Geoarchaeology in action: A sedimentological analysis of anthropogenic shell mounds from the Cape York region of Australia

Large mounded deposits of shell are prominent archaeological features across much of the north Australian tropical coast. Many of the shell mounds are composed almost entirely of the bivalve Anadara granosa (Linnaeus 1758), a food source for Aboriginal people in the past. A relatively long history of inquiry into the nature and significance of the shell mounds has focussed primarily on analysing the shell component as clues to Australian Aboriginal coastal economies in the past. This paper presents results of new analyses on the non-shell sediments, examining the physical and chemical signatures of depositional and post-depositional processes within shell mounds near Weipa in far north Queensland, Australia, with a view to obtaining insights into how they formed and for what purposes, and how their morphology, structure and content may have changed since they ceased accumulating. We also consider how such changes might relate to past and present environmental conditions. Physical and chemical analyses indicate that the primary purpose of mound building was most likely to discard the large volumes of shell resulting from A. granosa harvesting and consumption. Post-depositional diagenetic alteration has strongly influenced the present day composition and form of the shell mounds, in particular the accession of carbon and silica to the mounds by environmental burning aided by strong leaching under the seasonal high rainfall conditions. As such the mound chemistry is more likely to reflect modern environmental conditions rather than provide an archive of, or an opening to, the past.