Sedimentary System Of Deepwater Channel, The Slope Area Of Northern South China Sea

The oil industry is interested in the deepwater slope area of passive margin because of its contained large scale of oil & gas and gas hydrate resources.Submarine canyons and deepwater submarine channels act as the primary conduits for sediment transported by gravity (turbidity) currents into the deep slope and basin area, and also can be the repositories for coarse-grained sediment, which is the important study content of"Source to sink". Canyon and channel can be good reservoir of hydrocarbon have been proved by the well drilling on passive continental margin basins. So study of deepwater slope channel (canyon) has scientific and actual siginificance.Based on the 2D, 3D seismic data (acquired from 1979 to 2007) and well data, used 3D geophysical interpretation technologies (such as coherence time slice, RMS and 3D visualization) and sequence stratigrapy analysis, analysed the slope sequence and study the development of channel on the slope area of northern South China Sea. The south part of Qiongdongnan slope area has different provenance supply model compared to the north area. The provenance supply in rifting period was mainly from the southern Xisha Uplift and the SW mid-south peninsula and northern South China Block; whereas the provenance supply in post-rifting period was mainly from the mid-south peninsula.Trough the study of large scale of 2D seismic data, this dissertation discussed the extent and formation mechanism of the Qiongdongnan deep sea channel wholly first time. The Qiongdongnan deep sea channel is a large incised channel which extends from the east boundary of the Yinggehai Basin,through the whole Qiongdongnan and the Xisha trough, and terminates in the western part of the Northwest Subbasin of South China Sea. It is more than 570 km long, 4～8 km wide and developed in Pliocene strata. The channel formed as a complex result of global sea level drop during early Pliocene, large scale of sediment supply of the Yinggehai Basin, and the inversion event of the Red River strike-slip fault at 5.0 Ma induced slumps.Based on 3D seismic data and coherence time slice, RMS and 3D visualization, a series of deepwater channels were recognized on the slope that probably developed in the late Quaternary period. These channels trend SW-NE to W-E and show bifurcations, levees, meander loops and avulsions. Most of the detected channels are characterized by low-amplitude reflections and is likely to be dominated by mudstones with interbedded thin sandstones. These channels are formed by turbidity currents originated from the SW direction and were probably accompanied by a relative sea level drop, which related with the feed to west South China Sea by little scale of mountain river of the mid-south peninsula induced by earthquakes at that period.