1. Dating Techniques and Varnish

2. Dating Rock Art Relative Dating –Degree of weathering –Superimposition analysis –Stylistic analysis –Spatial Analysis (Inter-Site Patterning)

3. Dating Rock Art Absolute Dating –Historical information –Subjects –Stratified art –Association –Direct dating

4. ROCK ART DATING TECHNOLOGIES Amino Acid Racemisation AMS OSL Lichenometry Micro-erosion analysis

5. Rock / Desert Varnish Explained

6. Rock / Desert Varnish a biogenic deposit produced by mixotrophic bacteria living on rock surfaces, digesting organic debris. Layers may reach ages of 10^3 10^5 yrs Tiny Elvis Layers

7. Rock / Desert Varnish Environment –Arid – Semiarid environments are optimal for growth Hyper-arid environments lack water for bacterial growth Mesic environments: lichen growth destroys rock varnish

8. But what is it? It is a coating of clay particles with minerals deposits of iron and manganese oxides. Mostly wind blown. Other Minerals Include- –hydroxides plus silica and calcium carbonate

9. So how’s it formed? Nobody knows. Theory is… –Manganese oxides in rock varnish block the transmission of ultraviolet radiation. –SPF 300 for microbes?

10. Why the variety in color and appearance? Rate of bacterial growth relative to clay accumulation produces appearance –dark dull varnish = bacterial dominant light shiny varnish = clay dominant Fluctuations in clays and Fe and Mn oxides and hydroxides produce color –black: manganese-rich red: iron-rich