Abstract

Curve fitting of the first-order morphology of recent slope profiles shows that with only three basic types of equations, a linear, an exponential, and a Gaussian distribution function, over 80% of a random collection of 150 seismic profiles, covering most of the world's continental margins, can be quantified. Profiles from carbonate as well as siliciclastic margins, and from mud- to sand-dominated profiles, are present in each group. A small group of submarine slopes have a linear profile, and are interpreted to rest at the angle of repose. Oversteepening of this critical angle by sedimentation disturbs the entire planar surface, starting mass movements of variable style, number, and size. The exponential trend is attributed to the exponential decay of transport capacity or competence with increasing distance from the sediment source at the shelf break. The fact that the majority of slopes follow a Gaussian curve rather than an exponential one may be due to the disturbing effect of extrinsic processes. We propose as a working hypothesis that they represent regular exponential profiles whose upper parts have been disturbed by the interplay of wave-dominated transport with gravity-driven transport at the shelfbreak during base-level fluctuations. Gaussian profiles are also observed when sediment is eroded and redistributed at the shelfbreak by ocean currents during clinoform progradation. The geometry of slopes gives information on the depositional environment, whereas the shape parameters of the three governing equations offer some promising clues to deducing sediment composition. Mud-dominated slopes have a lower slope angle, curvature of exponential profiles, and peakedness of Gaussian curves than sand-dominated slopes.

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