Classification of modern and ancient volcaniclastic rocks of pyroclastic and epiclastic origins

Abstract

In this chapter we first provide classification schemes for modern pyroclastic deposits. We then describe an approach to the classification of lithified, indurated and metamorphosed volcaniclastic rocks of the rock record, stressing the problems, and the caution needed in giving names, even with basic genetic meanings, to such rocks. This is followed by a discussion of descriptive lithological criteria and their relevance in determining the genesis of ancient volcaniclastic rocks. The problems associated with the use of the terms ‘agglomerate’ and ‘vulcanian’ for ancient volcaniclastic rocks are discussed and, finally, we comment on the nomenclature of quench-fragmented and autobrecciated (flow brecciated) volcaniclastics.