Determining the Reliability of Using Cosmogenic Nuclides to Date Arctic Beach Sediment

本项目是一项为期一年的试验性研究，旨在确定宇宙成因10 Be、26 Al等核素用于海滩沉积物定年的可靠性。试验场位于西北地区威尔士亲王岛东部的普雷斯科特岛，有足够的不同岩性和碎屑大小的可测定年代的岩石;自出现以来一直保持在地磁纬度北纬60度以上（在该纬度上，核素的产生率大致保持不变）;并且已经根据46个漂流木放射性碳年代确定了明确的出现曲线。在1995年为期两周的实地调查期间，收集了40个代表从11 kyr到现代海岸线海滩的大型样本。需要对这些样品的物理和化学制备以及10 Be、26 Al、36 Cl和14 C的分析提供支持。抬升的海岸线，特别是那些具有宽的后滨带，跨越很长的时间范围，并有许多海滩脊，被用来构建相对海平面曲线的沿海地区，经历了构造隆起或均衡补偿冰消卸载。海岸线出露曲线提供了关于隆起类型和速率的信息，有助于探测局部和区域构造异常，有助于划定地壳块体的边界并确定它们在出露期间是否倾斜，提供了对古冰量和厚度的限制，已被用来帮助推断深部地幔流变参数，并有助于验证现有的均衡调整模型。在海滩上需要严格可靠的年表，以建立准确的出现曲线。在放射性碳测年无法获得可定年的有机物质的情况下，宇宙成因核素测年可提供一种可靠的替代方法。宇宙成因核素法确定个别海滩洋脊的年代或确定相对海平面曲线的可靠性尚不确定。单个海滩水平上宇宙成因核素年龄的总不确定度必须至少为6%或7%才有用。虽然这已经在冰碛上取得了艾德，但在确定海滩的年代时，必须考虑许多不同的环境因素。迄今为止，从未正式进行过陆地宇宙成因核素的效用测试。

This project is a one year pilot study of determine the reliability of using cosmogenic 10Be, 26Al, and other nuclides to date beach sediment. The test site, Prescott Island, on eastern Prince of Wales Island, NWT, has sufficient datable rocks of different lithologies and clast sizes; persisted above 60o N geomagnetic latitude since emergence (the latitude at which the production rate for the nuclides has been approximately constant); and already has a well-defined emergence curve based on 46 driftwood radiocarbon dates. Forty large samples representing beaches from 11 kyr to the modern shoreline were collected during a two week field season in 1995. Support is requested for the physical and chemical preparation and analyses of these samples for 10Be, 26Al, 36Cl, and 14C. Raised shorelines, especially those with wide backshore zones that span a long time range and have numerous beach ridges, are used to construct relative sea level curves for coastal regions that have undergone tectonic uplift or isostatic compensation for deglacial unloading. Shoreline emergence curves provide information on the style and rate of uplift, are useful for detecting local and regional tectonic anomalies, can help delimit the boundaries of crustal blocks and determine if they have tilted during the emergence period, provide constraints on paleo-ice mass and thickness, have been used to help infer deep mantle rheology parameters, and are useful in verifying existing isostatic adjustment models. Tight and reliable chronologies are required on suites of beaches to establish accurate emergence curves. Where datable organic material is not available for radiocarbon dating, cosmogenic nuclide dating may provide a reliable alternative. It is uncertain how reliable the cosmogenic nuclide methods can date individual beach ridges or define a relative sea level curve. Total uncertainties for cosmogenic nuclide ages on single beach levels must be at least 6 or 7% to be useful. Although this has been achiev ed on moraines, there are a number of different environmental factors which must be considered when dating beaches. A test of the utility of terrestrial cosmogenic nuclides to date beaches has never been formally conducted.