|Dakota Formation / Group|
Stratigraphic range: Cenomanian
Road cut into the lower Dakota Group at crest of Dinosaur Ridge, near Golden, Colorado
|Type||Geologic formation or group|
|Sub-units||Formation (type: Nebraska, Kansas):|
D/Johnson Clay Member
J/Terra Cotta Clay Member
Mesa Rica Sandstone
|Underlies||Graneros Shale (Great Plains)|
Mancos Shale (Southwest)
|Overlies||Precambian (Sioux Quartzite), Permian, Early Cretaceous, (Lytle), and Jurassic (Morrison Formation)|
|Primary||varying proportions of terrestrial sandstone, mudstone, and clay|
|Other||marine shale, lignite, coal|
|Region||Great Plains, Rocky Mountains, Colorado Plateau, Rio Grande rift valley|
|Country|| United States|
|Named for||Dakota City, Nebraska|
|Named by||Meek and Hayden|
The Dakota is a sedimentary geologic unit name of formation and group rank 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.
Owing to extensive weathering of older rocks during the Jurassic and Triassic, the Dakota strata lie unconformably atop many formations ranging in age from Precambrian to Early Cretaceous. With a few local exceptions, it is the oldest Cretaceous unit exposed in the northern Great Plains, including Kansas, Nebraska, Iowa, Minnesota, and Wisconsin, a well as the Desert Southwest. It generally consists of sandy, shallow marine or beach deposits with marine-influenced mudflat sediments, and occasional stream deposits.
Naming and Rank
F.B. Meek and F.V. Hayden first used Dakota in 1862 to name the distinctive red sandstone exposures along the Missouri River near Dakota City, Nebraska. But, with this name, they applied the term "group", which at that time had the meaning of formation rank, as presently used. Dakota Formation is the unit's primary name and rank in the Great Plains. Formation rank is also applied in western extents (e.g., northeast Utah) as the unit thins and exhibits formational characteristics, the marine shales are absent, and fossil pollen species correlate with those found in the unit on the Missouri River. In the San Juan Basin and other intermontane basins and plateaus of the Southwest, Dakota Sandstone is the formal name for the oldest Cretaceous sandstone as well as tongues of that terrestrial sandstone extending into the dark marine shales of the Mancos. However, Dakota Sandstone is everywhere a common informal name for the unit, especially for the sandstone beds.
The Dakota Group rank is employed along the territory of the Dakota Hogback in Colorado and Wyoming, the Colorado Plateau, the Dry Cimarron River, and the Denver Basin. This group ranking recognizes sequences and members that exhibit local formational characteristics, especially marine shales that are absent further from the center of the seaway. As these locations were at the time of formation the earliest and deepest areas of the seaway, these groups can include older ages of rocks than are usually included elsewhere under the Dakota name. The names of the member formations of the Dakota Group vary between these regions as the geology there is studied further; but, the key early unit consistently included in this Dakota Group, but excluded elsewhere, is the terrestrial Lytle Formation, which is older than any other Cretaceous rock in Colorado or Kansas. The Skull Creek Shale and Plainview Sandstone are also included in the Dakota Group; but, the pair represent a seaway sequence separate from the Lytle and Dakota sequences, and in the plains to the east, the same units are named Kiowa Shale and Cheyenne Sandstone, respectively, separate from the Dakota Formation.
Deposition of the sediments that would become the Dakota Formation began during the early Late Cretaceous (Cenomanian). This deposition marked a reversal from over 100 million years of erosion (most of the Mesozoic). This reversal was due to rising of the mouth of the rivers, called a rise in base level, as the Cretaceous Seaway formed. This rise lowered the gradient of the rivers causing them to deposit sediment inland because their velocity could no longer sustain high volumes of sediment.
Measurements show that the rivers flowed westward and southwestward towards the encroaching sea from source areas near the present-day Great Lakes. The point of deposition slowly moved eastward as the seaway rose. This change is seen by a gradual shift in the composition of sandstones from having a lot of Paleozoic-age rock detritus in Kansas to sandstones having all Precambrian crystalline rock debris in Iowa.
This shift means that the rivers had completely eroded away the Paleozoic rocks in the river source area by the time the Seaway rose high enough for the rivers to deposit sediments in Iowa. The very top of the Dakota Formation was deposited along the coast as indicated by some fossil marine invertebrates. Fossil plants, coal deposits and kaolinite clays show that the climate was warm and wet during deposition of the Dakota Formation. Some of the ancient preserved soils show that an extensive flood plain forest was present.
Western Interior Seaway sequences
This Cretaceous seaway experienced a number of geological sequences (rise and fall cycles of sea level relative to land elevation), which, during patricular lowstands, temporarily reestablished a land connection between the east and west continent at the ancestral Transcontinental Arch. Each sequence represents a cycle of major progression of the seaway into the western interior of North America followed by retreat (see Walther's Law of Facies). The sequences of the seaway typically express facies sequences of, first, a low-stand erosional surface discontinuity (possibly with development of soils), then a transgressive pattern of terrestrial sand and mud followed by near shore marine sediments, a high stand pattern that may establish far-shore marine shale and limestone, a regressive pattern of a return to near shore marine sediments to terrestrial mud and sand, and a final low-stand erosional surface. Five of the first sequences of the Western Interior Seaway are relevant to the Dakota classifications.
The first sequence, typified by the Lytle Formation, did not complete the linkage of the north and south embayments before retreating. The second sequence is typified by the corresponding Skull Creek and Kiowa formations. These first two sequences are not present at the type area along the Missouri River. The sediments broadly considered as Dakota then record the Mowry sequence with the Muddy, J or Lower Dakota sandstones and the D or Upper Dakota sandstones forming at the discontinuities at the beginning and end of that cycle. In the east the limited marine shales of the Mowry sequence are assigned to the Dakota Formation, while in the center the mudstones and marine shales are commonly assigned a separate unit between upper and lower sandstone units, and in the Southwest, the much thicker marine shales are assigned to tongues of the Lower Mancos. The Greenhorn Cycle is the final relevant sequence as it overlays all Dakota classifications, with the exception of certain sandstones of Graneros age, such as classified in Wisconsin and Iowa.
Over the range of the usage of the Dakota name, the unit is primarily known for its massive beds of sandstone, which commonly shows shades of red, but also gray, yellow, or white. The sand was carried and deposited by rivers or accumulated in dunes or shoreline strands, and later cemented by red iron oxide or white calcite, depending on the local groundwater conditions that followed the sedimentation. The degree of cementation can range from softly crumbling to resistant to hammering. The sandstone beds can have local conglomerations of gravel. The composition of the sand and gravel varies depending on the sources of the rivers that made each deposit.
The amount of sandstone, averaging 25-50%, can very greatly over short distances between extremes of 5% to 80%. The general remainder of the unit, however, generally in complementary 80% to 5% proportions, is layered mudstone and clay deposited on floodplains, swamps, and estuaries. Similar to the sand, the soil-forming mud was modified by groundwater conditions to accumulate iron oxide or calcite. Coloration can be dark to light red, grey, yellow, and white. Iron oxide accumulation can approach the hardness and luster of hematite.
Marine shale is also a part of the Dakota sequences. Less common in the remote extents, particularly in the east, the shale is more representative of the deeper portions of the inland seaway. Moreover, shales on top of the upper Dakota on the plains of the east are usually assigned to the Granola or equivalent units, while in the west the thickest interbedding "tongues" of shale are generally assigned to the lower Marcos. Nevertheless, near the western limits, where the Dakota "pinches out" between the Morrison and the Mowry, the unit returns to the totally terrestrial sand-mud-sand pattern and fossil pollens of the Nebraska type location.
These characteristics of chaotic, land-formed sandbanks and mudflats lying above flinty, whiter marine megacyclic Permian limestones and below grey, rhythmic, chalky shales, persist for thousands of miles, locally variable as they may be, causing common use of the name Dakota in spite of many efforts to apply localized names.
Two sides of the seaway
Historically, Lower Cretaceous strata in the Rocky Mountain region have been called the Dakota Formation based on assumed correlation with the type section of the Dakota of the Great Plains. Witzke and Ludvigson have argued that use of the name "Dakota" must reflect actual, not presumed correlation based on stratigraphy and composition of the sedimentary rock. To the west of the Rocky Mountains, such as on the Colorado Plateau, this sequence of Upper Cretaceous, predominately sandstone, sedimentary rocks was recommended to be known as the Dakota Group, to dispel any suggestion of direct facies correlation. However, few authors of papers on the Dakota west of the Rocky Mountains, especially on the Colorado Plateau, recognize the Dakota as the Dakota Group, instead using the term Dakota Sandstone, of formation rank. Its subdivisions are recognized as members. Many authors have emphasized the fact that the marine Dakota Sandstone on the Colorado Plateau is intertongued with the marine lower part of the Mancos Shale, resulting in valid lithostratigraphic names such as the Whitewater Arroyo Tongue of the Mancos Shale which is directly overlain by the Twowells Sandstone Tongue of the Dakota Sandstone. In the western San Juan Basin, the lowermost part of the Dakota Sandstone, although of marginal marine origin in the eastern San Juan Basin, is a complex of non-marine sandstones. These relationships are especially well displayed in the San Juan Basin of northwestern New Mexico
Beginning in the Early Cretaceous, the Cretaceous Seaway spread south from what is now the Arctic Ocean and connected with a short northward extension from the Gulf of Mexico. This marine transgression of the ocean onto what was formerly land, was completed by the late Albian (~100 MA) thereby dividing North America in half. On the eastern side of the Seaway, sediments that would become the Dakota Formation were deposited as coastal and nearshore marine sands and silts. As the seaway continued to deepen and widen, this eastern shoreline moved progressively eastward throughout the Cenomanian. Meanwhile, on the western side of the seaway, sediments were carried eastwards and northeastwards by rivers from mountains located along what is the Nevada-Utah border.
These western sediments accumulated as nearshore and coastal sands and silts as well, and are counterparts to the Dakota Formation on the eastern side of the Seaway. However, these counterpart sediments originated from the other side of the sea and were carried by rivers flowing in opposite directions. These western sediments are equivalent to the Dakota Formation of the Great Plains, but are not exactly the same strata. Individual formations in the western Dakota Group have local names. In Wyoming, the term Cloverly Formation has been expanded by some authors to include sediments formerly placed within the Dakota Formation. Along the Colorado Front Range, the lower, terrestrial beds, or facies, of the Dakota Group are sometimes called the Lytle Formation, and near-shore marine facies are called the South Platte Formation. In eastern Utah and western Colorado, Young introduced the term Naturita Formation for a series of facies in the larger "Dakota Group". However, despite Witzke and Ludvigson logic, geologist have continued to refer to the Lower Cretaceous sequence of formations on the Colorado Plateau and the Rocky Mountains as the Dakota Group.
The Dakota has provided several resources in the Plains states as well as in parts of the mountainous west.
The predominant shales and mudstones are a source of hydrocarbons while the lenses and channels of sandstone form exploitable hydrocarbon reserves. Thus, the Dakota Group is an oil and gas source in the Denver Basin.
When they are near the surface, these same structures function as aquitards and aquifers, respectively. The Dakota sandstones form crucial supplies of water on the Plains, especially on uplands between river valleys wherever it is found outside the boundaries of the Ogallala Aquifer.
As the formation is uniquely terrestrial in origin, in contrast to the vast marine formations of the Plains, the Dakota has additional unique resources. Lignite coal has formed in the unit and was mined briefly in the 19th century. This supply was immediately mined for fuel by early American settlers, but was decidedly inferior to larger supplies of coal in the southeast of Kansas. The widespread bog environments of the Dakota period resulted in concretions of iron, forming hematite, limonite, and beds of "ironstone", which are common in the Janssen clay member of Kansas. Smelting of this limited iron source was only briefly attempted in conjunction with the lignite mining. The iron-cemented sandstone was found to be a durable and colorful building material on the treeless 19th century Plains. Historic 1860s buildings of Fort Harker (Kansas) and Fort Larned are constructed of this stone. The Dakota clays are quarried for tile and brick manufacture.
Uranium is also found concentrated in the Dakota sandstone where percolating uranium-rich water has deposited the mineral in the aquifers.
Dinosaur fossils are very rare in the Dakota Formation and most of them come from Kansas. Some of them are found in Colorado. The most popular site for public viewing of Creteceous dinosaur fossils in Colorado is Dinosaur Ridge. The best specimen is a partial skeleton of a nodosaurid ankylosaur called Silvisaurus condrayi. Other isolated ankylosaur material may also belong to Silvisaurus. Fossil dinosaur tracks are also known and include theropod and ankylosaur. A large ornithopod femur is known from Burt County, Nebraska as well as fossil dinosaur tracks from Jefferson County.
- cf. Troodon sp
- cf. Paronychodon (? troodontid indet)
- cf. Richardoestesia sp. (theropod indet)
- ? Barosaurus lentus
- Silvisaurus condrayi – "Partial skeleton with skull, sacrum."
|Pterosaurs of the Dakota Formation|
||Known from both early and late Cretaceous strata in the Dakota Group. Found at the John Martin Reservoir in Colorado.||Specimens kept at the Dinosaur Tracks Museum, of the University of Colorado at Denver.|
- List of dinosaur-bearing rock formations
- Dinosaur Ridge is located west of Denver, Colorado
- Dakota Hogback
- "Geologic Unit: Woodbury". National Geologic Database. Geolex — Significant Publications. United States Geological Survey. Retrieved November 27, 2020.
- Molenaar, C.M., Cobban, W.A., Merewether, E.A., Pillmore, C.L., Wolfe, D.G., and Holbrook, J.M. (2002). "Regional stratigraphic cross sections of Cretaceous rocks from east-central Arizona to the Oklahoma Panhandle". National Geologic Map Database. USGS. Retrieved February 20, 2020.
[The left of sheet 1 illustrates Clay Mesa Tongue (Marcos), Paguate Tongue (Dakota), Whitewater Arroyo Tongue (Marcos), Twowells Tongue (Dakota)]CS1 maint: uses authors parameter (link)
- "Geologic Unit: Dakota". National Geologic Database. Geolex — Significant Publications. United States Geological Survey. Retrieved November 27, 2020.
- Meek, F.B. and Hayden, F.V., 1862, Descriptions of new Lower Silurian, (Primordial), Jurassic, Cretaceous, and Tertiary fossils, collected in Nebraska, by the exploring expedition under the command of Capt. Wm F. Reynolds, U.S. Top. Engineers, with some remarks on the rocks from which they were obtained: Academy of Natural Sciences of Philadelphia Proceedings, v. 13, p. 415-447.
- Monroe, James S. and Wicander, Reed (1997) The Changing Earth: Exploring Geology and Evolution (2nd edition) Wadsworth Publishing Company, Belmont, California, page 610, ISBN 0-314-09577-2
- "Geology of the Quarry: Dakota Sandstone" Dinosaur National Monument, National Park Service
- McLaughlin, Thad G. (1942) "Water-bearing Formations, continued: Cretaceous System: Dakota Group" Geology and Ground-Water Resources of Morton County, Kansas
- Douglas A. Sprinkel, Scott K. Madsen, James I. Kirkland, Gerald L. Waanders, and Gary J. Hunt (2012). "Cedar Mountain and Dakota Formations around Dinosaur National Monument—evidence of the first incursion of the Cretaceous Western Interior Seaway into Utah" (PDF). Utah Geological Survey Special Study. Utah Geological Survey (143): 9, 12-15. Retrieved February 21, 2021.
The Dakota Formation ... has undergone a colorful history of nomenclature changes. ... Naturita has generally not been an accepted name for this section of rocks on the Colorado Plateau. ... The term Dakota Sandstone has been formally used in geologic maps and reports in the eastern Uinta Mountains (...); however, we revise the descriptive term to formation to reflect the lithologic heterogeneity of the Dakota in this region and to be consistent with usage elsewhere in Utah.CS1 maint: multiple names: authors list (link)
- Jeremy McCreary. "Colorado Geology Photojournals - A Tribute to Colorado's Physical Past and Present - Colorado Geology Overview". cliffshade. Retrieved August 30, 2019.
- "The Geologic Framework of the Dakota Aquifer". The Dakota Aquifer Program Annual Report. Kansas Geological Survey (FY89): Part 3b.
(The report concludes that the Lytle Sequence is not present in Kansas or eastern Colorado, and states the Kiowa and Cheyenne correlate with the Skull Creek and Plainview. )
- Wang, Herb (2003) "Saga of the Dakota Sandstone"
- Bejnar, C. R. and Lessard, R. H. (1976) "Paleocurrents and depositional environments of The Dakota Group, San Miguel and Mora Counties, New Mexico" in Ewing, Rodney C. and Kues, Barry S. (eds.) (1976) Guidebook of Vermejo Park, Northeastern New Mexico: Twenty-seventh Field Conference, September 30, October 1 and 2, 1976 New Mexico Geological Society, Socorro, N.M., pp. 157–163, OCLC 2754478
- Witzke, B.J., and Ludvigson, G.A. 1994. The Dakota Formation in Iowa and its type area. In Shurr, G.W., Ludvigson, G.A., and Hammond, R.H. (eds). Perspectives on the eastern margin of the Cretaceous Western Interior Basin. Geological Society of America, Special Paper 287:43–78.
- R.J. Weimer (1984). J.S. Schlee (ed.). "Relation of unconformities, tectonics, and sea-level changes, Cretaceous of Western Interior, U.S.A.; in" (PDF). AAPG Memoir. American Association of Petroleum Geologists (Memoir 36, Interregional unconformities and hydrocarbon accumulation): 7-35. Retrieved February 21, 2021.
[The url is to a Rice University-hosted pdf of a book chapter adapted from the original Weimer 1984 paper.]
- Young, Robert G. (1960) "Dakota Group of Colorado Plateau" American Association of Petroleum Geologists Bulletin 44(2): pp 156–194
- Kauffman, E.G. 1984. Paleobiogeography and evolutionary response dynamic in the Cretaceous Western Interior Seaway of North America. In Westermann, G.E.G. (ed), Jurassic-Cretaceous Biochronology and Paleogeography of North America, Geological Association of Canada Special Paper 27: 273–306.
- Waage, K. M. (1955) Dakota Group in northern Front Range Foothills, Colorado U.S. Geological Survey Professional Paper 274-B:15–49.
- For example in east-central and northeast New Mexico the Dakota Group consists of the Mesa Rica Sandstone, the Pajarito Shale, and the Romeroville Sandstone, and includes the underlying Tucumcari Shale in the Tucumcari area and Glencairn Formation in Union County. "Dakota Group" U.S. Geological Survey
- Debra K. Higley and Dave O. Cox (2007). "Petroleum Systems and Assessment of Undiscovered Oil and Gas in the Denver Basin Province, Colorado, Kansas, Nebraska, South Dakota, and Wyoming—USGS Province 39 : Chapter 2 Oil and Gas Exploration and Development along the Front Range in the Denver Basin of Colorado, Nebraska, and Wyoming" (PDF). U.S. Department of the Interior / U.S. Geological Survey: 3. Retrieved April 19, 2020. Cite journal requires
- Alvin R. Leonard and Delmar W. Berry, U. S. Geological Survey (1961). "Geology and Ground-water Resources of Southern Ellis County and Parts of Trego and Rush Counties, Kansas". State Geological Survey of Kansas Bulletin 149. University of Kansas. Retrieved April 19, 2020.
- Walter H. Schoewe (1952). "Coal Resources of the Cretaceous System (Dakota Formation) in Central Kansas". Kansas Geological Survey, Bulletin 96, Part 2. University of Kansas. Retrieved April 19, 2020.
- "Welcome to Kansas Brick and Tile". Retrieved April 19, 2020.
Our three brick plants are nestled in the Dakota clay deposits right here in the heart of Kansas.
- Dr. John Hopkins (August 14, 2018). "Geology of Uranium Deposits in Colorado". Retrieved April 19, 2020.
- Eaton, T.H. 1960. A new armored dinosaur from the Cretaceous of Kansas. University of Kansas Paleontological Contributions, Vertebrata, 8:1–24.
- Carpenter, K. and J.I. Kirkland. 1998. Review of Lower and Middle Cretaceous ankylosaurs from North America. Lucas, S.G., Kirkland, J.I. and Estep, J.W., (eds.), Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin No. 14:249–270.
- Liggett, G.A. 2005. A review of the dinosaurs from Kansas. Transactions of the Kansas Academy of Science 108(1–2), p.1-14.
- Barbour, E. H. 1931. Evidence of dinosaurs in Nebraska. Bulletin of University of Nebraska State Museum, 1:187–190.
- Joeckel, R. M., Cunningham, J. M., Corner, R. G., Brown, G. W., Phillips, P. L. and Ludvigson, G. A. 2004. Late Albian Dinosaur Tracks from the Cratonic (eastern) Margin of the Western Interior Seaway, Nebraska, USA. Ichnos, 11:275-284.
- "Table 17.1," in Weishampel, et al. (2004). Page 365.
- Lockley, M.; Harris, J.D.; and Mitchell, L. 2008. "A global overview of pterosaur ichnology: tracksite distribution in space and time." Zitteliana. B28. p. 187-198. ISSN 1612-4138.