Abstract
The Pearl River Canyon system is a typical canyon system on the northern continental slope of the South China Sea, which has significant implications for hydrocarbon exploration. Through swath bathymetry in the canyon area combined with different types of seismic data, we have studied the morphotectonics and controlling factors of the canyon by analyzing its morphology and sedimentary structure, as well as the main features of the continental slope around the canyon. Results show that the Pearl River Canyon can be separated into three segments with different orientations. The upper reach is NW-oriented with a shallowly incised course, whereas the middle and lower reaches, that are located mainly in the Baiyun Sag, have a broad U-shape and have experienced consistent deposition. Seventeen deeply-cut canyons have developed in the slope north of the Baiyun Sag, playing an important role in the sedimentary processes of the middle and lower reaches of the Pearl River Canyon. These canyons display both asymmetrical V- and U-shapes along their lengths. Numerous buried channels can be identified below the modern canyons with unidirectionally migrating stacking patterns, suggesting that the canyons have experienced a cyclic evolution with several cut and fill phases of varying magnitude. These long established canyons, rather than the upper reach of the Pearl River Canyon, are the main conduits for the transport of terrigenous materials to the lower slope and abyssal basin during lowstand stage, and have contributed to the formation of vertically stacked deep-water fans in the middle reach. Canyon morphology is interpreted as a result of erosive sediment flows. The Pearl River Canyon and the 17 canyons in the slope area north of the Baiyun Sag probably have developed since the Miocene. Cenozoic tectonics, sea level change and sediment supply jointly control the morphology and sedimentary structure. The middle and lower reaches of the Pearl River Canyon developed on the paleo-terrain of the Baiyun Sag, which has been a persistently rapid depositional environment, receiving most of the materials transported via the canyons.
Highlights
Submarine canyons are common features incised into the continental shelves and slopes of all continental margins worldwide (Farre et al 1983; Hagen et al 1996; Klaus and Taylor 1991; Puig et al 2003; Deptuck et al 2003; Harris and Whiteway 2011)
The Pearl River Canyon system is the largest shelfindenting one on the northern continental margin of the South China Sea, including the Pearl River Canyon which displays three distinct trends, and seventeen sub-linear NNW–SSE oriented canyons developed in the slope area north of the Baiyun Sag
These deeply cut canyons are V-shaped at the canyon heads and widen to U shapes downstream. They are asymmetrical with steep walls on their eastern flanks and stepped and curved walls on the western sides caused by slumps and slides. This evidence suggests that these canyons currently are the main conduits for terrigenous sediment transport from the continental shelf to the lower slope and abyssal basin, rather than the upper reach of the Pearl River Canyon
Summary
Submarine canyons are common features incised into the continental shelves and slopes of all continental margins worldwide (Farre et al 1983; Hagen et al 1996; Klaus and Taylor 1991; Puig et al 2003; Deptuck et al 2003; Harris and Whiteway 2011). Compared with the course of the Pearl River Canyon in the east, the canyons in the slope area north of the Baiyun Sag cut much more deeply into the sediments (up to 200 m) with more unique sedimentary structures, which vary significantly as the thalweg gradient changes downdip (Fig. 6).
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