The geology of Wyoming includes some of the oldest

Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth Earth ...

rocks in North America, overlain by thick marine and terrestrial sediments formed during the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

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 ...

and

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

, including oil, gas and coal deposits. Throughout its geologic history, Wyoming has been uplifted several times during the formation of the Rocky Mountains, which produced complicated faulting that traps hydrocarbons.

Geologic history, stratigraphy and tectonics

The

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 basement rocks of Wyoming include

schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...

and

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...

in the

Wyoming Craton The Wyoming Craton is a craton in the west-central United States and western Canada – more specifically, in Montana, Wyoming, southern Alberta, southern Saskatchewan, and parts of northern Utah. Also called the Wyoming Province, it is the init ...

, which formed during the

beginning 3. 6 billion years ago. The Wyoming Craton was sutured together with the Superior Craton and

Hearne Craton The Hearne Craton is a craton in northern Canada which, together with the Rae Craton, forms the Western Churchill Province. Hearne is one of the six Archaean cratons of the Canadian Shield (the other being Slave, Rae, Wyoming, Superior, Na ...

during the

Trans-Hudson Orogeny The Trans-Hudson orogeny or Trans-Hudsonian orogeny was the major mountain building event (orogeny) that formed the Precambrian Canadian Shield and the North American Craton (also called Laurentia), forging the initial North American continen ...

. The Wyoming Craton was a separate continent until it joined the proto-North American continent

Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although ...

1.86 billion years ago. Along its southern margin, the Wyoming Craton is faulted against younger

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

rocks from 1.7 billion years ago, which form the

Front Range The Front Range is a mountain range of the Southern Rocky Mountains of North America located in the central portion of the U.S. State of Colorado, and southeastern portion of the U.S. State of Wyoming. It is the first mountain range encountere ...

, extending into Colorado. The Mullen Creek-Nash Fork fault zone extends northeast to the

Black Hills The Black Hills ( lkt, Ȟe Sápa; chy, Moʼȯhta-voʼhonáaeva; hid, awaxaawi shiibisha) is an isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, United States. Black Elk P ...

Paleozoic (539-251 million years ago)

Shallow tropical seas dominated Wyoming during the

. The

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

Gros Ventre Formation is made up of

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 ...

and

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

, overlain by the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

Bighorn Dolomite and the Mississippian

Madison Limestone The Madison Limestone is a thick sequence of mostly carbonate rocks of Mississippian age in the Rocky Mountain and Great Plains areas of the western United States. The rocks serve as an important aquifer as well as an oil reservoir in places. T ...

. Small

unconformities 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 o ...

appear in the stratigraphic record due to periodic erosion or lack of deposition on the Wyoming shelf. During the Pennsylvanian, the uplift of the

ancestral Rocky Mountains The geology of the Rocky Mountains is that of a discontinuous series of mountain ranges with distinct geological origins. Collectively these make up the Rocky Mountains, a mountain system that stretches from Northern British Columbia through cen ...

began, with a prong known as the Pathfinder uplift extending into Wyoming. However, most of the region was draped in erosion deposits, forming the

Tensleep Sandstone The Tensleep Sandstone is a geological formation of Pennsylvanian to very early Permian age in Wyoming. The formation is composed of fine- to medium-grained sandstone, light gray and yellowish gray; generally slightly to moderately calcareous; s ...

Mesozoic (251-66 million years ago)

More terrestrial conditions prevailed in the

, with the deposition of

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 ...

red bed formations and

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. ...

in rivers, which bear well-preserved dinosaur fossils. During the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

, a renewed

marine transgression A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...

produced 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, ...

forming sandstone and the thick, organic-rich Thermopolis Shale,

Mowry Shale The Mowry Shale is an Early Cretaceous geologic formation. The formation was named for Mowrie Creek, northwest of Buffalo in Johnson County, Wyoming. Description The Mowry Shale or Fish-scale Beds because of the abundance of fish scales, is ...

and

Cody Shale The Cody Shale is a Late Cretaceous geologic formation. It is mapped in Wyoming, Idaho, and 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 an ...

, which are a major source of oil.

Cenozoic (66 million years ago-present)

Dryland conditions have continued since the end of the Cretaceous, through the

and the

Laramide orogeny The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the o ...

uplifted the Rocky Mountains through the

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

. Wyoming has numerous Laramide orogeny-related

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

s, which form the

Wind River Range The Wind River Range (or "Winds" for short) is a mountain range of the Rocky Mountains in western Wyoming in the United States. The range runs roughly NW–SE for approximately . The Continental Divide follows the crest of the range and inclu ...

, Bighorn Range and

Laramie Range The Laramie Mountains are a range of moderately high peaks on the eastern edge of the Rocky Mountains in the U.S states of Wyoming and Colorado. The range is the northernmost extension of the line of the ranges along the eastern side of the Rock ...

, with more ductile sedimentary rocks folded over Precambrian igneous rocks at the core of each range. This foreland deformation is particularly visible in Clarks Fork Canyon, the

Beartooth Range The Beartooth Mountains are located in south central Montana and northwest Wyoming, United States, U.S. and are part of the Absaroka-Beartooth Wilderness, within Custer National Forest, Custer, Gallatin National Forest, Gallatin and Shoshone Natio ...

and the

Gros Ventre Range The Gros Ventre Range ( ) is part of the Central Rocky Mountains and is located west of the Continental Divide in U.S. state of Wyoming. The highest summit in the range is Doubletop Peak at . The Gros Ventre Range is mostly within the Gros Ven ...

. Large quantities of oil and gas are held beneath the

anticline In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is the ...

formations formed by the west dipping, low angle faults of the overthrust belt. Large coal beds formed as highlands eroded throughout the

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...

, burying organic material. In the

Fort Union Formation The Fort Union Formation is a geologic unit containing sandstones, shales, and coal beds in Wyoming, Montana, and parts of adjacent states. In the Powder River Basin, it contains important economic deposits of coal, uranium, and coalbed methane. ...

, coal beds are as much as 100 feet thick. Lake Gosiute and Lake Uinta were playa lakes in the

, that accumulated the

oil shale Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general composition of oil shales constitute ...

Green River Formation The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River in Colorado, Wyoming, and Utah. The sediments are deposited in very fine ...

, which include numerous fossils visible at

Fossil Butte National Monument Fossil Butte National Monument is a United States National Monument managed by the National Park Service, located west of Kemmerer, Wyoming, United States. It centers on an assemblage of Eocene Epoch (56 to 34 million years ago) animal and pla ...

. In the

Shirley Basin Shirley may refer to: Arts and entertainment * ''Shirley'' (novel), an 1849 novel by Charlotte Brontë * ''Shirley'' (1922 film), a British silent film * ''Shirley'' (2020 film), an American film * ''Shirley'' (album), a 1961 album by Shirley Bas ...

, south of

Casper, Wyoming Casper is a city in, and the county seat of, Natrona County, Wyoming, United States. Casper is the second-largest city in the state, with the population at 59,038 as of the 2020 census. Only Cheyenne, the state capital, is larger. Casper is nic ...

, the

Wind River Formation The Wind River Formation is a geologic formation in Wyoming. It preserves fossils dating back to the Paleogene period. A recent study by Stanford suggests that fracking has contaminated the entire ground water resource in the basin. Fossil conte ...

has a brilliant white color imparted by

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

ash fall in the

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

and

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Basin and Range Province The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating ...

. Young Cenozoic rocks are well preserved in a downfaulted area in the

Sweetwater Hills Sweetwater or Sweet Water may refer to: * Freshwater Places In the United States * Sweet Water, Alabama * Sweetwater, Arizona * Sweetwater River (California), San Diego County ** Sweetwater Dam, a dam across the Sweetwater River ** Sweetwate ...

. During the last 2.5 million years of the

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

continued uplift has accelerated erosion, as the

Teton Range The Teton Range is a mountain range of the Rocky Mountains in North America. It extends for approximately in a north–south direction through the U.S. state of Wyoming, east of the Idaho state line. It is south of Yellowstone National Park and ...

formed and the

Yellowstone Caldera The Yellowstone Caldera, sometimes referred to as the Yellowstone Supervolcano, is a volcanic caldera and supervolcano in Yellowstone National Park in the Western United States. The caldera and most of the park are located in the northwest corn ...

formed in its present location.

References

{{Geology of the United States by political division

Wyoming Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...