Luminescence dating indicates radiocarbon age underestimation in late Pleistocene fluvial deposits from eastern England

Abstract

Robust geochronological control is crucial for interpreting and correlating the environmental record from fragmentary terrestrial sequences from the last glacial period. Traditional terrestrial stratigraphies are typically reliant on radiocarbon dating, although estimates of antiquity for samples older than 40 ka may be unreliable. Optically stimulated luminescence (OSL) dating of sediments is an alternative for dating the whole of the last glacial period and also provides the opportunity to independently test radiocarbon based chronologies. This paper presents a set of nine directly comparable paired OSL and accelerator mass spectrometry (AMS) radiocarbon ages from multiple sites within Devensian fluvial sediments in lowland Britain and shows that it is possible to obtain robust OSL age estimates throughout this time period. The two techniques agree well for ages younger than ca. 29 14C ka BP (ca. 35 cal. ka BP) but disagree beyond ca. 35 14C ka BP (ca. 40 cal. ka BP). This is thought to be due to radiocarbon ages on older organic material having been contaminated by low levels of modern carbon. It is therefore suggested that all conventionally pre-treated radiocarbon ages greater than 35 14C ka BP should be treated with extreme caution.