Browsing by Author "Heaney, P"

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    12,000-Year-old Aboriginal rock art from the Kimberley region, Western Australia
    (American Association for Advancement of Science, 2020-02-05) Finch, D; Gleadow, AJM; Hergt, J; Levchenko, VA; Heaney, P; Veth, P; Harper, S; Ouzman, S; Myers, C; Green, H
    The Kimberley region in Western Australia hosts one of the world’s most substantial bodies of indigenous rock art thought to extend in a series of stylistic or iconographic phases from the present day back into the Pleistocene. As with other rock art worldwide, the older styles have proven notoriously difficult to date quantitatively, requiring new scientific approaches. Here, we present the radiocarbon ages of 24 mud wasp nests that were either over or under pigment from 21 anthropomorphic motifs of the Gwion style (previously referred to as “Bradshaws”) from the middle of the relative stylistic sequence. We demonstrate that while one date suggests a minimum age of c. 17 ka for one motif, most of the dates support a hypothesis that these Gwion paintings were produced in a relatively narrow period around 12,000 years ago. © 2020 American Association for the Advancement of Science.
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    Dating correlated microlayers in engraved, oxalate-rich accretions: new archives of paleoenvironments and human activity from Australian rock art shelters
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Green, H; Finch, D; Gleadow, AJM; Hoy, J; Levchenko, VA; Myers, C; Heaney, P; Pickering, R
    Distinctive, dark coloured, glaze-like mineral accretions, often found in rock shelters around the world, offer important opportunities for radiocarbon dating of associated rock art. The mineralogy of these accretions is dominated by well-crystallised calcium oxalate and sulphate minerals, most commonly whewellite and gypsum, with significant occurrences of phosphates in some samples. The accretions are typically several millimetres thick and characterised by distinctive internal laminations that exhibit regular stacked undulations giving a stromatolitic appearance under the microscope. Together with other apparently microbial features observed under the SEM, these features provide strong support for a microbiological origin for these oxalate-rich accretions. Risks surrounding contamination and open system behaviour, previously limiting the application of radiocarbon dating to these accretions, are addressed by the well-crystallised nature of the oxalates and the preservation of fine laminar features within their internal stratigraphies. In a case study from the north Kimberley region of north-western Australia, we demonstrate the use of sample characterisation and chemical pre-treatment techniques to pre-screen for evidence of open system behaviour and address potential contamination. The results provide stratigraphically consistent sequences of radiocarbon dates in mm-scale laminated accretions, with correlations between distinctive patterns in the layer sequences visible in rock shelters up to 90 km apart. This demonstrates that pre-screened samples offer opportunities to reliably date rock art, particularly symbolic markings commonly engraved into these relatively soft deposits and suggests their synchronised formation is not entirely shelter specific but broadly controlled by variations in regional environmental conditions. Consequently, these accretions also offer potential as paleoenvironmental archives, with radiocarbon dating of layers in nine accretions indicating four, approximately synchronous growth intervals covering the last 43 ka.
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    Dating correlated microlayers in oxalate accretions from rock art shelters: new archives of paleoenvironments and human activity
    (American Association for the Advancement of Science, 2021-08-13) Green, H; Gleadow, AJM; Levchenko, VA; Finch, D; Myers, C; McGovern, J; Heaney, P; Pickering, R
    Oxalate-rich mineral accretions, often found in rock shelters around the world, offer important opportunities for radiocarbon dating of associated rock art. Here, sample characterization and chemical pretreatment techniques are used to characterize the accretions, prescreen for evidence of open-system behavior, and address potential contamination. The results provide stratigraphically consistent sequences of radiocarbon dates in millimeter-scale laminated accretions, demonstrating their reliability for dating rock art, particularly symbolic markings commonly engraved into these relatively soft deposits. The age sequences are also consistent with correlations between distinctive patterns in the layer sequences visible in shelters up to 90 km apart in the Kimberley region of northwestern Australia, suggesting their synchronized formation is not entirely shelter specific but broadly controlled by variations in regional environmental conditions. Consequently, these accretions also offer potential as paleoenvironmental archives, with radiocarbon dating of layers in nine accretions indicating four, approximately synchronous growth intervals covering the past 43 ka. © The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution 4.0.
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    From radiocarbon dating of mud wasp nests to ages for early Australian rock art
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Finch, D; Gleadow, AJM; Hergt, J; Green, H; Levchenko, VA; Heaney, P
    Northern Australia is home to some of the richest rock art provinces in the world. It has long been thought that the oldest of the rock art still visible today may date back to the Pleistocene period, more than 11,000 years ago. Until recently, after more than 30 years of research, there were only one or two quantitative, radiometric, age determinations to support this view. Importantly, there was certainly insufficient data to say when some of the oldest, very distinctive, styles of rock art were created and there were no age estimates at all for the oldest style of figurative rock painting. Here, we report on the development of radiocarbon dating methods to provide the first estimates of the ages spanned by the two earliest styles of painted rock art in the Kimberley region in northwest Australia. Mud wasp nests overlying, or underlying rock art were dated to provide maximum and minimum age constraints for rock art motifs. Radiocarbon dating of fossilised mud that sits exposed on rock shelter walls for millennia poses many challenges. The sources of carbon in the nest when it is built need to be identified so that the relationship between the age of the nest, and the age of the carbon in it, is well characterised. As the nest ages, organic and inorganic components will undergo different taphonomic processes that need to be identified to determine if the fossilised nest behaves as a closed system for carbon and to understand which sources of carbon will be preserved. Mineral accretions commonly develop on all exposed surfaces in these rock shelters, including old wasp nests, so the mineralogy of these and any aeolian contamination such as ash and pollen needs to be understood so that appropriate treatments can be designed to remove any such contamination. Wasp nests gradually weather away so the older nests are small and have very low carbon concentrations. Many samples yield less than 10μg of carbon, challenging the limit of what is possible to measure reliably, so pretreatment methods must be optimised to maximise yield while minimising the risk of contamination. Here we review the methods used to address these challenges. We then report on the results of the dating program, so far, including the first chronometric estimates for the two earliest periods in the stylistic sequence of painted Kimberley rock art. We show that both periods date back to the terminal Pleistocene with evidence of the oldest art painted at the end of the Last Glacial Maximum, around 17,000 years ago.