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

合作研究：中西部上部黄土矿床测年和表征的理论和古环境意义

• 批准号: 0850830
• 负责人: Steven Forman
• 金额: $ 7.33万
• 依托单位: University of Illinois at Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2013-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0850830&HistoricalAwards=false
• 关键词: Collaborative; Research; Theoretical; Paleoenvironmental; Implications

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.

该奖项根据 2009 年美国复苏和再投资法案（公法 111-5）提供资金。美国中西部关键地貌事件的绝对日期和年龄非常缺乏，主要是因为冰川沉积物中缺乏用于放射性碳测年的木材。 该合作研究项目将通过丰富和更加精确的冰期后年代学来解决中西部冰期和冰期后环境中存在的地质年代学信息的缺乏问题，从而促进更好地了解中西部地区晚更新世景观演化的时间，这一点非常重要用于古环境模型。 为了帮助实现这一目标，研究人员将利用光激发光（OSL）技术对黄土（风沉积淤泥）沉积物进行测定。 这样做将确定黄土来源的地貌/冰川事件的年龄，例如冰川湖的排水或冰川的重新推进。 除了添加有关黄土沉积年代的关键信息外，该项目还将使研究人员能够评估用 OSL 测定薄层黄土沉积物的年代的程度以及该技术的局限性。 由于中西部的大多数黄土沉积物的厚度都小于两米，因此由于表面污染和混合过程，它们被认为无法测年。 研究人员将确定黄土的最小厚度，以便进行准确的光释光测年，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南。 他们的目标是开辟一套新的第四纪矿床，用于按照既定协议和注意事项进行测年。 该项目将集中在威斯康星州和密歇根州中小型黄土片的几个研究地点。 在每个地点，研究人员预计黄土中多个 OSL 样本的平均 OSL 年龄将确定地貌事件最可能的年龄。 黄土的光释光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性的方式进行；将系统地对黄土进行采样，并密切关注样本的空间分布。 通过这种方式，可以确定黄土沉积物的空间特征，并更清楚地阐明黄土来源。该项目将为中西部冰川文献提供有价值的信息和见解，并将产生方法论贡献。 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框架。 它将提供有关薄黄土和覆盖沙沉积物的重要特征和空间数据，这些沉积物长期以来一直困扰着土壤科学家和地质绘图人员。 对中西部上部冰消年表有更清晰、更准确的了解对于古环境模型和土地利用的持续进步至关重要。 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。