Submarine slopes with an exponential curvature

Abstract

The curvature of submarine slopes is a little used source of information on transport processes and sediment composition. In a survey of modern submarine slopes selected from all over the world, about 15% are characterized by very regular profiles with sharp shelfbreaks and concave-upward curvature. An exponential function describes this morphology very well. These exponential profiles are from three very different depositional settings: a continental margin close to a young mountain belt with very high rates of sedimentation, high-latitude continental margins with evidence of ice cover during Quaternary glacial intervals, and a carbonate platform margin. We propose that the curvature is controlled by the exponential decay of transport capacity with increasing distance from the shelf edge. While exponential decrease of transport may be a general property of most slopes, the development of a regular exponential profile is commonly disturbed by other factors, in particular by the interplay with wave-dominated transport at the upper boundary during sea level fluctuations, and with turbidite-dominated sedimentation at the lower boundary. The good exponential fit of the profiles described here results from the fact that vertical shifts of the shelfbreak are very small compared to the horizontal progradation. The three depositional settings mentioned above prevent the shelf edge from fluctuations in the vertical: high rates of sedimentation and therefore rapid progradation result in minimal movements of the shelfbreak, ice-covered margins are limited by the grounding level of the ice, and margins built by reef organisms are stationary because the hard limestone is relatively resistant to erosion during lowstands of sea level. The numerical value of the exponent is distinctly different for sandy and muddy slopes, indicating the possibility of using the curvature to deduce sediment composition of submarine slopes.