230Th/U burial dating of ostrich eggshell
230Th/U burial dating of ostrich eggshell
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DOI：
10.1016/j.quascirev.2019.06.037
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发表时间：
2019-09
影响因子：
4
通讯作者：
Warren D. Sharp;C. Tryon;E. Niespolo;N. Fylstra;Alka Tripathy-Lang;J. Faith
中科院分区：
文献类型：
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作者：
Warren D. Sharp;C. Tryon;E. Niespolo;N. Fylstra;Alka Tripathy-Lang;J. Faith
获得含有中石器时代或旧石器时代中期(约30-300ka)考古资料的第四纪晚期陆相序列的准确和准确的年代可能是具有挑战性的。许多这样的层序超出了放射性碳测年的极限(∼50ka)，缺乏适合于40Ar/39Ar测年的火山灰。我们报告了一种大约是放射性碳测年(∼500ka)范围十倍的测年方法，该方法基于一种新的协议，用于鸵鸟蛋壳的230Th/U测年，鸵鸟蛋壳是非洲、近东和亚洲考古序列的常见组成部分。鸵鸟蛋壳中的铀通常在几十到数百ppb的水平上，是在埋葬后获得的。然而，根据测量的230Th/U年龄，当通过扩散校正铀吸收时，可以确定准确的埋藏年龄。(1)用激光烧蚀电感耦合等离子体质谱(ICPMS)研究了鸵鸟蛋壳中铀和常见的钍(232Th)浓度的空间分布；(2)对选择性磨损的蛋壳进行了溶液电感耦合等离子体质谱分析，测定了蛋壳外层和内层的~(230)Th/U年龄；(3)用简单的铀扩散吸收模型计算了~(230)Th/U埋藏年龄。我们通过比较230Th/U的埋藏年龄(中位不确定度2.3%，1SD)和相同蛋壳中碳酸盐的放射性碳测年来评估我们的方法。我们在九个蛋壳中的七个中发现了很好的一致性，证实了他们的230Th/U模型年龄的准确性。不能产生可靠的230Th/U年龄的蛋壳可以通过明显的230Th/U年龄的异常模式来识别，这提供了230Th/U数据固有的可靠性标准。鸵鸟蛋壳抵抗成岩作用，与骨骼和牙齿相比，简化了230Th/U测年。在六个大陆上发现的鸵鸟、麋鹿、丽亚和其他现存和灭绝的鸟类的蛋壳具有相似的结构和组成，这表明我们的蛋壳230Th/U测年方法可能适用于不同的晚第四纪陆地环境。
Obtaining precise and accurate dates for late Quaternary terrestrial sequences containing Middle Stone Age or Middle Paleolithic archaeological materials (ca. 30–300 ka) can be challenging. Many such sequences lie beyond the limit of radiocarbon dating (∼50 ka) and lack volcanic ashes suitable for40Ar/39Ar dating. We report a dating approach with about ten times the range of radiocarbon dating (∼500 ka) based on a novel protocol for230Th/U dating of ostrich eggshell, a common component of African, Near Eastern and Asian archaeological sequences. Uranium in ostrich eggshell, typically at levels of tens to hundreds of ppb, is acquired after burial. However, accurate burial ages can be determined from measured230Th/U ages when corrected for uranium uptake via diffusion. Using ostrich eggshells from a Pleistocene-Holocene east African site, we have: (1) characterized the spatial distribution of uranium and common thorium (232Th) concentrations in ostrich eggshell by laser ablation ICP-MS, (2) determined apparent230Th/U ages on outer and inner layers of eggshells by solution ICP-MS analyses of selectively abraded eggshells, and (3) calculated230Th/U burial ages using a simple model for diffusive uptake of uranium. We assess our method by comparing the230Th/U burial ages (median uncertainty 2.3%, 1 SD) with radiocarbon dates on carbonate from the same eggshells. We find good agreement in seven out of nine eggshells, confirming the accuracy of their230Th/U model ages. Eggshells that fail to yield reliable230Th/U ages may be recognized by anomalous patterns of apparent230Th/U ages, providing a reliability criterion innate to the230Th/U data. Ostrich eggshells are resistant to diagenesis simplifying230Th/U dating compared to bones and teeth. Eggshells of ostrich, emu, rhea and other living and extinct ratites found on six continents share similar structure and composition, suggesting our new approach to230Th/U dating of eggshell may be applicable in diverse late Quaternary terrestrial settings.