D. Douglass, J.G. Bockheim*, D.M. Mickelson, B. Singer, and M. Kaplan

Thirty-four pedons on 12 moraines (4 moraine groups), were examined in Santa Cruz province, Argentina. Ages of the four moraine groups are 16-24, 110-185, 200-760, and 760-1016 ka based on cosmogenic surface exposure dates and stratigraphic relationships to 40Ar/39Ar dated basalt flows. The soils are classified primarily as Calcic Haploxerolls and occur under short grass steppe with about 200 mm yr-1 precipitation on glacial sediments derived from igneous and metamorphic rocks of the Andean Cordillera. The dominant soil-forming processes are melanization (accumulation of organic matter) and calcification (accumulation of secondary carbonates). Based on limited sampling, dust in Patagonia is enriched in organic carbon and CaCO3. Age related differences in soil development on moraines were tested with ANOVA and reported at the p <0.05 level. A-horizon organic carbon quantities increase with age (1.3, 1.4, 2.4 and 2.4 kg m-2 for the four groups). The maximum carbonate morphology stage, thickness of the calcic (Bk) horizon, profile development index, and profile accumulation of calcium carbonate (3.3, 16.6, 42.1 and 31.8 kg m-2) increase with age. Rates of carbonate accumulation are similar for the youngest three moraine groups, but much lower for the oldest group (183, 118, and 140 as opposed to 40 g m-2 kyr-1). The implications of these data are: 1) soil OC may be stable in this environment and continue to accumulate in soils over very long time periods, 2) rates of carbonate influx in this area are significant but less that in other semiarid areas, and 3) these rates have been constant for the last few glacial-interglacial cycles, but an equilibrium is approached after ~800kyr.