Measurement of equivalent doses in quartz from contemporary water-lain sediments using optically stimulated luminescence

Abstract

The single aliquot technique and its derivatives are very attractive for the measurement of the very small doses found in young materials, because they inherently avoid concerns about low-dose non-linearity and can offer high precisions. A modification is outlined to the single Aliquot/regeneration and added dose (SARA) protocol [Mejdahl and Bøtter-Jensen (1994), Quaternary Geochronology ( Quaternary Science Reviews), 13, 551–5541, to permit its application to sedimentary quartz using the optically stimulated luminescence signal. This revised protocol is then used to determine the doses found in several contemporary fluvial sediments and one coastal beach sand, thought to be deposi-ted by recent wave action. Two over-bank river deposits were both homogeneously well bleached, with doses of < 0.4 Gy. Although most of the grains in three channel deposits (from a range of catchment sizes) were also well bleached, ‘contamination’ by a small proportion of very poorly bleached quartz grains prevented the measurement of the dose in the majority. The beach deposit was homogeneously bleached and contained a dose of about 0.02 Gy. It is concluded that over-bank sites may provide accurate dates for samples older than a few hundred years, but that the heterogeneity of the channel sites limits the accuracy of dates less than a few thousand years.