iv Contents ABSTRACT 7 TERTIARY-QUATERNARY 47 INTRODUCTION 7 QUATERNARY 48 LOCATION 7 Bandelier Tuff 48 PHYSIOGRAPHY 9 Surficial deposits 48 PREVIOUS WORK 9 PALEOTECTONIC SETTING 48 ROCKS AND FORMATIONS 9 REGIONAL TECTONIC SETTING 49 PRECAMBRIAN 9 STRUCTURE 49 Northern Nacimiento area 9 NACIMIENTO UPLIFT 49 Southern Nacimiento area 15 Nacimiento fault 51 CAMBRIAN-ORDOVICIAN (?) 20 Pajarito fault 52 MISSISSIPPIAN 20 Synthetic reverse faults 52 Arroyo Peñasco Formation 20 Eastward-trending faults 53 Log Springs Formation 21 Trail Creek fault 53 PENNSYLVANIAN 21 Antithetic reverse faults 53 Osha Canyon Formation 23 Normal faults 53 Sandia Formation 23 Folds 54 Madera Formation 23 SAN JUAN BASIN 55 Paleotectonic interpretation 25 En echelon folds 55 PERMIAN 25 Northeast-trending faults 55 Abo Formation 25 Synclinal bend 56 Yeso Formation 27 Northerly trending normal faults 56 Glorieta Sandstone 30 Antithetic reverse faults 56 Bernal Formation 30 GALLINA-ARCHULETA ARCH 56 TRIASSIC 30 CHAMA BASIN 57 Chinle Formation 30 RIΟ GRANDE RIFT 57 JURASSIC 34 JEMEZ VOLCANIC FIELD 59 Entrada Sandstone 34 TECTONIC EVOLUTION 60 Todilto Formation 34 MINERAL AND ENERGY RESOURCES 63 Morrison Formation 34 COPPER 63 Depositional environments 37 Mineralization 63 CRETACEOUS 37 Origin 67 Dakota Formation 37 AGGREGATE 69 Mancos Shale 39 TRAVERTINE 70 Mesaverde Group 40 GYPSUM 70 Lewis Shale 41 COAL 70 Pictured Cliffs Sandstone 41 ΗUMΑTE 70 Fruitland Formation and Kirtland Shale URANIUM 70 undivided 42 GEOTHERMAL ENERGY 72 TERTIARY 42 OIL AND GAS 72 Ojo Alamo Sandstone 42 Production and shows 72 Nacimiento Formation 43 Potential hydrocarbon source rocks and San Jose Formation 43 reservoirs 73 Abiquiu Formation 44 Potential hydrocarbon traps 74 Zia Sand 46 REFERENCES 75 Volcaniclastic rocks 46 INDEX 80 Paliza Canyon Formation 47 Tables 1—Stratigraphic table 12 2—Chemical analyses and molecular norms of Precambrian rocks 13 v Figures 1—Index map showing location of Sierra Nacimiento vi 2—Location map showing Sierra Nacimiento and adjacent geologic provinces 8 3—Generalized geologic map of Precambrian rocks of northern Sierra Nacimiento 10 4—Generalized geologic map of Precambrian rocks of southern Sierra Nacimiento 16 5—Locations of measured sections and critical outcrops of Madera and other Pennsylvanian formations 22 6—Type section of Osha Canyon Formation 24 7—Fence diagram showing relations of Pennsylvanian stratigraphy 26 8—Thickness of Abo Formation at various localities 28 9—Thickness of Yeso Formation at various localities 29 10—Diagrammatic section showing stratigraphic relations of units in Chinle Formation 31 11—Thickness of Agua Zarca Sandstone Member of Chinle Formation at various localities 32 12—Nomenclature used for rock units in Morrison Formation 35 13—Columnar sections and inferred correlations of Morrison Formation 36 14—Intertonguing of sandstones and shales of upper Dakota Formation and lower Mancos Shale 38 15—Nomenclature and stratigraphic relations of units in Mancos Shale 39 16—Measured section of upper unit of Pedernal chert member of Abiquiu Formation 45 17—Tectonic map of Nacimiento uplift 50 18—View north of flat-lying Nacimiento fault 51 19—View northeast of Nacimiento fault 51 20—View north of Nacimiento fault 52 21—View north showing trace of Nacimiento and Señorito faults 52 22—View north of antithetic, high-angle reverse fault 53 23—Structure section showing relation of Leche and Nacimiento faults 56 24—View south of high-angle reverse faults in Dakota Formation 57 25—Diagrammatic cross section of flexure folding 57 26—Index map showing major basins of Rio Grande rift 58 27—Diagrammatic map showing faults and Zia Sand and correlative units between Rio Grande rift and Nacimiento uplift 58 28—View north of San Ysidro fault at White Mesa 59 29—Diagrammatic northwest—southeast structure section through Sierrita and adjacent antithetic faults 59 30—Regional tectonic sketch map showing Cordilleran foldbelt, Colorado Plateau, and Rocky Mountain foreland 60 31—View north of synclinal bend along east side of San Juan Basin 61 32—Diagrammatic structure sections showing development of range-marginal structures on west side of Naci- miento uplift 61 33—Diagrammatic structure sections showing strata younger than in footwall or hanging wall along Nacimiento fault 62 34—Locations of copper mines and prospects 64 35—Photomicrograρh of polished section of mineralized fossil wood 65 36—Map of Eureka mine and rose diagrams showing directions of dip of crossbeds and azimuths of fossil-wood fragments 66 37—East-west cross section through Nacimiento open pit showing geology prior to excavation 67 38—Generalized geologic map and structure section, San Miguel mine area 68 39—Occurrences of uranium-bearing minerals or radioactive anomalies 71 40—Generalized tectonic map showing wells and oil and gas occurrences 73 41—Potential hydrocarbon traps in a diagrammatic east-west structure section 74 Sheet 1—Generalized bedrock geologic map and structure sections of Sierra Nacimiento and adjacent areas (in back pocket) νi FIGURE 1—Index map of New Mexico showing location of Sierra Nacimiento and adjacent areas covered in this publication. 7 Abstract Precambrian igneous, metasedimentary, and meta-igneous rocks of Proterozoic age occur in two major outcrop areas in the Nacimiento area. Clastic sediments and volcanic rocks accumulated and underwent regional synkinematic metamorphism prior to emplacement of plutonic igneous and meta-igneous rocks that range in composition from ultramafic to leucogranitic. Syenite of probable Ordovician or perhaps Cambrian age intrudes Precambrian rocks and is nonconformably overlain by Paleozoic strata. Paleozoic strata, having a maximum composite thickness of 5,846 ft, include Mississippian, Pennsylvanian, and Permian units. Mississippian beds, which include, in ascending order, the Arroyo Peñasco and Log Springs Formations, are thin and only locally present. Pennsylvanian beds, which include, in ascending order, the Osha Canyon, Sandia, and Madera Formations, are marine deposits having a maximum thickness of 1,775 ft. Permian units are continental elastics and are, in ascending order, the Abo Formation, 100(?)-2,900(?) ft thick; the Yeso Formation, 10(?)- 525 ft thick; the Glorieta Sandstone, 0-100 ft thick; and the Bernal Formation, 0-80 ft thick. Mesozoic strata have a maximum composite thickness of 9,340 ft and include mainly clastic terrestrial deposits of Triassic and Jurassic age and mainly clastic marine Cretaceous beds. In ascending order the units are the Chinle Formation (Triassic); the Entrada Sandstone, Todilto Formation, and Morrison Formation (Jurassic); and the Dakota Formation, Mancos Shale, Mesaverde Group, Lewis Shale, Pictured Cliffs Sandstone, and Kirtland Shale and Fruitland Formation undivided (Cretaceous). Terrestrial deposits of Paleocene and Eocene age include, in ascending order, the Ojo Alamo Sandstone, the Nacimiento Formation, and the San Jose Formation; these units have a maximum composite thickness of 2,325 ft. Three different facies of a Miocene continental deposit up to 1,000 ft thick comprise the Zia Sand, the Abiquiu Formation, and an unnamed volcaniclastic unit. Volcanics of the Paliza Canyon Formation (Pliocene) and the Bandelier Tuff (Quaternary) are present locally. The Nacimiento uplift was initiated during the Laramide (Late Cretaceous—early Tertiary) and consists of a block tilted eastward and bounded on the west by reverse and thrust faults, with at least 10,000 ft of structural relief between the highest part of the uplift and the adjacent San Juan Basin. The uplift is internally segmented by high-angle faults. Laramide structures formed in a regional compressive stress field complicated by right shift between the uplift and the San Juan Basin, whereas the late Cenozoic evolution of the Rio Grande rift occurred as a result of crustal extension. Rejuvenation of some Laramide structures occurred during the late Cenozoic deformation. 1 Natural gas has been produced from the South Blanco Pictured Cliffs field in the Regina 7 /2- min quadrangle, and the potential exists for the discovery of additional hydrocarbons. Copper has been extracted from sandstone-type deposits in the Chinle Formation (Triassic), but the potential for additional commercial production is low. Numerous occurrences of uranium- bearing minerals and radioactive anomalies have been reported, but, to date, only minor production is recorded for five localities. Travertine, gravel, and gypsum are present, but only the gypsum and gravel have been exploited. Coal was mined underground, but currently no coal is being mined commercially. Introduction Location GM-46. Geology of Regina quadrangle, Rio Arriba and Sandoval Counties, New Mexico. The Sierra Nacimiento is located in north-central GM-47. Geology of Jarosa quadrangle, New Mexico. New Mexico (Fig. 1) in Sandoval and Rio Arriba From these previously published maps a generalized Counties. These mountains trend north over a bedrock geologic map and structure sections of the Sierra distance of approximately 50 mi and are 6-10 mi Nacimiento and adjacent areas were compiled (in back 1 wide. Twelve 7 /2-min quadrangles that cover most of pocket) . the mountains are available as geologic maps In addition to the Sierra Nacimiento, the following published by the New Mexico Bureau of Mines and parts of adjacent geologic provinces are discussed: the Mineral Resources (Fig. 2). These maps are the eastern edge of the San Juan Basin, the southern Galli primary sources of information for this report. na—Archuleta arch, the southwest corner of the Chama GM-25. Geologic map of Cuba quadrangle, New Mexico. Basin, the western part of the Jerez volcanic field, and GM-26. Geologic map of San Pablo quadrangle, New Mexico. GM-27. Geologic map and sections of Rancho del Chaparral the northwest part of the Albuquerque Basin of the Rio quadrangle, New Mexico. Grande rift (Fig. 2; map in back pocket). GM-28. Geologic map and sections of La Ventana quadrangle, Two principal paved highways are present, NM-44 New Mexico. in the southern and western parts of the area and GM-32. Geologic map and sections of Nacimiento Peak quad- rangle, New Mexico.