FINE-GRAINED TURBIDITES IN GMGS01 OF THE SHENHU AREA, NORTHERN SOUTH CHINA SEA AND ITS SIGNIFICANCE

Based upon the high-resolution seismic data acquired by the Guangzhou Marine Geological Survey and the cores collected by the First Hydrate Drilling Expedition (GMGS01), a kind of fine-grained turbidite is identified in the Shenhu Area of the northern South China Sea. According to the seismic profiles crossing hydrate drilling sites, two seismic units are recognized above the BSR (bottom simulating reflectors): the Unit 1 at the bottom consisting of thin-bedded lenticular chaotic seismic reflectors and the Unit 2 at the top consisting of thick continuous moderate-amplitude seismic reflectors with wavy structures. Grain size analysis illustrates that the deposits are composed of fine-grained silt or silty clay ranging 4-63 μm in grain size. Both the lithological features and grain size parameters are consistent from bottom to top without significant changes. It implies that all the deposits should be the results of a similar depositional process. Moreover, on the C-M diagram, the samples from the hydrate bearing sediments show a distribution pattern parallel to the C=M baseline, indicating an origin of fine-grained turbidites. Regional survey suggests that these fine-grained turbidites might be associated with some small-scale channels in the north of the Shenhu Area. The sediments provided by these small channels move downslopewards and re-deposited in the middle to lower slope as fine-grained turbidites. Based upon the above interpretation, a model is proposed to reveal the relationships between fine-grained tuebidites and hydrates, It says that the heterogeneous distributions of gas hydrates in GMGS01 of the Shenhu Area, northern South China Sea probably owes its origin to the uneven distribution of fine grained turbidites.