Structural Characterization of Charcoal Exposed to High and Low pH: Implications for 14C Sample Preparation and Charcoal Preservation

摘要: Chemical and structural similarities between poorly preserved charcoal its contaminants, as well low radiocarbon concentrations in old samples, complicate 14C age determinations. Here, we characterize 4 fossil samples from the late Middle Paleolithic early Upper strata of Kebara Cave, Israel, with respect to chemical changes that occur when they are subjected acid-base-acid (ABA) treatment. Differential thermal analysis TEM show acid treatment disrupts structure, whereas alkali results reformation molecular aggregates. The major ascribed formation salt bridges at high pH disruption graphite-like crystallites low pH. Weight losses during treatments consistently greater for older implying less preserved. Based on observed vitro due fluctuations, various methods removing contamination, a mechanism preferential preservation nature, proposed.