EXPERIMENTS ON THE ORIGIN OF FLASER, LENTICULAR AND SAND-CLAY ALTERNATING BEDDING.

In Dutch sub-tidal waters, mud settling from suspension can produce a layer with a thickness of only some millimetres in one slack-water period. However, consolidated mud layers of 10–25 mm thickness in sub-tidal deposits are often observed. This indicates that mud may be preserved over several slack-water periods. This is only possible if the critical shear velocity (U∗c) for the initiation of sediment movement is not surpassed after slack water. Tube and flume experiments reveal: (1) Thicker mud layers have smaller initial consolidation rates and lower values of U∗c. (2) A higher sand content of the mud always gives a more rapid initial consolidation. The U∗c-values increase to a maximum which is reached at a sand content of 40%. Higher sand contents lead to decreasing values of U∗c. (3) For one particular mud sample the U∗c-values increase linearly with the mud concentration Of the bed material. (4) After three hours of consolidation a mud layer may carry a sharply bounded sand layer 0.5 cm thick. By application of the results of the experiments to natural conditions in tidal water some tentative explanations are possible of the formation of flaser, lenticular and sand-clay alternating bedding. [ABSTRACT FROM AUTHOR]