Correlating seafloor gradient with morphology of bedforms from the terminal lobe of a submarine channel in abyssal Gulf of Mexico
Abstract
The characteristics of large-scale bedforms vary systematically downstream on the terminal lobe of a submarine channel at the base of slope near Green Canyon, Gulf of Mexico. This variation in the morphology of bedforms can be correlated with downstream change in the sea-floor slope. 3D seismic bedform measurements and simple numerical modeling suggest distinct changes in transport conditions in response to 1) sea-floor gradient variation, and 2) flow expansion associated with the channel-lobe transition. The bedform field examined extends from the channel-lobe transition to at least 5 Km within the lobe. Here, bedforms heights can be 20-40 m, whereas wavelengths are up to 400 m. Measurements show upstream migrating symmetric bedforms in the most proximal reaches of the terminal lobe and asymmetrical downstream migrating bedforms in the more distal reaches. Numerical estimates of transport conditions suggest that the majority of the bedforms were formed and sustained by supercritical currents. The supercritical conditions are attained at the channel lobe transition by the combined effect of an abrupt increase in slope and flow expansion. Bedforms at the most proximal area of the lobe likely represent long antidunes, whilst bedforms in the more distal and low-gradient regions of the lobe represent dunes. The transition between the two bedform types occurs where lobe gradient shows a marked decrease. Depending on initial flow properties, the change in bedform morphology may, or may not, represent a change from supercritical to subcritical flows.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMOS33C1802S
- Keywords:
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- 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICS;
- 3045 Seafloor morphology;
- geology;
- and geophysics;
- MARINE GEOLOGY AND GEOPHYSICS;
- 4219 Continental shelf and slope processes;
- OCEANOGRAPHY: GENERAL;
- 4558 Sediment transport;
- OCEANOGRAPHY: PHYSICAL