A soil chronosequence is useful for describing landscapes by quantifying soil development across geomorphic surfaces of varying ages that formed under similar conditions. A chronosequence can be constructed with data from stream terraces because these landscapes have soil profiles that developed under similar soil forming factors (parent material, relief, organisms, as well as climate if studied in a small enough region). This can be used to describe similar soils, and infer their ages, across a landscape. This study describes the development of a soil chronosequence in the Four Mile Creek floodplain that will be used for future surficial geologic mapping. To elucidate the pedogenesis of stream terrace deposits within the Four Mile Creek floodplain, soil samples were collected from excavated backhoe trenches at 10cm intervals throughout the soil profiles. The elemental composition of these soils was determined using X-ray fluorescence (XRF) analysis. It was found that older terraces have greater concentrations of relatively immobile elements, such as iron and titanium, and lower concentrations of the mobile base calcium. Calcium is also distributed more prominently in the top of profiles from younger terraces. If significant erosion or redeposition occurred, the soils may have formed from multiple parent materials. This was tested with titanium-zirconium ratios because if there is a significant change in the ratio within the profile, there is a higher chance that the soil developed from different parent materials. Future work will entail determining soil mineralogy using powder X-ray diffraction (XRD), radiocarbon dating the soil profiles, and expanding the project to include older soils on higher fluvial terraces within the Four Mile Creek floodplain.
Author: Ella Comerford
Faculty Advisor: Jason Rech, Department of Geology & Environmental Earth Science
Graduate Student Advisor: Christina Tenison, Department of Geology & Environmental Earth Science
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