PETROLOGY OF THE MEMPHIS SAND (EOCENE) IN THE NORTHERN MISSISSIPPI EMBAYMENT

We report here the results of a study of the petrology of the Memphis (Aquifer) Sand as part of a larger investigation of its stratigraphic variability in the Northern Mississippi Embayment. Results and interpretation are based on observation and sample collection at six exposures and samples collected from three wells. Based on point count analysis of 20 thin sections the Memphis Sand is a fine to coarse grained quartz arenite with visible intergranular porosity of about 30%. Polycrystalline quartz grains (metamorphic?) are more common to the northeast in the embayment. Grain size (sieved disaggregated samples) varied from 0.8 mm (coarse sand) in the northeast to 0.2 mm (fine sand) to the south and west. Cement is absent. Clay matrix exceeds 5% at only one location, that location is in the northeast where matrix is 19%. Matrix is secondary kaolinite with meniscus (vadose zone) texture. The mineralogy of associated clay units undergoes a transition from kaolinite in north Tennessee through mixed kaolinite/smectite to smectite dominated in north Mississippi. Lignite deposits are present throughout the study area. Glauconite is reported by others south of the Tennessee-Mississippi border. Our findings are consistent with a source area to the northeast of the embayment, deposition in a fluvial environment in Tennessee and northeast Arkansas, transitioning to mixed marine-nonmarine in north Mississippi and southeast Arkansas.