Quaternary Science Reviews 18 (1999) 1453 } 1466 Optical dating studies of postglacial aeolian deposits from the south-central interior of British Columbia, Canada Olav B. Lian *, D. J. Huntley Department of Earth Sciences, The University of Western Ontario, London, ON, N6A 5B7, Canada Department of Physics, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada Abstract Tests of the validity of optical dating of the "ne-grained (4}11 m) component of aeolian deposits from six sites in south-central British Columbia, using 1.4 eV (infrared) excitation of potassium feldspars, were made making use of known-age tephra beds. At one site on the western side of the Fraser Valley, samples bracketing the Mazama (7.5}7.6 ka, cal. yrs.) and Bridge River tephras (2.3 ka, cal. yrs.) yielded optical ages in accordance with the known ages when a correction for thermal-transfer was used. The same method was applied to aeolian deposits on the Fraser Plateau, known to have been deposited between 14 and 2.3 ka (cal. yrs). The ages obtained from "ve samples, from four separate exposures spanning 10 km, varied from 30 to 94 ka, clearly indicating that this sediment was not exposed to su$cient sunlight prior to burial. As a result of a detailed investigation it is suggested that the reason is that some grains had been transported over short distances ( ( 100 m) while shielded within carbonate-cemented clusters.  1999 Elsevier Science Ltd. All rights reserved. 1. Introduction The timing of deglaciation, and early postglacial sedi- mentation, in the relatively low-lying interior of south- central British Columbia is poorly de"ned. This is largely due to a paucity of suitable organic material for radiocar- bon dating (Ryder, 1971; Clague et al., 1990). The radiocarbon ages that do exist indicate that parts of the interior were ice-free by about 11 ka (13 ka, cal.yrs; Hughen et al., 1998), although less reliable ages suggest that deglaciation could have occurred as early as 12 ka (14 ka, cal. yrs.; Hughen et al., 1998) near the boundary of British Columbia and Washington State (Clague, 1981). In south-central British Columbia glacigenic deposits on the plateaux, on the valley sides, and on the dissected Pleistocene sediment "lls that occupy the valley bottoms, are in many places capped with up to several metres of aeolian sediments. These sediments are found to cap till, to rest directly on outwash, or lie on (or within) para- glacial deposits (Ryder, 1971), that were laid down dur- ing, or shortly after, deglaciation. The surfaces of these * Corresponding author. Present address: School of Earth Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand. E-mail: olav.lian @vuw.ac.nz. aeolian deposits are generally vegetated and stable; ac- tively eroding or accreting surfaces are rare. It is therefore likely that formation of these deposits commenced im- mediately after glacial meltwater activity had essentially ended, but before a signi"cant amount of stabilising vegetation had become established. In this region there- fore, aeolian deposits are expected to represent early postglacial sedimentation. Because aeolian sediments are usually expected to have received extended exposure to direct sunlight prior to deposition, they are considered to be one of the most suitable deposits for luminescence dating. Thus, within the interior of British Columbia, luminescence dating of aeolian sediments has the potential for supplying limiting ages on the time of deglaciation, and on the formation of early postglacial landforms. In this paper we report on the "rst research into the utility of optical dating of these postglacial aeolian de- posits. The only previous work was a pilot study conduc- ted by Godfrey-Smith (1991) using samples collected in the Kamloops region (Fig. 1 inset), about 100 km to the southeast of our sites. Godfrey-Smith used 2.4 eV (green, 514 nm) excitation from an argon ion laser to produce equivalent doses from two Holocene-aged aeolian sam- ples. One was consistent with what was expected, but the other was not; optical ages were not calculated. 0277-3791/99/$ - see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 3 7 9 1 ( 9 8 ) 0 0 0 8 5 - 7