Geology of Cedar Creek Anticline in Baker, Wibaux, and Glendive 30 ? 60-Min Quadrangles, Eastern Montana and Adjacent North Dakota: ABSTRACT

Abstract

Geology of the asymmetrical, northwest-trending Cedar Creek anticline, a major oil- and gas-producing structure of the Williston basin, was mapped in the Wibaux and Glendive Quadrangles as part of the USGS-funded Coal Lands Mapping Program. Thinning of stratigraphic units, unconformities, and relationships between tectonic structures provide suggestive evidence for the timing of Late Cretaceous and Tertiary uplift in this area. The Colgate Member of the Fox Hills Formation (Maestrichtian) pinches out toward the axis of the anticline. The contact between the Hell Creek Formation (Maestrichtian) and the underlying Colgate Member is disconformable near the axis of the anticline and becomes conformable about 8 km (5 mi) east of it. This suggests Late Cretaceous uplift during or after deposition of the Colgate Member. The Hell Creek Formation also thins by up to 40 m (131.2 ft) toward the axis. Part of the Fort Union Formation is not present on the eastern limb of the anticline and in an area southwest of the anticline, suggesting that these areas were uplifted at the time of or just following deposition of this part of the section during the middle Paleocene. The present anticline developed following deposition of the Fort Union Formation in the latemore » Paleocene. Several associated faults and folds developed subparallel to the axial trend, including a pronounced synclinal flexure along much of the western limb of the anticline. Subsequently, northeast-trending faults with a component of right-lateral slip offset the northwest-trending linear features associated with the anticline.« less