• Las Trampas, New Mexico: Dendrochronology of a Spanish Colonial Church

      Smiley, Terah L.; Ames, Martha Hyde; Bannister, Bryant; Stokes, Marvin A.; Ames, Martha Hyde (The University of Arizona., 1972)
      Wooden beams and planks from the Spanish Colonial church and other structures in Las Trampas, north-central New Mexico, have been sampled and dated by dendrochronology. Dates of AD 1735 imply Spanish occupation of the area 16 years prior to official grant. Stockpiling of timber for church construction began as early as 1758. Exterior walls were 15 feet high by 1762 and were completed to roof level by 1764. Late in 1776, wood was cut for a dust-guard over the adobe altar and mural. According to clustering of tree-ring dates, a new altar and wooden altar screen were constructed soon after 1785. Beam re-use was prevalent. Timbers bearing early dates were incorporated into the 1785 altar screen, indicating re-use from within the church or from other pre-1760 structures. A roof viga was later used as a floor plank after reroofing. In domestic buildings, re-use of beams is repeated. Replacement of beams supporting the balcony was made in the 1860's and 1870's. Tree-ring dates indicate repairs again in the 1930's and 1943. A survey of the literature pertaining to dendrochronology of historical sites revealed that shaping of beams and lack of thorough sampling have heretofore hindered successful application. The documentary record of Las Trampas art and architectural history has been further refined by tree -ring dating, and the study reaffirms the potentials for historical sites dendrochronology.
    • 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.
    • 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.
    • 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 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 Paleocene Paleomagnetic Pole from the Gringo Gulch Volcanics, Santa Cruz County, Arizona

      Barnes, Arthur E.; Smiley; Butler, R.E.; Barnes, Arthur E. (The University of Arizona., 1980)
      Paleomagnetic data from 25 sites (5 samples per site) in andesite flows of the Gringo Gulch Volcanics in Santa Cruz County, Arizona, were analyzed to determine a lower Paleocene paleomagnetic pole. Alternating-field demagnetization to 500 oe peak field was sufficient to erase secondary viscous components. The mean direction of magnetization (inclination = -58.8°, declination = 167.5 °) was obtained by averaging the site mean directions of the 25 sites, which are all reversed. The resultant lower Paleocene pole position is at lat. 77.0 °N, 1on. 201.0 °E (dp = 1.2 °, dm = 1.7 °).
    • Paleocurrent Analysis of the Upper Miocene Formation, Los Angeles Basin, California

      Bennett, John Newton, 1943-; Wright, Jerome J.; Pye, W. D.; Harshberger, J. W.; Schreiber, Joseph F. Jr.; Bennett, John Newton, Jr. (The University of Arizona., 1967)
      Almost all sandstone beds occurring in the Upper Miocene formations at the Los Angeles basin were deposited by turbidity currents. Primary textures and structures indicative of turbidites occur in fair abundance throughout all three Upper Miocene formations. All accessible outcrops of the Puente, Modelo, and Upper Miocene portion of the Monterey and Capistrano Formations were scrutinized for sandstone beds containing primary sedimentary structures. Through study of these structures, the direction of current movement was determined. The pattern of current movement displayed reveals that sediment was being transported into the Los Angeles basin from all sides. Current directions and mineralogic studies indicate that essentially three source areas were supplying sediment into the basin. These source areas are 1) the San Gabriel Mountains, 2) an area to the east of the Santa Ana Mountains, and 3) a ridge of metamorphic rock paralleling the present coast line. The majority of sediment was derived from an area in the San Gabriel Mountains located northeast or the basin. This is evidenced by the fact that the thickness, grain size, and total sand content of the Upper Miocene units decrease southwestward across the basin.
    • 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.
    • Paleomagnetism of Miocene Volcanic Rocks in the Mojave Region of Southeastern California

      Acton, Gary Dean; Butler, Robert F.; Acton, Gary Dean (The University of Arizona., 1986)
      Paleomagnetic data were collected from Miocene volcanic rocks in the Turtle Mountains, Clipper Mountain, Colton Hills, and Piute Range of the southern Basin and Range (SBR) province in southeastern California as well as in the Soledad Mountains of the Mojave block in southern California. The data from these two tectonic provinces yield significantly different paleomagnetic directions, which probably indicates the existence of a major crustal and /or lithospheric discontinuity in the area between the Barstow Basin and the Clipper Mountain. Comparing the mean direction from the SBR data to the Miocene expected direction indicates no statistically significant rotation (R = -0.2° ± 18.2°) or flattening (F = -6.5° ± 9.2°). A similar comparison for the Soledad Mountain data, which were combined with data of Burke et al. (1982) from the Barstow Basin, yields a significant rotation of -43.5° ± 12.9° and flattening of 19.3° ± 10.6° for the Mojave block. These Mojave block values may be exaggerated a few degrees due to inadequate averaging of secular variation and possible improper structural corrections.
    • 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.
    • Pollen in Fecal Pellets as an Environmental Indicator

      Bartos, Frances Maribel; Martin, Paul S.; Solomon, Allen M.; Kremp, G.O.W.; Bartos, Frances Maribel (The University of Arizona., 1972)
      Identification of pollen in fecal pellets is a potential technique for describing an animals diet and in turn the vegetation of an area. Mule deer and Bighorn Sheep pellets representing both summer and winter browsing and a variety of habitats were examined using relative percentages and the absolute pollen frequencies. In addition, fossil pellets from Stanton's Cave, Grand Canyon, Arizona, were examined and compared with modern pellets. Absolute pollen frequencies of individual pellets showed higher values and greater variation for summer pellets than for winter pellets. Relative pollen percentages for a specific vegetation type showed more variation in fecal pellets than in soil surface samples. Unless specifically being eaten, arboreal pollen types such as Pinus are less abundant in fecal pellets than in soil samples. Unlike soil surface samples, arboreal pollen types in fecal pellets are frequently limited to the immediate source area.
    • Precambrian Geology of the Cottonwood Cliffs Area, Mohave County, Arizona

      Davis, George H.; Beard, Linda Sue; Davis, George H.; Coney, Peter J.; Lucchitta, Ivo; Beard, Linda Sue (The University of Arizona., 1985)
      A belt of Early Proterozoic rocks crops out in the Cottonwood Cliffs area, northwest Arizona. The belt contains an eastern and a western assemblage separated by the Slate Mountain fault. The western assemblage consists of mafic to felsic metavolcanic rocks, metapelites, and metaconglomerates. The eastern assemblage consists of phyllites, felsic to intermediate metavolcanic rocks, metagraywackes, and metagabbro bodies. The belt is bounded to the east by foliated granodiorite. The Valentine granite intruded the belt on the west and north. Steeply-plunging lineations and fold axes, and northeast-trending vertical foliation dominate the structural fabric. The regional elongation direction is near-vertical, as indicated by mineral and pebble lineations, and is parallel to fold axes. Although only one deformational event is evident, the intensity of that event may have obliterated evidence of any earlier deformation. Tertiary basalts and the Peach Springs Tuff locally overly the metamorphic rocks. Cenozoic normal faults in the area are mostly of minor displacement.
    • Primary Sediment Production from Granitic Rocks in Southeastern Arizona

      Acaba, Joseph Michael; Schreiber, Joseph F., Jr.; Acaba, Joseph Michael (The University of Arizona., 1992)
      Isolated granitic rock bodies (granites, granodiorites, quartz monzonites) in the vicinity of Benson in southeastern Arizona were studied to trace the behavior of rock weathering. Thin sections of fresh granites were examined to characterize the original mineralogy which consisted mainly of quartz, feldspars, and micas. The weathering products show up on the granites as grus and soil profiles as well as down slope in the basin deposits. X -ray diffraction studies of the < 2 micrometers fraction of the weathering products proved illite, smectite, illite-smectite mixed layer, and kaolinite to be the dominant clays; quartz and feldspar also persisted into this size fraction. Silt sized material produced similar results. The quartz monzonite of Texas Canyon afforded a special study of the initial weathering stages of feldspars and micas. In the < 2 micrometers fraction obtained from granitic material placed in an ultra sonic bath, the feldspars weathered to a Na-montmorillinite while biotite weathered to vermiculite.
    • Provenance and Petrofacies, Upper Devonian Sandstones, Philip Smith Mountains and Arctic Quadrangles Brooks Range, Alaska

      Coney, Peter J.; Anderson, Arlene Verona; Coney, Peter J.; Anderson, Arlene Verona (The University of Arizona., 1987)
      A petrographic study of upper Devonian sandstones (Endicott and Hammond Terranes), Philip Smith Mountains and Arctic quadrangles, Brooks Range, Alaska, shows that the sand-sized detritus was derived from two petrographic provenances. Detrital modes, calculated from point counts of thin sections, show that the provenance for the Devonian clastic wedge (Endicott Terrane) was a recycled orogenic belt with major components of quartz, chert, and lithic fragments. Three petrofacies are distinguished. Their distribution indicates compositional changes vertically and laterally which reflect changing compositions in the source area. A petrographically different provenance supplied the sandstones that overlie the Skajit Limestone (Hammond Terrane). Characterized by high feldspar and abundant volcanic rock fragments, this petrofacies indicates first-cycle deposition close to the source area. A magmatica arc provenance is suggested.
    • 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.
    • Radius Effect of the Alkaline Earths on the Rate of Inversion of Aragonite to Calcite

      Bennett, Catheryn MacDonald; Schreiber, Joseph F. Jr.; Bennett, Catheryn MacDonald (The University of Arizona., 1972)
      The effect of magnesium, strontium, and other alkaline earths on the formation and persistence of metastable carbonates in the natural environment was investigated to determine the nature of the controlling mechanism. Barium and beryllium were studied to evaluate the effect of ionic radius; magnesium and strontium, in order to determine if the results correlate with the usual order of stability for complexes and adsorbed species. Known weights of aragonite were placed in contact with solutions of beryllium, magnesium, calcium, strontium, and barium. Samples were covered and periodically both pH and percent composition of aragonite determined; supernatant liquids and precipitates were analyzed for cation concentrations by atomic absorption spectroscopy and titrimetric methods. Results indicated that the order of effectiveness of alkaline earth metals in inhibiting recrystallization is : Be > Mg > Sr > Ba. This is the expected order of effectiveness for both surface and solution effects. A solution effect (i.e., sequestration of bicarbonate ions) is strongly suggested by the chemical behavior of each cation.
    • 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.
    • Regional Structure and Stratigraphy of Sierra El Aliso, Central Sonora, Mexico

      Stewart, John; Bartolini, Claudio; Coney, Peter J.; Ruiz, Joaquin; Bartolini, Claudio (The University of Arizona., 1988)
      Assemblages of Paleozoic age and less significant Triassic and possibly Cretaceous-Tertiary volcanic rocks constitute the Sierra El Aliso, 186 km east-southeast of Hermosillo, Sonora. The Paleozoic section consists of approximately 2000 m of allochthonous Ordovician to Permian pelagic and hemipelagic deposits that accumulated in continental slope, continental rise and ocean floor (?) environments. The lower Paleozoic is characterized by graptolitic black shale and radiolarian chert, quartzite, argillite and local limestone. The upper Paleozoic is predominantly turbidite carbonates rich in benthonic foraminifera, and conodont faunas, subordinate bedded chert, siltstone, sandstone and chert-clast conglomerate. After Early Permian time, but prior to the deposition of the Late Triassic Barranca Group the Paleozoic section was imbricated along south-southeast vergent thrust faults. The Triassic rocks unconformably overlie the Paleo-zoic strata and all thrust faults. The Triassic and older rocks are overlain by the Cretaceous-Tertiary volcanics.
    • Resistivity and Induced-Polarization Responses Over Two Different Earth Geometries

      Akman, Hulya Hayriye; Wait, James R.; Sumner, J. S.; Nabighian, M. N.; Sternberg, B.; Akman, Hulya Hayriye (The University of Arizona., 1988)
      The object of the thesis is to obtain the apparent- resistivity curves and induced-polarization (IP) effects that are utilized in geophysical exploration. Two different earth geometries, the thin horizontal conductive layer and vertical dike, were studied. The solution for both cases is identical. First, quasi- static electrical conditions were assumed, so that the problem could be solved using potential fields. The exact solution to the problem was obtained by using the Bessel integral formulation. Also, the image method was employed to find the potential fields. We noticed that the image -type series converges best when the dike or layer was thick (ratio of thickness to electrode spacing, b/a, is large) and the reflection coefficient was not near ±1. Otherwise, it is preferable to employ the thin conductive sheet model. The next step was to determine the dilution and distortion factors which are relevant to the induced polarization response. Finally, numerical results were obtained using a Fortran computer program. These calculations were compared with some results taken from the literature and good agreement is seen.
    • The San Alberto Lead-Zinc Ore Body at Cerro de Pasco Mine, Cerro de Pasco, Peru

      Ascencios C., Alejandro; Lacy, W. C.; Ascencios C., Alejandro (The University of Arizona., 1966)
      This thesis presents briefly the geology of the Cerro de Pasco district to acquaint the reader with the general geological setting of the district. A study of ore controls for a typical lead-zinc replacement body at the world famous Cerro de Pasco mine in Peru, 102 km northeast of Lima, was undertaken for purposes of better understanding. The particular body selected, the San Alberto Ore Body, occurs as a northeast extension of a main mass of pyrite, known as the "pyrite body", and is enclosed in Triassic- Jurassic limestone. Primary ore controls were determined to be a "Y"-like intersection formed by NS Longitudinal Faulting with a NE striking bedding fault. Resultant brecciation created the necessary permeable conditions whereby ore fluids were channeled away from the pyrite body into the limestone for ore emplacement. Three phases of hydrothermal rock alteration were identified as silicic alteration, chloritic alteration and an outer zone of bleaching and recrystallization. One peculiarity is found in the mineral composition of the silicic alteration, and a hypothesis is presented to explain it. The paragenetic sequence given for hypogene and gangue minerals was determined from the examination of more than 150 thin and polished sections.