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A zone of intense soft-sediment deformation, with associated spherules and shocked quartz grains, is identified over an area of ∼1000 km2 in southwestern South Dakota. This Disturbed Zone (DZ) is up to 5 m thick and is preserved within distal deltaic deposits of the Upper Cretaceous Fox Hills Formation. Localized structural development caused thinning and eventual subaerial exposure of several sections within Badlands National Park, whereas sections to the north of the park were unaffected. Although previously interpreted as an intense period of soil formation under tropical conditions, the degree of ancient soil overprinting of these sections is minimal, with the exception of bright coloration of the strata, and appears not to have had any effect on ejecta preservation. Biostratigraphic data suggest a middle to late Maastrichtian age for the DZ. When compared to other Cretaceous impactites, our study sections in southwestern South Dakota are most similar to, and may correlate with, the recently documented 68 Ma impactite within the Vermejo Formation of Berwind Canyon in southeastern Colorado. If this correlation is correct, the size of the ejecta within the Fox Hills and Vermejo Formations suggests that the sections in South Dakota represent distal deposits.

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