抄録
The term “turbidity current” was firstly proposed for the unknown subaqueous density current, weighted with sediments in water, which is proposed to explain the origin of submarine canyons (Daly, 1936 ; Johnson, 1938, 1939a, b). It was secondly introduced as the transportation medium of graded bedding on land and deep-sea sand in ocean (Kuenen and Migliorini, 1950 ; Natland and Kuenen, 1951). The term “turbidite” was coined to designate all deposits of turbidity current (Kuenen, 1957).
After that, some researchers insisted on defining that “turbidity current” is nearly or completely restricted to the turbulence current where sediment particles are supported only by fluid turbulence, and “turbidite” is limited to the deposits of “turbulence current” (Sanders, 1965 ; Middleton and Hampton, 1973, 1976 ; Shanmugam, 1996, 1997, 2000 ; Mulder and Alexander, 2001 ; Gani, 2004).
However, based on the historical facts, it is obvious that “turbidity current” was named to an unknown density current which is expected to exist actually in nature, therefore, it is very natural and reasonable to image that the supporting mechanism of sedimentary grains in “turbidity current”, the unknown gravity current in nature, is not restricted to a specific mechanism such as fluid turbulence, but includes various kinds of mechanisms (Kuenen in Sanders, 1965 ; Mutti et al., 1999 ; Kneller and Beckee, 2000).
Therefore, the recent definition or discussion that “turbidity current” is equal or nearly equal to “turbulence current” makes the fundamental mistakes and causes the endless confusions. To avoid the confusion, the author proposed to redefine these terms in a broad sense according to the historical facts, and stressed the importance of objective description of the deposits apart from the interpretation such as supporting mechanisms or fluid rheology.
