The Regina quadrangle is located in Sandoval and Rio Arriba Counties, New Mexico, along the boundary between the northwestern margin of the Nacimiento uplift and the east-central San Juan Basin. The uplift is composed of a core of Precambrian rocks overlain by a veneer of Mississippian through Triassic sedimentary rocks. Sedimentary rocks ranging in age from Jurassic to Tertiary are upturned along the margin of the San Juan Basin.
The Precambrian rocks in the area are primarily granite to granodiorite gneiss with xenoliths of mafic and felsic metavolcanic rocks and metasedimentary rocks. These rocks have undergone greenschist facies metamorphism. Late stage aplite dikes, mafic dikes, pegmatites and quartz veins are also present. There are between 3,300-3,400 m (10,700 and 11,100 ft) of sedimentary rocks exposed in the eastern part of the Regina quadrangle. The Mississippian and Pennsylvanian rocks are shallow water marine limestone, sandstone and shale. The Permian, Triassic and Jurassic rocks include sandstone, shale, gypsum and minor limestone that were deposited in continental environments, and the Cretaceous rocks are shallow water marine and coastal swamp and lagoon deposits. The Tertiary rocks are mainly sandstone and shale that are the result of deposition in continental flood plains and alluvial fans. Late Tertiary and Quaternary sediments include alluvium, landslide, terrace and pediment deposits.
The Nacimiento uplift and the San Juan Basin are the two main tectonic features in the Regina quadrangle and the boundary between them is the synclinal bend of the San Juan Basin which has been cut by the Nacimiento fault. The Nacimiento fault is a north- to northeast-trending, high-angle reverse fault that has associated antithetic and synthetic faults as well as southwest- to northwest trending faults that offset it.
These two tectonic features began development during Late Cretaceous time during the Laramide orogeny, when a monocline was formed between the uplift and the basin, probably as the result of shear folding over close-spaced vertical fractures in the basement rocks. Later uplift, in association with Rio Grande rifting, enhanced the structural relief between the basin and uplift, and resulted in the present configuration of the Nacimiento fault. There is a maximum of 900 m (3,000 ft) of stratigraphic separation along the Nacimiento fault, and a maximum of 3,350 m (11,000 ft) of structural relief between the basin and the uplift in the eastern Regina quadrangle.
Although there are no reports of economic mineral deposits in the eastern part of the Regina quadrangle, there is evidence of prospecting in the area. Minor copper and uranium are found in sandstones of the Madera and Abo Formations and thin beds of coal are present in the Menefee Formation of the Mesaverde Group.
Earth and Planetary Sciences
Level of Degree
Department of Earth and Planetary Sciences
First Committee Member (Chair)
Lee A. Woodward
Second Committee Member
Albert Masakiyo Kudo
Third Committee Member
Jonathan Ferris Callender
Merrick, Margaret Anne. "Geology Of The Eastern Part Of The Regina Quadrangle, Sandoval And Rio Arriba Counties, New Mexico." (1980). https://digitalrepository.unm.edu/eps_etds/299