Headroom and Human Trampling: Cave Ceiling-Height Determines the Spatial Patterning of Stone Artefacts at Petzkes Cave, Northern New South Wales

Article excerpt

Going into a cave or shelter, one walks where one can stand upright or has to crouch less. That affects which zones objects are trampled on, which zones they may be kicked out of, which zones they may be kicked into. And those effects interact with the usual spatial order - with its activity zones and drop zones - that develops through occupation of the enclosed cave or shelter.

As has been widely recognized (for example, by Schiffer 1983; Hivernal & Hodder 1984; Nash & Petragila 1987; Frankel 1989; Holdaway & Irwin 1993), identification of activity areas from maps of spatial artefact distribution is difficult because materials at archaeological sites are rarely recovered from their original position. Disturbance of the materials through postdepositional processes may alter the original spatial distribution and deliberate site maintenance at the time of occupation may also move artefacts horizontally. Human trampling, animal activity, water and wind disturbance are the main post-depositional processes, with human trampling regarded as a major disturbance agent in sandy rock-shelter deposits in Australia and elsewhere (Stockton 1973; Hughes & Lamperr 1977; Villa & Courtin 1983).

This paper investigates the effects of human trampling on the horizontal distribution of stone artefacts at Petzkes Cave, a large sandstone rockshelter in northern New South Wales. Stone artefacts were chosen for study; less subject to animal activity than organic artefacts, they are resistant to decay. Petzkes Cave [ILLUSTRATION FOR FIGURE 1 OMITTED]) was chosen for excavation because it is a large (25 m long) and relatively deep (9 m) rock-shelter. Its size makes it likely that a variety of activities took place at the site.

In this paper we find that trampling effects on the artefact distribution at Petzkes Cave can be predicted from ceiling-height. This allows us to focus on the artefacts and the cave zones which may be least affected by trampling, when investigating the original areas of activity. We predicted a generalized artefact distribution from previous work, and refined it for Petzkes Cave by a trampling experiment. When this 'hypothetical' distribution was compared with the actual distribution of artefacts in the top 3 cm of the deposit, we found good agreement between the expected and observed distribution of artefacts, suggesting that trampling was a major agent of disturbance.

Predicting the distribution of artefacts after trampling

Existing models for the effects of human trampling

Human trampling has long been recognized as a significant source of post-depositional disturbance in archaeological sites, especially in periodically re-occupied sites such as caves and rock-shelters (Hughes & Lampert 1977). In some caves, particularly sandstone caves such as Petzkes Cave, sediment may only accumulate at a rate of a few centimetres per century; materials near the surface are subjected to the combined trampling disturbance of all the occupations occurring in that time-span (Hughes & Lainpert 1977; 136; Villa & Courtin 1983: 270). Most experimental studies on the effects of human trampling on the distribution of archaeological materials in archaeological sites - for example, Gifford-Gonzalez et al, (1985), Stockton (1973) and Villa & Courtin (1983) - have mainly dealt with vertical displacement of artefacts and its implications for the temporal association of artefacts with archaeological strata.

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The little previous research on the effects of trampling on the horizontal distribution of artefacts may suggest that larger artefacts should be displaced further than smaller with a positive but statistically insignificant relationship between horizontal movement and artefact size (Nielson 1991: 490-93); the incidental results of Villa & Courtin (1983: 277) show an inverse relationship (also not significant) between lateral movement and artefact size. …