The sequence of sedimentary structures in turbidites, with special reference to dunes

Synopsis The relationship between bed form, grain-size of load, and flow power known from equilibrium-state, open-channel experiments, is revised for turbidity currents, whose power is time-dependent with respect to a point in their path. The revised relationship suggests that cross-bedding, indicative of dune beds, would occur in turbidite sandstones only if the parent turbidity currents had been furnished with sufficiently coarse-grained sediment. Otherwise, the turbidite sandstones are expected to show parallel laminations directly succeeded upward by cross-lamination. The available field evidence is consistent with these conclusions, and some previous difficulties regarding dune structures in turbidites appear now to be resolved.