WHOLE-ROCK GEOCHEMICAL CLIMATE SIGNATURES OF PALEOSOLS RECOVERED FROM PLAYA CORES, SOUTHERN HIGH PLAINS, TEXAS

The Southern High Plains (SHP) is a large plateau with ubiquitous playas accumulating sediment with little to no erosion for the past 1.6 Ma. The small size and ephemeral nature of playas make them sensitive to climatic fluctuations and often record high resolution archives. To date, climatic studies on the SHP largely pursued pedogenic, sedimentologic and/or isotopic data sets. Here we present whole-rock geochemical climatic signatures as a new paleoclimate proxy for future playa studies on the SHP. Many whole-rock geochemical ratios within soil horizons are largely driven by pedogenic processes. Moreover, whole-rock geochemical signatures are interchangeable between many modern soils and paleosols.

Four cores (up to 4.5 m deep) were recovered from two playas on the eastern half of the SHP (Bailey County Playa) and the western margin of the SHP (Floyd County Playa). 2-3 buried paleosols (~1-1.5 m thick) were recognized within each core by traditional observational techniques. Each core shows an upward progression of buried soil type from aridisol (30-40 kyBP), to inceptisol (~21 kyBP), to mollisol (~11 kyBP) representing a decrease in aridity. Whole-rock geochemical proxies largely follow this progression and indicate much higher CaO and salinized zones in the lower paleosols and an increase in leached or illuviated zones in higher paleosols. Thus, pedogenic processes observed through traditional observation methods and geochemical data sets agree.

Using empirically derived equations that utilize whole-rock geochemical data, precipitation and mean annual temperature increased upward in paleosols from ~275 mm/yr to 440 mm/yr (SE ± 147 mm/yr) and from ~ 12 to 16°C (SE ±0.6°C). Modern precipitation levels range from 330-450 mm/yr and mean annual temperature is 18.6°C. Thus, from the oldest paleosol to the present, these data sets indicate that precipitation increased by 50-175 mm/yr while mean annual temperature increased by ~6°C. Our age model utilizes previous published radiocarbon dates from nearby playas and suggests temperature has steadily increased during soil forming events for the past ~30 ky, whereas precipitation largely increased between 21ky and 11ky soil forming episodes. These results are similar to coeval temperature and precipitation changes estimated elsewhere on the Great Plains.