Developing a radiometrically-dated chronologic sequence for Neogene biotic change in Australia, from the Riversleigh World Heritage Area of Queensland
Graphical abstract
Introduction
Australia is one of the last continents to have a securely dated framework for the evolution of its Cenozoic terrestrial biotas. Until now, the vast majority of Australia's mammal-bearing deposits have been dated by biocorrelation, anchored by little more than half a dozen radiometric dates for the entire continent. Some regions have superpositional biotas but most of these are relatively limited in taxic biodiversity making biocorrelation much more difficult.
The oldest Australian Cenozoic terrestrial mammal-bearing assemblage is the Tingamarra Local Fauna (LF)1 from southeastern Queensland, radiometrically dated at (minimally) 54.6 Ma (Godthelp et al., 1992). This is the only terrestrial mammal-bearing assemblage for the whole continent in the gap between the early Cretaceous and the late Oligocene (Black et al., 2012a). The only late Oligocene assemblages that have been radiometrically dated are those of the upper Etadunna Formation in South Australia, to which a single reported date has been tentatively applied (Woodburne et al., 1994; see also below).
Australia's many Miocene assemblages include the most diverse mammal faunas known for the pre-Quaternary Cenozoic. Only one relatively impoverished assemblage has been radiometrically dated: the sparse early Miocene Geilston Bay LF of Tasmania (Tedford and Kemp, 1998). However, the early Miocene Wynyard LF (one taxon) of Tasmania, the middle Miocene Batesford Quarry LF of Victoria with one mammal taxon, and the mammal-poor late Miocene Beaumaris LF of Victoria (Black et al., 2012a) have been dated on the basis of marine biocorrelation. Among Pliocene assemblages, the early Pliocene Hamilton LF from northwestern Victoria (Turnbull and Lundelius, 1970, Turnbull et al., 2003), the early Pliocene Sunlands LF of South Australia (Pledge, 1987), the middle Pliocene Bluff Downs LF from northeastern Queensland (Rich et al., 1991, Mackness et al., 2000, Mackness and Archer, 2001) and the late Pliocene Awe LF of New Guinea (Plane, 1967, Hoch and Holm, 1986) have been radiometrically dated. In distinct contrast, there are hundreds of radiometrically dated Pleistocene assemblages.
Developing an accurate and precise chronology for Australia's Miocene assemblages is critical for many reasons. First, the majority of Australia's pre-Quaternary mammals and mammal assemblages are now known from this epoch. Second, these assemblages document an overlap and gradual transition between relatively archaic groups (e.g., ilariids and wynyardiids) that were common in the late Oligocene and relatively more derived groups (e.g., macropodids and vombatids) that dominated the Pliocene and Quaternary. Third, the history of climate change impacting the continent during this period included a particularly profound transition from the globally warm climates of the early and middle Miocene to late Miocene drier conditions with corresponding impacts on Australia's continental biotas (Kershaw et al., 1994, McGowran and Li, 1994, McGowran et al., 2000). Investigation of any causal links with climate change requires accurate anchoring of the faunal record with those of various climate proxies that are themselves often well-dated. Fourth, it was primarily during the Miocene that the continent's globally unique megafauna began to develop. Finally, most of Australia's modern families of marsupials appear to have developed or at least first appeared during the Miocene. As a result of all these considerations, radiometric dating of Miocene sequences from anywhere on the continent would provide a greatly improved and far more reliable basis for developing an understanding of the timing of these regionally and globally significant evolutionary and environmental processes.
Only two regions of the continent have a reasonably rich as well as demonstrably superpositional sequence of mammal assemblages: northern South Australia (the Lake Eyre and Lake Frome Basins); and the Riversleigh World Heritage Area of northwestern Queensland (Fig. 1). The former has thus far been represented by just one radiometric age determination, in this case a reported Rb–Sr age of 25 Ma for an illite from sediments unrelated to any actual fauna but tentatively correlated with members of the Etadunna Formation that contain LFs of Mammal Zones A–E (Norrish and Pickering, 1983, Woodburne et al., 1994). By calibrating magnetostratigraphic data to a biocorrelated foraminifera fauna and this date, Woodburne et al. (1994) assigned these sediments of the upper Etadunna Formation to the period spanned by palaeomagnetic chrons 6Cr to 7ar.
Although a sustained research programme since 1976 has suggested that Riversleigh's palaeoassemblages span the late Oligocene to early Miocene, middle Miocene, possibly late Miocene, Pliocene and Pleistocene, until now all of these age assessments have been based mainly on biocorrelation, supported in some cases by lithostratigraphic relationships (Arena, 2004, Black et al., 2012a, Arena et al., 2014). Hypothesised biostratigraphic relationships of Riversleigh's more than 200 species-rich assemblages (e.g., Creaser, 1997, Arena, 2004, Travouillon et al., 2006) to each other and to those from other areas of Australia (e.g., Black, 1997a, Black, 1997b, Myers and Archer, 1997, Travouillon et al., 2006, Black, 2010, Black et al., 2013) as well as intercontinentally (e.g., Sigé et al., 1982, Hand et al., 1997, Hand et al., 2005) are still to be tested using fauna-independent techniques.
The Riversleigh region encompasses two limestone units of very distinctive character: an extensive Cambrian (~ 500 Ma) marine dolostone, the Thorntonia Limestone, overlain, down-cut and/or framed by inliers of much younger freshwater limestones containing Cenozoic vertebrate fossils (Archer et al., 1989). These two carbonate types have very distinct chemistries with the Tertiary limestones characterised by low Sr and Mg in contrast to the dolomitised Cambrian limestones with slightly higher Sr but substantially greater Mg, and greatly reduced Ca/Mg ratios (Table 1).
Although providing direct radiometric ages for fossil deposits worldwide is often difficult, many of the sites at Riversleigh are intimately associated with speleothems (stalagmites, stalactites, flowstones, and other secondary cave carbonates) developed in this karst landscape (e.g. Arena et al., 2014). These provide an excellent opportunity for establishing a radiometric chronology. Recent years have seen the rapid development of the U–Pb chronometer for speleothems (e.g. Woodhead et al., 2006, Woodhead et al., 2012) which extends the range of the previously employed carbonate U–Th chronometer back beyond its ~ 600 ka age limit to samples many hundreds of millions of years in age (e.g., Woodhead et al., 2010). This new technique has widespread application across diverse fields of research, from human evolution, palaeontology and ecosystem development, through studies of weathering and erosion, to the influence of tectonics on landscape evolution (Woodhead and Pickering, 2012). This is the first documented application of the method to studies of Neogene biotic change.
Application of the U–Pb chronometer to Riversleigh speleothems, however, is particularly challenging. The majority of the Riversleigh fossil assemblages are hosted in the Cenozoic limestones that are characterised by relatively low U (typically ~ 200 ppb) and high Pb content (often ppm levels) — see Table 1. While the exact controls on Pb incorporation into speleothems remain to be determined (e.g., Woodhead et al., 2012), it is generally accepted that U contents broadly reflect the nature of the host karst, with superimposed climatic controls. It is therefore not surprising that these same low U concentrations are also observed in many speleothems formed in the Riversleigh karst: these typically have U contents significantly less than 1 ppm, especially in older materials (see later section). Pb contents are also often quite high (many tens of ppb) and these two factors result in ratios of radiogenic to ‘common’ Pb2 which are rather demanding for geochronological purposes.
Section snippets
Materials and methods
The basal unit of the Cenozoic Riversleigh limestone sequence has been interpreted to be late Oligocene in age (Archer et al., 1989, Archer et al., 1994, Archer et al., 1995, Archer et al., 1997). It consists largely of calcarenites with interspersed micritic muds, suggestive of a fluvial–lacustrine freshwater environment (Depositional Phase 1) containing faunas of Faunal Zone A (Archer et al., 1989, Arena, 2004, Travouillon et al., 2006). Slightly younger deposits, biocorrelated to early
Results
A wide variety of Riversleigh speleothem samples were assessed for dating potential including stalagmites, flowstones, cave pearls and thin calcite rafts. Ultimately, only stalagmites and flowstones contained a sufficiently high proportion of radiogenic to common Pb for geochronological purposes and, of these, only a small proportion displayed the necessary range in U/Pb ratios to allow for successful isochron construction; these are reported below in order of decreasing age.
Temporal and spatial variation in the Riversleigh deposits
All of the successfully dated Riversleigh samples are speleothems from undisputed cave deposits. Efforts to date Depositional Phase 1 deposits (e.g., D Site and Hiatus Site), biocorrelated to be late Oligocene in age, have so far been unsuccessful. Further, sites with more diverse depositional facies such as Neville's Garden were far better suited to geochronology because they contained well-developed speleothems. Of the Miocene speleothem types trialed for dating – stalagmites, flowstones,
Conclusions
For the first time, it is possible to independently place Australia's early to middle Miocene fossil faunas into a secure geochronological framework. Temporal correlations between faunal composition, evolutionary change and ecological adaptations in response to climatic and environmental drivers during the mid-Cenozoic have been evident for a considerable time (e.g., Archer et al., 1989) but, in the absence of independent and precise radiometric dating, have largely been confined to
Acknowledgements
We thank Alan Greig for assistance with the ICPMS trace element analyses. Development of the U–Pb speleothem chronometer at Melbourne University and continued investigations of the Riversleigh World Heritage Sites have been funded by a variety of grants from the Australian Research Council including LE0989067, LP0989969, LP100200486, DP0985214, DP0664621, DP1094569, DP130100197, and DE130100476, and support from the XSTRATA Community Partnership Program (North Queensland); the University of New
References (95)
- et al.
Application of benthic foraminiferal Mg/Ca ratios to questions of Cenozoic climate change
Earth and Planetary Science Letters
(2003) - et al.
Bearing up well? Understanding the past, present and future of Australia's koalas
Gondwana Research
(2014) - et al.
Precipitation patterns in the Miocene of Central Europe and the development of continentality
Palaeogeography, Palaeoclimatology, Palaeoecology
(2011) - et al.
The Middle Miocene climatic transition — East Antarctic ice-sheet development, deep-ocean circulation and global carbon cycling
Palaeogeography Palaeoclimatology Palaeoecology
(1994) - et al.
Australian Oligo-Miocene mystacinids (Microchiroptera): upper dentition, new taxa and divergence of New Zealand species
Geobios
(2005) - et al.
The Middle Miocene Yallourn coal seam — the last coal in Australia
International Journal of Coal Geology
(2007) - et al.
Seasonal Amazonian rainfall variation in the Miocene Climate Optimum
Palaeogeography, Palaeoclimatology, Palaeoecology
(2005) - et al.
The evolution of Miocene climates in North China: preliminary results of quantitative reconstructions from plant fossil records
Palaeogeography, Palaeoclimatology, Palaeoecology
(2011) - et al.
Palynology of the early Miocene Foulden Maar, Otago, New Zealand: diversity following destruction
Review of Palaeobotany and Palynology
(2014) - et al.
Improving isochron calculations with robust statistics and the bootstrap
Chemical Geology
(2002)
Palaeoecological analyses of Riversleigh's Oligo-Miocene sites: implications for Oligo-Miocene climate change in Australia
Palaeogeography, Palaeoclimatology, Palaeoecology
Tertiary climatic changes at middle latitudes of western North America
Palaeogeography, Palaeoclimatology, Palaeoecology
Beyond 500 ka: progress and prospects in the U–Pb chronology of speleothems, and their application to studies in palaeoclimate, human evolution, biodiversity and tectonics
Chemical Geology
U–Pb geochronology of speleothems by MC–ICPMS
Quaternary Geochronology
U and Pb variability in older speleothems and strategies for their chronology
Quaternary Geochronology
Fossil mammals of Riversleigh, northwestern Queensland: preliminary overview of biostratigraphy, correlation and environmental change
The Australian Zoologist
Riversleigh: The Story of Animals in Ancient Rainforests of Inland Australia
Description of the skull and non-vestigial dentition of a Miocene platypus (Obdurodon dicksoni n. sp.) from Riversleigh, Australia, and the problem of monotreme origins
Patterns in the history of Australia's mammals and inferences about palaeohabitats
Tertiary environmental and biotic change in Australia
Correlation of the Cainozoic sediments of the Riversleigh World Heritage fossil property, Queensland, Australia
Current status of species-level representation in faunas from selected fossil localities in the Riversleigh World Heritage Area, northwestern Queensland
Alcheringa Special Issue
The palaeontology and geology of Dunsinane Site, Riversleigh
Memoirs of the Queensland Museum
The geological history and development of the terrain at the Riversleigh World Heritage Area in the middle Tertiary
Exceptional preservation of plants and invertebrates by phosphatization, Riversleigh, Australia
PALAIOS
Reconstructing a Miocene pitfall trap: recognition and interpretation of fossiliferous Cenozoic palaeokarst
Sedimentary Geology
Mammalian lineages and the biostratigraphy and biochronology of Cenozoic faunas from the Riversleigh World Heritage Area, Australia
Lethaia
A new species of Palorchestidae (Marsupialia) from the late middle to early late Miocene Encore Local Fauna, Riversleigh, northwestern Queensland
Memoirs of the Queensland Museum
Diversity and biostratigraphy of the Diprotodontoidea of Riversleigh, northwestern Queensland
Memoirs of the Queensland Museum
Ngapakaldia bonythoni (Marsupialia, Diprotodontidae): new material from Riversleigh, northwestern Queensland, and a reassessment of the genus Bematherium
Alcheringa: An Australasian Journal of Palaeontology
First crania and assessment of species boundaries in Nimbadon (Marsupialia: Diprotodontidae) from the middle Miocene of Australia
American Museum Novitates
First comprehensive analysis of cranial ontogeny in a fossil marsupial-from a 15-million-year-old cave deposit in northern Australia
Journal of Vertebrate Paleontology
The rise of Australian marsupials: a synopsis of biostratigraphic, phylogenetic, palaeoecological and palaeobiogeographic understanding
Herds overhead: Nimbadon lavarackorum (Diprotodontidae), heavyweight marsupial herbivores in the Miocene forests of Australia
PLoS ONE
Revision in the marsupial diprotodontid genus Neohelos: systematics and biostratigraphy
Acta Palaeontologica Polonica
A new species of the basal “kangaroo” Balbaroo and a re-evaluation of stem macropodiform interrelationships
PLoS ONE
The Oligo-Miocene coal floras of southeastern Australia
A swiftlet (Apodidae: Collocaliini) from the Oligo-Miocene of Riversleigh, northwestern Queensland
Memoir of the Association of Australasian Palaeontologists
A new species of the wombat Warendja from late Miocene deposits at Riversleigh, north-west Queensland, Australia
Palaeontology
Silcrete plant fossils from Lightning Ridge, New South Wales: new evidence for climate change and monsoon elements in the Australian Cenozoic
Australian Journal of Botany
Oligocene-Miocene sediments of Riversleigh: the potential significance of topography
Memoirs of the Queensland Museum
On the mechanism of uranium binding to cell wall of Chara fragilis
European Biophysics Journal
Palorchestes azael (Mammalia, Palorchestidae) from the late Pleistocene Terrace Site Local Fauna, Riversleigh, northwestern Queensland
Memoirs of the Queensland Museum
Hydrologic cycling over Antarctica during the middle Miocene warming
Nature Geoscience
Earliest known Australian Tertiary mammal fauna
Nature
Eocene monsoon forests in central Australia?
Australian Systematic Botany
Plant macrofossil evidence for the environment associated with the Riversleigh fauna
Australian Journal of Botany
Cited by (85)
The role of inherited Pb in controlling the quality of speleothem U-Pb ages
2022, Quaternary GeochronologyCitation Excerpt :The capacity of speleothem U-Pb dating to access terrestrial records beyond the ∼650 ka limit of U-Th dating has grown considerably in two decades (Richards et al., 1998; Woodhead et al., 2006) with advances in both laser ablation and solution mass spectrometry. This in-turn has opened new applications of speleothems to solving ‘deep-time’ questions, particularly in the fields of palaeoclimatology (e.g., Bajo et al., 2020; Vaks et al., 2020), palaeontology (e.g., Woodhead et al., 2016; Sniderman et al., 2016), landscape reconstruction (e.g., Decker et al., 2018; Engel et al., 2020b), and human evolution (e.g., Pickering et al., 2019). The utility of this longer-lived chronometer differs from the speleothem U-Th method (Richards and Dorale, 2003; Scholz and Hoffmann, 2008) in that the longer timespans naturally associated with deep-time limits the application of palaeo-proxy time series to most U-Pb speleothem applications.
Paleobiological implications of the bone histology of the extinct Australian marsupial Nimbadon lavarackorum
2023, Journal of PaleontologyA conserved tooth resorption mechanism in modern and fossil snakes
2023, Nature Communications