• An Analysis and Interpretation of Gravity and Magnetic Anomalies of the Butte District, Montana

      Ahrens, Gary Louis; Sumner, John S.; Ahrens, Gary Louis (The University of Arizona., 1976)
      An interpretation of gravity and magnetic anomalies of the Butte district, Montana, is based on the analysis of five gravity profiles constructed from Bouguer gravity data of the Butte district observed during the summer of 1974 and give concurrent magnetic profiles constructed from U.S. Geological Survey high-level aeromagnetic data of the district. Of primary concern in this analysis is the interpretation of the Bouguer gravity high and aeromagnetic low associated with the Butte orebody. Results of this interpretation yield a configuration for the Butte orebody characterized by vertical contacts extending from the surface or directly beneath Cenozoic basin fill to 4,500 feet below sea level, with a central core, elongate in the north -south direction, surrounded by a variable outer zone, which is more pronounced in the southern and western portions of the district. The central core is interpreted as a region of zero magnetic susceptibility with three density distributions, all of which are of higher densities than the surrounding host rock and are related to the varying degrees of mineralization and alteration present in this region. The laterally variable outer zone is interpreted as a zone of low magnetic susceptibility with a density equal to that of the host rock. This zone is related to the peripheral mineralization and alteration of the Butte orebody.
    • Analysis of Insoluble Organic Material in Carbonaceous Meteorites by Combined Vacuum Pyrolysis-Gas Chromatography-Mass Spectrometry

      Bandurski, Eric Lord; Nagy, Bartholomew; Long, Austin; Denton, M. Bonner; Roemer, Elizabeth; Bandurski, Eric Lord (The University of Arizona., 1975)
      The polymer-like organic material in the Orgueil (Cl) chondrite was analyzed by high vacuum pyrolysis/gas chromatography/mass spectrometry, a new technique specially developed for this type of polymer analysis. Orgueil powder, previously solvent-extracted to remove all soluble organic compounds, whether indigenous or contaminant, was pyrolyzed in temperature steps at 150°, 300°, 450°, and 600°C. Gas chromatographic/mass spectrometric analysis of the vacuum pyrolyzates revealed a series of alkenes to C₈, an extensive series of alkylbenzene isomers, thiophene, alkylthiophenes, and benzothiophene, and the nitrogen compounds acetonitrile, acrylonitrile, and benzonitrile. Comparison of the Orgueil polymer fragments with those reported in polymer analyses of the Murchison and Allende meteorites suggests that qualitatively and quantitatively the Orgueil and Allende polymeric materials are very similar. The presence of acetonitrile, acrylonitrile, and benzonitrile, typical breakdown products of amino acids, in Orgueil pyrolyzates suggests the presence of amino acids in an insoluble form in the meteorite polymer matrix. Changes in the distribution of polymer fragments occurred during high vacuum pyrolyses as the temperature was increased stepwise from 150° to 600°C. These changes imply a progressive alteration in the character of the polymeric material toward a condensed aromatic structure through the preferential loss of aliphatic and heteroaromatic portions at lower temperatures. A possible inference is that the polymeric material in Orgueil is a complex mixture of polymerized materials having different thermal stability. Comparison of vacuum pyrolyzates of the Orgueil polymeric material with pyrolyzates of terrestrial kerogen indicates similarities in composition and structure. These similarities suggest the possibility that meteorite polymers may have formed near the surfaces of meteorite parent bodies by low temperature processes similar to those by which terrestrial kerogen is formed.
    • An Analysis of Some Regional Gravity Data in Arizona

      Bhuyan, Ganesh Ch.; Sumner, John S.; Lacy, W. C.; Titley, Spencer R.; Bhuyan, Ganesh Ch. (The University of Arizona., 1965)
      The need for accurate reference bases for any gravimetric work can hardly be overemphasized. During the months of March, April, and May, 1964, about 130 gravity observations were made in Arizona, with LaCoste Romberg Gravity Meter DL-1 and Worden Gravity Meter (Educator) No. 461. The purpose of this program was to establish 1) a 1st order control airport gravity base network, 2) a standard calibration range for the State of Arizona, and 3) to gain a structural interpretation of the Tucson Basin. Gravity data were analyzed as to their accuracies and reliabilities, taking into consideration errors involved in tidal corrections, drift corrections, reference datum, and nonlinearity of scale factor of the meters. It is concluded that the reliability of these data is .1 milligal or better. While correcting for the tidal variation of gravity, it was noticed that there was a discrepancy between the theoretical and observed tidal correction values. For any additional precise work, it is desirable to correct for tidal variations from actual records, if available, in conjunction with the theoretical tables. Causes for this discrepancy in tidal gravity variation need further study. Programs were written for a digital computer to calculate 1) the theoretical gravity values from the International Gravity Formula, and 2) Free-Air Anomalies, Bouguer Anomalies and Special Bouguer Anomalies from field data for various stations. Free-Air and Bouguer Anomaly values for different stations were analyzed as to their implications in terms of isostasy, crustal structures and local geological structures. Results from Simple Bouguer Anomaly values indicate a crustal thickness of 49 km to 33 km for Arizona with broad isostatic compensation for regional surface irregularities. An analysis of residual Bouguer gravity anomalies of the Tucson Basin in terms of local geological structures, indicates a basin and range structure for this region. The thickness of sediments ranges from more than 700 feet on the north to more than 8000 feet towards the south of the basin with faults indicated in it. Application of a limiting -depth interpretation method implies that the tops of the disturbing bodies can be no deeper than 2 miles below sea level. A total mass deficiency corresponding to the residual gravity low in this basin comes out to be 1.8 x 10¹⁷ grams according to two – dimensional form of Gauss' Theorem. This corresponds to a 135 cubic mile volume of material with a density .3 grams per cubic centimeter less than the enclosing rocks. From porosity and volume considerations of the sediments in the Tucson Basin, it is estimated that the total water holding capacity may be of the order of 4.6 x 10⁷ acre feet.
    • The Analysis of the Gravity Anomalies of Arizona

      Aiken, Carlos Lynn Virgil; Glass, Charles; Davis, G. H.; Butler, R. F.; Zonge, K. L.; Sumner, J. S. (The University of Arizona., 1976)
      The Bouguer correction using a mean sea level reduction datum compensates the gravitational effect of the mass of the terrain above sea level. This correction generally results in long -wavelength Bouguer gravity anomalies if the mass of the terrain is isostatically compensated. These anomalies correlate with regional elevations, especially in areas with significant regional variations in elevation, such as western North America. The adverse effect of this correlation is that other anomalies of potential interest in a tectonic or geologic analysis may be overshadowed. To circumvent this problem in an analysis of gravity in Arizona, a residual Bouguer gravity anomaly map has been constructed for the state in which a trend surface of the elevation is used as the reduction datum in the Bouguer correction. Elevation values from topographic maps and not gravity station elevations have been used to prepare the regional elevation datum because station elevations do not adequately sample the range in elevations. Small- and large-wavelength residual Bouguer gravity anomalies and trends of anomalies are brought out more clearly by the residual Bouguer gravity anomaly map than by previous gravity maps. The most prominent features in the residual anomalies are a strong gravity gradient 50 km wide striking west -northwest across southern Arizona and a large wavelength residual Bouguer gravity anomaly low in the Coconino Plateau of northwest Arizona . The long-wavelength residual Bouguer gravity anomalies reflect lateral density variations in the crust and mantle that may be related to lateral temperature variations.
    • Application of Growth Strata and Detrital-Zircon Geochronology to Stratigraphic Architecture and Kinematic History

      Barbeau, David Longfellow Jr.; DeCelles, P. G.; Johnson, Roy; Geslin, Jeff K.; Barbeau, David Longfellow Jr. (The University of Arizona., 2003)
      Growth strata analysis and detrital-zircon geochronology are useful applications of stratigraphy to tectonic problems. Whereas both tools can contribute to kinematic analyses of supracrustal rock bodies, growth strata are also useful for analyzing the influence of tectonics on stratigraphic architecture. This study reports: 1) a conceptual model for growth strata development; 2) stratigraphic and kinematic analyses of growth strata architectures from growth structures in southeastern Utah, the Gulf of Mexico, and northeastern Spain; and 3) the detrital-zircon geochronology of the Salinian block of central coastal California. Kinematic sequence stratigraphy subdivides growth strata into kinematic sequences that are separated by kinematic sequence boundaries. Kinematic sequences can be further partitioned into kinematic domains based on the termination patterns of strata within a kinematic sequence. Salt- related fluvial growth strata from the Gulf of Mexico and southeastern Utah contain stratigraphic architectures that are unique to different kinematic domains. Offlap kinematic domains contain fluvial strata indicative of high slopes, low accommodation rates, and strong structural influence on paleocurrent direction. Onlap kinematic domains contain fluvial strata indicative of moderate slopes, high accommodation rates, and decreased structural influence on paleocurrent direction. The stratigraphic architecture of alluvial -fan thrust -belt growth strata in northeastern Spain does not display a marked correlation with kinematic domain, and is most easily interpreted using existing models for autocyclic alluvial -fan evolution. Detrital- zircon (U -Pb) geochronologic data from basement and cover rocks of Salinia suggest that Salinia originated along the southwestern margin of North America, likely in the vicinity of the Mojave Desert. The presence of Neoproterozoic and Late Archean detrital zircons in Salinian basement rocks also suggest that Salinian sediments were recycled from miogeoclinal sediments of the western margin of North America.
    • Calibration and Interpretation of Holocene Paleoecological Records of Diversity from Lake Tanganyika, East Africa

      Alin, Simone Rebecca; Cohen, Andrew; Flessa, Karl; Overpeck, Jonathan; Reinthal, Peter; Robichaux, Robert (The University of Arizona., 2001)
      Lake Tanganyika is a complex, tropical ecosystem in East Africa, harboring an estimated 2,100 species. Extensive watershed deforestation threatens the biodiversity and ecological integrity of the lake. In this dissertation, ecological and paleoecological methods were employed to study the distribution of invertebrate biodiversity through space and time, with particular emphasis on linkages between biodiversity and land –use patterns. Ecological surveys of fish, mollusc, and ostracod crustacean diversity at sites in northern Lake Tanganyika representing different levels of watershed disturbance revealed a negative correlation between biodiversity and intensity of watershed disturbance. To elucidate the long -term relationship between disturbance and biodiversity, paleoecological records of invertebrates offshore from watersheds experiencing different degrees of anthropogenic disturbance were examined. Life, death, and fossil assemblages of ostracod valves were compared to assess the reliability and natural variability inherent to the paleoecological record. These comparisons indicated that paleoecological (i.e. death and fossil) assemblages reliably preserve information on species richness, abundance, and occurrence frequency at comparable -to- annual resolution. Unlike life assemblages, species composition of paleoecological assemblages reflects input of species from multiple habitat types. Ostracod paleoecological assemblages are characterized by spatiotemporal averaging that renders them representative of larger areas and longer time spans than life assemblages. Thus, paleoecological assemblages provide an efficient means of characterizing longer -term, site -average conditions. Natural variability in ostracod fossil assemblages from a sediment core representing the Late Glacial to the present indicates that abundance of individual ostracod species is highly variable. Ostracod assemblages were preserved in only the most recent 2,500 years of sediment. Species composition of ostracod assemblages reflects lake water depth. Core geochemical data indicate that the coring site may have been below the oxycline for ~2,000 years, inhibiting ostracod survival and preservation. Paleoecological, sedimentological, and stable isotope data revealed differences in biodiversity and watershed disturbance through time offshore from a pair of sites. The protected site is offshore from Gombe Stream National Park (Tanzania), the other offshore from a deforested watershed outside the park. Offshore from the deforested watershed, sedimentation rates increased, and turnover in ostracod species composition occurred during the past 50 years. Comparable changes were not observed offshore from the park.
    • The Chinle Formation of the Paria Plateau Area, Arizona and Utah

      Akers, J.P.; Harshbarger, John W.; Akers, J.P. (The University of Arizona., 1960)
      In the Paria Plateau area of northern Arizona and southern Utah the Chinle formation of Upper Triassic age consists of a thick series of Ienticular sandstone, siltstone, claystone, and limestone. The series thins northwestward from about 900 feet at Lees Ferry, Ariz., to about 800 feet at Paria, Utah. Four members of the Chinle formation are recognized—1) the basal Shinarump member composed of conglomeratic sandstone and subordinate shale, 2) a unit, herein named the Lowery Spring member, composed of sandstone and mudstone, 3) the Petrified Forest member composed of bentonitic siltstone and claystone and thin sandstone, and 4) the Owl Rock member composed of cherty limestone and calcareous siltstone. Only the Petrified Forest member is present at all localities in the Paria Plateau area. The Shinarump member was deposited in topographic low areas on an erosion surface and its distribution is irregular. The Lowery Spring and Owl Rock members grade and pinch-out toward the northwest and are not present at Paria, Utah. The upper contact of the Chinle formation is locally unconformable. The three lowermost members were deposited on a broad, flat plain between the Cordilleran geosyncline and highlands to the southeast. In Owl Rock time the rising Cordilleran geanticline cut off the north-westward drainage of Chinle streams and a depositional basin trending southwest was formed.
    • The Climatic Response in the Partitioning of the Stable Isotopes of Carbon in Juniper Trees from Arizona

      Arnold, Larry David; Long, Austin; Lerman, Juan Carlos; Wilson, Alex T.; Martin, Paul S.; Steelink, Cornelius (The University of Arizona., 1979)
      Juniper trees (Juniperus osteosperma, J. monosperma, J. deppeana and J. scopulorum) grow under widely varying climatic and edaphic conditions throughout the American southwest. This study is chiefly concerned with a test of the climatic response in the partitioning of the stable isotopes of carbon in such trees. The relationships developed here, for example, might be used to extract paleoclimatic information from ancient juniper samples preserved in cave middens. In order to test for a climatic response in the leaf cellulose δ¹³C values, leaves from a total of 29 trees were sampled in the immediate vicinity of 9 meteorological stations across the state of Arizona. Care was taken to insure that 22 of the trees experienced only the temperature and precipitation values reflected by their site meteorological stations. As a cross-check, 7 trees exposed to temperature and/or precipitation levels clearly deviant from their site averages were also sampled. In general, each tree was sampled at four places, approximately 2 m above the ground. All leaf samples were reduced to cellulose (holocellulose) before combustion and analysis for their δ¹³C value. The δ¹³C value for each site was derived from an average of 2 to 4 trees per site, the value of each tree being the average of its individual samples. The one sigma 13C variation found between trees at any given site is ±0.38‰; within a single tree, ±0.36‰; and for repeat combustions, ±0.20‰. The δ¹³C values of the juniper sites were regressed against the temperature and precipitation of the individual months and running averages of months across the year using polynomial, multiple regression analysis. Temperature and precipitation were entered as separate variables in a general multiple regression model and also as a combined, single variable (T /P) in a more specific approach. The pattern formed by the multiple correlation coefficients, when plotted by months across the year, closely follows the seasonal variations in photosynthetic activity. Cellulose δ¹³C values have minimum correlation with temperature and precipitation (considered jointly) during summer months and maximum correlation during spring months. For an individual month, the temperature and precipitation (jointly) of April correlated at the highest level with a multiple adj. R = 0.994 and an F = 166; for a maximum seasonal response, March-May reached a multiple adj. R = 0.985, F = 66. The results using the combined, single variable (T /P) were nearly equivalent for the same months: April's adj. R = 0.957, F = 45; March-May's adj. R = 0.985 with an F = 132. The ability of T and P as independent predictors is considerably less than their ability in combination; e.g., 13C g(T) for March-May has an adj. R = 0.80 and 6 13C = h(P) has an adj. R = -0.67 compared to their in- concert adj. R value of 0.985. The results of this study, therefore, strongly support a high degree of climatic sensitivity in the partitioning of the stable isotopes of carbon in juniper leaf cellulose: the correlation coefficients and their F statistics are sufficiently high to consider temperature and precipitation (acting jointly) as accurate predictors of cellulose δ¹³C values in the system studied.
    • The Conodont Biostratigraphy of the Black Prince Limestone (Pennsylvanian) of Southeastern Arizona

      Barrie, Kathleen Ann; Schumacher, Dietmar; Bryant, Donald L.; Schreiber, Joseph F. Jr.; Barrie, Kathleen Ann (The University of Arizona., 1975)
      The Black Prince Limestone of southeastern Arizona has been assigned to the Morrowan on the basis of several long-ranging fossils. Since these were not especially diagnostic, the exact time represented by the Black Prince within the Morrowan was uncertain. To date the Black Prince more precisely, six sections were systematically sampled for conodonts. The condonts found, especially Neognathodus bassleri, Rachistognathus muricatus, Idiognathoides convexus, and Spathoqnathodus coloradoensis, indicate a middle Morrowan to early Derryan age for the Black Prince in the study area. Four conodont zones can be recognized: the Neognathodus bassleri Zone, the Idiognathodus sinuosis.- Streptognathodus anteeccentricus Zone , the Idiognathoides convexus Zone, and the Spathognathodus coloradoensis-Neognathodus columbiensis Zone. These zones compare favorably with the zonation previously established in the type Morrowan. This biostratigraphic evidence suggests that the hiatus between the Black Prince and Horquilla Limestones increases in magnitude from southeastern to south-central Arizona. The Black Prince represents a sequence of tidal flat and shallow subtidal carbonate deposits. Mudstones and sparsely fossiliferous wackestones with low fossil diversity and abundance characterize the tidal-flat facies. Grainstones, packstones, and fossiliferous wackestones with high fossil diversity and abundance characterize the shallow subtidal facies.
    • 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.
    • Downward Continuation of Bouguer Gravity Anomalies and Residual Aeromagnetic Anomalies by Means of Finite Differences

      Arenson, John Dean; Sturgul, J. R.; Sumner, J. S.; Norton, D. D.; Arenson, John Dean (The University of Arizona., 1975)
      The depths to buried bodies, characterized by anomalous gravity and magnetic properties, are determined by a combination of two numerical techniques. An upward continuation integral is solved by a method by Paul and Nagy using elemental squares and low order polynomials to describe the behavior of the gravity or magnetic data between observed data points. Downward continuation of the magnetic or gravity data is done by a finite difference technique as described by Bullard and Cooper. The applicability of the techniques are determined by comparison to depths determined by other means over the same anomalies and by comparison to various rule-of-thumb methods prevalent in the geophysical literature. The relative speed and cost of the particular computer system used is also considered in the applicability. The results show that although the initial costs of the computer program are high, the combined technique is as good as and at times better than the rule-of-thumb methods in determining the depth to the anomaly-causing body and is useful when more than just an approximate depth is of interest.
    • The Economic Geology of Some Virginia Kyanite Deposits

      Bennett, Paul J.; Lacy, Willard C.; Anthony, John W.; Damon, Paul E.; Mayo, Evans B.; Titley, Spencer R.; Bennett, Paul J. (The University of Arizona., 1961)
      This kyanite quartzite deposits at Leigh, Baker and Willis Mountains located in the south central Virginia Piedmont were investigated to determine their genesis, extent, and geologic and petrographic character. Kyanite quartzite in Virginia typically contains 20-40 per cent kyanite, 0-5 per cent pyrite, 0.5-1.5 per cent rutile, a per cent or so of mica or clay with the balance quartz. They occur as single beds within metamorphic rocks ranging from slates and phyllites of the greenschist facies south of Leigh Mountain, to schists and gneisses of the amphibolite facies at Baker and Willis Mountains. Post-kyanite hydrothermal alteration along fractures has altered large segments of the Baker Mountain deposit to clay and topaz. The protolith of kyanite quartzite is believed to have been extraordinarily pure mixture of quartz and kaolinite which was produced by either Iateritic weathering or by circulating meteoric waters. Isochemical regional metamorphism is believed to have occurred in a high pressure, moderate temperature environment in which water was either deficient or able to escape. Fluorine may have had a catalytic effect in promoting kyanite crystallization. No evidence was found of hydrothermal introduction of alumina, or localization of kyanite as a result of differential stress. The rocks enclosing kyanite quartzite in the Leigh Mountain area are believed to be basal members of the lower Paleozoic (?) Volcanic-Slate series. The gneisses surrounding Willis and Baker Mountains may be more highly metamorphosed, infolded remnants of the same series. The kyanite deposits of Virginia are extensive and well situated for mining. Possible reserves of kyanite quartzite containing over 25 per cent kyanite available for open pit mining are measured in tens of millions of tons.
    • 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.
    • Environments of Deposition of the Moenkopi Formation in North-Central Arizona

      Baldwin, Evelyn Joan; Wilson, Richard F.; Bull, William B.; Bryant, Donald L.; Schreiber, Joseph F. Jr.; Wright, Jerome J.; Baldwin, Evelyn Joan (The University of Arizona., 1971)
      In north-central Arizona, the Moenkopi Formation of Triassic age consists of generally unfossiliferous red mudstones, siltstones, gypsum, and sandstones that contain abundant sedimentary structures, such as ripple marks, cross-stratification, ripple laminae, salt crystal casts, mud cracks, sole marks, parting lineation, and core-and-shell structures. Three informal members were established for this study: the lower member, the lower massive sandstone, and the upper member. Flaser, wavy, and lenticular bedding, bimodal distribution of ripple laminae dips, parallel ripple marks dominant over cuspate ripple marks, gypsum beds and veins, salt crystal casts, and lack of channel deposits are the suite of sedimentary features that are interpreted to indicate a tidal-flat environment during deposition of the lower member. The very fine grained lower massive sandstone can be divided into four subunits, which were formed by a transgression-regression of the sea. Wavy and ripple laminated beds in subunit one were probably deposited in very shallow water. Medium-scale wedge-planar and trough sets of cross strata with mean dip directions to the southeast make up subunit 2 and indicate megaripples formed by longshore drift. Subunit 3 consists of lenticular, wavy, pod-shaped beds that were created in water shallower than that for subunit 2. Continuous, large-scale, low-angle cross strata of uniform thickness and medium-scale wedge-planar and trough sets of cross strata characterize subunit 4 and are typical of beach deposits. The significant sedimentary features in the upper member are unimodal distribution of ripple laminae dips, cuspate ripple marks dominant over parallel ripple marks, channel deposits with shallow trough cross strata, an increase in the number and thickness of sandstone and siltstone beds compared with the lower member, plus vertebrate bones, tracks, and plant impressions. This suite of features indicates a flood-plain environment. Early in Moenkopi time, north-central Arizona was a tidal flat and sabkha. The sea to the west fluctuated east and west and finally transgressed over the entire area. As the sea regressed, a beach formed, and rivers flowing from the east deposited sediment on a westward-prograding flood plain. In the northern, southern, and central portions of the region, sabkhas existed for a time during regression. At the end of Moenkopi time, the entire area was a flood plain. Considering the association of red beds and evaporites, the absence of fossils in the lower member and the lower massive sandstone, the paleowind directions, and the theory of continental drift, the climate during early and middle Moenkopi time was probably hot and arid. The influx of sandstones, the presence of Calamites (?) impressions, and trackways and bones of amphibians in the upper member suggest that the climate became more humid at the end of Moenkopi time.
    • Exploratory Palynology in the Sierra Nevada, California

      Adam, David Peter; Martin, Paul S. (The University of Arizona., 1965)
      Pollen analysis of two surface transects of modern soil samples and four stratigraphic sections from the central Sierra Nevada of California have provided a climatic record covering the time interval since the recession of the last glaciers of the Wisconsin glaciation. Two separate warm intervals are recognized between the recession of the Wisconsin glaciers and the reappearance of glaciers in the Sierra during the Little Ice Age.
    • Fire Frequency, Nutrient Concentrations and Distributions, and δ13C of Soil Organic Matter and Plants in Southeastern Arizona Grassland

      Biggs, Thomas; Quade, Jay; Webb, Robert H.; Bull, William B.; Hendricks, David M.; Long, Austin; Biggs, Thomas (The University of Arizona., 1997)
      Over the past century, woody plants and shrubs have increased in abundance at the expense of grasslands in many semiarid regions. The availability and concentrations of nutrients influence the relative success of plants, but the effects of fire frequency on soil nutrients is unknown for semiarid grasslands. On the gunnery ranges of Fort Huachuca in southeastern Arizona, study sites were established to examine the effects of fire frequency on soil biogeochemistry, plant biochemistry, and δ¹³C values in soil organic matter (SOM). The sites were on homogeneous granitic alluvium where wildfire frequency history is known from 1973 to present and no cattle grazing has occurred in recent decades. Subplots represent fire frequencies of no burns, 3 fires per decade, and 5 fires per decade. The "no burn" plot has abundant C₃ Prosopis veleruina (mesquite) trees, whereas the burned plots are open C₄-dominated grasslands with scattered mesquite trees. Prosopis trees have altered SOM pools by the concentration of plant nutrients and the addition of isotopically light shrub litter. Frequent fires have altered the basic geochemistry and nutrient availabilities of the soil, and the changes appear to be significant enough to affect plant growth. Soil pH increases with burning frequency, and TOC, total nitrogen, and plant -available phosphorus show significant increases on the infrequently burned plot. Burning is advantageous for preservation or restoration of grasslands, as total living grass biomass is greater on the two burned plots. Root biomass is significantly lower on the "frequently burned" plot. Concentrations of the key nutrients nitrogen and phosphorus are reduced in plants on the burned sites compared to plants on the unburned site. Fires help re-distribute nutrients but evidence of nutrient concentrations and δ¹³C values are retained in SOM for many decades. Estimates of bulk carbon turnover rates range from 112 to 504 years. Evidence for modern C₃ shrub expansion is found in the shift of SOM δ¹³C values from values characteristic of C₄ grasses to C₃ shrubs in surface soil layers. δ¹³C(SOM) values indicate that the Holocene and Late Pleistocene were dominated by C₄ grasslands, and the pre-Late Pleistocene vegetation was a C₄-grass savanna with abundant C₃ plants.
    • 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.
    • Geologic Implications of a Geo-Chemical Study of Three Two-Mica Granites in Southern Arizona

      Damon, Paul E.; Guilbert, John; Arnold, Andrew Herbert; Damon, Paul E.; Ruiz, Joaquin; Arnold, Andrew Herbert (The University of Arizona., 1986)
      The biotite + muscovite ± garnet-bearing Texas Canyon (TC), Presumido Peak (PP), and Gunnery Range (GR) granites are members of an enigmatic suite of Eocene age granites in southern Arizona. The late orogenic granites intrude Precambrian through Jurassic metasediments and metavolcanics. The major and minor element geochemistry of the high silica, weakly peraluminous granites is rather uniform. However, trace element concentrations, REE patterns, and isotopic compositions imply gross similarities between the TC and GR granites when both are compared to the PP granite. The TC and GR granites were derived from a depleted Precambrian lower crustal source area with low Rb/Sr, while the PP granite was the result of anatectic melting of an enriched Precambrian mid-to-upper crustal source. The PP granite is an integral part of a metamorphic core complex, and this tectonic setting accounts for the geochemical differences between it and both the TC and GR granites.
    • Geologic Interpretations of a Siliceous Breccia in the Colossal Cave Area, Pima County, Arizona

      Lance, John F.; Acker, Clement John; Acker, Clement John (The University of Arizona., 1958)
      In the Colossal Cave area, Pima County, Arizona, massive blocks of Paleozoic sedimentary rocks have been thrust from a southerly direction over an irregular surface of Rincon Valley granite of Laramide age. The Paleozoic rocks involved in the thrusting are the Bolsa quartzite, Abrigo formation, Martin limestone, Escabrosa limestone, Horquilla limestone, and Andrada formation. The Pantano formation (Miocene ?) is also present under the thrust sheet. The thrusting is of an imbricate nature with slip-page mainly teaking place along incompetent rock units. Large folds occur in the Escabrosa limestone and Horquilla lime-stone. A siliceous breccia is associated with thrust planes in the area. The competent units of the Paleozoic sediments were fractured and brecciated along the thrust planes. Solutions dissolved part of the silica and hematite from the Bolsa quartzite and deposited it in the fractured and brecciated zones.
    • A Geologic-Geochemical Study of the Cat Mountain Rhyolite

      Damon, Paul E.; Bikerman, Michael, 1934-; 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.