Paleosol record of Neogene climate change in the Australian outback

Abstract

Effects in Australia of a global spike of warm-wet climate during the middle Miocene (ca16 Ma) have been controversial, with one faction arguing for inland rain forest and the other faction for dry woodland. This question is here addressed using the Oligocene–Miocene sequence of fossil mammal localities at Lake Palankarinna, South Australia, which includes numerous paleosols that have been dated by paleomagnetism, palynology, biostratigraphy, and radiometric methods to straddle this paleoclimatic event. Paleosols of the Oligocene–Miocene Etadunna and Pliocene Tirari Formations formed in arid paleoclimates and include pedogenic gypsum. The Maralji paleosol, developed on early Miocene Etadunna Formation and overlain by late Miocene–Pliocene Mampuwordu Sands, is middle Miocene in age based on mammal fauna at correlative horizons in nearby Lake Ngapakaldi. The Maralji paleosol has shallow calcareous nodules and stout root traces suggesting vegetation like dry woodland (mallee). Mallee vegetation now grows no closer than 1200 km to the southwest, so middle Miocene warm-wet climate enabled range extension of mallee and woody thickening of plants in the Australia outback. There is no evidence in the outback of middle Miocene rain forest, which may have expanded its range to form kaolinitic Ultisols near Sydney, Mudgee and Gulgong, all in New South Wales. Nor is there evidence so far inland of swamp woodlands and heaths like those producing brown coals in the Latrobe Valley, Victoria.