Trampas Group

The Trampas Group is a group of geologic formations 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.

Trampas Group
Stratigraphic range: Calymmian Pha. Proterozoic Archean Had.
Trampas Group beds in Picuris Mountains
Type	Group
Sub-units	Piedra Lumbre Formation Pilar Formation
Underlies	Marquenas Formation
Overlies	Ortega Formation
Thickness	1,000 m (3,300 ft)
Lithology
Primary	Schist, phyllite
Other	Quartzite
Location
Coordinates	36.202°N 105.872°W / 36.202; -105.872
Region	Picuris Mountains, New Mexico
Country	United States
Type section
Named for	Trampas, New Mexico
Named by	Daniel, Pfeiffer, Jones, and McFarlane
Year defined	2013
Trampas Group (the United States) Show map of the United States Trampas Group (New Mexico) Show map of New Mexico

Description

The Trampas Group consists of metasedimentary formations deposited in the reactivated Pilar Basin during the Picuris orogeny. Detrital zircon geochronology yields a maximum age of 1475 Mya, considerably younger than the underlying Hondo Group.^[1]

The formations included in the Trampas Group are the Pilar Formation, a carbonaceous phyllite, and the Piedra Lumbre Formation, which is primarily feldspathic schist with some quartzite and phyllite.

The Trampas Group likely was deposited in a basin formed during the breakup of the supercontinent of Columbia.^[2]

History of investigation

The formations of the Trampas Group were originally included by Bauer and Williams in the Hondo Group as part of their sweeping revision of northern New Mexico Precambrian stratigraphy in 1989.^[3] However, detrital zircon geochronology demonstrated that while the lower two formations of the original Hondo Group, the Ortega Formation and the Rinconada Formation, were Statherian in age, the upper two formations, the Pilar Formation and the Piedra Lumbre Formation, were Calymmian in age and they were removed into their own Trampas Group.^[1]