GRAIN SIZE OF TURBIDITE RIPPLES

SUMMARY Many, but not all, current ripples show log-normal grain-size distribution and good sorting (P. D. Trask). A range in medians was measured from fifty to several hundred microns. Turbidite ripples are log-normal, very well-sorted and are restricted to medians of very fine sand to silt (< 130 μ) because the particles have been supplied in suspension at rippling velocity. Experimental suspension current ripples formed at about 50–60 cm/sec are similar in composition and structure to turbidite ripples. The continuous supply results in climbing ripples. The restricted grain size and the internal structure of turbidite ripples both form strong evidence against the action of normal currents. The number of grain-size analyses is still rather small.