Sedimentary Features of Water-Laid Volcanic Deposits and Their Classificati on Based on the Mode of Emplacement

Abstract

A genetical classification of volcanic clastic deposits is proposed in this paper, which is based on the following four principal criteria:
1) place of the eruption by which the material was broughtinto the transporting media : W (subaqueous) or A(subaerial), or O(when it was unrelated directly with the eruption).
2) kind of media in which the material was transported to the depositional place : W (water) or A(air) or O(absence of media; this is used for some lava flows and dense landslide deposits).
3) place of deposition : W(subaqueous) or A(subaerial).
4) mechanism of transportation and settling : F(fall) or R(roll) or T(turbulent flow).
Any volcanic clastic deposits might be designated as WWW-T, AAW-F and so on, by putting the result according to the four criteria in a descending order. For lava flows(L), the same principle of classification is applicable, e. g., as WOW-L (or WWW-RL, when it is necessary to indicate rolling(R) mechanism of the emplacement in W media). By the use of O in the first term, this classification also applies to normal clastic sediments, e.g. OWW-T for turbidity current deposits.
Discriminating features for each kind of water-laid volcanic clastic deposits are described and several examples are presented.
The proposed classification concerns mainly with a sedimentary body as a whole, and not with. descriptive features of particles. Parallel usage of the classic descriptive terminology with the proposed one is recommended, as AAW-F tuff, WWW-T tuff breccia, or tuff breccia (WWW-T), etc.,