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  • James, Kristen
    2 May 2004
    Monte Amiata is a recently extinct volcano that produced trachydacites and a few small olivine latite flows. The Amiata suite showed crustal strontium, neodymium, and lead isotopic signatures. 87Sr/86Sr ratio values ranged from 0.712447 to 0.713068 and 143Nd/144Nd ratios ranged from 0.512094 to 0.512203. 207Pb/204Pb values ranged from 15.6694 to 16.2330 and 206Pb/204Pb ratios ranged from 18.7125 to 19.0882. The olivine latite flows towards the end of volcanic activity would suggest more mantle influence than the data suggests, but Amiata may be sourcing from a depleted mantle as well as the limestone that proliferates throughout Italy. Strontium concentrations are similar to those of rubidium, so neodymium-samarium comparisons were utilized, as they are more reliable. Neodymium concentrations, when placed against samarium concentrations, indicate crustal contamination, as do the isotope data.
  • Auerbach, David J.
    1 May 2004
    The Steptoean Positive Isotopic Carbon Excursion (SPICE) is a large (≥4 shift) positive carbon isotope (δ13C) excursion in the Upper Cambrian. The SPICE excursion begins at the base of the Pterocephaliid Biomere, which is coeval with a mass extinction of shelf fauna and the initiation of the second of two major regressions in the Cambrian. It peaks at the Sauk II-Sauk III subsequence boundary, which corresponds to the height of the regression. New carbon isotope (δ13C) data from the carbonate phase of phosphatic lingulid brachiopods from Upper Cambrian nearshore siliciclastic facies in the Upper Mississippi Valley, USA show the presence of the SPICE. The shape and magnitude of the SPICE are consistent with results from whole-rock carbonate analyses. However, values in this study are consistently ~6 lower than whole-rock analyses due to fractionated carbon delivered to the nearshore by rivers. This study also reports a surge in concentrations of Fe as well as trace elements (Pb, As, Co, Cu, Ni, and Mo) known to be toxic to marine invertebrates just above the base of the Pterocephaliid biomere. These perturbations were probably driven by the Sauk II-Sauk III regression, which exposed large areas of the Laurentian craton for the first time since inundation earlier in the Cambrian, allowing remobilization of Fe and toxic trace elements concentrated in sediments and soil. These elements were probably transported by rivers from exposed land to the epeiric sea, where concentrations would quickly have exceeded tolerances of most shelf fauna and caused widespread mortality. The influx of Fe could have stimulated primary productivity, resulting in increased burial of organic (12C-enriched) carbon and the positive excursion of the SPICE.
  • Bergmann, Kristin
    1 May 2004
    Within the last hundred years, landscapes across the western United States have experienced stream incision and vegetation change. In wet meadows in the southern Sierra Nevada Mountains, the streams are incising and sagebrush (Artemisia rothrockii) has displaced meadow vegetation, dramatically changing a unique alpine habitat. This study examines the relationship between vegetation and water table depth and the impacts of stream incision on the meadow hydrology in order to determine whether the hydrologic changes associated with stream incision are responsible for sagebrush encroachment. To document these relationships, Bullfrog Meadow on the Kern Plateau, Sierra Nevada Mountains was surveyed and 34 groundwater-monitoring wells were installed. Water table measurements and hydraulic conductivity data were collected during the summer of 2003. Data on stream discharge, sediment type, and vegetation distribution were also gathered. As observed in other studies, there is a strong correlation between vegetation type and water table depth. The water table is on average 50 cm below meadow vegetation within the study area, 120 cm below sage meadow vegetation, and on average 200 cm below sagebrush vegetation. In the incised region of the meadow, stream incision lowered the water table adjacent to the stream by up to 150 cm and approximately 50 cm further from the incised stream. The groundwater flow direction, water table gradient and stream discharge have also been altered by the incision. These results indicate that the hydrologic effects of stream incision may have significant impacts on vegetation change and should be considered in meadow restoration studies.
  • Bryan, Sean
    1 May 2004
    This study examines the basin morphology, sedimentology, and geologic evolution of a small proglacial lake, which is now almost completely drained, located less than a kilometer north of the terminus of the Matanuska Glacier, Alaska. The methods of analysis include pits dug into drained lake deposits, Livingston cores taken from two small lake remnants, and ground-penetrating-radar data (GPR) collected during the summer of 2003. The proglacial lake was approximately 120 m long by 85 m wide and had a maximum depth of 8 m as determined by a topographic survey of the modern lake bed. The lake developed in a topographic low as the Matanuska Glacier receded from a recessional moraine that probably formed 50-100 years ago; analysis of aerial photography indicates the lake drained most of its water sometime after 1966. The basin morphology was complicated by the development of a push moraine during a small re-advance early in lake development. Due to proximity of the lake to the glacier, it is assumed that the majority of water input was derived from glacial melt. Analysis of GPR transects, basin topography, and stratigraphy reveals three distinct facies: (1) a deltaic facies consisting of prograding forsets and interlayered laminated silt and gravelly-sand deformed by loading structures; (2) a basinal facies consisting of finely-laminated fine sand, silt and clay; and (3) a push-moraine facies consisting of diamicton found in a subtle ridge. Horizontal laminations, graded beds, and leveled topography, along with some inclined laminations and draping of the basinal facies onto topographic highs, indicate basinal sedimentation was controlled by a combination of density underflows and suspension settling from interflows/overflows. The influence of underflows and lack of consistent clay partings make annual varves indistinguishable. Since the draining of the lake basin, small-scale channel development and polygonal freezing features have appeared on the surface.
  • Desertification of the Gobi (4777663 KB PDF Document)
    Dorr, Jeff
    1 May 2004
  • Eipert, Annaliese
    1 May 2004
    This study checks the feasibility of optically stimulated luminescence (OSL) in the dating of very young (<200 yr) sandy tsunami deposits in south-central Chile. OSL dating determines the most recent deposition of silicate grains within a potential range of decades to one million years. In the case of tsunami sand sheets, accurate OSL ages will not be achieved unless sand grains were exposed to a certain amount of sunlight during their deposition or before burial. In Chuyaquén, a series of buried sand sheets in the recent geologic record provides a potential means for using OSL to help determine earthquake recurrence intervals. Quartz grains extracted from the top centimeters of the 1960 deposit returned a predicted OSL age of 40 +/- 15 yr BP, but modern tidal flat sediments (~12 cm deep) gave an age older than expected, of 130 +/- 40 yr BP. These results indicate two plausible options: only bleached tidal flat sand shallower than 12 cm was scoured and deposited by the 1960 tsunami, or sand received sufficient sunlight during or after deposition by tsunami. OSL can provide accurate and precise dates on a <200 yr scale, and shows potential to supplement current radiocarbon techniques in the dating of young sandy tsunami deposits.
  • Graly, Joseph
    1 May 2004
    Southeastern Mongolia is part of the series of volcanic arcs, micro-continents, and accretionary terranes that connects the Siberian craton with the North China block. Within the proposed Khövsgöl -Ulaanbadrakhin terrane, in the northern Toto Shan block, hundreds of dikes intrude a granodiorite pluton. At least six generations of cross-cutting dikes are found in the study area, each with unique magmatic source and structural conditions. Between the first and last dike event, the orientation of least horizontal compressional stress rotated 335° from N20°W to N5°E, with the most voluminous event orientated at N85°W.
  • Hilchey, Heather
    1 May 2004
    Hysteresis and ARM parameters for the top two meters of the 20 meter loess profile located at Gold Hill Steps, Alaska, indicate that variation in susceptibility, within the profile, is due to concentration and not composition of ferromagnetic grains, below the modern soil, and that this signal is not being influenced by pedogenic processes. As a result, the susceptibility profile can be used as a proxy for climate change, indicating that the region of increased susceptibility spanning a depth of 1.32-1.50m is part of a climate signal. Correlation between Gold Hill Steps and the Halfway House site, 50km away, whose susceptibility profile displays a similar increase in susceptibility dated at 11.6kyr ± 1.3kyr, provides preliminary evidence for the presence of the Younger Dryas climate change in Alaska.
  • Kanner, Lisa
    1 May 2004
    Recent data from gamma-ray and neutron spectrometers on Mars Odyssey and high-resolution images from Mars Orbital Camera (MOC) on Mars Global Surveyor were used to determine whether high concentrations of polygonal terrain exist in areas of modern, stable water-ice. Small-scale polygonal terrain on Mars, as seen in meter-scale detail by MOC, is assumed to form from thermal contraction processes in ice-rich soil analogous to similar terrain on Earth. Previous studies have shown that the locations of polygonal terrain at high latitudes exist in areas with high concentrations of near-surface water-ice, thus suggesting that the terrain formed in equilibrium with modern climate conditions. This study expands comparison of polygon location and spectroscopy data using all available MOC images at mid-northern latitudes, 30°N to 65°N. Results show that high concentrations of polygonal terrain at mid-latitudes exist in areas of limited near-surface ice and where water-ice is not currently stable. Additional comparisons show that polygonal terrain exists across more than six geologic units of diverse age and origin and at a 5 km range of elevations. In addition, high albedo polygons, indicative of water-ice, are constrained to 55°N to 65°N, and low albedo polygons, indicative of significantly less ice, are confined to 40°N to 55°N. Finally, quantification of the preferential orientation of polygonal terrain reveals that the dominant orientation trends north-south and aligns parallel to topographic contours, analogous to terrestrial studies of polygonal networks. These results support the hypothesis that Martian polygons behave in a similar way to terrestrial polygons and that the presence of polygonal terrain at midnorthern latitudes suggests that their formation is representative of a previous Martian climate when Mars was at high (35°) obliquity and water-ice was stable at the surface at these latitudes.
  • Koffman, Bess
    1 May 2004
    The Frasassi Caves are a currently forming limestone karst system in which biogenic sulfuric acid may play a significant role. High concentrations of sulfide have been found in the Frasassi aquifer, and gypsum deposits point to the presence of sulfur in the cave. White filamentous microbial mats have been observed growing in shallow streams in Grotta Sulfurea, a cave at the level of the water table. A mat was sampled and used in a bacterial phylogenetic study, from which eleven 16S ribosomal RNA (rRNA) gene clones were sequenced. The majority of 16S clones were affiliated with the δ- proteobacteria subdivision of the Proteobacteria phylum, and many grouped with 16S sequences from organisms living in similar environments. This study aims to extend our knowledge of bacterial diversity within relatively simple geochemical environments, and improve our understanding of the biological role in limestone corrosion.
  • Margoles, Sarah
    1 May 2004
    This study examines the connections between recent terrestrial sedimentation and carbon burial and discusses the implications for the global carbon cycle. Land-use change has mobilized large quantities of sediment, causing sediment to accumulate on valley floors, altering the terrestrial sediment cycle. This accumulated sediment may be sequestering much of the "missing carbon." Using a combination of fieldwork and laboratory work, I explored carbon storage within the well-studied Coon Creek watershed of southwestern Wisconsin. To examine the basin's sedimentation history, soil profiles were compared to existing sedimentation data and examined for carbon and nitrogen content. Two profiles reached buried pre-settlement soil, displaying the entire post-settlement sedimentation history of the valley. Recurring intervals of relatively low carbon percentages in site profiles indicate that most sediment eroded from heavily cultivated areas. Periods of high carbon values most likely represent eroded A-horizons from agricultural fields. The total amount of carbon found to be sequestered in the basin for the period 1850-1975 is 8.056 x 1011 grams. To bury this amount of carbon, these processes would have to occur over only 1.4392 x 1012 m2 or 3.0% of global land capable of sequestering carbon. These results suggest that terrestrial sedimentation may account for the "missing carbon sink."
  • Morgan, Leah
    1 May 2004
    The continental deep subsurface harbors a heterogeneous community of microorganisms that have yet to be well understood. The gold mines of the Witwatersrand Basin in South Africa provide economically feasible access to this environment. Molecular evidence for biologically-mediated sulfur cycling has been detected in fissure water in the Merriespruit mine and in groundwater from a dolomite aquifer in the Driefontein mine. PCR amplification, cloning, and sequencing of adenosine-5'-phosphosulfate reductase (APS) and 16S rRNA genes were used to assess the composition and diversity of sulfurmetabolizing microbial populations. Both APS reductase and 16S bacterial gene libraries from the Driefontein mine sample were dominated by sequences with high identity to Desulfomicrobium baculatum. The 16S archaeal library from Driefontein had a high percentage of sequences closely related to Methanomicrobium mazei and the ANME group of anaerobic methanotrophs. The 16S bacterial library from the Merriespruit mine sample was dominated by Thiobacillus-related species known to oxidize sulfur. The archaeal library showed a strong affiliation with Methanobacterium curvum. Most APS sequences from Merriespruit were from an undefined lineage but showed close association with clones from the mouse gastrointestinal tract; others were closely related to the sulfur-oxidizing bacterium Allochromatium vinosum. This study reports the first sulfate-reducing d-Proteobacterial sequences from the South African gold mines and greatly increases the known diversity of subsurface sulfur-metabolizing organisms. Geochemical data are consistent with molecular evidence for deep-subsurface sulfur cycling.