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

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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.