EAGER: Single-grain Optical Dating of Debris-flow Fans

EAGER：泥石流风扇的单粒光学测年

• 批准号: 1015665
• 负责人: Glenn Berger
• 金额: $ 2.04万
• 依托单位: Nevada System of Higher Education, Desert Research Institute
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-04-01 至 2012-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1015665&HistoricalAwards=false
• 关键词: EAGER; Single; grain; Optical; Dating

Debris flows are mass-movement deposits, occurring worldwide, that shape landscapes and have caused considerable damage in historic times. Knowledge of their prehistoric frequency may be obtained by use of various dating methods (e.g., dendrochronology or Carbon-14), but these are not often possible given the age, complexity, and setting of the debris flow. This proposal will test the suitability of an alternate dating tool, single-grain-quartz (SGQ) luminescence dating. Single-grain and multigrain optical dating of quartz is a proven technology but has never been attempted with debris flows. Accurate optical dating depends upon resetting the clock by exposure to solar radiation over a minimum of tens of seconds. The turbulent and rapid process by which debris flows occur may not always allow entrained quartz grains sufficient time for such exposure. Two sites have been chosen for this test. A debris]flow site near Reno occurred in 1983 over a short duration (8 to 10 minutes) and small spatial extent (0.57 sq. km.). A much larger debris flow deposit (105 sq. km.) is known in the Eastern Cordillera of Colombia that is prehistoric, but of an unknown age and duration. Thus these two settings represent approximate process]scale end members. The Colombia site has a Carbon-14 datable deposit for some age control of the SGQ results. If this project is successful, then a new dating tool will be available for such landscape deposits, a tool covering the range from historic times (last few decades) back to ca. 150 ka, well beyond the Carbon-14 dating range. Debris flows are significant and troublesome events. They usually occur catastrophically in response to another significant geological or climatic stimulus, such as a sub-glacial volcanic eruption, or heavy rains in a mountainous environment. Debris flows are often the major mechanism in the construction of alluvial fans in arid regions. In areas of human habitation, knowledge of the duration and frequency of debris flows can be essential for planning and emergency response. This project will test two end-member sites to see if debris flows contain sufficient single quartz grains that will allow determination of a reliable age profile. The Nevada site has a known age control, and the Colombian site has some organic carbon that can be used for an independent dating assessment. It is possible that the method will not be suitable, but if it does prove successful, it will provide a new avenue for establishing the chronology of these events. A successful test project will provide a new dating tool to address the relationship in time and space of prehistoric debris-flow deposits worldwide to a wide variety of likely geologic events, such as earthquakes or volcanic eruptions.

泥石流是发生在世界各地的大规模移动沉积，它塑造了历史时期的景观，并造成了相当大的破坏。关于它们史前频率的知识可以通过使用各种测年方法(例如树枝年代学或碳14)获得，但考虑到泥石流的年龄、复杂性和背景，这些通常是不可能的。这项提议将测试另一种测年工具--单颗粒石英(SGQ)发光测年的适用性。石英的单颗粒和多颗粒光学测年是一项经过验证的技术，但从未尝试过泥石流。准确的光学测年依赖于通过暴露在太阳辐射下至少几十秒来重新设置时钟。泥石流发生的湍急和迅速的过程可能并不总是允许夹带的石英颗粒有足够的时间进行这种暴露。这项测试选择了两个地点。雷诺附近的泥石流发生在1983年，持续时间短(8至10分钟)，空间范围小(0.57平方英尺)。公里。)。一个更大的泥石流堆积物(105平方英尺。千米。)已知于哥伦比亚东部科迪勒拉，这是史前的，但年代和持续时间未知。因此，这两个设置表示近似过程]缩放末端成员。哥伦比亚的网站有一个碳-14可测年沉积物，用于SGQ结果的一定年龄控制。如果这个项目成功，那么一种新的测年工具将可用于此类景观沉积物，该工具涵盖了从历史时代(过去几十年)到大约150 ka的范围，远远超出了碳14的测年范围。泥石流是重大而麻烦的事件。它们通常是对另一种重要的地质或气候刺激的灾难性反应，例如次冰川火山喷发，或山区环境中的暴雨。泥石流往往是干旱区冲积扇建设的主要机制。在人类居住地区，了解泥石流的持续时间和频率对于规划和应急反应至关重要。该项目将测试两个末端成员地点，以确定泥石流是否含有足够的单一石英颗粒，从而能够确定可靠的年龄分布。内华达州的网站有一个已知的年龄控制，哥伦比亚的网站有一些有机碳可以用于独立的年代评估。这种方法有可能不适用，但如果它真的被证明是成功的，它将为建立这些事件的年表提供一种新的途径。一个成功的测试项目将提供一种新的测年工具，以解决世界各地史前泥石流沉积与各种可能的地质事件，如地震或火山喷发在时间和空间上的关系。