Optical dating studies of postglacial aeolian deposits from the south-central interior of British Columbia, Canada

Tests of the validity of optical dating of the fine-grained (4-11 mu m) com ponent of aeolian deposits from six sites in south-central British Columbia , using 1.4 eV (infrared) excitation of potassium feldspars, were made maki ng use of known-age tephra beds. At one site on the western side of the Fra ser Valley, samples bracketing the Mazama (7.5-7.6 ka, cal. yrs.) and Bridg e 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, know n to have been deposited between 14 and 2.3 ka (cal. yrs). The ages obtaine d from five samples, from four separate exposures spanning 10 km, varied fr om 30 to 94 ka, clearly indicating that this sediment was not exposed to su fficient sunlight prior to burial. As a result of a detailed investigation it is suggested that the reason is that some grains had been transported ov er short distances (<100 m) while shielded within carbonate-cemented cluste rs. (C) 1999 Elsevier Science Ltd. All rights reserved.