Clay minerals as Quaternary climate change indicators in the Southern High Plains, West Texas

• In Event: Geosciences: Oral session 1

Abstract

The Southern High Plains in west Texas and eastern New Mexico forms a large plateau that was shaped during the last 2 Ma as the Pecos River incised to the west. Since that incision, the region has been mantled by eolian, both suspended and as sand sheets. Eolian sedimentation was cyclic, such that intervals of aggradation as loess or sand are followed by periods of landscape stability. Loess tops preserve paleosol, thus each cycle is a loess-paleosol couplet. Clay mineral composition of soil largely depends on the climatic conditions existing on land at successive periods of the geological history. The paleosols therefore comprise reliable indicators of paleo-climate. In this work, we performed a fine-scale mineralogical investigation of a 5-m thick profile punctuated by at least three paleosols within the Pleistocene Blackwater Draw Formation exposed near Slaton, Texas. Our data indicate a subtle clay-mineral transformation indicative of changing climatic conditions. XRD mineralogy demonstrated three distinct clay-rich paragenesis. First, the bottom of the section exhibits smectite as a major clay phase with minor kaolinite and illite. Upwards, smectite loses its crystallinity, and is represented by several illite-smectite intermediates (second paragenesis) whilst the remaining clay assemblage is static. Finally, the very top of the section exhibits a complete disappearance of smectite and prevalence of detrital illite and kaolinite. Given a maximum age (1.4 to 2.0 Ma) for the Blackwater Draw Formation, this evolutionary trend of clay minerals fits the progressive cooling in North America with a last glacial maximum set at ~20 ka.

Authors

• Moustapha Diaby, Texas Tech University

• Giovanni Zanoni, Texas Tech University

• Dustin Sweet, Texas Tech University

• Branimir Segvic, Texas Tech University