ON EXPERIMENTAL REFLECTED DENSITY CURRENTS AND THE INTERPRETATION OF CERTAIN TURBIDITES

Experimental results are reported concerning the nature of reflected f lows generated when density currents are incident upon ramp-type flow obstructions. The reflected flows are bores (moving hydraulic jumps th at transport mass) with flow characteristics in common with either a g roup of solitary waves (weak Type A bores) or the original density cur rent (strong Type C bores). Alternatively, the bore may have attribute s in common with both of these end-member forms (intermediate Type B b ores). Bore strength is positively correlated with the ratio of revers e flow thickness to that of the residual tail of the forward flow. The largest values of this ratio occur when 'proximal' reflections arrive at the steeper ramps. Measured particle paths in the bores indicate t hat natural examples will have the potential to transport and deposit sediment. Strong bores have velocity characteristics very similar to t he original current and thus in nature the generated sequence of sedim entary structures will resemble those of the original depositing curre nt. The train of solitary waves that make up a weak bore sequence exhi bits a pulsating velocity profile at a point. Such flows may thus gene rate repeated sequences of structures separated by fine 'drapes' that are distinguishable from the deposits of the original turbidity curren t. These conclusions are applied to examples of reflected turbidites d escribed from the Palaeozoic to Quaternary sedimentary record.