Thin-bedded plumites: an overlooked deep-water deposit

Abstract

Field observations suggest that hypopycnal plumes can generate thin-bedded sand/mud couplets, here termed plumites, that are virtually ubiquitous in turbidite systems. This close association is the best and most direct evidence of the relationship between turbidite and fluvial sedimentation. Plumes propagate in seawater as dilute surface flows and, depending upon their original volume, sediment concentration and basin size, may mantle the basin floor with their fine-grained deposits from shelfal to deep basin plain regions. They may trigger major hyperpycnal flows and deposit thick sand beds in basinal regions, but most commonly form thin beds displaying a spectrum of highly diagnostic facies. Much care must be taken not to mistake these facies for the distal or overbank sediments of turbidity currents. Most of the fine details of plumites are certainly better observed in cores; most cores should be therefore re-analyzed in the light of these new data.