Architecture and controlling factors of canyon fills on the shelf margin in the Qiongdongnan Basin, northern South China Sea

Most submarine canyons are documented as erosive features that cut deeply into the shelf margin, and are considered as important conduits for the transfer of sediment to the lower slope or abyssal plain. However, in this study we investigate a series of Late Miocene submarine canyons developed on the shelf margin in the Qiongdongnan Basin, northern South China Sea, which exhibit different morphological features and are characterized by unidirectional migration. High resolution3D seismic and borehole data have been used to investigate the morphology, lithology and stacking pattern of these submarine canyons. Seven submarine canyons have been distinguished, with a length of 10-30 km, a width of 500-5000 m and a maximum of 300 m of relief. They are generally oriented NW-SE, approximately perpendicular to the slope, but some of them show abrupt deflection in places. These submarine canyons also display both U-shape and V-shape morphology along their length. The each canyon fill is dominated by four kinds of architectural elements: erosion surface (ES), basal lag (BL), mass transport deposits (MTDs) and lateral accretion packages (LAPs). Unidirectional migration of up to 10 km is the most important characteristic of these submarine canyons. It is greatest at the head of the canyons and decreases along their length towards the shelf margin. The changes in migration distance are shown by variation in stacking patterns in different sections along the canyon length. The unidirectional migration of these canyons is attributed to the activity of the South China Sea Warm Current on the outer shelf. The evolutionary history of a single canyon form can be divided into three stages: erosion-dominated stage, erosion-deposition stage and deposition-dominated stage. The interplay of the along-canyon turbidity currents and bottom currents results in the lateral stacking pattern change of these submarine canyons. This discovery has important implications for understanding the mechanism and evolution of the South China Sea Warm Current.