Eolian dust as a factor in soil development on the Pajarito Plateau, Los Alamos area, northern New Mexico
Paul O. Eberly, Leslie D. McFadden, and Paula Muir Watt
Soils atop the Pajarito Plateau in northern New Mexico are variable with respect to degree of development and profile characteristics. This study focuses on the impact of eolian dust in the development of a clay-rich soil on the Bandelier Tuff. A constitutive mass-balance (CMB) model was used to assess the impact of dust accumulation. To identify an immobile constituent for use as a strain indicator, isoconcentration (isocon) plots were constructed for each illuvial B horizon and for the subjacent R horizon. The isocon plots suggest that Zr and Al are immobile in the solum. These constituents are, however, likely to be present in dust and so, if dust is a factor, are not immobile. The overall compositional similarity of the parent Bandelier Tuff to the continental crust makes it difficult to identify admixed dusts via the isocon method. To resolve this problem, Gresens-type equations (twocomponent mixing models) for a pair of constituents thought to be refractory with respect to chemical weathering, viz., Ti and Zr, were simultaneously solved for the dust fraction present in the illuvial B and R horizons. Compositional data for a post-Archean shale composite were assumed to represent eolian dust. Calculated dust fractions are consistent with the results of particle-size distribution analyses and decline with depth in the study soil. The calculated dust fractions permit correction of the measured Zr level and use of Zr as a strain indicator. The dust-corrected CMB model indicates that dust incorporation is a major component of soil development on the Pajarito Plateau and that Si and alkali removals are more closely balanced and Al, Fe, Ti, Zr, Ca, Sr and Ba are more enriched by eolian addition than indicated by the uncorrected CMB model. The modeling exercise shows that the study soil is not the result of processes associated with production of spodic horizons. Moreover, soil-forming processes at this location seem to reflect the long-term effects of semi-arid to sub-humid climates.
- Eberly, Paul O.; McFadden, Leslie D.; Watt, Paula Muir, 1996, Eolian dust as a factor in soil development on the Pajarito Plateau, Los Alamos area, northern New Mexico, in: The Jemez Mountains Region, Goff, Fraser; Kues, Barry S.; Rogers, Margaret Ann; McFadden, Les D.; Gardner, Jamie N., New Mexico Geological Society, Guidebook, 47th Field Conference, pp. 383-389.