Thermoluminescence dating applied to glaciolacustrine sediments from central British Columbia

Abstract

Glaciolacustrine and lacustrine sediments are important indicators of deglacial, interglacial, and nonglacial intervals within the Quaternary of Canada, yet there are no techniques for measuring their absolute deposition ages beyond the last ~ 50 000 years. In an attempt to develop an absolute dating tool for such sediments, we applied the partial bleach thermoluminescence (TL) dating technique to glaciolacustrine sediments of known age from central British Columbia. Samples were selected to represent both ice-proximal and ice-distal deposition and different modes of sedimentation.The results show clearly that both TL procedures and sedimentation processes, as reflected in the particle size and sedimentary structures of the samples, critically affected the accuracy of TL apparent ages. Specifically, care was required to isolate the effects of laboratory overbleaching, apparent glow-curve shifts, and inappropriate regression analysis. Clay-dominant layers lacking silt or sand interlayers produced expected ages, whereas sand- and silt-rich samples (with one exception) yielded excessive TL apparent ages. The single exception was a thin (9 mm), ice-distal, silt-rich layer.