Cretaceous fire in Australia: a review with new geochemical evidence, and relevance to the rise of the angiosperms

Abstract

Much of the Australian flora has high flammability. It is therefore of interest whether burning was a feature in the Cretaceous, the geological period in which angiosperms rose to dominance, and in which fossil and molecular evidence suggests the presence of lineages now prominent in regularly burnt habitats. Determining the extent of fire in the Australian Cretaceous is limited by a paucity of surface exposures of strata, and of published reports of definite charcoal from exploration cores. Nevertheless, charcoalified tissues occur much more widely than is currently reported in the international literature, and there are also numerous references to inertinite macerals in Australian Cretaceous coals. Combustion-related hydrocarbons can also be detected in ancient sediments using organic geochemical methods, and we demonstrate the potential of this approach here. Overall, the available evidence is in concert with that from elsewhere on Earth: fire was apparently widespread in the Australian Cretaceous, and can reasonably be invoked as a force that influenced the evolution of modern Australian environments. Just as in extant open, nutrient-limited regions, proteaceous lineages seem to have been important in burnt, open habitats in the Late Cretaceous, perhaps retaining dominance of such niches for >70 million years. However, there is so far no fossil evidence for the Cretaceous presence of Eucalyptus, the principal tree genus of modern Australian fire-prone vegetation.