Functional groups and common pyrolysate products of Odontopteris cantabrica (index fossil for the Cantabrian Substage, Carboniferous)

Abstract

Abstract Foliage of the tree-fern Odontopteris cantabrica (Order: Medullosales) is considered a reliable plant-fossil index for the Cantabrian Substage (Carboniferous, 306 Ma). Compared are two preservation states from Canada (fossilized-cuticles) and the Czech Republic (compression-cuticles), representing relatively uncommon and common preservation states, respectively. The main objective is deriving spectrochemical parameters for refining the taxonomic circumscription of the species. For the comparison, five sample categories (fossilized-cuticle, macerated fossilized-cuticle, compression, cuticle, and alkaline solution) are analyzed by methods of Fourier transform infrared (FTIR) spectroscopy, complemented by pyrolysis gas chromatography mass spectrometry (Py-GC/MS) for the Canadian sample. Variation of FTIR data in the latter sample is explained by the geochemical model for the formation of fossilized-cuticles by natural maceration. As a result, we propose a set of semi-quantitative FTIR ratios (spectral regions 1800–1000 cm − 1 and 3000–2800 cm − 1 ) as spectrochemical-taxonomic parameters for the index fossil: CH 2 /CH 3 , Al/Ox, C O/C C, C O cont, Ar/Al and Ar/C C. They contain molecular structural information related to aliphatic, aromatic and oxygen-bearing moieties. As expected, small overall spectrochemical differences occur, given converging preservation states, or similar fossilization trends for the cantabrica plant inhabiting the Variscan Forelands of the ancestral Canada–Czech geographical regions. Some chemical differences occurred due to preservations in the sample categories (i.e., fossilized-cuticle and compression) with the oxygen-bearing structures, the length and branching of polymethylenic side chains and aromatic structures. A biomacropolymeric structure is confirmed by Py-GC/MS, and deduced for the Czech sample from the higher CH 2 /CH 3 ratios.