The Marquenas Formation is a

geological 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 the

Picuris Mountains The Picuris Mountains are a mountain range in northern New Mexico. They are considered a subrange of the Sangre de Cristo Mountains. Geography The mountains are located to the east of Dixon and surround Picuris Pueblo to the west, north, and ...

of northern

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...

Detrital zircon geochronology Detrital zircon geochronology is the science of analyzing the age of zircons deposited within a specific sedimentary unit by examining their inherent radioisotopes, most commonly the uranium–lead ratio. Zircon is a common accessory or trace ...

gives it a maximum age of 1435 million years, corresponding to the Calymmian period.

Description

The Marquenas Formation was first believed to be over 80% quartzite, with the rest mostly

metaconglomerate Metaconglomerate is a rock type which originated from conglomerate after undergoing metamorphism. Conglomerate is easily identifiable by the pebbles or larger clasts in a matrix of sand, silt, or clay. Metaconglomerate looks similar to conglome ...

. The metaconglomerate lenses are found throughout the formation but particularly towards its top, and it was designated the Marquenas Quartzite. However, Bauer and Williams noted that the unit is about equally divided between quartzite and metaconglomerate, which led them to redesignate it as the Marquenas Formation. It can be divided into a lower, highly strained, poorly sorted boulder conglomerate; a middle quartzite member; and an upper, highly strained, pebble-to-cobble conglomerate. Cross stratification shows that the layering is overturned, and this supported the interpretation of the formation as part of the

Vadito Group 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, correspondi ...

, likely correlating with the Big Rock Formation of the

Tusas Mountains The Tusas Mountains are a mountain range in northern New Mexico, extending slightly into southern Colorado. They are considered the southeasternmost part of the San Juan Mountains. Grouse Mesa, , is the highest peak in the range. The mountains a ...

. However, detrital zircon geochronology establishes a maximum age of 1435 Mya, much younger than the Vadito Group. The provenance of the quartzite clasts in the Marquenas Formation remain uncertain, since they contain no aluminum silicate minerals and little crossbedding, but both are present in the

Ortega Formation 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 peri ...

, the most likely local source rock. One possibility is that the clasts were derived from quartzite units of the

Manzano Group 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 name ''Manzano Group'' was pr ...

to the south. A metamorphosed tuff bed in the

Pilar Formation The Pilar Formation is a geologic formation that crops out in the Picuris Mountains of northern New Mexico. It has a radiometric age of 1488 ± 6 million years, corresponding to the Calymmian period. Description The Pilar Formation consists of ...

yields an age of 1488 ± 6

Mya Mya may refer to: Brands and product names * Mya (program), an intelligent personal assistant created by Motorola * Mya (TV channel), an Italian Television channel * Midwest Young Artists, a comprehensive youth music program Codes * Burmese ...

, and the Piedra Lumbre Formation likewise contains zircons dated to 1425 Mya. This suggests that the Pilar Formation and Piedra Lumbre Formation should be removed from the Hondo Group, and grouped with the Marquenas Formation as sediments deposited by the Picuris orogeny. File:Marquenas Formation boulder conglomerate.jpg, Coarse conglomerate at the base of the Marquenas Formation File:Marqenas Formation middle.jpg, Middle quartzite section of Marquenas Formation File:Marquenas Formation quartzite.jpg, Sample of quartzite from the middle section of the Marquenas Formation File:Marquenas Formation upper conglomerate.jpg, Upper beds of Marquenas Formation

History of investigation

The beds were originally assigned to the lower conglomerate member of the Vadito Formation by Arthur Montgomery in 1953, who estimated the thickness as up to 600 meters. P.E. Long broke the beds out as the Marquenas Quartzite in 1976 and named them after Cerro de las Marquenas. Paul W. Bauer and Michael L. Williams redesignated the unit as the Marquenas Formation in their sweeping revision of the stratigraphy of

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 ...

rocks in northern New Mexico in 1989.

Footnotes

References

* * * * * * {{cite journal , last1=Montgomery , first1=Arthur , title=PreCambrian Geology of the Picuris Range, northcentral New Mexico , journal=State Bureau of Mines and Mineral Resources Bulletins , date=1953 , volume=30 , url=https://geoinfo.nmt.edu/publications/monographs/bulletins/downloads/30/Bulletin030.pdf Precambrian formations of New Mexico Paleoproterozoic geology Proterozoic North America