Aromatic hydrocarbons extracted from Upper Cretaceous (Maastrichtian and Campanian) Latrobe Group coaly shales and shales from the Gippsland Basin were investigated by gas chromatography–mass spectrometry. A variety of 2-ring to 6-ring aromatic hydrocarbons were identified, including both higher-plant-derived and combustion-derived polycyclic aromatic hydrocarbons (PAHs). These aromatic compounds indicate that the Upper Cretaceous coaly shales and shales were deposited in a fluvial/deltaic environment with significant higher plant input and are at a relatively low thermal maturity stage. Higher plant parameters and angiosperm/gymnosperm indices based on aromatic components suggest that higher land plants, including both angiosperms and gymnosperms, were an important part of the palaeovegetation in the Upper Cretaceous. The aromatic angiosperm/gymnosperm index that includes chrysene- and picene-type PAHs is not as reliable for evaluation of relative angiosperm and gymnosperm contributions as the aliphatic indices due to input of combustion-derived PAHs and the complexity of burning conditions altering the relative contributions. However, combustion-derived PAHs and aromatic angiosperm/gymnosperm indices supplement the information from aliphatic hydrocarbons and provide further evidence to support the hypothesis that palaeoclimate cooled from the Campanian to the Maastrichtian.
- Gippsland Basin
- Upper Cretaceous
- Polycyclic aromatic hydrocarbons
- Angiosperm/gymnosperm index
- Source rock