Rates of Modern Sedimentary Processes in Lydonia Canyon off Southern New England

Michael H. Bothner, Carol M. Parmenter, Richard R. Rendigs, Meyer Rubin

A 2-year study of Lydonia Canyon and the adjacent shelf and slope provided new evidence that the canyon is actively accumulating material derived from the continental shelf. ¹⁴C dates of cores collected in the head of the canyon indicate that silty sand originating from Georges Bank has been accumulating at a uniform rate of about 60 cm/1,000 years (2 g/m²/day) for the past 7,000 years. Modern transport of material from the shelf to the canyon is also inferred from an increase in barium concentration of resuspended sediment from the canyon axis. The increase is coincident with the period when barium-rich drilling muds were discharged during exploratory drilling on Georges Bank.

Material entering Lydonia Canyon is resuspended many times before it is permanently deposited. The flux of resuspended sediment collected in sediment traps 5 m above bottom in the canyon axis (300-m water depth) averaged 80 g/m²/day--a rate approximately 5 times higher than on the continental slope.

Compared with areas outside the canyon, the more intense resuspension of sediments in the canyon axis can cause greater scavenging of sediment-reactive contaminants from the water column. This hypothesis is supported by inventories of ²¹⁰Pb and ^239,240Pu measured in bottom sediments, which are about 2.5 times higher in the canyon axis than on the continental slope. Discharges of hazardous wastes on the outer continental shelf may cause greater stress to benthic organisms in canyons than to those on the continental shelf or slope.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.