Cabeço dos Pendentes (Mação, Portugal): OSL dating of an enigmatic monument

OSL dating can play a key role in untangling the chronology of damaged prehistoric sites. Cabeço dos Pendentes was first investigated in the 1930s but had been heavily disturbed by the removal of the megalithic orthostats a few years previously. The site was relocated in 2006 and excavations the following year demonstrated that it had traces of a polygonal megalithic chamber within
an earthen ring that was presumed to be the remains of the original mound. Initial OSL dates contradicted expectations, however, and in 2015 the original trenches were reopened, and a new set of dates obtained. These allowed the chronology of the deposits within the base of the chamber and within the earthen ring to be established. Despite clear artefactual evidence of Late Neolithic and Early Chalcolithic activity, however, none of the new OSL dates went back further than the 2nd millennium BC. We conclude that the artefacts are assignable to periods earlier than the sedimentary ages, and that their original contexts have not survived undisturbed in the areas investigated. The results illustrate the difficulty of establishing a secure chronology for such a heavily damaged site.