The 2004 Indian Ocean tsunami left significant sand deposits along the coastal tract of southeast India (Tamil Nadu state). These deposits serve as a benchmark to understand the effects of present day tsunami on the coastline. Additionally, the geological signatures of tsunami in the coastal stratigraphy can assist in providing modern analogs for identification and interpretation of ancient tsunami. This article presents the field observations of tsunami deposits, their internal stratigraphy and foraminiferal distribution, all of which varied from north to south depending upon coastal geomorphology, near shore bathymetry and sediment sources. In a few places, the tsunami deposits have been reworked due to subsequent events that caused modification in the internal stratigraphy. The tsunami deposits of the northern Tamil Nadu coast comprise at least 50% or more reworked foraminiferal specimens, indicating that the tsunami sediments may have been derived from a paleostrandline from a water depth of at least 45 m Key words: 2004 tsunami, geomorphology, foraminifera, sand deposits, southeast coast of India. Resumen El tsunami de 2004 en el Océano Índico acumuló una capa de sedimentos gruesos (depósitos de arena) a lo largo de la costa sureste de la India, particularmente en el estado de Tamil Nadu. Esos depósitos sedimentarios sirven como referencia para entender los efectos de tsunamis actuales en las zonas costeras. Además, las características geológicas de los depósitos de tsunami actuales en la estratigrafía costera asisten en identificación e interpretación de los tsunamis antiguos. En este artículo presentamos las observaciones del campo sobre los depósitos de tsunami, su estratigrafía interna y distribución de foraminíferos según varía de norte a sur, dependiendo de la geomorfología costera, de la batimetría somera, y de la proveniencia de los sedimentos. En algunas localidades, la estratigrafía interna de los depósitos fue perturbada debido a eventos subsiguientes. Los depósitos de tsunami de 2004 en la costa norte de Tamil Nadu constituyen al menos 50% o más de las foraminíferas retransportadas, lo cual indica que los sedimentos de tsunami fueron derivados de un paleo-costa, actualmente ubicado a una profundidad de al menos 45 m.

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Pumice clasts, partially and fully coated with ferro-manganese oxide from the Central Indian Ocean Basin (CIOB) were analysed for major, trace and rare earth elements; and glass and mineral grain chemistry to assess their possible source. These pumice clasts have similar to 95% glassy matrix with similar to 5% of plagioclase, ortho-pyroxene, amphibole, and spinel mineral grains. Pumice is rhyolitic, with high content of silica and total alkalis and show strong light rare earth element enrichment, with La 100 times enriched compared to chondritic abundance and exhibits a pronounced negative Eu-anomaly. Both the partially and fully coated pumice clasts have a similar composition, but this, and their, glass and mineral (orthopyroxene) chemistry differs from all tuffs known to have erupted from the Toba Caldera Complex. The partial to complete Fe-Mn oxide coating suggests the pumice probably predates activity from the Toba caldera. Their general composition is consistent with a volcanic arc origin, and show similarities to rhyolitic eruptives from Sumatra. The distribution of partially and fully coated pumice in the CIOB overlaps with that of uncoated pumice from the voluminous YTT eruption, suggesting that other large rhyolitic calderas active in Sumatra/Indonesia. Similarities in composition to ash layers from the CIOB suggest a possible Late Miocene - Late Pleistocene age for these pumices. (C) 2013 Elsevier Ltd and INQUA. All rights reserved.Peer reviewe

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