Isochron dating of sediments using luminescence of K-feldspar grains

Abstract

A new method for dating well-bleached sediments is presented, with results for thirteen samples from China. The method uses an isochron constructed from the measurement of natural radiation doses received by potassium-feldspar grains in a range of grain sizes using the infrared stimulated luminescence (IRSL) signal. The age of deposition of the sediment is calculated from this isochron and from the internal dose rate to the grains from 40K and 87Rb in the crystal lattice. This procedure appears to overcome age underestimation due to anomalous fading, a phenomenon that has precluded conventional luminescence dating of K-feldspars and would be applicable to K-feldspars for which the natural dose is beyond the linear dose response region. Also, since the isochron IRSL method is reliant on only the internal dose rate, it overcomes problems related to (1) changes in past dose rate due to postdepositional migration of radionuclides, (2) changes in water content as water-lain sediments dry out, (3) spatial heterogeneity in the gamma dose rate, and (4) uncertainties in the cosmic ray dose rate during the period of sample burial. Copyright 2008 by the American Geophysical Union.