14C dating of tsunami deposits in arid environments: how challenging can it be? The example of La Graciosa, Canary Islands

Abstract

14C dating of tsunami deposits in arid environments is often challenging, especially when there is no organic material available. The marine bioclasts found in the tsunami deposits thus become the main dating possibility. Apart from the reservoir effect, the main source of uncertainty is the age difference between the shells and the tsunami that transported them. Taking as an example a tsunami deposit on the island of La Graciosa (Canary Islands), we demonstrate that the marine shells (Patella) come from different sources, with 14C ages ranging from >45 kBP to 200 BP, the main source being an ancient marine terrace probably of MIS5e age. In addition, we propose a landslide source for this tsunami, the scar of which can be observed on the Famara cliff to the northeast of Lanzarote, just opposite the tsunami deposit outcrops at La Graciosa. In addition to the methodological aspects of shell dating, this study also serves as a reminder that local tsunamis generated by coastal cliff collapses are not a hazard to be neglected.