Semi-quantitative analysis by Infrared Spectroscopy of compressions and cuticles. A case study of Dicroidium and Johnstonia (Corystospermales, Corystospermaceae) from the Upper Triassic of Cacheuta, Mendoza, Argentina.

D`ANGELO, JOSÉ A; VOLKHEIMER, WOFGANG

Córdoba, Argentina

Congreso; 9 Congreso Argentino de Paleontología y Bioestratigrafía; 2006

Asoc. Pal. Arg., Acad. Nac. de Cienc. ,Univ. Nac. Córdoba

Over the last years several organic geochemical methods have been applied to the study of the chemical composition of fossil plant remains. However, the study of very small amounts of organic fossil plants has only been achieved by the development of rapid and non-destructive techniques such as Fourier Transform Infrared Spectroscopy (FT-IR) requiring only a few milligrams of sample. Recent investigations have focused in the determination by FT-IR of functional groups and semi-quantitative variables of Carboniferous remains with chemotaxonomic purposes (e.g., Zodrow et al., 2003; Zodrow and Mastalerz, 2001; Pšenièka et al., 2005). Geochemical studies of fossil plants from Argentina are still very limited (e.g., Almendros et al., 1999; D`Angelo, 2004; D`Angelo, in press) and are reviewed in another contribution to this congress (D`Angelo and Volkheimer). In the present contribution functional groups and FT-IR semi-quantitative variables were determined in several corystosperm specimens from the southern side of the Cacheuta hill (Cacheuta Formation, lower to upper Upper Triassic). Morphologically well-preserved leaf cuticles (and their corresponding compressions) of Dicroidium odontopteroides var. odontopteroides (Morris) Gothan and Johnstonia coriacea var. coriacea (Johnston) Walkom were analyzed by FT-IR. Infrared spectra obtained from cuticles and compressions of corystosperms showed a relatively rich aliphatic structure as well as hydroxyl, carbonyl and some other oxygen-containing functional groups. Semi-quantitative data derived from FT-IR spectra were statistically analyzed using one-way analysis of variance test (ANOVA). One-way ANOVA revealed significant differences between cuticles and their corresponding compressions (p < 0.05) regarding the FT-IR-derived variables here considered. However, there were no statistically significant differences (p > 0.05) between abaxial and adaxial cuticular surfaces neither in Johnstonia coriacea nor in Dicroidium odontopteroides. Infrared-derived ratios here considered in compression samples did not differ significantly between taxa (p > 0.05). Similarly, comparison between cuticles of the two taxa showed no statistical differences (p > 0.05) regarding the FT-IR variables here considered. Based on previously established morphological similarities (microscopical studies; e.g., Townrow, 1957; Archangelsky, 1968) and the novel, independent FT-IR features here presented, it might be stated that there are no differences between the cuticles of the two taxa here studied. Nevertheless, and despite these highly suggestive results, the likely application of FT-IR technique to the chemotaxonomic study of the Corystospermaceae foliage will require more data from these and some other taxa (including the use of some other analytical techniques, such as pyrolysis-gas chromatography/mass spectrometry) before obtaining definitive conclusions. Almendros, G., Dorado, J., Sanz, J., Alvarez-Ramis, C., Fernández-Marrón, M.T. and Archangelsky, S. 1999. Compounds released by sequential chemolysis from cuticular remains of the Cretaceous Gymnosperm Squamastrobus tigrensis (Patagonia, the Argentine). Organic Geochemistry 30: 623-634.Archangelsky, S. 1968. Studies on Triassic fossil plants from Argentina. 4. The leaf genus Dicroidium and its possible relation to Rhexoxylon stems. Palaeontology 11: 500-512.D`Angelo, J. 2004. FT-IR determination of aliphatic and aromatic C-H contents of fossil leaf compressions. Part 2: applications. Anuario Latinoamericano de Educación Química (ALDEQ) 18: 34-38.D`Angelo, J. in press. Analysis by Fourier transform infrared spectroscopy of Johnstonia (Corystospermales, Corystospermaceae) cuticles and compressions from the Triassic of Cacheuta, Mendoza, Argentina. Ameghiniana.Pšenièka, J. Zodrow, E.L. Mastalerz, M. and Bek, J. 2005. Functional groups of fossil marattialeans: chemotaxonomic implications for Pennsylvanian tree ferns and pteridophylls. International Journal of Coal Geology 61: 259-280.Townrow, J.A. 1957. On Dicroidium, probably a pteridospermous leaf and other leaves now removed from this genus. Transactions of the Geological Society of South Africa 60: 21-56.Zodrow, E.L. and Mastalerz, M. 2001. Chemotaxonomy for naturally macerated tree-fern cuticles (Medullosales and Marattiales), Carboniferous Sydney and Mabou Sub-Basins, Nova Scotia, Canada. International Journal of Coal Geology 47: 255-275.Zodrow, E. L., Mastalerz, M. and Simunek, Z. 2003. FTIR-derived characteristics of fossil-gymnosperm leaf remains of Cordaites principalis and Cordaites borassifolius (Pennsylvanian, Maritimes Canada and Czech Republic). International Journal of Coal Geology 55: 95-102.