AbstractIn recent years single-grain dating of quartz has been used to provide luminescence ages of proglacial sediments but the poor sensitivity of the optically stimulated luminescence (OSL) signal of quartz can make dating in some geographical regions challenging. The main aim of this study is to improve luminescence dating in glacial environments by developing and testing methods of single-grain dating of K-feldspars from proglacial sediments using the post-IR infra-red stimulated luminescence (pIRIR) signal. The Lago Buenos Aires valley in Patagonia was chosen as the study site because the existing chronology in the valley that constrains the ages of moraine deposition provides a rare opportunity to compare luminescence dating of proglacial sediments with ages determined using independent dating techniques.
A number of challenges associated with single-grain luminescence dating of Kfeldspar are addressed in this study in order to provide accurate ages using the technique. This includes developing a procedure using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to directly measure the internal K-content of individual grains of K-feldspar, and provide an average internal K-content appropriate for single-grain dating where geochemical measurements of individual grains are not available. Experiments are also performed in this study to demonstrate that the reproducibility of single-grain pIRIR luminescence measurements can be optimised by reducing the disc location temperature from an elevated temperature to room temperature and using the IR LEDs to bleach the grains during the SAR cycle. Laboratory bleaching experiments also demonstrate that the bleaching potential of the pIRIR signal is not expected to be a barrier for single-grain dating of samples in this study.
Finally, IRSL ages are provided for single grains of K-feldspar from two aeolian dune sand samples that were taken from above and below the Kawakawa tephra from North Island, New Zealand, and for a suite of ten proglacial samples from the Lago Buenos Aires valley that are associated with the deposition of moraine ridges dated using cosmogenic isotope dating and 40Ar/39Ar dating. The ages ranging from 15 – 111 ka presented in this study agree with the independent numerical age control within dating uncertainties. Therefore, this study suggests that the technique can be used to provide accurate ages for aeolian and proglacial sediments.
|Date of Award||10 Nov 2014|
|Sponsors||Natural Environment Research Council|
|Supervisor||Geoff Duller (Supervisor) & Neil Glasser (Supervisor)|