A Chronosequence Study of Soils Developing on Basalt Flows

in an Arid Environment; The Potrillo Volcanic Field,

Doña Ana County, NM

Eppes, Martha Cary, Harrison, Bruce

Earth and Environmental Science Department

New Mexico Institute of Mining and Technology

Socorro, NM 87801

One of the most widely referenced soil-geomorphic studies in the US is the Desert Project, near Las Cruces, New Mexico, in which Gile et al. Defined stages of calcic horizon development in soils of arid environments. Each stage of calcic horizon development incorporates an age range of several thousands of years. To place better age constraints on these stages of development in the desert southwest, soils forming as well dated basalt flow surfaces in the Potrillo Volcanic Field were examined.

Soils were described on four basalt flows (Aden, AD; Afton, AF; and two flows from Little Black Mountain, LBM & LBMX). Surfaces were dated using ⁴⁰Ar/³⁹Ar and He surface dating methods and their ages are: AD, ~20 ka; AF, ~90 ka; LBM, ~188 ka; LBMX >200 ka. Soil development on the surfaces varies according to whether the soil is forming on a high or a low point in the flow topography. Soils developing in low areas (deep soils) where more eolian material has accumulated have cummulic profiles and more apparent development than the soils of higher areas (shallow soils). Deep soils exhibit greater overall variability of soil parameters due to differences in catchment areas. The size of the catchment area determines the rate of dust accumulation. Thus, separate chronofunctions have been derived for deep and shallow soils. Buried soils are present on the AF and LBM surfaces indicating at least two significant changes in the dust flux in this area since ~200 ka. AD and AF soils have overall finer textures than LBM and LBMX soils.

Soil development in the Potrillo Volcanic Field is influenced not only by time, but also by changes in the regional dust flux, topography, and local sand sheet accumulation.