Reconstruction of Paleoenvironment and Identification of Historical Tsunami Deposits by Geochemical Analyses in Iwanuma City, Miyagi Prefecture, Japan

Identifying invisible tsunami deposits in the geological record is challenging and requires multiproxy analyses. In particular, geochemical signatures provide useful information for identifying paleo-tsunami deposits, as well as for reconstructing the paleoenvironment history, even when other proxies are equivocal. In addition, geochemical proxies help to provide an understanding of environmental changes that occur post-tsunami. As a result, they are now frequently used in paleotsunami research. Tsunami deposits are identified on the Sendai Plain, Japan, and environmental changes over time are reconstructed based mainly on geochemical data. Using a high-resolution elemental analysis with XRF core scanning, evidence of seawater inundation is discovered that is difficult to recognize with a naked eye. Based on the combined results of multi-proxy analyses, together with radiocarbon dating, not only a 1611 Keicho tsunami deposit but also a minor signal of a potential 1454 Kyotoku tsunami deposit are identified.