APPLICATION OF GEOCHEMISTRY AND ORGANIC PETROGRAPHY TECHNIQUES IN PALEOBOTANICAL STUDIES

This paper discusses the application of organic geochemistry and petrography to paleobotanical studies concerning the origin, composition and habitat of fossil plants of uncertain (or unknown) nature and chemical composition. Four components are considered in this study: 1. Fragments of Glossopteridales leaves, 2. Spongiophyton, 3. fragments of Protosalvinia, and 4. fossil wood. In the case of the Spongiophyton fragments (Ponta Grossa Formation, Devonian, Paraná Basin, South Brazil) the hydrogen index value of 780 mgHc/gTOC points out to hydrogen-rich organic matter type. In samples extracted mechanically from coalified compressions of Glossopteridales leaves (Rio Bonito Formation, Permian, Paraná Basin), the organic matter analyses indicate variable composition showing predominantly woody organic matter (TOC 17.6%). In the case of Protosalvinia, a peculiar fossil plant from Upper Devonian sequences of South and North America, its fragments occur associated with marine palynomorphs (Acritarchae and Prasinophytae algae). In respect of the geochemical data, the solvent extract from isolated Protosalvinia fragments yields n-alkanes in the range of C14-C35, with the predominance of C27 sterane, thus suggesting a marine origin for this fossil. Concerning the geochemical characterization of fossil woods (Irati Formation, Permian, Paraná Basin), elemental analyses were carried out using X-ray difractometry and ultraviolet light microscopy, coupled with vitrinite reflectance, in order to characterize the coalification level of the material.