Controls from Sinuosity Evolution Within Submarine Channels

Ian Kane, Bill McCaffrey, and Jeff Peakall
Institute of Geological Sciences, University of Leeds, Leeds, United Kingdom

Meandering fluvial channels are often characterized by meander loop cut-offs and frequent avulsion histories; conversely, submarine channels commonly lack these features and may exhibit long-lived and relatively stable planform geometries. Inner-bend deposition and outer-bend erosion within fluvial systems leads to the development of sinuosity. Within sinuous submarine channels, inner-bend deposits have been recognized from subsurface and seafloor images, from outcropping ancient channels, and have been demonstrated within physical models; a feature thought to be unique to subaqueous channels is the deposition of outer-bend sediment accumulations (so called ‘nested-mounds’). We report physical experiments on channelized, subaqueous, particle-driven turbidity currents which demonstrate that channel-fill architecture relates directly to the degree of flow bypass, in turn largely determined by the degree of confinement. In general, weakly bypassing flows deposit at the outer-bend whereas strongly bypassing flows deposit at the inner-bend. Therefore flows within aggradational channel-systems whose axes are bypass-dominated may preferentially deposit at the inner-bend, ultimately having the effect of increasing channel sinuosity through time; an evolution pattern commonly observed in subsurface images. Once developed, the apparent spatio-temporal longevity of sinuosity within many systems may be explained by the passage of turbidity currents of varying magnitude (and consequently bypass potential) depositing preferentially at either the inner- or outer-bank of the channel maintaining a quasi-stable morphological equilibrium. Fluvial channels do not have the ability to reduce or maintain their sinuosity in this way, which plausibly explains why they tend to develop cut-offs at higher rates than subaqueous channels.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas