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The Bouma Division A and the Possible Duration of Turbidity Currents

ABSTRACT Experimental data (Arnott and Hand 1989) combined with theoretical arguments suggest that the transition in a turbidite from division A to division B occurs at a deposition rate of unsupported grains of about 6.7 10-4 m s-1 in the case of fine-medium quartz sand. A second rate may be calculated from properties measured at the transition from division B to division C (Allen 1971b). These rates together permit an estimate to be made of the order of magnitude of the duration of deposition from a turbidity current. The calculated order of a few tens of minutes for a Mio-Pliocene turbidite described and interpreted hydraulically by Komar (1985) is in broad agreement with his independent estimate based on the sequenc of sedimentary structures.