• 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.
    • 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.
    • An Investigation of the Manner and Time of Formation of Malachite

      Titley, Spencer R.; Beane, Richard Edward, 1942-; Titley, Spencer R.; Damon, Paul E.; Guilbert, John M.; Beane, Richard Edward (The University of Arizona., 1968)
      A group of minerals typical of the oxidation zone of copper deposits was studied using chemical thermodynamics, mineral stability relationships, and petrography. It has been concluded that many processes, such as alteration, can be explained using thermodynamics and are compatible with natural relationships. A mineral assemblage consisting of basic carbonates of copper and zinc was investigated with carbon isotopes and mineral stability relationships. The results obtained are consistent with processes resulting from oxidation and leaching of a sulfide deposit followed by redeposition of copper and zinc in the zone of oxidation. Four processes have been suggested by which copper could be introduced into a near-surface environment from depth. Reactions which would occur under these conditions may result in formation of mesogene or hypogene malachite and chrysocolla. A vein deposit containing minerals typical of the zone of oxidation was investigated and it has been concluded that the minerals may have formed from a hydro-thermal solution related to near-surface volcanism.
    • Geology of the Gore Canyon-Kremmling Area, Grand County, Colorado

      Barclay, C. S. Venable; Mayo, Evans B.; Barclay, C. S. Venable (The University of Arizona., 1968)
      The Gore Canyon-Kremmling area is in the southwestern portion of the Kremmling 15-minute quadrangle, Colorado. Precambrian rocks are biotite gneiss, the Boulder Creek Granodiorite, granophyre dikes, and quartz veins. The Boulder Creek Granodiorite intrudes the biotite gneiss, and both of these units are cut by north-northwest-trending, granophyre dikes and quartz veins. Biotite gneiss contains structure elements of a northwest and a northeast fold system. Lineations and foliations in the Boulder Creek Granodiorite are generally concordant to the northeast fold system of the gneiss. Late Paleozoic to Mesozoic and Mesozoic sedimentary formations, in ascending order and with their approximate thicknesses, are the State Bridge Formation, 15 feet; the Chinle and Chugwater Formations undivided, 0-95 feet; the Sundance Formations 0?-100 feet; the Morrison Formation, 250 feet; the Dakota Sandstone, 225 feet; the Benton Shale, 340 feet; the Niobrara Formation, 600 feet; and the Pierre Shale. Quaternary deposits are terrace, landslide, and modern flood-plain deposits. Laramide rock deformation is related to the Park Reuse uplift and includes faulting and, in the sediments, some folding. Some of the faults, including the regional Gore fault, are Precambrian structures reactivated in Laramide time.
    • 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.
    • 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).
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • A geological Reconnaissance of the San Pedro del Gallo Area, Durango, Mexico

      Alor, Jerjes Pantoja; Titley, Spencer R.; Alor, Jerjes Pantoja (The University of Arizona., 1963)
      The San Pedro del Gallo area 1.8 in the north-central part of Mexico, between 25°30' and 26°00' N latitude, and 104°00' and 104°20' W longitude. It covers approximately 1,900 square kilometers at the western edge of the Sierra Madre Oriental. The oldest rocks exposed in the area belong to the Villa Juarez Formation of possible Late Triassic age. These rocks, of continental origin, comprise siltstone, sandstone, conglomerate, tuff, and intercalated lavas of characteristic red color. Jurassic and Cretaceous rocks form a section with a maximum thickness of about 3,580 m. The sediments were deposited in the Mexican Geosyncline, west of the Coahuila Peninsula of pre-Aptian age. The Villa Juarez Formation is overlain with angular unconformity by orthoquartzite, quartzose sandstone, and limestone lenses of the La Gloria Formation of Oxfordian age. The La Casita Formation, which is stratigraphically above the La Gloria Formation, probably ranges in age from late Oxfordian to early Neocomian. It consists of thin-bedded limestone, black shale, and varicolored sandstone, with intercalations of coal seams and abundant ammonites. The Lower Cretaceous rocks of the area comprise the Coahuila Series, La Pena Formation, Aurora Limestone, and Cuesta del Cura Formation. Neocomian and upper Aptian rocks are represented by thin-bedded limestone, marl, and shale of the Taraises, Las Vigas, Parritas, and La Pena Formations. This sequence of rocks is overlain with apparent conformity by the medium- to thick-bedded bank-type Aurora Limestone of middle to late Albian age. A notable change of facies occurs laterally in the upper Albian and lower Cenomanian rocks, the lithology of the Aurora Limestone grading westward into the thin-bedded limestone with wavy bedding planes and black chert intercalations that characterize the Cuesta del Cura Formation. An erosional unconformity developed on the surface of the Aurora Limestone and Cuesta del Cura Formation is covered by the Indidura and Caracol Formations of Turonian to Coniacian age. These consist or thin-bedded, platy limestone, shale, and marl beds, which grade upward into a thick sequence of poorly fossiliferous calcareous sandstone, siltstone, and shale. A period of intense folding and erosion preceded the deposit of the non-marine Ahuichila Formation, of probable late Eocene and early Oligocene age. This formation was deposited with marked angular unconformity on all the older rocks, including the Villa Juarez Formation. Both, porphyritic and equigranular igneous rocks in the form of dikes, sills, plugs, and stocks intrude the bedded rocks of the area. They range in composition from quartz rhyolite porphyry to andesite and from granadiorite to monzonite. The rocks around the intrusive bodies have been metamorphosed irregularly as far as 100 m from the igneous contacts. Irregular tactite aureoles occur around intrusive bodies in the Descubridora district, west of Cerritos de Los Victorinos, and in the Sierra del Mimbre. Marble and recrystallized limestone is found west of Descubridora and in the Bajio del Bailon, and hornfels has formed in Cerrito de La Cruz and Cerrito de Las Liebres near San Pedro del Gallo, as well as in the southern part of the Sierra del Mimbre. Folowing emplacement of the intrusive bodies mineralizing solutions reacting with sedimentary rocks gave origin to the different mineralized zones in the region. The beginning of the Laramide Orogeny in the San Pedro del Gallo region is marked by Late Cretaceous uplift, which probably continued until middle or late Eocene time. Compressive forces acting in an east-west to northeast-southwest direction folded the Mesozoic strata into a series of narrow asymmetrical anticlines and synclines overturned to the east, with axial, planes almost parallel to the borders of the Coahuila Peninsula. Thrusting and faulting were important in the vicinity of San Pedro del Gallo. There is no conclusive evidence of large-scale post-Triassic and pre-Laramide deformation in the area. Extrusion of lavas ranging in composition from basalt to rhyolite, accompanied by extensive block faulting, occurred during Miocene and Pliocene time. Late Tertiary uplift began during the Pliocene. The streams were rejuvenated and there was increased erosion, which caused, together with a change of climate, the overloading of some streams and local blocking of drainage by alluvial fans in the valleys, giving rise to the Santa Ines Formation. Erosion, more than deposition is the dominant event at present. Contact metasomatic silver, lead, and copper deposits in the Aurora Limestone have been mined in the Descubridora, Parranderas , and Sierra del Mimbre districts. Fluorite and barite have been extracted from veins in the La Gloria Formation and the Aurora Limestone. Thin beds and seams of coal in the La Casita Formation were mined within the town limits of San Pedro del Gallo. No important mining activity exists at present in the area studied. The area has never been tested for oil.
    • Geology of the Owl Head Mining District, Pinal County, Arizona

      Barter, Charles F.; Mitcham, Thomas W.; Barter, Charles F. (The University of Arizona., 1962)
      The Owl Head mining District is located in south-central Pinal County, Arizona, within the Basin and Range province. Land forms, particularity pediments, characteristic of this province are abundant in this area. Precambrian rocks of the Owl Head mining district include the Pinal schist; gneiss; intrusions of granite, quartz monzonite and quartz diorite; and small amounts of Dripping Spring quartzite and metamorphosed Mescal limestone. These have been intruded by dikes and plugs of diorite and andesite, and are unconformably overlain by volcanic rocks and continental sedimentary rocks of Tertiary and Quaternary age. No rocks of the Paleozoic and Mesozoic eras have been recognized. The structural trends of the Owl Head mining district probably reflect four major lineament directions. The dominant structural trends found in the area are north and northwest. Subordinate to these directions are northeast and easterly trends. The strike of the northerly trend varies from due north to N30°E and was probably developed during the Mazatzal Revolution. The northwest trend has probably been superposed over the northerly trend at some later date. Copper mineralization is abundant in the area and prospecting by both individuals and mining companies has been extensive. To date no ore body of any magnitude has been found, but evidence suggests that an economic copper deposit may exist within the area. The copper mineralization visible at the surface consists mainly of the secondary copper minerals chrysocolla, malachite, azurite, and chalcocite with chrysocolla being by far the most abundant. Copper minerals are found to occur in all rocks older than middle Tertiary age. Placer magnetite deposits are found in the alluvial material of this area, and one such deposit is now being mined.
    • The Geology of the Atlas Mine Area, Pima County, Arizona

      Agenbroad, Larry D.; Anthony, John W.; Lacy, W. C.; DuBois, R. L.; Agenbroad, Larry D. (The University of Arizona., 1962)
      The Atlas Mine is located on the northwest flank of the Silver Bell mountains; Silver Bell mining district, Pima County, Arizona. The deposit is high grade (?) sine-copper mineralization in an altered sedimentary sequence. Rocks in the area include Precambrian (?) alaskite; Permian (?) limestone, quartzite and siltstone; Tertiary (?) monzonite, quartz monzonite, quarts latite porphyry and dacite porphyry; and Quaternary alluvium. The limestone has been largely metamorphosed to a mass of tactite, siltstone has been locally metamorphosed to hornfels, and the quartzite has been silicified, locally shattered and altered. Mineralization is related to NE and E-W trending fault systems, and similarly trending intrusive dikes. Predominate ore minerals are sphalerite and chalcopyrite, associated with pyrite, specular hematite and “high temperature" silicates. Copper mineralization is related to the silicified sediments. Zinc mineralization is present in silicates but is more predominate in areas of recrystallized calcite and extensive garnetization, suggesting incomplete replacement of the original sediments by the silicates. Further exploration and development should be undertaken in areas of favorable structural control, and adjacent to favored intrusives.
    • 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.
    • The Geology and Geochemistry of Beryllium in Southern Arizona

      Balla, John Coleman, 1936-; Lacy, Willard C.; Erickson, Einar C.; Balla, John Coleman (The University of Arizona., 1962)
      Nine beryllium deposits were studied in order to determine the geological environment of beryllium mineralization in southern Arizona. Beryllium occurs in two pegmatite areas, two contact metamorphic deposits, two quartz-tungsten veins, two quartz-feldspar veins, and in one quartz monzonite stock. It is associated in almost all of these deposits with purple fluorite and tungsten. Beryllium mineralization is associated with granitic and quartz monzonite intrusions of Laramide age, and generally occurs at the intersection of northwest-trending lineaments and the Texas lineament.
    • 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.
    • 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.
    • The Geology and Mineralization of the Sedimentary Hills Area, Pima County, Arizona

      Bennett, Paul J.; Lacy, Willard C.; Bennett, Paul J. (The University of Arizona., 1957)
      Mildly metamorphosed Cretaceous siltstones, arkoses and limey shales and a small composite stock of granitic composition are the principal rocks exposed in the Sedimentary Hills area, which lies six miles west of Tucson, Arizona. About 2400 feet of sediments were measured and assigned to the Amole Arkose Formation. The beds dip to the south and strike northwesterly. The stock is composed of two granitic facies. The northern and earlier part of the stock is a quartz monzonite which is mildly altered. The southern part of the intrusive is a granite porphyry which is altered to a greater degree and exhibits significant disseminations of chalcopyrite and pyrite. A quartz-pegmatite plug, probably a late phase of the intrusions, intrudes the quartz monzonite. Structure in the area is dominated by a large thrust zone which strikes generally parallel to the bedding. Within the Sedimentary Hills area, normal faulting and drag folding are tributary to the thrusting. Minor copper oxide minerals are frequent along large and small faults, and in the granite porphyry stock. Wide brick-red and brown gossans occur along the major thrust plane.