Mariana Sontag-González , Bo Li , Kieran O'Gorman , Basran Burhan , Budianto Hakim , Adam Brumm , Richard G. Roberts
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Through various reliability tests, we establish the suitability of a post-IR IR stimulated luminescence (pIRIR) standardised growth curve (SGC) procedure for D<sub>e</sub> estimation of ‘micro-aliquots’ containing 5–10 grains of K-rich feldspar, and then combine this method with estimates of environmental dose rate to determine 10 new reliable and finite optical ages for the sedimentary deposits at LBB. Furthermore, by applying the L<sub>n</sub>T<sub>n</sub> method to circumvent truncation of the D<sub>e</sub> distribution caused by the non-linearity of the dose response curve in the higher dose range, we could extend the site's luminescence-based chronology to span the interval ∼15–210 ka. The new chronology is in keeping with previous radiocarbon and U-series ages for the site's upper layers. We show that the low fading rate of micro-aliquots relative to using large aliquots composed of hundreds of grains lies in a brightness-based selection. 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引用次数: 0
摘要
用基于发光的方法确定火山沉积物的年代具有挑战性。用于测定年代的两种主要矿物--石英和富钾长石--在火山成因中通常都具有次优的发光特性,主要是信号强度低,而对于富钾长石来说,异常衰减率高。本研究对印度尼西亚 Leang Bulu Bettue(LBB)考古遗址的沉积物样本进行了案例研究,该考古遗址是我们了解人类早期占领苏拉威西岛的关键地点。我们的研究表明,目前最先进的方法可以为火山沉积物提供可靠的光学年龄。通过各种可靠性测试,我们确定了后红外红外激发发光(pIRIR)标准化生长曲线(SGC)程序是否适用于估算含有 5-10 粒富含钾长石的 "微小碱块 "的年龄,然后将该方法与环境剂量率估算相结合,为 LBB 沉积物确定了 10 个新的可靠和有限的光学年龄。此外,通过应用 LnTn 方法来规避高剂量范围内剂量响应曲线的非线性所造成的 De 分布截断,我们可以将该遗址基于发光的年代学扩展到 15-210 ka 之间。新的年代学与之前遗址上层的放射性碳和铀系列年龄相一致。我们的研究表明,相对于使用由数百个颗粒组成的大样本,微样本的低衰减率在于基于亮度的选择。通过选择衰减率低的明亮颗粒,大大减少了对衰减校正的需求,而且在进行衰减校正时,最终年龄估计的不确定性较小,从而提高了火山沉积物光学年龄的准确性和精确度。
Survival of the brightest? pIRIR dating of volcanic sediments in Sulawesi, Indonesia, using micro-aliquots of K-rich feldspar
Volcanic sediments are challenging to date with luminescence-based methods. Both main minerals used for dating—quartz and K-rich feldspar—commonly have suboptimal luminescence properties when of volcanic origins, primarily a low signal intensity and, for K-rich feldspars, high rates of anomalous fading. The present work provides a case study of sediment samples from the Leang Bulu Bettue (LBB) archaeological site in Indonesia, a key site in our understanding of the early human occupation of the island of Sulawesi. We show that currently available state-of-the-art methods can provide robust optical ages for volcanic sediments. Through various reliability tests, we establish the suitability of a post-IR IR stimulated luminescence (pIRIR) standardised growth curve (SGC) procedure for De estimation of ‘micro-aliquots’ containing 5–10 grains of K-rich feldspar, and then combine this method with estimates of environmental dose rate to determine 10 new reliable and finite optical ages for the sedimentary deposits at LBB. Furthermore, by applying the LnTn method to circumvent truncation of the De distribution caused by the non-linearity of the dose response curve in the higher dose range, we could extend the site's luminescence-based chronology to span the interval ∼15–210 ka. The new chronology is in keeping with previous radiocarbon and U-series ages for the site's upper layers. We show that the low fading rate of micro-aliquots relative to using large aliquots composed of hundreds of grains lies in a brightness-based selection. By targeting bright grains with low fading rates, the need for fading corrections is greatly reduced and they can be made with a smaller uncertainty propagated through into the final age estimate, resulting in optical ages of improved accuracy and precision for volcanic sediments.
期刊介绍:
Quaternary Geochronology is an international journal devoted to the publication of the highest-quality, peer-reviewed articles on all aspects of dating methods applicable to the Quaternary Period - the last 2.6 million years of Earth history. Reliable ages are fundamental to place changes in climates, landscapes, flora and fauna - including the evolution and ecological impact of humans - in their correct temporal sequence, and to understand the tempo and mode of geological and biological processes.