Sedimentological and micropaleontological characteristics of tsunami deposits associated with the 2024 Noto Peninsula earthquake

A study of modern tsunami deposits can provide information to identify paleo-tsunami deposits. This study reports sedimentological and paleontological features of tsunami deposits in Suzu City, Japan, formed by the 2024 Noto Peninsula tsunami. The tsunami deposits were found up to 48 m inland from the shoreline along our transect, whereas the inundation area reached at least 160 m inland. The thickness of the tsunami deposit ranged from 0.6 to 11.2 cm, with the main body composed of fine to very fine sand at sampled locations. At the most seaward location, the deposit exhibited climbing ripples with their leeside seaward: the tops of these ripples had been dragged seaward and horizontally truncated. These sedimentary features and the inverse and normal grading in grain size of the deposit imply a strong seaward current and increasing and decreasing flow velocities during multiple waves at the study location. Diatom assemblages within the tsunami deposits were dominated by marine and brackish species, except freshwater terrestrial species were found in the troughs of the climbing ripples. Fragments of bivalves and sponge spicules were also recognized within the ripple troughs. These paleontological features suggest that the tsunami deposits at this study site were derived from more than one source.