Geology (Bryn Mawr)

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Now showing 1 - 5 of 9
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    The Benefits of Undrained Swamps: Late Holocene Variability in Carbon Sequestration by Salt Marshes in Delaware, North Carolina, and Florida.
    (2017) Letts, Abby; Barber, Donald
    Saltmarshes sequester large quantities of carbon due to the anaerobic conditions in coastal wetland soils. Thick saltmarsh peat layers can also record past environmental conditions at the coast. This study analyzed stable isotope ratios of organic carbon in order to elucidate the mechanisms by which carbon burial rates varied in response to climate and environmental perturbations over the last 2,000 years. Sediment cores from saltmarshes in Delaware, North Carolina, and northeastern Florida from were analyzed for carbon concentration and carbon isotopic composition. The largest isotopic shift (~10 per mille) resulted from paleoecological transition from C3 to C4 vegetation at the Delaware study site, but numerous smaller amplitude variations in δ13Corg and [Corg] are observed that did not result from changes in local marsh vegetation type. Shifts in δ13Corg and [C] of varying amplitude and duration coincide with decadal to multi-centennial climate perturbations such as the Medieval Warm Period, Little Ice Age, and the Maunder sunspot minimum. Greater temporal coherence is observed between the Delaware and North Carolina records, although the slower accretion rate of the Florida reduced its sampling resolution, hampering comparison with the other two sites. The findings indicate that relatively small changes in Late Holocene climate, as well as local environmental factors, cause buried carbon concentrations of East Coast saltmarshes to vary by a factor of two or more. The results also illustrate the potential usefulness and limitations of carbon isotopes in saltmarsh sediments for the reconstruction of past hydroclimate conditions. Overall, the findings imply that carbon sequestration rates of coastal marshes will continue to change in the future.
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    Soil survey and analysis of 'serpentinicity' at Unionville Serpentine Barrens, Chester Co., PA
    (2016) Fullem, Abby Kapan; Barber, Donald; Latham, Roger; Plante, Alain
    The Unionville Serpentine Barrens (USB) of Chester County, Pennsylvania is one of few remaining barrens in the Northeast United States. Serpentine barrens, named for their grassland ecosystem in typically temperate forested areas, form above ophiolitic and ultramafic serpentinite bedrock. They host rare and endangered plant species tolerant of harsh soil conditions. The serpentinicity of a soil increases with shallow soil horizons, a Ca:Mg ratio <1, and abundant heavy metal concentrations. Serpentinicity decreases as organic material is added, diluting the effects of the harsh serpentine minerals. This study reports an extensive soil survey, and analyzes relationships between soil chemistry, topographic and location features and vegetation. through an extensive soil survey, analyzes soil chemistry, topographic features, location amidst serpentinite bedrock and Chrome soil series, and serpentine-characteristic vegetation. This study was conducted as part of an adaptive management plan underway at USB in order to restore the shrinking barrens. The soil and vegetation monitoring transect dissects two restoration tactics: a 2012 tree removal area and a 2015 prescribed burn. Depth to bedrock was measured and O, A, B and C horizon samples were collected at each site. Samples were air dried, ground and sieved to < 2mm grain particle size. Mineral samples were extracted via the Mehlich- 3 procedure and concentrations of plant exchangeable cations (exch. Ca, Mg, Fe, and Ni) were detected using an ICP-OES. Organic samples were extracted via EPA 3050b’s acid digest protocol. In addition to characterizing the soil, we found that serpentine-characteristic flora require time to respond to restoration tactics.
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    The Resolution Mine Project of Oak Flat, Arizona: An Analysis of Social and Environmental Impact Assessments
    (2016) Cvitkovic, Adriana Turpin; Cull-Hearth, Selby
    The proposed Resolution Copper Mine at Oak Flat, Arizona is currently under review by the Environmental Protection Agency (EPA) and the Tonto National Forest (TNF) in accordance with the National Environmental Policy Act. The Resolution Project is associated with the Southeast Arizona Land Exchange bill (2014), in which 2,400 acres of the Tonto National Forest around Oak Flat are set up to be exchanged for 5,200 acres of Rio Tinto Copper Company property. This thesis examines the validity of the methods used by Resolution Copper, Rio Tinto’s subsidiary, to assess the social and environmental impacts of the Resolution Mine, and to determine how Resolution researches the potential environmental and social changes that will occur if the land swap and mine are approved. Resolution’s methods for predicting Acid Mine Drainage (AMD) are specifically examined and in this piece. Similarly, this thesis examines Resolution’s methods of assessing the social impact of the mine and land swap as it is felt by the San Carlos Apache, who consider Oak Flat a sacred site for the female coming of age ceremony, Na’ii’ees. Through literature review and primary research, it was determined that Resolution’s methods of AMD prediction and social assessment are insufficient. The EPA and the TNF are unable to effectively review the social and environmental risks of the Resolution Project with the insufficient social impact assessment and AMD prediction tests used in Resolution’s Baseline Geochemical Analysis. The Southeast Arizona Land Exchange and Resolution Mine should not be permitted until improved research is conducted and a more complete impact of these projects can be defined.
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    A terrane wreck? Or just a slip up? A paleomagnetic study of terrane accretion in the western Cordillera
    (2014) Beetle-Moorcroft, Fern; Weil, Arlo B., 1971-
    The North American Cordillera is composed of amalgamated allochthanous terranes that originated far southwest of their present-day location in the Panthalassic (paleo-Pacific) and Tethys oceans. Despite over thirty years of debate, the distance and mechanism of terrane transport continues to elude the geologic community. This is partially due to the fact that traditional geology and paleomagnetic studies yield contradictory results. Three main models have been proposed to reconcile the traditional geology and paleomagnetic data: 1) the Baja-British Columbia hypothesis, 2) the moderate tilt hypothesis, and 3) the westward subduction hypothesis. This paper presents case studies of the Triassic Nicola Group and the Early Cretaceous Spences Bridge Group – both exposed today in the Princeton, British Columbia region of Canada. Demagnetization results along with field tests indicate that the Nicola Group was remagnetized within the last 200 Ma and thus cannot be interpreted within the context of the terrane accretion debate. The Spences Bridge group’s characteristic remanent magnetization (ChRM) suggests either a pre-tilting or syn-tilting affiliation. If the ChRM is pre-tilting, it suggests about 3,400 km of transport northwards, whereas, if the ChRM is interpreted as syn-tilting, it indicates about 1,900 km of northward transport.
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    Explaining Anomalously High Magma Flux at Volcanic Centers on the Northern Kolbeinsey and Southern Mohns Ridges using Bathymetry and Basalt Geochemistry
    (2013) Davis, Rachel Joy; Elkins, Lynne
    The slow-spreading Northern Kolbeinsey Ridge (NKR) and Southern Mohns Ridge (SMR) segments immediately adjacent to the Jan Mayen Fracture Zone exhibit similar types of volcanism along their spreading axes. Each segment has small, flat-­topped cones and hummocky pillow basalt flows typical of slow-­spreading ridges as well as an unusually large volcanic edifice, indicating a focused zone of high magma flux to the ridge. The NKR has parallel axial valleys, an active fault line that is not parallel to the axial valleys, and monogenetic cones on the northern and southern parts of the NKR in addition to the large volcanic crater at the center. I compared the bathymetry (crustal thickness, ridge features) and mid-­ocean ridge basalt geochemistry of these two ridge segments to better understand oceanic crust formation at slow-spreading mid-­ocean ridges with anomalously high magma supply. These processes constrain melting dynamics beneath the two segments by fingerprinting the source of the unusually focused magmatism suggested by the large cones and locally thick crust. Trace element geochemistry (ICP-­‐MS) and bathymetric analyses indicate high degrees of melting and mantle source enrichment at the SMR similar to that observed for Jan Mayen Island (SMR La/SmN=3.139 to 3.710, Sm/YbN=2.107 to 2.674). The ratios indicate a residual garnet signature near Jan Mayen Island further suggesting a deep onset of melting. The NKR basalts are relatively depleted in light rare earth elements (La/SmN=1.427 to 2.152, Sm/YbN=0.826 to 1.026,), with the least enrichment in the western axial valley of the NKR (La/SmN=0.886, Sm/YbN=0.729). The extensive normal faulting in the eastern axial valley of the NKR in addition to hummocky terrain, non-­parallel faults, immature fault boundary near the central Kolbeinsey Ridge and relative enrichment of the NKR basalts from the eastern axial valley indicates a tectonically active axis that is likely being pulled eastward by a hotspot source. The large volcanoes, distinct changes in eruption, a shallow axis and enriched geochemical signature are evidence for a long-­lived mantle plume source in the area of the NKR and SMR ridge segments that has contributed to source enrichment and high magma supply.