Pedogenic Carbonate in Soils of the Isaacks' Ranch Surface, Southern New Mexico

Pedogenic carbonate has potential as a chronological tool for vast areas of arid and semiarid regions. However, much more work is needed on variations in carbonate accumulation in soils of the same age. A long gully and study trench in southern New Mexico provide continuous exposures of soils of a drainageway and ridge of Isaacks' Ranch age (8000–15 000 yr). A fine‐loamy Typic Haplargid in the drainageway has a Stage II carbonate horizon and 108 kg/m 2 of carbonate. Two coarse‐loamy Typic Haplargids of the ridge side have Stage II carbonate horizons and 78 and 97 kg/m 2 of carbonate, distinctly less than for the soil of the drainageway. The difference is attributed to finer texture (which would slow the wetting fronts) in the drainageway, and more water there for movement of carbonate into the soil. At the ridge crest, a facies change from coarse‐loamy to sandy materials caused a change from Stage II nodules to Stage I coatings on grains. In the sandy materials, a Typic Torripsamment has 22 kg/m 2 of carbonate. In the coarse‐loamy materials, a Typic Torriorthent has 60 kg/m 2 of carbonate; the coarse‐loamy materials must have captured carbonate that moved to greater depths in the Torripsamment. Although the totals obtained must be considered estimates, they indicate that the amount of pedogenic carbonate in Isaacks' Ranch soils may range up to fivefold, that landscape position is an important factor in this range, and that texture of the parent materials can have a major effect on the amount of carbonate in soils of a given age regardless of landscape position.