ABSTRACT

The Wilds and Lower Nichols sands at the Mary T. Smith et al. No. 1 well in Concordia Parish are subsurface stratigraphic units within the Paleocene Wilcox Holly Springs delta complex of east central Louisiana and southwest Mississippi. Electric-log responses and core data produced from thin sections, foraminiferal assemblages, and X-radiographs are used to analyze and to interpret the petrology, paleontology, and paleoenvironments of this deltaic sequence.

Both the Wilds and Lower Nichols range from fine- to very fine-grained sand and coarse silt interbedded with or as irregular laminations in illite-kaolinite shale; however, the Wilds Sand is somewhat coarser grained and better sorted than the Lower Nichols. The Wilds ranges from a lithic subarkose to a lithic arenite; the Lower Nichols is a lithic arenite. Cement for these units is silica that was probably released during burial diagenesis of interbedded and subjacent clays. Quartz grains show textual inversions that indicate a mixing of primary source and recycled older mature sandstone materials. Plagioclase and K-spar, as well as abundant polycrystalline quartz and metamorphic rock fragments, indicate crystalline source terranes. The most likely crystalline source area for these Louisiana Wilcox deposits is the Southern Appalachians.

The Wilds Sand paleoenvironment represents a distributary channel that prograded into the Paleocene northern Gulf of Mexico. The overlying Lower Nichols sedimentary sequence records a series of hyposaline bayfill paleoenvironments punctuated by periodic influxes of sediment. Lower Nichols paleoenvironments range from saltwater-influenced outer bays to freshwater-influenced inner bays.