FOLDING IN MONTANA ROCKIES
FIELD TRIP STOPS – FOLDING INTENSITY AT BEAVER CREEK, MT.
LOCATION: In western Montana, between LaHood Park and Choteau, MT.
GEOLOGIC FEATURES: Progressive folding of Mississippian Limestone
DESCRIPTION: At this outcrop we can see horizontal beds of limestone that rapidly plunge to the vertical and beyond.
STUDENT QUESTIONS:
(1) What is the Law of Original Horizontality?
(2) When did the Laramide Orogeny take place? What was the direct cause of this tectonic event?
(3) Define: Overturned Fold.
SELECTED REFERENCES:
-Devaney, Sarah Anne. “Structural Geology of the Rock Mountain Front.” The Montana Heritage Project. Accessed on 4/19/20: https://serc.carleton.edu/research_education/mt_geoheritage/sites/augusta_choteau/structural_geol.html
-English, Joseph and Stephen Johnston. 2004. “The Laramide Orogeny: What Were the Driving Forces?” International Geology Review, 46(9), pp. 833-838 in Researchgate. Accessed on 4/29/20: https://www.researchgate.net/publication/242170712_The_Laramide_Orogeny_What_Were_the_Driving_Forces
PHOTOS:
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Figure 1 - Photomosaic of the canyon at Beaver Creek, MT. Here we see Mississippian strata folded in various orientations.
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Figure 2 - The left side of Figure 1 illustrating horizontal to near-horizontal layering of Mississippian strata.
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Figure 3 - Central portion of Figure 1 illustrating the bending of horizontal strata into a vertical or near-vertical
orientation.
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Figure 4 - Right side of Figure 1 illustrating beds dipping to the left that have likely been overturned.
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Figure 5 - Photo taken along a view near parallel to the ridge and showing the geological features illustrated in Figures 1 -4.