Cenozoic climatic shifts in southern Australia

• Published in: Transactions of the Royal Society of South Australia
• Main Authors: McGowran, B., Hill, R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Taylor & Francis 2015
• Subjects: Cenozoic; climatic shifts; southern Australia; foraminifera; plant fossils; paleobiogeography; rain forests; environment change and evolution; Antarctic; The Antarctic; Antarc*; Ice Sheet
• Online Access: http://hdl.handle.net/2440/94340; https://doi.org/10.1080/03721426.2015.1035215

Early Paleogene southern Australia, which comprises the north shore of the Australo- Antarctic Gulf, was covered in the equivalent of extant wet-tropical lowland vegetation at 60 – 65°S, most richly during the Early Eocene Climatic Optimum. Cooling at ~50 Ma triggered the spread of Nothofagus warm-temperate rainforests. Cooling reversed at the Khirthar transgression at ~42 Ma with extensive neritic carbonate seas, diverse rainforest biomes and massive coals on the continental margins. Coals and limestones are strongly associated in time, from the late Paleogene at ~42 – 40 Ma (the Middle Eocene Climatic Optimum) to the early Neogene at~16 – 14 Ma (the Miocene Climatic Optimum). Photosymbiotic foraminifera from north of Australia ingressed into the neritic biomes on the Leeuwin Current, signalling warm pulses. Terrestrial floras were still wet-temperate at the continental margins, but during the Oligocene various plants, already coping with low nutrients from extensive deep weathering in the Paleogene, had to cope with cooling, sudden drops in global CO 2 levels and a drying-out in the continental interior. The rapid expansion of the Antarctic ice sheet in the early Oligocene had biotic impacts and responses, but not the dramatic impact of the subsequent expansion at ~14 Ma. Late Neogene and modern Australia became a subdued, undernourished, arid continent with damp fringes. Neritic seas and their carbonate factories shrank; rainforests reduced in aerial extent and coal formation ceased. The last major warming, which temporarily interrupted the overall cooling into the late Neogene (Pleistocene) icehouse was in the early Pliocene, although the biogeographic pulses on the Leeuwin Current have continued to the present. The modern, fire-adapted Eucalyptus forests have deep Neogene roots but underwent significant expansion only recently. Brian McGowran, Robert S. Hill