Density Cascading: Off-shelf Sediment Transport, Evidence and Implications, Bahama Banks

Abstract

ABSTRACT Suspended-sediment concentrations in shelf waters are often appreciable, but sediments on their own rarely contribute enough to cause suspension currents to transport them offshelf. However, sediment-charged hyperpycnal (high-density) waters are often generated over continental shelves because of the same set of air-sea interactions (intense heat and moisture flux) responsible for thermohaline production and circulation of deep-ocean water masses. We propose the term density to describe the processes by which hyperpycnal waters are released from shelf areas and, together with entrained sediments, sink to their compensation level in the adjacent ocean. Density cascading probably involves a range of physical processes from pelagic draping of slopes and basins with shelf muds to initiating turbidity currents capable of scouring canyons and plunge pools, sediment bypassing of slopes, and deposition of sands in deep basins. Thermodynamic air-sea interactions can generate hyperpycnal water at all latitudes. Therefore, cascading has important implications not only to the sedimentology of modern carbonate platforms such as the Florida Shelf and Bahama Banks and stratigraphy in ancient limestones but also to offshelf sediment flux in siliciclastic environments.