Evolution of the Cordilleran Foreland Basin System in Northwestern Montana, U.S.A
Evolution of the Cordilleran foreland basin system in northwestern Montana, U.S.A. Facundo Fuentes†, Peter G. DeCelles, Kurt N. Constenius, and George E. Gehrels Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA ABSTRACT episode of marine inundation and black shale 1989; Fermor and Moffat, 1992; Stockmal et al., deposition (Marias River Shale) occurred be- 1992; Beaumont et al., 1993; Plint et al., 1993; New lithostratigraphic and chronostrati- tween the Cenomanian and mid-Santonian, Ross et al., 2005; Miall et al., 2008; Yang and graphic, geochronologic, and sedimentary and was followed by a regressive succession Miall, 2009). This bimodal focus was mainly petrologic data illuminate the history of represented by the Upper Santonian–mid- driven by either the presence of anomalously development of the North American Cor- Campanian Telegraph Creek, Virgelle, and good surface exposures, as in the case of the dilleran foreland basin system and adjacent Two Medicine Formations. Provenance data western interior United States, or by hydro- thrust belt from Middle Jurassic through do not resolve the timing of individual thrust carbon exploration and a large subsurface data- Eocene time in northwestern Montana. The displacements during Cenomanian–early base, as in Canada (Miall et al., 2008). The oldest deposits in the foreland basin system Campanian time. The Upper Campanian ~300-km-long segment of the foreland basin consist of relatively thin, regionally tabu- Bearpaw Formation represents the last major lying within and east of the Cordilleran belt in lar deposits of the marine Ellis Group and marine inundation in the foreland basin . By northwestern Montana remains comparatively fl uvial-estuarine Morrison Formation, which latest Campanian time, a major epi sode of poorly understood in terms of its stratigraphy, accumulated during Bajocian to Kimmerid- slip on the Lewis thrust system had com- basin evolution, and relationship with the kine- gian time.
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