Modern accumulation rates and a budget of sediment off the Kaoping River, SW Taiwan: a tidal and flood dominated depositional environment around a submarine canyon
Abstract
Ninety-two box cores collected during 2004-2006 from an area of ~3,000 km2 off the Kaoping River, SW Taiwan, were analyzed for fallout radionuclides (210Pb, 137Cs and 7Be) to elucidate sedimentation rates and processes, and for the calculation of a sediment budget. The study area is located at an active collision margin with a narrow shelf and a submarine canyon extending essentially into the river’s mouth. The results indicate fairly constant hemipelagic sedimentation in much of the open margin and for most of the time except in the inner shelf and along the axis of the canyon where sediment transport is more dynamic and is controlled by tidal current and wave activities constantly, and by fluvial floods or gravity-driven flows episodically. Sedimentation rates in the study area derived from 210Pb and constrained by 137Cs vary from 0.04 to 1.5 cm/yr, with the highest rates (>1 cm/yr) flanking the Kaoping canyon over the upper slope (200-600 m) and the lowest rates (< 0.1 cm/yr) in the distal basin beyond the continental slope. The depocenter delineated from 210Pb-based sedimentation rates overlaps with the area covered by a flood layer resulting from super-typhoon Haitang in July 2005. Such correspondence supports the notion that the processes operating on event timescale have bearing on the formation of the sediment strata over centennial or longer timescales.
From the distribution of sedimentation rates, sediment deposited in the study area annually is estimated to be 6.6 MT/yr, accounting for less than 20% of Kaoping River’s sediment load. The calculated budget, coupled with the presence of 7Be and non-steady-state distribution of low levels of 210Pb in sediments along the canyon floor, suggests rapid transport of sediment from Kaoping rivers’s mountainous watershed (the source) via the Kaoping Canyon and adjacent channels (as the conduit and temporary sink) to the abyssal plain and the Manila Trench in the South China Sea (the ultimate sink).