Modern sedimentary processes in the Wilmington Canyon area, U.S. east coast

Abstract

Sedimentary processes active in the Wilmington Canyon area during the past century are documented from geochronologic, sedimentologic, and radiographic analysis of sediment cores collected using primarily D.S.R.V. Alvin. Site selection for the Alvin dives, and for collection of box and kasten cores, was achieved using Sea MARC and SeaBeam data, allowing accurate sampling of numerous subenvironments from this extensively dissected area of the continental margin. 210Pb sediment accumulation rates from intercanyon areas are highest on the upper slope, 1.7 mm/yr (140 mg/cm 2/yr), and decrease with water depth to about 0.4 mm/yr (36 mg/cm 2/yr) on the upper rise. Within submarine canyons, accumulation rates vary dramatically, from a maximum of > 6 mm/yr (> 500 mg/cm 2/yr) to less than 0.3 mm/yr (22 mg/cm 2/yr). Higher accumulation rates in canyons occur as a result of additional supply of older sediment, probably from bioerosion of the canyon walls. This is supported by observations from D.S.R.V. Alvin, reduced 210Pb activities, and indurated mud clasts observed in several canyon cores. Extremely low accumulation rates in Wilmington and South Wilmington canyons are probably the result of strong episodic boundary currents. Non-steady-state 210Pb profiles and sedimentologic data indicate small-scale mass wasting in South Heyes Canyon and on the lower slope and rise just north of Wilmington Canyon.