Stranger than fiction: distinguishing between anthropogenic and non-anthropogenic rock markings

This paper first briefly reviews a classification of geological and biological rock markings. It then examines the nature of a previously baffling geological phenomenon in western Victoria, found so far at four sites. The clustered groups of circular rock markings have been defined as Aboriginal petroglyphs by both archaeological and geological review- ers. They are 'cannonballs' - spherical inclusions in the sandstone that became sectioned by unloading events, and they are attributable to inherent diagenic features of the rock. The circle 'petroglyphs' are, in fact, reaction fronts where carbon derived from decaying animal tissue caused the spherically expanding precipitation of CaCO3 before the final lithification of the sandstone. The paper then reports several examples of misidentification of rock markings in recent years that led to the discoveries of geological processes, such as compressive-tensile rock marking, kinetic tree root marking and kinetic energy metamorphosis. In such cases, it was through their connection with rock art rather than basic geological research that under- standings of these effects were secured.