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Giant comet marks

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Abstract

Large longitudinal bedforms (comet marks) occur on the current-swept shelf off southeast Africa. They emanate from tight clusters of low rock outcrops and are as long as 135 m and as wide as 30 m. The low length/width ratio (1:4.5) is explained by lateral coalescence of several narrow tails associated with individual obstacles. They seem to form by removal of sediment from the wake region of the obstacles. Hydrodynamic considerations indicate a high probability for sonic suspension transport, yet no sand shadows occur in the velocity-defect region of the inner wake. It is concluded that shear velocities must exceed the minimal velocity required to sustain sediment transport.

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Author notes

  1. Burg Flemming

    Present address: Senckenberg Institut, Schleusenstr. 39a, D-2940, Wilhelmshaven, West Germany

Authors and Affiliations

  1. National Research Institute for Oceanology (CSIR), P.O. Box 320, 7600, Stellenbosch, South Africa

    Burg Flemming

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  1. Burg Flemming
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Flemming, B. Giant comet marks. Geo-Marine Letters 4, 113–115 (1984). https://doi.org/10.1007/BF02277081

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  • DOI: https://doi.org/10.1007/BF02277081

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