Doctoral Dissertation Improvement Grant: Oxygen Isotope Signatures and the Identification of Chert in the Southern Plains

在David J.Meltzer博士的监督下，Joanna Roberson将研究氧同位素分析作为确定北美西部南部平原冰河时代晚期人们使用的一种隐晶沉积岩来源的方法的应用。硅质岩的特性使其成为生产石器的绝佳材料，但由于这种石头的露头在地质上并不常见，而且分散在南部平原，这些猎人和采集者经常不得不在很远的地方追踪才能获得这些石头。因此，知道石头是在哪里开采的，就成为了一种手段，揭示了人类为了获得这种对他们的工具制造至关重要的资源需要走多远，从而打开了一扇重要的窗口，让我们了解人类对与今天截然不同的景观的适应。然而，识别正在使用的石头的来源是复杂的，尤其是因为源于硅质岩本身的问题。复杂的形成过程可以在硅质岩中产生巨大的多样性，包括可见的、微观的和化学变化。此外，一些硅质岩具有广泛的地理分布，而另一些硅质岩具有在其他地方出现的相似之处，还有一些可能没有记载，甚至今天可能看不到。这项研究将通过元素氧的同位素分析来测试鉴定硅质岩的可行性，这是一种在地质学中常见的技术，但在考古学中并不经常用于硅质岩。虽然其他方法受到硅质岩变化的阻碍，但氧同位素分析实际上可能是有益的。氧同位素比值(18O/16O)因氧存在的物质的环境来源而异，因此硅质岩的同位素组成反映了沉积物的原始来源、硅质岩沉积的当地条件以及任何沉积后的影响。因此，同位素比率有望在硅质岩来源之间表现出可测量的差异。如果成功，这种方法可以通过消除鉴定方法中的歧义，通过区分视觉上相似的材料，以及通过识别单一材料类型的空间分离露头之间的可变性，来改进石材来源。虽然这项研究将重点放在南部平原的硅质岩来源和文物上，但如果这种方法被证明是可行的，它将对任何地理区域和年代时期的考古学家大有用处，因此有望在这一地区以外做出重要贡献。此外，通过将考古学家和地质学家聚集在一起，它将产生更广泛的影响，促进跨学科关系，并鼓励其他人从不同和非传统来源寻求研究问题的解决方案。这种合作将对许多学科做出巨大贡献，因为技术和信息在研究领域之间共享。

Under the supervision of Dr. David J. Meltzer, Joanna Roberson will investigate the application of oxygen isotope analysis as a method for identifying the source of the chert - a cryptocrystalline sedimentary rock - used by late Ice Age peoples on the Southern Plains of western North America. Chert has properties that make it an excellent material for producing stone tools, but because outcrops of this stone are geologically uncommon and scattered in the Southern Plains, these hunters and gatherers often had to track great distances across the landscape to obtain the stone. Thus, knowing where stone was quarried becomes a means of revealing just how far groups had to move to obtain this resource vital to their tool-making, and therefore opens an important window into understanding human adaptations to what was a very different landscape than is present today.However, identifying the source of the stone in use is complicated, not least because of problems that stem from the nature of chert itself. Complex formation processes can create great diversity among cherts, including visible, microscopic, and chemical variations. In addition, some cherts have extensive geographic distributions, while others have look-alikes that occur elsewhere, and still others may not be documented or even visible today. This research will test the feasibility of identifying chert through isotopic analyses of elemental oxygen, a technique common in geology, but not regularly used on chert in archaeology. While other methods are hindered by the variations in chert, oxygen isotope analysis may, in fact, benefit. Oxygen isotopic ratios (18O/16O) vary according to the environmental origin of the material in which the oxygen occurs, such that the isotopic make-up of chert reflects the original sources of the sediments, the local conditions of chert deposition, and any post-depositional influences. Thus, isotopic ratios are expected to exhibit measurable variation between chert sources. If successful, this method can improve stone sourcing by eliminating ambiguity in identification methods, by discriminating between visually similar materials, and by recognizing variability between spatially separated outcrops of a single material type. Although this study will focus on chert sources and artifacts from the Southern Plains, if the method proves viable it will be of great use to archaeologists working in any geographic region and chronological period, and is thus poised to make important contributions beyond this area. Moreover, by bringing together archaeologists and geologists, it will have a broader impact by fostering inter-disciplinary relationships and encouraging others to seek solutions to research problems from diverse and unconventional sources. Such collaborations will make great contributions to numerous disciplines, as techniques and information are shared between research fields.