Vermetid bioconstructions have been widely used as Holocene paleo-sea level indicators along the Brazilian coast, due to their abundance and accuracy, especially in the case of Petaloconchus varians (d’Orbigny, 1841). Most age determinations for this species have been performed using conventional 14C dating of bulk bioconstruction samples. However, this type of sample may contain several types of carbonate or carbonaceous impurities, including remains of other organisms such as mollusks and barnacles, which can affect the reliability of the age. This work compares previous conventional 14C ages of vermetid bioconstruction bulk samples with 14C AMS ages of shells from different species dated individually. The objectives are: i. To establish the relationship among the ages of different species in order to reveal the direction or tendency of past sea-level changes; ii. To evaluate the error in dating bulk samples; iii. To analyze the reliability of the ages obtained from each species, based on aspects such as purity, alteration and neomorphism. The dating results obtained for fossil shells of different species were in agreement with the relative ages expected based on the observed spatial relationship between them. Tetraclita stalactifera parietal plates were older than overgrowing vermetids shells, and shells of the bivalve Leiosolenus aff. bisulcatus in life position, which perforate the bioconstruction, were younger. The ages of individual shells were older than those obtained by dating bulk vermetid bioconstructions, and this difference increased with the age. Taking the paleolevels previously determined for the studied samples and using the revised ages reported here, we infer that relative sea level in southern Brazil was more than 2 m above present between 6000 and 7000 cal aBP. The differences in ages between bulk and individual shell samples highlight that paleo-sea levels inferred from bulk vermetid remains and respective Holocene sea-level curves need revision. More data for separate species are therefore necessary to improve the accuracy of Holocene sea-level curves from Brazil. Furthermore, methodological care must be taken to avoid the influence of micritic envelopes, bioturbation, biofouling, and cement infill on the age.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)