Alkali extraction of archaeological and geological charcoal: evidence for diagenetic degradation and formation of humic acids

Ascough, Philippa L., Bird, Michael I., Francis, S.M., and Lebl, T (2011) Alkali extraction of archaeological and geological charcoal: evidence for diagenetic degradation and formation of humic acids. Journal of Archaeological Science, 38 (1). pp. 69-78.

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Charcoal forms a crucial source of archaeological and palaeoenvironmental data, providing a record of cultural activities, past climatic conditions and a means of chronological control via radiocarbon (14C) dating. Key to this is the perceived resistance of charcoal to post-depositional alteration, however recent research has highlighted the possibility for alteration and degradation of charcoal in the environment. An important aspect of such diagenesis is the potential for addition of exogenous “humic acids’ (HAs), to affect the accuracy of archaeological and palaeoenvironmental reconstructions based upon chemical analyses of HA-containing charcoal. However the release of significant quantities of HA from apparently pristine charcoals raises the question whether some HA could be derived via diagenetic alteration of charcoal itself. Here we address this question through comparison of freshly produced charcoal with samples from archaeological and geological sites exposed to environmental conditions for millennia using elemental (C/H/O) and isotopic (δ13C) measurements, Fourier Transform Infrared Spectroscopy (FTIR) and proton Liquid-State Nuclear Magnetic Resonance (1H NMR). The results of analyses show that the presence of highly carboxylated and aromatic alkali-extractable HA in charcoal from depositional environments can often be attributable to the effects of post-depositional processes, and that these substances can represent the products of post-depositional diagenetic alteration in charcoal.

Item ID: 11903
Item Type: Article (Research - C1)
ISSN: 1095-9238
Keywords: charcoal; humic acid; oxidative degradation; radiocarbon
Date Deposited: 15 Sep 2010 23:44
FoR Codes: 21 HISTORY AND ARCHAEOLOGY > 2101 Archaeology > 210102 Archaeological Science @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970105 Expanding Knowledge in the Environmental Sciences @ 50%
97 EXPANDING KNOWLEDGE > 970121 Expanding Knowledge in History and Archaeology @ 50%
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