Silver Abyssal Plain Carbonate Turbidite: Flow Characteristics

Abstract

Approximately 20000 years ago, the main part of a large turbidity current was channeled between the Caicos Outer Ridge and the Bahama Escarpment until it spread fanwise across the central Silver Abyssal Plain floor. Unusual grain size and compositional changes in the turbidite appear to have been produced by surges superimposed on the main flow. Sharp decreases in the thickness and grain size of the turbidite on the slopes of the Caicos Outer Ridge indicate that the depth of the current was approximately 35 m as deposition began at the first abyssal plain core site. Estimates based on the fall velocity of the fastest settling particles deposited from suspension suggest that the flow velocity was approximately 3 m/sec as the current began to move across the abyssal plain floor. The transition from deposition of turbidite sediments with graded bedding to deposition of parallel-laminated sediments appears to have occurred at similar or slightly lower flow velocities than those predicted for the transition from antidunes to upper flat bed conditions in rivers and estuaries.