• Stratigraphy and Depositional History of the Pantano Formation (Oligocene-Early Miocene), Pima County, Arizona

      Schreiber, J. F. Jr.; Balcer, Richard Allen; Schreiber, J. F. Jr.; Dickinson, W. R.; Balcer, Richard Allen (The University of Arizona., 1984)
      The Pantano Formation comprises 1,250 m of alluvial, fluvial, lacustrine, and volcanic rocks deposited in a basin formed in response to regional extension during mid- Tertiary time in southeastern Arizona. During deposition, the locations and composition of sediment source areas varied as contemporaneous uplift occurred adjacent to the basin. The lower half of the formation was deposited as alluvial fans that prograded northward, westward, and southward; the upper half was deposited during southwestward retreat of alluvial fan deposition and the onset of lacustrine deposition. An andesite flow separates the two depositional regimes. Radiometric dates of 24.4 ± 2.6 m.y. B.P. for the andesite and 36.7 ± 1.1 m.y. B.P. for a rhyolitic tuff disconformably underlying the formation indicate that deposition occurred during Oligocene to early Miocene time. Proper stratigraphic sequencing and description, paleocurrent analysis, and gravel provenance study aided in understanding the depositional history of the formation.
    • Stratigraphy and Sedimentology of the Bisbee Group in the Whetstone Mountains, Pima and Cochise Counties, Southeastern Arizona

      Dickinson, W. R.; Archibald, Lawrence Eben; Schreiber, Joseph F., Jr.; Flessa, Karl; Archibald, Lawrence Eben (The University of Arizona., 1982)
      The Aptian-Santonian(?) Bisbee Group in the Whetstone Mountains comprises 2375 m of clastic sedimentary rocks and limestones. The basal Glance Conglomerate unconformably overlies the Pennsylvanian-Permian Naco Group. It consists of limestone conglomerates which were deposited in proximal alluvial fan environments. The superadjacent Willow Canyon Formation contains finer grained rocks which were deposited in the distal portions of alluvial fans. The lacustrine limestones in the Apache Canyon Formation interfinger with and overlie these alluvial fan facies. The overlying Shellenberger Canyon Formation is composed mostly of terrigenous rocks derived from westerly terranes. This formation contains thick sequences of fluvio-deltaic facies as well as a thin interval of estuarine deposits which mark a northwestern extension of the marine transgression in the Bisbee -Chihuahua Embayment. The youngest formation (Upper Cretaceous?) in the Bisbee Group, the Turney Ranch Formation, consists of interbedded sandstones and marls which were deposited by fluvial and marine(?) processes.
    • 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.
    • Structural Geologic Controls at the San Luis Mines, Tayoltita, Durango, Mexico

      Ballard, Stanton Neal; Davis, George H.; Coney, Peter J.; Guilbert, John M.; Ballard, Stanton Neal (The University of Arizona., 1980)
      In the San Dimas district, on the western flank of the Sierra Madre Occidental, near the small town of Tayoltita, Durango, gold and silver epithermal ore deposits are mined from the complex Arana fault system. The structural relationships of the Tayoltita system are well-mapped, but their kinematic relationship to ore deposition is unclear. In plan view and in cross-section, the Arana system has a horsetail or wedge-shaped geometry. Subsurface mapping of slickenside striae as movement indicators suggest that the N13°W-striking Arana fault, forming the eastern boundary of the system, is a normal slip fault with at least 250 m of throw. Subsidiary system faults display normal separation with varying degrees of dextral horizontal separation (which is a function of fault orientation). Experimental modeling of the Arana system indicated that the system formed under simple shear as the σ₂ and σ₃ stress axes rotated in a subhorizontal plane about σ₁. Rotational strain caused the developing fault strands to rotate and to be captured by the Arana fault, forming the typical wedge-shaped geometry. Later, a more complex rotation of the three major stress axes enabled hydrothermal fluids to progressively mineralize faults, which had more northerly strikes, by a process similar to progressive strain. This is documented by mineral assemblages that record the instants of fault opening and by the lack of mineralization along the high-angle, northwest- striking faults.
    • Structural Investigations of the Italian Trap Allochthon, Redington Pass, Pima County, Arizona

      Benson, Gregory Scott; Davis, George H.; Coney, Peter; Schreiber, Joseph F. Jr.; Benson, Gregory Scott (The University of Arizona., 1981)
      Italian Trap Allochthon is a rare upper-plate exposure of Paleozoic metasedimentary and Precambrian to Tertiary crystalline tectonites in the Santa Catalina-Rincon metamorphic core complex. Elsewhere in the complex, metasedimentary tectonite is usually restricted to an autochthononous position. The internal structures of the allochthon consist of numerous low-angle faults, tear faults, and overturned asymmetric and upright folds. Close association of the low-angle faults and asymmetric folds, and vergence of the folds, indicates that these folds were formed during westward transport along the low-angle faults. The structures of the allochthon are truncated and rotated to the northeast by a listric (?) normal fault. The probable shape of the fault surface, together with the northeastward rotation of the internal structures, suggests translation of the allochthon from the northeast to the southwest. The fact that metasedimentary tectonites are found in upper- plate position indicates that the listric (?) normal faulting post-dates the metamorphism of the Paleozoic and Mesozoic strata. Metamorphism in turn was part of the development of the Santa Catalina-Rincon metamorphic core complex. It is inferred that the Italian Trap Allochthon was emplaced in the final stages of profound regional extension which prevailed during the mid-Tertiary in southern Arizona.
    • Structure of Golden Gate Mountain, Pima County, Arizona

      Assadi, Seid Mohamad; Mayo, Evans B.; Harshbarger, John M.; Pye, Willard D.; Assadi, Seid Mohamad (The University of Arizona., 1964)
      Golden Gate Mountain appears as a spur projecting westward from the Tucson Mountain range. It is made up of the capping Cat Mountain Rhyolite, the slope - forming Amole Formation, and a variety of intrusions of differing compositions. The emplacement of the andesitic portion of the intrusions occurred during, and probably lasted long after, the deposition of Amole Formation. The hot magma fluidized the wet sediments. Part of the fluidized materials formed pipes and dikes of tuffisites and part was brought up into the basin and contributed to the sedimentation of Amole Formation. During upper Amole time the intrusion of andesite increased in intensity. Part of the basin rapidly subsided and thick deltaic sediments and graywacke were formed. The development of a hinge line accompanied this subsidence. The hinge line controlled the occurrence of fluidization which undercut the Amole beds. The beds slumped into the fluidized parts. The process culminated in forming a large orifice through which the Cat Mountain Rhyolite welled up. The orifice is reflected in the sedimentary beds by the development of a funnel- shaped structure in the central part of which the capping of Cat Mountain Rhyolite is located. The bordering brecciated Amole beds represent the associated slump effects.
    • The Structure of the Pantano Beds in the Northern Tucson Basin

      Harschbarger, J. W.; Abuajamieh, M. M.; Sumner, John S.; Abuajamieh, M. M. (The University of Arizona., 1966)
      A gravimetric survey has proved its usefulness in the Tucson Basin in locating important structural features, their geometric shapes and extensions. Interpretation was made possible through the correlation of available geologic and hydrologic data from water well logs and water table contour maps. Geophysical logs from a recently drilled test well in North Tucson have been interpreted and have confirmed the existence of another promising aquifer, namely, the deformed gravel which underlies the upper basin-fill aquifer. In most cases, it is apparently separated by a thin aquiclude of clay which results in artesian condition in the lower aquifer. Gravity interpretation discloses the presence of buried channels that may be of importance to groundwater exploration. The buried high basement ridges or faulted blocks as interpreted from gravity data add more information to the understanding of the hydrologic behavior of the basin. Deep drilling of test wells, such as the one drilled recently on Orange Grove Road, will be a useful check to the structures interpreted from gravity data. Geophysical logs of bore holes are of utmost importance in correlation of lithologic units and structures in addition to the hydrologic interpretation that is possible from these logs. The Pantano beds as described here are not promising for new groundwater sources that may be used for domestic needs due to the very low permeability and the expected poor quality of the water. Still more information is necessary to determine clear answers to many problems related to the geology and hydrology of this basin.
    • Supergene Mineralogy and Processes in the San Xavier Mine Area-Pima County, Arizona

      Arnold, L. Clark; Titley, Spencer R.; Anthony, John W.; Mitcham, Thomas W.; Arnold, L. Clark (The University of Arizona., 1964)
      This is a study of the supergene mineralogy of the San Xavier West mine located in the Pima mining district, Pima County, Arizona. The number and composition of secondary species collected are found to be closely related to the relative amounts of the various primary minerals and to the manner in which they were emplaced in the host rock. Supergene mineral species were selected that appeared to be in equilibrium with their environment, and certain assumptions are made concerning the stability fields of these minerals. The equilibrium conditions in most cases can be narrowed and often closely defined by combining the stability fields of several secondary minerals. On this basis, two acid environments and one alkaline environment are found to exist and are separable on the basis of mineralogy. The fields of chalcanthite and melanterite define a highly acid environment while those of goslarite and malachite define an environment of lower acidity. The association of calcite, rosasite, hemimorphite, and malachite indicate an alkaline environment. The acidity of the environments is principally determined by the amount of pyrite present, and pH may be lower than 3 if pyrite is abundant and reactive carbonate material lacking. Also, knowledge of stability relations allowed the history of enrichment and subsequent oxidation to be followed in a case where a transitional species had been removed from reaction by inclusion with gypsum.
    • The Tertiary Igneous Terrain in the Vicinity of the King Tonopah Mine, Tonopah, Nevada: An Exploration Case Study

      Barker, Walter Blaine; Eastoe, C. J.; Ruiz, Joaquin; Titley, Spencer R.; Barker, Walter Blaine (The University of Arizona., 1986)
      Uneconomic epithermal precious metal mineralization and associated alteration occur in the Tonopah Property, and are similar in style, although much less intense, to the deposits of the Tonopah camp two miles south. Mineralization is localized within a set of northwest-trending faults within the Tonopah, Mizpah, and King Tonopah Member of the Fraction-Tuff formations, and is associated with widespread propylitic and sparse fracture-localized potassic and argillic alteration. A younger set of Mn-calcite veins, anomalous in manganese, mercury, arsenic, and antimony, occurs in northeast-trending faults cutting older formations as well as the younger Tonopah Summit Member of the Fraction Tuff. This mineralization is possibly associated with silicification, zeolitization, and clay-alteration of the Fraction Tuff. The Tonopah Summit Member of the Fraction Tuff is reinterpreted as younger than the King Tonopah Member. Mega-breccia and basin morphology in the northeast may indicate an eruptive vent in this area.
    • 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.
    • Upper Cretaceous Palynomorphs from Coal Canyon, Coconino County, Arizona

      Agasie, John M.; Kremp, Gerhard O. W.; Cranwell, Lucy M.; Agasie, John M. (The University of Arizona., 1967)
      The coal-bearing Dakota Sandstone at Coal Canyon, Arizona, which is located in the western portion of the Black Mesa basin, has yielded abundant, diverse, and generally well-preserved spores, pollen, and microplankton. The formation is characterized by high frequencies of fern spores, especially striate spores belonging to the Schizaeaceae, and angiospermous pollen consisting primarily of simple tricolpate and tricolporate grains. Gymnospermous pollen is comparatively uncommon. The microflora assemblage contains many exclusively Cretaceous species previously reported from Australia, western Europe, Siberia, and other localities of North America. A microflora which compares closely with the Dakota assemblage occurs in the Woodbine strata of Oklahoma. On the basis of palynologic evidence, the age of the Dakota Sandstone at Coal Canyon, is interpreted as lowermost Upper Cretaceous (Cenomanian).
    • Variable Denudation in the Evolution of the Bolivian Andes: Controls and Uplift-Climate-Erosion Feedbacks

      Pelletier, Jon D.; Barnes, Jason B.; Chase, Clement G.; DeCelles, Peter G.; Barnes, Jason B. (The University of Arizona., 2002)
      Controls on denudation in the eastern Bolivian Andes are evaluated by synthesis of new and existing denudation estimates from basin-morphometry, stream - powered fluvial incision, landslide mapping, sediment flux, erosion surfaces, thermochronology, foreland basin sediment volumes, and structural restorations. Centered at 17.5 °S, the northeastern Bolivian Andes exhibit high relief, a wet climate, and a narrow fold- thrust belt. In contrast, the southeastern Bolivian Andes have low relief, a semi-arid climate, and a wide fold-thrust belt. Basin -morphometry indicates a northward increase in relief and relative denudation. Stream-power along river profiles shows greater average incision rates in the north by a factor of 2 to 4. In the south, profile knickpoints with high incision rates are controlled by fold-thrust belt structures such as the surface expressions of basement megathrusts, faults, folds, and lithologic boundaries. Landslide and sediment-flux data are controlled by climate, elevation, basin morphology, and size and show a similar trend; short -term denudation-rate averages are greater in the north (1- 9 mm/yr) than the south (0.3-0.4 mm/yr). Long-term denudation-rate estimates including fission track, basin fill, erosion surfaces, and structural restorations also exhibit greater values in the north (0.2-0.8 mm/yr) compared to the south (0.04-0.3 mm/yr). Controls on long-term denudation rates include relief, orographic and global atmospheric circulation patterns of precipitation, climate change, glaciation, and fold-thrust belt geometry and kinematics. The denudation synthesis supports two conclusions: 1) denudation rates have increased towards the present 2) an along-strike disparity in denudation (greater in the north) has existed since at least the Miocene and has increased towards the present. Denudation rates and controls suggest that Bolivian mountain morphology is controlled by both its orientation at mid-latitude, and the feedbacks between uplift, kinematics, orographic effects on precipitation, glaciation, and the increased erosion that accompanies orogenesis.