Late Miocene drying of central Australia

Abstract

A back to the future approach to climate change refines Neogene records of paleoclimatic cooling and drying as future climate states for a warming world. Near Alcoota station in central Australia is a late Miocene fossil mammal site for Alcoota (10 Ma) and Ongeva (8 Ma) local faunas. The Alcoota fauna includes the largest known land bird (Dromornis stirtoni) and early diprotodontid (Kolopsis torus), but the geologically younger Ongeva fauna has a larger diprotodontid (Zygomaturus gilli). These faunas are evolutionary predecessors of Australian Pleistocene megafauna. Calcareous paleosols recorded a marked turn toward aridity compared with underlying thick lateritic duricrusts which lack fossils. Laterites of likely middle Miocene age are evidence of wet (>1100 mm mean annual precipitation) tropical (>17 °C mean annual temperature) paleoclimates, but these were deeply eroded and redeposited by the time of the late Miocene mammals. A succession of 19 paleosols of 5 pedotypes were recognized in the 19 m thick section, with shallow calcareous nodule (Bk) horizons as evidence of mean annual precipitation ranges from 100 to 400 mm, and mean annual range of precipitation of 50 mm, very similar to the modern climate of Alcoota (296 mm precipitation with 56 mm difference between wet and dry month). This was neither a rainforest nor monsoonal paleoclimate, and vegetation inferred from paleosols was open woodland and gallery woodland similar to that of today. Central Australia was not covered by monsoon rainforest during the late Miocene and its paleoclimatic history of Neogene desertification matches well that of other parts of the world.