Chemical characterization of Lower Devonian vascular plants

• Published in: Organic geochemistry 1996-12, Vol.25 (8), p.461-473
• Main Authors: Ewbank, Greg, Edwards, Dianne, Abbott, Geoffrey D.
• Format: Article
• Language: English
• Subjects: cutan; Earth sciences; Earth, ocean, space; Exact sciences and technology; flash pyrolysis; fossil leaves; fossil wood; Hydrocarbons; lignin; Lower Devonian plants; Paleobotany; Paleontology; Sedimentary rocks; vascular plant evolution
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/S0146-6380(96)00140-4

Vegetative remains of three coalified Lower Devonian vascular plants ( Zosterophyllum, Psilophyton, Renalia) were analyzed using flash pyrolysis-gas chromatography-mass spectrometry. The distributions of pyrolysis products are compared with those from younger vascular plant fossil xylem ( Cordaixylon, Callixylon) and cuticle ( Pachypteris). The likelihood of the chemical preservation of characteristic higher plant macromolecules (e.g., lignin and cutan) in the Lower Devonian plant fossils is considered in light of this comparison and associated thermal maturity assessments. Reflectance values from vitrinite-like macerals, which may not be vitrinite sensu stricto in the Lower Devonian host rocks for the fossils selected for this study, are shown to provide a reasonable assessment of the thermal maturity of these early vascular plant fossils. Although lignin altered through burial maturation is the most likely source of the prominent alkylphenols and aromatic hydrocarbons in the Lower Devonian tracheophyte flash pyrolysates, a contribution from thermally modified tannins cannot be ruled out. Comparison of the highly aliphatic pyrolysates from the Zosterophyllum and Psilophyton axes with that of a thermally mature fossil gymnosperm leaf revealed that cutan was an important component in the Devonian plant remains. This is the earliest chemical evidence for the presence of cutan in vascular plants.