Atlantic continental shelf and slope of the United States - Color of marine sediments

Abstract

A systematic examination of the regional color distribution of the upper sediment layer on the Atlantic continental margin between Nova Scotia and southern Florida reveals that brown, dark green, and yellow predominate on the shelf north of Cape Hatteras, whereas olive, gray, and yellow predominate to the south. Color is affected by composition. texture, physiography, and geological events in the recent past. Many of the color patterns on the shelf are more closely related to Pleistocene and Holocene sedimentary events than to modern dispersal processes. Relict color patterns occur in areas such as Georges and Browns Banks, which were exposed during lower stands of sea level. Linear but discontinuous belts of yellow sediment on the outer shelf and along the shelf break south of Cape Hatteras are probably also related to strandline features formed during the Pleistocene low stands of sea level and during the transgressive advance of the Holocene sea. Color patterns on the continental slope and rise and on the Blake Plateau, unlike those on the shelf, are arranged in linear belts that trend parallel or subparallel to the shelf break. Major trends vary di redly with depth, ranging from olive and green at the top of the slope, through light gray and pale yellowish brown, to brown and yellow at. the top of the continental rise. These trends are probably related to the oxidation-reduction Potential of the environment, which results from a balance between the rate of deposition and the rate of bacterial decomposition of organic matter deposited with the sediment. Isolated areas of color on the slope and rise seem to be due to the slumping of sediment masses downslope and to the exposure of pre-Holocene outcrops. Red Pleistocene till masses, which were once exposed on the Scotian Shelf during the glacial epoch, may have been reworked during the Holocene rise in sea level. This may explain why 'brown and reddish-brown sediments are found at progressively shallower depths northeastward on the rise and slope off the Gulf of Maine and Nova Scotia.