Abstract
<p>Sediments were investigated for the United States east coast continental margin between Wilmington and Lindenkohl Canyons. Sediment sampling was carried out in a series of closely spaced shelfbreak normal transects from the outer-shelf to the upper rise consisting of grab samples and box, hydroplastic, and piston cores.Detailed grain-size data was analyzed by Q-mode factor analysis and component analysis. Grain shape signatures were derived by Fourier shape analysis. Conclusions arrived at by factor analysis were independently confirmed by the other two methods.Q-mode factor analysis of the 179 sieved sands identified three significant end-member size distributions. For the surface sediment end-member I dominates the slope below 400 m south of and 200 m north of Spencer Canyon. The shelf, shelfbreak, and upper-slope to the foregoing respective depths are dominated by end-member II and III sands. These boundaries are breached on the slope in at least two places. The breaches appear to be pulses of shelf sand which extend down the slope to at least 500 m, producing soft-sediment deformation at the contact between the sands and the underlying muds.The most dramatic soft-sediment deformation structures were recovered in a box core taken at 400 m depth north of Wilmington Canyon. A thick sandy surface layer extended downward as load casts interdigitating with the underlying muds to > 30 cm. Below this, isolated sand pillows up to 10 cm in diameter extend into the matrix mud to > 50 cm. Ratios of end-member I and II sand in the pillows were significantly different from the sand above. Trends in the end-member ratios in the surficial and load-cast sands suggest that dynamic emplacement of the shelf sand produced these structures. Owing to the size and isolation of the sand pillows in three dimensions, and lack of primary structures in the mud, a bioturbation origin was ruled out.The slope core sediments in both canyon and intercanyon areas are primarily bioturbated, olive-gray, sandy silts with local features indicative of gravity-induced mass sediment movements (i.e., graded sequences and load structures). . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI</p>