Abstract

The classifications of sediment gravity flows in use by geologists are based on rheology and dominant clast-support mechanism of uniform and steady sediment flow. This paper discusses a classification based on the ultimate flow character of a sediment gravity flow, which is more likely to be reflected in the deposit.

Three constitutive conditions prevail during sedimentation that define the flow character of a sediment gravity flow in its final stage: (I) the flow is either laminar or turbulent; (II) the flow behavior is either plastic (cohesive) or fluidal (cohesionless); (III) its concentration is either low or high. The resulting eight theoretical rheological models are each likely to be characterized by only one type of deposit. A comparison with Lowe's (1979) classification, for example, shows that (low-density) turbidity current and cohesive debris flow correlate quite well (because the steady-flow state is not much different from their ultimate rheological state), but that liquefied flow, fluidized flow, grain flow, and modified grain flow all belong to the same rheological model—namely, laminar, high-concentration, cohesionless sediment flow. An analysis of grain-support mechanisms shows that these four types of gravity flows behave in virtually similar fashion during deposition, and all must be considered as fluidal flows.

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