Collaborative Research: Spatial Variability in Eroded Sediment Size and Geomorphic Processes Inferred From Detrital Thermochronometry and Cosmogenic Nuclides

合作研究：从碎屑测温法和宇宙成因核素推断出的侵蚀沉积物尺寸和地貌过程的空间变化

• 批准号: 1325033
• 负责人: Clifford Riebe
• 金额: $ 11.55万
• 依托单位: University of Wyoming
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-08-15 至 2016-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1325033&HistoricalAwards=false
• 关键词: Collaborative; Research; Spatial; Variability; Eroded

Understanding patterns of erosion and sedimentation in mountains is important for Earth scientists and land-use managers alike. Over management timescales, eroded sediment affects water quality, influences the amount and quality of aquatic habitat in rivers, and determines the lifespan of both natural and manmade reservoirs by setting the pace of sedimentation within them. Over longer, geologic timescales, eroded sediment also influences landscape erosion by providing rivers with the tools they need to cut into underlying bedrock and thereby adjust to changes in climate and tectonic forcing. Thus, the erosion of sediment is both the product of and a key driving force behind landscape change. Work funded by this grant will develop new methods for interrogating sediment about where it comes from, how it is generated, and how fast it moves across landscapes. This should permit progress on understanding erosional processes and how they influence landscape response to climatic and tectonic forcing. Geologists have long recognized that sediment contains a wealth of information about its journey from intact rock on hillslopes to the jumbles of particles that cover modern riverbeds and fill ancient sedimentary deposits. Extraction of this information has become increasingly sophisticated with recent technological and methodological advances. As a result, understanding of surface processes has become increasingly quantitative. For example, rates of erosion from slopes can now often be measured from cosmogenic nuclides, which build up in sediment grains when they are near Earth's surface. Meanwhile, recent studies have shown that the clockwork-like buildup of radiogenic helium in the mineral apatite can be used as a fingerprint of where sediment comes from on catchment slopes. Here, this apatite-helium tracing technique will be used together with cosmogenic nuclides in a completely new way, to simultaneously unveil spatial variations in both the erosion rates and sizes of sediment produced on hillslopes by bedrock weathering. This marks an important advance in sediment tracing; until now, there was no way to quantify how the sizes of eroded sediment vary over catchment scales. Preliminary results show a connection between the elevation of slopes and the sizes of sediment that they produce by weathering and erosion. Higher-elevation slopes, which are colder and less vegetated, produce coarser sediment. This points to climate as a key regulator of sediment size. The proposed research will test the new sediment tracing approach in a steep catchment and explore hypotheses about linkages between climate and the sizes of eroded sediment. Expected outgrowths of this research include fresh insight on common, but as-yet incompletely understood downstream trends in landscapes, such as: fining in grain size in mountain streambeds; shifts from braided to meandering channel forms; and changes in aquatic habitats and the organisms that populate them.

了解山区侵蚀和沉积的模式对于地球科学家和土地利用管理者来说非常重要。在管理时间尺度上，侵蚀沉积物会影响水质，影响河流中水生栖息地的数量和质量，并通过设定天然水库和人造水库内的沉积速度来决定其寿命。在较长的地质时间尺度上，侵蚀沉积物还通过为河流提供切入底层基岩所需的工具来影响景观侵蚀，从而适应气候和构造强迫的变化。因此，沉积物侵蚀既是景观变化的产物，也是景观变化背后的关键驱动力。这笔赠款资助的工作将开发新方法来询问沉积物的来源、产生方式以及在景观中移动的速度。这应该有助于理解侵蚀过程以及它们如何影响景观对气候和构造强迫的响应。地质学家早就认识到，沉积物包含着丰富的信息，涉及从山坡上完整的岩石到覆盖现代河床和填充古代沉积物的杂乱颗粒的旅程。随着最新技术和方法的进步，这些信息的提取变得越来越复杂。因此，对表面过程的理解变得越来越定量。例如，现在通常可以通过宇宙成因核素来测量斜坡的侵蚀率，宇宙成因核素在靠近地球表面的沉积物颗粒中积累。与此同时，最近的研究表明，矿物磷灰石中放射源氦的类似发条状的积累可以用作流域斜坡上沉积物来源的指纹。在这里，这种磷灰石-氦示踪技术将以全新的方式与宇宙成因核素一起使用，以同时揭示基岩风化在山坡上产生的沉积物的侵蚀率和尺寸的空间变化。这标志着沉积物追踪的重要进展；到目前为止，还没有办法量化流域范围内侵蚀沉积物的大小如何变化。初步结果显示，斜坡的海拔与其风化和侵蚀产生的沉积物的大小之间存在联系。海拔较高的斜坡温度较低且植被较少，产生的沉积物较粗。这表明气候是沉积物大小的关键调节因素。拟议的研究将在陡峭的流域测试新的沉积物追踪方法，并探索有关气候与侵蚀沉积物大小之间联系的假设。这项研究的预期成果包括对常见但尚未完全了解的景观下游趋势的新见解，例如：山地河床颗粒尺寸的细化；从辫状通道形式转变为蜿蜒通道形式；以及水生栖息地和栖息在其中的生物体的变化。