The South China Sea(SCS)is the largest marginal sea in West Pacific formed by a combined effect of the Eurasian plate,Pacific plate and India-Australian plate,and is thus considered to be a unique natural laboratory to study oceanic dynamics and tectonic evolutions(Xie et al.,2006;Luan and Zhang,2009).Besides,the SCS contains enormous petroleum resources for its favorable conditions of oil-gas generation,accumulation and preservation.It is therefore imperative to intensively study the marine in-situ The South China Sea (SCS) is the largest marginal sea in West Pacific formed by a combined effect of the Eurasian plate, Pacific plate and India-Australian plate, and therefore therefore considered to be unique ocean laboratory to study oceanic dynamics and tectonic evolutions (Xie et al., 2006; Luan and Zhang, 2009). Besides, the SCS contains enormous petroleum resources for its favorable conditions of oil-gas generation, accumulation and preservation. It is therefore imperative to intensively study the marine in-situ