Elemental and Mineralogical Analysis of Tsunami Deposits from Phra Thong Island, Thailand

Abstract:

Characterizing sediment provenance from the geologic and geomorphic records left by natural disasters may shed light on the sedimentary and hydrodynamic processes happening during such events. In this study, we collected modern sediment samples from onshore, offshore, the 2004 Indian Ocean Tsunami and three palaeotsunamis and a 2007 storm deposit from Phra Thong Island, Thailand. To explore the relationship between the sedimentary deposits, we examined grainsize parameters, mineralogy (from X-Ray Diffraction) and trace element geochemistry (from X-Ray Fluorescence) from each deposit and applied a series of statistical analyses including cluster analysis, principal component analysis and discriminant function analysis.

Our results show that the mineral content and grainsize parameters are statistically inadequate to distinguish the provenance of tsunami deposits, but that trace element geochemistry is potentially a good discriminator. In most of our statistical analyses, the trace elements show that the onshore samples are distinguished from the offshore and tsunami sediment samples. Also, the near-shore samples and tsunami deposits are very similar. This reveals that the near-shore marine sediments significantly contributed to the 2004 tsunami deposits. In addition, our analyses show that all four tsunami units statistically differ from each other, and that the storm deposits are similar to the second palaeo-tsunami group. This indicates that sediment sources are diverse and that the tsunami deposits did not come from the same source. Such complexity raises questions about the origin of various sedimentary environments and it also reflects the importance of local context and paleogeography that cannot be ignored in tsunami provenance studies.