Organic geochemical approaches to identifying formation processes for middens and charcoal-rich features

Abstract Charcoal is an important component of archaeological sites that can yield fundamental information useful in understanding past human activities. We applied a suite of organic geochemical tools to identify and quantify anthropogenic molecular charcoal fragments in an archaeological site in Panola County, N Texas to determine the provenance of a buried melanic horizon. The site is a small Middle-Late Caddo occupation inhabited principally between ca. 1450 and 1600 AD. We tested three molecular techniques to determine their ability to constrain site formation processes: solid state 13 C nuclear magnetic resonance spectroscopy (NMR), lignin free phenols and lignin oxidation products (LOPs) and anhydrosugar analysis. We demonstrated that, in conjunction, the three afforded the identification and quantification of anthropogenic molecular charcoal fragments at this archaeological site. The approach allowed reconstruction of the fire history and vegetation type around the site during the occupation period. The NMR and anhydrosugar analysis pointed to temperature conditions associated with thermal refuse in different contexts. In particular, geochemical signatures in a smudge pit indicated a higher combustion temperature than for the charcoals in the other paleosol samples, suggesting multiple fire uses. The data also showed differential persistence of fire signals in environmental samples, likely as a result of differential decomposition rate and solubility, which may lead to heterogeneous fates of different forms of pyrogenic C in the environment. The techniques expand the tool kit available to archaeologists and soil scientists in detecting the human footprint in soil formation, especially in warm, humid climates where decomposition is rapid.