Collaborative Research: Theoretical and Paleoenvironmental Implications of Dating and Characterizing Loess Deposits in the Upper Midwest

该奖项是根据2009年《美国复苏和再投资法案》(Public Law 111-5)资助的。美国中西部的关键地貌事件的绝对日期和年龄严重缺乏，主要是因为用于放射性碳测年的冰川沉积物中缺乏木材。这一合作研究项目将解决中西部冰川和冰后环境中存在的地质年代学信息匮乏的问题，方法是丰富和提高冰后年代学，从而促进更好地了解中西部上段更新世晚期地貌演变的时间，这对古环境模型非常重要。为了帮助实现这一目标，研究人员将用光激发发光(OSL)技术测定黄土(风积粉土)的沉积年代。这样做将确定产生黄土的地貌/冰川事件的年龄，例如冰川湖的排水或冰川回升。除了增加有关黄土沉积日期的关键信息外，该项目还将使研究人员能够评估薄黄土沉积物可以在多大程度上使用OSL测年，以及这项技术的局限性。由于中西部的大多数黄土沉积物厚度都不到两米，因此由于表面污染和混合过程，它们被认为是无法确定年代的。研究人员将确定黄土的最小厚度，以便进行准确的OSL测年，并为其他希望采样此类沉积物的研究人员提供经验指导。他们的目标是开发一套新的第四纪矿藏，用于测年，具有既定的协议和警告。该项目将集中在威斯康星州和密歇根州的几个中小型黄土层的研究地点。在这些地点中的每一个，研究人员预计，黄土中几个OSL样本的平均OSL年龄将确定地貌事件的最可能年龄。黄土的OSL测年可能是确定这些地貌事件的年代的唯一方法。因为这项研究将以高度地理的方式进行；黄土将被系统地采样，并密切关注样品的空间分布。这样，可以确定黄土沉积的空间特征，更清楚地阐明黄土的来源，为中西部冰川文献提供有价值的信息和见解，并将产生方法论上的贡献。该项目将丰富地理学家、生态学家、古环境学家和地球科学家使用的年代学框架。它将为长期困扰土壤学家和地质制图人员的薄黄土和覆盖砂层提供重要的特征和空间数据。对中西部上段的冰川消融年代学有一个更清晰、更准确的理解，这对于在古环境模拟和土地利用方面继续取得进展至关重要。该项目还将为研究生和本科生提供良好的教育和培训机会。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Absolute dates and ages for key geomorphic events in the Midwest U.S. are sorely lacking, mainly because of the paucity of wood in glacial deposits for radiocarbon dating. This collaborative research project will address the paucity of geochronologic information that exists for Midwestern glacial and postglacial environments by enriching and making more precise the post-glacial chronology, thereby facilitating a better understanding of the timing of Late Pleistocene landscape evolution for the upper Midwest so important for paleoenvironmental models. To help accomplish this goal the investigators will date loess (wind-deposited silt) deposits with optically stimulated luminescence (OSL) techniques. Doing so will establish the age of the geomorphic/glacial event that sourced the loess, such the draining of a glacial lake or a glacial readvance. In addition to adding critical information regarding the dates of loess deposits, the project will enable the investigators to evaluate the extent to which thin loess deposits can be dated with OSL and the limits to this technique. Because most loess deposits in the Midwest are thinner than two meters in depth, they had been deemed undateable because of surface contamination and mixing processes. The investigators will determine the minimum thickness of loess that allows for accurate OSL dating and provide empirical guidelines for other researchers who wish to sample such deposits. Their goal is to open up a new suite of Quaternary deposits for dating with established protocols and caveats. The project will be centered at several research sites in small to medium-sized loess sheets in Wisconsin and Michigan. At each of these sites the investigators expect that the mean OSL age of several OSL samples in loess will establish the most likely age of a geomorphic event. OSL dating of loess may be the only way that the dates of these geomorphic events can be determined. Because this research will be performed in a highly geographic manner; loess will be sampled systematically, with a keen eye on the spatial spread of the samples. In this way, the spatial character of the loess deposits can be determined and loess sources more clearly elucidated.The project will provide valuable information and insights for the Midwestern glacial literature, and it will yield methodological contributions. The project will enrich the chronologic framework used by geographers, ecologists, paleoenvironmentalists, and geoscientists. It will provide important characterization and spatial data on the thin loess and cover sand deposits that long have puzzled and confounded soil scientists and geologic mappers. Developing a clearer and more accurate understanding of the deglacial chronology for the upper Midwest is essential for continued advances in paleoenvironmental modeling and land use. The project also will provide excellent education and training opportunities for graduate and undergraduate students.