Evaluating the effectiveness of heavy liquid density separation in isolating K-feldspar grains using alluvial sediments from the Hajar Mountains,Oman |
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| Institution: | 1. School of Geography and the Environment, University of Oxford, Oxford, UK;2. Human Origins and Palaeoenvironments Research Group, Oxford Brookes University, Oxford, UK;3. Mansfield College, University of Oxford, Oxford, UK;4. Geography, Archaeology & Environmental Studies, University of the Witwatersrand, Johannesburg, South Africa |
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| Abstract: | Heavy liquid density separation is commonly utilised in isolating specific minerals from bulk sediment for luminescence dating. K-feldspars are commonly separated from other minerals by isolating the <2.58 g cm?3 fraction which yields infrared stimulated luminescence (IRSL) signals conducive to dating. However, initial measurements of the IRSL and thermoluminescence (TL) signals from the <2.58 g cm?3 fraction of alluvial fan sediments from the Hajar Mountains, northern Oman, were atypical of K-feldspar luminescence signals reported in the literature. In this study, three different density separates (<2.58 g cm?3, 2.58–2.54 g cm?3 and <2.565 g cm?3) were trialled to attempt to isolate pure K-feldspar samples for dating, to measure K-feldspar IRSL signals which are not contaminated with inputs from other feldspar, quartz and/or heavy mineral signals. The mineralogy of these separates was explored using microscopy, X-ray diffraction and mass spectrometry. We found that despite more refined heavy liquid density separation, the proportions of K-feldspar in these separates had a maximum of 40% by weight, remaining significantly contaminated by other minerals. IRSL and TL signals were atypical of K-feldspar for all density separates and it is likely that there is a contribution of signal from IR-sensitive contaminants, such as muscovite. This highlights the importance of investigating the mineralogy of samples for luminescence dating, especially in regions where little prior work has been undertaken. |
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| Keywords: | K-feldspar IRSL Density separation Sample purity Mineralogy |
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