Soil-forming processes on the Pajarito Plateau: Investigation of a soil chronosequence in Rendija Canyon
— Eric V. McDonald, Steven L. Reneau, and Jamie N. Gardner

Soils formed on alluvial terraces in Rendija Canyon, near Los Alamos National Laboratory, provide a stratigraphic framework in which to evaluate time-dependent soil-forming processes. Soils formed on three Holocene terraces, ranging in age from about 0.5 ka to 7.0 ¹⁴C ka, typically have weakly developed Bw horizons that increase in thickness from 20 to >60 cm with increasing soil age. Soils formed on two of the Pleistocene terraces that are >13.8 ¹⁴C ka have moderately to strongly developed Bt horizons that typically increase in thickness from about 150 to 250 cm. The oldest soil formed on a third Pleistocene terrace has been severely truncated by erosion. Many of the soils have been influenced by the subsequent addition of alluvium and/or colluvium. Addition of silt and clay from eolian sediment has probably also occurred. The Soil Development Index was used to provide preliminary numerical comparisons of soil development and to develop a soil chronofunction capable of providing ages for the undated Pleistocene terraces. The resulting soil chronofunction suggests that soils on the two youngest Pleistocene terraces began forming at about 70-80 and 105-180 ka, respectively. Although these age estimates are preliminary and will undergo revision as soil-forming processes on the Pajarito Plateau become better understood, the results of this study are encouraging and indicate the potential for using soils to greatly improve understanding of local geomorphic history.