• 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.
    • Geological and Geochemical Studies of the Roskruge Range, Pima County, Arizona

      Bikerman, Michael, 1934-; Damon, Paul E.; Mayo, Evans B.; Bikerman, Michael (The University of Arizona., 1965)
      A combined field and laboratory investigation of the primarily volcanic Roskruge range, Pima County, Arizona, produced the following results: The rocks in the area fall into three major and several minor divisions. The major groups are: (1) The pre-Laramide dark-colored andesites and sediments that floor the range. A K-Ar date on one of the andesites produced a number, 108 m. y. , on a whole rock analysis. (2) The brightly colored and widespread Laramide volcanics and an associated hypabyssal pluton at Cocoraque Butte, which gave K-Ar mineral ages in the 74 m. y. to 66 m. y. spread. (3) The mid-Tertiary potassic basaltic andesites found on an eroded plain that is cut into the Laramide volcanics. These dark-colored extrusives were dated at 23 m. y. by whole rock K-Ar. Amongst the minor units in distribution is the petrographically unusual Recortado ash flow, a small 13 m. ye old unit that preserves a vitrophyre just above its base. Also included in the miscellaneous group of units are the post-orogenic true basalts, which appear as dikes and as a flow(?) at Brawley Wash and which gave whole rock K-Ar dates of about 10 m. y. Initial strontium 87/86 ratios indicate that the Laramide and mid-Tertiary rocks (including the Recortado ash flow) have values ranging from . 7056 to .7092, while the Brawley Wash basalt has a true deep-seated basalt ratio of .7038. The combination of radiochemical assay, petrographic and field study, and isotopic data has established good gross correlation with the already known sequence of formations and plutons in the Tucson Mountains.
    • The Relationship of Laramide Stocks to Regional Structure in Central Arizona

      Balla, John Coleman, 1936-; Peter, W. C.; Mayo, Evans B.; Abel, John F.; Mitcham, T. W.; Guilbert, John M.; Balla, John Coleman (The University of Arizona., 1972)
      The area of this study is a northeast trending zone which is approximately ninety miles long, extending from Casa Grande to Globe, Arizona. A number of porphyry copper deposits and barren Laramide stocks occur within this zone. Geological mapping of the various Laramide granitic stocks shows that all of the stocks are composite, epizonal granitic stocks, which are all elongate in a N45°E to N80°E direction. Sulfide bearing veins also trend N45°E to N80°E. The configuration of the stocks defines the structural framework into which they were intruded. The consistent elongation of the granitic stocks shows that the stocks were intruded into a series of parallel, regional faults that trend approximately N60°E to N80°E. Isotopic dating of the stocks shows that they become progressively younger from west to east. Typical isotopic ages are 71 m.y. on the west portion of the zone, and 61 m.y. on the east portion. The porphyry copper deposits also show a trend of decreasing age from west to east. The granitic Laramide stocks are localized where the N45°E to N80°E regional faults intersect the Precambrian granite-Pinal Schist contact. In some cases the regional faults are parallel to the Precambrian granite-Pinal Schist contact, in which case the Laramide stocks are parallel to the contact. The Laramide quartz diorite stocks only occur along the "San Pedro hinge line" and farther to the east. Although the individual quartz diorite stocks are aligned in an east-northeast direction, the overall geographical trend of the quartz diorite is north-northwest. The quartz diorite stocks may also become progressively younger proceeding to the east. The defining of the regional faults or lineaments, based upon the orientation of the Laramide granitic stocks, permits a rather precise projection of these lineaments into areas of complete post-mineral rocks. This allows a large area of post-mineral rocks to be reduced to a rather small area, where exploration for porphyry copper deposits can be intensified.
    • Some Palynological Applications of Multivariate Statistics

      Adam, David Peter (The University of Arizona., 1970)
      Palynology involves the study of past climatic and environmental changes through changes in the relative frequencies of different pollen types through time. Several multivariate statistical methods are suggested which can help in the description of patterns within pollen data. These techniques are based on comparisons between samples. Samples were compared using the product-moment correlation coefficient computed from data which had been subjected to a centering transformation. The methods are described using a geometric model. If there are m samples and n pollen types, then the data can be regarded as a set of m points in an n-dimensional space. Cluster analysis produces a dendrograph or clustering tree in which samples are grouped with other samples on the basis of their similarity to each other. Principal component analysis produces a set of variates which are linear combinations of the pollen samples, are uncorrelated with each other, and do the best job of describing the data using a minimum number of dimensions. This method is useful in reducing the dimensionality of data sets. Varimax rotation acts on a subset of the principal components to make them easier to interpret. Discriminant analysis is used to find the best way to tell groups of samples apart, where the groups are known a priori. Once a means of discrimination among groups has been established using samples whose groups are known, unknown samples may be classified into the original groups. Canonical analysis produces a way to display the maximum separation between groups in a graphic manner. Examples of applications of these methods in palynology are shown using data from Osgood Swamp, California, and from southern Arizona. These methods offer the advantages of reproducibility of results and speed in pattern description. Once the patterns in the data have been described, however, their interpretation must be done by the palynologist.
    • A Stratigraphic Analysis of Rico Strata in the Four Corners Region

      Bailey, James S.; Bailey, James S. (The University of Arizona., 1955)
      Rico strata are recognised throughout the Four Corners region of southwestern Colorado, southeastern Utah, northeastern Arizona, and northwestern New Mexico. The term Rico has been applied to a group of strata which exhibit a lateral and vertical transition between two contrasting environments, the marine Hermosa and the non-marine Cutler. Two faunal provinces reflect these widely diverse conditions of sedimentation. However, few fossils of diagnostic value have been discovered despite the abundance of fossiliferous strata within the Rico. Rico strata are believed to range between Desmoinesian and Virgilian in age. Lithofacies data on the Rico were assembled from literature, outcrop sections, and various well logs. These data were then compiled on an isopach-lithofacies map. The isopach-lithofacies map shows the thickness trends and the lithologic variations of Rico strata throughout the region of study. The tectonic framework of the region is reconstructed from the isopach-lithofacies map and mechanical analyses of the elastic strata. Clastic material in the Rico increases in average grain size from west to east toward the Uncomphagre Uplift suggest that this area was actively positive during Rico time. The vertical variation of normal marine limestone and clastic red beds in the Rico reflect an alternately transgressing and regressing sea over much of the Four Corners region. This intricate intertonguing of normal marine limestone and clastic red beds probably resulted from deposition in a shallow basin on an unstable shelf. The occurrence of oil, gas, and cement quality limestone in the Rico is examined from an economic aspect. A. brief review of the general geology and geologic history of tile region is also included.
    • Structural geology along the southeastern margin of the Tucson basin, Pima County, Arizona

      Arnold, Leavitt Clark, 1940-; Mayo, Evans B.; Bryant, Donald L.; Lacy, William C.; Anthony, John W.; Harshbarger, John W.; Titley, Spencer R.; Arnold, Leavitt Clark (The University of Arizona., 1971)
      The Cienega Gap area, located about 27 miles southeast of Tucson, Arizona, has long been noted for its structural complexity. Discordances between sedimentary rocks of Paleozoic, Mesozoic, and Cenozoic age and between these rocks and their granitic basement have led previous workers to propose large -scale northward thrusting in an effort to explain the complex structures observed. An alternative hypothesis invoking southward gliding has been considered by several authors but has been assigned a subordinate role in explaining the deformation. The present study was undertaken in an effort to evaluate the relative suitability of dominantly northward versus dominantly southward movement. In the course of this study nine separate localities were examined and mapped in detail in an effort to evaluate movement direction. Evidence of displacement on low -angle faults or glide surfaces was found in each of the areas examined, and definite evidence of movement direction was recognized in five of these. Large-scale recumbent folding, previously unrecognized in the Colossal Cave and Agua Verde Wash areas, was found to be closely related to local uplift. The asymmetry of the folds, plus a very few observed offsets marginal to the uplifts, were the only criteria found for determining the direction of movement. Evidence of northward, southward, and nearly westward movement was found in the course of the study. Areas in the northern Empire Mountains south of Cienega Gap gave evidence of west – northwestward and northward movement. Areas in the southern Rincon Mountains north of Cienega Gap were found to have undergone dominantly southward movement. Involvement of the Pantano Formation in several of the localities suggests that deformation occurred at least as late as early Oligocene time and probably after middle Miocene time. Cienega Gap was therefore the focus of movement for material which was moving laterally away from areas undergoing uplift in Tertiary time.
    • 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.