Parent Materials of Alabama Blackland Prairie Vertisols.

Alkaline soils (predominately Vertisols) in the Blackland Prairie region of Alabama largely develop from Cretaceous-aged chalk, while proximate acidic Vertisols are believed to have developed from acidic clayey sediments, possibly from the Eocene epoch. However, evidence suggests the more acidic soils may have developed in place (residuum) or from sediments locally deposited after weathering. Considering acid, residual soils have developed over calcareous parent materials in humid environments in several other settings, the potential exists for a residual weathering genesis of these acid Vertisols. The relatively high non-calcareous residues of these Selma chalks (typically 50 to 60% CaCO₃) may further promote a weathering hypothesis. Identification of lithologic discontinuities can provide information about parent materials, landform stability, and soil genesis. The objectives include investigation of soil-parent material relationships and evaluation of the degree of parent material uniformity for improved understanding of pedogenesis of Alabama Blackland Prairie Vertisols. Replications of alkaline (Sumter- Rendollic Eutrudept and Okolona- Oxyaquic Hapludert) and acidic soils (Vaiden- Aquic Dystrudert and Oktibbeha- Chromic Dystrudert) were sampled to chalk. Particle size analysis was conducted for depth trends and fractionation was utilized to isolate separates for detailed mineralogical and elemental analyses.  Coarse silt and sand fractions were digested using lithium metaborate fusion, and concentrations of Sr, Ti, Y, Zr, and rare earth elements (La to Lu) were measured. Calcium carbonate was quantified using thermogravimetric analyses, and clay separates were analyzed using X-ray diffraction. Soil-parent material relationships will be evaluated using elemental, mineralogical and grain size data.