Thesis (M.S.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 137-149).

The ecotone between aspen parkland and mixed-grass prairie in mid-eastern Alberta is a climatically-sensitive area that has been subject to periods of enhanced aridity occurring at multi-decadal to centennial-scale cycles throughout much of the last 6000 years. To assess the ecotonal response to changes in effective moisture, as inferred by diatom-inferred salinity, temporal variations in pollen and charcoal preserved in a sediment core from Chauvin Lake were analyzed over several diatom-inferred moisture-cycles from c. 5,400 to 3,300 YBP. Changes in landscape vegetation were inferred by variation in both the percent relative abundance and influx rates of pollen taxa found in a sediment core from Chauvin Lake. Variation in sediment charcoal accumulation rates for both total charcoal and morphotypes, as well as the percent relative abundance of charcoal morphotypes, were used to infer changes in landscape fire regimes during these aridity cycles. One-way ANOVAs were used to determine significant differences in average accumulation rates or relative abundances between the arid and more mesic periods. Changes in the relative abundance of Cyperaceae and Ambrosia pollen between wet and dry periods suggests a shift in the spatial arrangement of vegetation, and a decrease in the sediment influx of most taxa, suggests a decrease in production of landscape vegetation during periods of aridity. Charcoal morphotype analysis, especially variation in Type M, Type D and Type B, suggests fewer, more intense fires during periods of drought. Lack of change in total charcoal may be related to increased secondary sedimentation of charcoal during periods of drought due to increased soil erosion. This study suggests that the spatial arrangement and production of landscape vegetation is dependent on climate, and fire prevalence decreases during periods of drought due to reduced fuel availability. / Thesis (Master, Biology) -- Queen's University, 2009-01-29 12:15:32.137

<p> Late Jurassic through Early Cretaceous strata of the Gannett Group record initial development of the Sevier thrust belt and adjacent foreland basin. Concepts of nonmarine sequence stratigraphy were used to determine the depositional and base level history of the Gannett Group in southeastern Idaho and western Wyoming. Base level fluctuations were driven entirely by tectonic processes, while tectonic uplift in the source area was a major control on sequence development. Six measured sections were revisited or measured and correlated using the concepts of sequence stratigraphy. Four distinct sequences were identified and correlated. Each sequence can be divided into degradational, transitional, or aggradational systems tracts. Where the degradational systems tracts are preserved, they are represented by thin conglomerates. Transitional systems tracts overly the degradational systems tracts and consist of thick sections of laterally discontinuous sandstone and fluvial overbank muds, which grade laterally into continuous limestone and calcareous mudstones that comprise the aggradational systems tract.</p>

<p> The purpose of this study was to identify the geologic signature of paleostorm events within the mid-continent region. This research aimed to create a better understanding of the long-term geologic history of major storms and to allow for better-informed projections regarding future return periods for such storms. The study locations were Cheyenne Bottoms Wildlife Refuge, Kansas and Canton Lake, Oklahoma. To determine the geologic signature of major storms, sediment cores were taken at both locations and sampled at high resolution (3 mm) intervals for grain size analysis using a Cilas laser particle size analyzer. Downcore chronology was determined through Pb-210, Cs-137 and C-14 dating methods. Using a recent known major storm occurrence at Canton Lake, the signature created by storms in the geologic record was identified. The resulting signature was then used to identify paleostorms in the longer-term record in the Cheyenne Bottoms core. The results were also used to determine storm/climate cycles in the long-term geologic record, and to calculate true return periods for major storms. A better understanding of true return periods and possible increases in frequency or intensity of large storms is essential in the effort to mitigate future damage to infrastructure and loss of human life</p>

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<p> Cretaceous Period. There is limited research on organic carbon content of the Pierre Shale in South Dakota. Frequent volcanic eruptions combined with climate change resulted in an increase in carbon dioxide in the atmosphere, leading to decreases in marine oxygen content. Decreasing marine oxygen has been attributed to higher amounts of preserved organic matter in marine sediment. Impact of volcanic ash deposition in the Cretaceous Interior Seaway has not been thoroughly studied. The Pierre Shale also contains the Crow Creek Member, a 5 foot thick layer of unconsolidated sand and rip-up clasts which may indicate a high-energy depositional event. Some hypothesize that it was deposited by a tsunami generated by the Manson impact. Others believe the Crow Creek Member is evidence of a marine low-stand that occurred before the Bearpaw Cyclothem. It is possible that the depositional event that deposited the Crow Creek Member may have led to increases in organic carbon preservation depending on the burial rates and amount of organic carbon preserved. </p><p> To investigate the connection between volcanic ash deposition, the Crow Creek Member deposition, and organic matter preservation of the coastal Cretaceous Interior Seaway, stable isotope geochemistry, trace element geochemistry, and total organic carbon analyses were performed on a 500 foot core drilled near Fort Pierre, South Dakota. Ash beds were identified using X-ray diffraction analysis. Core sampling was driven by location of the Crow Creek Member (above below and within one foot) and by location of ash beds (above below and within one inch), but samples were also taken based on highest and lowest gamma ray values for each five foot (1.52m) core segment. Core sampling was restricted because every other five foot (1.52 meter) section of the Treedam core segement was available for sampling. Statistical T-tests and Z-tests were performed on sample data to determine if there was a significant difference in geochemical signatures between core deposited before and after ash bed deposition and Crow Creek Member deposition. Results and T and Z statistical analyses show no significant changes in stable isotopes nor trace elements as a result of ash bed deposition nor the Crow Creek Member depositional event. Results also indicate that variability of the coastal brackish marine system made any significant trends harder to isolate on such a small scale. Overall &delta;¹³C_org signatures ( -27 to -26 &permil;) indicate that the Cretaceous Interior Seaway was deposited in a brackish shallow marine environment and that there were no drastic changes in sea level throughout the deposition of the Pierre Shale Group that was sampled (Gregory Member up through Virgin Creek Member). The &delta;<p style="font-variant: small-caps">15</p>N data range (-6 to +1 &permil;) show that fixed nitrogen was scarce during the deposition of the Pierre Shale and that most of the available marine nitrogen was likely fixed by cyanobacteria.</p>