Eocene paleoclimate and young mountain-building in the Australian Eastern Highlands

Abstract

Through new palynological and chronostratigraphic (40Ar/39Ar dating) analyses we constrain the ages of important Australian Eastern Highland macrofloral sites. The Cambalong Creek site is late Paleocene (Selandian-Thanetian), with an age range of ∼57.3–59.8 Ma as inferred from palynostratigraphy (Proteacidites angulatus Subzone of the Lower Lygistepollenites balmei Zone). The Brandy Creek, Hotham Heights and Mount Buller sites are middle Eocene (Lutetian-Bartonian), with a minimum age of 39.58 ± 0.30 Ma, as inferred from 40Ar/39Ar analyses of overlying basalts, and a maximum age of ∼44 Ma inferred from palynostratigraphy (Lower Nothofagidites asperus Zone). The Kiandra Diggings site is early Miocene (Aquitanian), with a minimum age of 21.67 ± 0.26 Ma as inferred from 40Ar/39Ar dating and a maximum age of 23.03 Ma inferred from palynostratigraphy (Middle Proteacidites tuberculatus Zone). In the context of their revised ages, the recovered macrofloras suggest that subtropical climates prevailed during the late Paleocene (Cambalong Creek) and middle Eocene (Brandy Creek and Hotham Heights), whereas temperate climates existed during the early Miocene (Kiandra Diggings). For the middle Eocene sites, there is no discernible difference in paleotemperature estimates between lowland and highland sites, suggesting relatively low (<550 m) paleoelevations for the present-day highland sites during the middle Eocene. This suggests that most of the present-day elevation (>1400 m) was produced by post-middle Eocene uplift.