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（公法111-5）资助的。美国中西部主要地貌事件的绝对年代和年龄严重缺乏，主要是因为冰川沉积物中缺乏用于放射性碳定年的木材。这个合作研究项目将通过丰富和更精确的后冰期年代学来解决中西部冰川和后冰期环境地质年代学信息的缺乏，从而促进对中西部上游晚更新世景观演化时间的更好理解，这对古环境模型非常重要。为了实现这一目标，研究人员将利用光激发发光（OSL）技术测定黄土（风沉积泥沙）沉积物的年代。这样做将确定形成黄土的地貌/冰川事件的年代，如冰湖排水或冰川推进。除了增加有关黄土沉积物日期的关键信息外，该项目还将使研究人员能够评估用OSL测定薄黄土沉积物日期的程度以及该技术的局限性。由于美国中西部的大多数黄土沉积物深度都不到两米，由于地表污染和混合过程，它们被认为是无法确定的。研究人员将确定黄土的最小厚度，以允许准确的OSL测年，并为其他希望对此类沉积物进行采样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沉积层，根据已建立的协议和警告进行定年。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研究地点。在每一个这样的地点，研究人员期望黄土中几个OSL样品的平均OSL年龄将建立一个地貌事件的最可能的年龄。黄土的OSL测年可能是确定这些地貌事件日期的唯一方法。因为这项研究将以高度地理的方式进行；黄土将进行系统采样，并对样品的空间分布进行敏锐的观察。这样可以确定黄土沉积的空间特征，更清楚地说明黄土的来源。该项目将为中西部冰川文献提供有价值的信息和见解，并将产生方法学上的贡献。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科学家和地质制图者的薄黄土和覆盖砂沉积物提供重要的表征和空间数据。对中西部上游的去冰期年代学有一个更清晰、更准确的认识，对古环境模拟和土地利用的持续发展至关重要。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.