Sedimentary Process, Distribution And Mechanism Of Mass Transport Deposits, The Slope Area Of Northern South China Sea

Mass transport deposits are one kind of sedimentary system driven by gravity flow indeep-water settings, which play an important role in the research of "source to sink"of continental margins. Mass transport deposits may not only cause geologic hazards,but also have close relationships with the formation and accumulation of marine gashydrates and hydrocarbon. Owing to the important academic value and very goodengineering practical value, mass transport deposits become a hot topic in marinegeology and oil industry. Therefore, this paper studied the caused reason and theprocesses of the oil company BP exploded and sank in Gulf of Mexico. Current paceof ocean oil and gas resources exploration and production construction is acceleratedincreasingly, this study focused on mass transport deposits has scientific and actualsignificance in the northern of the South China Sea.Based on the2D and3D high resolution seismic data in nearly two decades, thedistribution area, architectures and development processing of quaternary masstransport deposits on the slope area of northern South China Sea are confirmed bycombining with interpretation of multi-beam imaging and sequence stratigraphyanalysis. The relationships between gas hydrate dissociation and mass transportdeposits are emphatically discussed.The distribution area of mass transport deposits in the study area is first systematicallydetermined through interpretation of seismic sections in this paper. Mass transportdeposits are primarily concentrated in four regions: a. North Slope of theQiongdongnan basin; b. Huaguang sag of the Qiongdongnan basin; c. Baiyun sag of the Pearl River Mouth Basin; and d. North Slope of the Taixinan Basin.Through the study of high resolution bathymetric data and seismic data, identificationof mass transport deposits from seismic profiles are weak amplitude, semitransparentand chaotic reflection. In the boundary contact region, it can identify normal faultsand extension faults with strong amplitude and continuous reflection; in thetranslation domain area, the seismic facies are weakly continuous reflection; in the toedomain area which is controlled by compressional action, and where most of foldsand synsedimentary thrust structures are developed.In order to further the correlationship clearly between mass transport deposits and thedissociation of gas hydrate, on the basis of2D seismic profile in gas hydrate samplingarea, we established geomechanical mode and estimated the stability of submarineslope through ultimate equilibrium method. Six different gas hydrate dissolutionmodels are chosen to calculate the safety factors. We found that the stability ofsubmarine slope decreases with the increasing dissolution of gas hydrate, whiledissociation reached critical value the slope will fail totally. Consequently, we regardthe dissociation of gas hydrate as an inductive effect of mass transport depositsdevelopment. Meanwhile，we did some sensitivity analysis about water depth, slopeangle and thickness of gas hydrate for the development of MTDs. The results showedthat the increasing of water depth could restrain the development of MTDs，but theincreasing of slope angle and gas hydrate thickness are significant inducing factor ofMTDs.