Abstract

Under constant stage, reactivation surfaces can be produced in the cross-stratification of a flume delta with superimposed ripples. When it is washed out over the delta crest, the rate of erosion of a ripple's stoss-side increases. As the reattachment flow, causing this erosion, is controlled by the migration of the next ripple upstream, erosion of the delta crest may continue after the first ripple is washed out. The rounding of the delta crest and its subsequent burial by the next ripple produces an inclined erosion surface similar in form to many described reactivation surfaces. In natural environments, this type of reactivation surface probably forms in superimposed bedforms and small-scale deltas. The marked variation in avalanche rates in superimposed bedforms should also produce pronounced foreset lamination.

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