HYDRAULIC SORTING OF HEAVY-MINERAL GRAINS BY SWASH ON A MEDIUM-SAND BEACH

ABSTRACT: Hydraulic sorting of detrital mineral grains in the swash zone was investigated using data on sedimentology and flow dynamics obtained from Fishermans Beach, on the east coast of Australia. The beach is characteristically reflective, displaying a steep beach face com-posed of medium sand and virtually no surf zone. Samples were taken from two beds enriched in heavy minerals, and from the adjacent beds above and below. The mineralogy of the samples was determined, and measurements of grain size and settling velocity were obtained. The heavy-mineral grains had both a smaller intermediate diameter and a smaller settling velocity than the light-mineral grains; the difference between the two mineral types was typically in the range 0.25–0.50 f and 2.0–2.5 cm s21, respectively. On the basis of these sedimentological measurements alone, any one of three mineral sorting mechanisms could provide a feasible explanation for the development of the heavy-mineral-enriched beds: suspension sorting, entrainment sorting, o