The influence of cave topography on the spatial patterning of stone artefacts: A GIS assisted study in horizontal taphonomy at Petzkes Cave, northern New South Wales

Abstract

Spatial patterns of artefacts produced by purposeful human behaviour are often, if not always, affected by subsequent disturbance processes. The precise effects of these disturbances on spatial patterning must be understood and identified before interpretation in terms of human behaviour can proceed. In cave sites there is also reason to believe that the effects of disturbance processes are concentrated in space by aspects of cave topography, such as the shape of walls and overhang, ceiling height, and sediment compaction. This research project aims to establish the extent to which the spatial pattern of stone artefacts at Petzkes Cave is the result of two types of disturbance, human trampling and drip-line run-off, operating under the influence of these aspects of cave topography. A model is developed from the literature which predicts the frequency and average size of artefacts expected to occur in spatial 'zones' defined by particular conditions of cave topography, from the action of human trampling and drip-line disturbance. The exact spatial positions of individual artefacts were recorded during excavation using an EDM theodolite, and the topography at Petzkes Cave was subsequently mapped by taking point measurements of ceiling height using the EDM and sediment compaction using a home-made penetrometer. An innovative aspect of the study is the use of a Geographical Information System (GIS) to electronically capture and recreate both cave topography and the artefact distribution in three dimensional space. This facility makes it possible to test the model by providing a means to link the spatial distribution of artefacts directly to cave topography. To verify the human trampling component of the model, a trampling experiment was conducted at the site. This confirms that cave topography, especially ceiling height, does indeed influence the spatial distribution and size-sorting of stone artefacts produced by human trampling. The horizontal displacement of artefacts is greater in areas of the cave with a high ceiling, where human movement is not restricted. Larger artefacts are displaced more than smaller artefacts, presumably because they are more likely to be scuffed by passing feet. Sediment compaction also influences lateral displacement of artefacts, but only in areas of the cave where ceiling height allows people to walk freely. The experimental results were used to refine the model, and the predictions of the refined model were then sought in the excavated sample at Petzkes Cave. The match found is sufficiently close to conclude that the spatial pattern of stone artefacts at Petzkes Cave is mainly the result of human trampling and drip-line disturbance operating under the control of cave topography. Drip-line disturbance is the dominant factor, creating dense artefact clusters along the drip-line; but, as in the experimental results, there is also a strong inverse relationship between artefact frequency/weight over space and cave ceiling height which can be linked to human trampling disturbance. In fact, the demonstrated influence of cave topography on the effects of such ubiquitous disturbance processes suggests that the spatial patterns of stone artefacts found in most caves will be extremely site-specific, reflecting variations in local topography as much as the original patterns produced by purposeful human behaviour. These findings suggest that Petzkes and other cave sites are inappropriate for the spatial study of discrete human activities.  Â