Variables derived from Fourier transform infrared cuticular spectra of Dicroidium and Johnstonia: a new proxy for paleo-CO2 levels?

ESCUDERO L B; VOLKHEIMER W; D`ANGELO J A

Jujuy, Argentina

Congreso; XVII Congreso Geológico Argentino; 2008

Over the last years a growing number of studies have used the plant species-specific inverse relationship between atmospheric CO2 concentration and stomatal density (SD) or stomatal index (SI) as paleobarometer of atmospheric CO2 (e.g., Retallack, 2001, 2002, Royer, 2001). Paleo-CO2 concentrations obtained using stomatal frequency data have compared well with previously published paleo-CO2 levels derived from geochemical proxies such as sedimentary mass balance models (Berner, 1997), boron isotopic composition of marine foraminifera (Pearson and Palmer, 2000) and carbon isotopic composition of pedogenic carbonate (Ekart et al, 1999). Several recent studies have focused in the chemical analysis of cuticular remains employing Fourier Transform Infrared Spectroscopy (FTIR). This new information includes functional groups and semi-quantitative variables of Carboniferous remains (e.g., Zodrow et al., 2003; Zodrow and Mastalerz, 2001, 2007). FTIR studies of fossil plant cuticles from Argentina are still very limited (e.g., D`Angelo, 2006; D’Angelo and Volkheimer, 2007; D’Angelo et al., 2007). In this contribution is proposed the use of this novel (chemical) information as a proxy for the determination of paleo-CO2 levels. Several cuticular samples of Dicroidium and Johnstonia (Corystospermales, Corystospermaceae) from the Triassic of Cacheuta, Mendoza, Argentina were analyzed. Simple linear relationships have been found between some FTIR-derived variables and SI for all the samples studied. Using these relationships and a transfer function, past partial pressures of CO2 were estimated. A good correlation has been found comparing the new results (FTIR) with those of stomatal index model estimates. One-way analysis of variance statistical test did not show significant differences (p< 0.05) between CO2 levels obtained using SI and those derived from FTIR variables. Though the results obtained are suggestive of the likely application of the FTIR technique for determining paleo-CO2 concentrations, more data are needed from these and some other taxa before obtaining definitive conclusions.   REFERENCES   Berner, R. A., 1997. The rise of plants and their effect on weathering and atmospheric CO2. Science, 276: 543-546. D’Angelo, J. A., 2006. Analysis by Fourier transform infrared spectroscopy of Johnstonia (Corystospermales, Corystospermaceae) cuticles and compressions from the Triassic of Cacheuta, Mendoza, Argentina. Ameghiniana, 43(4): 669-685. D’Angelo, J. A. and Volkheimer, W., 2007. Searching for chemotaxonomic signals by Fourier Transform Infrared Spectroscopy in cuticles and compressions of perilacustrine remains of Corystospermales (Upper Triassic of Cacheuta, Mendoza, Argentina). 4th International Limnogeology Congress, Barcelona, Spain. Abstract: 206-207. D’Angelo, J. A., Zodrow, E. L. and Mastalerz, M., 2007. Compression or cuticle - What is the difference? The Society for Organic Petrology Newsletter, 24(4): 8-9. Ekart, D. P., Cerling, T. E., Montañez, I. P. and Tabor, N. J., 1999. A 400 million year carbon isotope record of pedogenic carbonate: implications for paleoatmospheric carbon dioxide. American Journal of Sciences, 299: 805-827. Pearson, P. N. and Palmer, M. R., 2000. Atmospheric carbon dioxide concentrations over the past 60 million years. Nature, 406: 695-699. Retallack, G. J., 2001. A 300-million-year record of atmospheric carbon dioxide from fossil plant cuticles. Nature, 411: 287-290. Retallack, G. J., 2002. Carbon dioxide and climate over the past 300 Myr. Philosophical Transactions of the Royal Society of London. Series A, Mathematical, physical, and engineering sciences, 360(1793): 659-673. Royer, D. L., 2001. Stomatal density and stomatal index as indicators of paleoatmospheric CO2 concentrations. Review of Palaeobotany and Palynology, 114: 1-28. 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. and Mastalerz, M., 2007. Functional groups in a single pteridosperm species: Variability and circumscription (Pennsylvanian, Nova Scotia, Canada). International Journal of Coal Geology, 70: 313-324. Zodrow, E. L., Mastalerz, M. and Šimůnek, 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.