Light Thrown on History – The Dating of Stone Surfaces at the Geoglyphs of Palpa Using Optically Stimulated Luminescence

Abstract

A foremost goal of the Nasca-Palpa project was the development of a method allowing the numeric dating of the renowned geoglyphs. Hitherto, the various types of geoglyphs had been dated solely by the principles of superposition and archaeological style. Due to the almost total lack of organic materials, radiocarbon dating is not applicable in this case. Because the geoglyphs were constructed by moving away stones of the desert pavement and depositing them at the geoglyph rim, it seemed near at hand to adapt the OSL sediment technique for dating the last exposure of the stones to daylight. A new high resolution OSL (HR-OSL) technique was successfully developed, using the quartz and feldspar grains within in their original stone surfaces. In this way, the last light exposure of the lower, dark surface and thus the last movement of the stones was dated. The HR-OSL ages of granitoid stones sampled on different types of geoglyphs are in good agreement with archaeological and geomorphological reasoning. Our sampling procedure left no visible traces on the geoglyphs.