The Laramie Formation is a geologic

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

(

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...

) age, named by

Clarence King Clarence Rivers King (January 6, 1842 – December 24, 1901) was an American geologist, mountaineer and author. He was the first director of the United States Geological Survey from 1879 to 1881. Nominated by Republican President Rutherford B. Hay ...

in 1876 for exposures in northeastern

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...

, in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

.King, C. 1876. Report of the Geological Exploration of the Fortieth Parallel. U.S.Geographical and Geological Survey. It was deposited on a coastal plain and in coastal swamps that flanked the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient sea, ...

. It contains

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

and

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

deposits, as well as plant and animal

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s, including

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

remains.

Stratigraphy and Lithology

The Laramie Formation is exposed around the edges of the

Denver Basin The Denver Basin, variously referred to as the Julesburg Basin, Denver-Julesburg Basin (after Julesburg, Colorado), or the D-J Basin, is a geologic structural basin centered in eastern Colorado in the United States, but extending into southeast W ...

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 An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

underlies the Arapahoe Conglomerate. The formation can be divided into an unnamed lower member containing bedded

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

and

; and an unnamed upper member composed predominately of 90 to 190 m of drab-colored

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

, some sandstone, and thin coal beds.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.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. Nodular

ironstone Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical replacement, that contains a substantial proportion of an iron ore compound from which iron (Fe) can be smelted commercially. Not to be con ...

concretions A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular ...

occur in the mudstones that contain plant remains. Some of the material in the sandstones originated from silicic volcanoes far to the west.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.

Resources

The coal and clay deposits of the Laramie Formation were once economically important. Clay mining began in the

Golden, Colorado Golden is a List of municipalities in Colorado#Home rule municipality, home rule city that is the county seat of Jefferson County, Colorado, Jefferson County, Colorado, United States. The city population was 20,399 at the 2020 United States Censu ...

area in 1877 and continued until the mid-twentieth century. Most of the clay was used to make bricks and tiles for building construction.Van Horn, R. 1957. Bedrock geology of the Golden Quadrangle, Colorado. U.S. Geological Survey, Map GQ-103. 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 Room and pillar or pillar and stall is a variant of breast stoping. It is a mining system in which the mined material is extracted across a horizontal plane, creating horizontal arrays of rooms and pillars. To do this, "rooms" of ore are dug out ...

operations, and where the seams are steeply inclined to vertical, stope mining was used. Relatively little

surface mining Surface mining, including strip mining, open-pit mining and mountaintop removal mining, is a broad category of mining in which soil and rock overlying the mineral deposit (the overburden) are removed, in contrast to underground mining, in which ...

was done. 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 Weld County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 328,981. The county seat is Greeley. Weld County comprises the Greeley, CO Metropolitan Statistical Area, which is included in the Denver ...

, and near the town of Grover, Colorado. (See ''

Uranium mining in Colorado Uranium mining in Colorado, United States, goes back to 1872, when pitchblende ore was taken from gold mines near Central City, Colorado. The Colorado uranium industry has seen booms and busts, but continues to this day. Not counting byproduct u ...

'')

Paleofauna

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 United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

. 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).Report on the vertebrate paleontology of northern Colorado. Geological Exploration of the Fortieth Parallel. U.S. Geological and Geographical Survey. Cope named three species of dinosaurs without description: ''Cinodon arctatus'' (later changed to ''

Cionodon ''Cionodon'' (meaning 'column tooth') is a dubious genus of hadrosauridJ. R. Horner, D. B. Weishampel, and C. A. Forster. 2004. Hadrosauridae. In D. B. Weishampel, H. Osmolska, and P. Dodson (eds.), ''The Dinosauria'' (2nd edition). ''Universi ...

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).Vertebrate fauna of the Laramie Formation (Maastrichtian), Weld County, Colorado. Contributions to Geology, University of Wyoming 17: 37-49. More recent work in and around the Pawnee National Grasslands in Weld County has produced a diverse collection of 10 different fossil mammal species, including six multituberculates and four therians.Wilson, G.P., Dechesne, M. and Anderson, I.R., 2010. New latest Cretaceous mammals from northeastern Colorado with biochronologic and biogeographic implications. ''Journal of Vertebrate Paleontology'', ''30''(2), pp.499-520. List of Fossil Vertebrates (data from Carpenter 1979;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. Hutchinson and Holroyd 2003)

Cartilaginous fishes

Bony fishes

Amphibians

Turtles

Squamates

Crocodilians

Dinosaurs

Mammals

Paleoflora

Fossil

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...

(palynomorphs) include bryophyte and pteridophyte spores, gymnosperm pollen, and abundant angiosperm pollen, including ''Aquilapollenites striatus'', ''Ilexpollenites compactus'', ''Interpollis'' cf. ''I. supplingensis'', and ''Tricolpites interangulus''.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. The palynomorphs indicate an early Maastrichtian age (68-69 mya), which is supported by

magnetostratigraphy Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their '' ...

.*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. Magnetostratigraphy also shows that the Laramie Formation becomes progressively younger eastward as deposition followed the regression of the

. Fossil leaves are abundant, especially in the shales and sandstones associated with coal.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. 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''.

Footnotes

References

* Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. . {{Chronostratigraphy of Colorado, Mesozoic state=expanded Maastrichtian Stage of North America Cretaceous geology of Utah Geologic formations of Colorado Geology of the Rocky Mountains Cretaceous geology of Wyoming Ichnofossiliferous formations