Slope-confined submarine canyons in the Baiyun deep-water area, northern South China Sea: variation in their modern morphology

Abstract

On the basis of newly collected multibeam bathymetric data, chirp profiles and existing seismic data, we presented a detailed morphological interpretation of a series of slope-confined canyons in water depths of 300-2000 m in the Baiyun deep-water area, northern margin of the South China Sea. Although these canyons are commonly characterized by regular spacing and a straightline shape, they vary in their lengths, starting and ending water depths, canyon relief, slope gradients, wall slope gradients and depth profiles along the axis. The eastern canyons (C1-C8) have complex surface features, low values in their slope gradient, canyon relief and wall slope gradient and high values in their length and starting and ending depth contrasting to the western ones (C9-C17). From the bathymetric data and chirp profiles, we interpret two main processes that have controlled the morphology and evolution of the canyons: axial incision and landsliding. The western part of the shelf margin where there were at least four stages of submerged reefs differs from the eastern part of the shelf margin where sedimentary undulations occurred at a water depth of *650 m. We consider that the variation in morphology of submarine canyons in the study area is the result of multiple causes, with the leading cause being the difference in stability of the upper slope which is related to the submerged reefs and sedimentary undulations.

Occurrence of submarine canyons, sediment waves and mass movements along the northern continental slope of the South China Sea

“…Mass transport deposits (MTDs) and slumps are also well developed on the slope area due to canyon margin or head failure. The results of previous research have also indicated that submarine canyons on the northern slope of the South China Sea record different upper slope stabilities, which are related to the presence of submerged reefs and sedimentary undulations (Li et al 2016).…”

“…A series of parallel canyons and gullies, which trend in the NNW-SSE, NNE-SSW, and NE-SW directions and are thus oriented approximately perpendicular to the slope, were discovered along the northern slope of the South China Sea at water depths of 400-1800 m (He et al 2014;Li et al 2015Li et al , 2016Chen et al 2016). These canyons may have been formed by the backstepping of failures at the shelf break, which may be related to minor faulting in the shelf margin followed by subsequent headward erosion.…”

“…Furthermore, erosion-dominated, over-steepened slopes created by insufficient sediment supply are more common in larger canyons and gullies (Chen et al 2016) (table 5). Numerous submarine landslides and a series of downslope-extending canyons are also welldeveloped in the middle northern continental slope of the PRMB area, where slope gradients are approximately 10 • -15 • (He et al 2014;Li et al 2016) (table 5). These canyons are characterized by their linearity and regular spacing (Li et al 2016).…”

“…Numerous submarine landslides and a series of downslope-extending canyons are also welldeveloped in the middle northern continental slope of the PRMB area, where slope gradients are approximately 10 • -15 • (He et al 2014;Li et al 2016) (table 5). These canyons are characterized by their linearity and regular spacing (Li et al 2016). Bathymetric and chirp data further reveal that axial incisions and landslides represent the main geological processes controlling the morphology and evolution of these canyons.…”

“…Submarine landslides on passive continental margins are predominantly distributed along slopes and are often associated with sediment waves, submarine canyons, or channel systems (e.g., Greene et al 2002;Chaytor et al 2009;Puga-Bernabeu et al 2011;Li et al 2015;Chen et al 2016;Li et al 2016). Although much research has been performed in this field (Lüdmann et al 2005;Gong et al 2012;Chen et al 2014), most studies have used multi-channel seismic data and well data from the continental shelf and slope areas, thereby omitting detailed information about the seafloor geomorphology and shallow seismic sequences of canyons and mass movements along the northern slope of the South China Sea.…”