Fourier Transform Infrared Spectroscopy Studies of Cretaceous Gymnosperms from the Santa Cruz Province, Patagonia, Argentina

Abstract

Premise of research. In this contribution, the spectroscopic characterization of gymnosperm fossil remains belonging to Pteridospermophyta, Cycadophyta, Ginkgophyta, and Coniferophyta collected from the Anfiteatro de Tico and Punta del Barco Formations (Baquero Group; Aptian) and Springhill (Hauterivian-Barremian) and Piedra Clavada/Kachaike (Albian) Formations, outcropping in the Santa Cruz Province, Argentina, is presented. From these lithostratigraphic units, specimens of several fossil taxa showing the existence of a diverse plant assemblage during the Lower Cretaceous in Patagonia were selected. Methodology. The fossils consist of foliar compressions with very well-preserved cuticles, which are chemically characterized by Fourier transform infrared spectroscopy. Foliar remains are analyzed in two sample forms: (1) compressions (Cps; including coalified mesophyll and cuticles) and (2) cuticles (Cts). Additionally, semiquantitative data are evaluated through principal component analysis, revealing the functional groups preserved at the mesophyll and cuticle levels for all analyzed fossil taxa. Pivotal results. In general, the species from the Baquero Group show similar chemical compositions between the Cp and Ct sample forms, whereas the chemistry of the foliar compressions from the Springhill and Piedra Clavada/Kachaike Formations reveals the presence of a high contribution of aromatic structures making up the cuticles. Conclusions. The compressions of Pseudoctenis ornata, Ginkgoites tigrensis, and Squamastrobus tigrensis probably underwent, during and after diagenesis, a natural oxidation process most likely caused by the recurrent volcanic activity that occurred during the Aptian sedimentation of the Baquero Group. In contrast, Ruflorinia orlandoi, Ptilophyllum micropapillosum, and Ginkgoites skottsbergii have cuticles presumably composed of highly aromatic structures (such as phenylpropanoids and aromatic domains) in cutins and cutans as well due to the presence of other phenolic compounds. A new term, vitrinitic compression, is proposed here for G. skottsbergii, while P. ornata, G. tigrensis, S. tigrensis, P. micropapillosum, and R. orlandoi are called liptinitic compressions.