Eolian Contribution to Soil Weathering and Pedogenesis in the San Francisco Volcanic Field, AZ
AuthorFolk, Cody Duane
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PublisherThe University of Arizona.
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AbstractThe Colorado Plateau offers a unique window to document pedogenic processes in a semiarid environment. We analyzed soil samples collected from a three million-year chronosequence of basalt flows in the San Francisco Volcanic Field near Flagstaff, Arizona. We hypothesized that eolian inputs provide a significant amount of material to the soil and largely control chemical weathering and soil formation processes. We quantified chemical, elemental, mineralogical, and physical characteristics of the soils. Results demonstrated distinct time trends in soil properties, with observed decreases in pH of 8.1 to 7.8, of total elemental Ti:Zr from 53:1 to 25:1, of total elemental Fe from 7.6% to 2.7%, and in the relative fraction of poorly crystalline to crystalline Fe-oxyhydroxides (FeO:FeD) from 0.44% to 0.31%. In contrast, the data indicated an increase in average clay content from 14% to 56% and an increase in the amount of pedogenic Fe-oxyhydroxides relative to total elemental Fe (FeD:FeT) from 0.36% to 1.18% with time. The mineral assemblage and geochemical signature of soils indicated increasing contribution of dust to the mineral fraction with increasing age, with the oldest site estimated to be nearly 100% eolian derived in the upper 50 cm. The combined data document a clear role for dust control on pedogenesis across this semiarid chronosequence.
Degree ProgramGraduate College
Soil, Water & Environmental Science