Textural Evidence for Deposition of Many Western North Atlantic Deep-Sea Sands by Ocean-Bottom Currents Rather than Turbidity Currents

Abstract

In contrast to the turbidity-current hypothesis uniformly proposed in the literature, the structural and textural properties of the sands and silts in the western North Atlantic suggest that ocean-bottom currents may also be of primary volumetric importance in the transportation of sand and silt from the continental shelf through the submarine canyons and down to the deep-sea floor. The sinusoidal trends present on scatter diagrams between mean size and size sorting, and between mean size and skewness, are similar to the trends known for sediments deposited in continental, littoral, and shallow marine environments. There are evidently no unique trends (or the absence of any trends) that could be considered typical of deep-sea sands and slits deposited from turbidity currents. Furthermore, the deep-sea sand and silt layers are commonly current-laminated throughout their thickness. The deep-sea sands and silts consistently contain less than 5 per cent clay (\<0.004 mm.), and none exceeds 12 per cent. The well-documented lack of clay in the sands that were deposited in Pleistocene time on the continental shelf during lowered sea levels suggests that the characteristic deficiency of clay in the deep-sea sands is largely inherited from the source sands, rather than the result of removal of substantial amounts of clay during deposition.