Experiments on Ripple Lamination

Abstract Laboratory experiments have demonstrated that an essential factor in forming appreciable deposits of ripple–laminated sand is the introduction of an abundance of sediment into an area of ripple movement. A sequence of ripple laminae developed under such conditions changes both laterally and vertically as the result of changing stream regime during the time of deposition. Ripple laminae formed from stream currents show few or no important differences from those developed by waves with a forward component, but both types show many variations in size and shape of ripple profiles, caused by differences in water depth, wave or current strength, and other factors. Both stream currents and waves may develop either symmetrical or asymmetrical ripple marks. Recognition of ripple lamination in ancient rocks is believed important as an aid in interpreting the environment of deposition. Ripple lamination is especially characteristic of areas, like river flood plains, where a great abundance of sand is introduced and deposited quickly. It is not necessarily developed wherever ripple marks are being formed, however, for in many such places the necessary excess of sand may be lacking and a constant reworking of sand results. At many places ripple lamination in ancient rocks is not readily apparent because sections cut at angles not parallel to current or wave direction may not have distinctive structure patterns; also, many sandstones that appear massive have been shown by selective etching or by X–ray studies to contain ripple lamination structure.