Aliphatic and aromatic terpenoid biomarkers in Cretaceous and Paleogene angiosperm fossils from Japan

The distributions of aliphatic and aromatic terpenoids in Cretaceous and Paleogene angiosperm fossils from Japan were investigated. Aliphatic A ring-degraded oleanane, ursane and lupane were found in all samples. In addition, aliphatic gymnosperm-derived diterpenoids were detected in significant quantities. Aromatic oleanane-type triterpenoids were the major components, with ursane- and lupane-type triterpenoids being minor compounds in all angiosperm fossils. In a Cretaceous gymnosperm fossil, major components included aliphatic labdane-, isopimarane- and abietane-type diterpenoids, aromatic abietane-type diterpenoids, and chrysene- and picene-type polyaromatic hydrocarbons (PAHs). Trace amounts of oleanane-, ursane- and lupane-type triterpenoids were also identified. It is likely that the aromatic triterpenoids were introduced to the gymnosperm fossil from the angiosperm-derived material in the sediments. We defined an angiosperm/gymnosperm index (al-AGI′) as an alternative to the aliphatic triterpenoid/diterpenoid ratio proposed in the literature. The al-AGI′ index may underestimate the angiosperm contribution, because the aliphatic angiosperm-derived triterpenoids are more readily converted to aromatic counterparts than the diterpenoids during diagenesis. An aromatic angiosperm/gymnosperm index (ar-AGI) can be calculated using aromatic diterpenoids and triterpenoids. We suggest that ar-AGI is best calculated using only the oleanane-, ursane- and lupane-type aromatic triterpenoids, and that the chrysene- and picene-type PAHs be excluded.