This article was downloaded by: [Retallack, Gregory J.][University of Oregon] On: 28 September 2010 Access details: Access Details: [subscription number 917394740] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37- 41 Mortimer Street, London W1T 3JH, UK Australian Journal of Earth Sciences Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t716100753 Paleosol record of Neogene climate change in the Australian outback C. A. Metzgera; G. J. Retallacka a Department of Geological Sciences, University of Oregon, Eugene, OR, USA Online publication date: 24 September 2010 To cite this Article Metzger, C. A. and Retallack, G. J.(2010) 'Paleosol record of Neogene climate change in the Australian outback', Australian Journal of Earth Sciences, 57: 7, 871 — 885 To link to this Article: DOI: 10.1080/08120099.2010.510578 URL: http://dx.doi.org/10.1080/08120099.2010.510578 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Australian Journal of Earth Sciences (2010) 57, (871–885) Paleosol record of Neogene climate change in the Australian outback C. A. METZGER AND G. J. RETALLACK* Department of Geological Sciences, University of Oregon, Eugene, OR 97403-1272, USA. 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. KEY WORDS: Miocene, paleosol, paleoclimate, mammals, mallee, rain forest. INTRODUCTION Australian outback has been disputed (Megirian et al. 2004). The differences between soils of rain forest The middle Miocene thermal maximum was a period of (Ultisols, Oxisols), woodland (Alfisols) and desert past climate change similar in its global geographic (Aridisols) are profound (Retallack 1997), and this study scale and the extrapolated magnitude of temperature of paleosols is a test of these conflicting reconstructions change to the change predicted to occur by the year 2100 of Miocene paleoclimate in central Australia. (Alley et al. 2007; Retallack 2009). For example, benthic In northern South Australia, Cenozoic sediments foraminiferal oxygen isotope records (Figure 1) reveal around the Lake Eyre basin, an extensive network of that middle Miocene deep ocean waters were 68C ephemeral salt-pan lakes (Figure 2), are famous for fossil warmer than present (Flower & Kennett 1994; Lear vertebrates (Stirton et al. 1961, 1967; Woodburne & et al. 2000). Cooling from 15 Ma onwards coincided with Tedford 1975; Vickers-Rich 1979; Wells & Callen 1986; the onset of glaciation in Antarctica (Zachos et al. 2001). Woodburne et al. 1993). Oligocene–Pliocene sediments As another example, paleosol records in central Oregon, are best exposed and most easily accessed at Lake USA (Figure 1), are evidence of paleotemperatures Palankarinna, located at the southern extent of the peaking at 15 + 4.48C and mean annual precipitation of Tirari Desert, surrounded by northwest-striking sand Downloaded By: [Retallack, Gregory J.][University of Oregon] At: 20:56 28 September 2010 as much as 1096 + 181 mm (Retallack 2007a, 2008a), dunes. Lake Palankarinna is one of the most productive compared with 9.28C and 340 mm, respectively, now in Australian localities for mammal fossils, and its John Day, Oregon (Taylor 2005). The middle Miocene sequence of fluviatile-lacustrine sediments has been thermal maximum is characterised globally by exten- previously dated by paleomagnetism, palynology, bios- sion of thermophilic plant and animal taxa to high tratigraphy, and radiometric dating (Woodburne et al. paleolatitudes (Christensen 1975; Bown & Fleagle 1993; 1993), although its paleosols have not been studied until Wolfe 1994; Blisniuk et al. 2005; Bestland et al. 2008). now. In the Australian outback, the magnitude of this This study presents new work on the paleosols from global climatic change has proven controversial. Fossil Lake Palankarinna that provides an understanding of mammal assemblages at Riversleigh, Queensland, have landscape and ecosystem evolution during middle been used as evidence of middle Miocene rain forest Miocene climate change in the Australian outback. expansion into the desert (Archer et al. 1991), although Woody thickening has already been documented during such dramatic paleoclimatic transformation of the 20th century warmer and wetter conditions in central *Corresponding author: [email protected] ISSN 0812-0099 print/ISSN 1440-0952 online Ó 2010 Geological Society of Australia DOI: 10.1080/08120099.2010.510578 872 C. A. Metzger and G. J. Retallack at 28845.770S 138824.1290E, including the best-known fossil quarry at Mammalon Hill (Figure 3). In addition, a paleosol was sampled in the Mampuwordu Sand 100 m south of Mammalon Hill in Lawson’s quarry (28845.7940S 138824.1070E). Field descriptions included Munsell colour (Munsell 1975), grainsize, soil structure, horizonation, horizon boundaries, and the presence of other soil features such as root traces, nodules, animal or insect burrows, or fossils. Thickness of the calcic (Bk) or gypsic (By) horizon and depth to carbonate or gypsum nodules were measured. Detailed stratigraphic sections were also drafted in the field (Figure 4). Paleosols were classified into groups using the pedotype approach (Retallack 2001) which characterises different paleosol types using field criteria. Descriptive names were given to each pedotype from the local Dieri language (Schoknecht & Schoknecht 1997). Naming conventions for the paleosols in this study follow USDA Soil Survey (Soil Survey Staff 2000) nomenclature to soil-order level Figure 1 Middle Miocene (16 Ma) thermal maximum from as well as the Australian soil nomenclature (Isbell 1998). paleosols in Oregon (grey after Retallack 2007a, 2008), and A 35 m-section of drill-core (BMR Palankarinna-2) from oxygen (A) and carbon (B) isotopic composition of was examined, described, and sampled at Geoscience foraminifera in the Southern Ocean (after Zachos et al. Australia, in Canberra in September 2006 (Figure 5). The 2001). very close correspondence of these sections is unsur- prising considering that the drill site on the nearby plateau at 28845.6330S 138824.1240E is only 75 m northeast of the badlands outcrop sampled. The core was very helpful in revealing the nature of paleosols at depth, unencrusted with gypsum common in outcrop. Samples were collected from every horizon within a type section for each pedotype for geochemical analysis of major and trace elements and analyzed by the Washington State University XRF laboratory in Pull- man. Bulk composition is useful for investigating geochemical processes active during soil formation. Molecular weathering ratios, calculated from the weight percent of an element in its oxide form, are commonly used as proxies of compositional changes in a rock or soil due to weathering (Marbut 1935). These ratios can illuminate the dominant chemical reactions at work in a soil, such as hydration, oxidation, and leaching (Retallack 1997, 2001), and are also useful as paleocli- matic proxies (Table 1). Some widely used geochemical climofunctions based on North American soils (Sheldon et al. 2002; Sheldon & Tabor 2009) were not pursued here Downloaded By: [Retallack, Gregory J.][University of Oregon] At: 20:56 28 September 2010 Figure 2 Location of