Evolution of Geochemical Processes in Soils on Elevated Marine Terraces in Coastal Oregon

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Flights of elevated marine terraces near Cape Blanco, Oregon, have soil chronosequences that include, from youngest to oldest, Andisols, Spodosols, bisequal soils (Spodosols/Ultisols), and Ultisols. The goal of the project is to determine the evolution of geochemical processes in these soils. Quantitative changes in soil constituents over time will be determined from the geochemical mass-balance approach and measurements of particle-size distribution, bulk density, extractable Fe, Al, Si, and C, exchangeable bases and acidity, and total elemental analysis (NAA and XFA). Thermodynamic stability indices will be estimated from soil mineralogical data (petrography and XDA) and aqueous solution- chemistry data (pH, redox potential, Fe, Al, Si, DOC, DIC in bulk precipitation, canopy throughfall, and soil solutions collected) using the GEOCHEM chemical-equilibrium model. The geochemical mass balances and modeling will be used to test hypotheses regarding the origin of the parent materials (aeolian deposition vs. weathering of beach sediments. Soil-forming processes will be elucidated from the forementioned data and microscopic analyses (soil micromorphology and SEM) of diagnostic soil features (melanic epipedons, placic and ortstein horizons, and argillic horizons).