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2013-2014

2 hits

  • Thumbnail for Obsidian artifact provenance study of the Piedras Marcadas Pueblo, Albuquerque, New Mexico
    Obsidian artifact provenance study of the Piedras Marcadas Pueblo, Albuquerque, New Mexico by Freeman, Alexandra

    This study conducts provenance research on 65 artifacts from the Piedras Marcadas (PM) Pueblo in Albuquerque, New Mexico. Late Tertiary and Quaternary eruptions prompted by regional continental extension, associated with the formation of the Rio Grande Rift and volcanism of the Jemez Lineament, produced a number of obsidian-bearing rhyolitic units from several major volcanic fields in western New Mexico that are relevant to this study. Obsidian nodules were collected from the two most proximal volcanic provinces, the Jemez and Mount Taylor volcanic fields, to the PM site for geochemical comparison to the subsurface artifacts. Archived data for three sources in the Jemez Mountains (Canovas Canyon, Paliza Canyon, and El Rechuelos Rhyolite) and two sub sources of the Taos Plateau (No Agua Peaks North and West) were also used for comparison. Trace element data were collected on each sample using energy dispersive X-ray fluorescence spectrometry (ED XRF). The chemical relationship between each obsidian flake artifact and all source chemical groups was analyzed on bivariate plots comparing trace element concentrations of Y, Nb, Rb, Zr, and Sr using the SPSS program. Cluster analysis paired with T –test verification, using the Minitab program, successfully correlated each artifact to its corresponding geologic source of origin. Comparison between geochemical signatures of 9 sources and 62 artifacts identified 53 Cerro Toledo, 4 Canovas Canyon, 3 Valles, 1 Paliza Canyon, and 1 El Rechuelos artifacts. Three outlier samples are non-obsidian. The dominance of Cerro Toledo obsidian in the artifact samples directly relates to proximity and availability of Cerro Toledo nodules in Rio Grande alluvium, found adjacent to the PM site. The water-worn physical condition of the Cerro Toledo nodules suggests secondary sources played a major role in distributing and providing closer obsidian sources for the PM pueblo. The presence of three Valles Rhyolite obsidian samples provides evidence for procurement from the primary source in the Valles Caldera, as the source occurs in minor abundance and sizes in Rio Grande river deposits. The absence of Mount Taylor artifacts suggests that the PM pueblo did not interact with the Zuni pueblo who controlled Mount Taylor region at the time when the artifacts were deposited.

  • Thumbnail for Variations in hadrosaurid behavior, soil processes, and forest structure over the Late Cretaceous landscape of southern Utah (Kaiparowits Formation, Grand Staircase Escalante National Monument)
    Variations in hadrosaurid behavior, soil processes, and forest structure over the Late Cretaceous landscape of southern Utah (Kaiparowits Formation, Grand Staircase Escalante National Monument) by Crystal, Victoria F.

    During the Late Cretaceous, western North America was flooded by an inland sea, the coasts of which were covered by broad, low-relief fluvial/alluvial plains on which a wide variety of dinosaurs and plants lived. Although these “actors” are known, their “actions” are not as clear; in particular, details of surface processes, dinosaur behavior and forest structure are not known for certain. In this study, stable isotopes of fossilized teeth from hadrosaurid dinosaurs collected in two different areas within the Kaiparowits Formation are used to investigate possible surface methane production, dinosaur niche partitioning, and the nature of the forest canopies in southern Utah during the Late Cretaceous to answer some of these outstanding questions. Comparison of carbon isotope ratios of tooth enamel between the two areas reveals significant offsets, which can be explained by differences between the areas in either (1) plant communities, (2) environmental and climatic stressors, or (3) the cycling of carbon within a forest canopy. Regardless of the exact cause, the preservation of these differences in hadrosaurid tooth enamel provides evidence of dietary niche partitioning amongst hadrosaurid sub-families within low-lying fluvial environments in southern Utah during the Late Cretaceous. Significant differences in both means and ranges of carbon isotope ratios of tooth dentine also exist between areas. Unlike enamel, dentine does not preserve primary isotopic information; rather, its chemical composition is strongly influenced by chemical processes taking place in soils near the surface. In this case, unusually high carbon isotope ratios of dentine from some sites within the two areas provide the first direct evidence of CH4 production in coastal floodplains of western North America during the Late Cretaceous. Such production of CH4 likely played an important role as a feedback that helped maintain “hothouse” climate conditions during this time. Since CH4 production has a pronounced impact on carbon isotope ratios of gases being emitted from the soil surface, it is possible to trace the movement of these gases into the biotic reservoir. In particular, the existence of hadrosaurid tooth enamel with high carbon isotope ratios suggests that these gases were incorporated into low-level forest vegetation before being eaten by the animals. In order for such “recycling” of carbon to occur, it is necessary for there to be a closed canopy near the surface, meaning that the forest understory is isolated from the open atmosphere due to dense vegetation cover. Thus, results from this study provide the first direct evidence for dense closed canopy forests in southern Utah during the Late Cretaceous.