Organic geochemistry of artificially matured conodonts

Organic geochemical methods for conodont analysis have been developed. Coni form elements of the conodont genus Drepanodus from the Ordovician Emanuel Formation and pectiniform elements of the conodont genus Polygnathus from t he Devonian Napier Formation both from the Canning Basin, Australia have be en shown to contain different organic matter. Both conodont samples have be en artificially matured and the structure of organic matter present related to the conodont alteration index (CAI) and maturation temperature (TM). Th e carbon Is X-ray photoelectron spectra (XPS) acquired from both sample set s contain six peaks. These peaks are assigned to highly ordered graphitic l ike carbon (282.9 eV), sp(3) hybridised carbon bonded to only carbon or hyd rogen (284.7 eV), ether (286.1 eV), alcohol (287.0 eV), carbonyl (287.6 eV) and carboxyl (289.0 eV) functional groups. Alkene and aromatic carbon is a lso probably present but is difficult to delineate. During artificial matur ation, XPS analysis monitors the main chemical modifications expressed by t he carbon-oxygen functional groups. The first stage of maturation begins wi th the removal of carboxyl and alcohol groups before a CAI of 2 (TM 450 deg reesC. Between a CAI of 3-6 (TM 450-800 degreesC) an increase of sp 3 hybri dised carbon bonded to only carbon or hydrogen is found, which is accompani ed by a decrease in ether and carbonyl functional groups. From a CAI of 6-7 (TM 800-950 degreesC, sp(3) hybridised carbon bonded to hydrogen or carbon and carbonyl decreases while the development of highly ordered graphitic l ike carbon is observed. The first order laser Raman spectra recorded for bo th sample sets show a low degree of structural order from a CAI of 2-3, and from CAI 4-6 show a progressive increase in structural disorder of conodon t organic matter. The D/G band (band at approximately 1345-1365/band at 161 0 cm(-1)) line width ratio correlates with CAI. Conodont colour during arti ficial maturation occurs by migration of compounds to the surface. As the n itrogen compounds are volatilised from the surface, colour disappears. (C) 2001 Elsevier Science Ltd. All rights reserved.