Sand-wave immobility and the internal master bedding of sand-wave deposits

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Abstract
Summary: Sand waves are such comparatively immobile transverse bedforms because they occur in tide-induced oscillatory bottom boundary layers typified by a steady velocity-component that generally is small compared to the amplitude of the periodic part. Consequently, the net bed-material transport rates, responsible for the long-term translation of the sand waves, typically are very small compared with the larger of the instantaneous rates. Sand waves should, therefore, be marked internally by series of erosional or, under restricted circumstances, non-depositional master bedding surfaces, each such surface, together with an associated comparatively thin sediment increment, being attributable to one sand-driving tide. Studies of modern sand waves, and investigations in the stratigraphic record, lend support to this conclusion. A further consequence of the regime of intense reworking under which sand waves exist is that their component grains should be in all ways more mature, other things being equal, than particles transported the same net distance by rivers.