Contourite drift types and their distribution in the North and South Atlantic Ocean basins

Abstract

Patterns of sediment accumulation under the control of deep bottom currents depend on interacting factors: intensity of the regional deep circulation, morphology of the sea-floor, Coriolis effects, abundance of terrigenous and biogenic supplies, subsequent turbidity of deep nepheloid layers, and depth of the CCD. Based on many examples of bottom current deposits, from the Atlantic and from other oceans, we recognise three major types of contourite accumulation: (1) giant elongate drifts, (2) contourite sheets, and (3) channel-related drifts. They generally occur in distinct topographic settings and show different geometries, facies and rates of deposition. In the North Atlantic, strong bottom circulation, an open basin system and high sediment supply have led to the construction of large elongate contourite drifts, which have striking relief (200–1000 m) above the surrounding sea-floor and are composed of muddy contourites, rich in calcareous pelagic material. In the South Atlantic, strong bottom-currents are often trapped in gyre-like circulation patterns around topographically closed basins or are accelerated through deep, narrow, connecting passages. The resulting deposits are mainly extensive contourite sheets, covered by fields of large sediment waves, and channel-related drifts, including “contourite fans” constructed at the downstream exit of deep passages.