Biomarkers in the fossils from the Miocene-aged Chukurovo lignite, Bulgaria: sesqui- and diterpenoids

The attention is focused on the “Chukurovo” lignites of the Sofia coal-bearing province. The coal sediments are of Neogene age: petrological studies have indicated a Badenian-Sarmatian age, while the paleobotanical interpretations have indicated the Karpatian-Badenian, respectively Early-Middle Miocene boundary. Fossilized trees are common in the Chukurovo lignites, as well as petrified wood tissue consisting of stems and twigs impregnated by silica and other minerals and enriched in macroscopic organic matter. In this study organic geochemistry is applied toward the identification of molecular indicators for the coal-forming fossil communities. Fractions isolated by sequential extraction from resinite were analyzed by GC and GC-MS to identify a variety of biomarkers. Diterpenoids receive special attention in the present study. Triand tetracyclic diterpenoids, the so-called “regular” diterpenoids, are discussed in detail. The combination of high sesqui-/diterpenoid contents is evidence for the input of higher plant residues (conifers), especially when accompanied by the diterpenoid dominance. Resins containing sesquiand diterpenoids are produced by species of all contemporary conifer families, and hence conifers are a possible coal-forming vegetation in fossil swamps.