气候变化领域集成服务门户(CCPortal): Improved accuracy of U-series and radiocarbon dating of ostrich eggshell using a sample preparation method based on microstructure and geochemistry: A study from the Middle Stone Age of Northwestern Ethiopia

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DOI	10.1016/j.quascirev.2020.106525
	Improved accuracy of U-series and radiocarbon dating of ostrich eggshell using a sample preparation method based on microstructure and geochemistry: A study from the Middle Stone Age of Northwestern Ethiopia
	Loewy S.L.; Valdes J.; Wang H.; Ingram B.; Miller N.R.; Medina K.D.L.C.; Roberts A.; Yanny S.; Banner J.; Feseha M.; Todd L.; Kappelman J.
发表日期	2020
ISSN	0277-3791
卷号	247
英文摘要	The Middle Stone Age (MSA) is important to studies of human evolution because it witnessed the origin of modern Homo sapiens and its dispersal out of Africa and across the rest of the Old World. Obtaining accurate ages for these and other events that occurred during this time interval is of critical importance. Ostrich eggshell (OES) is commonly found in MSA sites, and OES calcite can be dated by radiocarbon and U-series geochronologic techniques. It is important to understand how both techniques are potentially compromised when the eggshell's pore clusters and intercrystalline microporosity are infilled with younger calcite and/or soil-derived detrital materials. We investigated this question by using high-resolution X-ray computed tomography (HRXCT) to reveal the extent and three-dimensional structure of the pore clusters, and element mapping to evaluate concentrations of detrital elements in modern versus ancient OES within the pore clusters and the crystal (outer) and cone (inner) layers relative to the palisade (central) layer. HRXCT results support earlier findings that OES pores are generally composed of one to several openings on the cone surface that develop into a complex three-dimensional cluster of anastomosing and branching pores that extend through the palisade layer to exit on the crystal surface. These hollow pore clusters provide a considerable total volume for the potential ingress of detrital materials. Element mapping revealed high concentrations of detrital mineral indicator elements (Al, Mg) in ancient relative to modern OES, and in the cone and crystal layers relative to the palisade layer. Within the palisade layer of ancient OES, there are relatively high detrital mineral indicator element concentrations within filled pore clusters. Extracted pore cluster infill from the palisade layer yields significantly higher and more variable concentrations of 232Th (2,200-10,000 ppt) and 238U (35–54 ppb) relative to the non-porous palisade layer (150–3,100 ppt 232Th, and 19–25 ppb 238U). Based on these results, we developed a mechanical preparation method that combines the removal of the pore cluster infill with the more common removal of the cone and crystal layers. Using this method, U–Th analyses of four OES from an MSA archaeological site in NW Ethiopia yielded a mean age of 75.7±4.7 ka (2 SD). The inclusion of the pore cluster infill with the palisade in a different OES from the same site produced a much younger age of 53±1.2 ka (1 SE). Splits of several of these same OES samples prepared by this new method yield AMS 14C ages that are beyond the range of 14C dating (∼50 ka), while ∼60% of the OES analyses of the palisade layer that retained the pore cluster infill yielded much younger ages (27–38 ka). Our results demonstrate that dating OES that retains the pore cluster infill shifts both U–Th and 14C analyses to younger ages. In order to obtain more precise and accurate ages, we recommend that preparation of OES for both U-series and 14C dating include the mechanical removal of both the pore cluster infill and the cone and crystal layers in order to more fully account for the incorporation of Th, U, and C from detrital and authigenic minerals within the OES structure. © 2020 Elsevier Ltd
英文关键词	Africa; AMS 14C dating; Geochronology; Human evolution; Middle Stone Age; Ostrich eggshell; Quaternary; U–Th series Dating
语种	英语
scopus关键词	Birds; Calcite; Computerized tomography; Cones; Crystals; Infill drilling; Mapping; Archaeological site; Authigenic minerals; Element concentrations; High-resolution X-ray computed tomographies; Sample preparation methods; Three-dimensional clusters; Three-dimensional structure; Variable concentration; Crystal structure; accelerator mass spectrometry; dispersal; eggshell; geochemical survey; geochronology; hominid; human evolution; Mesolithic; microstructure; radiocarbon dating; uranium series dating; Ethiopia; Homo sapiens; Struthioniformes
来源期刊	Quaternary Science Reviews
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/151312
作者单位	Department of Geological Sciences, The University of Texas, Austin, TX, United States; National Science Foundation Research Experience for Undergraduates Program, Department of Anthropology, The University of Texas, Austin, TX, United States; Geochronology Laboratories, University of Illinois at Urbana-Champaign, Champaign, IL, United States; Now Interdisciplinary Research Center of Earth Science Frontier, Beijing Normal University, China; Paleoanthropology and Paleoenvironment Program, Addis Ababa University, Addis Ababa, Ethiopia; Department of Anthropology, The University of Texas, Austin, TX, United States
推荐引用方式 GB/T 7714	Loewy S.L.,Valdes J.,Wang H.,et al. Improved accuracy of U-series and radiocarbon dating of ostrich eggshell using a sample preparation method based on microstructure and geochemistry: A study from the Middle Stone Age of Northwestern Ethiopia[J],2020,247.
APA	Loewy S.L..,Valdes J..,Wang H..,Ingram B..,Miller N.R..,...&Kappelman J..(2020).Improved accuracy of U-series and radiocarbon dating of ostrich eggshell using a sample preparation method based on microstructure and geochemistry: A study from the Middle Stone Age of Northwestern Ethiopia.Quaternary Science Reviews,247.
MLA	Loewy S.L.,et al."Improved accuracy of U-series and radiocarbon dating of ostrich eggshell using a sample preparation method based on microstructure and geochemistry: A study from the Middle Stone Age of Northwestern Ethiopia".Quaternary Science Reviews 247(2020).