GEOLEX

Summary of Citation: Ortega

Publication:
Just, E., 1937, Geology and economic features of the pegmatites
   of Taos and Rio Arriba Counties, New Mexico: New Mexico School
   of Mines Bulletin, no. 13

Usage in Publication:
Ortega quartzite

Modifications:	Geologic Province:	Dominant Lithology:
Named	Southern Rocky Mountain region	Quartzite Schist

Summary:
Name applied to a quartzite and schist sequence that occurs in Petaca and Picuris areas, Rio Arriba and Taos Cos, NM in the Southern Rocky Mountain region. Is the most widespread pre-Cambrian formation in the area. Is exposed west of Rio Vallecitos, Ortega Mountains [source of name?], do La Madera Mountain, Mesa la Jarita, Kiawa Mountain and Jawbone Mountain. Geologic map. No type locality designated. Source of name not stated. Is a white to bluish-gray quartzite that has a schistose phase named Rinconada schist [unranked] in the Picuris area and called Petaca schist [unranked] in the Petaca area. Overlies Hopewell series (new). Is succeeded by Hondo slate (new) in Picuris area and by Picuris basalts in Petaca area. Has conglomeratic phases. Pebbles of white quartz, jasper, and black chert occur in Petaca area and flattened or drawn out pebbles occur in Picuris area. Is up to 2 mi thick over much of Picuris area and up to 4 to 5 mi thick in Petaca area. Was originally a sandstone. Of Proterozoic age.

Summary of Citation: Ortega

Publication:
Montgomery, A., 1953, Pre-Cambrian geology of the Picuris Range,
   north-central New Mexico: New Mexico Bureau of Mines and
   Mineral Resources Bulletin, no. 30, 89 p.

Usage in Publication:
Ortega formation

Modifications:	Geologic Province:	Dominant Lithology:
Redescribed Revised Areal limits	Southern Rocky Mountain region	Quartzite Schist Phyllite

Summary:
Ortega quartzite of Just (1937) redescribed, revised, and areally extended into report area, Picuris Range area, Taos and Rio Arriba Cos, NM, Southern Rocky Mountain region. Just (1937) used Ortega for quartzite exposed in Ortega Mountains, 25 mi northwest of Picuris Range. Redescribed in this report as Ortega formation, is made up of wholly metasedimentary rocks and comprises (ascending): 1) a lower, quartzite member 2,500+ ft thick (base not exposed in this area); 2) Rinconada schist member, which contains 4 mappable units--andalusite-biotite hornfels, staurolite gneiss and schist, quartzite, and muscovite-quartz-biotite-garnet phyllite--totaling 1,800 ft; and Pilar phyllite member (here named), a gray-black carbonaceous phyllite which was termed Hondo slate by Just (1937) (Hondo here abandoned--name used for other rocks prior to Just's usage), 2,300 ft thick. Total thickness of Ortega formation is 6,600 ft. Underlies the conglomerate member of Vadito formation (here named) unconformably--Vadito is at least the partial equivalent of Hopewell series of Just (1937). Name Hopewell is preempted, and here abandoned. Lithology and distribution described in detail. Ortega formation is of pre-Cambrian age. Geologic map, cross sections, columnar section.

Summary of Citation: Ortega

Publication:
Barker, Fred, 1958, Precambrian and Tertiary geology of Las
   Tablas quadrangle, New Mexico: New Mexico Bureau of Mines
   and Mineral Resources Bulletin, no. 45, 104 p.

Usage in Publication:
Ortega quartzite

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Southern Rocky Mountain region

Summary:
Revised in map area, Rio Arriba Co, NM, Southern Rocky Mountain region. Includes only the quartzite equivalent to the quartzite of the Ortega Mountains and to the overlying quartzite that extends up to, but does not include, the Big Rock conglomerate member (new) of the Kiawa Mountain formation. Consists in the Rio Vallecitos area of 90 to 95 percent quartz with accessory kyanite, hematite, ilmenite, muscovite and rutile. Is gray to pink, vitreous, dense, massive and has conglomeratic layers of rounded quartz pebbles. Has tabular cross beds. On the southwest slope of La Jarita Mesa the quartzite is similar to the Rio Vallecitos area, except that it contains abundant muscovite and is slightly feldspathic. Seven thin layers of amphibolite present locally. Is 5,000 to 7,000 ft thick, although it could be as thick as 20,000 ft. Is a miogeosynclinal shelf sandstone of Precambrian age, and older than Moppin metavolcanic series (new) and younger than Petaca schist. Geologic map.

Summary of Citation: Ortega

Publication:
Miller, J.P., 1963, Precambrian rocks, IN Miller, J.P., Montgomery,
   A., and Sutherland, P.K., Geology of part of the southern
   Sangre de Cristo Mountains, New Mexico: New Mexico Bureau of
   Mines and Mineral Resources Memoir, no. 11, p. 7-21

Usage in Publication:
Ortega Formation

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Southern Rocky Mountain region

Summary:
Ortega Formation revised--Rio Pueblo Schist named as an unranked unit in lower quartzite member of Ortega in this report. Rio Pueblo is exposed near bridge over Rio Pueblo Creek, a mi southeast of village of Rio Pueblo, Rio Arriba Co, NM in Southern Rocky Mountain region, where it extends to south for about 1 mi. Similar rock makes up all of a small hill 1/2 mi northwest of U.S. Hill and northerly part of adjacent larger hill to north. Mapped as a separate migmatitic unit because this rock is so distinct from normal Ortega quartzite. Rio Pueblo may represent granitized arkosic quartzite, but in large part appears to consist of granitic material intruded into and probably intermixed with quartzite. Is of Precambrian age. Geologic map.

Summary of Citation: Ortega

Publication:
Barker, Fred, 1970, Ortega Quartzite and the Big Rock and Jawbone
   Conglomerate members of the Kiawa Mountain Formation, Tusas
   Mountains, New Mexico, IN Cohee, G.V., Bates, R.G., and
   Wright, W.B., Changes in stratigraphic nomenclature by the
   U.S. Geological Survey, 1968: U.S. Geological Survey Bulletin,
   1294-A, p. A21-A22

Usage in Publication:
Ortega Quartzite*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Southern Rocky Mountain region

Summary:
Name applied only to the 14,000-20,000 ft thick lower part of original (Just, 1937) Ortega as exposed in sec 25, T27N, R8E, Rio Arriba Co, NM in Southern Rocky Mountain region. Base not exposed in Tusas Mountains. Rocks above revised Ortega belong to the Kiawa Mountain Formation. Definition of Ortega used in this report follows use of Barker's earlier work. [Statement that the Ortega Mountains are the type locality is misleading because Just did not designate a type locality.] Is of Precambrian age.

Summary of Citation: Ortega

Publication:
Wobus, R.A., 1985, Changes in the nomenclature and stratigraphy
   of Proterozoic metamorphic rocks, Tusas Mountains, north-central
   New Mexico: U.S. Geological Survey Bulletin, 1571, 19 p.

Usage in Publication:
Ortega Quartzite*

Modifications:	Geologic Province:	Dominant Lithology:
Revised Principal reference	Southern Rocky Mountain region

Summary:
Barker's (1958) terminology, definitions, and stratigraphic sequence revised. Name Ortega Quartzite applied only to vitreous quartzite. Is interlayered quartz-pebble conglomerates, and thought to be younger than the metavolcanic rocks of the Burned Mountain Metarhyolite (revised) and the Moppin Metavolcanics (redescribed). This usage conforms with that of Just (1937) and Gresens and Stensrud (1974). Use of Kiawa Mountain Formation and its Jawbone Conglomerate Member abandoned. The upper vitreous quartzite and the Jawbone assigned by Barker to the Kiawa Mountain Formation are the same as Ortega; the quartzite is interlayered with the pebble-conglomerate. Just did not select a type locality. Barker's type locality (1970) not appropriate because it is the Petaca Schist. Principal reference section designated in canyon of Rio Vallecitos in east-central part of sec 34, T26N, R8E, La Madera 7 1/2 min quad, 3.5 mi south-southeast of village of Vallecitos, Rio Arriba Co, NM in Southern Rocky Mountain region. Is the youngest of the Proterozoic units in the Tusas Mountains. Cross sections; nomenclature chart.

Summary of Citation: Ortega

Publication:
Bauer, P.W. and Williams, M.L., 1989, Stratigraphic nomenclature
   of Proterozoic rocks, northern New Mexico; revisions,
   redefinitions, and formalization: New Mexico Geology, v. 11,
   no. 3, p. 45-52

Usage in Publication:
Ortega Formation

Modifications:	Geologic Province:	Dominant Lithology:
Revised Reference	Southern Rocky Mountain region

Summary:
Ortega Group formerly included Ortega Formation and overlying schists and quartzites of Rinconada Formation of Hondo Group (new) of this report. Name changed from Ortega Quartzite to Ortega Formation [reason for change not stated], stratigraphically restricted to quartzites, and reassigned as basal formation of four formations of Hondo Group (new). Lower boundary placed at base of massive quartzite (Ortega) with immature metasedimentary rocks of Vadito Group (revised). Upper contact placed at top of uppermost massive quartzite (Ortega) with pelitic schist (Rinconada). Reference sections designated [but not described]: 1) Ortega Mountains; 2) cliffs near Pilar, northern Picuris Mountains; 3) Jawbone syncline, northern Tusas Mountains; 4) Rattlesnake Canyon, south end of Copper Hill, south-central Picuris Mountains. Stratigraphic chart. Geologic map. Lies in Rio Arriba and Taos Cos, NM in the Southern Rocky Mountain region. Considered to be younger than 1,700 Ma. Of Early Proterozoic age.

Summary of Citation: Ortega

Publication:
Aleinikoff, J.N., Reed, J.C., Jr. and Wooden, J.L., 1993, Lead
   isotopic evidence for the origin of Paleo- and Mesoproterozoic
   rocks of the Colorado province, U.S.A.: Precambrian Research,
   v. 63, nos. 1-2, p. 97-122

Usage in Publication:
Ortega Quartzite*

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Southern Rocky Mountain region

Summary:
Basal formation of Hondo Group whose depositional age is between 1,690 and 1,710 Ma. Age of this formation in north-central NM in the Southern Rocky Mountain region is based on 1.) light-colored, euhedral to subhedral populations of zircon from the Ortega in the Tusas Mountains and Picuris Range that suggest provenance of about 1,710 Ma, 2.) 1,700 Ma age of rhyolite beneath Ortega in the Tusas Mountains, and 3.) age of a stock dated at about 1,690 which cuts the Hondo Group in central NM.