HR: 1400h
AN: T43B-03    [Abstracts]
TI: Luminescence Dating of Tsunami sediments : Residual Signal Levels in Sediments from the 26th December 2004 Indian Ocean Event in Thailand.
AU: * Sanderson, D C
EM: D.Sanderson@suerc.gla.ac.uk
AF: Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride, G75 OQF, United Kingdom
AU: Bishop, P
EM: paul.bishop@ges.gla.ac.uk
AF: Department of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
AU: Hansom, J
EM: Jim.Hansom@ges.gla.ac.uk
AF: Department of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
AU: Curry, G
EM: gordon.curry@ges.gla.ac.uk
AF: Department of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
AU: Chaimanee, N
AF: Department of Mineral Resources, Bangkok, Thailand
AB: Luminescence dating has been applied in the past to several tsunami deposits, notably from Northern Australia, the Scilly Isles, Scotland and Chile. Providing initial signals levels are close to zero, optically stimulated luminescence (OSL) dating is a promising method for dating palaeo-tsunami sediments, and providing an indication of past frequencies of occurrence of at least large scale events. The time resolution available, however, is critically dependent on initial signal levels in zero age deposits. With that in mind we have undertaken a study of sediments deposited in Phang Nga province and Phuket in Thailand by the 26th December 2004 tsunami. Approximately 250 sediment samples were collected from a diverse range of settings early in 2005 and prior to monsoonal disturbance. A newly developed portable OSL reader was used to assist fieldwork by making real- time measurements during the fieldwork period of more than 100 samples. This proved invaluable in confirming that all tsunami deposited material retained measureable luminescence signals, and guiding sampling towards an examination of the underlying factors that influence residual levels. Samples were collected from pre-tsunami ground surfaces, from basal and superficial tsunami deposits, from stratified sediments showing multiple sequences of coarse and fine sediments associated with different parts of the wavetrain, from a series of open and shaded back-beach locations, and from a transect reaching inland for approximately 1 km. Laboratory studies have now been conducted to extend initial screening measurements to all samples, and to perform calibrated analyses of mineral separates from selected samples. The work has confirmed that non-zero initial signal levels are present in all samples. The magnitude of such signals ranges over 4 orders of magnitude apparently controlled by the inherited age of the source sediment being entrained in the tsunami wave prior to redeposition. The lowest residual signal levels are associated with the surfaces of old ground surfaces; the initial coarse fractions, and the finer fractions settling out late in the depositional sequence. In these cases residuals ages can be decadal, which would not inhibit accurate dating of palaeo-tsunami sediments where these can be identified. Recommendations can thus be made for sampling tsunami deposits for chronometric studies.
DE: 3020 Littoral processes
DE: 4558 Sediment transport (1862)
DE: 4564 Tsunamis and storm surges
DE: 7221 Paleoseismology (8036)
SC: Tectonophysics [T]
MN: 2007 Joint Assembly