An extensive series of 44 radiocarbon (14C) and 37 optically stimulated luminescence
(OSL) ages have been obtained from the site of Riwi, south central Kimberley (NW Australia).
As one of the earliest known Pleistocene sites in Australia, with archaeologically sterile
sediment beneath deposits containing occupation, the chronology of the site is important in
renewed debates surrounding the colonization of Sahul. Charcoal is preserved throughout
the sequence and withinmultiple discrete hearth features. Prior to 14C dating, charcoal has
been pretreated with both acid-base-acid (ABA) and acid base oxidation-stepped combustion
(ABOx-SC) methods at multiple laboratories. Ages are consistent between laboratories
and also between the two pretreatment methods, suggesting that contamination is easily
removed from charcoal at Riwi and the Pleistocene ages are likely to be accurate. Whilst
some charcoal samples recovered from outside hearth features are identified as outliers
within a Bayesian model, all ages on charcoal within hearth features are consistent with
stratigraphy. OSL dating has been undertaken using single quartz grains from the sandy
matrix. The majority of samples show De distributions that are well-bleached but that also
include evidence for mixing as a result of post-depositional bioturbation of the sediment.
The results of the two techniques are compared and evaluated within a Bayesian model.
Consistency between the two methods is good, and we demonstrate human occupation at
this site from 46.4–44.6 cal kBP (95.4% probability range). Importantly, the lowest archaeological
horizon at Riwi is underlain by sterile sediments which have been dated by OSL
making it possible to demonstrate the absence of human occupation for between 0.9–5.2
ka (68.2% probability range) prior to occupation.