A mid-Holocene candidate tsunami deposit from the NW Cape (Western Australia)

• We present stratigraphic evidence of a prehistoric palaeotsunami from NW Western Australia.
• We used μCT scans of oriented sediment cores to infer sediment fabrics.
• Sedimentary and microfaunal data point to 3 run-up phases and littoral source areas.
• The analyses of μCT scans reveal landward flow directions.
• The candidate tsunami deposit was OSL-dated to 5400–4300 years ago.

Although extreme-wave events are frequent along the northwestern coast of Western Australia and tsunamis in 1994 and 2006 induced considerable coastal flooding locally, robust stratigraphical evidence of prehistoric tropical cyclones and tsunamis from this area is lacking. Based on the analyses of X-ray computed microtomography (μCT) of oriented sediment cores, multi-proxy sediment and microfaunal analyses, optically stimulated luminescence (OSL) and 14C-AMS dating, this study presents detailed investigations on an allochthonous sand layer of marine origin found in a back-barrier depression on the NW Cape Range peninsula. The event layer consists of material from the adjacent beach and dune, fines and thins inland, and was traced up to ~ 400 m onshore. Although a cyclone-induced origin cannot entirely be ruled out, the particular architecture and fabric of the sediment, rip-up clasts and three subunits point to deposition by a tsunami. As such, it represents the first stratigraphical evidence of a prehistoric, mid-Holocene tsunami in NW Western Australia. It was OSL-dated to 5400–4300 years ago, thus postdating the regional mid-Holocene sea-level highstand.