Date of Degree
MS (Master of Science)
Elmer A. Bettis
First Committee Member
Second Committee Member
Third Committee Member
Mark K Reagan
Soil development on upland landscapes in east-central Iowa Peoria Loess deposits has been occurring for approximately the last 12,500 years. Weathering zone and pedogenic processes depend on environmental factors such as climate, precipitation, time, parent material, biota, and topography, among others. Analyzing the weathering zones of modern and paleosol profiles provides insight into current and paleo-environmental processes. This study employs several bulk geochemical analytic techniques (XRF, pXRF, LIBS, ICP-MS) to examine the weathering profiles formed in modern Peoria Loess deposits and underlying weathering profiles formed during the Farmdale Interstadial and the Sangamon Interglacial. Results indicate advanced weathering occurred in the paleosol sequences of the Farmdale and Sangamon compared to the modern weathering zone, based on depletion and enrichment of elemental concentrations. The interstadial/last interglacial paleosol weathering profiles exhibit increased depletion in CaO, MgO, Na2O, and K2O compared to the Holocene weathering profile formed in Peoria Loess. Enrichment of CaO and MgO in non-pedogenically altered Peoria Loess deposits is a possible indication of rapid loess accumulation, representing insufficient weathering of deposited material synchronous with deposition. Post-depositional weathering and hydrogeological mechanisms may also account for this mid-profile enrichment, providing for some complexity for interpretation. Regional comparison between three sediment cores - an agricultural field, a restored prairie and a pioneer cemetery - exhibit minor land-use influence on geochemical evolution with the agricultural field core exhibiting greater relative depletion in most oxides in the upper one meter, compared to the other sediment cores. However, slight regional heterogeneity in parent material, vegetation cover, and slope position may also account for geochemical variations. Therefore, it is difficult to conclude how the last 150 years of extensive land-use from human activity has impacted weathering and pedogenesis in this region. Additionally, this study validates using pXRF technology on Quaternary weathering profiles, and documents its technological shortcomings which provides essential information for drawing interpretations from these data.
Soil development is a complex process involving many environmental components. Evaluating the geochemical changes that occur throughout a vertical soil profile is essential for understanding the weathering processes that occur within the soil profile. This study is supported by the Intensively Managed Landscape Critical Zone Observatory (IML-CZO) of the National Science Foundation’s CZO network, which seeks to understand processes acting at the intersection of the geosphere, hydrosphere, biosphere and atmosphere. One common goal of the CZO network is to further our understanding of weathering at the watershed and regional scale as an important component of landscape development. This study seeks to answer these three questions: First, is the use of the technology of portable X-Ray fluorescence (pXRF) a valuable instrument in discerning bulk geochemical variations in a soil profile? How does the modern soil profile weathering zone differ geochemically from a buried paleosol weathering zone in this region? Lastly, do the current land-use practices impact the geochemical trends of the modern soil profile weathering zone? By employing bulk geochemical analyses of multiple sediment cores from the Clear Creek Watershed in east-central Iowa, I aim to identify geochemical differences within and between soil profiles of this region. This study found that using portable analytical technology, pXRF, is conclusively useful for this application because of its versatility, mobility and low-cost. However the results are not as accurate as those of laboratory XRF technology. Concentrations and depletions in elements are considerably different in the paleosol weathering profile, which indicates a period of more intense weathering or more sufficient time for weathering to occur. Lastly, current regional land-use practices appear to have a small influence on the weathering zone chemistry in the top one meter of the modern upland soil profiles. However, future work is needed to determine conclusively.
Chemical weathering, Iowa, Paleoenvironment, Paleosols, pXRF, Quaternary
xi, 138 pages
Includes bibliographical references (pages 81-85).
Copyright © 2017 Kathleen Roselle Goff
Goff, Kathleen Roselle. "Geochemical analysis of weathering zones from Clear Creek watershed: implications for modeling Quaternary landscape evolution." MS (Master of Science) thesis, University of Iowa, 2017.