ELSEVIER Marine Geology 155 (1999) 243–248 Letter Section New occurrence of Youngest Toba Tuff in abyssal sediments of the Central Indian Basin J.N. Pattan a , Phil Shane b,L , V.K. Banakar a a National Institute of Oceanography, Dona Paula, Goa, 403 004, India b Department of Geology, University of Auckland, Private Bag 92019, Auckland, New Zealand Received 11 March 1998; accepted 14 August 1998 Abstract Volcanic glass and pumice found in siliceous abyssal sediments of the Central Indian Basin, south of the Equator, have previously been assigned various origins including intra-basin volcanism, Indonesian arc, and Krakatau. Rhyolitic glass shards dispersed in sediments from 8 cores that we have examined are compositionally identical to those of fallout deposits of the Youngest Toba Tuff erupted at 74 ka from northern Sumatra. The correlation extends the distribution of coarse (>63 μm) glass shards some 1500 km south of the previously known fallout zone, and into the Southern Hemisphere (reaching latitudes of ca. 14ºS). This provides evidence for bi-hemispheric dispersal of the ash cloud and supports global dispersal of gas and aerosols from the eruption. Such dispersal could have facilitated the global impact of the eruption.  1999 Elsevier Science B.V. All rights reserved. Keywords: tephra; glass chemistry; Indian Ocean; Youngest Toba Tuff; volcanism 1. Introduction Silicic pumice clasts, tephra beds and dispersed glass shards on the seafloor and in Pliocene and Quaternary sediments of the Central Indian Basin (CIB), south of the Equator (Fig. 1) have been re- ported by numerous workers. Attention has focused on the pumice and shards because they are com- monly the nucleus for Mn nodules (e.g. Iyer and Sudhakar, 1993; Martin-Barajas and Lallier-Vergas, 1993), and because they are far (ca. 2000–3000 km) from known silicic eruptive centres such as the In- donesian arc, and thus must be the products of very explosive eruptions. Several origins for the silicic L Corresponding author. Fax: C64 (9) 373-7435; E-mail: pa.shane@auckland.ac.nz volcanic detritus have been proposed including local intra-basinal submarine volcanoes of the CIB (e.g. Iyer and Sudhakar, 1993; Iyer et al., 1997), distal fallout from Sumatra island arc volcanoes (Mar- tin-Barajas and Lallier-Vergas, 1993), and sea-rafted pumice from Krakatau volcano (Mudholkar and Fu- jii, 1995). Large pumice clasts (0.5–15 cm) found on the surface of the CIB have a well demonstrated geo- chemical similarity to products of the 1883 Krakatau eruption (Mudholkar and Fujii, 1995), and were em- placed via sea-rafting. However, geochemical data previously presented for the dispersed glass shards found in the sediments have not provided a definitive source. The eruption of the Youngest Toba Tuff from northern Sumatra at ca. 74 ka produced a widespread fallout tephra (Rose and Chesner, 1987) found 0025-3227/99/$ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII:S0025-3227(98)00160-1