A discussion and classification of subaqueous mass-transport with particular application to grain-flow,slurry-flow,and fluxoturbidites

Sediments will remain at rest on the sea-floor provided forces of shear resistance exceed the downslope shear stress imposed by gravity. The shear resistance of granular water-saturated sediments is discussed within the constraints imposed by the Coulomb model of shear failure, and the phenomena of thixotropy, liquefaction, retrogressive flow sliding and fluidization are discussed as mechanisms for producing the mass-mobilisation of sediment. Processes of laminar mass-flow (= inertia flow) are broadly divided into those involving water as the interstitial fluid (grain-flow) and those having an interstitial fluid of enhanced viscosity (slurry-flow). Recent and experimental examples of inertia-flow are summarised and discussed under the headings grain-fall, grain-flow, slump-creep and fluxoturbidites. It is concluded that grain-flow and slump-creep deposits may be more widespread in the sedimentary record than present reports indicate. It is recommended that the term fluxoturbidite be restricted to its original sense, to describe the deposits of proximal turbidites in which the immediately pre-depositional transport was by inertia-flow. A suggested terminology for subaqueous mass-transport processes and their products is summarised in the form of a flow-chart, terminological distinction being drawn between the processes of mobilisation, transport and deposition of the sediment, and between the various sedimentary beds or facies that result from emplacement by mass-transport.