Abstract
We have developed a new physical dating method for Late Pleistocene tephrochronometry. Tests of laboratory procedures applied to independently dated samples show that the thermoluminescence (TL), additive-dose dating method can yield accurate ages for both proximal and distal tephra from a few hundred years to at least 400 ka. The technique involves purification of 4–11 μm glass by heavy liquid centrifugation, pre-TL-readout heating at 50–75°C for eight days and careful regression analysis of TL growth curves. Five unknown-age tephra beds from Summer Lake, Oregon, were dated directly by this method for the first time. The TL ages for these tephra are: 67.3 ± 7.5 ka (ash 2), 102 ± 11 ka (ash N), 165 ± 19 ka (ash R), 200 ± 27 ka (ash KK), and 162 ± 35 ka (ash LL). These results indicate a nonuniform sedimentation rate for the enclosing pluvial lake deposits, a sedimentation hiatus in the interval 100–160 ka, and maximum ages roughly half of the previous indirectly inferred ages.
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