Expanding the proxy toolkit to help identify past events

Abstract

Some ofthe proxiesusedtoidentify palaeotsunamis arereviewed inlightof new findingsfollowing the2004 Indian Ocean Tsunami and the 2009 South Pacific Tsunami, and a revised toolkit provided. The new applicationofanisotropyofmagneticsusceptibility (AMS)tothestudyoftsunamidepositsanditsusefulness todeterminethehydrodynamicconditionsduringtheemplacementoftsunamisequences,togetherwithdata from grain size analysis, are presented. The value of chemical proxies as indicators of saltwater inundation, associated marine shell and/or coral, high-energy depositional environment, and possible contamination, is demonstrated and issues of preservation addressed. We also provide new findings from detailed studies of heavy minerals. New information gathered during the UNESCO — International Oceanographic Commission (IOC) International Tsunami Survey of fine onshore sediments following the 2009 South Pacific Tsunami is presented, and includes grain size, chemical, diatom and foraminifera data. The tsunami deposit varied, rangingfrom fining-upwardsandlayerstothinsandlayersoverlainbyathicklayeroforganicdebrisand/ora mud cap. Grain size characteristics, chemical data and microfossil assemblages provide evidence for marine inundation from near shore, and changes in flow dynamics during the tsunami.