DIAPIRIC STRUCTURES IN ARCHAEOLOGY: A CASE STUDY FROM EASTERN AUSTRALIA.

Differential vertical movements within an archaeological deposit can be triggered by variations in the density and plasticity of the archaeological layers. Acute stratigraphic disturbance can occur where archaeological deposits consist of swelling clays overlain by more massive, less clay-rich sediment mantles. Such movements can displace artefacts, bones and charcoal in such a way that depth is no guide to age and stratigraphic inversions can be the norm rather than the exception. In the case of a late Quaternary archaeological site in eastern Australia, the stratigraphic units were very distinctive in terms of colour, texture, structure, consistence, fabric and plasticity. As a result, the effects of internal mass movements and viscous soil flows were both striking and obvious. In many instances, however, the visible differences in colour and other physical attributes may be less evident and are often hard to discern in trial trenches of limited size. Archaeologists and geoarchaeologists need to be alert to these possible forms of disturbance, particularly when excavating fine-grained sediments. They may be more common than generally recognised. [ABSTRACT FROM AUTHOR]