GEOPHYSICAL MASS FLOWS FROM A COSMIC IMPACT DURING THE MID PLEISTOCENE MAY HAVE PERTURBED LANDSCAPE EVOLUTION ACROSS NORTH AMERICA

Beginning with Earth’s accretion during the Hadean, cosmic impacts have been an external force on its landscape evolution. A collision with a protoplanet generated our Moon - credited with many beneficial controls on the Earth's environment such as moderating the wobble of its axis and the action of tides. Impacts can present as caldera lakes and often control surficial and subterranean hydrology. They may have contributed to plate tectonics initiation. The effects of ancient impacts on the landscape are often poorly constrained due to weathering and burial. More recently, a significant impact ~788 ka distributed billions of tons of tektites across >30% of Earth. A protracted search for the impact site has not been fruitful. Tektite chemistry demands a continental sedimentary target, and a visible scar on the Earth's landmass seems likely. The missing artifacts may have been attributed to gradualistic mechanisms. The Davias-Harris hypothesis (2022) speculates the impactor struck North America obliquely, engaging the MIS 20 Laurentide ice sheet before excavating late Paleozoic to early Mesozoic sedimentary strata of Michigan’s Intracratonic Basin. Energetic hydrated geophysical mass flows of vaporized ice and mobilized sediments from the impact effectively repaved large areas in blankets of anomalously nonfossiliferous quartzose sediments. As posited, the creation on low-relief terrains of copious quantities of hydraulically closed oriented ovoid basins would have had a remarkable influence on the landscape evolution of North America. In areas of higher relief, increased bed load due to the rapid initial erosion of those blankets may have contributed to the evolution of highly braided over-fit drainage channels. Expected are surviving deposits on upland terrace surfaces, which would appear anomalous. We encourage and support attempts by the community to falsify the hypothesis. 26Al/10Be cosmogenic nuclide burial dating techniques applied to the implied blanket's sub-adjacent surfaces may well deny or confirm a unique and widespread repaving event at ~800 ka. Due to the temporal association of the event just prior to the Matuyama-Brunhes geomagnetic transition, primary depositions will demonstrate negative polarity, but subsequent secondary transport and re-depositions may show positive polarity.