UNDERSTANDING THE ORIGIN AND PALEOCLIMATE IMPLICATIONS OF PALEOSOLS FROM THE BLACKWATER DRAW FORMATION IN BUSHLAND PLAYA NEAR AMARILLO, TX

The Blackwater Draw Formation is a series of stacked paleosols formed as a result of repetitious periods of aeolian deposition followed by landscape stability and pedogenesis. The accumulation of the Blackwater Draw Formation is coeval with the Mid-Pleistocene Transition and, therefore, likely records climate and environmental changes across this time period. This study aims to build a comprehensive pedogenetic framework of paleosols using clay mineralogy and geochemistry as well as K-Ar ages of illite. Further on, it will shed light on sediment provenance and provide information on the dynamics of pedogenesis in the context of evolving paleoenvironmental and paleoclimatic conditions.

Soil clay minerals are highly susceptible to changes in environmental and climatic conditions. The clay mineral speciation and their geochemical and morphological variability can, therefore, be used to infer on the condition of clay formation, which in turn serves as an indicator of paleoclimate.

This research examines the entire 14 m of profile of the Blackwater Draw Formation, which was cored in the vicinity of Amarillo in Northern Texas. Representative samples were taken from 18 locations throughout the entire length of the core and were analyzed by X-ray diffraction, laser ablation inductively coupled plasma mass spectrometry, and X-ray fluorescence. Our preliminary results show firm evidences of pedogenesis, most notably being the formation of multiple generations of illite-smectite characterized by variable amounts of smectite component. Geochemical correlations of transitional metals (e.g. Mn, Fe, Co, V, and Cr) are indicative for the emergence of the peculiar pedogenetic features like Fe-Mn nodules, which is subject to further microbeam investigation. We hypothesize that the clay mineralogy of the core is susceptible to the sediment cyclic deposition and ensuing pedogenesis in the context of the prevailing climatic conditions, which is corroborated by our preliminary data showing a relatively good correlation between the geochemical index of alteration (CCPI) and abundance of smectite component in I-S.