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

9725836查德威克需要资金，以进一步开发和应用热电离质谱(TIMS)U系列测年技术，以测定成土碳酸盐和硅石的年龄。这项研究将通过在两个气候和岩石学截然不同的地区进行详细研究，试图了解U系列测年在化学/矿物学特征的微采样碎屑皮上的潜力和局限性。两个地区将被研究，使用的技术建立在P.I.S最近的独立研究结果的基础上。内华达州的凯尔峡谷提供了从全新世到780ka的碳酸盐碎屑冲积沉积和地貌面，而风河盆地(怀俄明州)从全新世到早更新世提供了以花岗岩碎屑为主的冲积沉积序列。在这两个地方，第四纪地质学和土壤学都得到了这一提议的一名或多名调查者的充分研究。这是三个机构的合作方案：伯克利地质年代学中心的Ken Ludwig和Warren Sharp将使用新的TIMS设施和BGC的清洁实验室负责采样和铀系列分析；加州大学伯克利分校的Ron Amundson和加州大学圣巴巴拉分校的奥利弗·查德威克将提供第四纪地质学和土壤学的野外和实验室专业知识，并熟悉研究地点。所有被点名的调查人员将参与成壤碳酸盐和二氧化硅的化学和微观表征，阿蒙森将负责稳定同位素工作和解释。路德维希和J.B.佩斯为最近在内华达州陨石坑平地进行的一项研究开发的单一样品/单一日期方法，即对单个碳酸盐/二氧化硅表层进行亚毫米级的微采样，以避免碎屑污染，将应用于两地仔细描述的矿床碎屑皮。将探讨该方法的局限性，包括碎屑230校正的可靠性，开放系统的结构和地球化学指标，以及利用234U/238U将该方法推广到早更新世的可行性。对全新世碎屑的分析将特别有意义，因为这些样品将提供对碎屑沉积和可测定日期的碳酸盐或碳酸盐/硅屑堆积之间可能存在的时差的理解。了解这一时间滞后(以及它在不同气候和岩性背景下的变异性)将是使用最内部碎屑岩U系列测年来确定第四纪矿床年龄的关键。要探索样本大小和空间分辨率的极限，将需要开发一些微采样技术，但这可以用相对较小的设备来完成。实验室的挑战主要涉及小样本230分析，其中一位私家侦探S拥有丰富的经验。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。有限数量的稳定同位素分析将被用于评估冰盖作为古气候记录的有用性，以及检查更新世中期和早期冰盖的开放系统历史。

9725836 Chadwick 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 distinct areas. Two localities will be studied, using techniques that build on the results of recent, independent studies by the P.I.'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 analyses 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 textural 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 will be of special interest, as these samples will provide an understanding of the likely time-lag between clast deposition and the accumulation of datable carbonate or carbonate/silica 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 P.I.'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.