向南的地震反射差异、研究区北部小型水道的侵蚀边界，本次研究利用两点确定一线和相似平行的方法，在整个神狐海域初步确定了峡谷群脊部细粒浊积体的分布范围。细粒浊积体沉积边界的识别，将为从深水沉积的角度探讨神狐海域水合物不均匀性分布提供依据，同时也能进一步揭示该区域峡谷群脊部水合物的成藏机制和富集规律。

Distribution of fine-grained turbidites on canyon ridges in the Shenhu area of northern South China Sea and its implications

Based on the high-resolution seismic data acquired by the Guangzhou Marine Geological Survey (GMGS) in the Shenhu area of northern South China Sea, supported by the cores collected by the first Chinese drilling expedition of marine hydrate in 2007 (GMGS01), in particular the seismic reflection attributes and grain size data, the fine-grained turbidites deposited in the inter-canyons area were identified and described. There are two depositional units occurred above the bottom simulating reflectors (BSR) In the study area. The first one (Unit 1) at the bottom, is characterized by thin-bedded lenticular chaotic seismic reflections in seismic profiles and the samples of the hydrate layer with a grain size distribution pattern approximately parallel to the C M line on the C-M diagram. It is interpreted as fine-grained turbidites. Eight seismic profiles from north to south crossing the submarine canyons No. 16 in the study area are used to reveal the spatial variations of the interval above the stratigraphy boundary T1. In terms of depositional processes, these fine-grained turbidites are interpreted as re-worked sediments from the small-scale channels in the north of the Shenhu area. The northern boundary of small-scale channels could be traced through the 2-D seismic data covering the study area. The distribution of fine-grained turbidites are parallel to the northern boundary of small-scale channels. Understanding the spatial distribution of fine-grained turbidites located at the canyons ridges would not only be used to explain the heterogeneous distribution of gas hydrate in GMGS01, but also provide some new insights for revealing the forming mechanism of hydrate-bearing deposits in the Shenhu area of the northern South China Sea.