Abstract

In southeastern Utah, the Middle Jurassic Carmel Formation and Slickrock Member of the Entrada Sandstone locally show convolute bedding and syndepositional folds. Newly recognized liquefaction features indicate that this deformation occurred rapidly. None of the five explanations found in the literature fully accounts for these features. The large scale of liquefaction and soft-sediment deformation is distinctive and implies strong disturbances that are difficult to explain by traditional structural or stratigraphic interpretations. Upheaval Dome, within the area of the deformation, displays in detail the structures expected of a complex, central-peak impact crater representing energy release at least equivalent to that of a magnitude 8 earthquake. Upheaval Dome is not well dated, but may be the same age as the deformation. We suggest that the Carmel–Slickrock Entrada deformation may be an example of folding and liquefaction due to impact shaking; if so, it would be one of a very few known cases. Although this kind of deformation should not be common, other examples should be recognizable in outcrop and from subsurface information.

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