Geology

Flooding in the Badlands

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Science  30 Nov 2001:
Vol. 294, Issue 5548, pp. 1791-1793
DOI: 10.1126/science.294.5548.1791e

In the Late Cretaceous, the Western Interior Seaway inundated the middle of the North American continent, covering an area from the Gulf of Mexico to North Dakota. Available geologic data indicate that the seaway had retreated by the time of the Chicxulub impact event at the end of the Cretaceous.

Terry et al. have discovered disrupted sedimentary rock layers in the Badlands region of South Dakota. The disrupted beds contain large-scale slump-roll structures consistent with the movement of seaway shelf edge deposits caused by shock waves from the impact event. Above these layers is a thin bed of spherules that might be impact ejecta, and these deposits are overlain by a thicker sequence of shallow marine sediments. This newly discovered distal signal of the impact indicates that the Western Interior Seaway may have been present from the Late Cretaceous into the Early Tertiary, given the continuous sequence of marine sediments found in the Badlands.—LR

Geology29, 1055 (2001).

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