COLLABORATIVE RESEARCH: Coordinated TIMS U-Series Dating and Paleoenvironmental Interpretations of Pedogenic Carbonate, Wind River Basin, Wyoming

在美国国家科学基金会（NSF）的支持下，我们已经证明，TIMS（热电离质谱）u系列碳酸盐岩定年可以提供精确的成土年表，并为适当的第四纪冲积矿床提供可靠的年龄（Sharp等人，已接受）。虽然内华达州凯尔峡谷以碳酸盐碎屑为主的冲积层的成壤碳酸盐U/Th比值过低，但怀俄明州风河盆地以花岗质碎屑为主的砾石中的成壤碳酸盐非常适合U系列测年。精确的u系列年龄（1- 2%,2）可以在几立方毫米的成壤碳酸盐上测量，并且只需要对碎屑230进行很小的校正。年龄组可以使用u系列结果固有的标准筛选可靠性。碎屑沉积与可测定碳酸盐聚集之间的时间差。如果要用最内层碎屑壳的u系列日期来测定宿主第四纪矿床的年代，这是一个关键参数。在风河流域估计为5+ 5kyr。对一套碳酸盐岩成土样品的O-和c -同位素分析表明，用u系列定年的碳酸盐岩成土样品可以建立一个时间分辨的稳定同位素古气候记录。需要资金进一步发展成壤碳酸盐u系列定年及其在落基山脉冰川年代学精化中的应用。重点将放在根据其他区域和全球气候记录解决布尔湖冰川推进的时间（在其类型地点）。此外，我们还提出了在晚更新世至晚更新世沉积物的残余土壤中表征成壤碳酸盐的时空聚集特征，并测量了u系列碳酸盐样品的O和c同位素组成。我们将解释这些数据，以提供贯穿伊利诺伊州晚期和威斯康星州冰川循环的风河盆地古环境变化的综合历史。最终，我们的目标是将基于土壤的古环境记录与古气候变化的地貌表达联系起来。保存完好的冰川冰碛和盆地的冰川-河流阶地。通过建立一个基于精确u系列年龄的共同时间框架。这是一个合作提案。沃伦·夏普和肯·路德维希（伯克利地质年代学中心）将负责u系列分析和年龄解释；罗恩·阿蒙森（加州大学伯克利分校）将在土壤学和稳定同位素分析和解释方面提供现场和实验室专业知识；奥利弗·查德威克（加州大学圣巴巴拉分校）将提供第四纪地质学、地貌学和土壤地层学方面的专业知识，并熟悉风河地区。

PROJECT SUMMARY With prior support from NSF, we have shown that TIMS (Thermal Ionization Mass Spectrometry) U-series dating of pedogenic carbonate can provide a precise chronology of pedogenesis and reliable ages for appropriate Quaternary alluvial deposits (Sharp et al., accepted). Though the U/Th ratios of pedogenic carbonate of carbonate-clast dominated alluvium at Kyle Canyon (Nevada) are too low for U-series dating, pedogenic carbonate in granitic-clast dominated gravels of the Wind River Basin (Wyoming) is highly suitable. Precise U-series ages (1-2 percent, 2) may be measured on a few cubic millimeters of pedogenic carbonate and require only very small corrections for detrital 230Th. Suites of ages may be screened for reliability using criteria inherent in the U-series results. The time lag between clast deposition and accumulation of datable carbonate.a critical parameter if U-series dates of innermost clast-rinds are to be used to date host Quaternary deposits.is estimated to be 5+ 5 kyr in the Wind River basin. O- and C-isotope analyses of a trial suite of pedogenic carbonate samples shows that a temporally resolved stable isotope paleoclimatic record can be constructed using pedogenic carbonate dated by U-series. Funds are requested to further develop U-series dating of pedogenic carbonate and its application to the refinement of a Rocky Mountain glacial chronology. Emphasis will be placed on resolving the timing of Bull Lake glacial advances (at their type locality) with respect to other regional and global climate records. Moreover, we propose to characterize the spatial and temporal accumulation of pedogenic carbonate in relict soils of Late-Middle to Late Pleistocene deposits, and measure the O- and C-isotopic compositions of carbonate samples dated by U-series. We will interpret these data to provide a comprehensive history of paleoenvironmental change in the Wind River Basin throughout much of the late Illinoian and Wisconsin glacial cycles. Ultimately, our goal is to correlate the soils-based paleoenvironmental record with the geomorphic expressions of paleoclimatic change.the well-preserved glacial moraines and glacio-fluvial terraces of the Basin.by establishing a common chronological framework based on precise U-series ages. This is a collaborative proposal. Warren Sharp and Ken Ludwig (Berkeley Geochronology Center) will be responsible for U-series analyses and age interpretations; Ron Amundson (U.C. Berkeley) will provide field and laboratory expertise in pedology and stable isotope analysis and interpretation; Oliver Chadwick (U.C. Santa Barbara) will provide expertise in Quaternary geology, geomorphology and soil stratigraphy as well as familiarity with the Wind River area.