Browsing by Author "Dr. Elana Leithold, Committee Chair"

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    Clay Mineralogy and Organic Carbon Associations in Two Adjacent Watersheds, New Zealand
    (2007-12-07) Lloyd, Kristen Helen; Dr. Neal Blair, Committee Member; Dr. Elana Leithold, Committee Chair; Dr. Dean Hesterberg, Committee Member
    Research conducted on the Waipaoa and Waiapu Rivers on the North Island of New Zealand has recognized and characterized geomorphologic and geochemical processes responsible for the control and delivery of sediment and associated OC to the adjacent margin. Clay mineral compositions from specimens of bedrock, volcanic soils and tephras, suspended river sediment, and recent marine sediments were studied. Identification of the clay minerals was made chiefly by X-ray (XRD), infrared (FTIR), and selective mineral dissolution analyses. Geochemical analyses included organic carbon (OC) concentrations and stable carbon isotopic compositions. Characteristic clay minerals indicative of bedrock contributions include chlorite and illite. Smectite and kaolinite are also present but in lesser quantities. Soil and tephra mineralogy could not be as easily quantified from x-ray diffraction due to the presence of poorly crystalline minerals (i.e. allophane). FTIR spectrometry proved to be a beneficial tool for the identification of clay minerals in the soil. Allophane and the higher concentration of smectite signify material being derived from the soils and tephra. Suspended sediment samples collected during moderate to high river flows exhibited a mixed clay mineral composition derived from both bedrock and soil. Within the Waiapu River, bedrock contributions appeared to be greater due to gullying being the more dominant geomorphologic process. The Waipaoa River showed soil contributions to be as important as rock contributions. Recent marine sediments off the Waiapu River were similar in composition to the suspended Waiapu River sediment. Spatial variability in clay mineralogy associated with cross shelf transport reveal chlorite increases at the expense of illite off the Waiapu shelf. A downcore study was conducted on the Waipaoa shelf to examine temporal variability. The sediments in the flood layer and below resemble the river suspension, with smectite being the dominant clay mineral. The presence of allophane in the flood layers suggests a greater contribution from the soil and subsequent rapid burial. The mineralogy of the top layer resembles that seen in the Waiapu, with illite being the dominant clay. After the clay mineralogy was established, geochemistry was employed to examine contributions from the sources of particulates being delivered to the margin. However, due to the wide range of results, overlap between characteristic isotopic signatures of the sources prevented the successful application of this method. %OC illustrates the mixing of ancient and modern carbon in the rivers and bulk %OC of the rivers is roughly two times greater than the %OC from the rocks. XRD and FTIR results are consistent with and further confirm the mixing of rock and soil particulates in both margins.
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    Use of Stable Isotopes and GIS Modeling to Study Late Pleistocene to Holocene Environmental Change in the Waipaoa Sedimentary System, New Zealand
    (2009-08-10) Childress, Laurel; Dr. Christopher Osburn, Committee Member; Dr. David DeMaster, Committee Member; Dr. Helena Mitasova, Committee Member; Dr. Elana Leithold, Committee Chair
    The source to sink investigation of complex sedimentary systems necessitates chemical (stable isotope and elemental) and physical (modeling) analyses to elucidate temporal changes in volume and provenance of sediment supply. The stable isotopic composition of organic matter in continental margin sediments provides a useful, long-term record of environmental change. The Waipaoa River watershed, New Zealand, represents a system of interest due to its location on an active margin, very large sediment supply, and well known, relatively recent history of anthropogenic disturbance. Radiocarbon measurements of three continental shelf cores taken aboard the RV Marion Dufresne in January 2006 offshore from the river mouth suggest a record extending into the late Pleistocene, dating as far back as 14,000 years. Geographic information systems (GIS) modeling suggests large increases in erosion with reduction in landcover due to natural volcanic events and anthropogenic disturbances. Carbon and nitrogen isotope analyses of terrestrial sources including soil profiles, sedimentary rocks and riverine sediments from within the watershed suggest terrestrial processes such as shoreline progradation, hillslope erosion and gully incision, volcanic eruptions, and the capture of river tributaries are possibly influencing isotopic ratios and impacting the marine stratigraphic record. Unique isotopic signatures of soil profiles from disparate areas of the watershed could explain some isotopic variation seen in the cores as deviation in delivery volume from certain tributaries. Within the marine record in all three cores exists a distinct excursion of carbon isotopes to more positive values. Possible explanations for this include: 1) an increase in the flux of an isotopically heavy terrestrial fraction from the erosion of kerogen and 2) a decrease in the proportion of terrestrial organic matter due to dilution of river sediments with volcanic ash. Increasing nitrogen isotope values also within the excursion could suggest an increase in marine organic matter, however this could be the result of increased input of degraded refractory terrigenous organic matter or contributions of inorganic nitrogen.