CARBONATE STAGES IN SANDY SOILS OF THE LEASBURG SURFACE, SOUTHERN NEW MEXICO

Abstract

Stages of carbonate accumulation are major indicators of soil age in many soils of arid and semiarid regions. The total amount of carbonate in these soils also has potential as a valuable tool for estimating the actual ages of specific soils and their landscapes. However, much more work is needed on factors that can affect the amount and distribution of carbonate in soils of the same age. A roadcut across a ridge in southern New Mexico exposed both stages I and II carbonate in soils of the Leasburg surface (early Holocene-latest Pleistocene). On the ridge crest, most soils have a stage I carbonate horizon characterized by faint coatings on grains. A ridge-crest Torripsamment in Leasburg sediments has a total of 28 kg/m2 of pedogenic carbonate. On ridge sides, the steeper slopes have increased runoff, thus lifting the wetting fronts and the zone of carbonate accumulation, and most soils have a nodular stage II carbonate horizon. Although the ridge sides must be younger than the crest, they are thought to be only slightly younger because the stage II horizon is typical of Leasburg soils in nongravelly materials. A ridgeside Torriorthent in Leasburg sediments has a total of 46 kg/m2 of carbonate. Thus in sandy soils of stable ridge crests, some carbonate apparently moves to substantial depths, causing anomalously low totals of carbonate for the soils concerned. For this reason, in chronological studies involving carbonate in sandy soils, long and deep exposures are required for a proper assessment of the stage of carbonate accumulation and the total amount of illuvial carbonate associated with soil development. Because a buried soil may be present, carbonate in the horizons concerned was not included in the totals of pedogenic carbonate, and the reported totals are, therefore, minimum values for soils of the Leasburg surface.