Sedimentology of coastal chevron deposits - tsunamigenic versus aeolian origin

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The origin of v-shaped sediment bodies, so-called chevrons, is currently controversially discussed. The term chevron is presently only defined in terms of the morphology of the sediment body, but not in terms of its genesis. Both an aeolian and an impact-tsunami origin are discussed. In this study, the sedimentology and origin of chevrons is investigated, examining deposits from the US west coast and the coast of Western Australia. Ground-penetrating radar has helped to detect internal cross bedding and soil horizons. Determined depositional ages underline active migration of the structures since the ages are younger in transport direction. In contrast, sediment bodies of tsunami origin should exhibit contemporaneous ages both in transport direction and within vertical successions. Furthermore, tsunami sediments generally display only few sedimentary structures (e.g. grading). Unimodal grain-size distributions (mean diameter: 0.11-0.25 mm) underline an aeolian origin, since tsunami sediments should be coarser and less sorted. The preliminary results point to an aeolian origin of chevrons. This assumption needs to be strengthened during the continuation year by comparing the chevron sediment with possible material sources, such as beaches, rivers and cliffs. Here, marine microorganisms from water depths below storm wave base, may be used as indicator for a possible tsunamigenic origin.