Infrared spectroscopy of Triassic conodonts: a new tool for assessing conodont diagenesis

Abstract

ABSTRACT The Fourier transform infrared spectra of individual conodonts with various CAI values indicate definite changes in conodont francolite during diagenesis. Steady decarbonation can be observed in the increasing intensity of the band with the wavenumber 2340 an ‐1 , which is assigned to trapped molecular CO 2 . Carbon dioxide originates from decomposing CO 2‐ 3 ‐ions occupying the B‐site in francolite. Furthermore, the intensity of the water‐deformation band at 1644 cm ‐1 decreases with higher CAI values. These changes of intensity can be quantified by calculating the maximum extinction (E max ) for the corresponding absorption maxima and correlated with the CAI. Unaltered conodonts have a relative variable water ‘content’ and very little CO 2 . Up to a CAI value of 4 conodont francolite continuously expells water and carbon dioxide is trapped. Conodonts with CAI = 5 have similar water ‘contents’ to CAI = 4 conodonts, but decarbonation continues to take place during this stage of diagenesis.