Higher-plant evolution during the Cretaceous to Palaeogene in the Gippsland Basin, Australia

Diverse higher plant-derived biomarkers have been detected in the Upper Cretaceous−Palaeogene Latrobe Group hydrocarbon source rocks in the Gippsland Basin. Interpretation of aliphatic and aromatic sesqui-, di- and triterpenoids indicates that gymnosperms (e.g. Araucariaceae and Podocarpaceae) contributed more organic matter than angiosperms (e.g. Nothofagus, Ilex and Proteaceae) to the Upper Cretaceous palaeofloras in the Gippsland Basin. However, angiosperms gradually began to dominate the Palaeogene rainforests, especially with Nothofagus, Proteaceae and Euphorbiaceae. Analyses of the oleanane index and various AGIs, combined with previous studies, enables the inference that the palaeoclimate changed from warming to relative cooling and then back to warming again, over the time period from the T. lilliei biozone to the P. asperopolus biozone. This is consistent with palynological evidence and estimates of sea-surface temperature changes recorded in the Gippsland Basin (Wagstaff et al., 2006; Macphail, 2007).