Megaturbidite, An Acceptable Term?
Arnold H. Bouma
Terminology should facilitate communication, and inaccuracies lead to misunderstanding. New and revived terms often add to the confusion. In the field of deep marine clastic deposition, a continuum of depositional processes and products occurs: sliding, slumping, debris flow, high-density turbidity current, turbidity current, grain flow, fluidized flow, and hemipelagic transport. Additional terms are fluxoturbidite and megaturbidite. No single term will provide a discrete criterion; overlap is common, and more than one process may occur within any given transport event.
Megaturbidite has become a common term in Europe, used to identify a thick, extensive, relatively homogenous deposit from a turbidity current. The range in grain size can be large with coarser fragments floating in a finer matrix. The term is often restricted to thick, redeposited carbonate layers intercalated in a siliciclastic turbidite series. Some of these layers, with or without different lithology than the surrounding beds, can be good markers.
In general, the term megaturbidite is used for a thick layer, or set of layers, that may be described by others as debris-flow deposits, and previously as fluxoturbidites. Reference to thickness seems to be more relative than absolute. Thickness and sedimentary characteristics may change laterally. Identifying a well-correlatable layer by name may have advantages. However, the term should not be applied to cores. Because of the generalities in the definition and its restrictive use to outcrops, there is no reason to support the term megaturbidite.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.