Continuous Deep-Seated Slope Failure Recycles Sediments and Limits Levee Height in Submarine Channels

Abstract

Channel-levee systems are responsible for constructing deep sea fans, among the largest sedimentary deposits on Earth. Levee height plays a key role in defining the volume and texture of the material that is deposited in the bounding levees and thus the morphology of submarine fans. Models of channel formation and evolution generally assume that levees aggrade in response to the cumulative overspill of turbidity flows, and that their height is controlled by these flows. In contrast, we show that levee growth in the Ursa Basin (Gulf of Mexico) is limited by the mechanical strength of the levee, not the flow behavior. While many studies document sidewall failures in levee systems, our poromechanical model is the first to demonstrate that collapse of levees is a large-scale, deep-seated, process driven by the interaction of levee formation and high fluid pressure. Rapid deposition of a regional sand unit induced large fluid overpressure in the underlying mud, which preconditioned the system for levee failure, which ultimately fed a large volume of sediment back into the channel-levee system. Long-lived levee failures continually reintroduced previously deposited levee material back into the channel system. This implies that a large volume of sediment was continuously recycled, which has not been previously understood. Turbidite flow models generally assume that flows progressively lose their fine-grained component due to levee overspill as they traverse the channel. In contrast, we show a mechanism by which fine-grained material can re-enter the system in large quantities, and this has significant and broad importance for models of channel and fan evolution. We interpret that deep-seated channel margin failures, record paleo-overpressure and significantly alter the fluid flow field in these common deepwater reservoir systems by disconnecting permeable sands. Finally, we also show that that levee failure introduces significant unconformities, in contrast with the common assumption that levees offer complete and high-resolution records of climate, tectonics, and sea-level.

AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014