FTIR spectroscopic features of the pteridosperm Ruflorinia orlandoi and host rock (Springhill Formation, Lower Cretaceous, Argentina)

Abstract

Ruflorinia orlandoi (Pteridospermophyta) fronds are chemically analyzed for the first time by semi-quantitative Fourier transform infrared (FTIR) spectroscopy. This analysis allows the chemical characterization of the mesophyll and cuticle revealing the functional groups preserved in different frond parts (pinnae and rachis). The specimens collected in the Springhill Formation at the Río Correntoso locality (Lower Cretaceous, Santa Cruz province, Argentina) are compressions with very well-preserved cuticular features. The R. orlandoi remains (pinnae and rachis) are spectroscopically analyzed into two samples: compressions (Cp) and cuticles (Ct). Additionally, a third sample form from the host rock and named associated coal (V) is spectroscopically analyzed. Semi-quantitative data derived from Cp, Ct, and V spectra are evaluated by principal component analysis. The results indicate that Cp samples have a similar chemical composition whereas Ct samples show a greater variability. The latter could be related to intraspecific variability of foliar characters (e.g., trichomes and cuticular striations). Furthermore, Ct samples exhibit high contents of aromatic carbon groups suggesting a distinctive composition, likely including cutin/cutan biomacropolymers and/or phenolic compounds. Considering each specimen, the rachis shows a higher aromatic carbon content than pinnae as a consequence of the presence of more lignified tissues in the former. The V samples have the lowest relative intensity of aliphatic groups. On the other hand, the functional-group composition of R. orlandoi remains and V samples are compared with kerogen types and coal macerals showing a general chemical composition similar to type II kerogen. The latter is related to cuticles, spores, pollen grains, and resins.