Volcanic Ash and its Enigma: A Case Study from the Central Indian Ocean Basin

An ash layer occurs between 10-35 cm depth in sediment cores from the Central Indian Ocean basin. Morphology, major, trace and rare earth element composition of glass shards from the ash layer suggest that the Youngest Toba Tuff of ∼74 ka from Northern Sumatra may be its source. To understand the implication of ash on the elemental distribution, a sediment core (NR-54) where abundant Youngest Toba glass shards occur at 30-35 cm depth interval, was studied. The presence of ash layer resulted in the enrichment of coarse fraction (260%), Al_excess (104%), K (43%) and Al/AI+Fe+Mn (28%), and depletion of Mg (58%), Fe (55Oh) , Mn (50%) , Ti (44%) and biogenic opal (37%). compared to their average concentrations in the core. Therefore, precaution should be taken while studying the parameters indicative of productivity (biogenic opal, coarse fraction and Al_excess), detrital terrigenous influx (AI/AI+Fe+Mn,T i, K and Mg) and redox sensitive metal (Mn), whose concentration is affected by the presence of glass shards from the ash layer in the sediment cores from Bay of Bengal, Central Indian Ocean basin, South China Sea basin arid Western continental margin of India where the widespread Youngest Toba ash is reported.