Optical and geochemical characterization of Upper Sinemurian (Lower Jurassic) fossil wood from the Lusitanian Basin (Portugal)

Abstract

Copyright © 2013 by The Geochemical Society of Japan. Pienkowski, 2011). It is assumed that when the δ13C record of both marine carbonates and fossil wood show a coupled trend, (reflecting the oceanic and atmospheric carbon reservoirs), it is an indication that there was a global perturbation of the carbon cycle. However, the use of fossil wood isotopic data are related to two main assumptions: 1) that the δ13C of fossil wood reflects, to some extent, the δ13C of the atmosphere at the moment of tree growth; 2) although diagenesis has altered the original δ13C values, it is likely that through a given section all samples have undergone similar diagenetic changes. Although the first assumption may seem fairly reasonable, the second assumption raises concerns as it tends to ignore lithological constraints (e.g., Grocke, 1998), the process of degradation associated with residence time in the continental and marine environments prior to deposition (e.g., Tyson, 1995), the early diagenetic/coalification processes (e.g., Suarez-Ruiz and Crelling, 2008), a shift in composition due to severe oxidation (including burning) (e.g., Czimczik et al., 2002) and the impact of these processes on the isotopic composition of fossil wood (e.g., Rimmer et al., 2006). In conOptical and geochemical characterization of Upper Sinemurian (Lower Jurassic) fossil wood from the Lusitanian Basin (Portugal)