ROLE OF BIOTURBATION IN BURIED PALEOSOL PEDOGENESIS

Brady Soil pedogenesis on the central Great Plains occurred during the Pleistocene-Holocene transition (PHT), forming as a cumulative soil within the uppermost Last Glacial Maximum Peoria Loess and later extinguished by Holocene Bignell Loess accumulation. Excavation of the loess-paleosol sequence has revealed considerable bioturbation by plant roots, invertebrates, and small vertebrates during this time of rapid climate change. Bioturbation was not restricted to a single time period, but rather, occurred continually throughout soil development as evidenced by differing sediment fills and crosscutting relationships, yet distinct communities are temporally defined. Large chamber (~30cm high x 40cm long) and burrow (~6 to 12 cm wide) systems dominate the Ab and upper ABb horizons and are found throughout the soil profile. Size and architecture of these large structures and scratch marks noted on burrow walls suggest that a rodent, such as a prairie dog (Cynomys sp.) or ground squirrel (Spermophilus sp.), is responsible for their construction and possible partial backfill. The lower ABb and Bkb horizons, however, are dominated by extensive, small (~2cm wide), backfilled burrows with distinctive menisci that are assigned to the ichnotaxon Naktodemasis bowni. This burrow morphotype is typically produced by cicada nymphs (Cicadae) or burrower bugs (Cydnidae) in fine-grained sediment. The purpose of this research is to evaluate the degree of bioturbation in the formation of the Brady Soil during the PHT. Pedogenic features produced by faunal and floral activity were differentiated from those produced by abiotic pedologic processes through the use of micromorphology and the identification and classification of granular and spongy microstructures indicative of excrement, calcitic biospheroids, infilling, meniscate backfilling, channel microstructures, and well-oriented clay coatings. Sediment morphology and biosilicate assemblages were used to trace the material to the source sediment location to define localized (shallow mixing) versus nonlocal (deep-mixing) translocation of soil material.