THE USE OF GLASS FOR DATING VOLCANIC ASH BY THERMOLUMINESCENCE

The development of a new physical dating method for late Pleistocene tephrochronometry is described here. Tests of laboratory procedures applied to glass from 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- to 11-mu-m glass by heavy liquid centrifugation, pre-TL readout heating at 50-degrees-75-degrees-C for 8 days, and careful regression analysis of TL growth curves. Several unknown-age tephra are dated directly by this method for the first time. These include rive ash beds from Summer Lake, Oregon (67-200 ka), a Sheep Creek Valley ash from Alaska (81 +/- 9 ka), an ash from Nevada (200 +/- 50 ka) correlated to the Wadsworth Tephra, an unknown ash (210 +/- 30 ka) from Rye Patch Dam in Nevada previously correlated to the 400- to 600-ka Dibekulewe tephra, and ash 9M from Washtucna in eastern Washington (250 +/- 30 ka).