EP12A-01
Supercritical Submarine Channel Morphodynamics from Integrated Investigation of the Western North American Continental Margin
Monday, 14 December 2015: 10:25
2005 (Moscone West)
Jacob A Covault, Bureau of Economic Geology, The University of Texas at Austin, Austin, TX, United States, Andrea Fildani, Statoil Gulf ASA, Houston, TX, United States, Stephen Michial Hubbard, University of Calgary, Calgary, AB, Canada, John E Hughes Clarke, University of New Brunswick, Fredericton, NB, Canada, Svetlana Kostic, San Diego State University, San Diego, CA, United States, Charles K Paull, Monterey Bay Aquarium Research Institute, Watsonville, CA, United States and Zoltan Sylvester, Chevron Energy Technology Company, Houston, TX, United States
Abstract:
Submarine channels are conduits through which turbidity currents and related mass movements transport sediment into the deep sea, thereby playing important roles in the development of continental margins and biogeochemical cycles. To gain a better understanding of submarine channel morphodynamic evolution we explore a variety of channel systems from the western North American continental margin with varying sinuosity and levee geometry, terraces, channel cut-offs, and sediment waves in incipient channels, along thalwegs of well-developed channels, and on levees. Repeat bathymetric surveys of submarine channels in fjords of British Columbia and the Monterey canyon underscore the transience of fine-scale detail in channelized geomorphology, and multi-phase bed reworking, local deposition, and bypass of turbidity currents. Numerical modeling is combined with interpretations of channel geomorphology and strata in the Monterey and San Mateo canyon-channel systems to demonstrate that some of the sediment waves are likely to be cyclic steps. Submarine cyclic steps are long-wave, upstream-migrating bedforms in which each bedform in the series is bounded by a hydraulic jump in an overriding turbidity current, which is Froude-supercritical over the lee side of the bedform and Froude-subcritical over the stoss side. Submarine turbidity currents are susceptible to supercritical flow because of the reduced gravitational acceleration of dilute suspensions. Higher submarine slopes common to the North American continental margin also promote supercritical flow, which might not be as common across lower slopes of large passive margins such as the Amazon, Indus, and Bengal submarine fans. We posit that cyclic steps are a common morphodynamic expression in many continental margins. Continued integration of high-resolution data, such as repeat geophysical surveys, acoustic doppler current profiler measurements, and turbidite outcrops, which provide insights into the longer-term stratigraphic evolution of submarine channels, and approaches, including empirical experimentation and numerical modeling, are aimed at improved understanding of submarine channel morphodynamics.
