Forgotten news: shellfish isotopic insight into changing sea-level and associated impact on the first settlers of the Mariana Archipelago

Petchey, Fiona, Clark, Geoffrey, Lindeman, Ingrid, O'Day, Patrick, Southon, John, Dabell, Kathleen, and Winter, Olaf (2018) Forgotten news: shellfish isotopic insight into changing sea-level and associated impact on the first settlers of the Mariana Archipelago. Quaternary Geochronology, 48. pp. 180-194.

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The colonisation of the Pacific is an important chapter in human dispersal for which chronological control is primarily provided by radiocarbon (14C) dates. In this context, the ability to reliably date shellfish is important because alternative dating materials, such as charcoal and bone, are typically highly degraded. However, the interpretation of shell 14C results is not always black and white because 14C is not evenly distributed throughout the marine environment, with estuarine taxa more likely to incorporate terrestrial sources of carbon. Regions where water has percolated through limestone bedrock provide an additional problem since ancient carbon is introduced into the estuarine waters. This “hardwater” has been put forward to explain old 3500 cal. BP results from culturally significant shells recovered from the site of Unai Bapot (Bapot-1) on the island of Saipan (Petchey et al. 2017). While arguments for (Carson and Hung 2017) and against (Rieth and Athens 2017) early settlement dates remain polarised, little attention has been given to the idea of change in the marine 14C reservoir over time, or to possible species-specific offsets in shell 14C.

In this paper, we further develop a tri-isotope approach using 14C, δ13C, δ18O to identify carbon source. To investigate which shellfish are more prone to erroneous ages we have selected shell taxa that cover a range of nearshore environments commonly found in Pacific archaeological sites; including Anadara antiquata, Gafrarium pectinatum (both estuarine) and Tridacna (marine/reef). To test the possibility of change over time we extend the dating of the site beyond the earliest occupation layers to deposits considered to post-date the end of the mid-Holocene drawdown in sea-level.

Item ID: 56018
Item Type: Article (Research - C1)
ISSN: 1878-0350
Keywords: reservoir offset; radiocarbon dating; hardwaters; mariana islands; colonisation
Copyright Information: Copyright © 2018 Elsevier B.V. All rights reserved.
Additional Information:

Author's post-print (accepted manuscript) on open access repository after an embargo period of 24 months

Funders: Australian Research Council (ARC), University of Waikato
Projects and Grants: ARC Discovery grant DP0771841
Date Deposited: 06 Nov 2018 01:06
FoR Codes: 43 HISTORY, HERITAGE AND ARCHAEOLOGY > 4301 Archaeology > 430101 Archaeological science @ 70%
45 INDIGENOUS STUDIES > 4513 Pacific Peoples culture, language and history > 451301 Archaeology of New Guinea and Pacific Islands (excl. New Zealand) @ 30%
SEO Codes: 95 CULTURAL UNDERSTANDING > 9505 Understanding Past Societies > 950599 Understanding Past Societies not elsewhere classified @ 100%
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