FTIR characterisation of the chemical composition of Silurian miospores (cryptospores and trilete spores) from Gotland, Sweden

To better understand the biological affinities of cryptospores, micro-FTIR (Fourier transform infrared) spectroscopy analysis has been carried out on isolated specimens from the Upper Silurian of Gotland. The geobiochemical results have been compared to spectra of trilete spores, chitinozoans and leiospheres from the same sample. The palynomorphs are all very well preserved as attested by their pale yellow to orange colour indicative of a low thermal maturity. Micro-FTIR spectroscopy indicates that cryptospores display very similar spectra to those of the trilete spores, which are composed of sporopollenin characterised by absorption bands from aliphatic C-H in methylene (CH₂) and methyl (CH₃) groups, aromatic (C=C and C-H) groups and C=O groups of carboxylic acids. The sporopollenin composition of the cryptospore wall observed here is additional evidence demonstrating the embryophytic affinity of the cryptospores. In addition, several variations in other bands in the spectra of the different miospore morphospecies are evidenced and may be linked to their biological affinity or palaeoecological history.