The Greater Green River Basin (GGRB) is a 21,000 square mile basin located in Southwestern

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 ...

. The Basin was formed 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 ...

period sourced by underlying

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

and

deposits. The GGRB is host to many

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 ...

s created during 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 ...

trapping many of its hydrocarbon resources. It is bounded by the Rawlins Uplift,

Uinta Mountains The Uinta Mountains ( ) are an east-west trending chain of mountains in northeastern Utah extending slightly into southern Wyoming in the United States. As a subrange of the Rocky Mountains, they are unusual for being the highest range in the con ...

, Sevier overthrust belt, Sierra Madre Mountains, and the Wind River Mountain Range. The Greater Green River Basin is subdivided into four smaller basins, the Green River Basin,

Great Divide Basin The Great Divide Basin or Great Divide Closed Basin is an area of land in the Red Desert of Wyoming where none of the water falling as rain to the ground drains into any ocean, directly or indirectly. It is thus an endorheic basin, one of severa ...

, Washakie Basin, and Sand Wash Basin. Each of these possesses hydrocarbons that have been economically exploited. There are 303 named fields throughout the basin, the majority of which produce natural gas; the largest of these gas fields is the Jonah Field.

Geologic setting

The GGRB was formed during the

and is split into an east and west region by the

Rock Springs Uplift The Rock Springs Uplift is an area of uplifted Cretaceous to Eocene rocks in Wyoming surrounded and once covered by sediments of the Green River Formation which were deposited in the Eocene Lake Gosiute.Surdam, Ronald C. and K. O. Stanley, ''Lacustr ...

; an intrabasin

uplift that consists of units formed at the end of the

into 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' ...

. Prior to the basins formation in the

, many of the basins source rocks come from the

Phosphoria Formation The Phosphoria Formation of the western United States is a geological formation of Early Permian age.Behnken, F.H., Wardlaw, B.R. and Stout, L.N., 1986, Conodont biostratigraphy of the Permian Meade Peak Phosphatic Shale Member, Phosphoria Format ...

. The

was deposited in a Successor Basin (a basin that is formed directly after a tectonic event) that lies between the

Sevier Orogeny The Sevier orogeny was a mountain-building event that affected western North America from northern Canada to the north to Mexico to the south. The Sevier orogeny was the result of convergent boundary tectonic activity, and deformation occurred fr ...

to the west and the ancient Rocky Mountain

orogeny Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. An ''orogenic belt'' or ''orogen'' develops as the compressed plate crumples and is uplifted t ...

to the east. The Phosphoria Sea was a shallow, sediment starved sea that produced lots of carbonates and phosphorus rich sediments that source many of the hydrocarbon reservoirs found in the Rocky Mountain region today. The

was not a single event, but a prolonged tectonic event that had different affects across the large Greater Green River basin. Due to the GGRB size each sub-basin has its own unique geologic history and deposition. Cretaceous_Seaway_H

Rock Springs Uplift

The

is a 1,200 square mile asymmetric

composed of Late

Baxter Shale. This

anticlinal Anticlinal may refer to: *Anticline, in structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. *Anticlinal, in stereochemistry, a torsion angle between 90° to 150°, and –90° to –150°; see Alkane_st ...

uplift separates the Green River Basin to the West from the Greateat Divide, Washakie, and Sand Wash Basins to the East. The Baxter Shale is extremely eroded forming a deep depression surrounded by sandstone

escarpments An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations. The terms ''scarp'' and ''scarp face'' are often used interchangeably with ''escar ...

that are part of the

Mesaverde Group The Mesaverde Group is a Late Cretaceous stratigraphic group found in areas of Colorado, New Mexico, Utah, and Wyoming, in the Western United States. History The Mesaverde Formation was first described by W.H.Holmes in 1877 during the Hayden ...

. Above the

are incised valleys that contain the

Lewis Shale The Lewis Shale is a geologic formation in the Western United States. It preserves fossils dating back to the Campanian to Maastrichtian stages of the late Cretaceous period. Description The Lewis Shale is an olive-gray marine shale with some t ...

, Fox Hills Sandstone, and the

Lance Formation The Lance (Creek) Formation is a division of Late Cretaceous (dating to about 69 - 66 Ma) rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the late ...

. The next unit exposed is 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. ...

deposited in 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 ...

, followed by lower

Wasatch Formation The Wasatch Formation (Tw)Shroba & Scott, 2001, p.3 is an extensive highly fossiliferous geologic formation stretching across several basins in Idaho, Montana Wyoming, Utah and western Colorado.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 ...

into the Early

Sub-basins

Green River Basin

The Green River Basin is the largest sub-basin in the GGRB area at 10,500 square miles. It is defined by multiple outcrops the most prominent being Oyster Ridge, a North to South angled hogback that exposes the

Frontier Formation The Frontier Formation is a sedimentary geological formation whose strata date back to the Late Cretaceous. The formation's extents are: northwest Colorado, southeast Idaho, southern Montana, northern Utah, and western Wyoming. It occurs in many ...

sandstone. The next outcrop is White Mountain containing Mid-

exposure. The North and South margins of the basin are composed of gravels and

conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** Co ...

s that are

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

in age.

deposits dominate the outcrops in the Green River Basin.

Great Divide Basin

The

is located in the Northeastern part of the GGRB. Earned its name due to its location right on the

Continental Divide A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not ...

. The basin is 3,500 square miles with no significant outcropping. It is made up of low hills, dunes, alkali flats, and arid lakes. It is a desert plains environment separated from the Green River Basin by the

to the West.

Washakie Basin

The Washakie Basin is a 3,000 square mile, rimmed basin in the South central part of the GGRB just below the Great Divide Basin. The rimmed parts of the basin are about 1,000 ft higher than the basin floor and are capped by the Laney Member of the

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 ...

(Mid-

). Below the Laney Member is the exposure of the

Wasatch Formation The Wasatch Formation (Tw)Shroba & Scott, 2001, p.3 is an extensive highly fossiliferous geologic formation stretching across several basins in Idaho, Montana Wyoming, Utah and western Colorado.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' ...

Sand Wash Basin

The Sand Wash is the smallest of the four sub-basins at just 2,000 square miles in size. It is in the Southeastern portion of the GGRB and dips into Northwestern

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 ...

. There are a few central exposures of

aged rocks that form ridges. The Laney Member of the

is exposed along these ridges followed by the

Source rocks, traps, and seals

There are many source rocks in the GGRB, up to 9 viable units, but the most abundant producers of hydrocarbons are the

, the

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 the

. The

source rocks are all marine shales that were deposited in a

foreland basin A foreland basin is a structural basin that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithospher ...

created by the Cretaceous seaway. The marine shales experienced

subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope move ...

from the

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

of the

as well as

Progradation In sedimentary geology and geomorphology, the term progradation refers to the growth of a river delta farther out into the sea over time. This occurs when the volume of incoming sediment is greater than the volume of the delta that is lost through ...

al accumulation that topped these

anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...

marine shales with clastic alluvium. The clastic alluvium units now serve as a great reservoir rock for the marine shales deposited from the

into the

. Phosphoria Formation is made up of

Shales. It is believed that the organic rich shales are the primary source to much of the oil in the region. It is thought that the oil from these shales have migrated into the Pennsylvanian

Tensleep Formation 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 ...

, and

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 ' ...

reservoirs of Central and Eastern

. Due to its carbonate and

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...

rich depositional environment, the oil found in the

as a high sulfer content making it Type-IIS

kerogen Kerogen is solid, insoluble organic matter in sedimentary rocks. Comprising an estimated 1016 tons of carbon, it is the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold. It ...

. This is important to note because sulfur rich oils have been known to mature at much lower temperatures than normal. The

is the most prominent

reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contro ...

rock hosting approximately 142 million barrels of oil with about 12 fields producing from this unit. The

was sealed by the marine shale units of the

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 ...

Dinwoody Formation The Dinwoody Formation is a geologic formation in Montana. It preserves fossils dating back to the Triassic period. See also * List of fossiliferous stratigraphic units in Montana * Paleontology in Montana Paleontology in Montana refers to pale ...

. This shale seal was broken during the

leading to the migration of oil into the

. The oil now is trapped in

s formed by the

Laramide 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 ...

. The Mowry Shale is a well-known source rock of

reservoirs in

with the highest total organic content in the area. It is known to source the

Dakota Sandstone The Dakota is a sedimentary rock, sedimentary geologic unit name of Formation (stratigraphy), formation and Group (stratigraphy), group rank in Midwestern North America. The Dakota units are generally composed of sandstones, mudstones, clays, and ...

and

both prolific reservoirs in the Rocky Mountain Region. The

is oil prone for the most part due to the collection of Type-II

at deposition. The Mowry is unique because it is sealed by marine shales and trapped by both

s and faults. The

s are estimated to hold 6.6 million barrels of oil and about 2 billion cubic feet of gas. Southwestern_Wyoming_Upper_Cretaceous_Unit_cross_section

The Cretaceous Mesaverde Group supplies much of the gas to GGRB. The

was a product of two major transgressions and regressions that lasted approximately 6 million years followed by another sequence that lasted 3 million years. Though much of the Mesaverde units were eroded and this is observed by the

unconformity 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 ...

that splits the lower

from the Upper. The

is dominated by Type-III

Kerogen Kerogen is solid, insoluble organic matter in sedimentary rocks. Comprising an estimated 1016 tons of carbon, it is the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold. It ...

making it a great source for gas and a decent source for oil. The

is predominately sealed by marine shales that overlie the group. The

experiences anticline traps, fault traps, and stratigraphic pinch-out traps in the fields it functions as source rock for throughout the GGRB. The Mesaverde has an estimated production level of 2.3 million barrels of oil, and about 25.83 trillion cubic feet of gas making the

the ideal source for gas exploration.

References

{{Reflist Structural basins of the United States Geology of Wyoming Geology of Colorado Geology of Utah