Monthly archives of “January 2017

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Aboriginal Paintings of the Kimberley- very old Pleistocene or not so old Holocene?

Many of the real advances in science seem to come from a sudden ‘insight’ ( think Archimedes and “Eureka!”) – and there is often no simple connection between collecting data and that ‘aha!’ moment.  The tedious data collection happens, but at some moment, the brain, perhaps quite subconsciously, puts two and two together, and comes up with something more than four. Grahame Walsh was a man who dedicated most of his life to studying the ancient rock paintings of Australia. After having spent about twenty years recording paintings in the Canarvon Gorge region of Queensland (and many other parts of the state), he also spent thirty working in the Kimberley – the remote, north-west corner of the continent.

The extraordinary Grahame Walsh - an authority on Australian rock paintings.

The extraordinary Grahame Walsh – an authority on Australian rock paintings.

The fundamental part of his research was a grueling regime of surveying. Scattered over the rock outcrops in the Kimberley there is a series of often very distinct painting styles. There are rock faces where there are layers of paintings, one over the other. Oddly, the older paintings are often better preserved than the younger, as they are ‘sealed’ by a layer of natural silica varnish.  These superimposed layers provide a kind of stratigraphy of painting styles, and persistent study by Walsh and others, worked out the relative order of these painting styles. But the big mystery, was not the relative but the absolute date. Just how old were they? Almost all of the sites with paintings do not have associated archaeological  material that can be easily  dated.

Thousands of years of overlapping rock paintings in Australia's Kimberley region. Instances like these provide a kind of 'stratigraphy' that allowed researchers such as Grahame Walsh, to work out the relative order of painting styles.

Thousands of years of overlapping rock paintings in Australia’s Kimberley region. Instances like these provide a kind of ‘stratigraphy’ that allowed researchers such as Grahame Walsh, to work out the relative order of painting styles.

Walsh came up with a compelling scenario. A part of the painting style sequence could be interpreted as passing from an earlier time of abundance, where the paintings emphasised personal adornment, with no indication of aggression or violence. These have been called the ‘Bradshaw’ style, although ‘Gwion’ is used by some researchers (see figure below and the featured image).  The paintings then become militaristic, including regimented ‘toy soldier’ like individuals, with weapons. Then there was an apparent long gap, where no paintings were made, but existing paintings were ‘sealed in’ with a layer of natural rock varnish. After an unknown period of time, painting began again, but in an entirely different style. These continued to be painted until the Europeans invaded.

An example of the Bradshaw style of Kimberley rock paintings. Nice the costume 'finery' and ornate hair styles.

An example of the Bradshaw style of Kimberley rock paintings. Nice the costume ‘finery’ and ornate hair styles.

To Walsh, it seemed like this particular sequence recorded first a time of resource abundance – essentially ‘good-times’, which then passed to scarcity, resulting in violence. Then there was a time gap – when environmental conditions may have been so bad, that no one was in the area at all. Finally, when conditions improved again, a new culture moved into the area with different ideas about what to paint. Walsh’s insight was to suspect that this sequence was the run-up to the peak of the Last Glacial Maximum (around 17,000-21,000 years ago), and then the return to good times in the post-glacial Holocene. At Glacial Maximum, there was so  much water tied up in the worlds ice caps, that parts of Australia became super dry and humans were probably driven out of some areas – hence a gap in painting.  It was so dry that constant dust storms were blowing – and these were the cause of  the rock varnish.

Confirming this scenario was the problem. Walsh collaborated with some other researchers who had developed specialised techniques to date minute pieces of material. Richard Roberts used a technique (Optically Stimulated Luminescence – OSL)  that determines how long ago quartz grains were exposed to sunlight. The brilliant part here is that mud wasps in the Kimberley build their nests in the same rock overhangs as the paintings. Mud containing quartz grains is collected bit by bit by the wasp- and it is exposed ti the sun. But when it gets packed away into a next, it is sealed in darkness.

The core of one mud wasp nest yielded an age of  around 17,500 years (Roberts et al. 1997). This implied that a possible Bradshaw figure was even older, and the stencil of a hand below that, older still. It meant that these were painted at, or even before the Last Glacial Maximum. It supported Walsh’s insight. This date makes the Bradshaw Paintings remarkably old – perhaps older than the famous paintings at Lascaux in France, which are about 18,000 years old.

An example of a typical rock outcrop with Bradshaw rock paintings. There may be hundreds of paintings in such a spot - but little or no trace of who painted them in the ground below.

An example of a typical rock outcrop with Bradshaw rock paintings. There may be hundreds of paintings in such a spot – but little or no trace of who painted them in the ground below.

Another researcher involved in the study of the paintings was Alan Watchman. One of his specialties is the carbon dating very small fragments, and as well, he has an interest in the kind of rock varnish that covers the older paintings. Watchman collaborated with Walsh to collect material from paintings that could be dated, for example, a beeswax resin component . However, when he published his results, in the same year as Roberts and co-authors work on the mud wasp nests (Watchman 1997; Watchman et al. 1997), Walsh was not included as a co-author, and Watchman came up with very different results. Watchman’s pioneering estimates for the age of some Bradshaw figures and some from an even older painting style, were in the range of (only) 3,000-4000 years.

An example of a much younger painting style than the Bradshaws.

An example of a much younger painting style than the Bradshaws.

Robert’s Pleistocene results came under intense scrutiny. For instance, Aubert (2012) focused on both the location of the wasp nests with relation to the paintings, and details of their sampling and, in a blow to Team-Walsh,  concluded that there was “no substantial evidence” for a Pleistocene age. On the other hand, Bednarik (2014) threw a life-line to Team-Walsh by arguing that the organic material within the paint residues  may have been “acquired subsequent to the time of rock art production”.  In other words, there was now a mechanism to account for the young dates obtained by Watchman, but still have old paintings.

However, at around this time another group of workers came up with a new scenario for the sequence of Kimberley paintings.  They basically agreed with Walsh about the climatic significance of a ‘gap’ – but they incorporated Watchman’s younger Holocene dates.  Based on a record of fossil pollen, charcoal and dust, McGowan et al. (2012) found evidence for an exceptionally dry phase in the Kimberley in the mid Holocene. Thus, they proposed that Walsh’s ‘gap’ was not at the height of the Last Glacial Maximum, but relates to a ‘mega drought’ that occurred around 6300-3400 years ago and which was triggered by changes in the El Niño Southern Oscillation. This paper got my attention, and it was what stimulated me to write this. Was Walsh’s claim of amazingly old paintings wrong after all?

Come 2016 and out came a new paper (Ross et al 2016) using the OSL technique on mudwasp nests. It was mostly  a new group of researchers and a far more rigorous procedure was used than the pioneering work of Roberts et al. The minimum age of one painting was established at 16,000 years old. Unfortunately that particular figure could not be clearly placed into one of Walsh’s painting styles. That is disappointing, but the important conclusion is that Pleistocene aged rock painting in the Kimberley has probably been solidly established. McGowan et al’s drought was surely real, but just not the cause of the gap in the painting sequence.

Science seems to jump forward with ‘insights’. They may or not actually be right, but they do tend to stimulate more research, and that’s a good thing. In any case, my money is on Walsh being on the mark.

References

Aubert, M., 2012. A review of rock art dating in the Kimberley, Western Australia. Journal  of Archaeological  Science 39, 573–577.

McGowan, H., Marx, S., Moss, P.T., Hammond, A., 2012. Evidence of ENSO mega-drought triggered collapse of prehistory Aboriginal society in northwest Australia. Geophysical Research Letters 39, L22702.

Morwood, M.J., Walsh, G.L., Watchman, A.L., 2010. AMS Radiocarbon Ages for Beeswax and Charcoal Pigments in North Kimberley Rock Art. Rock Art Research: The Journal of the Australian Rock Art Research Association (AURA) 27, 3-8

Roberts, R., Walsh, G., Murray, A., Olley, J., Jones, R., Morwood, M., Tuniz, C., Lawson, E., Macphail, M., Bowdery, D., Naumann, I., 1997. Luminescence dating of rock art and past environments using mud-wasp nests in northern Australia. Nature 387, 696-699.

Ross, J., Westaway, K., Travers, M., Morwood, M.J., Hayward, J., 2016. Into the Past: A Step Towards a Robust Kimberley Rock Art Chronology. PLoS ONE 11, e0161726. doi:0161710.0161371/journal.pone.0161726.

Walsh, G.L., 1994. Bradshaws: Ancient Rock Paintings of North-West Australia. The Bradshaw Foundation, Geneva.

Watchman, A.L., 1997. Dating the Kimberley rock paintings, in: Kenneally, K.F., Lewis, M.R., Donaldson, M., Clement, C. (Eds.), Aboriginal Rock Art of the Kimberley. The Kimberley Society, Perth, pp. 39-45.

Watchman, A.L., Walsh, G.L., Morwood, M.J., Tuniz, C., 1997. AMS radiocarbon dating age estimates for early rock paintings in the Kimberley, N. W. Australia: Preliminary results. Rock Art Research: The Journal of the Australian Rock Art Research Association (AURA) 14, 18–26.

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The Biggest Tree Stump in the Curio Bay Jurassic Forest

Back in the late 1980s I had the pleasure of meeting the English scientist David Bellamy. Bellamy was famous at the time as ‘The Botanic Man’, and he was in New Zealand to film for ‘Moa’s Ark’, a TV series and book about the development of New Zealand’s flora and fauna (including the extinct moa birds) over time. ‘Moa’s Ark’ describes the view that New Zealand broke away from the edge of Gondwana (in this case, Australia and Antarctica) and drifted into the Pacific with a compliment of life that was then preserved in isolation for many millions of years. I don’t subscribe to that view – but hats off to the series and the book (and the title!). They were an inspired bit of science communication.

Curio Bay is a petrified forest of Jurassic age, located in southernmost New Zealand. This was when New Zealand was firmly attached to Gondwana. You could have walked to what was going to become  Australia or Antarctica from Curio Bay at the time. If you wanted a place to start talking about the voyage of ‘Moa’s Ark’, you could hardly beat the real Gondwanan fossil forest at Curio Bay.

The largest tree stump in the Jurassic fossil forest at Curio Bay, New Zealand.

The largest tree stump in the Jurassic fossil forest at Curio Bay, New Zealand.

 

I ended up in contact with Bellamy because of my work on Curio Bay. I had mapped part of the forest, studied the rocks that encompass the fossil forest, and searched the coastline for many kilometers either side of it for additional clues.

Curio Bay seems to have been a first generation forest. There was a flood that deposited sediment over a large area, forming a ‘clean slate’ for a new forest to grow. When the forest was preserved – by another flood, silica from the sediment percolated the wood and preserved it. In many cases you can walk around the forest and can see at least some of the growth rings in the tree stumps. On this basis, most of the trees in the forest were rather young when they were preserved, say 50-60 years. There are a few that much older, perhaps around 200 years. These may have been the very first trees to colonise the new flood plain surface. Gradually, the space around them was filled in by more trees. The fact that there are growth rings at all, tells us that there was some kind of seasonality – perhaps temperature, or even light conditions (the forest grew much nearer the South Pole than it is today.

David Bellamy (arm outstretched) and his Moa's Ark crew beside the largest tree stump at the Jurassic fossil forest of Curio Bay, New Zealand (1989).

David Bellamy (arm outstretched) and his Moa’s Ark crew beside the largest tree stump at the Jurassic fossil forest of Curio Bay, New Zealand. (1989).

I showed David Bellamy and his crew around the fossil forest, taking them to what is the most prominent large fossil stump. The idea at the time was that Bellamy would be Robin Hood, in Sherwood Forest, England, and shooting off an arrow. The arrow was to fall, and bounce off one of the petrified logs at Curio Bay, and story would begin. When I pointed out the big stump, and its growth rings (see the featured image), Bellamy, a gifted communicator – placed the arrow head-down, its tip on one of the growth rings. “I wonder what story this might tell us?” he asked – and proceeded to run round and round the stump, like a record player (note to younger generations, these were devices to play music from flat disks. The typical speed was 33 rpm, or a faster 45 rpm). After a couple of revolutions, Bellamy announced: “Wrong speed!”, and ran round and round even faster.

“What story?” indeed. I’ve added to it, but Curio Bay and its fossil forest will have more to tell us yet.

References

*Clicking on these links will take you to my Academia.edu site, where you can download a pdf of the paper.

Pole, M.S., 2001. Repeated flood events and fossil forests at Curio Bay (Middle Jurassic), New Zealand. Sedimentary Geology 144, 223-242.

Pole, M.S., 1999. Structure of a near-polar latitude forest from the New Zealand Jurassic. Palaeogeography, Palaeoclimatology, Palaeoecology 147, 121-139.

Pole, M., 2004. Early-Middle Jurassic stratigraphy of the Fortrose-Chaslands region, southernmost South Island, New Zealand. New Zealand Journal of Geology & Geophysics 47, 129-139.

Pole, M., 2009. Vegetation and climate of the New Zealand Jurassic. GFF 131, 105 – 111.