Another common practice is to compa

Another common practice is to compare depositsof subaqueous turbidity currents with those of subaerial river currents on the ground that both currentsare turbulent, and therefore their deposits must bequite similar. This is not true. River currents andturbidity currents are not one and the same, althoughboth are turbulent. River currents are low in suspended sediment (l-5%), whereas turbidity currentsare relatively high in suspended sediment (l-23%,see Shanmugam, 1996a), although both currents areconsidered to be Newtonian in rheology. River currents are ,fluid-gravity flows, whereas turbidity currents are .yediment-gravity flows (Middleton, 1993).In river currents, sand and gravel fractions are transported primarily by bed load (traction) mechanism,and therefore river deposits are characterized bydune bedforms (cross-bedding). In contrast, sands inturbidity currents are transported by suspended load,and thus sandy turbidites show a general lack ofcross-bedding.