COLLABORATIVE RESEARCH: Dating Quaternary Deposits and Soils with TIMS U-Series on Pedogenic Carbonate and Silica

9810209路德维希基金被要求进一步开发和应用TIMS（热电离质谱）U系列测年成壤碳酸盐和二氧化硅。该研究将通过在两个气候和岩性不同的地区开展详细工作，寻求了解化学/矿物学特征的微取样碎屑皮上U系列日期的潜力和局限性。两个地方将进行研究，使用的技术，建立在最近的结果，独立研究的PI的。凯尔峡谷（内华达州）提供了一系列从全新世到780 ka的碳酸盐碎屑冲积层和地貌表面，而风河盆地（怀俄明州）提供了一系列从全新世到早更新世的花岗岩碎屑为主的冲积层。在这两个地方，第四纪地质和土壤学已经很好地研究了一个或多个调查员的这一建议。这是三个机构的合作提案：伯克利地质年代学中心的肯·路德维希和沃伦·夏普将负责取样和铀系列分析，使用BGC新的TIMS设施和清洁实验室;加州大学的罗恩·阿蒙森。伯克利和加州大学的奥利弗·查德威克。圣巴巴拉将提供第四纪地质学和土壤学方面的实地和实验室专业知识，以及对研究地点的熟悉。所有指定的研究人员将参与成土碳酸盐和二氧化硅的化学和微观表征，Amundson将负责稳定同位素工作和解释。Ludwig和J.B.最近在内华达州的火山口平原进行的一项研究，其中对单个碳酸盐/二氧化硅外壳的亚毫米层进行微取样，以避免碎屑污染，将应用于这两个地方矿床的仔细表征的碎屑外壳。将探讨该方法的局限性，包括碎屑230 Th校正的可靠性，开放系统的结构和地球化学指标，以及使用234 U/238 U将该方法扩展到早更新世的实用性。全新世碎屑分析在利用最内层碎屑岩的U系列测年来确定第四纪沉积物本身的年代时，了解这种时滞（以及它在不同气候和岩性背景下的变化）是必不可少的。为了探索样本大小和空间分辨率的限度，需要发展一些微取样技术，但这可以用相对简单的设备来完成。实验室的挑战主要涉及小样本230 Th分析，其中一个PI具有丰富的经验。测年研究的结果将用于了解凯尔峡谷侵蚀和沉积的历史和时间，以及风河流域的冰川事件。数量有限的稳定同位素分析将被用来评估作为一个古气候记录，以及检查开放系统的历史更新世中期和早期的外皮的有用性。

9810209 Ludwig Funds are requested to further develop and apply TIMS (Thermal Ionization Mass Spectrometry) U-series dating to pedogenic carbonate and silica. The research will seek to understand the potential and limitations of U-series dates on chemically/mineralogically-characterized, micro-sampled clast rinds by detailed work in two climatically and lithologically and distinct areas. Two localities will be studied, using techniques that build on the results of recent, independent studies by the PI's. Kyle Canyon (Nevada) provides a sequence of carbonate-clast alluvial deposits and morphologic surfaces ranging from Holocene to 780 ka, whereas the Wind River Basin (Wyoming) provides a sequence of granitic-clast dominated alluvial deposits from Holocene to early Pleistocene age. In both localities, the Quaternary geology and pedology have been well studied by one or more of the investigators of this proposal. This is a collaborative proposal among 3 institutions: Ken Ludwig and Warren Sharp at the Berkeley Geochronology Center will be responsible for sampling and uranium-series analysis, using the new TIMS facility and clean lab at BGC; Ron Amundson at U.C. Berkeley and Oliver Chadwick at U.C. Santa Barbara will provide field and laboratory expertise in Quaternary geology and pedology, as well as familiarity with the study localities. All of the named investigators will participate in the chemical and microscopic characterization of the pedogenic carbonate and silica, and Amundson will be responsible for the stable-isotopic work and interpretation. The single-sample/single-date approach developed by Ludwig and J.B. Paces for a recent study at Crater Flat, Nevada, in which sub-millimeter laminae of individual carbonate/silica rinds are micro-sampled to avoid detrital contamination, will be applied to carefully-characterized clast rinds of the deposits in both localities. The limitations of the approach will be explored, including the reliability of the detrital 230Th corrections , the textrual and geochemical indicators of open systems, and the practicality of extending the method into the Early Pleistocene using 234U/238U. Analyses of Holocene clast-rinds. Knowledge of this time-lag (and its variability in different climatic and lithologic contexts) will be essential in using U-series dates of innermost clast-rinds to date the Quaternary deposits themselves. Some development of micro-sampling techniques will be required to explore the limits of sample size and spatial resolution, but this can be done with relatively modest equipment. The laboratory challenges involve mainly those of small-sample 230Th analyses, in which one of the PI's has extensive experience. The results of the dating studies will be applied to understanding the history and timing of erosion and sedimentation in Kyle Canyon, and of glacial events in the Wind River Basin. A limited number of stable-isotope analyses will be used to evaluate the usefulness of the rinds as a paleoclimate record as well as to check for open-system histories of the mid-and early Pleistocene rinds.