A model for the long-profile shape of submarine canyons

Submarine canyons are shaped by turbidity currents flowing down the continental slope. But canyon morphology also depends on the patterns of sediment deposition that drive long-term outbuilding of continental margins. Relating the importance of each to the shape of canyon long profiles provides a tool for inferring process from observed (modern and buried) canyon morphologies. Here we present a morphodynamic model that predicts the equilibrium long-profile curvature of a canyon affected by turbidity currents and background sedimentation, with the latter defined by the average sigmoidal shape of many clastic margin clinoforms. The model includes the effects of margin progradation (i.e., seaward advance through time) and the down canyon evolution of turbidity currents. We contrast predictions for equilibrium long-profile shape under three sets of conditions. In the absence of background sedimentation and progradation, the graded canyon long profile is concave and described by a simple power law slope-distance relationship that arises from down canyon increases in discharge due to flow evolution. Similar slope-distance predictions exist for rivers where discharge instead increases from tributary input. Adding background sedimentation can generate graded convex long-profile segments in a manner analogous to rivers experiencing uplift. The curvature of an equilibrium long profile that progrades basinward with constant form depends on the relative importance of turbidity-current deposition and background sedimentation. To illustrate and quantify model predictions in the field, we present examples of canyons from modern continental margins thought to reasonably approximate each of the three cases.