Fourier Transform Infrared analysis of fossil remains with different modes of preservation

J. A. DANGELO; L. B. ESCUDERO; E. L. ZODROW; W. VOLKHEIMER

San Salvador de Jujuy - Jujuy -

Congreso; XVII CONGRESO GEOLÓGICO ARGENTINO; 2008

Asociación Geológica Argentina

Chemical knowledge of fossil remains preserving organic matter has greatly benefited from the advent of new techniques of chemical analysis requiring small sample amounts only (a few milligrams, except for Nuclear Magnetic Resonance, NMR, which requires at least 20-30 mg). This is particularly the case of plant and invertebrate remains. Over the last years several studies have focused in the chemical analysis of leaf cuticles by means of Fourier Transform Infrared spectroscopy (FTIR). This novel information includes functional groups and semi-quantitative variables derived from FTIR spectra of Carboniferous gymnosperms and ferns (e.g., Zodrow et al., 2003; Zodrow and Mastalerz, 2001, 2007). Chemical studies (specially FTIR) of fossil plant remains from Argentina are still very limited (e.g., D`Angelo, 2006; D`Angelo and Volkheimer, 2007; D`Angelo et al., 2007). In this contribution we present semi-quantitative FTIR-derived data of fossil remains with different pathways of organic transformation. Spectroscopic information was obtained from fossil plant remains including cuticle-free compressions, liquid compression extracts, cuticle from compression, and naturally macerated cuticles (leaf, rachis, mid-vein and stem). For comparative purposes, cuticle of co-occurring, non-marine, invertebrate (carapace) was also analyzed. Plant remains included in this contribution, originated from the Triassic of Argentina and the Carboniferous of Canada and the U.S.A. Selected taxa from the Upper Triassic of Cacheuta, Mendoza, Argentina include Dicroidium odontopteroides var. odontopteroides, Johnstonia coriacea var. coriacea (Corystospermales, Corystospermaceae), an undetermined stem and Euestheria forbesi (Conchostraca, non-marine bivalve crustacean co-occurring with Dicroidium leaves). Those selected from the Upper Carboniferous of Sydney Coalfield, Canada, include Alethopteris ambigua and A. subzeilleri (Medullosales), and from Illinois Coalfield, U.S.A. Karinopteris sp. (pteridosperm) of the famous Indiana paper coal (DiMichele et al., 1984). This FT-IR study reports chemical data of animal and plant contributions to sedimentary organic matter and provides some information on the survival of organic matter in Carboniferous and Triassic sediments. Infrared spectra obtained from fossil remains showed a relatively rich aliphatic structure as well as hydroxyl, carbonyl and some other oxygen-containing functional groups. Semi-quantitative data were obtained from different regions of FTIR spectra, using some area-integration methods (e.g., Sobkowiak and Painter, 1992). Semi-quantitative analysis clearly shows the dissimilarities between fossil remains with different preservation modes. As part of our intensive ongoing research activities, cuticles and compressions of different Carboniferous- Mesozoic plant groups are currently being analyzed by solid and liquid state proton and 13C NMR (400, 700 and 800 MHz instruments), liquid-state FTIR techniques, and by gas chromatography coupled to mass spectrometry. Ensuing results are expected to furnish new information (complementary to solid-state FTIR data) regarding the palaeophytochemistry of certain fossils, pathways of organic matter transformation, which as a whole will prove useful palaeochemotaxonomically for evolutionary systematics of Carboniferous-Mesozoic seed ferns, which cannot be achieved solely by morphology.