Developing a Cosmogenic Chronology of Late-Pleistocene Glaciation, Wallowa Mountains, Oregon

9725554克拉克冰川记录是美国西部晚更新世气候变异性的重要记录，在许多地区也是唯一的记录。阿尔卑斯山冰川对相对较小的气候扰动敏感，并能对相对较小的气候变化(约1(-2(K))量级)做出快速响应(101年至102年期间约100101年)。因此，建立高山冰川年表是提取与晚更新世气候变化有关的古气候信息的重要战略。使用宇宙成因核素对来自冰雹的大巨石进行曝光年代测定，为编制这种年代学提供了巨大的希望，但这种曝光年代年代学能够达到的分辨率水平仍然存在问题。我们的主要目标是直接测定瓦洛瓦山脉保存完好的冰川序列的年代，或使用宇宙成因核素来开发山脉冰川波动的数字年表。此外，我们将能够解决这样一个问题，即具有相似风化特征的、相距较近、保存良好的冰雹的暴露年龄是否可以解决冰雹形成时间上的重大差异(即5-10ka)。无论分辨率问题如何，这些数据将有助于现有冰川记录的地理覆盖面，以检查晚更新世山脉冰川的空间和时间变异性。作为对基于宇宙成因核素的暴露年龄年代学评估的进一步贡献，我们还建议对北部黄石出口冰川沉积的冰雹进行采样。已有的U系列年代学和放射性碳年代学表明，冰雹代表了14~30ka之间出口冰川的3次主要进动。因此，我们的黄石公园数据将比较宇宙成因年代学和已建立的(U系列)年代学的年龄分辨率。

9725554 Clark Glacial record are an important and, in many areas, the only archive of late-Pleistocene climate variability from the western U.S. Alpine glaciers are sensitive to relatively small climatic perturbations and can respond rapidly (on order of 100-101 km within 101-102yr) to relatively small climate change (on order of 1(-2( K). Developing a chronology of alpine glaciation thus represents a significant strategy for extracting paleoclimate information associated with late-Pleistocene climate change. Exposure-ages of large boulders from moraines using cosmogenic nuclides offer great promise for developing such chronologies, but questions remain as to the level of resolution that such an exposure-age chronology can achieve. Our primary objective is to directly date a well-preserved moraine sequence in the Wallowa Mountains, OR using cosmogenic nuclides in order to develop a numerical chronology of mountain glacier fluctuations. In addition, we will be able to address the issue of whether exposure ages of closely spaced; well-preserved moraines having similar weathering characteristics can resolve significant differences (i.e., 5-10 ka) in the timing of moraine formation. Regardless of the resolution issue, these data will contribute geographic coverage to existing glacial records for examining spatial and temporal late-Pleistocene mountain glacier variability. As a further contribution to evaluating an exposure-age chronology based on cosmogenic nuclides, we also propose sampling moraines deposited by the northern Yellowstone outlet glacier. The existing U-series and radiocarbon chronology indicate that the moraines represent 3 major advances of the outlet glacier between 14 and 30 ka. Our Yellowstone data thus will compare the age resolution of a cosmogenic chronology with an established (U-series) chronology.