Crust of the Earth: A Symposium
Sediment Deposition in Deep Atlantic *
Published:January 01, 1955
Investigation of a large number of long sediment cores from the North Atlantic shows that during the Pleistocene epoch uninterrupted particle-by-particle deposition has been confined to very gently sloping areas on more or less isolated rises. Elsewhere the sedimentary sequence is broken either by removal of a part of the section or by intercalation of layers of sediment transported and deposited by turbidity currents. Evidence for turbidity-current deposition of the intercalated layers is of two kinds: the nature of the beds themselves, and their distribution with respect to bottom topography—that is, in the beds of submarine canyons, in deltalike regions at the terminal ends of canyons, and in basins and depressions.
Decrease in turbidity-current activity with amelioration of climate and rise of sea level toward the close of the Wisconsin glacial stage is indicated by decrease in number and thickness of graded layers in the upper parts of most cores. It is inferred that the Pleistocene epoch and the glacial stages in particular were times of exceptionally rapid sediment accumulation. Lithologic characteristics of older sediments cored in various parts of the North Atlantic suggest slow accumulation in clear and relatively quiet water.
Older sediments from the vicinity of the continental slope give evidence of marked steepening of the slope through faulting or monoclinal folding in late Cenozoic time. This is in harmony with the evidence presented by Stetson that the submarine canyons off the northeast coast of North America were eroded during the Pleistocene epoch.