Three Dimensional Geometries of Bank-attached Bar-forms in Sinuous Submarine Channels

Sinuous submarine channels often show bank-attached bar-forms, which are interpreted as the preserved deposits associated with lateral or downstream migration of channel bends. Processes responsible for the formation of these deposits are uncertain. We have used geometric properties of imaged bars and the geometry of associated channel bends to analyze possible flow and sediment-transport fields associated with preserved channel-bend forms and kinematics. We present a detailed geometric analysis of accretion surfaces mapped in the deposits of 12 channel bends from two buried sinuous channels that are imaged by high resolution seismic data. Channel 1 has an average depth of 50m, average width of 550m and sinuosity of 1.95. Channel bends have maximum curvatures of 0.08-0.25 degree/m and are separated by straight channel segments with lengths 1.5-3 times average channel width. Channel 2 has an average depth of 35m, an average width of 270m and a sinuosity of 2.36. These bends show curvature maxima of 0.12-0.26 degree/m and are connected by straight channel segments that are 2-6 times average channel width in length. Packages of inclined strata defining bar growth are 0.5-1.5 times the associated channel width, indicating limited channel migration. This limited channel motion is consistent with systematic spatial changes in the heights of accretion surfaces that indicate bar and bend growth occurred during phases of weak but overall channel incision. The identification of concave benches positioned immediately downstream from the strongly accreting bars suggests that sedimentation in low velocity zones associated with separated flow occurred in these channels. The geometries and temporal evolutions of all studied bar forms will be synthesized in order to estimate the patterns and processes of sediment transport associated with evolution of these two sinuous submarine channels.