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

在NSF先前的支持下，我们已经表明，土壤成因碳酸盐的TIMS(热电离质谱)U系列测年可以提供准确的成壤作用年代学和合适的第四纪冲积沉积物的可靠年龄(Sharp等人，接受)。尽管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的U/Th值太低，无法进行U系列测年，但风河盆地(怀俄明州)花岗岩碎屑为主的砾石中的成壤碳酸盐是非常合适的。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，只需要对230碎屑进行非常小的校正。可以使用U系列结果中固有的标准来筛选年龄组的可靠性。风河盆地碎屑沉积与碳酸盐岩堆积之间的时间差估计为5.5Kyr。一套土壤成因碳酸盐样品的氧和碳同位素分析表明，利用U系列测年的土壤成因碳酸盐可以建立时间分辨的稳定同位素古气候记录。需要资金进一步开发土壤成因碳酸盐的U系列测年，并将其应用于完善落基山脉冰川年代学。重点将放在解决与其他区域和全球气候记录有关的牛湖冰川推进的时间(在其类型地点)。此外，我们还提出了土壤碳酸盐在晚-中-晚更新世沉积残积土壤中的时空积累特征，并测定了碳酸盐样品的U系列测年的氧、碳同位素组成。我们将解释这些数据，以提供风河流域在伊利诺斯晚期和威斯康星州冰川周期的大部分时间内的古环境变化的全面历史。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相关联。通过建立基于精确U系列年龄的共同年代学框架，研究保存完好的冰川冰雹和盆地的冰河阶地。这是一份协作性提案。Warren Sharp和Ken Ludwig(加州大学伯克利分校地质年代学中心)将负责U系列分析和年龄解释；Ron Amundson(加州大学伯克利分校)将提供土壤学和稳定同位素分析和解释方面的野外和实验室专业知识；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、地貌学和土壤学方面的专业知识以及对风河地区的熟悉程度。

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.