Doctoral Dissertation Research: The Origin and Development of Cryoplanation Terraces

博士论文研究：冰冻梯田的起源与发展

• 批准号: 1817665
• 负责人: Frederick Nelson
• 金额: $ 1.66万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-04-01 至 2019-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1817665&HistoricalAwards=false
• 关键词: Doctoral; Dissertation; Research; Origin; Development

This doctoral dissertation research project will determine the age and development rates of cryoplanation terraces, terraces formed through the erosive action of snow and frost. Cryoplanation terraces are large upland landform features that give the impression of gigantic staircases, found in periglacial, or cold but nonglacial environments. Although these elevated bedrock terraces have been identified and discussed in scientific literature for more than a century, debate continues about the nature of the processes responsible for their formation. Development rates, calculated from dates of rock exposure across terrace treads, will be used to test one of the more prominent hypotheses advanced in the literature. This hypothesis states that these terraces are formed through intensified erosion associated with snowbanks that last well into the summer months. Recent methodological developments in geochemistry, specifically the method known as cosmogenic nuclide dating, will provide the infusion of contemporary technology necessary to make progress on this long-standing scientific issue, and has the potential to make transformative advances in the understanding of landscape development in periglacial regions. Results from this research will be shared with the U.S. National Park Service and used to enhance park management as well as the experiences of park visitors through development of interpretive displays and trail guides in several national parks and monuments. Further, the project will enable a graduate student to establish an independent research career.The great antiquity of cryoplanation terraces makes terrestrial cosmogenic nuclides the most appropriate dating method for determining their age and rates of development. Rock samples for cosmogenic nuclide dating were collected from two locations in the interior of Alaska using a transect-based sampling strategy across individual terrace treads. Dating the exposure of the clastic rocks (clasts) will facilitate calculation of erosion rates for individual terraces, and can be compared to known erosion rates at existing late-lying snowbanks. The PIs hypothesize that: (a) calculated development rates will be comparable with those of measured snowbank erosion; (b) exposure dates for individual rock clasts will coincide with Quaternary cold intervals; and (c) terrace treads are time-transgressive surfaces with the exposure age of clasts increasing toward the outer edge of terraces. The landforms in this region where the rocks for this analysis were collected are representative of those in the much larger domain of unglaciated landscapes of the Northern Hemisphere. Therefore, the methodologic and analytic approach adopted for this project are potentially applicable throughout this vast region.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

这个博士论文研究项目将确定冻夷梯田的年龄和发展速度，通过雪和霜的侵蚀作用形成的梯田。冻夷台地是一种大型高地地貌特征，给人以巨大阶梯的印象，发现于冰缘或寒冷但非冰川环境中。 虽然这些隆起的基岩阶地已经在科学文献中被发现和讨论了世纪，但关于其形成过程的性质的争论仍在继续。 开发率，计算从岩石暴露跨阶面的日期，将被用来测试在文献中提出的一个更突出的假设。 这一假说指出，这些阶地是通过与持续到夏季的雪堤相关的加剧侵蚀形成的。 最近在地球化学方法方面的发展，特别是称为宇宙成因核素测年的方法，将为在这一长期存在的科学问题上取得进展注入必要的当代技术，并有可能在了解冰缘地区景观发展方面取得变革性进展。 这项研究的结果将与美国国家公园管理局分享，并用于加强公园管理，以及通过在几个国家公园和纪念碑中开发解释性展示和步道指南来改善公园游客的体验。 此外，该项目将使研究生能够建立一个独立的研究生涯，低温夷平面梯田的巨大的古老性使陆地宇宙成因核素的最适当的定年方法，以确定其年龄和发展速度。 宇宙成因核素测年的岩石样品收集在阿拉斯加内陆的两个地点，使用基于横断面的采样策略，在各个阶地踏板。 确定碎屑岩（碎屑）暴露的年代将有助于计算单个阶地的侵蚀速率，并可与现有晚期雪堆的已知侵蚀速率进行比较。 PI假设：（a）计算出的开发速率将与测量的雪堤侵蚀速率相当;（B）单个岩石碎屑的暴露日期将与第四纪冷间隔相一致;以及（c）阶地阶面是随时间推移的表面，碎屑的暴露年龄向阶地的外边缘增加。 在这个地区的地貌，在这里收集的岩石进行分析，是那些在北方半球更大范围的未冰川景观的代表。 因此，该项目采用的方法和分析方法可能适用于整个广阔的区域。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估。