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

Abstract

Tests of the validity of optical dating of the fine-grained (4–11 μm) 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 five samples, from four separate exposures spanning 10 km, varied from 30 to 94 ka, clearly indicating that this sediment was not exposed to sufficient 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.