Chronologies in context: reconciling the optical dating of quartz with its sedimentary environment

The occurrence of overdispersion (OD) in single-grain optically stimulated luminescence (OSL) equivalent dose (De) distributions is an issue affecting both natural and laboratory irradiated grains of quartz. The presence of this additional spread beyond statistical expectations is often explained as the result of factors either intrinsic or extrinsic to the grains being dated, or a combination of both. The designation of one, or both, of these factors to explain the OD is compounded by the destruction of the sedimentary context during sample preparation. With the original context destroyed, the De distribution and associated OD are disconnected from the sedimentary environment. The explanation of OD is often made using either macroscopic field observations or by comparison to previously published data. This thesis is motivated by the overarching aim to reconcile the De distribution, and the associated OD, with the sedimentary context from which the samples were collected. To address this aim, two locations – MacCauley’s Beach and Pech de l’Azé IV – were chosen as study sites. The former is a geogenic receded barrier beach deposit located near Wollongong, New South Wales, Australia, whereas the latter is a Neanderthal occupation site containing anthropogenic sediments located in the Department of the Dordogne, France. A total of 12 samples, six from each site, were collected as part of a broad aim to construct temporal frameworks and assess the site formation processes at each site. In 11 of the 12 samples the resulting De distributions were overdispersed, with OD values between 27 ± 2 and 87 ± 5%.