USE OF ARCHAEOLOGICAL SITES IN DEVELOPMENT OF LICHEN GROWTH CURVE, COLCA VALLEY, PERUVIAN ANDES

Lichenometry uses the diameter of a radially growing lichen to date surface exposure. This technique depends on the development of a local growth curve for the lichen species used. Typically, lichen growing on surfaces of known age, such as tombstones, landslide scars, and glacial moraines, are used to develop the curves. Usually, this means that accurate data points are only available from the past 200 years. This study uses archaeological sites of well constrained age (both the dates that the structures were erected and abandoned are known from documentary evidence), as well as data collected from area tombstones and a recently constructed bridge to develop a growth curve for the Colca Valley (elevation 3800-4500 m) in the southern Peruvian Andes. This growth curve (for Rhizocarpon geographicum) comprises data from sites ranging from 17 to 437 ya, a wider range with much older points than typical growth curves. If a linear growth rate is assumed, the lichen diameters are found to increase at a rate of 0.885 mm/yr. This growth rate can be used to accurately date glacial moraines, archaeological sites, and other surfaces of unknown age into the late Holocene. Both the development and the application of this growth curve have multidisciplinary aspects that include Earth sciences and archaeology.