Structure of organic matter in conodonts with different colour alteration indexes

Devonian conodont samples from the Beechwood Member of the North Vernon Limestone, IN, USA and Garra Formation Wellington, NSW, Australia with Colour Alteration Index (CAI) values of 2 and 4, respectively, were analysed using X-ray photoelectron spectroscopy (XPS), pyrolysis gas chromatography mass spectrometry (py-GC/MS) and Fourier transform infrared emission spectroscopy (FTIRES). The results show the organic matter is different for the two conodont samples, but contrary to that predicted if only thermal processes were operating. The organic matter in the Beechwood Member conodonts appears to be reduced whereas conodonts from the Garra Formation appear to be oxidised. Pyrolysates from organic matter in the Beechwood Member conodonts are dominated by an n-alkane series of hydrocarbons from C8 to C19, and simple aromatic hydrocarbons, however pyrolysates of organic matter from conodonts in the Garra Formation are dominated by nitrogen compounds and ketones. It is concluded that CAI values should be checked spectroscopically since CAI values indicating oil potential will be misleading if the organic matter is oxidised.