U-Series Comminution Age Constraints on Taylor Valley Erosion

U 系列粉碎年龄对泰勒谷侵蚀的限制

基本信息

批准号：
1644171
负责人：
Terrence Blackburn
金额：
$ 35.92万
依托单位：
University of California-Santa Cruz
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-06-15 至 2021-05-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1644171&HistoricalAwards=false
关键词：
Series Comminution Age Constraints Taylor

项目摘要

A nontechnical description of the project The primary scientific goal of the project is to test whether Taylor Valley, Antarctica has been eroded significantly by glaciers in the last ~2 million years (Ma). Taylor Valley is one of the Dry Valleys of the Transantarctic Mountains, which are characterized by low mean annual temperatures, low precipitation, and limited erosion. These conditions have allowed fragile glacial landforms to be preserved for up to 15 Ma. Sediment eroded and deposited by glaciers is found on the valley walls and floors, with progressively younger deposits preserved at lower elevations. Scientists can date glacial deposits to understand the process and timing of past glacial erosion. Previous work in the Dry Valleys region suggested that extremely cold glaciers like Taylor Glacier, a major outlet glacier entering the valleys, were not erosive during the last several million years. This research will test a new hypothesis that glacial erosion and sediment production beneath Taylor Glacier have been active in the last few million years. This hypothesis will be tested using a new isotopic dating method called "comminution dating' which determines when fine-grained sediment particles called silt were formed. If the sediment age is young, then the results will suggest that glacial processes have been more dynamic than previously thought. Overall, this study will increase our understanding of the nature and extent of past glaciations in Antarctica. Because the silt produced by erosion sediment is a nutrient for local ecosystems, the results will also shed light on delivery of nutrients to soils, streams, and coastal zones in high polar regions. This project will be led by an early career scientist and includes training of a Ph.D. student. A technical description of the project There is a long-standing scientific controversy about the stability of the East Antarctic Ice Sheet with much evidence centered in the Dry Valleys region of South Victoria Land. A prevailing view of geomorphologists is that the landscape has been very stable and that the effects of glaciation have been minimal for the past ~15 Ma. This project will distinguish between two end-member scenarios of glacial erosion and deposition by Taylor Glacier, an outlet glacier of the East Antarctic Ice Sheet that terminates in Taylor Valley in the Dry Valleys region of Antarctica. In the first scenario, all valley relief is generated prior to 15 Ma when non-polar climates enabled warm-based glaciers to incise and widen ancient river channels. In this case, younger glacial deposits record advances of cold-based glaciers of decreasing ice volume and limited glacial erosion, and sediment generation resulted in glacial deposits composed primarily of older recycled sediments. In the second scenario, selective erosion of the valley floor has continued to deepen Taylor Valley but has not affected the adjacent peaks over the last 2 Ma. In this scenario, the "bathtub rings" of Quaternary glacial deposits situated at progressively lower elevations through time could be due to the lowering of the valley floor by subglacial erosion and with it, production of new sediment which is now incorporated into these deposits. While either scenario would result in the present-day topography, they differ in the implied evolution of regional glacial ice volume over time and the timing of both valley relief production and generation of fine-grained particles. The two scenarios will be tested by placing time constraints on fine particle production using U-series comminution dating. This new geochronologic tool exploits the loss of 234U due to alpha-recoil. The deficiency in 234U only becomes detectable in fine-grained particles with a sufficiently high surface-area-to-volume ratio which can incur appreciable 234U loss. The timing of comminution and particle size controls the magnitude of 234U loss. While this geochronologic tool is in its infancy, the scientific goal of this proposal can be achieved by resolving between ancient and recently comminuted fine particles, a binary question that the preliminary modeling and measured data show is readily resolved.

该项目的非技术描述该项目的主要科学目标是测试泰勒山谷（Taylor Valley）在过去的大约200万年中冰川是否已被冰川大大侵蚀（MA）。泰勒山谷（Taylor Valley）是跨北极山脉的干山谷之一，其特征是平均年温度低，精度低和侵蚀有限。这些条件使脆弱的冰川地面可保存至15 mA。在山谷的墙壁和地板上发现了冰川侵蚀并沉积的沉积物，逐渐保存在较低海拔处的较年轻的沉积物。科学家可以对冰川沉积物进行约会，以了解过去冰川侵蚀的过程和时机。在干山谷地区的先前工作表明，在过去的几百万年中，泰勒冰川（Taylor Glacier）等极冷的冰川进入了山谷，并没有侵蚀。这项研究将检验一个新的假设，即泰勒冰川下面的冰川侵蚀和沉积物在过去几百万年中一直活跃。该假设将使用一种称为“粉刺约会”的新型同位素约会方法进行检验，该方法决定何时形成了被称为淤泥的细粒沉积物颗粒。如果沉积物年龄很小，那么结果将比以前想到的冰川过程更具动态性。总的来说，这项研究会增加我们对过去的Silrient stracient for Antrient for Antrient for Antrient for Antrient for Antrient strient。生态系统还将揭示出高极性地区的土壤，溪流和沿海地区，并由早期的科学家进行培训。地貌学家是景观非常稳定，过去〜15 mA的冰川作用最少。该项目将区分冰川侵蚀的两种末日情景和泰勒冰川的沉积，泰勒冰川是南极冰盖的出口冰川，该冰原终止于南极干谷地区的泰勒山谷。在第一种情况下，当非极性气候使基于温暖的冰川能够切开和宽阔的古老河道时，就会在15 mA之前产生所有山谷浮雕。在这种情况下，年轻的冰川沉积物记录了冰量减少和有限的冰川侵蚀的冷基冰川的进步，而沉积物产生产生了主要由较旧的再生沉积物组成的冰川沉积物。第二种情况下，山谷地板的选择性侵蚀继续加深了泰勒山谷，但在过去2 MA中没有影响相邻的峰。在这种情况下，位于时间逐渐降低海拔的第四纪冰川沉积物的“浴缸环”可能是由于通过亚冰层侵蚀降低了山谷地板的降低，随之而来的是，新的沉积物的产生现已结合到这些沉积物中。尽管这两种情况都会导致当今的地形，但随着时间的推移，区域冰冰体积的隐含演变以及山谷缓解产生和细粒颗粒的产生的时间差异。这两种情况将通过使用U系列委员会日期将时间限制放置在细粒子生产上来测试。这种新的年代学工具利用了由于alpha-recoil引起的234U的损失。 234U中的缺陷仅在具有足够高的表面面积与体积比的细粒颗粒中被检测到，这会捕捉到234U损失。佣金和粒度的时间控制234U损耗的幅度。尽管这种年代学工具仍处于起步阶段，但可以通过在古代和最近的通勤细节之间解决该提案的科学目标，这是一个二元问题，即初步的建模和测量数据很容易解决。