Collaborative Research: An Absolute Chronology of the Southernmost Advances of the Laurentide Ice Sheet

这项合作下的工作将提供关键信息，以解决北美第四纪地质学中的一个长期问题：将重复冰川作用的大陆物理证据与海洋氧同位素记录相关联。在很大程度上，我们对过去几百万年冰川的了解是从一个替代物中推断出来的，d18 O的节律性变化反映了海水和冰中淡水之间的平衡。这些变化可以通过将它们与地球对太阳的倾斜度和轨道偏心率的变化联系起来来确定日期-这两个因素都会改变表面接收的能量。然而，关于冰在大陆表面分布的信息很少，关于为什么冰的周期性变化不能用轨道变化来解释的信息也很少。通过绘制大陆上冰碛物的地图来确定冰川前进的时间是非常困难的，直到这个团队开创的宇宙成因核素技术的出现。 铍-10/铝-26测年技术提供了其他计时器无法提供的分辨率。从密苏里州向北到爱荷华州的冰碛物的年代测定将为劳伦泰德冰盖最南端的至少五次前进提供直接的年代。该团队将能够为有关冰盖在上新世-更新世气候中的作用以及它们在气候突变中的作用的问题提供数据。通过与国家地质调查局的广泛合作，该团队将能够将该技术转移到对关联不同冰碛物感兴趣的水文地质测绘领域。此外，该小组还广泛报道了以前对含化石沉积物以及大陆最古老的年代测定工作的报道，并期望继续公众对宇宙成因核素年代测定技术应用的兴趣。

Work under this collaborative will provide key information to address a long-standing issue in North American Quaternary geology: correlating continental physical evidence of repeated glaciations with the marine oxygen isotope record.To a great extent, what we know about the glaciations of the last several million years has been deduced from a proxy - rhythmic variations in d18O that reflect the balance between seawater and freshwater locked up in ice. These variations can be dated by relating them to changes in the Earth's inclination towards the Sun, and the eccentricity of the orbit - both factors which change how much energy the surface receives. However, there is little to no information on the distribution of that ice over the continental surfaces, and little information on why there are changes in ice periodicity not explained by orbital changes.Dating of glacial advances by the mapping of tills on the continent has been extremely difficult until the advent of a cosmogenic nuclide technique pioneered by this team. Beryllium-10/Aluminium-26 dating is a technique that provides resolution not provided by other chronometers. Dating of tills from Missouri northwards into Iowa will yield direct dates for at least five of the southernmost advances of the Laurentide Ice Sheet. The team will be able to provide data for questions about the role of ice sheets in Plio-Pleistocene climate, and their role in abrupt climate change.Through extensive collaboration with state geological surveys, the team will be able to transfer the technique into areas of geohydrological mapping that are interested in correlating different tills. In addition, the team has received extensive coverage for previous work on dating of fossil bearing sediments as well as the continent's oldest dated till, and expects to continue this public interest in the applications of cosmogenic nuclide dating techniques.