Editing Morrison Formation (section)

== Stratigraphy ==
[[File:Type SW-2.jpg|thumb|Type locality of the Salt Wash Member near White Wash, Grand County, Utah. The Morrison Formation is underlain by the brick-red Summerville Formation.]]
[[File:Morrison-Cedar Mountain Formations.jpg|thumb|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.]]
[[File:Brushy Basin Mbr, Morrison Fm.jpg|thumb|Brushy Basin Member showing the purple and red colors of paleosols (ancient soils). East side of the San Rafael Swell, Emery County, Utah.]]
[[File:Ralston Mbr.jpg|thumb|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):<ref name="USGS Geolex: Morrison Formation">{{Cite web|title=Geologic Unit: Morrison|url=https://ngmdb.usgs.gov/Geolex/Units/Morrison_9394.html|access-date=December 30, 2020|website=USGS Geolex}} </ref><ref>{{Cite web|title=Geologic Unit: Windy Hill|url=https://ngmdb.usgs.gov/Geolex/Units/WindyHill_11198.html|access-date=December 30, 2020|website=USGS Geolex}} </ref>
*[[Bluff Formation|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.<ref>{{cite web |last1=Condon |first1=S.M. |title=Stratigraphic Sections of the Middle Jurassic Wanakah Formation, Cow Springs Sandstone, and adjacent rocks, from Bluff, Utah, to Lupton, Arizona: U.S. Geologic Survey Oil and Gas Investigation Chart, OC-131 |url=https://ngmdb.usgs.gov/Prodesc/proddesc_5160.htm |website=USGS Geolex |publisher=U.S. Geological Survey |access-date=December 31, 2020}}</ref>
[[File:Saltwash Tidwell.JPG|thumb|

Reddish mudstones of the Tidwell Member underlying the whitish sandstones of the Saltwash Member, south of Cisco, Utah.

]] [[File:BrushyBasin.jpg|thumb|

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 [[Dry lake|playas]].<ref> 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. </ref>
*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 [[Dakota Formation]].<ref>{{cite journal |last1=Peterson |first1=Fred |title=Revisions to Stratigraphic Nomenclature of Jurassic and Cretaceous Rocks of the Colorado Plateau |journal=U.S. Geological Survey Bulletin |date=1988 |volume=1633 |issue=B |page=13-56 |url=https://pubs.usgs.gov/bul/1633a-c/report.pdf |access-date=December 31, 2020}}</ref>
*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.<ref name="owen-etal-1984">{{cite journal |last1=Owen |first1=Donald E. |last2=Walters | first2=Lester J. Jr. |last3=Beck |first3=Ronald G. |title=The Jackpile Sandstone Member of the Morrison Formation in west-central New Mexicoby Donald E. jwen, Consulting Geologist, Tulsa, 0K 74152, and Lester J.Walters, Jr. and Ronald G. Beck, ARCO Oil and Gas Co., Dallas, IX75221 a formal definiti |journal=New Mexico Geology |date=August 1984 |volume=6 |issue=3 |doi=10.58799/NMG-v6n3.45 |url=https://geoinfo.nmt.edu/publications/periodicals/nmg/6/n3/nmg_v6_n3_p45.pdf |access-date=4 June 2020}}</ref> However, recent [[detrital zircon geochronology]] results have suggested that the Jackpile Sandstone Member is part of the [[Burro Canyon Formation]].<ref>{{cite journal |last1=Dickinson |first1=William R. |last2=Gehrels |first2=George E. |title=Implications of U-Pb ages of detrital zircons in Mesozoic strata of the Four Corners region for provenance relations in space and time |journal=New Mexico Geological Society Field Conference Series |date=2010 |volume=61 |pages=135–146 |url=https://nmgs.nmt.edu/publications/guidebooks/downloads/61/61_p0135_p0146.pdf |access-date=27 October 2020}}</ref><ref>{{cite journal |last1=Cather |first1=Steven M. |title=Jurassic stratigraphic nomenclature for northwestern New Mexico |journal=New Mexico Geological Society Special Publication |date=2020 |volume=14 |pages=145–151 |url=https://nmgs.nmt.edu/publications/special/14/NMGS_SP-14.pdf |access-date=31 October 2020}}</ref>
*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.<ref>{{Cite journal|last1=Carpenter|first1=Kenneth|last2=Lindsey|first2=Eugene|date=2019-01-31|title=Redefining the Upper Jurassic Morrison Formation in Garden Park National Natural Landmark and vicinity, eastern Colorado|url=https://giw.utahgeology.org/giw/index.php/GIW/article/view/37|journal=Geology of the Intermountain West|language=en|volume=6|pages=1–30|doi=10.31711/giw.v6.pp1-30|issn=2380-7601|doi-access=free}}</ref> 
*Recapture Member (AZ, CO, NM, UT): forms the bottom of the Morrison across most of its range, overlying the [[Entrada Sandstone|Entrada]] and [[Wanakah Formation|Wanakah]] Formations.<ref>{{cite journal |last1=Condon |first1=S.M. |last2=Huffman |first2=A.C. |title=Revisions in nomenclature of the Middle Jurassic Wanakah Formation, Northwest New Mexico and northeast Arizona |journal=U.S. Geological Survey Bulletin |date=1988 |volume=1633 |issue=A |page=1-12 |url=https://ngmdb.usgs.gov/Prodesc/proddesc_92777.htm |access-date=8 February 2021}}</ref> Consists of clayey sandstone and [[Mudstone|claystone]], representing a fluvial setting, interbedded with purely aeolian sandstone facies;<ref name="Kirk-Condon-in-BACS-1989">{{cite book |author1=Allan R. Kirk |author2=Steven M. Condon |chapter= 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 |editor1-last=Turner-Peterson |editor1-first=C.E. |editor2-last=Santos |editor2-first=Elmer S. |editor3-last=Fishman |editor3-first=Neil S. |title=Basin Analysis Case Study: The Morrison Formation, Grants Uranium Region, New Mexico |date=1986 |publisher=The American Association of Petroleum Geologists |location=Tulsa |page=110-111}}</ref> in places, it also contains a large (up to nineteen percent) of [[orthoclase]] feldspar inclusions.<ref>{{cite journal |last1=Peterson |first1=Fred |last2=Turner-Peterson |first2=C.E. |title=The Morrison Formation of the Colorado Plateau: recent advances in sedimentology, stratigraphy, and paleotectonics |journal=Hunter |date=1987 |volume=2 |issue=1 |page=1-18 |url=https://ngmdb.usgs.gov/Prodesc/proddesc_91414.htm |access-date=8 February 2021}}</ref>
*Salt Wash Member (CO, UT): composed of fluvial sandstone,<ref name="Kirk-Condon-in-BACS-1989"> </ref> with occasional [[Conglomerate (geology)|conglomeratic]] tendencies.<ref name="O'Sullivan-1984">{{cite journal |last1=O'Sullivan |first1=R.B. |title=The base of the Upper Jurassic Morrison Formation in east-central Utah |journal=U.S. Geological Survey Bulletin |date=1984 |volume=1561 |page=17 |url=https://ngmdb.usgs.gov/Prodesc/proddesc_92737.htm |access-date=8 February 2021}}</ref>
[[File:Tidwell-Peterson stratotype.jpg|thumb|Tidwell Member at the type section, Shadscale Mesa, Emery County, Utah.]]
*{{anchor|Tidwell Member}}'''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.<ref name="O'Sullivan-1984"></ref> Depositional environments range from mudflats to fluvial, to evaporate and [[lacustrine]]. The Morrison as a whole resembles the Tidwell.<ref name="Peterson-1988">{{cite journal |last1=Peterson |first1=Fred |title=Stratigraphy and Nomenclature of Middle and Upper Jurassic rocks, western Colorado Plateau, Utah and Arizona |journal=U.S. Geological Survey Bulletin |date=1988 |volume=1633 |issue=B |page=13-56 |url=https://ngmdb.usgs.gov/Prodesc/proddesc_92778.htm |access-date=9 February 2021}}</ref>
*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.<ref name="Mapel-Chisholm-1962">{{cite journal |last1=Mapel |first1=W.J. |last2=Chisholm |first2=W.A. |title=Nonopaque heavy minerals in sandstone of Jurassic and Cretaceous age in the Black Hills, Wyoming and South Dakota |journal=U.S. Geological Survey Bulletin |date=1962 |volume=1161 |issue=C |page=1-59}}</ref> Locally overlain by the [[Lakota Formation]] or the main body of the Morrison, and overlies the Redwater Shale Member of the [[Sundance Formation]].<ref>{{cite book |author1=Szigeti, G.J |author2=Fox, J.E. |chapter=Unkpapa Sandstone (Jurassic), Black Hills, South Dakota; an eolian facies of the Morrison Formation |editor1-last=Ethridge |editor1-first=F.G. |editor2-last=Flores |editor2-first=R.M. |title=Recent and Ancient non marine depositional environments: models for exploration |date=1979 |publisher=Society of Economic Paleontologists and Mineralogists Special Publication |location=Casper, WY |page=331-349}}</ref> Occasionally referred to as a separate formation, chiefly within the [[Black Hills]] region.<ref name="Mapel-Chisholm-1962">{{cite journal |last1=Mapel |first1=W.J. |last2=Chisholm |first2=W.A. |title=Nonopaque heavy minerals in sandstone of Jurassic and Cretaceous age in the Black Hills, Wyoming and South Dakota |journal=U.S. Geological Survey Bulletin |date=1962 |volume=1161 |issue=C |page=1-59}}</ref>
*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.<ref name="Kirk-Condon-in-BACS-1989"> </ref> The Westwater Canyon Member is the main source of uranium ore in the Morrison, especially in the [[San Juan Basin]].<ref name="Turner-Peterson-in-BACS-1989">{{cite book |author1=Christine E. Turner-Peterson |chapter=Fluvial Sedimentology of a Major Uranium-Bearing Sandstone-- A Study of the Westwater Canyon Member of the Morrison Formation, San Juan Basin, New Mexico |editor1-last=Turner-Peterson |editor1-first=C.E. |editor2-last=Santos |editor2-first=Elmer S. |editor3-last=Fishman |editor3-first=Neil S. |title=Basin Analysis Case Study: The Morrison Formation, Grants Uranium Region, New Mexico |date=1986 |publisher=The American Association of Petroleum Geologists |location=Tulsa |page=110-111}}</ref>
*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.<ref>{{cite book |author1=Fred Peterson |chapter=Sand dunes, sabkhas, streams, and shallow seas: Jurassic paleogeography in the southern part of the Western Interior Basin |editor1-last=Caputo |editor1-first=M.V. |editor2-last=Peterson |editor2-first=J.A. |editor3-last=Franczyk |editor3-first=K.J. |title=Mesozoic Systems of the Rocky Mountain Region, USA |publisher=Society of Economic Paleontologists and Mineralogists, Rocky Mountain Section |page=233-272}}</ref> Composed of limey, fossiliferous sandstone, generally interpreted to be deposited in a marine setting.<ref name="Pipiringos-1968">{{cite journal |last1=Pipiringos |first1=G.N. |title=Correlation and Nomenclature of some Triassic and Jurassic Rocks in south-central Wyoming |journal=U.S. Geological Survey Professional Paper |date=1968 |volume=594 |issue=D |page=1-26 |url=https://ngmdb.usgs.gov/Prodesc/proddesc_92909.htm |access-date=8 February 2021}}</ref>
[[Image:Popcorn Texture.JPG|thumb|"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;<ref>{{cite journal |last1=Daniel |first1=J.A. |last2=Bartholomew |first2=M.J. |last3=Murray |first3=R.C. |title=Geological Characteristics of the Stockett Bed Coal in the Central Great Falls Coal Field, Montana |journal=Montana Bureau of Mines and Geology Special Publication |date=1992 |volume=102 |page=145-157}}</ref> the outdated terms Casamero, Chavez, and Prewitt Sandstone for the Brushy Basin, Recapture, and Westwater Canyon, respectively;<ref name="smith-1954">{{cite journal |last1=Smith |first1=C.T. |title=Geology of the Thoreau quadrangle, McKinley and Valencia Counties, New Mexico |journal=New Mexico Bureau of Mines and Mineral Resources |date=1954 |volume=31}}</ref><ref name="Robertston-1990">{{cite journal |last1=Robertson |first1=J.F. |title=Geologic map of the Thoreau quadrangle, McKinley County, New Mexico |journal=U.S. Geological Survey |date=1990}}</ref> and the Bullington Member, which has been discarded entirely.