Into the Past: A Step Towards a Robust Kimberley Rock Art Chronology

Dating correlated microlayers in oxalate accretions from rock art shelters: New archives of paleoenvironments and human activity

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.

A global environmental crisis 42,000 years ago

Geological archives record multiple reversals of Earth's magnetic poles, but the global impacts of these events, if any, remain unclear. Uncertain radiocarbon calibration has limited investigation of the potential effects of the last major magnetic inversion, known as the Laschamps Excursion [41 to 42 thousand years ago (ka)]. We use ancient New Zealand kauri trees (Agathis australis) to develop a detailed record of atmospheric radiocarbon levels across the Laschamps Excursion. We precisely characterize the geomagnetic reversal and perform global chemistry-climate modeling and detailed radiocarbon dating of paleoenvironmental records to investigate impacts. We find that geomagnetic field minima ~42 ka, in combination with Grand Solar Minima, caused substantial changes in atmospheric ozone concentration and circulation, driving synchronous global climate shifts that caused major environmental changes, extinction events, and transformations in the archaeological record.

Ages for Australia's oldest rock paintings

Naturalistic depictions of animals are a common subject for the world's oldest dated rock art, including wild bovids in Indonesia and lions in France's Chauvet Cave. The oldest known Australian Aboriginal figurative rock paintings also commonly depict naturalistic animals but, until now, quantitative dating was lacking. Here, we present 27 radiocarbon dates on mud wasp nests that constrain the ages of 16 motifs from this earliest known phase of rock painting in the Australian Kimberley region. These initial results suggest that paintings in this style proliferated between 17,000 and 13,000 years ago. Notably, one painting of a kangaroo is securely dated to between 17,500 and 17,100 years on the basis of the ages of three overlying and three underlying wasp nests. This is the oldest radiometrically dated in situ rock painting so far reported in Australia.

Archaeology and art in context: Excavations at the Gunu Site Complex, Northwest Kimberley, Western Australia

The Kimberley region of Western Australia is one of the largest and most diverse rock art provenances in the world, with a complex stylistic sequence spanning at least 16 ka, culminating in the modern art-making of the Wunumbal people. The Gunu Site Complex, in the remote Mitchell River region of the northwest Kimberley, is one of many local expressions of the Kimberley rock art sequence. Here we report excavations at two sites in this complex: Gunu Rock, a sand sheet adjacent to rock art panels; and Gunu Cave, a floor deposit within an extensive rockshelter. Excavations at Gunu Rock provide evidence for two phases of occupation, the first from 7-8 to 2.7 ka, and the second from 1064 cal BP. Excavations at Gunu Rock provide evidence for occupation from the end of the second phase to the recent past. Stone for tools in the early phase were procured from a variety of sources, but quartz crystal reduction dominated the second occupation phase. Small quartz crystals were reduced by freehand percussion to provide small flake tools and blanks for manufacturing small points called nguni by the Wunambal people today. Quartz crystals were prominent in historic ritual practices associated with the Wanjina belief system. Complex methods of making bifacially-thinned and pressure flaked quartzite projectile points emerged after 2.7 ka. Ochre pigments were common in both occupation phases, but evidence for occupation contemporaneous with the putative age of the oldest rock art styles was not discovered in the excavations. Our results show that developing a complete understanding of rock art production and local occupation patterns requires paired excavations inside and outside of the rockshelters that dominate the Kimberley.

12,000-Year-old Aboriginal rock art from the Kimberley region, Western Australia

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.