Sedimentary processes and sedimentology help test whether coastal archaeological artefact scatters are underwater and in situ, NW Australia

Piers Larcombe & Ingrid Ward - University of Western Australia

The absence of known prehistoric underwater cultural heritage (UCH) sites on the inner continental shelf of Australia stands in stark contrast to the thousands of sites revealed elsewhere in the world. Two recent claims – Dortch et al. (D2019) and Benjamin et al. (B2020) – put forward the first in situ (i.e., primary context) marine UCH sites in the shallow waters of the Dampier Archipelago, NW Australia. Each paper argued that the stone artefact scatters are at least 7000 years old and are submerged (D2020) or intertidal (D2019) because of post-glacial sea-level rise. Huge international publicity resulted.
From the data published in D2019 and B2020, we use oceanography, sedimentary processes and geological logic to assess the explicit and implicit assumptions and uncertainties of these claims. We include results of new hydrodynamic modelling, data on coastal erosion and bathymetric data of northern Flying Foam Passage, which together help contribute to a reinterpretation of the sites’ sedimentary settings and the archaeology.
These and similar sites in the region (and elsewhere) would benefit from a thorough appraisal of past and present coastal processes to produce a sedimentologically defensible understanding of site formation processes. Even if the artefacts are not in original position, if investigated appropriately and dated effectively, they would still inform our understanding of process and change and might then inform us about past cultures.