Laramie Formation

The Laramie Formation is a geologic formation of Late Cretaceous (Maastrichtian) age, named by Clarence King in 1876 for exposures in northeastern Colorado, in the United States.[2] It was deposited on a coastal plain and in coastal swamps that flanked the Western Interior Seaway.[3] It contains coal, clay and uranium deposits, as well as plant and animal fossils, including dinosaur remains.[1]

Laramie Formation Stratigraphic range: Maastrichtian, 69–68 Ma
A typical outcrop of the Laramie Formation in northeastern Colorado.
Type	Geological formation
Underlies	Arapahoe Formation
Overlies	Fox Hills Formation
Thickness	200-400 ft (60-120 m)
Lithology
Primary	Sandstone, mudstone, clay, coal[1]
Location
Region	Colorado
Country	United States
Type section
Named by	Clarence King[2]

Stratigraphy and Lithology

The Laramie Formation is exposed around the edges of the Denver Basin and ranges from 400–500 feet (120–150 m) on the western side of the basin, and 200–300 feet (60–90 m) thick on the eastern side. It rests conformably on the Fox Hills Sandstone and unconformably underlies the Arapahoe Conglomerate. The formation can be divided into an unnamed lower member containing bedded sandstone, clay and coal; and an unnamed upper member composed predominately of 90 to 190 m of drab-colored mudstone, some sandstone, and thin coal beds.[4][5] Nodular ironstone concretions occur in the mudstones that contain plant remains. Some of the material in the sandstones originated from silicic volcanoes far to the west.[6]

Resources

The coal and clay deposits of the Laramie Formation were once economically important.[5] Clay mining began in the Golden, Colorado area in 1877 and continued until the mid-twentieth century. Most of the clay was used to make bricks and tiles for building construction.[7]

It is estimated that about 130 million short tons of sub-bituminous coal were mined from the Laramie Formation between 1884 and 1979, mostly from seams in the lower part of the formation. Where the seams are relatively flat lying or gently dipping most of the mines were underground room and pillar operations, and where the seams are steeply inclined to vertical, stope mining was used. Relatively little surface mining was done.[3]

The Laramie Formation also hosts uranium deposits. The Leyden Coal Mine produced uranium for a few years as a byproduct of the coal mining. Uranium deposits also occur in sandstones of the Laramie Formation in Weld County, Colorado, and near the town of Grover, Colorado. (See Uranium mining in Colorado)

Paleofauna

Skull of Triceratops from the Laramie Formation. This skull may be the oldest known for the genus. Currently on display at the courthouse in Greeley, Colorado

Fossil vertebrates from the Laramie Formation were among the first dinosaurs to be discovered in the American West (Carpenter and Young 2003). In 1873, Edward D. Cope accompanied Ferdinand V. Hayden, who was leader of the U.S. Geological and Geographical Survey of the Territories. The route of the expedition included eastern Colorado where Cope collected specimens in what is now the Laramie Formation along Bijou Creek on the east side of the Denver Basin (Cope, 1874).[8]

Cope named three species of dinosaurs without description: Cinodon arctatus (later changed to Cionodon arctatus), Polyonax mortuarius and Agathaumas milo (later renamed Hadrosaurus occidentalis). These specimens are currently in the American Museum of Natural History. These specimens are very scrappy and the names no longer considered valid. Subsequent discoveries of dinosaurs occur through the formation, and include a nearly complete skull of Triceratops. Non-dinosaur vertebrates also occur (Carpenter 1979).[9]

List of Fossil Vertebrates (data from Carpenter 1979;[10] Hutchinson and Holroyd 2003)

Cartilaginous fishes

Cartilaginous fishes of the Laramie Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes
Ischyriza	cf. I. avonicola				Sclerorhynchidae
Lonchidion	L. selachos				Lonchidiidae
Myledaphus	M. bipartitus				Rhinobatidae
Squatirhina	S. americana				Ginglymostomatidae

Bony fishes

Bony fishes of the Laramie Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Amia	Indeterminate				Amiidae	A living Amia.
Atractosteus	A. occidentalis				Lepisosteidae

Amphibians

Amphibians of the Laramie Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Albanerpeton	Indeterminate				Albanerpetontidae	Albanerpeton
Lisserpeton	L. bairdi				Scapherpetontidae
Opisthotriton	O. kayi				Batrachosauroididae
Scapherpeton	S. tectum				Scapherpetontidae

Turtles

Turtles of the Laramie Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes
Adocus	Indeterminate				Adocidae
Basilemys	cf. B. sinuosa				Nanhsiungchelyidae
Compsemys	C. victa				Pleurosternidae
Helopanoplia	cf. H. distincta				Trionychidae
Plesiobaena	cf. P. antique				Baenidae

Squamates

Squamates of the Laramie Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes
Odaxosaurus	O. piger				Anguidae

Crocodilians

Crocodilians of the Laramie Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Borealosuchus?	Indeterminate					Borealosuchus

Dinosaurs

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Dinosaurs reported from the Laramie Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Ceratopsipes	C. goldenensis				Ceratopsidae	Dromaeosaurus Edmontonia Edmontosaurus Ornithomimus Thescelosaurus Torosaurus Triceratops Tyrannosaurus
Dromaeosaurus	Indeterminate				Dromaeosauridae
cf. Edmontonia[11]	Indeterminate[11]				Nodosauridae (possibly Denversaurus)
Edmontosaurus[11]	E. annectens[11]				Hadrosauridae
Ornithomimus[11]	O. minutus[11]			"Partial metatarsals II-IV."[12]	The specimens are now lost.[12]
Paronychodon[11]	Indeterminate[11]
Thescelosaurus[11]	T. neglectus[11]				Thescelosauridae
Torosaurus[11]	T. latus[11]				Ceratopsidae
Triceratops[11]	T. horridus[11]				Ceratopsidae
Tyrannosaurus	T. rex				Tyrannosauridae

Mammals

Mammals of the Laramie Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes
Gypsonictops	Indeterminate				Leptictidae
Meniscoessus	Indeterminate				Cimolodontidae
cf. Mesodma	Indeterminate				Neoplagiaulacidae

Paleoflora

Fossil pollen (palynomorphs) include bryophyte and pteridophyte spores, gymnosperm pollen, and abundant angiosperm pollen, including Aquilapollenites striatus, Ilexpollenites compactus, Interpollis cf. I. supplingensis, and Tricolpites interangulus.[13] The palynomorphs indicate an early Maastrichtian age (68-69 mya), which is supported by magnetostratigraphy.[14] Magnetostratigraphy also shows that the Laramie Formation becomes progressively younger eastward as deposition followed the regression of the Western Interior Seaway.

Fossil leaves are abundant, especially in the shales and sandstones associated with coal.[15] Dicot angiosperms dominate, with lesser amounts of ferns, palms, and herbaceous lycopods. Conifers are rare. Common plants include "Ficus" planicostata, "Myrica" torreyi, Sabalites sp., Platanites marginata, and Marmarthia pearsonii.

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Flora of the Laramie Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Aquilapollenites	Aquilapollenites striatus					Ficus Myrica
"Ficus"	"Ficus" planicostata
Ilexpollenites	Ilexpollenites compactus
Interpollis	Interpollis cf. I. supplingensis
Marmarthia	Marmarthia pearsonii
"Myrica"	"Myrica" torreyi
Platanites	Platanites marginata
Sabalites	Sabalites sp.
Tricolpites	Tricolpites interangulus

See also

• List of dinosaur-bearing rock formations

Footnotes

1. U.S. Geological Survey. "Geologic Unit: Laramie". Retrieved 2014-12-27.
2. King, C. 1876. Report of the Geological Exploration of the Fortieth Parallel. U.S.Geographical and Geological Survey.
3. "U.S. Geological Survey Professional Paper 1625-A, Chapter SD" (PDF). Archived from the original (PDF) on 2003-05-05. Retrieved 2014-09-28.
4. Eldridge, G.H., 1888, On some stratigraphical and structural features of the country about Denver, Colorado: Colorado. Scientific Society Proceedings, v. 3, pt. 1, p. 86 118.
5. Shroba, R.R., and Carrara, P.E., 1996, Surficial geologic map of the Rocky Flats environmental technology site and vicinity, Jefferson and Boulder Counties, Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map, I 2526.
6. Wilson, M. 2002. Petrographic provenance analysis of Kiowa Core sandstone samples, Denver Basin, Colorado. In K.R. Johnson, R.G. Raynolds and M.L. Reynolds (eds), Paleontology and Stratigraphy of Laramide Strata in the Denver Basin, Pt. I., Rocky Mountain Geology 37: 173-187.
7. Van Horn, R. 1957. Bedrock geology of the Golden Quadrangle, Colorado. U.S. Geological Survey, Map GQ-103.
8. Report on the vertebrate paleontology of northern Colorado. Geological Exploration of the Fortieth Parallel. U.S. Geological and Geographical Survey.
9. Vertebrate fauna of the Laramie Formation (Maastrichtian), Weld County, Colorado. Contributions to Geology, University of Wyoming 17: 37-49.
10. Carpenter, K. and Young, B. 2002. Late Cretaceous dinosaurs from the Denver Basin, Colorado. In K.R. Johnson, R.G. Raynolds and M.L. Reynolds (eds), Paleontology and Stratigraphy of Laramide Strata in the Denver Basin, Pt. I., Rocky Mountain Geology 37:237-254.
11. "3.4 Colorado, United States; 4. Laramie Formation," in Weishampel, et al. (2004). Page 581.
12. "Table 11.1," in Weishampel, et al. (2004). Page 216.
13. Nichols, D.J., and Fleming, R. F. 2002. Palynology and palynostratigraphy of Maastrichtian, Paleocene, and Eocene strata in the Denver Basin, Colorado. In K.R. Johnson, R.G. Raynolds and M.L. Reynolds (eds), Paleontology and Stratigraphy of Laramide Strata in the Denver Basin, Pt. I., Rocky Mountain Geology 37: 135-163.
14. • Hicks, J.F., Johnson, K.R., Obradovich, J. D., Miggins, D.P., and Tauxe, L. 2003. Magnetostratigraphyof Upper Cretaceous (Maastrichtian) to lower Eocene strata of the Denver Basin,Colorado. In K.R. Johnson, R.G. Raynolds and M.L. Reynolds (eds), Paleontology and Stratigraphy of Laramide Strata in the Denver Basin, Pt. II., Rocky Mountain Geology 38: 1-27.
15. Johnson, K. R., Reynolds, M.L., Werth, K.W., and Thomasson, J.R. 2003. Overview of theLate Cretaceous, early Paleocene, and early Eocene megafloras of the Denver Basin, Colorado. In K.R. Johnson, R.G. Raynolds and M.L. Reynolds (eds), Paleontology and Stratigraphy of Laramide Strata in the Denver Basin, Pt. II., Rocky Mountain Geology 38: 101-120.

References

• Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. ISBN 0-520-24209-2.