Stomatal indices of Peltaspermum martinsii (Pteridospermopsida, Peltaspermaceae) from the Upper Permian Bletterbach Gorge and their possible applicability as CO2 proxies
Abstract:Stomatal parameters (stomatal density and stomatal index) of fossil cuticles have often been used as proxy indicators for the palaeoatmospheric CO2 concentration, not only for the Cenozoic, but also for the Mesozoic and Palaeozoic. Especially, the cuticles of cycads, ginkgos, conifers and pteridosperms have frequently been used. However, this methodology produces reliable results only with fossils that have close living relatives. Within this study cuticles of Peltaspermum martinsii (Germar) Poort & Kerp (Pteridospermopsida, Peltaspermaceae) from the Upper Permian of the Bletterbach Gorge, Southern Alps, Italy have been used to asses their applicability for the determination of ancient CO2 levels. For this species the stomatal density (SD) and index (SI) have been assigned. The mean SI value (SImean) has been determined and compared with the SI values of Peltaspermum martinsii cuticles from different coeval localities. The palaeoatmospheric CO2 concentration has been calculated with the SI value of Peltaspermum martinsii, using a previously published transfer function established for fossil Ginkgo leaves, a genus which still has a living relative. This transfer function has already been applied for other pteridosperm species. This study is a test, whether it is suitable for reconstructing CO2 values with the SI values of Peltaspermum martinsii. The CO2 result has been compared with other palaeoatmospheric CO2 concentrations inferred with the SI value of Peltaspermum martinsii from different localities that have been calculated or where taken from the literature. Finally, the results of other proxies and geochemical modelling for this time period provided in the literature have been used for concluding comparisons.
Document Type: Research Article
Publication date: 2008-05-01
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