Polar aromatic biomarkers in the Miocene Maritza-East lignite, Bulgaria

Aromatic and polar compounds of lignite lithotype bitumens (Maritza-East) were analyzed. Diterpenoid phenols and ketophenols, i.e., mainly ferruginol, sugiol, hinokione, and products of their diagenetic transformations, were identified as the dominant biomarkers. A variety of sesquiterpenoids was present as well. These compounds provided evidence for the assumption that members of the Cupressaceae s. 1. are the coal precursors. Polar triterpenoids, i.e., lupeol, lupenone, adiantone and hopanones were present in subordinate quantities in the humoclarain sample. These biomarkers support an input of deciduous (angiosperm) vegetation to the peat swamp source matter. Three diagenetic transformation schemes for the diterpenoid phenols/ketophenols are proposed: (1) ferruginol and/or sugiol alteration through dehydrogenation, demethylation and ring-B-cleavage; (2) hinokione aromatization to simonellite; and (3) 7-ketototarol change through 7-ketototar-5-enol to 20-nor-3-oxo-totara-5(10),6-dienol. The identified diterpenoids demonstrated the presence of Gymnospermae in the coal forming community. Furthermore, the phenolic diterpenoids indicated a specific input of organic matter from conifers of the Cupressaceae/Taxodiaceae or Podocarpaceae as the most abundant trees in the coal forming swamp.