The bedrock of

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 ...

was assembled from island arcs accreted onto the edge of the ancient

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 ...

. The Sonoma orogeny uplifted the ancestral Rocky Mountains in parallel with the diversification of multicellular life. Shallow seas covered the regions, followed by the uplift current Rocky Mountains and intense volcanic activity. Colorado has thick sedimentary sequences with oil, gas and coal deposits, as well as base metals and other minerals.

Stratigraphy, tectonics and geologic history

In the early Proterozoic, between 1.78 and 1.65 billion years ago, the continental crust of Colorado was assembled from several older island arcs, along the coast of the

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 ...

. The Colorado Province took shape as a mobile belt—an area of thinner, orogeny related continental crust lacking the deep "keel" of rock, which stabilized the neighboring Wyoming Craton and other

cratons A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...

like it. Throughout Colorado's geologic history, rocks have often been deformed, metamorphosed and overprinted, obscuring the ancient record. Beginning 1.7 billion years ago

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...

and

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...

intruded. The Routt Plutonic Suite is dated to 1.66 to 1.79 billion years old and is an important rock formation in Rocky Mountain National Park and Buffalo Mountain. The Berthoud orogeny from 1.45 to 1.35 billion years ago created granite intrusions, uplifts, rifts and ductile shear zones, grouped as the Berthoud Plutonic Suite. The

Grenville orogeny The Grenville orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent orogenic belt which spans a significant portion of the North American continent, f ...

intruded large granites throughout much of

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, althoug ...

, the Proto-North American continent, although Pike's Peak was the only location significantly affected by Grenville granite intrusions in Colorado. The region's crystalline basement rock finished forming with a massive batholith 1.1 billion years ago. The breakup of Rodinia one of the oldest supercontinents, produced rifts between 900 million and 600 million years ago in the

Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is ...

. These deep extensional basement faults filled with sediments, such as the Uinta rift basin and were often reactivated more recently in Earth history by orogenies. The Uinta Formation and Uncompahgre Formation are both examples of remnant Precambrian rift basin sediments. The end of the Neoproterozoic is not known from the rock record, indicating a period of long-running terrestrial erosion which produced by the

Great Unconformity Of the many unconformities (gaps) observed in geological strata, the term Great Unconformity is frequently applied to either the unconformity observed by James Hutton in 1787 at Siccar Point in Scotland,Rance, H (1999''Historical Geology: The ...

, from 1.1 billion to 510 million years ago. Ten kilometers of basement rock and almost all Precambrian sediments eroded away.

Paleozoic (539-251 million years ago)

In 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 ' ...

, as multicellular life became common, Colorado was covered in a shallow tropical sea. Thick sequences 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) ...

, shale 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 ...

were laid down on the Precambrian bedrock. The Sonoma orogeny uplifted the ancestral Rocky Mountains around 300 million years ago, which reached heights of around 10,000 feet. The Laurentian continent was colliding with the supercontinent

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

to the south, to form the larger supercontinent

Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...

. This continental collision generated two large island mountain ranges, the Frontrangia and Uncompahgria. Erosion quickly wore away at the mountains, shedding sediments across the landscape.

Mesozoic (251-66 million years ago)

Dark red

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

shale and wind-blown sands transformed into sandstone overlie Permian rocks, marking the beginning 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 ...

. The sea reached western Colorado and the area was blanketed in ash fall from eruptions to the west.

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...

dune sands were covered over by the sandstone and shale of the Morrison Formation, until a large scale marine transgression flooded the region in 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 ...

. As sea levels fell, the Dakota Formation sands and pebbles took shape, followed by another marine transgression that deposited several thousand feet of shale as the Mancos Formation and Pierre Formation. Intermediate water depths filled with the Niobrara limestone. Sand layers point to periodic regression and shale layers contain extensive marine fossils. With the beginning of 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 ...

that uplifted the Rocky Mountains, coastal wetlands formed large coal deposits. Thick coal and sandstone layers that grow thicker to the west are known as the Mesaverde Group.

Cenozoic (66 million years ago-present)

The Laramide orogeny continued in the

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 ...

up until 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' ...

with tectonic forces shifting from north–south mountain ranges to east–west. The Uinta Range is unique, trending east–west due to older tectonic constraints. In the Denver Basin, the Denver Formation and Dawson Formation formed 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 ...

from sand and gravel eroded out of the Rockies. To the west, rivers filled the lowlands with the Wastach Formation. Erosion and uplift occurred in sync, creating mountains that tended to have gradual slopes. After the end of uplift 20 million years ago, erosion cut down to bedrock in the mountains. In the northwest, the Green River Formation siltstones formed as a lake deposit in a basin formed along Proterozoic faults and was covered over with siltstone and sandstone of the Uinta Formation. Together with Utah and Nevada,

Farallon Plate The Farallon Plate was an ancient oceanic plate. It formed one of the three main plates of Panthalassa, alongside the Phoenix Plate and Izanagi Plate, which were connected by a triple junction. The Farallon Plate began subducting under the west ...

related volcanism in the Oligocene produced enormous eruptions that built up the San Juan Mountains in the southwest. One third of the region was covered in ash flow. Throughout 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 ...

, large scale regional uplift elevated Colorado, New Mexico, Utah and Arizona 5000 feet above sea level. Erosion in the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

, glaciers formed in the mountains, carving out valleys and straightening streams.

Stratigraphy, tectonics and geologic history

Paleozoic (539-251 million years ago)

Mesozoic (251-66 million years ago)

Cenozoic (66 million years ago-present)

See also

References

External links