The Dakota is a
sedimentary
Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentati ...
geologic unit name of
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 ...
and
group
A group is a number of persons or things that are located, gathered, or classed together.
Groups of people
* Cultural group, a group whose members share the same cultural identity
* Ethnic group, a group whose members share the same ethnic ide ...
rank in Midwestern North America. The Dakota units are generally composed of
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) ...
s,
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. ...
s,
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 ...
s, and
shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
s deposited in the Mid-Cretaceous opening of 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, ...
.
[Monroe, James S. and Wicander, Reed (1997) ''The Changing Earth: Exploring Geology and Evolution'' (2nd edition) Wadsworth Publishing Company, Belmont, California, page 610, ] The usage of the name Dakota for this particular
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...
-
Cenomanian
The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...
strata is exceptionally widespread; from
British Columbia
British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
and
Alberta
Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...
to
Montana
Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...
and
Wisconsin
Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...
to
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 ...
and
Kansas
Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the ...
to
Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
and
Arizona
Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
. It is famous for producing massive colorful rock formations in the
Rocky Mountains
The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...
and the
Great Plains
The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, an ...
of the United States, and for preserving both
dinosaur footprints
A fossil track or ichnite (Greek "''ιχνιον''" (''ichnion'') – a track, trace or footstep) is a fossilized footprint. This is a type of trace fossil. A fossil trackway is a sequence of fossil tracks left by a single organism. Over the year ...
and early deciduous tree leaves.
Owing to extensive weathering of older rocks during the
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
and
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
, the Dakota strata lie
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 ...
atop many different formations ranging in age from
Precambrian
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
to Early Cretaceous. With a few local exceptions, it is the oldest Cretaceous unit exposed in the northern Great Plains, including
Kansas
Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the ...
,
Nebraska
Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the southwe ...
,
Iowa
Iowa () is a state in the Midwestern region of the United States, bordered by the Mississippi River to the east and the Missouri River and Big Sioux River to the west. It is bordered by six states: Wisconsin to the northeast, Illinois to the ...
,
Minnesota
Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over to ...
, and
Wisconsin
Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...
, as well as the
Desert Southwest
The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural region of the United States that generally includes Arizona, New Mexico, and adjacent portions of California, Colorado, N ...
. It generally consists of
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...
y, shallow
marine or beach deposits with marine-influenced
mudflat
Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal fl ...
sediments, and occasional
stream
A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a stream ...
deposits.
[McLaughlin, Thad G. (1942]
"Water-bearing Formations, continued: Cretaceous System: Dakota Group"
''Geology and Ground-Water Resources of Morton County, Kansas''
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
The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, an ...
. 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
The San Juan Basin is a geologic structural basin located near the Four Corners region of the Southwestern United States. The basin covers 7,500 square miles and resides in northwestern New Mexico, southwestern Colorado, and parts of Utah a ...
and other
intermontane
Intermontane is a physiographic adjective formed from the prefix " inter-" (''signifying among, between, amid, during, within, mutual, reciprocal'') and the adjective "montane" (inhabiting, or growing in mountainous regions, especially cool, moi ...
basins and
plateaus
In geology and physical geography, a plateau (; ; ), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. Often one or more sides ha ...
of the
Southwest
The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each sepa ...
, 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
Mancos is a statutory town in Montezuma County, Colorado, United States. The population was 1,196 at the 2020 census, down from 1,336 in 2010.
The town is in southwestern Colorado, at the base of Mesa Verde National Park, and holds the trademar ...
.
[ heet 1 illustrates Clay Mesa Tongue (Marcos), Paguate Tongue (Dakota), Whitewater Arroyo Tongue (Marcos), Twowells Tongue (Dakota)/ref> 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
: North terminus:
: South terminus:
The Dakota Hogback is a long hogback ridge at the eastern fringe of the Rocky Mountains that extends north-south from southern Wyoming through Colorado and into northern New Mexico in the United St ...
in Colorado and Wyoming, the Colorado Plateau
The Colorado Plateau, also known as the Colorado Plateau Province, is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. This province covers an area of ...
, the Dry Cimarron River
The Cimarron River ( ; iow, Ñíxgu, script=Latn or , meaning 'Salt River'; chy, Hotóao'hé'e) extends across New Mexico, Oklahoma, Colorado, and Kansas. The headwaters flow from Johnson Mesa west of Folsom in northeastern New Mexico. Mu ...
, and 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 ...
. This group ranking recognizes sequences and members that exhibit local formational characteristics, especially marine shales that are less developed or 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 earliest unit included in Dakota Groups, excluded elsewhere, is the terrestrial Lytle Formation, which is older than any other Cretaceous rock in Colorado or Kansas. The Skull Creek Shale
The Skull Creek Shale is a Cretaceous geologic formation in Wyoming as well as Colorado and Nebraska, United States.
The Skull Creek Shale corresponds with the Kiowa Shale.
See also
* List of fossiliferous stratigraphic units in Colorado
* ...
and Plainview Sandstone Plainview or Plain View may refer to:
*Plainview, Arkansas
*Plainview, California
* Plainview, Georgia
* Plainview, Illinois
* Plainview, Louisville, Kentucky
* Plainview, Minnesota
*Plainview, Nebraska
*Plainview, New York
*Plain View, North Carol ...
of Colorado are also included in the Dakota Group, as is the Cedar Mountain Formation
The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah, spanning most of the early and mid-Cretaceous. The formation was named for Cedar Mountain (Utah), Cedar Mountain in northern Emery Coun ...
of Utah and its Buckhorn Conglomerate member. However, these units represent a separate seaway sequence in the time between the Lytle and "upper Dakota" (Mowry) sequences, and in the plains to the east, the same units are named Kiowa Shale and Cheyenne Sandstone, which are considered separate from the Dakota Formation as defined in Kansas and, moreover, do not appear at the type location in Nebraska.[ (The report concludes that the Lytle Sequence is not present in Kansas or eastern Colorado, and observes that the Kiowa and Cheyenne correlate with the Skull Creek and Plainview. )] However, subsequent sequence stratigraphic and palynostratigraphic research has demonstrated that the Dakota Formation at the type location includes sand and mudstones covering the same ages and sequences as the "marine shale facies of the Graneros" and "early Late Albian Kiowa-Skull Creek".
In certain places, the classification is undivided; for example, in far southwest Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
, the strata is designated the Dakota Conglomerate without further division.
When nearer the surface (within a couple thousand feet/hundreds of meters), the sandstone beds of the Dakota Formation form various Dakota Aquifers, important water sources in some areas of the Great Plains and the Southwest, far greater in extent than the High Plains Aquifer, and famous for its artesian properties.
Elsewhere, when deeper, especially in 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 ...
, these same sands have been sought after for hydrocarbon reserves. " Drillers", who navigate deep strata by monitoring material brought to the surface in the drilling mud
In geotechnical engineering, drilling fluid, also called drilling mud, is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also us ...
, alphabetically designated the hydrocarbon "producing sands" of the Dakota in the Denver Basin as (highest) "D", "J", "M", and "O" (lowest). Colorado's "D" and "J" of the driller's Denver Basin have been particularly important to Nebraska, Kansas, and Oklahoma in their efforts of correlating their eastern outcrops with the Dakota units in the Denver Basin and the western units in general.
Geological history
Deposition of the sediments that would become the Dakota Formation began during the late Early Cretaceous (Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...
). This deposition marked a reversal from over 100 million years of erosion (most of the Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
). 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 Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five 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 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) ...
s having all Precambrian
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
crystalline rock debris in Iowa.[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.]
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
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
. 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 The Transcontinental Arch refers to the islands of North America which extended from New Mexico to Minnesota and the Great Lakes region. These islands were present during the Sauk sequence, the earliest cratonic sequence. As a result of the Sauk ...
. 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
In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...
sequences of, first, a low-stand erosional surface discontinuity (possibly with development of soils
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former term ...
), 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
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, ...
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
Kiowa () people are a Native American tribe and an indigenous people of the Great Plains of the United States. They migrated southward from western Montana into the Rocky Mountains in Colorado in the 17th and 18th centuries,Pritzker 326 and eve ...
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
Mancos is a statutory town in Montezuma County, Colorado, United States. The population was 1,196 at the 2020 census, down from 1,336 in 2010.
The town is in southwestern Colorado, at the base of Mesa Verde National Park, and holds the trademar ...
. 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.[ he url is to a Rice University-hosted pdf of a book chapter adapted from the original Weimer 1984 paper./ref>]
Lithology
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
Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...
or white calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
, 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
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. ...
and 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 ...
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
Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
.
In evidence of the general low-lying nature of the Dakota's lush, hot-house Earth environment, lignite
Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...
and 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 ...
have formed within in various areas.
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
Lower may refer to:
*Lower (surname)
*Lower Township, New Jersey
*Lower Receiver (firearms)
*Lower Wick
Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eight ...
strata in the Rocky Mountain region have been called the Dakota Formation based on assumed correlation with the type section A stratotype or type section in geology is the physical location or outcrop of a particular reference exposure of a stratigraphic sequence or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the stan ...
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,[Young, Robert G. (1960) "Dakota Group of Colorado Plateau" ''American Association of Petroleum Geologists Bulletin'' 44(2): pp 156–194] to dispel any suggestion of direct facies
In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...
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.[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.] This marine transgression of the ocean onto what was formerly land, was completed by the late Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...
(~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; however, accumulation of abundant sedement delivered by massive rivers limited shoreline advancement past the type location throughout the Cenomanian until overtopped by the Greenhorn Seaway in the early Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded by t ...
. 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
The Cloverly Formation is a geological formation of Early and Late Cretaceous age (Valanginian to Cenomanian stage) that is present in parts of Montana, Wyoming, Colorado and Utah in the western United States. It was named for a post office on th ...
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.[Waagé, K. M. (1955) ]
Dakota Group in northern Front Range Foothills, Colorado
' U.S. Geological Survey Professional Paper 274-B:15–49. In eastern Utah and western Colorado, Young introduced the term Naturita Formation
The Naturita Formation is a classification used in western Colorado and eastern Utah for a Cretaceous Period sedimentary geologic formation. This name was "applied to the upper or carbonaceous part of Dakota Formation, Dakota Group" by R.G. Youn ...
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
The Colorado Plateau, also known as the Colorado Plateau Province, is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. This province covers an area of ...
and the Rocky Mountains as the Dakota Group.
Economic geology
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
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 ...
.
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
The Ogallala Aquifer () is a shallow water table aquifer surrounded by sand, silt, clay, and gravel located beneath the Great Plains in the United States. One of the world's largest aquifers, it underlies an area of approximately in portio ...
.
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
Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...
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
Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
, limonite
Limonite () is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·H2O, although this is not entirely accurate as the ratio of oxide to hydroxid ...
, 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)
Fort Harker, located in Kanopolis, Kansas, was an active military installation of the United States Army from November 17, 1866 to October 5, 1872. The fortification was named after General Charles Garrison Harker, who was killed in action at th ...
and Fort Larned
Fort Larned National Historic Site preserves Fort Larned which operated from 1859 to 1878. It is approximately west of Larned, Kansas, United States.
History
The Camp on Pawnee Fork was established on October 22, 1859 to protect traffic al ...
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.
Paleoenvironment
The sands and muds of the Dakota represent wet lowlands, rivers, flood plains, and beaches with a shoreline deeply undulating between deltas and brackish marine embayment
A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a narr ...
s. Ground water flowing from inland reacted with changes in pH, oxygenation
Oxygenation may refer to:
* Oxygenation (environmental), a measurement of dissolved oxygen concentration in soil or water
* Oxygen saturation (medicine), the process by which concentrations of oxygen increase within a tissue
* Water oxygenation, t ...
, and salinity
Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...
as it encountered seawater, depositing iron oxide and calcite in underground layers near shorelines. These minerals hardened the material and fossils to preserve evidence of the ecology of those environments. Sandstone with dinosaur tracks in the upper Dakota above the marine Skull Creek Shale
The Skull Creek Shale is a Cretaceous geologic formation in Wyoming as well as Colorado and Nebraska, United States.
The Skull Creek Shale corresponds with the Kiowa Shale.
See also
* List of fossiliferous stratigraphic units in Colorado
* ...
near Denver demonstrates that the seaway occasionally retreated from the area.
Vertebrate paleofauna
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 ...
fossils are very rare in the Dakota Formation and most of them come from Kansas. Some of them are found in Colorado and Nebraska. The most popular site for public viewing of Cretaceous dinosaur fossils in Colorado is Dinosaur Ridge
Dinosaur Ridge is a segment of the Dakota Hogback in the Morrison Fossil Area National Natural Landmark located in Jefferson County, Colorado, near the town of Morrison, Colorado, Morrison and just west of Denver.
The Dinosaur Ridge area is one ...
. The best specimen is a partial skeleton of a nodosaurid ankylosaur called ''Silvisaurus
''Silvisaurus'', from the Latin silva "woodland" and Greek sauros "lizard", is a nodosaurid ankylosaur from the Early to Late Cretaceous period.
Discovery and species
A fossil of the species was discovered in the fifties by rancher Warren H. ...
condrayi''.[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.] Other isolated ankylosaur material may also belong to ''Silvisaurus''.[Liggett, G.A. 2005. A review of the dinosaurs from Kansas. Transactions of the Kansas Academy of Science 108(1–2), p.1-14.] 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.[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.] Goniopholidids are also found here with '' Dakotasuchus kingi''.
* cf. ''Troodon'' sp
* cf. ''Paronychodon'' (? troodontid indet)
* cf. ''Richardoestesia'' sp. (theropod indet)
* ? ''Barosaurus lentus''
* ''Silvisaurus condrayi
''Silvisaurus'', from the Latin silva "woodland" and Greek sauros "lizard", is a nodosaurid ankylosaur from the Early to Late Cretaceous period.
Discovery and species
A fossil of the species was discovered in the fifties by rancher Warren H. C ...
'' – "Partial skeleton with skull, sacrum."["Table 17.1," in Weishampel, et al. (2004). Page 365.]
* ''Dakotasuchus kingi'' - a goniopholidid.
Pterosaurs
Plant Fossils
See also
* List of dinosaur-bearing rock formations
This list of dinosaur-bearing rock formations is a list of geologic formations in which dinosaur fossils have been documented.
Containing body fossils
* List of stratigraphic units with dinosaur body fossils
** List of stratigraphic units with ...
* Dinosaur Ridge
Dinosaur Ridge is a segment of the Dakota Hogback in the Morrison Fossil Area National Natural Landmark located in Jefferson County, Colorado, near the town of Morrison, Colorado, Morrison and just west of Denver.
The Dinosaur Ridge area is one ...
is located west of Denver
Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the Unit ...
, Colorado
* Dakota Hogback
: North terminus:
: South terminus:
The Dakota Hogback is a long hogback ridge at the eastern fringe of the Rocky Mountains that extends north-south from southern Wyoming through Colorado and into northern New Mexico in the United St ...
References
Further reading
Current stratigraphic correlation charts
* : Charts West Shore Dakota unit from Arizona to Kansas border. See Ludvigson 2010 for completion of East Shore Dakota through to Minnesota.
* : ''Isochronous'' stratigraphic chart correlates current usage from the eastern plains to the western border of Colorado. While the entire succession is illustrated, the reader can see the interaction of the West Shore Dakota stage with the Mesozoic discontinuities that preceded the seaway as well as the mountain building stages after the seaway.
* : ''Isochronous'' stratigraphic chart based on the CGS's chart and other sources, the focus entirely on the complex sequences of the Western Interior Seaway. By thereby expanding the vertical scale, the mechanism for vertically changing age of the West Shore Dakota over horizontal distances is clearly illustrated. Missing is the details of the Skull Creek/Kiowa sequence embodied within Colorado's particular definition of the Dakota Group.
:: ''Isochronous'' : The vertical scale is evenly progressing time rather than thickness; everything at the same level happened at the same time.
History of exploration
* : Introduces the Dakota geologic name and type.
* : Reports the essential early study of Colorado Arkansas Valley geology, ''bridging'' the Kansas studies of the lower Meek and Hayden Cretaceous in the Smoky Hills
The Smoky Hills are an upland region of hills in the central Great Plains of North America. They are located in the Midwestern United States, encompassing north-central Kansas and a small portion of south-central Nebraska.
The hills are a disse ...
(central to early studies of the Dakota) with the Colorado studies of the same Cretaceous groups in the Rocky Mountain Front Range.
* Waagé, K. M. (1955)
Dakota Group in northern Front Range Foothills, Colorado
. ''U.S. Geological Survey Professional Paper'' 274-B:15–49. : Defines the Lytle and South Platte
The South Platte River is one of the two principal tributaries of the Platte River. Flowing through the U.S. states of Colorado and Nebraska, it is itself a major river of the American Midwest and the American Southwest/ Mountain West. Its ...
formations of the Dakota Hogback
: North terminus:
: South terminus:
The Dakota Hogback is a long hogback ridge at the eastern fringe of the Rocky Mountains that extends north-south from southern Wyoming through Colorado and into northern New Mexico in the United St ...
as regional members of the Dakota Group introduced by Lee (1923).
* : Provides detailed descriptions of the processes, as understood at that time, that formed the first deposits of the Cretaceous on the Plains as the Western Interior Seaway made its first advance to the east, with mention of similar faces observed on the western shore. It was not yet recognized that the sequence that deposited the Skull Creek/Kiowa also deposited the lowest sands of the Dakota in eastern Nebraska.
* : Illustrates the many coastal deposition mechanisms active today and their application to the sediment records of the Western Interior Seaway, including early charts (Figure 10 and Figure 11) of the major sequences of the seaway.
* : Original classifications in Kansas were Lithostratigraphic
Lithostratigraphy is a sub-discipline of stratigraphy, the geology, geological science associated with the study of stratum, strata or rock layers. Major focuses include geochronology, comparative geology, and petrology.
In general, strata are ...
. This study of potential hydrostratigraphic coupling of Colorado and Kansas aquifers commences correlative application of advanced west shore sequence stratigraphy
Sequence stratigraphy is a branch of geology, specifically a branch of stratigraphy, that attempts to discern and understand historic geology through time by subdividing and linking sedimentary deposits into unconformity bounded units on a variety ...
to the east shore lithostratigraphy. This correlation was later supported by subsequent palynostratigraphy (Ludvigson - Witzke, 2010).
* : Application of sequence and palynostratographic methods matured on the West Shore to the East Shore. Reports new understandings of the marine influences on the development of the Dakota units, particularly at the Nebraska/Iowa type location. Identifies previously unreported discontinuity in the Dakota type, extending the upper Dakota/Woodbury member into the late Albian. Charts the Dakota unit and adjacent units with the new understanding of the discontinuities from the Kansas west border through the type location to Minnesota.
* : The new type section of the Tokay Tongue integrally establishes the temporal correlation of the terrestrial sequence tongues of the West Shore Dakota Sandstone classification with the X-bentonite reference horizon, biological horizons of the Colorado Group
Colorado is a geologic name applied to certain rocks of Cretaceous age in the North America, particularly in the western Great Plains. This name was originally applied to classify a group of specific marine formations of shale and chalk kn ...
, and lithological sequence horizons of the Greenhorn Limestone
The Greenhorn Limestone or Greenhorn Formation is a geologic formation in the Great Plains Region of the United States, dating to the Cenomanian and Turonian ages of the Late Cretaceous period. The formation gives its name to the Greenhorn cycle ...
and Graneros Shale
The Graneros Shale is a geologic formation in the United States identified in the Great Plains as well as New Mexico that dates to the Cenomanian Age of the Cretaceous Period. It is defined as the finely sandy argillaceous or clayey ''near-shore/ ...
. The following reports temporally correlate the very same Pueblo, Colorado
Pueblo () is a List of municipalities in Colorado#Home rule municipality, home rule municipality that is the county seat and the List of municipalities in Colorado, most populous municipality of Pueblo County, Colorado, Pueblo County, Colorado ...
, horizons with the sequences of the ''upper'' East Shore Dakota Formation classification.
* : Extends Brenner 2000 with additional data. With this increased resolution, proposes the Muddy-Mowry marine cycle and lists and illustrates (Figure 7) the record of parasequences (of marine-influenced deposition/non-marine downcutting) within the east Dakota sedimentary record of the terrestrial effects of the Skull Creek, Muddy- Mowry, and Graneros
Graneros is a Chilean commune and city in Cachapoal Province, O'Higgins Region.
Deportes
Graneros se conoce como unas de las candidatas a ganar la copa de la región Libertador Bernardo Ohiggins
Tiene su Estadio renovado,El Estadio Miguel Riffo ...
- lower Greenhorn marine cycles.
* : Figure 3 illustrates the third-order block thrusting events correlated with the resulting formation rank facies sequences of the seaway. Contemporary to Ludvigson-Witzke 2010, indicates just the two previously recognized Dakota terrestrial discontinuities.
*
External links
From Colorado perspective, animations of the Western Interior Seaway including the landbridge between the Mowry retreat and the Graneros advance:
* Ludvig Rhodin, James Adson, and Joseph Rogers
"Western Interior Seaway: Cretaceous Shorelines of Colorado"
''Interactive Geology Project'', University of Colorado Boulder
The University of Colorado Boulder (CU Boulder, CU, or Colorado) is a public research university in Boulder, Colorado. Founded in 1876, five months before Colorado became a state, it is the flagship university of the University of Colorado syst ...
.
* Ron Blakey and Teresa Hill
Colorado Paleogeography - Mesozoic 65ma-250ma
''Colorado Stratigraphy''.
{{Chronostratigraphy of Colorado, Mesozoic state=expanded
Cretaceous Colorado
Cretaceous formations of New Mexico
Cretaceous Kansas
Cretaceous geology of Nebraska
Cretaceous Iowa
Cretaceous Minnesota
Cretaceous Manitoba
Cretaceous geology of Utah
Geologic formations of Wisconsin
Cretaceous geology of Wyoming
Upper Cretaceous Series of North America
Cenomanian Stage
Sandstone formations of Canada
Sandstone formations of the United States
Mudstone formations
Shale formations
Shale formations of the United States
Shallow marine deposits
Ichnofossiliferous formations