On the origin and paleoclimate implications of paleosols from the blackwater draw formation at Bushland Playa near Amarillo, TX

Abstract

The Blackwater Draw Formation (BDF) is composed of a series of Quaternary aged, stacked loess- paleosol couplets, that form a relatively thin mantle over the ~120,000 km2 Southern High Plains (SHP) in west Texas and eastern New Mexico. The current geomorphology of the Southern High Plains began to develop around approximately 1.6 Ma as large river systems established themselves, isolating the SHP from surrounding landforms, thus allowing eolian deposition to dominate. This study utilizes clay mineral speciation and variations in mineralogy and geochemistry to construct a pedogenic framework and extrapolate on prevailing paleoclimate conditions during the Quaternary Period from a 14 m core acquired near Amarillo TX. Furthermore, K-Ar dating of detrital and authigenic illite throughout the extent of the core was utilized to determine changes or variations in provenance and paleoclimate. Geochemistry, mineralogy, K-Ar ages of authigenic clay minerals and their speciation indicate the BDF at Bushland is composed of 5 buried paleosols and a surface soil. The formation itself at this locality was further divided into an upper and lower member. The paleosols in the upper member, Paleosol I through IV were deposited under more temperate climatic conditions, while the lower member, composed of Paleosol V, was deposited under more arid conditions. A difference in detrital illite ages and variations in geochemistry indicate a shift or change in sediment input from a secondary provenance.