a, Ages (n = 11) have been modelled in OxCal version 4.2.4. Only random errors are included in the age model. Pale probability distributions represent the unmodelled ages (likelihoods) and dark grey distributions represent the modelled ages (posterior probabilities). The narrow and wide brackets beneath the distributions represent the 68.2% and 95.4% probability ranges, respectively. Start and end ages have been modelled for each phase, with age ranges (95.4% confidence interval, random-only errors) given in years and rounded off to the closest decade. b, Comparison of single-grain OSL ages for quartz and single-grain pIRIR ages for K-feldspar for 47 samples (28 from Main Chamber, 15 from East Chamber and 4 from South Chamber), with age uncertainties shown at 2σ. The dashed line indicates the 1:1 ratio.