Morphology of the Volcanic Ash from the Kukadi River Section, Pune District, Maharashtra

An ash bed varying in thickness from 20 cm to 2 m occurs within the lower part of 10 m thick yellowish-brown clay and calcareous silt unit that contains occasional lenses of calcrete, gravels and channel lag gravels both at the base and top of the sequence. The volcanic ash has yielded a K/Ar age of 1.4 Ma. The volcanic ash is highly siliceous in composition with SiO₂ content varying between 72 to 78%. It is dominantly constituted of silt sized angular glass shards, and pumice fragments with sharp edges. Petrography, SEM and chemical composition of the glass shards helps in relating the ash morphology to magma composition and the type of eruption. On the basis of petrographic and morphological characters displayed by the volcanic ash, the formation of the glass shards is attributed to magmatic processes.