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How the natural “glaze” on the walls of the rock shelter in Kimberly helps reveal the world in which the artist lived

Cuple, or circular artificial indentations, are crushed into dark mineral coatings at the Rock Art Site on the Drysdale River in Balangala. Credit: Damien Finch

The Kimberley region is home to Australia’s oldest known rock painting. However, people carved some of these rocks before making the painting.


There are many such sculptures on the rock art site of Barangara Country in northeastern Kimberley. The oldest paintings are at least 17,300 years old, and the sculptures are considered even older, but so far they have proven to be much more difficult to date accurately.

But in research Released today Science AdvancesWe will report on important clues that will help you date the sculptures and clarify what the environment of the artist who created them was.

Some rocks themselves are covered with a natural glaze-like mineral coating that helps reveal important evidence.

What are these glazes?

These dark and shiny deposits on the surface of stone The thickness is less than 1 cm.Still they give details Internal structureIt is characterized by alternating bright and dark layers of different minerals.

Our aim was to develop a method to reliably dating the formation of these coatings and to provide an age group for the associated engraving. However, during this process, we also found that it was possible to match the layers found in the samples collected in. Rock shelter It is up to 90 kilometers away.

How the natural

At a rock art shelter in northeastern Kimberley, a marsupial truck was glazed like a coating. Credits: Photo by Cecilia Myers / Dunkeld Pastoral Company.Illustration by Pauline Heaney / Rock Art Australia

Radiocarbon dating suggests that these layers were deposited at about the same time, and their formation is not endemic to any particular ledge. Environmental changes On a regional scale.

Therefore, dating these deposits provides a reliable age group for the associated sculptures, while at the same time helping to better understand the climate and environment in which the artist lived.

Microorganisms and minerals

Our research is Previous findings Its layers within the glaze structure represent alternating Environmental condition At the Kimberley ledge, it has been repeated for thousands of years.

Our model suggests that wildfires produce ash during a drier condition, which accumulates on the surface of the shelter. This ash contains various minerals such as carbonates and sulfates. Under the right conditions, these minerals propose to provide nutrients that allow microorganisms to live on the surface of these shelters. In the process of digesting these nutrients, microorganisms excrete a compound called oxalic acid. Oxalic acid combines with calcium in ash deposits to form calcium oxalate.

How the natural

A: Dark, smooth mineral coating at the rock shelter in Kimberley. B: Alternating layers as seen in the field. C: Alternating layers seen in the cross-section coating under a microscope.Credit: Cecilia Myers; Microscopic image by Helen Green

When this process is repeated for thousands of years, the minerals are combined into alternating layers, each layer creating a record of the state of the ledge at that time.

Glaze samples were collected for close collaboration and consultation analysis with local traditional owners from the native title area of ​​Balangala, our research project partner. A laser was used to evaporate a small sample from the coating to study the chemical composition of each layer. The dark layer was mainly made of calcium oxalate, while the light layer was mainly containing sulfate. It is suggested that the dark layer represents the period when the microorganisms were more active and the light layer represents the drier period.

Layer link

These dark calcium oxalate layers also contain carbon that has been absorbed from the atmosphere and digested by the microorganisms that produced these deposits.This meant that we could use a technique called Radiocarbon dating Determine the age of these individual layers.

A small drill was used to remove samples from different dark layers of nine glazes collected from various rock shelters in northeastern Kimberley.

How the natural

A: Microdrill samples from individual layers for radiocarbon dating. B: Laser ablation map showing the distribution of calcium elements in different layers. C: Radiocarbon dating of individual layers identified four major growth periods.Credits: Andy Gleadow; Illustration by Pauline Heaney

Despite coming from different locations, all of these layers appear to have been deposited simultaneously during the four major intervals over the last 43,000 years.

This suggests the formation of each layer It was determined primarily by changes in environmental conditions throughout Kimberley, rather than the individual conditions of each particular ledge.

Records held by these glazes over a very long period of time, including the recent ice age, mean that they may help to better understand the environmental changes that directly affected human habitation and adaptation in Australia. increase.

Stone story

Study us Published earlier this year It shows how Kimberly’s early rock art themes changed from predominantly flora and fauna about 17,000 years ago to predominantly decorated figures about 12,000 years ago.

How the natural

A fictitious example of how layered mineral coatings can be used to dating rock paintings carved at the Kimberley ledge. Credit: Pauline Heaney

other researcher During the last 5,000 years, we have discovered that sea levels have risen sharply and rainfall has increased, especially about 14,500 years ago.

Changes in rock art style are interpreted as a response to the social and cultural adaptations caused by climate change and rising sea levels. Pictures of people using new techniques such as javelin throw may show how people have adapted their hunting styles to changing environments and the availability of different types of food.

We hope that by dating the natural mineral coatings on the surface of the rock that acted as the canvas for this art, we can better understand the world in which these artists lived. This is not only more certain about the position of a particular painting in the whole. Kimberly style rock art sequenceBut it also tells us about the environment experienced by Kimberly’s indigenous peoples.


A new dating technique reveals Australia’s oldest known rock painting, and it’s a kangaroo


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How the natural “glaze” on the walls of the rock shelter in Kimberly helps reveal the world in which the artist lived

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