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The AAPG/Datapages Combined Publications Database
Williston Basin Symposium
Abstract
SKGS-AAPG
Sixth International Williston Basin Symposium, October 7,
THE STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF THE FOX HILLS FORMATION, BOWMAN COUNTY, NORTH DAKOTA
ABSTRACT
The marginal marine deposits of the Fox Hills Formation (Maastrichtian) in the Williston Basin consist, along with the overlying terrestrial Hell Creek Formation and the upper portion of the underlying offshore marine Pierre Formation, of strata laid down during the penultimate retreat of the sea from the Western Interior. In the Little Missouri Badlands on the southeast flank of the Cedar Creek anticline, the Fox Hills is typically exposed as a 37 m (122 ft) thick, tabular, upward coarsening sequence consisting of (from the base): mixed or interbedded silt and clay (Trail City Member; 10 m [33 ft], offshore transition), very fine to medium hummocky-bedded sand containing a limited suite of trace fossils dominated by Ophiomorpha (Timber Lake Member, 19-22 m [62-72 ft], inner shelf), and a cross-bedded fine to medium-grained sand containing carbonaceous material (Colgate Member, shoreface). The Pierre - Fox Hills contact is placed at the horizon above which clay changes to silty clay, mixed or interbedded strata occur, and trace fossils appear, whereas the upper contact with the Hell Creek is placed at the base of the first substantial carbonaceous bed. Stratigraphic sequences are similar over the southwestern flank of the basin, but are half the thickness and lack the abundant marine fossil fauna and the well-developed upper sequence exposed on the southeastern flank of the basin, including the type area.
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