Differenciation among passive and active percussion elements using GIS image analysis in the Mesolithic site of Font del Ros (Spain)

Abstract

Macro lithic tools gestures and kinematic allow distinguishing two main roles: active elements (hammer stones) and passive elements (anvils). Usually these two categories have been differentiated from physical attributes as measures or weight. It has also been proposed that the types of stigmas distinguish between hammers and anvils. However, these considerations are mainly based on descriptive criteria. We propose GIS image analysis together with metrological data to distinguish between these two categories. To test the validity of this method has been selected a sample of artifacts developed for a pilot program and a number of pieces from the Mesolithic site of Font del Ros (Southeastern Pyrenees, Spain). Spatial analysis with ArcGIS, was produced by georeferenced photographs of objects. The digitization and mapping of the outline and use-wear visible on the photos allow positioning attributes and tags on each instrument. The collected data is used to calculate spatial pattern indices. From a technofuntional point of view use-wear on active and passive percussion tools tend to be positioned in different areas of the objects, especially in the freehand hammer stones used in tangential percussion and anvils involved in processing activities (axial percussion). However, the bipolar technique or indirect percussion on anvil makes difficult to differentiate between the two categories. The marks identified show a certain degree of variability, and pose a problem of equifinality in the precise determination of the functional context these tools. This hinders the quantitative differentiation between active and passive element and determines the ambivalent nature of these tools.