Call number: LD2668 .T4 1963 R44 / Master of Science

No description available.

No description available.

The Jhus Canyon area, located on the northeastern flank of the Chiricahua Mountains, Cochise County, Arizona, contains rock units from Precambrian to Mid-Tertiary in age. Precambrian granite, Paleozoic and Early Cretaceous sedimentary rocks, and Late Cretaceous(?) andesitic lava flows have been intruded by a complex Mid-Tertiary stock. The youngest rocks present are Mid-to-Late Tertiary rhyolite dikes. The effects of hydrothermal alteration are conspicuous both within and adjacent to the stock. The igneous rocks of the stock display propylitic, argillic, and phyllic alteration. Sedimentary hosts were altered to skarn, hornfels, and marble. Silicification is prominent in both the igneous and sedimentary rock types. Pyrite is the most abundant sulfide mineral in the area, but minor amounts of chalcopyrite and molybdenite are also present. The existing level of erosion is believed to expose the most intense and extensive alteration and mineralization that developed. No ore deposit is thought to exist here, but molybdenum values from rock chip samples suggest that the southwestern lobe of the stock is worthy of closer examination, especially for skarn occurrences. Mineralization in the nearby Hilltop Mine area is not related to the Jhus Canyon Stock, and its ore potential must be evaluated independently.

No description available.

No description available.

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

The Late Mesozoic Bisbee basin of southeastern Arizona was an intracratonic back-arc rift basin. Extension was coupled with seafloor spreading in the Gulf of Mexico and back-arc extension behind a magmatic arc along the convergent Pacific continental margin. Tectonostratigraphic evolution of the basin occurred in three phases. Initial mid-Jurassic rifting of the basin, marked by eruption of the Canelo Hills Volcanics, may have been complicated by sinistral strike-slip motion along the Mojave-Sonora megashear. During continued rifting, from latest Jurassic to Early Cretaceous time, the Glance Conglomerate was deposited by alluvial fans and braided streams in grabens, half-grabens, and caldera-related depressions; locally interbedded volcanic rocks represent waning rift-related back-arc magmatism. The upper Bisbee Group was deposited during Early to earliest Late Cretaceous passive thermotectonic subsidence. The Bisbee Group and correlative strata occur in most mountain ranges in southeastern Arizona, and are subdivided into southeastern, northwestern, northern, and western facies. Southeastern facies were deposited in alluvial fan, meandering fluvial, estuarine, marginal marine and subtidal shelf environments as a transgressive-regressive sequence including a marine interval that was continuous with Gulf Coast assemblages during Aptian-Albian marine transgression. Northern facies were deposited in alluvial fan and braided stream environments along the northern rift shoulder of the basin. Southeastern and northern facies sandstones are dominantly quartzose, and were derived mainly from cratonic sources to the north. Subordinate volcaniclastic sandstones in the southeastern facies become more abundant to the west, proximal to eroding Jurassic and Cretaceous volcanic arcs. Basal northwestern facies arkosic strata deposited in alluvial fan, braided stream and lacustrine environments were derived from local basement uplifts, and were ponded in a northwestern depocenter by rift-related topography. A thin estuarine interval within overlying dominantly fluvial facies indicates integration of regional drainage networks by the time of maximum transgression. Transition upward to quartzose sandstone compositions reflects wearing down of local basement uplifts and increasing abundance of craton-derived sediment in the northwestern part of the basin. Western facies alluvial fan, braided stream and lacustrine intramontane deposits are composed of locally-derived arkose and lithic arkose.

The primary factors that influence stratigraphy are tectonic subsidence, eustasy, and sediment supply. Change in any of these factors potentially produces a similar response in the form of a change in accommodation space. Accordingly, distinguishing the origin of a stratigraphic response is difficult, but theoretically possible by analysis of temporal and spatial extents of the accommodation signal. Correlation is critical for distinguishing eustasy from tectonism. Upper Pennsylvanian strata of the Pedregosa and Orogrande basins (southern Ancestral Rocky Mountains) were deposited during a time of continental collision and extensive continental glaciation, and contain a composite record of changing tectonism, eustasy, climate, and sediment supply. High-frequency stratigraphic cyclicity expressed as repetitive stacks of lithofacies at the scale of 10¹ m pervades all sections and displays features that collectively imply a primary glacioeustatic origin, notably: (1) abrupt juxtaposition of dissimilar lithofacies, signaling a rapid rate of baselevel change, (2) apparent intrabasinal, interbasinal and, provisionally, interregional correlation of high-frequency cycles across and between contrasting tectonic environments, and (3) cycle frequencies that approach the 413 ka periodicity of orbital eccentricity, the probable forcing mechanism for Pennsylvanian glaciations. Glacial-interglacial climate change expressed as precipitation and circulation fluctuations in the equatorial Pedregosa and Orogrande basins accompanied Pennsylvanian glacioeustasy. Intensified aridity and wind strength during peak glacials led to decreased fluvio-deltaic sedimentation and increased eolian activity where siliciclastics were available. Conversely, increased precipitation during interglacials reactivated and/or intensified fluvio-deltaic sediment yield. Eustasy dictated fluvial aggradation versus degradation and coastal sediment trapping versus bypassing. Coupled glacioeustatic-glacioclimatic change was sufficiently severe to reconfigure environments between climatic extremes, which implies that Pennsylvanian stratigraphic cycles should be viewed in at least partially non-Waltherian terms. Each cycle potentially recorded contrasting facies mosaics that were to some degree temporally exclusive. Multiple-cycle trends in facies and/or thickness also occur to define low-frequency stratigraphic patterns at the scale of 10² m. Qualitative analysis of these trends implicates distinct eustatic and tectonic processes as contributing influences. The eustatic component may derive from low-frequency glacioeustasy as well as tectonoeustasy related to evolving continental paleogeography. The tectonic component probably reflects late Paleozoic Marathon-Ouachita collisional orogenesis.

Sedimentology, stratigraphy, and stable-carbon isotopy were used to reconstruct geologic and climatic events on the Texas southern High Plains from ca. 13,000 yr B.P. to the present. The alluvial sediments in Yellowhouse and Blackwater Draws were used to construct the geologic history. The oldest valley alluvium comprises the > 13,000-yr-B.P. fluvial sediments that were incised and buried by fluvial and lacustrine sediments dating ca. 13,000 to 4900 yr B.P. Lacustrine waters changed from oligotrophic to eutrophic and finally calcalitrophic. Regional valley erosion at 4900 yr B.P. developed a widespread disconformity within the Yellowhouse Draw formation, which separates lower fluvial and lacustrine sediments (ca. 13,000-4900 yr B.P.) from the overlying sediments dating 4900 yr B.P. to present. After 4900 yr B.P., intermittent streams and eolian processes deposited several meters of sand the length of each valley. Cienegas returned to downstream reaches of both draws after 1500-2000 yr B.P. Methods were developed to extract purified collagen residues and hydroxyproline from heavily contaminated fossil bones. Reliable δ¹³C measurements on collgen require isolation of single amino acids, whereas less specific purifications may yield accurate bone collagen ¹⁴C dates. Collagenous residues were extracted from 13,000-200-yr-B.P. fossil bison bones from the Lubbock Lack Site at Lubbock, Texas, and δ¹³C values were determined. Collagen δ¹³C values changed from -8 per mil at 200 yr B.P. to -10 per mil at 4900 yr B.P. and to -17 per mil at 12,500 yr B.P. The δ¹³C changes imply that the Lubbock area grasslands contained 30 to 40 percent C₄ grass biomass at 12,500 yr B.P. in contrast to the 95 percent C₄ grass biomass in today's grasslands. The stratigraphic and isotopic results gave similar paleoecological histories for the Texas southern High Plains. At 12,500 yr B.P. permanent streams existed and grasslands may have resembled those in the northern central Great Plains today. The climate warmed gradually, and the water table dropped until 5000 yr B.P. when a major hydrologic shift occurred. After 4900 yr B.P., modern climatic depositional and vegetation communities were developed. Geomorphic thresholds apparently controlled the regional disconformities, depositional events, and pedogenetic episodes. Climatic change was the ultimate cause of stratigraphic changes, but individual geologic events were not coeval with any similar climatic shift.