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

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

San Salvador de Jujuy - Jujuy - Argentina

Congreso; XVII CONGRESO GEOLÓGICO ARGENTINO; 2008

Asociación Geológica Argentina

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 menor a 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.