Geomorphologic and infilling characteristics of the slope-confined submarine canyons in the Pearl River Mouth Basin, northern South China Sea

Abstract

Submarine canyons, classified as shelf-incision and slope-confined types, are considered as the most important sediment transportation conduits in the continental margins. Being one of the obvious submarine landforms in the northern continental slope of the Pearl River Mouth Basin (PRMB) in the northern South China Sea, the Shenhu Submarine Canyon Group (SSCG) is composed of 17 NW-SE oriented slope-confined submarine canyons. The SSCG serves as a routing system for delivering large volume of terrestrial sediments, which generate canyon infillings and was deposited further toward the basin. Using the high-resolution bathymetric and seismic data, the geomorphologic features and internal architectures of these slope-confined submarine canyons have been quantitatively analyzed and described in this study. Based on the differentiations in geomorphologies, four canyon segments could be divided from north to south, including upper, middle and lower reaches, and the canyon mouth area. Corresponding to the geomorphological segmentation of these submarine canyons, the variations in the Quaternary infillings were also interpreted clearly downstream, revealing the interaction between gravity flows along the canyon axis and lateral sediment transportation by mass movements. Supported by variation in geomorphologies, infilling characteristics and thickness of the Quaternary sediments from north to south, the sedimentary processes in the different segments of the slope-confined submarine canyons could be documented as erosional-dominant processes in the shelf-edge to the upper slope and depositional-dominant processes in the toe area. The head area of the Pearl River Canyon (PRC) is characterized by the thinner Quaternary strata and shallow-incised small-scale channels. In addition, no considerable change of Quaternary sediment thickness is observed from upper-middle reach of the PRC in other large-scale submarine canyon in the PRMB, indicating lower rate of sediment accumulation and limited sediment redistribute to deep-water basinfloor. Previous study envisaged by Ding et al. (2013) demonstrated the main contribution of the SSCG to deep-sea basins. In this study, we confirm that the SSCG were proposed as the major sediment routing system within the PRMB, which transport abundant terrestrial sediments from the Pearl River Delta via shelf and upper slope in the north to the deep-sea environments in the south.