.TOURING
COLORADO GEOLOGY
Rooney
Roadcut|
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.TOURING COLORADO GEOLOGY |
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Rooney
Roadcut |
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| Fox Hills (upper) | Pierre | Fox Hills (lower) | Pierre |
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The left part of the road cut consists of white, fine-grained sandstone with some thin interbedded shales representing the Upper Fox Hills. These rocks represent distributary mouth bars. On the extreme left of the outcrop is the lowermost Laramie Sandstone. |
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To the right of this sandstone, dark gray shales of the Pierre Formation are exposed. These sediments are probably lagoonal based on the large amounts of organic material present and specimens of Haplophragmoides sp.. There also is a fault running diagonally through the cut seen to the left - low angle running from lower left to upper right. Offsetting of the sandstone beds in the shale is very slight. |
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To the right of the gray Pierre
Shale is another section of sandstones, these more tan with
concretions present in some of the beds. This sandstone represents
the lower Fox Hills. Cross-bedding is prominent in many of these
beds as well as soft-sediment deformation. .
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To the extreme right, gray shale of the Pierre shale are again exposed. The shales, dark gray fissile marine shales probably represent pro-delta deposits containing ammonites and some foraminifera. As you can see from the photo, the beds are almost vertical. |
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Along the top of the center portion of the road cut is an erosional surface (angular unconformity) with a conglomerate. These pebbles and cobbles probably represent a channel deposit of Pleistocene age. Clasts are of igneous and metamorphic rocks. |
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Weimer, R. J. and Tillman, R. W., 1980, Tectonic influence on deltaic
shoreline facies, Fox Hills Sandstone, west-central Denver basin: Guidebook
for SEPM Field Trip #2, National AAPG-SEPM-EMD Meeting, CSM Professional
Contributions 10, p. 7 Weimer, R. J., and LeRoy, L. W., 1987, Paleozoic-Mesozoic section: Red Rocks Park I-70 road cut, and Rooney Road, Morrison area, Jefferson County, Colorado: Geol. Soc. of Amer. Centennial Field Guide-Rocky Mtn. Section, p. 315-319. Weimer, R. J., 1996, Guide to the Petroleum Geology and Laramide Orogeny, Denver Basin and Front Range, Colorado: Colorado Geological Survey, Bulletin 51. |
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