Geotechnical properties of surficial sediments in a mega-corridor: U.S. Atlantic continental slope, rise, and deep-sea basin

Abstract

Marine geotechnical studies at The National Oceanic and Atmospheric Administration's (NOAA) Atlantic Oceanographic and Meteorological Laboratories (AOML) for the past fourteen years have resulted in a considerable amount of sediment mass physical properties data, which have provided the basis for a comparative analysis of the surficial sediments of the U.S. Atlantic continental margin and deep-sea basin in a mega-corridor. A synthesis of available mass physical properties data for the Atlantic and Pacific basins was made by Keller and Bennett (1968, 1970). An extensive coring program initiated in 1974 by NOAA along the U.S. Atlantic outer continental margin (outer shelf, slope, and upper rise) between Hydrographer and Hatteras Canyons has provided data for an initial synthesis of the sediment geotechnical properties of the continental slope (Keller et al., 1979). Recent completion of laboratory analyses of the continental rise sediment cores (Lambert et al., in press) offer an opportunity to compare these suites of data. Although the data for the Atlantic deep-sea basin cover a considerably more extensive area than the data for the Atlantic continental margin, there is now adequate geotechnical properties information to show a sharp contrast between predominantly pelagic and hemipelagic deep-sea sediments and continental margin deposits which are primarily terrigenous in origin. In concert with the fining of sediments seaward off the continental margin (Bennett et al., 1977a; Keller et al., 1979), the mean water contents are higher on the rise (95%) than on the slope (88%) and deep basin (86%). In general, average water contents are significantly higher than the liquid limits for surficial slope, rise and basin sediments. Undrained shear strengths average 5–8 kPa for slope, rise and North Atlantic basin deposits, with values for the slope and rise sediments generally higher than the Atlantic basin deposits. Basin deposits have the greatest range in shear strength, as would be expected for such an extensive and sedimentologically diverse area. Sediments associated with the outer Hudson Canyon display the lowest average water content (73%), highest wet unit weight (1.60 Mg/m 3, wet bulk density) and grain specific gravity (2.76, average grain density) as compared with continental slope, rise and deep-sea Atlantic basin deposits.