Click here to view fulltext PDF

Permanent link:
https://www.ias.ac.in/article/fulltext/jess/129/0175

Glass shards; Indian Ocean; microtektites; tephrochronology; in-situ events; Toba eruptive.

We report the widespread extent of Toba volcanic glass shards in the Central Indian Ocean Basin. Investigation of four sediment cores (7$^{\circ}$–17$^{\circ}$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 <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 $\delta^{18}$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.

ANKEETA AMONKAR^{1 2} SRIDHAR D IYER¹ BABU E V S S K³ MANJU S³

1. CSIR-National Institute of Oceanography, Dona Paula, Goa 403 004, India.
2. Marine Science, School of Earth, Ocean and Atmospheric Sciences, Goa University, Taleigao, Goa 403 206, India.
3. CSIR-National Geophysical Research Institute, Hyderabad, Telangana 500 007, India.

Published

22 August 2020

Manuscript received

6 September 2019

Manuscript revised

19 April 2020

Accepted

29 April 2020

Final version published online

18 August 2020