Now showing items 13209-13228 of 19641

    • P-glycoprotein: Expression and function in normal circulating leukocytes

      Klimecki, Walter Thomas.; Dalton, William; Cress, Anne; Bowden, G. Tim; Dorr, Robert; Gandolfi, A. Jay (The University of Arizona., 1994)
      P-glycoprotein (P-gly) is a well characterized membrane protein, expressed in cancer cells, functioning as an efflux pump. This function confers drug-resistance. P-gly is also expressed in normal tissues such as the liver and kidney. In normal tissues P-gly has restricted expression. In the kidney P-gly is expressed in tubular brush border. This suggests a physiologic role for P-gly. A goal of this work was to determine whether P-gly, if present in leukocytes, followed the cell-type restriction seen in other P-gly positive normal tissues. Assays measuring P-gly included immunofluorescence, immunocytochemistry, and immunoblot analysis. Northern blot analysis and RT-PCR were used to measure mdr1 mRNA. P-gly function was assayed by measuring the verapamil-sensitive retention of rhodamine 123 (rh123). Immunofluorescent staining of leukocytes for lineage and P-gly revealed high levels of P-gly in CD56+ cells. CD8+ cells followed in staining, with CD4+ and CD19+ cells at intermediate levels, and CD14+ and CD15+ cells staining at background. RNA analysis by RT-PCR confirmed the immunofluorescence data, except for CD15+ cells, which demonstrated mdr1 mRNA similar to CD4+ cells. Function assays confirmed the immunofluorescence results, with efficient clearing of dye from CD56+ cells, followed by CD8+, CD4+, and CD19+ cells. CD14+ and CD15+ cells did not demonstrate P-gly function. Immunoblot analysis of membranes and immunocytochemical analysis of CD15+ cells demonstrated P-gly. The high level of functional P-gly observed in CD56+ cells prompted experiments to determine whether P-gly was involved in the CD56+ mediated cytolytic response. Using 4 inhibitors of P-gly mediated efflux, cyclosporine A, PSC 833, R-verapamil, and S-verapamil, NK cells were assayed for cytolytic function. Each compound demonstrated dose-response relationships in inhibiting NK-mediated cytolysis. Each compound also demonstrated a dose-response in inhibition of P-gly mediated efflux, although there was not an exact correlation between efflux inhibition and cytolysis inhibition. Nevertheless, the data in this study demonstrate a relatively high level of P-gly expression in CD56+ and CD8+ cells. In addition, the data support a role for P-gly in the cytolytic function of NK cells, although the point of P-gly involvement in the process of cytolysis remains to be defined.
    • The p53 homolog p63 modulates acute and chronic damage in irradiated salivary glands

      Limesand, Kirsten H; Mitchell, Geoffrey C; Limesand, Kirsten H; Burd, Randy; Gerner, Eugene; Briehl, Margaret; Martinez, Jesse (The University of Arizona., 2010)
      Head and neck cancer is diagnosed in more than 50,000 Americans each year, resulting in roughly 11,000 deaths. For this disease, a typical therapeutic regimen involves cisplatin, a radiosensitizer, given alongside targeted irradiation. While technological advances such as IMRT have been useful in sparing normal tissues from radiotherapy, the salivary glands occupy much of the head and neck and surround several lymph nodes, and thus, non-diseased salivary glands are often damaged. This causes reduced salivary output, damaged oral mucosa, dysphagia, malnutrition and tooth decay. Often, these side-effects are so severe that patients discontinue treatment, however, in many cases, salivary gland damage is permanent, and treatment options are palliative. Specifically, muscarinic-cholinergic agonists are used to enhance secretion from remaining salivary cells, although due to non-specific action, these drugs have a number of ill-effects. It is clear that therapies are needed to prevent radiation-induced salivary gland damage, as well as to restore glandular function in patients who are already suffering.Previous work from our group has shown that salivary gland dysfunction results from loss of acinar cells to radiation-induced apoptosis. Importantly, a single intravenous dose of IGF1 can prevent apoptosis and preserve salivary output when given immediately prior to irradiation. Because of its broad effects, however, IGF1 may never be a viable clinical option. Instead, our goal is to identify signaling events that mediate the radioprotective effects of IGF1 downstream of Akt. Because radiation-induced apoptosis in salivary glands is p53-dependent, we assessed the contributions of the p53 homologs p63 and p73 to the DNA damage response. Here, we show that IGF1 enhances cell cycle arrest following irradiation by reducing inhibitory binding of deltaNp63 to the p21 promoter. We hypothesize that IGF1-induced cell cycle arrest may allow time for DNA repair, thus preventing apoptosis and maintaining salivary function. In addition, we indicate chronic signaling events downstream of p63 that may contribute to permanent loss of salivary function by blocking differentiation of salivary progenitor cells. Together, these results indicate that p63 may be a valid therapeutic target for both prevention of damage and restoration of function in irradiated salivary glands.

      Kratochwill, Thomas; Brown, Douglas Kirby (The University of Arizona., 1980)
      An instructional package is presented for training pre-intern psychologists in behavioral interviewing techniques. A specific interview format, the Problem Identification Interview, was combined with microsetting technology to provide an efficient method of training consultation verbal skills. The instructional package was evaluated with a multiple baseline across subjects design. Results of the study indicated that verbal skills specific to the interviewing format were acquired when the instructional package was used. The acquired skills were maintained across several experimental sessions and at a two month follow-up. A social validation questionnaire revealed that subjects of the study found the training to be preferable to traditional methods and relevant to future applied practice. The implications of this study for the training of psychologists and other professionals providing problem solving services were discussed.
    • Packrats, plants, and the Pleistocene in the lower Grand Canyon

      Phillips, Arthur Morton, 1947- (The University of Arizona., 1977)
    • Pad-Wafer and Brush-Wafer Contact Characterization in Planarization and Post-Planarization Processes

      Philipossian, Ara; SUN, TING; Philipossian, Ara; Muscat, Anthony; Ogden, Kimberly; Lynch, David C. (The University of Arizona., 2009)
      This dissertation presents a series of studies relating to pad-wafer and brush-wafer contact characterization in planarization and post-planarization processes. These are also evaluated with the purposes of minimizing environmental impact and reducting cost of ownership.Firstly, a new method using spectral analysis based on real-time raw friction data is developed to quantify the total amount of mechanical interaction in the brush-fluid-wafer interface in terms of stick-slip phenomena in post-planarization scrubbing. This new method is remarkable from the standpoint of its potential to eliminate having to perform a multitude of experiments needed for constructing and interpreting Stribeck curves, and its application to processes where Stribeck curves fail to yield any useful data. Moreover, this method is applied to investigate the effect of brush roller design on scrubbing process and to analyze behaviors of eccentric brushes.In order to study pad-wafer contact in planarization processes, a mechanical characterization method (incremental loading test) is developed and applied to analyze different types of pads and pad surfaces subjected to various treatments. Along with optical interferometry and theoretical analysis, flow resistance due to pad land area topography can be estimated.The greatest contribution of this dissertation involves development of real pad-wafer contact area measurement technique using confocal microscopy. The real pad-wafer contact area is a difficult property to measure in planarization, yet it is a key feature to further understand the process. A custom-made sample holder with a sapphire window and a miniature load cell is used to collect confocal images at controlled values of down force.At last, the two newly developed techniques (incremental loading test and real pad-wafer contact area measurement using confocal microscopy) together with dual emission UV enhanced fluorescence imaging are utilized to investigate conditioning effects in planarization process.

      Porreca, Frank; Edelmayer, Rebecca M.; Vanderah, Todd W.; French, Edward D.; Ossipov, Michael H.; Sherman, Scott J. (The University of Arizona., 2009)
      Migraine patients often demonstrate cutaneous allodynia, defined as a hypersensitivity of the skin to touch or mechanical stimuli that is considered non-noxious under normal circumstances. The allodynia sometimes begins intracranially and spreads, via unknown mechanisms, to extracranial regions. The goal of the study was to develop and validate a model of cutaneous allodynia triggered by dural inflammation for pain associated with headaches, and to explore neuronal and glial mechanisms underlying generalized allodynia. Inflammatory mediators (IM) were applied to the dura of unanesthetized rats via previously implanted cannulas and sensory thresholds of the face and hindpaws were characterized. IM elicited robust and time-related facial and hindpaw allodynia which peaked after approximately three hours as well as FOS expression in the trigeminal nucleus caudalis (TNC), indicative of central sensitization. These effects were reminiscent of cutaneous allodynia seen in patients with migraine or other primary headache conditions, and were reversed by agents used clinically in the treatment of migraine including sumatriptan, naproxen, CGRP-antagonist, and morphine. Consistent with clinical observations, the allodynia was unaffected by an NK-1 antagonist. Having established facial and hindpaw allodynia as a useful animal surrogate of headache-associated allodynia, we next showed that blocking pain-facilitating processes from the rostral ventromedial medulla (RVM) interfered with its expression. Inactivation of the RVM with local anesthetic, destruction of putative pain-facilitation cells, and blockade of cholecystokinin receptors all prevented or significantly attenuated IM-induced allodynia. Electrophysiological studies confirmed activation of pain-facilitating "ON" cells and transient suppression of "OFF" cells in the RVM following IM. Additionally, microinjection of the RVM with a microglial inhibitor or sumatriptan also inhibited the expression of IM-induced cutaneous allodynia as well as microglial activation. Facial and hindpaw allodynia associated with dural stimulation is a useful surrogate of pain associated with primary headache including migraine and may be exploited mechanistically for the development of novel therapeutic strategies for headache pain. The data also demonstrate a requirement for activation of descending facilitation from the RVM, likely reliant on neuronal-glial interactions, for the expression of cranial and extracranial cutaneous allodynia. Consequently, the findings are consistent with a brainstem generator of allodynia associated with headache disorders.
    • Pain Facilitatory Cells in Rostral Ventromedial Medulla: Neurons Coexpressing Cholecystokinin-2 and Mu-Opioid Receptors

      Lai, Josephine; Zhang, Wenjun; Lai, Josephine; French, Edward; Porreca, Frank; Rance, Naomi; Vanderah, Todd (The University of Arizona., 2005)
      This dissertation will examine the phenotype of pain facilitatory neurons in the rostral ventromedial medulla (RVM) and its role in neuropathic pain states. Activation of the descending facilitation pathways might be the result of plasticity in the RVM that is driven, at least in part, by the presence and activity of cholecystokinin type-2 receptors (CCK2R) mRNA expressing neurons. The expression of either opioid mu receptors (MOR) or CCK2R mRNA in the RVM was confirmed by in situ hybridization (ISH). Pretreatment with CCK8(s)-saporin resulted in a significant loss of CCK2R mRNA positive cells in the RVM, concomitant with a blockade of CCK8(s) induced hyperalgesia. The same treatment also significantly reduced the number of neurons labeled for MOR mRNA, hinting that MOR and CCK2R mRNA signals may be co-localized in some RVM cells. Consistent with these data, pretreatment with dermorphin-saporin significantly reduced the number of MOR mRNA labeled cells in the RVM, blocked RVM CCK8(s) induced hyperalgesia and reduced the number of CCK2R mRNA positive cells in the RVM. The co-localization was further confirmed by a dual label ISH approach using 35S-labeled CCK2R and Digoxigenin-labeled MOR riboprobes. Data showed that over 80% of labeled RVM neurons co-expressed both MOR and CCK2R mRNA, ~15% expressed only CCK2R mRNA, and very few cells expressed only MOR mRNA. The above findings may suggest that elimination of CCK2R mRNA expressing neurons result in removal of the driving force for descending facilitation from RVM, hereby block the development of neuropathic pain. Rats pretreated with CCK8(s)-saporin conjugates had a full reversal of thermal sensory threshold and partial reversal of tactile threshold starting at day 5 after SNL. The lesion effects of RVM CCK-SAP were evaluated by ISH. Comparing to saporin pretreated groups, CCK8(s)-saporin pretreatment significantly reduced the numbers of CCK2R mRNA labeled neurons within RVM. The data suggest that selective ablation of CCK2R mRNA expressing cells in RVM is sufficient to block the development of neuropathic pain, and thus confirm the hypothesis that CCK2R mRNA expressing cells may be an important player in descending facilitation from RVM as a mechanism of neuropathic pain.
    • Pain-modulating effects of peripheral (CB2) cannabinoid receptors

      Malan, T. Philip, Jr.; Ibrahim, Mohab Mohamed (The University of Arizona., 2004)
      Cannabinoid receptor agonists diminish responses to painful stimuli. Extensive evidence implicates the CB1, receptor in the production of antinociception, inflammatory hyperalgesia, and peripheral nerve injury-induced sensory hypersensitivity. In previous work included in my masters thesis, our laboratory has demonstrated the capacity of CB2 receptors located outside the central nervous system (CNS) to inhibit acute nociception and inflammatory hyperalgesia. In this thesis, I use AM1241, a CB2 receptor-selective agonist to test the hypothesis that CB2 receptor activation reverses the tactile and thermal hypersensitivity characteristic of neuropathic pain in L5/L6 spinal nerve ligation model. The CB2 receptor-mediated nature of these effects was demonstrated using receptor-selective antagonists, as well as mice deficient in the genes coding for CB1 or CB2 receptors. Experiments using site-specific injections suggest AM1241 acts peripherally at the site of nerve injury and the site of application of the sensory stimulus. The peripheral nature of the effects of AM1241 is consistent with the peripheral distribution of CB 2 receptors. Given the peripheral actions of AM1241, I hypothesized and demonstrated that topical application of AM1241 modulates pain responses. Additionally, I began to examine the mechanisms by which CB2 receptor activation modulates pain responses. The effects of AM1241 were reversed by the opioid receptor antagonist, naloxone and by a sequestering antiserum to beta-endorphin. In addition, the effects of AM1241 were not observed in beta-opioid receptor knockout mice. These results suggest that the endogenous opioid peptide, mu-endorphin plays an essential role in CB2 receptor mediated pain inhibition. Further, AM1241 stimulated release of beta-endorphin from rat skin tissue and cultured human keratinocytes. The stimulation of beta-endorphin release by AM1241 was inhibited by the CB2 receptor-selective antagonist, AM630, and was not observed in skin from CB2 receptor knockout mice, demonstrating that it is mediated by CB2 receptor. These results suggest that CB2 receptor activation produces antinociception by stimulating the release of beta-endorphin from local cells and that beta-endorphin released acts at beta-opioid receptors to inhibit the responsiveness of primary afferent neurons.
    • Painleve Analysis, Lie Symmetries and Integrability of Nonlinear Ordinary Differential Equations

      Lu, Yixia; Ercolani, Nicholas M.; Ercolani, Nicholas M.; Flaschka, Hermann; Tabor, Michael (The University of Arizona., 2005)
      The Painleve analysis plays an important role in investigating local structure of the solutions of differential equations, while Lie symmetries provide powerful tools in global solvability of equations. In this research, the method of Painleve analysis is applied to discrete nonlinear Schrodinger equations and to a family of second order nonlinear ordinary differential equations. Lie symmetries are studied together with the Painleve property for second order nonlinear ordinary differential equations.In the study of the local singularity of discrete nonlinear Schrodinger equations, the Painleve method shows the existence of solution blow up at finite time. It also determines the rate of blow-up. For second order nonlinear ordinary differential equations, the Painleve test is introduced and demonstrated in detail using several examples. These examples are used throughout the research. The Painleve property is shown to be significant for the integrability of a differential equation.After introducing one-parameter groups, a family of differential equations is determined for discussing solvability and for drawing more meaningful conclusions. This is the most general family of differential equations invariant under a given one-parameter group. The first part of this research is the classification of the integrals in the general solutions of differential equations obtained by quadratures. The second part is the application of Riemann surfaces and algebraic curves in the projective complex space to the integrands. The theories of Riemann surfaces and algebraic curves lead us to an effective way to understand the nature of the integral defined on a curve. Our theoretical work then concentrates on the blowing-up of algebraic curves at singular points. The calculation of the genus, which essentially determines the shape of a curve, becomes possible after a sequence of blowing-ups.The research shows that when combining both the Painleve property and Lie symmetries possessed by the differential equations studied in the thesis, the general solutions can be represented by either elementary functions or elliptic integrals.
    • Paleo-upwelling and the distribution of Mesozoic marine reptiles

      Parrish-Jones, Judith T.; Montague-Judd, Danielle Dawn (The University of Arizona., 1999)
      Marine upwelling occurs when surface currents diverge or are deflected. Deeper water, often nutrient-rich, rises and generates a cascade of biological effects including elevated productivity and a unique assemblage of organisms. Macrofaunal characteristics of upwelling provide key evidence for oxygen-minimum zones, upwelling of cool water, and high productivity and are potentially useful indicators of ancient upwelling. The Upper Triassic Luning Formation in Nevada contains abundant, large ichthyosaurs and was deposited in a back-arc basin that could have experienced upwelling conditions. Luning Formation rocks at West Union Canyon were analyzed for sedimentological, geochemical, and paleontological upwelling indicators. Abundant suspension feeders, lack of corals and calcareous algae, modest total organic carbon and minor element concentrations in deeper marine facies, abundant cosmopolitan molluscs but no taxa restricted to low latitudes, and abundant fecal pellets and clotted fabrics in most facies suggest that upwelling could have influenced Luning deposition. Moderate-scale upwelling likely contributed to eutrophic conditions and ichthyosaur abundance at West Union Canyon. Marine reptiles might have had ties to upwelling areas to provide food, as do modern whales. A relational database containing 817 locality records and 1365 taxon-localities was assembled for ichthyosaurs, plesiosaurs, and mosasaurs. Marine reptile localities were compared with model-predicted upwelling and with upwelling-related lithologies (organic-rich rock, biogenic silica, phosphorite, and glauconite). Marine reptile occurrences intersected predicted upwelling more often than expected by chance for the Upper Cretaceous, Callovian, and Norian stages, and for all of the data together (P = 0.05). For age-restricted data, occurrences of Mosasauridae, Pliosauridae, and Plesiosauria intersected upwelling more often than expected by chance (P = 0.05). Average shortest distances between reptile fossil and upwelling lithology occurrences were smallest (one grid cell adjacent or smaller) for the Pliensbachian and four of five Cretaceous stages. Analytical biases and other aspects of reptile ecology may have affected the results, but overall, upwelling could have influenced marine reptile distribution, particularly for the Upper Cretaceous. Multiple radiations into the high-productivity, top-predator niche over the Mesozoic are suggested by the dominance of different taxa in grid cells containing upwelling lithologies: ichthyosaurs (early Mesozoic), plesiosaurs (middle Mesozoic), and finally mosasaurs (late Mesozoic).
    • Paleoclimate studies for controversial continental paleogeographies: The application of spherical geodesic grids and climate models to Gondwana's Devonian apparent polar wander path

      Parrish-Jones, Judith Totman; Moore, Thomas Leonard (The University of Arizona., 1999)
      Paleomagnetic data acquired in the last 10 to 15 years have failed to clearly delineate the Devonian apparent polar wander (APW) path for Gondwana. Consequently, many paleogeographers and paleomagnetists have turned to paleoclimate data to assist in locating Gondwana. Paleoclimate data have been used to either support proposed paleomagnetic-based positions for Gondwana or to independently position the continent. Both of these approaches have problems, including how paleoclimate data are handled and the assumption of a zonal climate system. Several improvements of these approaches are proposed in this study. First, paleoclimate data were grouped into occurrences using a spherical geodesic grid system when statistical manipulations were to be performed. The use of occurrences reduces errors caused by variations in sampling resolution and post-depositional processes. Grid cells in the spherical geodesic grid systems are near-equal area and shape. A comparison between spherical geodesic grid systems with other grid systems showed that the spherical geodesic grids were the most stable grid system if used in combination with a technique called rotational minimization, which finds the fewest possible occurrences for a given data set. Second, two techniques commonly used in paleogeographic studies were modified and a third technique was introduced. The first two techniques, called the palepole zonality method and the modified pole-finder method, were designed to rate proposed pole positions for Gondwana using latitude-distribution models for paleoclimate data. The final method, the parametric climate-model method, uses a conceptual climate model to predict the climate of the continent, which was compared to regional climate inference models. The results of these techniques when applied to Gondwana suggested that the continent moved little during the Devonian: the pole moved from west-central Gondwana in the Early Devonian to the northwest or to the east by the Carboniferous. The results also show, however, that all of these techniques are limited in their ability to pick a single position for Gondwana. Consequently, the best path identified by these methods cannot be assumed to be correct and confirming paleomagnetic data are still required.
    • Paleoecology and taphonomy of vertebrate faunas from the Anza-Borrego Desert of California

      Lindsay, Everett H.; Cassiliano, Michael Louis; Lindsay, Everett H.; Parrish, Judith T.; Davis, Owen; White, John A. (The University of Arizona., 1994)
      Sedimentary deposits in the Salton Trough of California record the infilling of the northern part of the Gulf of California. The final phase of deposition began about 4.0 Ma with development of the delta plain of the Colorado River and ended about 0.9/0.7 Ma after a period during which deposition was dominated by bedload streams. During the final phase of deposition, a diverse assemblage of mammals characteristic of the Blancan and Irvingtonian Mammal Ages inhabited the area. The Blancan-Irvingtonian boundary is placed in the Fish Creek-Vallecito Creek section at the lowest stratigraphic occurrence of Hammuthus at about 1.77 Ma. The Fish Creek-Vallecito Creek section contains superposed Blancan and Irvingtonian faunas separated by a newly recognized Blancan-Irvingtonian boundary in continuously deposited sediments correlated with the magnetic polarity time scale. It is proposed that the Fish Creek-Vallecito Creek section be recognized as the standard section in which to define the Blancan-Irvingtonian boundary. Taphonomic analysis indicates that skeletal elements accumulated in five major depositional environments: tidal flat, lacustrine, channel, channel "fill", and floodplain. Only the fluvial environments produced significant skeletal abundances and taxonomic diversity. Taphonomic analysis indicates that pre-transport taphonomic processes were more important than fluvial transport in modifying thanatacoenoses. Taphonomic analysis also suggests that taxonomic diversity and relative abundances of large and small mammals are reliably preserved so that assemblages can be used in realistic, but general, analyses of paleoecology and paleocommunity structure. Actualistic and cenogram methods were used to study the Fish Creek-Vallecito Creek paleocommunity. Both methods suggest a savannah-community. The cenogram analysis shows the structure of the paleocommunity based on body size distribution. The data are grouped into assemblages based on the following criteria: change in fluvial environment, change in taxonomic composition, and change in paleoclimate. Stable, discrete small- and large-sized components with homogeneous body-size distributions are separated by an unstable medium-sized component. Results are consistent regardless of how the data are grouped, suggesting confidence in the results, stability in the paleocommunity despite environmental change, and a reality to the existence of the paleocommunity.
    • Paleoecology of an archaeological site near Snowflake, Arizona

      Bohrer, Vorsila L. (The University of Arizona., 1968)

      BROWN, ROY BERNARD.; Culbert, T. Patrick; Davis, Owen K.; Dean, Jeffery; Haury, Emil; Markgraf, Vera (The University of Arizona., 1984)
      While the archaeology of the Northern Frontier of Mesoamerica is poorly understood, Pedro Armillas' hypothesis that climatically induced environmental change was the limiting factor for cultural change has become the ruling theory. In order to test this hypothesis original lacustrine pollen profiles were compared with a detailed inspection of the known archaeological record and the previously published paleoecological record. The archaeological evidence suggests that there was a dense human occupation in the northern reaches of Mesoamerica between about AD 600-900. The first indications of human settlements are related to the Chupicuaro culture that reached its apogee about 2000 years ago located along the Rio Lerma. A rustic variant of the Chupicuaro culture spread north and is associated with scattered hamlets. About AD 600 the sedentary population expanded considerably in conjunction with the development of regional centers and the Coyotlatelco red-on-buff ceramic tradition. This expansion can be seen all along the Northern Frontier of Mesoamerica from Alta Vista south to Tula. Between AD 900-1000 there was a dramatic change in settlement patterns and by about AD 1000 most of the northern reaches of Mesoamerica were once again under the control of semi-nomadic hunters and gatherers. A suite of four cores was collected in a transect that crosses the Northern Frontier of Mesoamerica. The goal of selecting sites that minimized human impact was not altogether successful since these cores identify the impact of agriculture. Within the limits of the dating and material available, the pollen profiles from these cores suggest an environmental change between AD 1000 and 1500. From the data available it is not clear if this change, or changes, was the result of changes in human settlement patterns or climatic change. As such Armillas' hypothesis remains unproven.
    • Paleoenvironmental and stratigraphic implications of taphonomic processes: Case studies from Recent and Pleistocene shallow marine environments.

      Flessa, Karl W.; Meldahl, Keith Heyer.; Cohen, Andrew S.; Bottjer, David J.; Dickinson, William R.; Schreiber, Joseph F. (The University of Arizona., 1990)
      Taphonomic data can be applied to problems in paleoenvironmental analysis, stratigraphy and paleobiology. Ecologic and taphonomic data from molluscan assemblages in Recent clastic shallow marine environments (northern Gulf of California, Mexico, and Cape Cod, Massachusetts, U.S.A.) furnish different and complementary types of environmental information. Ecological data (species composition, trophic and life habit data) are regulated principally by substrate variation. In contrast, taphonomic data (abrasion, fragmentation, corrosion, bioerosion and encrustation) variously track shifts in surface residence time of shells, water energy, and tidal submergence time. Taphonomic contrasts between sedimentary environment arise because shells in different environments are altered along distinct "taphonomic pathways". Variation in residence time, water energy and tidal submergence time elicit responses in unique suites of taphonomic attributes. Taphonomic processes affect the distribution of fossils in strata, and this has important stratigraphic and paleobiologic ramifications. Shell concentrations in Pleistocene shallow marine strata in the northern Gulf of California formed either as beach ridge accumulations, tidal channel lags, autochthonous communities, or "unconformity beds". The latter are significant stratigraphic markers, capping angular unconformities. The "unconformity beds" are identified taphonomically as transgressive lags derived from beach face reworking during erosion of structural bulges that formed by periodic deformation along the Pleistocene shoreline. These shell beds are products of sedimentary processes along tectonically active continental margins. Preservational incompleteness of fossils hampers reconstruction of patterns of mass extinction, because biostratigraphic last occurrences nearly always underestimate times of lineage extinction. The distribution of biostratigraphic last occurrences of mollusc species in sediment cores from a Recent tidal flat indicates that sudden extinction can appear gradual, due to error in biostratigraphic range endpoints (Signor-Lipps effect). Extinction is typically not accurately recorded for species with less than 15% stratigraphic abundance (i.e. occurring in less than 15% of the sample intervals). Extinction simulations demonstrate that stratigraphic abundance and last occurrence data (readily available in the fossil record) can be used together to distinguish between sudden, stepwise and gradual patterns of mass extinction.
    • Paleogeography of Western North America: Insights from Detrital Zircon U-Pb Geochronology and Hf Isotope Geochemistry

      Gehrels, George E.; Pecha, Mark Ernest; DeCelles, Peter G.; Carrapa, Barbara; Kapp, Paul (The University of Arizona., 2019)
      Reconstructing the geologic and tectonic evolution of western North America from Paleozoic through Eocene time is the goal of this dissertation. Three geographical regions were selected for analysis using modern analytical techniques including U-Pb geochronology and Hf isotope geochemistry of detrital zircons, as well as, geologic mapping and paleocurrent analysis. The Neoproterozoic through Pennsylvanian Yukon-Tanana terrane (YTTs) in the Coast Mountains of southeastern Alaska, the Cretaceous through Eocene strata in the San Juan basin of northwestern New Mexico and southwestern Colorado, and the Paleocene Wilcox Group in the Gulf of Mexico are the regions selected for analysis. The project also includes a large compilation of εHft from the eight main elements that comprise the North American Cordilleran arc: Coast Mountains batholith, North Cascades Range, Idaho batholith, Sierra Nevada batholith, Transverse Ranges, Peninsular Ranges, Sierra Madre Occidental, and the Porphyry Copper Province. Identifying changes in sediment provenance from Sevier thin-skinned thrusting through the formation of Laramide basement block uplifts was accomplished by conducting U-Pb geochronologic and Hf isotopic analyses on 32 detrital zircon samples from across the entire San Juan basin. The detrital zircon U-Pb results indicate four stratigraphic intervals with internally consistent age peaks. Based on a combination of U-Pb ages and paleocurrent indicators, three transitions in sediment provenance were identified, resulting in a refined paleogeographic model for Late Cretaceous through Eocene time. This model includes a transition from initial reworking of the Paleozoic and Mesozoic cratonal blanket to unroofing of distant basement cored-uplifts and Laramide plutons, then a final transition to more local Laramide uplifts. Hf isotopes were also collected on zircons from the San Juan basin, and also for a select group of samples of the Paleocene Wilcox Group in the Gulf of Mexico. This was done because Hf isotopes in zircon not only provide crustal evolution information, they also supply complementary isotopic information that is combined with U-Pb age to create a zircon fingerprint. This information refines the understanding of the Late Paleocene sediment pathways across the western United States, including a new provenance connection between the Coast Mountains batholith in British Columbia, Canada and the Gulf of Mexico. This information also allowed for the generation of a Laramide-age (ca. 80-50 Ma) detrital signature map of zircons that can now be used for referencing detrital zircons for researchers working in and around the Cordilleran magmatic arc.
    • Paleolithic Ungulate Hunting: Simulation and Mathematical Modeling for Archaeological Inference and Explanation

      Beaver, Joseph Edward; Kuhn, Steven L.; Stiner, Mary C.; Kuhn, Steven L.; Stiner, Mary C.; Olsen, John W. (The University of Arizona., 2007)
      Formal models, those which explicitly specify the postulates on which they are based, the development of their 'predictions' from those postulates, and the boundary conditions under which they apply, have the potential to be useful tools in archaeological inference and explanation. Detailed examination of one such model, the mathematical model commonly referred to as the diet breadth or prey choice model, shows that its archaeological application is severely complicated by two factors that are difficult or impossible to specify for prehistoric cases: 1) limits on the amount of meat consumable by a food-sharing group before spoilage or loss to scavengers and 2) hunting failure rates. The former introduce significant uncertainties into the food yield or energetic return term of resource rankings, while the latter affect both resource rankings and the resouce encounter rates leading to prey inclusion or exclusion from the diet. Together, these factors make rigorous diet breadth / prey choice model-based inferences from ungulate archaeofaunas impractical, especially in Paleolithic cases. Following success in recent years in making diet breadth model-based inferences about Paleolithic demography from small game analyses that involved computer simulation modeling of prey species' resilience to hunting pressure, the development and employment of a similar model applied to ungulate species reveals that, in general, the differences in the abilty of populations of different ungulate species to sustain harvest rates are not sufficient to allow the relative representation of ungulate remains in archaeological sites to be a viable basis for human demographic inferences. However, in cases where ungulate remains allow the determination of both prey age structure and sex ratio, it is possible to distinguish low exploitation rates, high exploitation rates, and overhunting. In some cases, the sex ratio data may also alter relative hunting resilience levels in such a way that it may be possible to infer that one species was capable of supporting a larger human population than another.

      MAY, STEVEN ROBERT. (The University of Arizona., 1985)
      Jurassic volcanic rocks in southeastern Arizona provide an opportunity to study the paleomagnetism of an autochthonous segment of the Mesozoic Cordilleran magmatic arc. The Corral Canyon sequence in the Patagonia Mountains is a 650 meter thick homoclinal sequence consisting of interbedded volcaniclastic red-beds, welded ash-flow tuff, and lavas. Rb/Sr isotopic analysis of eight whole rock tuff samples yields an isochron age of 171 ± 3 Ma. Welded tuffs in the Corral Canyon sequence possess a stable, primary magnetization carried in both magnetite and hematite that defines a paleomagnetic pole at 61.8°N, 116.0°E, alpha₉₅= 6.2°. This pole is considered to be a reliable Middle Jurassic reference pole for cratonic North America. Paleomagnetic study of the Canelo Hills volcanics welded tuff member also yields a stable, primary magnetization throughout a stratigraphic thickness of 600 meters. However, results from this formation are enigmatic and the mean pole is discordant with respect to Middle Jurassic reference poles. Various aspects of the paleomagnetic data indicate that discordance of the Canelo Hills volcanics pole is probably due to acquisition of remanent magnetization during a period of non-dipole behavior of the geomagnetic field. Dispersion of paleomagnetic directions suggests that the welded tuff member represents at most two cooling units and can be interpreted as a caldera-fill sequence. A revised Jurassic APW path differs significantly from available paths and has important implications for North American plate motion and paleolatitude. The spatio-temporal progression of reliable Jurassic paleopoles, in conjunction with Triassic and Early Cretaceous poles, is well described by paleomagnetic Euler pole analysis. The APW path is divided into three tracks, separated by two cusps. These cusps represent changes in the direction of North American absolute plate motion and can be correlated with global plate motion and intraplate deformation events at approximately 200-210 Ma and 150 Ma. Finally, the APW path presented herein predicts more southerly Late Triassic and Jurassic paleolatitudes for North America than have been suggested by previous authors. Using revised reference poles, there are no inclination anomalies within paleomagnetic data from Late Triassic and Early Jurassic rocks of Stikinia and Quesnellia (B.C., Canada).
    • Paleomagnetism of Late Triassic and Jurassic sediments of the southwestern United States.

      Butler, Robert F.; Bazard, David Richard.; Coney, Peter J.; Dickinson, William R.; Chase, Clement G.; Wallace, Terry C. (The University of Arizona., 1991)
      Paleomagnetic poles were obtained from the Chinle, Kayenta, Summerville, and Morrison Formations. Combined with paleomagnetic poles from the Moenave Formation, poles from the Chinle and Kayenta formations record ∼30 m.y. of North American apparent polar wander (APW) within a regional stratigraphic succession. During the Carnian and Norian stages of the Late Triassic, Chinle poles progress westward. During the Hettangian through Pliensbachian stages of the Early Jurassic, the pattern of APW changed to an eastward progression. Even after correction for 4° clockwise rotation of the Colorado Plateau, a sharp corner in the APW path (J1 cusp) is resolved near the pole from the Hettangian/Sinemurian (∼200 Ma) Moenave Formation (59.4°N; 59.2°E). The J1 cusp implies an abrupt change from counterclockwise rotation of Pangea prior to 200 Ma to clockwise rotation thereafter. Paleomagnetic poles obtained from the Summerville and Morrison formations are consistent with the Middle and Late Jurassic APW path described by the Corral Canyon and Glance Conglomerate paleomagnetic poles as well as a Late Jurassic Cusp (J2 cusp) in the APW path. The APW path described by the J2 cusp, a single Morrison Formation pole, and mid-Cretaceous paleomagnetic poles suggest from ∼150-126 Ma the North American plate experienced a minimum rate of motion of 0.93°/m.y. which is similar to rates calculated for the Late Triassic (0.73°/m.y.) and Jurassic (0.66°/m.y.). This rate is much lower than rates based on previous APW paths. Thermal demagnetization and data analysis indicate that within-site dispersion is an important criterion for selecting sites which retain a high unblocking-temperature, characteristic remanent magnetization (ChRM). This criterion was used to define at least three stratigraphically-distinct, antipodal polarity-zones within each member/formation, suggesting the ChRM was acquired soon after deposition. ChRMs from 15 to 22 sites in the Upper Shale Member of the Chinle Formation define an early Norian paleomagnetic pole position of 57.4°N, 87.8°E (K = 60, A₉₅ = 5.0°). ChRMs from 18 to 43 sites in the Owl Rock Member of the Chinle Formation define a middle Norian paleomagnetic pole position of 56.5°N, 66.4°E (K = 183, A₉₅ = 2.6°). ChRMs from 23 of 35 sites in the Kayenta Formation define a Pliensbachian pole position of 59.0°N, 66.6°E (K = 155, A₉₅ = 2.4°). ChRMs from 15 to 35 sites in the Summerville Formation define a late Callovian pole position of 53.8°N, 133.6°E (K = 25, A₉₅ = 7.5°). ChRMs from 15 sites in the Morrison Formation (9 from the study of Steiner and Helsley [1975]) define a single, ∼147 Ma, paleomagnetic pole position of 64.1°N, 152.4°E (K = 113, A₉₅ = 3.6°).