• Time-Space Variations in Mesozoic and Cenozoic Meteoric Waters, Southwestern North America

      Becker, Jennifer L.; Titley, Spencer R.; Quade, Jay; Barton, Mark D.; Becker, Jennifer L. (The University of Arizona., 1999)
      Mesozoic and Cenozoic hydrothermal systems of the southwestern North American Cordillera contain a complex record from which meteoric water stable isotope compositions (δ¹⁸O and δ D) can be inferred. This record is therefore of interest as a proxy for climate. New analytical results combined with systematic review of isotopic values from more than 200 locations in the southwestern North American Cordillera show regular isotopic patterns in time and space. Jurassic isotopic ratios are high, and Late Cretaceous values are more negative. During the Oligocene, there is a transition to more negative values. The ancient dD values are higher from most locations when compared to younger and present day values. This enrichment is compatible with warmer climates in the past and with changes in tectonic environments and paleoelevation and paleolatitude estimates over the same time interval. Complications in the application of the data include uncertainties in the estimated temperatures, alteration ages, isotopic disequilibrium, and incorporation of multiple fluids.
    • Late Quaternary Plant Zonation and Climate in Southeastern Utah

      Betancourt, Julio L.; Anthony, John W.; Martin, Paul S.; Davis, Owen K.; Turner, Raymond M.; Betancourt, Julio L. (The University of Arizona., 1983)
      Plant macrofossils from packrat middens in two southeastern Utah caves outline development of modern plant zonation from the late Wisconsin. Allen Canyon Cave (2195 m) and Fishmouth Cave (1585 m) are located along a continuous gradient of outcropping Navajo Sandstone that extends from the Abajo Mountains south to the San Juan River. By holding the site constant, changes in the floral composition for a plot of less than one hectare can be observed, even if sporadically, over tens of millennia. At Allen Canyon Cave, engelmann spruce-alpine fir forest was replaced by the present vegetation consisting of pinyon-juniper woodland on exposed ridgetops and cliffside stands of Douglas fir, ponderosa pine, and aspen. Xerophytic woodland plants such as pinyon, Plains prickly pear, and narrowleaf yucca arrived sometime in the middle Holocene between 7200 and 3400 B.P. At Fishmouth Cave, Utah juniper in Holocene middens replaced blue spruce, limber pine, Douglas fir, and dwarf and Rocky Mountain junipers in late Wisconsin samples. Disharmonious associations for the late Wisconsin occur only at the lower site with the xerophytes Mormon tea, Plains prickly pear, and narrowleaf yucca growing alongside subalpine conifers. One possible explanation involves the late Wisconsin absence of ponderosa and pinyon pines from the Colorado Plateaus. Released from competition at their lower limits, subalpine conifers were able to expand into lower elevations and mix with xerophytic plants found today in understories of pinyon-juniper and ponderosa pine woodlands. Quantitative climatic estimates are derived for the late Wisconsin by applying vertical lapse rates for temperature and precipitation to the amount of vegetation depression. The Fishmouth Cave sequence indicates a minimum lowering of 850 m for blue spruce, limber pine, and dwarf juniper. A depression of at least 700 m for engelmann spruce and alpine fir is suggested for the Allen Canyon locality. Use of conservatively low lapse rates for stations below 2080 m yields a 3-4°C cooling from present mean annual temperature and 35 to 60 percent more rainfall than today. Steeper lapse rates associated with more mountainous terrain suggest a 5°C lowering in temperature and up to 120 percent increase over modern precipitation.
    • Hillside Gullies and Possible Glacial Landforms Associated with the Degradation of Highland Craters on Mars

      Berman, Daniel Craig; Baker, Victor R.; Berman, Daniel Craig (The University of Arizona., 2003)
      The discovery of recent water and ice related landforms on Mars has led to a new understanding of the planet. Hundreds of examples of gullies and tongue-shaped ridges have been found on hillsides in images from the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC). I conducted a thorough survey of these images and compiled a database of those containing gullies and tongue-shaped ridges, which may form as the result of flow of ice-rich materials. These features are found in similar mid-latitude bands. Crater counts on the ice flow features show estimated ages of the order 10⁶ y to 10⁷ y, similar to the timescale calculated for the last episode of high obliquity, when Models suggest ice deposition at these latitudes. Specific craters and various ice flow features were studied and compared in three regions: Newton Basin, Eastern Hellas, and Northern Elysium, leading to a model for crater degradation. Gullies, tongue ridges, debris aprons, and mantle deposits all may stem from recent cycles of ice deposition.
    • A Flexural Model for the Paradox Basin: Implications for the Tectonics of the Ancestral Rocky Mountains

      Barbeau, David Longfellow Jr.; Dickinson, William R.; DeCelles, Peter G.; Chase, Clement G.; Demko, T.; Geslin, Jeff K.; Garzione, C.; Sussman, A.; Bump, A.; Barbeau, David Longfellow Jr. (The University of Arizona., 2000)
      The Paradox Basin is a large (200 km x 265 km) asymmetric basin that developed along the southwestern flank of the basement-involved Uncompahgre uplift during the Pennsylvanian-Permian (Desmoinesian-Wolfcampian) Ancestral Rocky Mountain (ARM) orogenic event. Traditionally interpreted as a pull-apart basin, the Paradox Basin more closely resembles intraforeland flexural basins such as those that developed between the basement-cored uplifts of the Late Cretaceous-Eocene Laramide orogeny. The width, shape, subsidence history, facies architecture, and structural relationships of the Uncompahgre-Paradox system are exemplary of typical 'immobile' foreland basin systems. Along the southwest-vergent Uncompahgre thrust, ~5 km of coarse-grained syntectonic Desmoinesian-Wolfcampian sediments were shed from the Uncompahgre uplift by alluvial fans and were reworked by fluvial megafan deposystems in the proximal Paradox Basin. The coeval rise of an uplift-parallel barrier ~250 km southwest of the Uncompahgre front restricted reflux from the open ocean south and west of the basin, and promoted deposition of thick evaporite-shale and biohermal carbonate facies in the medial and distal, submarine parts of the basin, respectively. Nearshore carbonate shoal and terrestrial siliciclastic deposystems overtopped the basin during the late stages of subsidence during the Missourian through Wolfcampian. Reconstruction of an end-Permian two-dimensional uplift-basin profile from seismic, borehole, and outcrop data depicts the relationship of these deposystems to the differential accommodation space (i.e., foreland basin depozones) generated by Pennsylvanian-Permian subsidence. Flexural modeling of the restored basin profile indicates that the Paradox Basin can be described by flexural loading of a fully broken continental crust (Te = 25 km; D = 10²³ N m) by a model Uncompahgre uplift (A(c-s) = 214 km², ρ = 2670 kg /m³) and accompanying synorogenic sediments (ρ = 2325 kg /m³). The Paradox Basin's lack of flexural interference by competing loads, its location on the relatively undeformed Colorado Plateau, and its well-exposed and well-studied basin-fill provide a rare glimpse into a Paleozoic intraforeland flexural basin. Other thrust-bounded basins of the Ancestral Rocky Mountains are not so optimal for study. However, similarities in basin profiles, structural relationships and facies architectures suggest that many ARM basins share a geodynamic and tectonic history similar to the Paradox Basin's. Therefore, plate tectonic models that attempt to explain the development of ARM uplifts need to also consider the province's intraforeland flexural basins.
    • Stratigraphy, Taphonomy, and Fauna-Substrate Associations in a Gulf of California Pleistocene Marine Terrace Near Punta Chueca, Sonora, Mexico

      Chase, Clement G.; Beckvar, Nancy; Chase, Clement G.; Kidwell, Susan M.; Prisrid, P. P.; Beckvar, Nancy (The University of Arizona., 1986)
      A richly fossiliferous Pleistocene terrace located near Punta Chueca, Sonora, Mexico, contains sediments that were deposited at the interface of an alluvial fan and shallow marine environment. Shell beds range from extremely dense fossil concentrations in sand, gravel, and cobble sized sediments to sparsely fossiliferous shell hashes. Three subenvironments were recognized: 1) shallow-subtidal to lower intertidal; 2) mid- to upper intertidal; and 3) supratidal. Shallow-subtidal to lower intertidal facies consist of shell beds with infaunal bivalves in life position, shell beds with fauna not in life position, and a Porites biostrome. Mid- to upper-intertidal facies include shell hash layers, and pebble and cobble lenses that are characterized by abundant autochthonous epi- faunal gastropods (i.e. limpets). Sparsely fossiliferous supratidal sands are overlain by Holocene alluvial fan deposits. Coarse conglomerates were not reworked by marine processes whereas finer conglomerates were, as evidenced by horizontal bedding and segregation of gravel and sand. The coarsest sediments - metamorphic cobbles - are relict and were probably derived from an earlier terrace. The following criteria were used to interpret the mode of shell bed formation: encrustation frequency, valve articulation, bivalve orientation, shell condition, and shell density (hardpart abundance). Storms played a major role in the formation of fossil concentrations. Four shell beds were interpreted as storm beds and one shell bed was interpreted as a condensed bed. Storm beds differ from condensed beds in having lower encrustation frequencies, higher percentages of articulated bivalves, and shells in very good condition. Association of hard-substrate faunas with gravel sediments and of infaunal molluscs with sand substrates suggests that little transport between habitats occurred. The high percentage of articulated valves, unworn appearance of most shells, predominance of concave-up oriented valves, and strong association of fauna with grain size all reflect a generally low energy environment, but one periodically disturbed by storm events.
    • Correlation of Some Mid-Mesozoic Redbeds and Quartz Sandstones in the Santa Rita Mountains, Mustang Mountains, and Canelo Hills, Southeastern Arizona

      Chase, Clement G.; Beatty, Barbara; Chase, Clement G.; Dickinson, William R.; Reynolds, Stephen J.; Shafiqullah, Muhammad; Beatty, Barbara (The University of Arizona., 1987)
      Mid-Mesozoic redbeds in the Santa Rita Mountains, Mustang Mountains, and Canelo Hills are lithologically and petrographically correlative. Quartz sandstone overlying the redbeds in the Mustang Mountains and Canelo Hills is also lithologically and petrographically correlative. The sediments were deposited during one or more breaks in volcanism associated with a continental magmatic arc that was active in southern Arizona during Triassic (?) and Jurassic time. The exact timing of sedimentation cannot be determined without more accurate dating of volcanics associated with the redbed strata. Redbeds of the Gardner Canyon Formation in the Santa Rita Mountains were probably deposited during and after eruption of the Mount Wrightson volcanics, the lower member of which is presently dated at 210 ±3 Ma. The Monkey Canyon redbeds and the Dark Canyon sandstone in the Canelo Hills and identical rocks in the Mustang Mountains are probably equivalent and were deposited between or during one or more hiatuses in two volcanic episodes presently dated at 165-185 Ma and 150-155 Ma, or before the 165-185 Ma volcanism and possibly as early as the period when the Gardner Canyon Formation was deposited. The Gardner Canyon Formation and Monkey Canyon redbeds are sequences of interbedded mudstone, siltstone, fine- to coarse-grained volcaniclastic sandstone, and volcanic conglomerate. They are interpreted as the product of meandering fluvial systems developed in close proximity to local volcanic sources, probably in distal alluvial fan or floodplain environments. The Dark Canyon and upper member Mount Wrightson quartz sandstones are bimodal, fine- and medium-grained, and average 93 percent monocrystalline quartz. They were probably deposited by both fluvial processes in stream channels and as windblown sand.
    • Migration of Recharge Water Downgradient from the Santa Catalina Mountains into the Tucson Basin Aquifer

      Long, Austin; Barger, Erin E.; Long, Austin; Eastoe, Christopher J.; Bassett, R. L.; Barger, Erin E. (The University of Arizona., 1996)
      Aquifers in the arid alluvial basins of the southwestern U.S. are recharged predominantly by infiltration from streams within the basins and by water entering along the margins of the basins from surrounding mountains (mountain -front recharge). The Tucson Basin of Southeastern Arizona is such a basin. The Santa Catalina Mountains form the northern boundary of this basin and receive more than twice as much precipitation (about 70 cm/yr) as the basin does (about 30 cm/yr). In this study environmental isotopes were employed to investigate the migration of precipitation basinward through joints and fractures. Water samples were obtained from springs in the Santa Catalina Mountains. Stable isotopes and thermonuclear bomb-produced tritium enabled qualitative characterizations of flow paths and flow velocities. Stable isotopic measurements fail to display a direct altitude effect. Tritium values indicate that although a few springs discharge pre-bomb water, most springs discharge waters from the 1960's or later.
    • The Geology of the Bajo El Durazno Porphyry Copper-Gold Prospect, Catamarca Province, Argentina

      Guilbert, John M.; Allison, Antonia E.; Guilbert, John M.; Ruiz, Joaquin; Eastoe, Christopher J.; Allison, Antonia E. (The University of Arizona., 1986)
      The Bajo El Durazno prospect is a small, gold-rich porphyry copper-type prospect located in Catamarca Province, northwest Argentina. It is one of a cluster of at least fourteen porphyry copper-type occurrences and numerous younger polymetallic epithermal veins, all of which are genetically related to the waning stages of magmatism that produced the Farallon Negro volcanic complex, an isolated Upper Miocene shoshonitic andesitic volcanic center. Porphyry copper-type hydrothermal activity at the Bajo El Durazno prospect is associated with a small east-northeasterly elongated andesite porphyry stock. The stock was emplaced at 8.7 m.y. into comagmatic and petrologically similar andesitic volcanic breccias that form the highly dissected basal remnants of the main eruptive center of the volcanic complex. Intramineral, crudely radial andesite porphyry dikes accompanied the development of concentric zones of hydrothermal alteration centered on the stock. These alteration zones of potassium-silicate alteration in the stock and adjacent wallrocks surrounded by an essentially coeval, weakly developed propylitic alteration zone. The propylitic alteration assemblage, which occurs as both pervasive replacement and as veinlets, consists mainly of chlorite, epidote, calcite, and magnetite, with lesser clays and zeolites. The potassium-silicate alteration zone is character iced by the replacement of primary minerals by secondary biotite, magnetite, anhydrite, quartz, sericite, and calcite. Roughly coeval and coextensive with the earliest stages of potassium-silicate and propylitic alteration was a brief period of magnetite alteration consisting mainly of well-banded magnetite ± quartz ± biotite veins. This volume also includes the development of irregular magnetite-rich masses in the stock of probable late-magmatic origin. Major copper-gold mineralization with minor silver and molybdenum developed during later stages of potassium-silicate alteration after the magnetite alteration event, although highest grade mineralization is commonly localized in areas of most intense magnetite alteration. The bulk of the mineralization occurs as veins within the stock and its wallrocks near their mutual contact; these veins contain quartz, calcite, magnetite, pyrite, chalcopyrite, and lesser sericite, chlorite, orthoclase, biotite, siderite, molybdenite, bornite, sphalerite, galena, tetrahedrite-tennantite, and native gold. Some of the gold and silver occur in solid solution in sulfide minerals, and supergene enrichment of copper is not economically significant. Copper and gold grades are generally less than 0.4% and 1 ppm, respectively. The three early alteration assemblages were later overprinted by patchy areas of phyllic alteration consisting mainly of the assemblage sericite, quartz, pyrite, and anhydrite/gypsum in an irregular northeasterly elongated halo. Phyllic alteration is developed to its greatest extent in an irregular annular zone straddling the boundary between the potassium- silicate and propylitic alteration zones and is generally coincident with the most highly fractured rocks in the prospect. Irregular patches of weak to intense silicification are superimposed on all other alteration types, and a number of distinctive, poorly mineralized, phyllically altered and silicified fracture zones are distributed in a somewhat radial pattern around the stock. Low grade disseminated(?) gold mineralization is found over one square kilometer in phyllically and propylitically altered rocks surrounding the central mineralized zone. A fluid inclusion study has revealed the presence of two hypersaline liquid-rich fluid inclusion types having salinities of 73.0-87.0 and 50.0-79.5 weight percent NaC1 + KCl equivalent, respectively, a single low salinity liquid-rich inclusion type (6.6-8.0 weight percent NaCl equivalent), and abundant vapor-rich inclusions. Hematite, anhydrite, and a variety of unidentified opaque and nonopaque minerals occur in many inclusions. Magnetite, potassium-silicate, and phyllic-silicic alteration in silicified zones formed at temperatures between 310° C and 500° C and were the product of the less saline of the two hypersaline fluids; this fluid episodically boiled. Copper-gold mineralization in potassium-silicate rocks probably peaked at about 395° C. Fluid salinities and temperatures gradually decreased with time, and during later stages of alteration they also decreased with greater distance from the hot center of the system, perhaps as a result of dilution. Although proof is lacking, the two high salinity fluids and the low salinity vapor may be magmatic in origin, and the low salinity fluid may represent a late-stage influx of meteoric water that encroached on the waning magmatic hydrothermal system. A depth of formation of 1.6 kilometers is estimated for the presently exposed portion of the Bajo El Durazno prospect based on the fluid inclusion data.
    • The Nucleation and Evolution of Riedel Shear Zones as Deformation Bands in Porous Sandstone

      Davis, George H.; Ahlgren, Stephen G.; Davis, George H.; Chase, Clement G.; DeCelles, Peter G.; Ahlgren, Stephen G. (The University of Arizona., 1999)
      Riedel shear zones are geometric fault patterns commonly associated with strike-slip fault systems. The progressive evolution of natural Riedel shear zones within the Navajo Sandstone of southern Utah is interpreted from the spatial evolution of small-scale, incipient Proto-Riedel Zones (PRZs) to better-developed Riedel shear zones using field mapping and three-dimensional digital modeling. PRZs nucleate as a tabular zone of localized shearing marked by en èchelon deformation bands, each of which is no more than a few mm wide and tens of cm long, and oriented at 55° - 85° to the trend of the zone. With increasing strain, deformation bands and sedimentary markers are sheared ductily through granular flow and assume a sigmoidal form. The temporal and spatial evolution of bands comprising a Riedel shear zone suggests that PRZs nucleate as transitional-compactional deformation bands under localized, supra-lithostatic fluid pressure. Subsequent bands develop under modified regional stresses as conjugate shear fractures within the strain- hardened axis of the PRZ. These antithetic driven systems are not compatible with traditional synthetic driven models of Riedel shear zones. Unlike most synthetic driven examples, these antithetic driven systems are not controlled by preexisting "basement" structures, thus their geometries reflect a primary propagation or secondary passive deformation mechanism.
    • A Palynological Analysis of Part of Death Valley Core DV93-1: 166-114 KA

      Davis, Owen K.; Bader, Nicholas E.; Davis, Owen K.; Quade, Jay; Dettman, David; Bader, Nicholas E. (The University of Arizona., 1999)
      Salt Core DV93 -1, from Badwater Basin in California's Death Valley, spans the past 192 ka. An analysis of fossil palynomorphs from 151.8 m (ca. 166 ka) to 103.5 m (ca. 114 ka) delimits four pollen zones. Zone 1, the "cheno -am" zone (151.8 to 143.5 m depth, 166 -154 ka), contains high percentages of Chenopodiaceae /Amaranthus pollen, and correlates with marine Oxygen Isotope Stage (OIS) 7. Zone 2, the juniper zone (143.5 to 117.3 m, 154 -124 ka), correlates with OIS 6 and contains high percentages of Cupressaceae pollen and low percentages of Ambrosia pollen. A simultaneous drop in juniper and increase in oak (Quercus) pollen, followed by replacement of Artemisia with Ambrosia, occurs at the Zone 2 /Zone 3 (oak zone) boundary (124 ka), corresponding to OIS Termination II warming. Zone 4, the Asteraceae zone (108.8 to 103.5 m, 119 -115 ka), contains higher percentages of Asteraceae and cheno -am pollen, indicating further warming.
    • Spatial Ability Development in the Geosciences

      Hall-Wallace, Michelle; Baldwin, Tammy Katherine; Hall-Wallace, Michelle; Wallace, Terry C.; Butler, Robert; Baldwin, Tammy Katherine (The University of Arizona., 2003)
      We designed an experiment to evaluate change in students' spatial skills as a result of specific interventions. Our test subjects included high school students in earth science classes, college level non-science majors enrolled in large enrollment introductory geoscience courses and introductory level geoscience students. All students completed spatial tests to measure their ability to mentally rotate three-dimensional objects and to construct a three-dimensional object from a two-dimensional representation. Results show a steady improvement in spatial skills for all groups. They also indicate that students choosing science majors typically have much higher spatial skills as they enter college. Specific interventions to improve spatial skills included having a subgroup of the non-science majors and high school students complete a suite of Geographic Information System (GIS) activities. The intervention at the high school level was more extensive and resulted in significant improvements in both categories of spatial ability. At the college level, the non-science majors that received the intervention showed no significant difference from those that did not, probably because the time spent on the intervention was too short. The geoscience majors had nearly three times the improvement of non-science majors in both categories of spatial ability attributed to hands-on weekly laboratory experiences. These results reveal a wide range of abilities among all groups of students, and suggest that we evaluate teaching strategies in all courses to ensure that students can interpret and understand the visual imagery used in lectures.
    • A Re-Os Study of Sulfides from the Bagdad Porphyry Cu-Mo Deposit, Northern Arizona, USA

      Ruiz, Joaquin; Barra-Pantoja, Luis Fernando; Ruiz, Joaquin; Patchett, P. Jonathan; Titley, Spencer R.; Barra-Pantoja, Luis Fernando (The University of Arizona., 2001)
      Use of Re-Os systematics in sulfides from the Bagdad porphyry Cu-Mo deposit provide information on the timing of mineralization and the source of the ore -forming elements. Analyzed samples of pyrite, chalcopyrite and molybdenite mainly from the quartz monzonite and porphyritic quartz monzonite units are characterized by a moderate to strong potassic alteration (secondary biotite and K- feldspar). Rhenium concentrations in molybdenite are between 330 and 730 ppm. Two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite provide a Re-Os isotope age of 71.7 ± 0.3 Ma. A third sample from a molybdenite vein in Precambrian rocks yields an age of 75.8 ± 0.4 Ma. These molybdenite ages support previous suggestions of two mineralization episodes in the Bagdad deposit. An early event at 76 Ma and a later episode at 72 Ma. Pyrite Os and Re concentrations range between 0.008-0.016 and 3.9-6.8 ppb, respectively. Chalcopyrite contains a wide range of Os (6 to 91 ppt) and Re (1.7 to 69 ppb) concentrations and variable ¹⁸⁷Os/¹⁸⁸Os ratios that range between 0.13 to 22.27. This variability in the chalcopyrite data may be attributed to different copper sources, one of them the Proterozoic volcanic massive sulfides in the district, or to alteration and remobilization of Re and Os. Analyses from two pyrite samples yield an eight point isochron with an age of 77 ± 15 Ma and an initial ¹⁸⁷Os/¹⁸⁸Os ratio of 2.12. This pyrite Re-Os isochron age is in good agreement with the molybdenite ages. We interpret the highly radiogenic initial 1870s/188Os as an indication that the source of Os and, by inference, the ore-forming elements for the Bagdad deposit, was mainly the crust. This conclusion agrees with previous Pb and Nd isotope studies and supports the notion that a significant part of the metals and magmas have a crustal source.
    • Quaternary Ostracode Paleoecology and Its Link to Climate Change in the Bonneville Basin: A Detailed Study of the Glad800 Core GSL00-4, Great Salt Lake, Utah

      Cohen, Andrew; Balch, Deborah P.; Cohen, Andrew; Flessa, Karl W.; Davis, Owen; Balch, Deborah P. (The University of Arizona., 2003)
      We report the results of a detailed paleoecological study of the Bonneville Basin covering the last ~240,000 years. Our study used fossil ostracodes and a sedimentological record obtained from the August 2000 GLAD800 drilling operation at the Great Salt Lake. We analyzed 125 samples, taken at ~1 meter intervals from core GSL00-4, for ostracodes and other paleoecologic and sedimentological indicators of environmental change. Multivariate analyses applied to the ostracode data indicate an alternation between three major environments at the core site over the cored interval. The environments fluctuated most often between shallow saline, open -water lake conditions (when the lake was high enough to inundate the core site) and salt or freshwater, spring -fed marsh (when the water level was at or lower than the core site). But occasionally, the core site was submerged by deep fresh water. Immediately following deep lake phases, crashes in lake level from rapid desiccation resulted in the deposition of thick evaporite units. These environmental changes are consistent with shoreline studies of regional lake level fluctuations, but provide considerable new detail on both the timing and environmental conditions associated with the various lake phases. Our age model (using dates obtained from ¹⁴C, U- series, tephra and biostratigraphic chronologies) allowed us to associate the core's record of regional paleohydrology to the marine oxygen isotope stages record of global climate change. The core contains high resolution, continuous records for the last three glacial/interglacial sequences. In each case we found that fresh open-water conditions (i.e. lake highstands) correspond with maximum glacial advances, except for the smaller, less intense OIS 4 glaciation, when the lake remained saline. Salt and freshwater marshes were dominant environments for most of the interglacials. However, throughout most of the Quaternary, this basin has contained a shallow, saline open-water lake.
    • Linkages of Laramide Thrusts, Northern Sangre de Cristo Range, Colorado

      Chase, Clement G.; Bedford, Janice M.; Chase, Clement G.; Davis, George H.; Coney, Peter J.; Bedford, Janice M. (The University of Arizona., 1994)
      Laramide thrust belts in the Colorado Rocky Mountains have been mapped as discrete units with little investigation into the linkage between displacements. The Elk Range-Sawatch and Elkhorn thrust systems displaced Precambrian, Paleozoic, and Mesozoic rocks toward the southwest. The Sangre de Cristo Range and Wet Mountains thrust systems displaced rocks toward the northeast. The opposite vergence and oppositely directed displacements between these systems must be accommodated, both at present levels of exposure and at depth. Mapping of the Kerber Creek area west of the northern Sangre de Cristo Range by J.M. Bedford helped answer the question of the linkage between the opposing Elk Range-Sawatch and Sangre de Cristo Range thrusts. In the Elk Range-Sawatch system the westward displacement on the thrusts is interpreted as a minimum of 11 km in the southern Elk Range with displacement decreasing toward the north. Bryant (1966) interpreted the timing of faulting as Paleocene in age. In the Sangre de Cristo Range northeast-verging thrust system the minimum estimated eastward displacement is 8 km. Burbank and Goddard (1937) interpreted the displacement as Eocene in age. The timing of the faulting in the two areas is not necessarily different. The Kerber Creek area lies between the two regions of oppositely facing displacement. Its internal structure most closely resembles that of the more proximal Sangre de Cristo deformation. Thrusts in the Kerber Creek area place Precambrian rocks over Laramide(?) and Paleozoic sedimentary rocks. The structures verge toward the north-northeast and represent a minimum of several kilometers of displacement. These Laramide structures are exposed where overlying Tertiary volcanics are eroded. In the Northern Sangre de Cristo Range a set of E-W trending faults intersects the generally N-S trending Laramide thrusts, possibly representing a partitioning of northeast transport into N-S and E-W components. The E-W trending deformation can be correlated across the San Luis Valley with the thrust faults in the Kerber Creek area. Correlation of the Kerber Creek thrusts with Sangre de Cristo faults extends the northeast directed Laramide deformation 22 km northwest of the edge of the Sangre de Cristo Range. Thus the link between the oppositely verging structures must continue toward the northwest, possibly beneath the Bonanza volcanic field. Further mapping toward the southern extent of the Elk Range-Sawatch thrust system may reveal how the opposite vergence and minimum 8-10 km of displacement are accommodated.
    • The Geology of the Atlas Mine Area, Pima County, Arizona

      Agenbroad, Larry D.; Anthony, John W.; Lacy, W. C.; DuBois, R. L.; Agenbroad, Larry D. (The University of Arizona., 1962)
      The Atlas Mine is located on the northwest flank of the Silver Bell mountains; Silver Bell mining district, Pima County, Arizona. The deposit is high grade (?) sine-copper mineralization in an altered sedimentary sequence. Rocks in the area include Precambrian (?) alaskite; Permian (?) limestone, quartzite and siltstone; Tertiary (?) monzonite, quartz monzonite, quarts latite porphyry and dacite porphyry; and Quaternary alluvium. The limestone has been largely metamorphosed to a mass of tactite, siltstone has been locally metamorphosed to hornfels, and the quartzite has been silicified, locally shattered and altered. Mineralization is related to NE and E-W trending fault systems, and similarly trending intrusive dikes. Predominate ore minerals are sphalerite and chalcopyrite, associated with pyrite, specular hematite and “high temperature" silicates. Copper mineralization is related to the silicified sediments. Zinc mineralization is present in silicates but is more predominate in areas of recrystallized calcite and extensive garnetization, suggesting incomplete replacement of the original sediments by the silicates. Further exploration and development should be undertaken in areas of favorable structural control, and adjacent to favored intrusives.
    • Economic Geology of the Big Horn Mountains of West-Central Arizona

      Allen, George B.; Chase, Clement G.; Reynolds, Stephen J.; Capps, Chris; Ruiz, Joaquin; Damon, Paul E.; Allen, George B. (The University of Arizona., 1985)
      The Big Horn Mountains are a geologically complex range that extends over 500 square km in west-central Arizona. Three major lithologic terranes outcrop: (1) Proterozoic amphibolite, phyllite, schists, gneiss, and granite; (2) Mesozoic monzonite to diorite intrusives; and (3) Cenozoic mafic to silicic volcanic rocks and clastic rocks. The entire area is in the upper plate of a detachment fault and, consequently, contains many low- to high-angle normal faults. Each lithologic terrane has its associated mineral occurrences. The Big Horn district is exclusively hosted in the pre- Tertiary terrane. Most of its mineral occurrences are spatially related to the Late Cretaceous intrusive rocks. One occurrence, the Pump Mine, may be a metamorphic secretion deposit, and therefore, would be middle Proterozoic. The vast majority of the mineral occurrences in the Big Horn Mountains are middle Tertiary in age and occur in three districts: the Tiger Wash barite - fluorite district; the Aguila manganese district; and the Osborne base and precious metal district. Fluid inclusions from Tiger Wash fluorite (T(h) 120 to 210° C, NaCl wt. equivalent 17 to 18 percent not corrected for CO₂) and nearby detachment - fault- hosted Harquahala district fluorite (T(h) 150 to 230° C., NaC1 wt. equivalent 15.5 to 20 percent not corrected for CO₂) suggest cooling and dilution of fluids as they are presumed to evolve from the detachment fault into the upper plate. Mass-balance calculations suggest that the proposed evolution of fluids is sufficient to account for the observed tonnage of barite and fluorite. The Tiger Wash occurrences grade directly into calcite- gangue-dominated manganese oxides of the Aguila district. A wide range of homogenization temperatures (T(h) 200 to 370° C.), an absence of CO₂ and low salinities (NaC1 wt. equivalent 1 to 2 percent) in the Aguila district calcite-hosted fluid inclusions argue for distillation of fluids during boiling or boiling of non saline-meteoric waters. Mass - balance calculations modeling the evolution of Ca and Mn during potassium metasomatism of plagioclase in basalt suggest that little if any influx of these cations is necessary to form the calcite –dominated manganese oxide tonnage observed. The Aguila district grades directly to the east into the base-metal and precious-metal occurrences of the Osborne district. Preliminary data describing geological settings, fluid inclusions, and geochemistry suggest that the Osborne district has a continuum between gold-rich to silver-rich epithermal occurrences. The gold-rich systems have dominantly quartz gangue, with or without fluorite, and are hosted in a variety of rocks, but are proximal to Precambrian phyllite or mid-Tertiary rhyolite. Fluid inclusions from two occurrences representative of the gold -rich systems spread across a minor range (T(h) 190 to 230° C., NaC1 wt. equivalent 17 to 23 percent not corrected for CO₂). Dilution of highly saline fluids is the inferred mechanism for precipitation of gold in the gold-quartz systems. The silver-rich systems have dominantly calcite gangue with or without quartz, and are hosted in mid-Tertiary basalt. Calcite fluid inclusions from a representative high-silver occurrence display a wide range of homogenization temperatures and salinities (T(h) 120 to 370° C., NaC1 wt. equivalent 7 to 23 percent). Boiling and consequent neutralization of acidic solutions is the inferred mechanism for the silver-rich, calcite gangue systems. A model inferring a regional fluid-flow regime and local sources of metals is proposed. Four possible regional and local causes of fluid flow in upper-plate detachment regimes are proposed: (1) regional elevation of geothermal gradients as a result of middle-crustal, lower-plate rocks rising to upper crustal levels; (2) meteoric water recharge along the southeast flank of the Harquahala antiform and consequent displacement of connate waters in the upper-plate of the Big Horn Mountains; (3) local emplacement of feeder stocks to rhyolitic flows; (4) and tilting of major upper-plate structural blocks.
    • A Geologic-Geochemical Study of the Cat Mountain Rhyolite

      Damon, Paul E.; Bikerman, Michael; Bikerman, Michael (The University of Arizona., 1962)
      The main rock unit exposed in the southern part of the Tucson Mountains, Pima County, Arizona, is the Cat Mountain rhyolite. It forms the eastward dipping slope and the western escarpment of the mountain range, capping the large fault blocks which make up the range. Petrographic and radiometric data combine to show that the Cat Mountain rhyolite, as originally defined, consists of two major ash flow eruption sequences. The lower sequence is less uniform and continuous than the highly welded characteristically jointed upper unit. A basal non welded unit is found along the western escarpment, a partly welded transition zone is found between the welded units, and a capping partly-to-non-welded unit is exposed in protected parts of the eastern slope. The volcanic history of the area began with the emplacement of a nuee ardente deposit forming the “chaos” unit. This was followed by two ash flow pulses through the same vents, and the sequence was terminated by the intrusion of spherulitic rhyolite sealing up the vents.
    • Geology and Origin of the Breccias in the Morenci-Metcalf District, Greenlee County, Arizona

      Bennett, Kenneth Carlton; Guilbert, John M.; Titley, Spencer R.; Anthony, John W.; Bennett, Kenneth Carlton (The University of Arizona., 1975)
      Rocks of the Morenci-Metcalf district consist of Precambrian metaquartzite-schist, granodiorite, and granite overlain by Paleozoic and Mesozoic sediments. Intrusion of igneous rocks, emplacement of breccia masses, and associated hydrothermal activity occurred in Laramide time. Breccias of the district are associated with the youngest sialic intrusive complex. This sequence includes intrusion of the Older Granite Porphyry stock, main stage district hydrothermal alteration, quartz veining, breccia formation, main stage district hydrothermal mineralization, and intrusion of the Younger Granite Porphyry plug. Breccia formation in the Morenci-Metcalf district is similar to breccia descriptions reported in the literature for other porphyry copper deposits. Three breccia types, of separate and distinct origins, are herein described as the Morenci, Metcalf and King, and Candelaria Breccias. The Morenci Breccia is an intrusion breccia that has formed along a pre-existing structural feature during the ascent and emplacement of the Older Granite Porphyry stock. It exhibits an oblate lenticular shape with angular to subrounded fragments in a matrix of quartz, K-feldspar, biotite, and minor rock flour. The Metcalf-King Breccias and numerous smaller breccia masses are the remnants of an original Older Granite Porphyry mantle above the ascending Younger Granite Porphyry complex. The breccia masses occur as large 'xenoliths' floating within the Younger Granite Porphyry plug and were formed by surging and collapse during emplacement of this intrusive. Fragments in the Metcalf and King Breccias grade from angular in the central core to rounded at the contacts and occur in a matrix of sericite, K- feldspar, quartz, and rock flour. The Candelaria Breccia is an explosion pipe and is the largest continuous breccia mass in the district. It is oval with an inverted cone appearance consisting of angular to subangular equidimensional fragments in a matrix of sericite, quartz, specularite, and rock flour. All the breccia masses occur within and subsequent to the district phyllic (quartz-sericite-pyrite) alteration zone. Main stage district copper mineralization postdates emplacement of the Older Granite Porphyry stock and breccia formation, and is prior to the intrusion of the Younger Granite Porphyry plug. Late stage quartz-sericite-pyrite-chalcopyrite veinlets occur in the Metcalf-King Breccia group. Field mapping and laboratory studies indicate that the Older Granite Porphyry stock appears to have been the main district mineralizer.
    • The Geology and Mineralization of the Sedimentary Hills Area, Pima County, Arizona

      Bennett, Paul J.; Lacy, Willard C.; Bennett, Paul J. (The University of Arizona., 1957)
      Mildly metamorphosed Cretaceous siltstones, arkoses and limey shales and a small composite stock of granitic composition are the principal rocks exposed in the Sedimentary Hills area, which lies six miles west of Tucson, Arizona. About 2400 feet of sediments were measured and assigned to the Amole Arkose Formation. The beds dip to the south and strike northwesterly. The stock is composed of two granitic facies. The northern and earlier part of the stock is a quartz monzonite which is mildly altered. The southern part of the intrusive is a granite porphyry which is altered to a greater degree and exhibits significant disseminations of chalcopyrite and pyrite. A quartz-pegmatite plug, probably a late phase of the intrusions, intrudes the quartz monzonite. Structure in the area is dominated by a large thrust zone which strikes generally parallel to the bedding. Within the Sedimentary Hills area, normal faulting and drag folding are tributary to the thrusting. Minor copper oxide minerals are frequent along large and small faults, and in the granite porphyry stock. Wide brick-red and brown gossans occur along the major thrust plane.
    • Paleocurrents and Depositional Environments of the Dakota Group (Cretaceous), San Miguel County, New Mexico

      Bejnar, Craig Russel; Wilson, Richard F.; Schreiber, Joseph F. Jr.; Kremp, Gerhard O. W.; Bejnar, Craig Russel (The University of Arizona., 1975)
      The Dakota Group surrounding Las Vegas, New Mexico, consists of three units: 1) a basal, predominately trough cross-stratified, conglomeratic sandstone, 2) middle intercalated, thin-bedded sandstone and carbonaceous shale, and 3) upper, predominately tabular-planar cross-stratified, sandstone containing trace fossils. These units represent, respectively, 1) a fluvial piedmont plain, 2) fluvial coastal plain, and 3) a beach, littoral, and shallow marine complex. The cross-stratification in the lower sandstone unit indicates an easterly paleoslope. The cross-stratification in the upper sandstone unit has a bimodal distribution almost at right angles to the paleoslope, suggesting deposition by longshore currents. The standard deviation of the cross-stratification in the lower sandstone unit of 78° is typical of fluvial deposits. The standard deviation in the upper sandstone unit of 97° indicates a marine origin.