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.