Comprehensive Investigation of Submarine Slide Zones and Mass Movements at the Northern Continental Slope of South China Sea

摘要

Multi-beam bathymetry and seismic sequence surveys in the northern slope of the South China Sea reveal detailed geomorphology and seismic stratigraphy characteristics of canyons,gullies,and mass movements.Modem canyons and gullies are roughly elongated NNW-SSW with U-shaped cross sections at water depths of 400-1000m.Mass movements include slide complexes,slide scars,and debris/turbidity flows.Slide complexes and slide scars are oriented in the NE-SW direction and cover an area of about 1790 and 926 km2,respectively.The debris/turbidity flows developed along the lower slope.A detailed facies analysis suggests that four seismic facies exist,and the late Cenozoic stratigraphy above the acoustic basement can be roughly subdivided into three sequences separated by regional unconformities in the study area.The occurrence of gas hydrates is marked by seismic velocity anomalies,bottom-simulating reflectors,gas chimneys,and pockmarks in the study area.Seismic observations suggest that modern canyons and mass movements formed around the transition between the last glacial period and the current interglacial period.The possible existence and dissociation of gas hydrates and the regional tectonic setting may trigger instability and mass movements on the seafloor.Canyons may be the final result of gas hydrate dissociation.Our study aims to contribute new information that is applicable to engineering construction required for deep-water petroleum exploration and gas hydrate surveys along any marginal sea.