Shellmounds are archaeological sites found across the Brazilian coast and form an important record of the human occupation of this area during the Holocene. The presence of both terrestrial and marine remains within the same archaeological context enables the comparison of different carbon reservoirs. There is only a small number of similar studies for the coast of south-southeastern Brazil. Previous work was based on the analysis of pre-bomb shells from museum collections and paired charcoal/marine shells from archaeological sites. This article assesses the potential use of terrestrial shells as representative of atmospheric carbon reservoir in the calculation of the marine reservoir effect (MRE) of the southeastern Brazilian coast. The presence of both terrestrial and marine shells over several archaeological layers represents a great potential for calculating reservoir corrections and their temporal variation.

The Saquarema archaeological site, on the Atlantic coast of the Rio de Janeiro State, is one of many shellmounds built on the Brazilian coast by hunter-gatherer populations during the Holocene. We used archaeological material from this site with the aim of evaluating the marine reservoir effect (MRE) in the region. Radiocarbon ages of 45 marine and 6 terrestrial samples from this shellmound provided data for assessing the MRE and the influences of freshwater and seasonal coastal marine upwelling in this specific locality. Samples of charcoal, fish otoliths, and mollusk shells were analyzed and the ¹⁴C dates were modeled in the OxCal platform to determine the marine reservoir correction. The result obtained is R = 265 ± 70 ¹⁴C yr and the offset ΔR was found to be –140 ± 66 ¹⁴C yr. To support the accuracy of this value for correcting conventional ¹⁴C marine ages, taxonomic analyses of the samples were performed.