Experiments in Late Archaic methods of heat-treating Ogallala Formation quartzarenite clasts along the Southern High Plains eastern escarpment of Texas

Abstract

World-wide, flintknappers typically reduced clasts into smaller packages (e.g., bifaces, flake blanks, preforms) prior to heat-treatment. Research along the eastern escarpment of the Southern High Plains of Texas (USA) uncovered evidence of a Late Archaic (4500–2000 radiocarbon years B.P.) industry that heat-treated whole Ogallala Formation quartzarenite clasts rather than smaller lithic packages. A series of controlled and outdoor replicative experiments were conducted to ascertain the temperature range and time necessary to heat-treat quartzarenite clasts effectively, and the possible techniques used to heat-treat whole clasts without thermal shock. Roughness (Ra) and color change (R/L) were measured to quantify the results of heat-treatment.Results indicate that a minimum temperature range of 246–273°C (475–525°F) is necessary to heat-treat quartzarenite clasts. Successful heat-treatment requires placing the clasts directly on coals to achieve the necessary temperatures for heat-treatment. Avoidance of thermal shock requires that the temperature of the clasts be raised gradually. This procedure involves incrementally moving the clasts closer to the coals before directly placing the clasts on the coals. Heat-treatment results in a significant decrease in roughness (Ra) and moderate increase in cortical and interior redness. This study demonstrates that preparing smaller lithic packages for heat-treatment is not always necessary, and provides new insights into the process of heat-treatment.