GEOLOGICAL EVIDENCE FOR PALEO-TSUNAMIS IN SRI LANKA

After the 2004 Indian Ocean tsunami inundation event, thin sediment films of fining up sequences were located in several topographic depressions of the southern coastal belt of Sri Lanka. The films consisting of silty fine sand with particular microfossil assemblages were located also in closed containers, bottles and kitchen tables. Well preserved microfossils such as foraminifera, radiolarians as well as spicules of sponges were noted in these recent tsunami sediments.Random augur holes were drilled into some selected depressions in the southern coastal villages of Peraliya and Denuwala situated at locations separated by about 50km. In several such holes, at least two fining up sequences were located below the surface in soil horizons separated from each other by 35cm to 1m. These soil profiles were overlying older coral reefs developed on lateritic formations. The microscopic observations on particular size fractions of the soil horizons showed microfossil assemblages with textures, color and organic C contents strikingly comparable to those observed in the recent tsunami sediments of Sri Lanka. Our findings imply the occurrence of at least two paleo- tsunami events of different ages in Sri Lanka originating apparently from a common source.