CYCLICITY WITHIN THE PALEOCENE PORTERS CREEK AND NAHEOLA FORMATIONS FROM ARCHIVAL CORE DRILLED IN NORTHERN MISSISSIPPI, USA

Archival core drilled in Benton and Tippah counties, Mississippi, by the Mississippi Mineral Resources Institute, provides the opportunity to observe stratigraphic patterns in the Paleocene Porters Creek and Naheola formations. Study of these units is important for establishing a baseline for regional conditions prior to perturbations caused by Eocene hyperthermals. Initial core descriptions were performed at the Continental Scientific Drilling Facility, University of Minnesota, where measurements and descriptions were completed, and a suite of high-resolution geophysical and geochemical data was collected. This is being paired with ongoing observations of thin sections and X-ray diffraction analyses. Preliminary results from investigations into cyclicity show potential patterns at multiple scales. At the coarsest scale, autocorrelation of magnetic susceptibility data produces a strong peak at a lag position of about 30 m. Additional work is being conducted to determine the cause of this pattern, but trends in magnetic susceptibility appear to indicate changes in proximity of the detrital sediment source as related to sea-level changes or deltaic evolution. At the meter scale, one particular interval with repeated patterns of marginal marine sediment, paleosols, and lignites is interpreted as the result of delta lobe switching. At the centimeter scale, instances of rhythmically bedded claystone alternate between expansive and nonexpansive clay laminae. This is interpreted as the result of salinity-driven seasonal flocculation of clays in a prodelta to proximal shelf setting. Planned X-ray diffraction of clay laminae will allow us to further investigate this interpretation. Additional work will estimate paleoclimate parameters through these sections of the core. For example, application of the chemical index of alteration minus potassium to elemental data from paleosols provides mean annual precipitation estimates between 1350 mm and 1388 mm. Stable isotopes of clay minerals in paleosols will also be explored for reconstructing temperatures of crystallization.