Factors that interfere with the age determination of rock varnish

Over the past few years the rock varnish literature has proliferated. More than a dozen research groups in at least six countries are now investigating the potential of rock varnish as a Quaternary dating technique for geomorphical and archaeological studies. New backscattered electron microscopy imagery of varnishes from southwestern North America illustrates the need for great caution in the selection of samples for all varnish dating methods. Nine general factors that may interfere with varnish dating are presented. For varnish dating to be successful, these factors must be evaluated by careful examination of samples in the field and by analyses of many cross-sections in the laboratory.