The White Ledges Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

that crops out in central

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

, US.

Detrital zircon geochronology Detrital zircon geochronology is the science of geochronology, analyzing the age of zircons deposited within a specific sedimentary rock, sedimentary unit by examining their inherent radioisotopes, most commonly the uranium–lead dating, uranium ...

establishes a maximum age for the formation of 1726 million years ( Mya), in the

Statherian The Statherian Period (; , meaning "stable, firm") is the final geologic period in the Paleoproterozoic Era and lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically. Th ...

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

of the

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, 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 t ...

. The formation is typical of

quartzite Quartzite is a hard, non- foliated metamorphic rock that was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tecton ...

s deposited around 1650 million years ago in the southwestern part of

Laurentia Laurentia or the North American craton is a large continental craton that forms the Geology of North America, 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 ...

, the ancient core of the North American continent.

Description

The White Ledges Formation consists of of

orthoquartzite Quartzite is a hard, non- foliated metamorphic rock that was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tectoni ...

. The quartzite is cut by small

reverse fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic f ...

s dipping to the north. It is the lowest member of the Hess Canyon Group and is disconformably overlain by the Yankee Joe Formation. It overlies and interfingers with the Redmond Formation, which has been radiometrically dated as 1657 ± 3 million years old, and it contains detrital

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of th ...

s dated to not less than 1726 million years old. The White Ledges Formation is thought to be sediments deposited in a nearshore tidal and fluvial environment. Together with other formations in the region, it records a long-lived tectonic margin along southern Laurentia through much of the

Proterozoic The Proterozoic ( ) is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, and is the longest eon of Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozo ...

(1800 to 1000 million years ago.) This helps geologists reconstruct the assembly and breakup of

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continent, continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", ...

s during this interval of time.

History of investigation

The beds making up the formation were first noted by N.H. Darton in 1925, who assigned them to the

Pinal Schist Pinal may refer to: People *Pinal or Pinaleño, a band of the Native American Apache tribe * Silvia Pinal (1931–2024), Mexican actress * Pinal Shah (born 1987), Indian World Cup wicket-keeper Places *Pinal County, Arizona Pinal County is a ...

. The White Ledges Formation was first designated by D.E. Livingston in 1969 in his doctoral dissertation and named for the White Ledges, a set of quartzite ridges along the Salt River canyon north of

Globe, Arizona Globe ( "Place of Metal") is a city in and the county seat of Gila County, Arizona, Gila County, Arizona, United States. As of the 2020 United States census, 2020 census, the population of the city was 7,249. Globe was founded c. 1875 as a mini ...

References

{{Reflist Precambrian Arizona Quartzite formations Geologic formations of Arizona