Abstract

Interference ripple marks form during floods along many ephemeral streams. Cuspate (linguoid) ripples Form first when flood water in the channel is deep enough to flow over marginal and channel sand bars. As the water level falls, downstream currents are refracted shoreward over the marginal sand bars and linear ripple sets are formed on the tops and flanks of the bars. The linear ripples are oriented at right angles to the cuspate ripples and commonly form interference sets with them. Refracted waves and changing water level over the irregular bottom can complicate further the patterns of asymmetric ripple marks and other directional structures. On the basis of study of modern ephemeral streams, we conclude that paleocurrent patterns of fluvial deposits are probably more complex than has been generally recognized. Still, the distribution of directional structures in modern streams is, in general, unimodal and the dominant inclinations of foreset laminae are downstream.

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