Fox Hills Formation

The Fox Hills Formation is a Cretaceous geologic formation in the northwestern Great Plains of North America. It is present from Alberta on the north to Colorado in the south.

Fox Hills Formation
Stratigraphic range: Late Cretaceous, Maastrichtian PreꞒ Ꞓ O S D C P T J K Pg N
A ridge capped by a sandstone bed of the Fox Hills Formation west of Limon, Colorado
Type	Geological formation
Unit of	Montana Group (MT, ND)
Sub-units	Fairpoint member (SD), Trail City member (ND, SD), Timber Lake (ND, SD), Lincoln member (CO), etc.
Underlies	Lance (WY)/Hell Creek (MT)[1] Laramie Formation (CO)
Overlies	Pierre (USA)/Bearpaw (CAN)[1] Lewis Shale (WY, MT)[1]
Thickness	75-225 feet
Lithology
Primary	Sandstone
Other	Shale
Location
Region	Alberta, Colorado, Montana, North Dakota, South Dakota and Wyoming
Country	United States/Canada
Type section
Named for	Fox Hills between Cheyenne and Moreau Rivers, South Dakota
Named by	Meek and Hayden[1]
Year defined	1862[1]

Fossil remains of dinosaurs, including tyrannosaurs, as well as large marine reptiles, such as mosasaurs, have been recovered from the formation.^[2]

Lithology

The Fox Hills Formation consists of marginal marine yellow to grey sandstone with shale interbeds.^[1][3] It was deposited as a regressive sequence of barrier islands during the retreat of the Western Interior Seaway in Late Cretaceous time.^[4] In its eastern extents, the formation is underlain by the marine Pierre Shale in the United States and by the equivalent Bearpaw Formation in Canada, while in western ranges in Montana and Wyoming it overlies the Lewis Shale. The Fox Hills is overlain by continental sediments of the Laramie Formation in Colorado and the Lance Formation in Wyoming, the later being the equivalent of the overlying Hell Creek Formation in Montana.^[1]

See also

• Earth sciences portal
• Paleontology portal
• Dinosaurs portal

• List of dinosaur-bearing rock formations
  • List of stratigraphic units with indeterminate dinosaur fossils

References

1. "Geologic Unit: Fox Hills". National Geologic Database. Geolex — Significant Publications. United States Geological Survey. Retrieved 2017-02-13.
2. Getman, Myron RC (1994). "Occurrences of Mosasaur and other reptilian fossil remains from the Fox Hills Formation (Maastrichtian: late Cretaceous) of North Dakota" (Document). St. Lawrence University Dept. of Geology theses.
3. Lexicon of Canadian Geologic Units. "Fox Hills Formation". Archived from the original on 2013-01-12. Retrieved 2010-02-01.
4. Henry W. Roehler (1993). "Stratigraphy of the Upper Cretaceous Fox Hills Sandstone and Adjacent Parts of the Lewis Shale and Lance Formation, East Flank of the Rock Springs Uplift, Southwest Wyoming". U.S. Geological Survey Professional Paper (1532). Washington: United States Government Printing Office.