Piedra Lumbre Formation

Piedra Lumbre Formation
Stratigraphic range: Calymmian Pha. Proterozoic Archean Had.
Outcrop of Piedra Lumbre Formation along highway from Dixon to Picuris Pueblo, New Mexico, USA
Type	Formation
Unit of	Trampas Group
Underlies	Marquenas Formation
Overlies	Pilar Formation
Thickness	300 m (980 ft)
Lithology
Primary	Schist
Other	Quartzite
Location
Coordinates	36°12′32″N105°49′33″W / 36.2088292°N 105.8257916°W / 36.2088292; -105.8257916
Region	Picuris Mountains, New Mexico
Country	United States
Type section
Named for	Canada de Piedra Lumbre
Named by	Long
Year defined	1976
Piedra Lumbre Formation (the United States) Show map of the United States Piedra Lumbre Formation (New Mexico) Show map of New Mexico

The Piedra Lumbre Formation is a geologic formation that crops out in the Picuris Mountains of northern New Mexico. Detrital zircon geochronology yields a maximum age of 1475 million years, corresponding to the Calymmian period.

Description

The Piedra Lumbre Formation consists of light gray to black phyllite or schist. ^[1] The formation has been subject to extreme deformation within the Hondo syncline that confuses the stratigraphic picture. ^[2]

The formation can be divided into three members, beginning with a lower member, about 40 meters (130 feet) thick, of quartz-muscovite-biotite-garnet-staurolite phyllitic schist. This is characterized by light gray crenulated cleavage surfaces sprinkled with small garnet, biotite, and staurolite crystals. The middle member is interbedded light gray schist and quartzite, with the top 10 meters (33 feet) primarily black phyllitic schist with white banding. The quartzite beds towards the base of this member contain thin calcareous beds. The upper member is 5–10 meters (16–33 feet) of phyllitic slate that resembles the Pilar Formation but is distinguished by its stratigraphic position. ^[3]

Detrital zircon geochronology yields a maximum age of 1475 Mya, similar to the underlying Pilar Formation but considerably younger than the lower Hondo Group. This suggests that the Pilar Formation and Piedra Lumbre Formation should be removed from the Hondo Group and provides evidence supporting the Picuris orogeny. ^[4]

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  Piedra Lumbre Formation, upper left, in contact with thinner beds of Pilar Formation, lower right

History of investigation

The unit was originally mapped as part of the Rinconada Schist Member of the Ortega Formation by Arthur Montgomery in 1958., ^[5] which it resembles except for having less abundant garnet. ^[1] Nielsen recognized in 1972 that the beds were distinct from the upper Rinconada Schist ^[6] but erroneously assigned them to the Pilar Formation. ^[1] Long assigned these beds to the Piedra Lumbre Formation in 1976, naming the unit after the Cañada de Piedra Lumbre. ^[1]

Footnotes

1. Long 1976, p.37
2. Bauer 2004, p.200
3. Long 1976, pp.40-44
4. Daniel et al. 2013
5. Montgomery 1958, p.15
6. Nielsen 1972

References

• Bauer, Paul W. (2004). "Proterozoic rocks of the Pilar Cliffs, Picuris Mountains, New Mexico" (PDF). New Mexico Geological Society Field Conference Series. 55: 193–205. Retrieved 15 April 2020.
• Daniel, Christopher G.; Pfeifer, Lily S.; Jones, James V III; McFarlane, Christopher M. (2013). "Detrital zircon evidence for non-Laurentian provenance, Mesoproterozoic (ca. 1490–1450 Ma) deposition and orogenesis in a reconstructed orogenic belt, northern New Mexico, USA: Defining the Picuris orogeny" . GSA Bulletin. 125 (9–10): 1423–1441. Bibcode:2013GSAB..125.1423D. doi:10.1130/B30804.1 . Retrieved 17 April 2020.
• Long, P.E. (1976). "Precambrian granitic rocks of the Dixon-Peñasco area, northern New Mexico, a study in contrasts" (PDF). New Mexico Bureau of Mines and Mineral Resources Open-file Report Series. 71. Retrieved 17 April 2020.
• Montgomery, Arthur (1953). "PreCambrian Geology of the Picuris Range, northcentral New Mexico" (PDF). State Bureau of Mines and Mineral Resources Bulletins. 30.
• Nielsen, K. C., 1972, Structural evolution of the Picuris Mountains, New Mexico: Chapel Hill, N. C., University of North Carolina M.S. thesis.