The Unkar Group is a sequence of strata of Proterozoic age that are subdivided into five geologic formations and exposed within the Grand Canyon, Arizona, Southwestern United States. The 5-unit Unkar Group is the basal member of the 8-member Grand Canyon Supergroup. The Unkar is about 1,600 to 2,200 m thick and composed, in ascending order, of the Bass Formation, Hakatai Shale, Shinumo Quartzite, Dox Formation, and Cardenas Basalt. Units 4 & 5 are found mostly in the eastern region of Grand Canyon. Units 1 through 3 are found in central Grand Canyon. The Unkar Group accumulated approximately between 1250 and 1104 Ma. In ascending order, the Unkar Group is overlain by the Nankoweap Formation, about 113 to 150 m thick; the Chuar Group, about 1,900 m (6,200 ft) thick; and the Sixtymile Formation, about 60 m (200 ft) thick. These are all of the units of the Grand Canyon Supergroup. The Unkar Group makes up approximately half of the thickness of the 8-unit Supergroup.
The Hakatai Shale is a Mesoproterozoic rock formation with important exposures in the Grand Canyon, Coconino County, Arizona. It consists of colorful strata that exhibit colors varying from purple to red to brilliant orange. These colors are the result of the oxidation of iron-bearing minerals in the Hakatai Shale. It consists of lower and middle members that consist of bright-red, slope-forming, highly fractured, argillaceous mudstones and shale and an upper member composed of purple and red, cliff-forming, medium-grained sandstone. Its thickness, which apparently increases eastwards, varies from 137 to 300 m. In general, the Hakatai Shale and associated strata of the Unkar Group rocks dip northeast (10–30°) toward normal faults that dip 60° or more toward the southwest. This can be seen at the Palisades fault in the eastern part of the main Unkar Group outcrop area. In addition, thick, prominent, and dark-colored basaltic sills and dikes cut across the purple to red to brilliant orange strata of the Hakatai Shale.
The Bass Formation, also known as the Bass Limestone, is a Mesoproterozoic rock formation that outcrops in the eastern Grand Canyon, Coconino County, Arizona. The Bass Formation erodes as either cliffs or stair-stepped cliffs. In the case of the stair-stepped topography, resistant dolomite layers form risers and argillite layers form steep treads. In general, the Bass Formation in the Grand Canyon region and associated strata of the Unkar Group-rocks dip northeast (10°–30°) toward normal faults that dip 60+° toward the southwest. This can be seen at the Palisades fault in the eastern part of the main Unkar Group outcrop area. In addition, thick, prominent, and dark-colored basaltic sills intrude across the Bass Formation.
The Vishnu Basement Rocks is the name recommended for all Early Proterozoic crystalline rocks exposed in the Grand Canyon region. They form the crystalline basement rocks that underlie the Bass Limestone of the Unkar Group of the Grand Canyon Supergroup and the Tapeats Sandstone of the Tonto Group. These basement rocks have also been called either the Vishnu Complex or Vishnu Metamorphic Complex. These Early Proterozoic crystalline rocks consist of metamorphic rocks that are collectively known as the Granite Gorge Metamorphic Suite; sections of the Vishnu Basement Rocks contain Early Paleoproterozoic granite, granitic pegmatite, aplite, and granodiorite that have intruded these metamorphic rocks, and also, intrusive Early Paleoproterozoic ultramafic rocks.
The Manzano Group is a group of geologic formations in central New Mexico. These have radiometric ages of 1601 to 1662 million years (Ma), corresponding to the late Statherian period of the Paleoproterozoic.
The Mazatzal orogeny was an orogenic event in what is now the Southwestern United States from 1650 to 1600 Mya in the Statherian Period of the Paleoproterozoic. Preserved in the rocks of New Mexico and Arizona, it is interpreted as the collision of the 1700-1600 Mya age Mazatzal island arc terrane with the proto-North American continent. This was the second in a series of orogenies within a long-lived convergent boundary along southern Laurentia that ended with the ca. 1200–1000 Mya Grenville orogeny during the final assembly of the supercontinent Rodinia, which ended an 800-million-year episode of convergent boundary tectonism.
The Picuris orogeny was an orogenic event in what is now the Southwestern United States from 1.43 to 1.3 billion years ago in the Calymmian Period of the Mesoproterozoic. The event is named for the Picuris Mountains in northern New Mexico and interpreted either as the suturing of the Granite-Rhyolite crustal province to the southern margin of the proto-North American continent Laurentia or as the final suturing of the Mazatzal crustal province onto Laurentia. According to the former hypothesis, this was the second in a series of orogenies within a long-lived convergent boundary along southern Laurentia that ended with the ca. 1200–1000 Mya Grenville orogeny during the final assembly of the supercontinent Rodinia, which ended an 800-million-year episode of convergent boundary tectonism.
The Moppin Complex is a Precambrian geologic complex found in the Tusas Mountains of northern New Mexico. It has not been directly dated, but is thought to be Statherian based on a minimum age of 1.755 Gya from radiometric dating of magmatic intrusions.
The Vadito Group is a group of geologic formations that crops out in most of the Precambrian-cored uplifts of northern New Mexico. Detrital zircon geochronology and radiometric dating give a consistent age of 1700 Mya for the group, corresponding to the Statherian period.
The Burned Mountain Formation is a geologic formation that crops out in the Tusas Mountains of northern New Mexico. It has a U-Pb radiometric age of 1700 Mya, corresponding to the Statherian period.
The Ortega Formation is a geologic formation that crops out in most of the mountain ranges of northern New Mexico. Detrital zircon geochronology establishes a maximum age for the formation of 1690-1670 million years (Mya), in the Statherian period of the Precambrian.
The Marquenas Formation is a geological formation that crops out in the Picuris Mountains of northern New Mexico. Detrital zircon geochronology gives it a maximum age of 1435 million years, corresponding to the Calymmian period.
The Uncompahgre Formation is a geologic formation in Colorado. Its radiometric age is between 1707 and 1704 Ma, corresponding to the Statherian period.
The Sevilleta Metarhyolite is a geologic formation in central New Mexico. It has a radiometric age of 1665 ± 16 Ma, corresponding to the Statherian period.
The Los Pinos Mountains are a small mountain range in the central part of New Mexico, US. The are the southernmost part of a mountain front, running north to south, that also includes the Sandia Mountains and the Manzano Mountains. The Los Pinos Mountains are separated from the Manzano Mountains by Abo Pass, which was cut by a small tributary to the Rio Grande. The mountains run slightly west of south for 15 miles (24 km) and widen to a maximum of about 4 miles (6.4 km) across before narrowing again. The southern end of the range is ill-defined, being marked by cuestas that merge into badlands to the south.
The White Ridge Quartzite is a geologic formation in central New Mexico. It has a maximum age of 1650 million years (Ma), corresponding to the Statherian period.
The Blue Springs Formation is a geologic formation expoed in the Los Pinos Mountains of central New Mexico.
The Sais Quartzite is a geologic formation exposed in the Los Pinos Mountains of central New Mexico.
The Tijeras Greenstone is a geologic formation in central New Mexico. It has a radiometric age of 1660 million years (Ma), corresponding to the Statherian period.
The White Ledges Formation is a geologic formation that crops out in central Arizona, US. Detrital zircon geochronology establishes a maximum age for the formation of 1726 million years (Mya), in the Statherian period of the Precambrian. The formation is typical of quartzites deposited around 1650 million years ago in the southwestern part of Laurentia, the ancient core of the North American continent.
