CARBONATE STABLE ISOTOPES FROM SOIL CORES FROM PLAYA LAKES, SOUTHERN HIGH PLAINS, TEXAS

The Southern High Plains is a large plateau that experiences little net erosion and contains numerous playa. These playas are particularly useful in recovering paleoclimate information because of their sensitivity to changes in the precipitation and temperature due to their transitory nature and small size. Here we present isotopic data from soil carbonate recovered from buried soils within core samples from playa lakes on the Southern High Plains.

Two to three buried soils were recognized in four cores recovered from playas in Bailey and Floyd Counties. The oldest buried soil is an aridisol estimated between 30-40 ky. The second buried soil is an inceptisol estimated around 21 ky. The third buried soil is characterized as a mollisol and estimated at 11 ky. The top of the cores represents the modern mollisol common in the region.

Cores were sampled at 10 cm intervals for CaCO₃ contents and stable isotope analyses. The percentage of CaCO₃ varied throughout core samples from 0.01% to 1.0% to greater than 5.0% dependent upon the specific soil horizon. Inorganic oxygen isotopes from the Bailey Playa cores show a broad range from -4 to -13‰ whereas the Floyd Playa data ranges from -4 to -9‰. The large ranges in δ¹⁸O values from individual soil horizons indicate that the soil carbonates did not form under uniform climatic conditions, but rather indicate varying meteoric water influence. δ¹³C values of soil carbonate range from an average of -6.5‰ at the bottom of the cores to -21.1‰ in the first buried mollisol soil, such that each individual paleosol provides a lower average value than the paleosol below. This decreasing upward trend in the δ¹³C values can be explained as an increase in contribution of carbonate from organic sources rather than atmospheric CO₂. We relate this trend to an increase in vegetation through time resulting from a decrease in aridity upward as shown by the soil progression of aridisol—inceptisol—mollisol.