Abstract:
We report the widespread extent of Toba volcanic glass shards in the Central Indian Ocean Basin. Investigation of four sediment cores (7 degree-17 degree S) revealed several shard-rich horizons (SRH) that provide the first detailed tephrochronology for volcanic glass shards in the CIOB. A comparative study of surface sediments floored with Youngest Toba Tuff (YTT), indicate that irrespective of the rate of sedimentation, YTT in the basin is restricted to a depth of less than 35 cm-bsf. We utilized microtektites (0.77 Ma), associated with the Oldest Toba Tuff (OTT) glass shards, as a proxy for age calculation of the SRH. The results are comparable with well-established ages derived from paleomagnetic and delta sup(18) O methods for the Leg 21 ODP Site 758. The other significant finding of this study includes the first report of Middle Toba Tuff (equivalent to Layer C) and Layer D that are present between YTT and OTT (Layer E) and also Layers G, H, h, I, J, K, L and M. All these layers correspond with those reported for ODP Site 758. Furthermore, two SRH between layers G and H show signatures of localized in-situ phreatomagmatic origin, suggesting that CIOB is apparently more active - tectonically and volcanically than it is presumed.
