YTT ash from Quaternary sediments of Kapileshwar area, Purna alluvial basin, Central India

Abstract

A thick pocket of volcanic ash (∼2.5 m) represented by various shades of gray, powdery, massive to laminated in nature, hosted in yellowish brown, thinly bedded, laminated silty-clay lithocolumn, has been studied for its preservational and geochemical aspects. The ash column shows preservations of both primary and reworked ashes which are distinguishable on the basis of their field criteria including colors, bedding geometries and thicknesses. Petrological study of the same reveals high representation of glass shards with bubble wall, blocky and pumice morphologies, minor occurrences of light and heavy minerals and unidentifiable admixture of fine grained sediments. Geochemistry of both bulk ash and glass shards through ICP-AES and EPMA respectively suggest high percentages of SiO2, Al2O3, Na2O and K2O. REE data generated through ICP-MS show strong negative Eu anomaly. The effects of weathering or, aqueous solution on the geochemistry are also noticeable as evident by the variations in the values of both mobile and immobile elements, however, the data obtained from both bulk ash and glass shards are within the limits of YTT composition. Calm to very low energy environment of deposition is suggested for their deposition. Paleoclimatic proxies represented by rhizoliths, rhizospheres, rhizolith balls, ant traces and vertebrate remains preserved in the pre-tephra succession have also been commented.