A STRATIGRAPHIC AND GEOCHEMICAL ANALYSIS OF NORTH MISSISSIPPI BAUXITES

There is abundant research pertaining to the bauxites of North Mississippi, yet controversy still exists regarding its genesis, stratigraphic position, and economic value. Detailed research has not been conducted since the 1980s, so we apply newly available technologies to reinterpret exposures of the Paleogene Porters Creek sites in the Midway and Wilcox Groups of Pontotoc and Benton Counties, Mississippi. We will investigate the genesis and associated paleoclimate using X-ray diffraction (XRD), X-ray fluorescence, stable isotope geochemistry, and scanning electron microscopy (SEM). Preliminary results of plotting published XRD data from modern ternary diagrams plot over a wide area, suggesting either a complex history (e.g., sedimentary genesis or multiple generations of bauxites with different origins). Fieldwork has yielded possible rhizoliths, pisoliths, and horizonation (pallid zone), which support a lateritic genesis. We hypothesize that geochemical data, particularly abundances of nickel and chromium as well as percentages of SiO₂, Al₂O₃, and Fe₂O₃, will confirm this in addition to providing information regarding degree of lateritization, potential dismantlement pathways, and protolith. We hypothesize that lanthanum to yttrium ratios of the bauxite will be greater than 1.0, representing a basic environment influenced by adjacent siliciclastic strata. Use of the SEM should reveal the presence of an organic influence during bauxite genesis; we would expect to see this in the form of framboidal pyrite or fossil bacteria, both of which have been absent during early macroscale examinations and the latter of which is unobservable. Additionally, we expect oxygen and hydrogen isotope values to be consistent with subaerial exposure at the regional paleolatitude.