Storegga tsunami sand in peat below the Tapes beach ridge at Haroy, western Norway, and its possible relation to an early Stone Age settlement

One of the early problems with the Storegga tsunami deposit was how to distinguish it from deposits of the mid-Holocene (Tapes) transgression. An excavation on Haroy, an island on the outermost western coast of Norway, shows a distinct, clean sand bed embedded in peat and clearly separated from the overlying Tapes beach deposits. This sand bed continues in the peat landwards of the beach ridge for at least 60 m. Radiocarbon dates of the peat show that the sand was deposited some time between 6900 and 7700 yr BP. The sedimentary structures of the bed, the C-14 dates, and the fact that this is the only sand bed in the peat, suggest that the sand bed was deposited by a short-lived event, the Storegga tsunami. On the neighbouring island, Fjortoft, a Stone Age settlement, dated to 7500 yr BP, was discovered in the early 1970s. The settlement was found underneath a sand bed that later had been covered by the Tapes beach ridge deposits. When discovered, the sand covering the settlement was inferred as eolian sand. However, this investigation shows that the Storegga tsunami deposited a widespread sand bed on the land surface around this time with a similar grain size distribution to eolian sand. It is therefore suggested that the sand bed covering this settlement was deposited from the Storegga tsunami. Both the stratigraphy and C-14 dates demonstrate that the Tapes transgression maximum was reached well after the Storegga tsunami on Haroy, between 6500 and 6100 yr BP.