Laramie Formation | |
---|---|
Stratigraphic range: Maastrichtian, 69–68 Ma | |
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] |
The Laramie Formation is a geologic formation of the 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] The formation contains some of the oldest records of Grass in western North America. [4]
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. [5] [6] 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. [7]
The coal and clay deposits of the Laramie Formation were once economically important. [6] 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. [8]
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 )
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). [9]
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). [10]
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. [11]
List of Fossil Vertebrates (data from Carpenter 1979; [12] Hutchinson and Holroyd 2003)
Cartilaginous fishes of the Laramie Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Abundance | Notes | |
cf. I. avonicola | ||||||
L. selachos | ||||||
M. bipartitus | ||||||
S. americana | ||||||
Bony fishes of the Laramie Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Abundance | Notes | Images |
Indeterminate | ||||||
A. occidentalis | ||||||
Amphibians of the Laramie Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Abundance | Notes | Images |
Indeterminate | ||||||
L. bairdi | ||||||
O. kayi | ||||||
S. tectum | ||||||
Turtles of the Laramie Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Abundance | Notes | |
Indeterminate | ||||||
cf. B. sinuosa | ||||||
C. victa | ||||||
cf. H. distincta | ||||||
cf. P. antique | ||||||
Squamates of the Laramie Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Abundance | Notes | |
O. piger | ||||||
Crocodilians of the Laramie Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Abundance | Notes | Images |
Indeterminate | ||||||
Color key
| Notes Uncertain or tentative taxa are in small text; |
Dinosaurs reported from the Laramie Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
C. goldenensis | ||||||
Indeterminate | ||||||
cf. Edmontonia [13] | Indeterminate [13] | Nodosauridae (possibly Denversaurus) [14] | ||||
E. annectens [13] | ||||||
O. minutus [13] | "Partial metatarsals II-IV." [15] | The specimens are now lost. [15] | ||||
Indeterminate [13] | ||||||
Two teeth [16] | ||||||
T. latus [13] | ||||||
T. horridus [13] | ||||||
T. rex | ||||||
Mammals of the Laramie Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Abundance | Notes | |
Indeterminate | ||||||
Indeterminate | ||||||
cf. Mesodma | Indeterminate | |||||
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. [17] The palynomorphs indicate an early Maastrichtian age (68-69 mya), which is supported by magnetostratigraphy. [18] 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. [19] 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
| Notes Uncertain or tentative taxa are in small text; |
Flora of the Laramie Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Abundance | Notes | Images |
Aquilapollenites striatus | ||||||
" Ficus " | "Ficus" planicostata | |||||
Ilexpollenites compactus | ||||||
Interpollis cf. I. supplingensis | ||||||
Marmarthia pearsonii | ||||||
" Myrica " | "Myrica" torreyi | |||||
Platanites marginata | ||||||
Sabalites sp. | ||||||
Tricolpites interangulus | ||||||
Meniscoessus is a genus of extinct multituberculates from the Upper Cretaceous Period that lived in North America.
The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone, and limestone and is light gray, greenish gray, or red. Most of the fossils occur in the green siltstone beds and lower sandstones, relics of the rivers and floodplains of the Jurassic period.
The Denver Basin, variously referred to as the Julesburg Basin, Denver-Julesburg Basin, or the D-J Basin, is a geologic structural basin centered in eastern Colorado in the United States, but extending into southeast Wyoming, western Nebraska, and western Kansas. It underlies the Denver-Aurora Metropolitan Area on the eastern side of the Rocky Mountains.
Denversaurus is a genus of panoplosaurin nodosaurid dinosaur from the late Maastrichtian of Late Cretaceous Western North America. Although at one point treated as a junior synonym of Edmontonia by some taxonomists, current research indicates that it is its own distinct nodosaurid genus.
The Horseshoe Canyon Formation is a stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. It takes its name from Horseshoe Canyon, an area of badlands near Drumheller.
The Fruitland Formation is a geologic formation found in the San Juan Basin in the states of New Mexico and Colorado, in the United States of America. It contains fossils dating it to the Campanian age of the late Cretaceous.
The Scollard Formation is an Upper Cretaceous to lower Palaeocene stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. Its deposition spanned the time interval from latest Cretaceous to early Paleocene, and it includes sediments that were deposited before, during, and after the Cretaceous-Paleogene (K-Pg) extinction event. It is significant for its fossil record, and it includes the economically important coal deposits of the Ardley coal zone.
The Dakota is a sedimentary geologic unit name of formation and group rank in Midwestern North America. The Dakota units are generally composed of sandstones, mudstones, clays, and shales deposited in the Mid-Cretaceous opening of the Western Interior Seaway. The usage of the name Dakota for this particular Albian-Cenomanian strata is exceptionally widespread; from British Columbia and Alberta to Montana and Wisconsin to Colorado and Kansas to Utah and Arizona. It is famous for producing massive colorful rock formations in the Rocky Mountains and the Great Plains of the United States, and for preserving both dinosaur footprints and early deciduous tree leaves.
The Milk River Formation is a sandstone-dominated stratigraphic unit of the Western Canada Sedimentary Basin in southern Alberta, Canada. It was deposited in near-shore to coastal environments during Late Cretaceous time. Based on uranium-lead dating, palynology and stratigraphic relationships, deposition occurred between ~84.1 and 83.6 Ma.
The Foremost Formation is a stratigraphic unit of Late Cretaceous (Campanian) age that underlies much of southern Alberta, Canada. It was named for outcrops in Chin Coulee near the town of Foremost and is known primarily for its dinosaur remains and other fossils.
The Wapiti Formation is a geological formation of the Western Canada Sedimentary Basin in northwestern Alberta, and northeastern British Columbia, Canada. Its deposition spanned the time interval from the lower Campanian through to the upper Maastrichtian, between approximately 80 and 68 Ma. It was named by G.M. Dawson in 1881, presumably for exposures along the lower part of the Wapiti River and downstream along the Smoky River in Alberta.
The North Horn Formation is a widespread non-marine sedimentary unit with extensive outcrops exposed in central and eastern Utah. The formation locally exceeds 3,600 feet (1,100 m) in thickness and is characterized by fluvial, lacustrine, and floodplain dominated systems, representing a terrestrial, high energy, depositional environment. The sediments date from Late Cretaceous (Maastrichtian) to early Paleocene in age and include the K-Pg extinction event boundary; however, this boundary is extremely difficult to locate and there is no strong stratigraphic evidence available that indicates a specific marker bed such as an iridium rich clay layer. Thus far, the only visible evidence is represented in the form of faunal turnover from dinosaur to mammal-dominated fossil assemblages. Taxa from the Cretaceous part of the formation include squamates, testudines, choristoderes, crocodyliforms, sharks, bony fishes, amphibians, mammals, dinosaurs, eggshell fragments, trace fossils, mollusks, plant macrofossils, such as wood fragments, and palynomorphs.
The McRae Group is a geological group exposed in southern New Mexico whose strata, including layers of the Hall Lake Formation and Jose Creek Formation, date to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from this unit.
The Denver Formation is a geological formation that is present within the central part of the Denver Basin that underlies the Denver, Colorado, area. It ranges in age from latest Cretaceous (Maastrichtian) to early Paleocene, and includes sediments that were deposited before, during and after the Cretaceous-Paleogene boundary event.
The Arapahoe Formation is a geological formation of latest Cretaceous (Maastrichtian) age that is present within the Denver Basin that underlies the Denver, Colorado, area. The formation includes fossil leaves and dinosaur remains, although none of the latter have yet been referred to a specific genus. It also includes aquifers that are important sources of water for the area.
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.
The Straight Cliffs Formation is a stratigraphic unit in the Kaiparowits Plateau of south central Utah. It is Late Cretaceous in age and contains fluvial, paralic, and marginal marine (shoreline) siliciclastic strata. It is well exposed around the margin of the Kaiparowits Plateau in the Grand Staircase – Escalante National Monument in south central Utah. The formation is named after the Straight Cliffs, a long band of cliffs creating the topographic feature Fiftymile Mountain.
Ceratopsipes goldenensis is an ichnospecies of dinosaur footprint, described in 1995 from the Laramie Formation in Colorado. It is represented by massive pes prints approaching 80 centimetres (31 in) in width. If undistorted, the tracks may represent an unusually large Ceratopsian dinosaur that could have potentially been as large as 12 metres.
The Benton Shale is a geologic formation name historically used in Montana, Wyoming, North Dakota, South Dakota, Colorado, Kansas, and Nebraska. In the "mile high" plains in the center of the continent, the named layers preserve marine fossils from the Late Cretaceous Period. The term Benton Limestone has also been used to refer to the chalky portions of the strata, especially the beds of the strata presently classified as Greenhorn Limestone, particularly the Fencepost limestone.
The Dawson Arkose is a geologic formation in the Denver Basin that underlies the Denver area in Colorado. It is characterized by alternating beds of arkosic sandstone and mudstone. The Dawson Arkose contains plant remains and other nonmarine fossils, and hosts aquifers that are important sources of water for the area.