Fingerprinting paleotsunami deposits using sedimentary biomarkers – A succinct review and case study from a paleotsunami record on the Sanriku coastline (Noda, Japan)

Organic geochemical indicators have proven suitable to identify and characterize deposits of recent tsunamis, such as the 2011 CE Tōhoku-oki event, providing insights into erosional and transport processes of marine and terrestrial sediment inland (inundation) and offshore (backwash). However, lipid biomarkers have rarely been applied to historic and paleotsunami archives. We review lipid biomarkers suitable for paleotsunami research and present a case study using a targeted multi-compound approach on a geoslicer core from the Maita River Valley at Noda (Iwate Prefecture, Japan). At this site four paleotsunami deposits have previously been documented. In the analyzed samples, we quantified homologous series ( n -alkanes, n -aldehydes, fatty acids), isoprenoids (pristane, phytane), terpenoids, diagenetically stable compounds (steranes, hopanes), and evaluated diagnostic ratios. All four paleotsunami sand layers show a coherent marine fingerprint relative to background sediment. This fingerprint is expressed by enrichment of short-chain homologues, C 27 steranes and reduced C 29 /C 27 sterane ratios, low pristane/phytane (≤0.7) with aquatic-sources clustering in the pristane/ n -C 17 vs phytane/ n -C 18 cross-plot, and lower sterane/hopane ratios. Terrigenous inputs are suppressed (lower long-chain homologues and TAR indices), while elevated OEP, CPI, and EOP ratios indicate rapid burial of relatively fresh plant waxes co-transported during inundation. These results demonstrate that lipid biomarkers preserve paleotsunami signatures for millennia and can refine source allocation, sediment transport pathways, and complement sedimentological approaches, by characterizing and reconstructing the inundation of paleotsunamis. Such multi-compound lipid biomarker approaches enable more robust paleotsunami detection and improve constraints for regional tsunami-hazard assessments.