Soils of the Rio Grande Valley Border in Southern New Mexico

Abstract

AbstractMany kinds of desert soils occur along the border of the Rio Grande Valley in southern New Mexico. These include series in the Torripsamments, Torriorthents, Camborthids, Haplargids, Paleargids, Calciorthids, and Paleorthids. Soil morphology and distribution are related to soil age, texture of parent materials, present and past climate, soil biota, geomorphic surface, and degree of landscape stability. Increase in soil development with age is shown by increasing carbonate accumulation, by increasing silicate clay accumulation in some soils, and by increasing thickness of solum.Radiocarbon ages of buried charcoal show that some soils are of Holocene age while others are much older and started their development at various times in the Pleistocene. Morphology of the Holocene soils indicates present processes of pedogenesis in this desert region. Certain morphological similarities of Holocene soils to those of Pleistocene age also suggest the character of present processes of pedogenesis in soils that started their development in the Pleistocene. The illuviation of carbonate in nearly all soils and the illuviation of silicate clay in some soils are features of pedogenesis at the present time.The argillic horizons have been turncated in many soils along the valley border and in others have been engulfed by carbonate or mixed by soil biota. Horizons of carbonate accumulation in these soils are commonly compact and some are indurated, thus are more resistant to erosion and disruption by soil biota. Development of the horizon of carbonate accumulation is therefore a more reliable indicator of approximate soil age than morphology of the B horizon.Soils discussed in this report have formed in alluvial parent materials derived from noncalcareous rocks, and calcareous dust is virtually the sole source of pedogenic carbonate. Percentages of CaCO3 equivalent for such soils, as determined in the laboratory and controlled by soil morphology, are measures of approximate amounts of dust‐derived illuvial carbonate.