LINKING SOIL CHRONOSEQUENCE PROPERTIES TO THE PALEOCLIMATE RECORD IN SOUTHERN ARIZONA

Soil chronosequences quantify changes in soil chemical and physical properties over time and are useful tools for understanding local spatial and temporal patterns in soil-landscape evolution. Few past chronosequence studies explore specific relationships between iron content and Aridisols of the Southwestern United States in the context of glacial-interglacial cycling. Here we focus on a series of alluvial fans located on the northeastern flank of the Pinaleno Mountains near Safford, AZ; the alluvial surfaces ranged in age from late Pliocene to late Pleistocene. Color, pH, EC, and organic matter content were measured to understand changes in soil properties with time. We found depth weighted average redness rating increased linearly with time from youngest to oldest surfaces (r² = 0.67), which suggests increased hematite content with age. Further, depth weighted average pH KCl decreased linearly over time (r²= 0.64), indicative of increased chemical weathering. With further analyses, we expect to find that pedogenic iron concentration increases with time, and thus functions as a suitable proxy for soil age and degree of soil development. These results show that soil chronosequences serve as acceptable models for understanding local, geomorphologic and climatic fluxes, and may enable interpretation of the influence of past climate change on soil formation and survival.