A geological and sedimentological approach to inferring paleoclimate from buried soils within playa fills, southern high plains, Texas
MetadataShow full item record
Paleoclimate can be used as a frame work for predicting variability and thresholds of future climate change. The small size and ephemeral nature of inundation make playa wetlands highly sensitive to climatic fluctuations and consequently playas may be able to provide a high resolution terrestrial archive of paleoclimate (Bowen and Johnson, 2012). Holliday et al., (1996) study playa wetlands on the Southern High Plains which are contemporaneous with the Blackwater Draw Formation. The multiple buried soil profiles observed in these playas may extend back 1.6 million years, giving them the potential to be utilized as quaternary climate proxies. Previous studies that use playa lake sediments as a paleoclimate proxy (Bowen and Johnson, 2012, Holliday et al., 2008, Holliday et al., 1996) focus on carbon dating, stratigraphy and analysis of soil profiles. Paleosols preserved in continental settings may be able to provide a long term, continuous climatic record, equal in resolution to marine isotope records (Retallack, 2007), especially under aggradational conditions. Paleosols form at the Earth’s surface in direct contact with the atmosphere, giving them potential as one of the most powerful tools in paleoclimate interpretation (Sheldon and Tabor, 2009). Sheldon and Tabor (2009) summarize whole-rock geochemistry methods to study paleosols in a range of depositional setting. Geochemical ratios and trends observed within major oxides and selected trace elements indicate pedogenic processes in paleosols such as, weathering, leaching and illuviation that are largely climatically driven (Sheldon & Tabor, 2009). Whole-rock geochemistry is interchangeable between paleosols and modern soils allowing comparative studies and inferences to be made regarding the conditions under which paleosols formed (Dreise et al., 2005). The aim of this study is to determine whether the well-established geochemical methods of paleosol analysis as described by Sheldon and Tabor (2009) can be successfully applied to the buried soil profiles of playa wetlands, an area where this type of study has not been previously explored. The objective is to apply these methods to data collected from playa wetlands on the Southern High Plains to; · Assess the degree of weathering within the buried soil profiles. · Assess the grain size distribution within the soil profile. · Assess the variability in buried soil profiles between the playa floor and playa edge. · Asses the variability in buried soil profiles between the eastern and western margins of the Southern High Plains. Comparisons between our finding and the findings of others working in the same area which date their sediments e.g. Bowen and Johnson (2012, Holliday et al., (2008) and Holliday et al., (1996) can be used to determine if the whole-rock geochemistry of playa sediment can be used as a viable proxy for interpreting quaternary climate on the Southern High Plains. Absolute age control of the cores was not assessed; however, we utilize grain size distribution data in comparison with the well-established northerly fining trend observed in the Blackwater Draw Formation to assess reworking and thus, a relatively younger age. Results indicate that buried soils grain size distributions are inconsistent with the range expected within the Blackwater Draw Formation, thus we infer that these paleosols were developed on reworked Blackwater Draw Formation sediments, and thus younger than ~ 40,000 years. Furthermore, C14 dates from nearby playas are used to bolster the grain size comparison trends and suggest that the buried soils analyzed range from ~11-20 ky. The cores were obtained from the center and edge of two playas in Texas, one located in Floyd County, which is on the edge of the eastern escarpment and the other from Bailey County, which is further to the west (Fig 1.0). The cores crossed between two and three buried soil profiles. Samples were obtained from each core at 100 mm intervals for analysis. For each sample data on grain size, major elements (Wt %) and minor elements (PPM) was collected. This data was plotted against depth and trends were analyzed to infer the boundaries of the buried surfaces and different horizons within the buried soil profiles. To determine the degree of weathering within each profile ratios of mobile versus immobile elements were plotted against depth. The pedogenic processes that we attribute as the cause, of the physical and geochemical properties within our core, can be compared with modern pedogenic processes resulting in similar characteristics to infer climatic conditions at the time of their formation.