There is a need to record and document rock art images as they face deterioration from environmental, industrial and human impacts. A new pilot project by Jennifer Lynn Milani (Flinders University, Adelaide, South Australia ) trials the use of magnetic susceptibility (MS) meter to non-invasively detect and spatiallly resolve ochre rock art images.
Ochre is frequently used in rock art production and research has shown that it emits a MS signature due to its magnetic characteristics. These ochre images can be hidden behind silica or carbonate crusts or may deteriorate ove time limiting their visibility. The rock art images that lie behind such crusts are likely to be protected from weathering and are amenable to dating using such techniques as uranium mass spectometry (AMS).
The new Australian research demonstrates that, if present in sufficient abundance, red ochre can be imaged and spatially resolved with a MS meter when applied to a rock face in a variety of geological environments. The type of binder used, pre-application heating or the rocktype itself does not appear to have a significant effect on the viability of the technique. Imaging ochre beneath a proxy crust was also trialled without success; however this is attributed to poor survey design rather than a fundemental problem with the technique.
This pilot project demonstrates that more important to the success of a survey is the equipment setting, the spatial resolution of the survey and the use of a correction to control instrument drift. It also demonstrates the validity of continuing investigations in the emerging field of rock art geophysics ad highlights the importance of future trials on field sites.
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