Primary volcaniclastic rocks

We propose a classification scheme that unifies terminology for all primary volcaniclastic deposits, assigns initial depositional mechanism as the basis for classifying them, and refines the grain-size classes used to pigeonhole samples. By primary volcaniclastic deposits and rocks, we mean the entire range of fragmental products deposited directly by explosive or effusive eruption. This definition thus focuses on the primary transport and deposition of particles, rather than those processes by which the particles form or the nature of the fluid in which they are carried. We favor this approach for all primary volcaniclastic deposits because they typically contain assemblages of clasts formed by different processes and/or at different times that are subsequently brought together during eruption.

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