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  • UA Geosciences Newsletter, (Fall 1996)

    University of Arizona Department of Geosciences (Department of Geosciences, University of Arizona (Tucson, AZ), 1996)
  • UA Geosciences Newsletter, (Spring 1996)

    University of Arizona Department of Geosciences (Department of Geosciences, University of Arizona (Tucson, AZ), 1996)
  • UA Geosciences Newsletter, Volume 3, Number 2 (Spring 1997)

    University of Arizona Department of Geosciences (Department of Geosciences, University of Arizona (Tucson, AZ), 1997)
  • UA Geosciences Newsletter, Volume 5, Number 2 (Spring 2000)

    University of Arizona Department of Geosciences (Department of Geosciences, University of Arizona (Tucson, AZ), 2000)
  • UA Geosciences Newsletter, Volume 5, Number 1 (Fall 1999)

    University of Arizona Department of Geosciences (Department of Geosciences, University of Arizona (Tucson, AZ), 1999)
  • UA Geosciences Newsletter, Volume 4, Number 2 (Spring 1999)

    University of Arizona Department of Geosciences (Department of Geosciences, University of Arizona (Tucson, AZ), 1999)
  • UA Geosciences Newsletter, Volume 3, Number 1 (Fall 1997)

    University of Arizona Department of Geosciences (Department of Geosciences, University of Arizona (Tucson, AZ), 1997)
  • UA Geosciences Newsletter, Volume 4, Number 1 (Fall 1998)

    University of Arizona Department of Geosciences (Department of Geosciences, University of Arizona (Tucson, AZ), 1998)
  • 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.
  • Structure and Petrology of the Oracle Granite, Pinal County, Arizona

    Banerjee, Anil K.; Mayo, Evans B.; Lacy, W. C.; Banerjee, Anil K. (The University of Arizona., 1957)
    Oracle granite, probably emplaced in older Precambrian time contains the relic pattern imposed on the Pinal schist by the Mazatzal orogeny. The "granite" of that time was a granodiorite. It is now a porphyritic quartz monzonite that varies unsystematically toward granodiarite and biotite granite. The trend of its principal Precambrian foliation is northeast-southwest and this is crossed by northwesterly-trending Precambrian foliation. After the Mazatzal orogeny, peneplanation, and deposition of the younger Precambrian Apache group, a series of dikes was emplaced in the Oracle granite, beginning with coarse and medium grained diabase and ending with andesite and rhyolite. The earlier members of the sequence, including diabase, aplite, pegmatite, quartz and latite were emplaced when tensional stresses opened a series of northwest trending fractures. The tension seems to have been related to right lateral strike-slip along the Mogul fault zone, which forms the southern border of the granite. In Jurassic or Cretaceous time the strike-slip on the Mogul fault was reversed; northeast-trending Pinal schist south of the fault was rotated counter-clockwise into partial parallelism with the fault, a transition zone north of the fault was likewise dragged and andesite and rhyolite dikes were emplaced in northeast-trending "feather fractures." The structural and petrographic evidence suggests that metasomatism was important in the origin of the Precambrian granodiorite, but the existence of some magma cannot be precluded. Likewise the evidence suggests that the potash metasomatism that changed the granodiorite to quartz monzonite may have taken place at the time of the later intense movements, that is, during Jurassic or Cretaceous time. However, an earlier age of potash introduction is not unlikely.

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