Temporal variability in shell mound formation at Albatross Bay, northern Australia

We report the results of 212 radiocarbon determinations from the archaeological excavation of 70 shell mound deposits in the Wathayn region of Albatross Bay, Australia. This is an intensive study of a closely co-located group of mounds within a geographically restricted area in a wider region where many more shell mounds have been reported. Valves from the bivalve Tegillarca granosa (Linnaeus, 1758) were dated. The dates obtained are used to calculate rates of accumulation for the shell mound deposits. These demonstrate highly variable rates of accumulation both within and between mounds. We assess these results in relation to likely mechanisms of shell deposition and show that rates of deposition are affected by time-dependent processes both during the accumulation of shell deposits and during their subsequent deformation. This complicates the interpretation of the rates at which shell mound deposits appear to have accumulated. At Wathayn, there is little temporal or spatial consistency in the rates at which mounds accumulated. Comparisons between the Wathayn results and those obtained from shell deposits elsewhere, both in the wider Albatross Bay region and worldwide, suggest the need for caution when deriving behavioural inferences from shell mound deposition rates, and the need for more comprehensive sampling of individual mounds and groups of mounds

Temporal variability in shell mound formation at Albatross Bay, northern Australia

We report the results of 212 radiocarbon determinations from the archaeological excavation of 70 shell mound deposits in the Wathayn region of Albatross Bay, Australia. This is an intensive study of a closely co-located group of mounds within a geographically restricted area in a wider region where many more shell mounds have been reported. Valves from the bivalve Tegillarcca granosa were dated. The dates obtained are used to calculate rates of accumulation for the shell mound deposits. These demonstrate highly variable rates of accumulation both within and between mounds. We assess these results in relation to likely mechanisms of shell deposition and show that rates of deposition are affected by time-dependent processes both during the accumulation of shell deposits and during their subsequent deformation. This complicates the interpretation of the rates at which shell mound deposits appear to have accumulated. At Wathayn, there is little temporal or spatial consistency in the rates at which mounds accumulated. Comparisons between the Wathayn results and those obtained from shell deposits elsewhere, both in the wider Albatross Bay region and worldwide, suggest the need for caution when deriving behavioural inferences from shell mound deposition rates, and the need for more comprehensive sampling of individual mounds and groups of mounds

Beyond consumption and discard : a comparative sedimentological analysis of two shell deposits from Albatross Bay, Australia, and the Farasan Islands, Saudi Arabia

We use a sedimentological approach to examine the formation and deformation processes associated with the accumulation of shell deposits in two major clusters of shell mounds, the Weipa group in the monsoonal environment of Albatross Bay in the Cape York Peninsula of northern Queensland, Australia, and the Farasan Islands group in the semi-arid environment of the southern Red Sea sector of Saudi Arabia. The comparison of such disparate case studies is deliberate, intended to highlight generic issues of shell accumulation and degradation irrespective of the taxonomic composition of the shells or cultural and environmental histories. It also reflects recent fieldwork in both regions conducted in parallel with collaborative arrangements for sharing of ideas and approaches and exchange of personnel in order to establish a common baseline for comparison. Comparative analysis of shell composition, fragmentation, and accumulation highlights similarities despite the different cultural and environmental contexts of the two case studies. These similarities suggest that the size and form of shell deposits are altered by a combination of processes reflecting ongoing changes in deposit composition unrelated to human actions of shell discard. Even where large shell deposits are visible and available for sampling, what is preserved is neither a static reflection of initial deposition nor of undisturbed or “completed” form. We consider the influence of such processes on assessments of rates of deposition and the interpretation of variations in the shape and size of shell deposits

The Wathayn study area on the north bank of the Embley River, showing the locations of the shell mounds.

<p>Contours derived from airborne LiDAR data indicate the topography. Both LiDAR and air photography data provided courtesy of RioTintoAlcan (Weipa) Pty Ltd. (Modified from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0183863#pone.0183863.ref030" target="_blank">30</a>] under a CC BY license, with permission from Elsevier, original copyright 2016).</p

Large shell mound in the vicinity of the study area.

<p>Predominantly composed of the shells of the bivalve <i>Tegillarca granosa</i> (syn. <i>Anadara granosa</i> (Linnaeus 1758)), some mounds attain heights of ten metres or more. (Source of image: PCF. The individual pictured gave written informed consent (as outlined in PLOS consent form) to publish his image).</p

Conventional radiocarbon age determinations, calibrated mean age ± 1σ and rates of accumulation, calculated using depth below surface, of the Wathayn shell mounds.

<p>Conventional radiocarbon age determinations, calibrated mean age ± 1σ and rates of accumulation, calculated using depth below surface, of the Wathayn shell mounds.</p

Location map of the study area.

<p>Albatross Bay is a shallow, semi-circular embayment on the northwestern coast of Cape York Peninsula in far north Queensland, Australia, that opens into the Gulf of Carpentaria. The study area of Wathayn is situated on the northern side of the Embley River, one of four estuaries draining into Albatross Bay. The map also shows the location of other places mentioned in the text. (Modified from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0183863#pone.0183863.ref030" target="_blank">30</a>] under a CC BY license, with permission from Elsevier, original copyright 2016).</p