(U-TH)/HE GEOCHRONOLOGY OF MCGRATHS FLAT LAGERSTÄTTE

The newly discovered Lagerstätte, McGraths Flat (MF), found in southeastern Australia, represents a novel and well-preserved continental record of Miocene paleoclimatic conditions. The Lagerstätte at MF is comprised of finely bedded goethite that primarily preserved leaf and insect fossils. Fossil deposition is hypothesized to have occurred within an ancient oxbow lake in a mesic environment bordered by drier habitats from ~16-11 Ma based on biostratigraphy and leaf physiognomy (McCurry et al., 2022). During this time interval, the climate became increasingly dry and rainforest lineages became less diverse, while lineages associated with sclerophyll biomes experienced increased speciation (Crisp et al., 2004).

McGraths Flat is geologically significant considering the scarcity of both continental fossil records and paleoclimatic information related to the large-scale aridification of Australia that helped to shape present-day ecosystems on the continent. However, the large age uncertainty makes it difficult to understand temporal and spatial variations of climate and biodiversity. Fossil preservation by replacement with goethite allows us to address this problem by obtaining a direct age of MF using (U-Th)/He geochronology (Farley, 2002; Shuster et al., 2005).