Late Pleistocene to Recent sediment transport pathways of the Green Canyon OCS area, northern Gulf of Mexico

Abstract

This study addresses some of the complexities of sediment transport systems on the continental slope of the Green Canyon OCS area south of the Louisiana coast. Five Late Pleistocene to Recent sedimentary sequences are identified using a combination of seismic and well data. Sediments are transported through pathways characterized by erosional surfaces and numerous channels which form as sediments remobilize and become transported downslope. Pathway margins are constricted by physiographic highs. Several processes are identified as means of carrying fine-grained sediments to and across the continental slope. The most important of these are mass movements (slumps and slides), debris flows, and turbidity currents. Faulting and/or slumping at the shelf edge remobilizes sediments which are then carried further downslope. These remobilized sediments may be transported as debris flows or other undifferentiated high-density flows, or may develop into turbidity currents which deposit graded sediments in response to decreases in slope gradient. Slumps and slides off salt uplifts also deposit large volumes of sediments into adjacent intraslope basins and sediment transport pathways, where they may contribute significant amounts of material to the downslope transport of sediments. Discrete channels are not often observed in the pathways due to multiple episodes of channel formation and erosion which occurred during a single sea level lowstand. These multiple episodes tend to remove or obscure prominent channel features. Sedimentation is cyclic. During one sea level lowstand a sequence is deposited in and along narrow pathways which successively fill intraslope basins from the shelf edge downslope. As each basin is filled, sediments spill over and continue downslope to a lower basin. Sedimentation during the next sea level lowstand occurs in broader pathways. Less sediments are deposited in the intraslope basin areas because they remain filled from the previous sequence. By the time of deposition of the next sequence, movement of underlying salt sheets has changed the shape of the pathway. The sedimentation pattern repeats as lower depressions fill and sediments spill over. Pathways transport slope sediments in the Green canyon area. Discrete channels are not often observed in the pathways. This is a result of two mechanisms: 1) multiple episodes of erosion during a sea level lowstand tend to remove or obscure prominent channel features, and 2) most sediments deposited within the pathways are mass transport deposits which do not often become channelized. The pathways are characterized by erosional surfaces and numerous conduits which form as sediments remobilize and become transported downslope. They are laterally relatively persistent, being constricted by structural highs,