AN UNDERGRADUATE RESEARCH PROJECT ASSESSING PETROGRAPHIC AND GEOCHEMICAL CHARACTERISTICS OF LITHIC MATERIALS FROM SOUTHERN ALABAMA ARCHAEOLOGICAL SITES

Several distinct varieties of chert and other materials used by Paleolithic Indians to manufacture lithic tools are found in southern Alabama. Undergraduate students have targeted three of the most ubiquitous materials and are attempting to resolve them on the basis of petrographic and geochemical criteria. Tallahatta Sandstone is a light gray quartz arenite with a distinct snow-flake pattern. It was one of the most common lithic materials used by Paleolithic Indians in southern Alabama and Tallahatta artifacts are widely distributed across this region. Tallahatta Sandstone is composed of well-sorted, medium grained quartz sand that is well indurated by weakly luminescent, multigenerational phases of opal CT, chalcedony and drusy quartz cement. The snowflake pattern is caused by patchy distribution of chert cement. Tallahatta Agate is a seam material that is interbedded within Tallahatta Sandstone in southwestern Alabama . It varies in color (amber-red-blue), but is predominantly composed of cryptocrystalline quartz. Drusy quartz-filled voids and silica-replaced shells are common components in the agate and support a silicified limestone origin of this lithic material. Like its quartz arenite counterpart, Tallahatta Agate is only weakly luminescent. Coastal Plain Chert is distributed in southeastern Alabama within a region mapped as “residuum” by the Geological Survey of Alabama, but sedimentological and paleontological characteristics suggest that the chert is being sourced from limestone units in the Jackson Group. Coastal Plain Chert is composed of variably limonite-stained, weakly to moderately luminescent cryptocrystalline chert. That the chert formed through replacement of a former fossiliferous limestone by silica is clearly evident in thin section as “ghost fossils” (most commonly foraminifera), are present in most specimens examined in this study. Larger void space and pores within Coastal Plain Chert are filled by drusy, non-luminescent quartz cement.