Collaborative Research- Laterally Extensive Breccias in the Mesoproterozoic Atar Group, Mauritania: Tsunami Deposition resulting from a Marine Extraterrestrial Impact?

合作研究——毛里塔尼亚中元古代阿塔尔群横向广泛的角砾岩：海洋外星撞击造成的海啸沉积？

• 批准号: 0819542
• 负责人: Keith Milam
• 金额: --
• 依托单位: Ohio University
• 依托单位国家: 美国
• 项目类别: Continuing grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-15 至 2011-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0819542&HistoricalAwards=false
• 关键词: Collaborative; Research; Laterally; Extensive; Breccias

Tsunamis are oceanic waves with long wavelengths, long periods, and high velocities, and are most commonly caused by catastrophic displacement of the water column by submarine fault movements, landslides, volcanic eruptions, or the marine impact of extraterrestrial bodies. Energy conserved during wave propagation in the deep ocean is translated to wave height as tsunami waves cross the continental margins, and is gradually dissipated through friction with the sediment substrate. Although mobilization of the substrate can occur over wide areas of the continental shelf, the most devastating effects of tsunami occur during wave inundation of coastal zones, which experience significant erosion and transport of sediment that is then deposited en masse in inland zones, and during tsunami back-surge, which can result in additional erosion and seaward transport of sedimentary materials. Despite their frequent recurrence and their potentially extraordinary sedimentologic effect, our understanding of tsunami deposits is largely restricted to Holocene and younger deposits. Although more ancient geologic deposits have been attributed to tsunami waves, only recently has the detailed analysis of wave behavior and related sedimentary deposition permitted a more systematic compilation of sedimentary signatures that can be ascribed to processes acting during passage of a tsunami wave-train. Within such a framework, detailed analysis of ancient tsunami deposits potentially allow differentiation of specific tsunami processes. The largest deposits (i.e. mega-tsunami deposits), if well preserved in terms of their stratigraphic thickness, stratigraphic variability, and lateral extent, may even provide sufficient data to differentiate among potential tsunamigenic source mechanisms. Carbonate strata within the Proterozoic Atar Group, Mauritania, contain a 4 to 6 meter-thick breccia interval that has been attributed previously to seismic liquefaction. The wide lateral extent of deposits over a thousand kilometers across the West African craton, as well the presence of amalgamated beds with distinct intrabreccia scours, variable clast grading, and indication of bi-directional imbrication, suggests formation via passage of a series of anomalously large waves (e.g. a tsunami wave-train). Furthermore, facies reconstruction indicates transport of meter-scale boulders up to 150 km across a shallow cratonal seaway, suggesting a tsunamigenic source of extraordinary magnitude. This project, a collaboration between the University of Tennessee Knoxville and Ohio University, will carry out a detailed sedimentologic, petrographic, and geochemical analysis of these deposits to characterize the sedimentological effect of tsunami processes, to explore tsunami behavior and energy depletion in a shallow epicratonic seaway, and test the hypothesis that the wave energy originated from a marine extraterrestrial impact. This project aims to advance discovery while promoting teaching, training, and learning by linking sedimentologic and planetary expertise of the two Investigators and involving both graduate and undergraduate students in international collaboration and the process of scientific inquiry. Both investigators have a long history of public outreach. The University of Tennessee will support a local middle school teacher to construct a series of physically contained, hand-on exercises (and associated web materials) that explore tsunamis and extraterrestrial impacts as geologic phenomena that shape our world. These exercises will be provided to a number of regional schools, and funding will also support undergraduate and graduate ?student ambassadors? to visit up to ten local middle schools to work with students and teachers in implementing these exercises, thereby enhancing secondary science education in eastern Tennessee.

海啸是波长长、周期长、速度快的海浪，最常见的是由海底断层运动、山体滑坡、火山爆发或地外天体对海洋的影响造成的水柱灾难性位移引起的。当海啸波穿过大陆边缘时，波浪在深海传播过程中储存的能量被转化为波高，并通过与沉积物基底的摩擦逐渐消散。虽然在大陆架的广大地区都可能发生基底的动员，但海啸最具破坏性的影响发生在波浪淹没沿海地区期间，沿海地区经历了严重的侵蚀和沉积物的搬运，这些沉积物随后大量沉积在内陆地区，海啸反潮期间可能导致额外的侵蚀和沉积物质的向海搬运。尽管海啸沉积物的频繁发生和潜在的非同寻常的沉积作用，我们对海啸沉积物的了解在很大程度上局限于全新世和更年轻的沉积物。虽然更古老的地质沉积被归因于海啸波，但直到最近，对波浪行为和相关沉积的详细分析才允许对沉积特征进行更系统的汇编，这些特征可以归因于海啸波列通过过程中的作用。在这样的框架内，对古代海啸沉积物的详细分析可能使具体海啸过程的区分成为可能。最大的沉积物（即大海啸沉积物），如果在地层厚度、地层变异性和横向范围方面保存良好，甚至可以提供足够的数据来区分潜在的海啸成因机制。毛里塔尼亚元古宙Atar群的碳酸盐岩地层含有4 - 6米厚的角砾岩层，以前认为这是地震液化造成的。横跨西非克拉通的宽横向范围超过1000公里，以及具有明显滨砾岩冲刷作用的合并层的存在，多变的碎屑级配，以及双向叠瓦作用的迹象，表明形成是通过一系列异常大波（例如海啸波列）。此外，相重建表明，米级的巨石在一个浅克拉通海道上移动了150公里，表明这是一个非常巨大的海啸成因。这个项目是田纳西大学诺克斯维尔分校和俄亥俄大学的合作项目，将对这些沉积物进行详细的沉积学、岩石学和地球化学分析，以表征海啸过程的沉积学影响，探索浅海道的海啸行为和能量消耗，并测试波浪能量来自海洋外撞击的假设。该项目旨在通过将两位研究人员的沉积学和行星专业知识联系起来，并让研究生和本科生参与国际合作和科学探究过程，在促进教学、培训和学习的同时推进发现。两位调查人员都有长期的公众宣传历史。田纳西大学将支持一名当地中学教师构建一系列实际操作的练习（以及相关的网络材料），将海啸和外星撞击作为塑造我们世界的地质现象进行探索。这些练习将提供给一些地区学校，资金也将支持本科生和研究生。学生大使吗?访问多达10所当地中学，与学生和教师一起实施这些练习，从而加强田纳西州东部的中学科学教育。