ABSTRACT

Salt ridges and domes underlie much of the present Louisiana slope. The bathymetric expression of underlying salt could be either a mound or a flattening of the normal rate of descent down the slope. The "mounded" salt features form barriers to the gravity-driven sediments from the shelf-break. Much industrial research has been done in the search for reservoir sands related to such an obstruction. Clues to depositional patterns related to salt features may be obtained from studies done in the deep ocean around seamounts located in pathways of ocean-bottom currents. Parallel-bedded sediments form fore-drifts on the upcurrent side of a seamount. These fore-drift sediments were deposited where the prevailing ocean bottom currents were locally decelerated by the obstructing seamount. In waters overlying the obstruction, a Taylor column of dead water or a slow cyclonic eddy provides tranquil oceanographic conditions permitting a greater fallout of sediments. Moats are found on the sides of the obstruction and are the result of erosion or non-deposition due to acceleration of deflected waters. Lee-drifts are found on the downcurrent side of the obstruction. Current gyres result from deceleration of accelerated currents along the obstruction's flanks, and a complex sedimentation pattern results. Flow over the obstruction's top is determined by size and shape of the obstruction relative to size and velocity on the bottom-following current. A turbulent wave may be set up with sufficient amplitude to influence sedimentation on the downcurrent side. There are appreciable differences in the sedimentation patterns influenced by a dome versus a ridge.

If ocean bottom currents equal gravity-driven terrigenous sediment movement and seamounts equal salt domes and ridges, then the result of deep ocean surveys are directly applicable to sedimentation on slopes with underlying salt basement. The salt-related sedimentation pattern of the present slope should be applicable to similar paleo-environments.