CONICET | Buscador de Institutos y Recursos Humanos

Leaves of Squamastrobus tigrensis Archangelsky et Del Fueyo (Podocarpaceae) from the Aptian Anfiteatro de Ticó Formation (Baqueró Group), Santa Cruz Province, Argentina, are analyzed for the first time using Fourier transform infrared spectroscopy (FTIR) with the aim of finding the spectroscopic patterns that distinguish this taxon. Three sample forms are analyzed: (1) compressions, (2) cuticles, and (3) associated coal samples. The fossils are preserved as the usual foliar compressions (i.e. one coalified layer with the cuticle), exhibit several shades of brown color and show foliar morphological and anatomical features very well preserved. Cuticles were obtained from compressions by chemical oxidizing treatment. To improve the qualitative information that provides the FTIR technique different treatments were applied to digitized spectra, yielding semi-quantitative data of the chemical composition of the three sample forms. The IR-derived data were evaluated by principal component analysis (PCA) showing the different grouping of data as a function of chemical structure (functional groups) and reflecting the nature of the three sample forms. The results indicate minor differences between compressions and derived cuticles, revealing a high degree of natural oxidation in S. tigrensis leaves. This is most likely attributed to the intense volcanic activity and the fall of cold ash occurred during Aptian sedimentation in Patagonia. Furthermore, as a result of the morphological studies in this taxon and the particularities of the preservation of the Baqueró Group several terms used in previous studies of chemical characterization are discussed.