Reconstruction of Late Pennsylvanian CO2 levels based on Odontopteris brardii (Pteridospermopsida, ?Medullosales) cuticles from France and Germany
Abstract:Stomatal density and index of fossil seed plants are today routinely used as proxies in the reconstruction of palaeoatmospheric CO2 levels. The value of late Palaeozoic pteridosperm stomatal indices as climate proxies remains incompletely understood because these plants lack close extant relatives that could be used for comparison. Moreover, little is known about intraspecific variability in pteridosperm stomatal density (SD) and index (SI), and the influence of ecological factors other than CO2 on these parameters. Cuticles of Odontopteris brardii (?Medullosales) from two coeval but geographically and ecologically disparate late Stephanian B (Pennsylvanian) sites, i.e. Reisbach (Saar-Nahe Basin, Germany) and Blanzy-Montceau (Massif Central, France), were analysed. We found nearly identical SI values in all specimens, which suggests that habitat-specific factors did not significantly affect SI. The palaeoatmospheric CO2 concentrations inferred from the SI values based on a previously published transfer function are lower than CO2 estimates for the Late Pennsylvanian provided elsewhere, but generally corroborate the hypothesis that a drawdown in CO2 occurred during the Late Palaeozoic. Although CO2 concentration estimates obtained from Late Palaeozoic pteridosperm cuticles from single localities in general remain problematic, our study shows that corresponding SI values in specimens of a single taxon from several coeval but otherwise disparate sites can be used as complementary data in strengthening or refuting published models of the palaeoatmospheric CO2 concentration.
Document Type: Research Article
Publication date: November 1, 2009
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