At the time, the supercontinent of
Laurasia had recently split into the continents of North America and Eurasia, although they were still connected by land bridges. North America moved north and was passing through the
The Morrison Basin, which stretched from New Mexico in the south to Alberta and Saskatchewan in the north, was formed during the
Nevadan orogeny, a precursor event to later orogenic episodes that created the Rocky Mountains started pushing up to the west. The deposits from their east-facing
drainage basins, carried by streams and
rivers from the Elko Highlands (along the borders of present-day Nevada and Utah) and deposited in
swampy lowlands, lakes, river channels and
floodplains, became the Morrison Formation.
In the north, the
Sundance Sea, an extension of the
Arctic Ocean, stretched through Canada down to the United States.
Coal is found in the Morrison Formation of Montana, which means that the northern part of the formation, along the shores of the sea, was wet and swampy, with more vegetation.
Aeolian, or wind-deposited sandstones, are found in the southwestern part, which indicates it was much more arid—a
desert, with sand
Type locality of the Salt Wash Member near White Wash, Grand County, Utah. The Morrison Formation is underlain by the brick-red Summerville Formation.
The Jurassic-Cretaceous boundary is seen where the red and purple beds of the Morrison Formation abruptly contact the drab, gray bed of the overlying Cedar Mountain Formation. The contact is the K1 unconformity. Jessie's Twist, southwest of Green River City, Utah.
Brushy Basin Member showing the purple and red colors of paleosols (ancient soils). East side of the San Rafael Swell, Emery County, Utah.
Gypsiferous facies of the Ralston Creek Member exposed in a road cut, Fremont County, Colorado.
The Morrison Formation is subdivided into several members, the occurrence of which are varied across the geographic extent of the Morrison. Members are (in alphabetical order):
Bluff Sandstone Member (AZ, CO, NM, UT): Well-sorted, light brown to white sandstone with large grains and components of chert. Interpreted as being deposited in an aeolian setting, at the edge of a dune field.
Reddish mudstones of the Tidwell Member underlying the whitish sandstones of the Saltwash Member, south of Cisco, Utah.
Brushy Basin Member on the Colorado Plateau
Brushy Basin Member (AZ, CO, NM, UT): conglomerate interbedded with mudstone; up to fifty percent by volume is made up of altered vitric ash, which originated as felsic ash falls. Deposition likely occurred in a fluvial-lacustrine environment, with the lacustrine component tending towards
Fiftymile Member (UT): Mainly present in the Kaiparowits basin, consisting of interbedded sandstone and mudstone, with minimal conglomerate. Locally, it is the uppermost member and has contact with the
Jackpile Sandstone Member (NM): primarily a whitish crossbedded subarkose sandstone with a clay matrix. It is interbedded with variegated, pale-green to red, bentonitic mudstone lenses. However, recent
detrital zircon geochronology results have suggested that the Jackpile Sandstone Member is part of the
Burro Canyon Formation.
Ralston Creek Member (CO): formerly a considered separate formation and recently reclassified as the basal member of the Morrison in eastern Colorado. It appears analogous to the Tidwell and Salt Wash Members. This reclassification is supported by more detailed examination of the contacts and radiometric dating. The Ralston Creek contains conglomerate, sandstone, gypsum-mudstone, and gypsum-sandstone-mudstone facies; it is undetermined if the gypsum is of marine or lacustrine origin.
Recapture Member (AZ, CO, NM, UT): forms the bottom of the Morrison across most of its range, overlying the
Wanakah Formations. Consists of clayey sandstone and
claystone, representing a fluvial setting, interbedded with purely aeolian sandstone facies; in places, it also contains a large (up to nineteen percent) of
orthoclase feldspar inclusions.
Salt Wash Member (CO, UT): composed of fluvial sandstone, with occasional
Tidwell Member at the type section, Shadscale Mesa, Emery County, Utah.
Tidwell Member (AZ, CO, NM, UT): in the northern part of the
Colorado Plateau, it is the basal member of the Morrison. Mainly composed of siltstone, shale, and sandstone, and occasionally incorporates limestone
clasts, along with thin beds of limestone. Depositional environments range from mudflats to fluvial, to evaporate and
lacustrine. The Morrison as a whole resembles the Tidwell.
Unkpapa Sandstone Member (SD): occurs primarily in western South Dakota as a well-sorted, fine-grained sandstone, consisting primarily of quartz, with some feldspar inclusions. Locally overlain by the
Lakota Formation or the main body of the Morrison, and overlies the Redwater Shale Member of the
Sundance Formation. Occasionally referred to as a separate formation, chiefly within the
Black Hills region.
Westwater Canyon Member (AZ, CO, NM, UT): consists of sandstone interbedded with mudstone lenses and the occasional conglomerate component. Deposited in a braided-stream environment, high in organic matter. The term "Poison Canyon Sandstone" is informally applied to the upper sandstone sections of the member. The Westwater Canyon Member is the main source of uranium ore in the Morrison, especially in the
San Juan Basin.
Windy Hill Member (CO, SD, UT, WY): Formerly included as the upper member of the Sundance Formation, as, like the rest of the Sundance, it was deposited in marine settings; however, it is separated by an
unconformity and interfingers with the Morrison, meriting the nomenclature shift. Composed of limey, fossiliferous sandstone, generally interpreted to be deposited in a marine setting.
"Popcorn" texture due to
bentonite, formed from volcanic ash, characterizes the Brushy Basin Member
Other informal or disused designations of the Morrison include the Stockett Bed in Montana, an unofficial sub-unit which contains bituminous coal; the outdated terms Casamero, Chavez, and Prewitt Sandstone for the Brushy Basin, Recapture, and Westwater Canyon, respectively; and the Bullington Member, which has been discarded entirely.
Sauropods that have been discovered include Diplodocus (most famously, the first nearly complete specimen of D. carnegii, which is now exhibited at the
Carnegie Museum of Natural History, in Pittsburgh, Pennsylvania), Camarasaurus (the most commonly found sauropod), Brachiosaurus, Apatosaurus, Brontosaurus, Barosaurus, the uncommon Haplocanthosaurus and Supersaurus. The very diversity of the sauropods has raised some questions about how they could all co-exist. While their body shapes are very similar (long neck, long tail, huge elephant-like body), they are assumed to have had very different feeding strategies, in order for all to have existed in the same time frame and similar environment.
Locations where significant Morrison Formation fossil discoveries have been made include:
Fruita Paleontological Resource Area. One of the sites is denoted by the arrow.
Garden Park, Colorado: One of the three major sites excavated by the paleontologists
Othniel Charles Marsh and
Edward Drinker Cope during the Bone Wars in 1877, though most of the specimens were too incomplete to classify (nomina dubia) during the 1877-78 field seasons. The first nearly complete skeletons of Stegosaurus,
Ceratosaurus, and Allosaurus were discovered at the site, including the type specimens of the former two and the proposed neotype of Allosaurus fragilis, in the 1883-1886 Yale field seasons. In 1992, a specimen of Stegosaurus stenops was discovered with its
armor still in place, which confirmed that the dinosaur had two rows of plates on its back.
Fruita Paleontological Resource Area: Badlands sites located south of
Fruita, were actively worked by George Callison from California State University and the Los Angeles County Museum of Natural History. Numerous specimens of mammals, lizards, and crocodiles were found. Most recently, Fruitafossor windscheffelia and the new dinosaur Fruitadens were described from the area.
Cleveland-Lloyd Dinosaur Quarry, Utah: First excavated by geologists from the University of Utah in the late 1920s.
William Lee Stokes led an expedition from Princeton in 1939. During the Jurassic, the quarry was a mudhole where several enormous sauropods got stuck and apparently caused a feeding frenzy that lured and trapped many carnivorous dinosaurs. Most of the allosaurs are from this site, as well as the unique Stokesosaurus and Marshosaurus.
Como Bluff, Wyoming: One of the most renowned fossil sites in North America. It was first worked by Cope and particularly Marsh in 1877 and has been the source of many different sauropods and non-dinosaur species. The
Cloverly Formation from the Cretaceous and some
Triassic strata are also exposed at this location.
Ten Sleep, including Dana Quarry from where at least 12 sauropods and theropods are recovered.
The Morrison Formation contains
uranium deposits, including the Jackpile uranium body discovered near
Grants, New Mexico in 1951. The ore deposits in the rich Grants mineral belt are concentrated in sandstone beds of the Westwater Canyon Member and the Jackpile Member. Mines in this belt produced 340,000,000 pounds (150,000,000 kg) of
U3O8 between 1948 and 2002. The uranium was precipitated by plant debris and
humate that acted as reducing agents.
^Trujillo, K.C.; Chamberlain, K.R.; Strickland, A. (2006). "Oxfordian U/Pb ages from SHRIMP analysis for the Upper Jurassic Morrison Formation of southeastern Wyoming with implications for biostratigraphic correlations". Geological Society of America Abstracts with Programs. 38 (6): 7.
^Bilbey, S.A. (1998). "Cleveland-Lloyd Dinosaur Quarry - age, stratigraphy and depositional environments". In Carpenter, K.; Chure, D.; Kirkland, J.I. (eds.). The Morrison Formation: An Interdisciplinary Study. Modern Geology. Vol. 22. Taylor and Francis Group. pp. 87–120.
^Mateus, O. 2006. Late Jurassic dinosaurs from the Morrison Formation, the Lourinhã and Alcobaça Formations (Portugal), and the Tendaguru Beds (Tanzania): a comparison. in Foster, J.R. and Lucas, S. G. R.M., eds., 2006, Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 36: 223-231.
^ Bell, Thomas, "Deposition and Diagenesis of the Brushy Basin Member and the Upper Part of the Westwater Canyon Member of the Morrison Formation, San Juan Basin, New Mexico," in A Basin Analysis Case Study: The Morrison Grants Uranium Region New Mexico, edited by Neil S. Fishermen, Elmer S. Santos, and Christine E. Turner-Peterson, American Association of Petroleum Geolgists, Tulsa, 1986.
abcAllan R. Kirk; Steven M. Condon (1986). "Structural Control of Sedimentation Patterns and the Distribution of Uranium Deposits in the Westwater Canyon Member of the Morrison Formation, Northwestern New Mexico--A Subsurface Study". In Turner-Peterson, C.E.; Santos, Elmer S.; Fishman, Neil S. (eds.). Basin Analysis Case Study: The Morrison Formation, Grants Uranium Region, New Mexico. Tulsa: The American Association of Petroleum Geologists. p. 110-111.
abMapel, W.J.; Chisholm, W.A. (1962). "Nonopaque heavy minerals in sandstone of Jurassic and Cretaceous age in the Black Hills, Wyoming and South Dakota". U.S. Geological Survey Bulletin. 1161 (C): 1-59.
^Szigeti, G.J; Fox, J.E. (1979). "Unkpapa Sandstone (Jurassic), Black Hills, South Dakota; an eolian facies of the Morrison Formation". In Ethridge, F.G.; Flores, R.M. (eds.). Recent and Ancient non marine depositional environments: models for exploration. Casper, WY: Society of Economic Paleontologists and Mineralogists Special Publication. p. 331-349.
^Christine E. Turner-Peterson (1986). "Fluvial Sedimentology of a Major Uranium-Bearing Sandstone-- A Study of the Westwater Canyon Member of the Morrison Formation, San Juan Basin, New Mexico". In Turner-Peterson, C.E.; Santos, Elmer S.; Fishman, Neil S. (eds.). Basin Analysis Case Study: The Morrison Formation, Grants Uranium Region, New Mexico. Tulsa: The American Association of Petroleum Geologists. p. 110-111.
^Fred Peterson. "Sand dunes, sabkhas, streams, and shallow seas: Jurassic paleogeography in the southern part of the Western Interior Basin". In Caputo, M.V.; Peterson, J.A.; Franczyk, K.J. (eds.). Mesozoic Systems of the Rocky Mountain Region, USA. Society of Economic Paleontologists and Mineralogists, Rocky Mountain Section. p. 233-272.
^Daniel, J.A.; Bartholomew, M.J.; Murray, R.C. (1992). "Geological Characteristics of the Stockett Bed Coal in the Central Great Falls Coal Field, Montana". Montana Bureau of Mines and Geology Special Publication. 102: 145-157.
^Smith, C.T. (1954). "Geology of the Thoreau quadrangle, McKinley and Valencia Counties, New Mexico". New Mexico Bureau of Mines and Mineral Resources. 31.
^Robertson, J.F. (1990). "Geologic map of the Thoreau quadrangle, McKinley County, New Mexico". U.S. Geological Survey.
^Saleiro, A., & Mateus O. (2017). Upper Jurassic bonebeds around Ten Sleep, Wyoming, USA: overview and stratigraphy. Abstract book of the XV Encuentro de Jóvenes Investigadores en Paleontología/XV Encontro de Jovens Investigadores em Paleontologia, Lisboa, 428 pp.. 357-361.
Foster, J. 2007. Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. 389pp.
Foster, J.R. 2003. Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. Bulletin 23.
Jenkins, J.T. and J.L. Jenkins. 1993. Colorado's Dinosaurs. Denver, Colorado: Colorado Geologic Survey. Special Publication 35.
Mateus, O. 2006. Late Jurassic dinosaurs from the Morrison Formation, the Lourinhã and Alcobaça Formations (Portugal), and the Tendaguru Beds (Tanzania): a comparison. in Foster, J.R. and Lucas, S. G. R.M., eds., 2006, Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 36: 223-231.