Abstract: Channel-Fill and Spillover Facies of Northwest Atlantic Mid-Ocean Channel of Labrador Sea

S. K. Chough, R. Hesse

A band of terrigenous sediments follows the course of the Northwest Atlantic Mid-Ocean Channel (NAMOC), the world's largest deep-sea channel, and cuts across the pelagic and hemipelagic sediments of the Labrador Sea. The channel is accompanied on both sides by natural levees built up to an average height of 60 m above the adjacent turbidite plains. Levees and plains attest to the origin of the channel as a depositional-erosional feature resulting from sedimentary mass flows such as turbidity currents, grain flows, or debris flows. Some of these flows extend over the entire length of the channel or nearly 3,800 km. They are associated with a meandering channel containing a meandering thalweg and point-bar-like features.

Coarse-grained mass-flow deposits (up to gravel size) are present in the channel down to 4,200-m water depth and up to a distance of 1,600 km from the nearest possible source on the Labrador Shelf. Turbidite sands extend all along the channel down to Sohm Abyssal Plain. The fine sandy to silty spillover sediments on the levees are thinly laminated and show climbing-ripple cross-lamination at the base of individual depositional units. They also are present on the flat turbidite plains that accompany the levees laterally up to a distance of more than 100 km. Channel depth of 100 to 200 m apparently prevents coarser material from spilling over except on the left-hand levee which is consistently lower than the right-hand levee by 30 to 90 m (Coriolis-force effect). Ice-rafted tephra of Ic landic origin is present in a pelagic layer dated as 17,200±600 years B.P. A layer-by-layer matching is possible between two levee cores 70 km apart.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC