A model for the long‐profile shape of submarine canyons

Abstract

[1] 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.

Topography of inland deltas: Observations, modeling, and experiments

“…Concavity in the surface profile along the delta is expected. This has been demonstrated both in fluvially-formed landscapes [e.g., Sinha and Parker, 1996] and in the shape of submarine canyons [e.g., Gerber et al, 2009] under equilibrium steady-state conditions. Concavity in the surface profile is the result of the physically-based formulation of water and sediment fluxes in the model.…”

Geomorphic response of submarine canyons to tectonic activity: Insights from the Cook Strait canyon system, New Zealand

“…Many studies have dealt with quantitative analyses of digital elevation models, 95 particularly focusing on channel morphology, to obtain information on the character, 96 pattern and rates of tectonic deformation, and to develop long-term landscape evolution 97 models (e.g. Howard, 1994 from that of rivers because of the increase or loss of flow power with suspension or 144 deposition of particle load (Gerber et al, 2009). It has also been suggested that drainage 145 basin area in submarine canyons is not related to flow discharge as in terrestrial systems, 146 but results from the aggregation of random walks (Straub et al, 2007).…”

Survival of a submarine canyon during long-term outbuilding of a continental margin

“…In contrast, we think that long-profi le concavity in the modern canyon is a consequence of a shift in the relative importance of turbidity current sedimentation in the canyon. Long-profi le concavity is expected in submarine canyons and channels shaped by sediment transport in sustained, fully developed turbidity currents (Mitchell, 2005;Gerber et al, 2009;Spinewine et al, 2011), and will thus characterize equilibrium long profi les under conditions of sediment bypass or net deposition, the latter balancing subsidence and/or causing basinward progradation.…”

“…3B) similar to all Valencia Trough turbidite system modern canyons along the EM (Amblas et al, 2011). Following the model of Gerber et al (2009), we interpret this change in long-profi le curvature as a change in the relative importance of background sedimentation, construed here as a mix of hemipelagic settling and deposition from weak shelf gravity fl ows that dissipate below wave base (sensu Parker, 2006). The mid-Pleistocene (Pt2) canyon long profi le resembles the interfl uve long profi le, and its convex reach is located near the clinoform infl ection point that defi nes the midPleistocene shelf break.…”

“…Yet none of these models consider canyon evolution in light of well-established ideas for how margin clinoforms prograde. Gerber et al (2009) tackled this problem by proposing a model for the long-profi le (i.e., along-thalweg depth profi le) shape of canyons based on the competition between turbidity currents and background sedimentation from the water column. The key element of their approach is the treatment of canyons on constructional margins as clinoforms which, together with intercanyon open slopes, defi ne the strikeaveraged longprofi le shape of the margin.…”