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

这项合作的工作将提供关键信息，以解决北美第四纪地质学的一个长期问题：将反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的冰期的了解是从一种代用物——18o年的节奏变化中推断出来的，这种变化反映了被锁在冰中的海水和淡水之间的平衡。这些变化可以通过将它们与地球对太阳的倾斜度和轨道的偏心率的变化联系起来来确定时间——这两个因素都会改变地球表面接收到的能量。然而，关于这些冰在大陆表面的分布几乎没有任何信息，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。在这个团队首创的宇宙核素技术出现之前，通过绘制大陆上的山丘来确定冰川前进的年代一直是极其困难的。铍-10/铝-26测年法是一种提供其他计时器无法提供的分辨率的技术。对从密苏里州向北进入爱荷华州的冰川进行测年，将得出至少五个劳伦泰德冰盖最南端移动的直接测年结果。该小组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的广泛合作，该小组将能够将该技术转移到对不同山丘相关感兴趣的地质水文测绘领域。此外，该小组已经收到了广泛的报道，因为以前的工作是关于含化石沉积物的年代测定，以及大陆最古老的年代测定，并希望继续这种公众对宇宙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.