EPR dating of shells from Malhada Marsh, Rio de Janeiro, Brazil

The formation of the coastal plain of the Brazilian sea is mainly due to the fluctuation of relative sea level in the past. Armação dos Buzios or simply Buzios is a municipality in the microregion of lakes, in the state of Rio de Janeiro. In this region there is a lowland area about two meters above current sea level. This lowland areais also known as coastal plain of Una River. It is expected that during the Holocene period the sea level reached a maximum about 2.5 meters above the current level. During that time billions of mollusks lived and proliferated in the shallow waters around the coastal plain of the Una River. As they died their shells formed a layer in the soil including Malhada Marsh that belongs to the Una River plain. In this study, shells were collected from this region and dated using the techniques of Electronic Paramagnetic Resonance (EPR). Ages from 2480±130 to 4490±270 years were obtained. Radiocarbon dating were performed at the Beta Analytic Lab, USA for comparison with the EPR results. Shells ages obtained are compatible with geological data from the Holocene period relative to past sea level fluctuations

Electron Spin Resonance and Thermoluminescence dating of shells and sediments from Sambaqui (shell mound) Santa Marta II, Brazil

In Tupi, the word Sambaqui means “mound of shells”. These archaeological sites are cultural vestiges left by the prehistoric occupation of the Brazilian coast from five to six thousand years ago. Mollusks, fishes, and other marine edible foods were important for the survival of this population. The remains of foods, mainly shells, were heaped up, giving a mound of different proportions, which became part of the landscape of the Brazilian coastal plain. Due to the large number of Sambaquis in Brazil and considering that Sambaqui Santa Marta II, Laguna, SC, has not yet been dated, Electron Spin Resonance (ESR) measurements were performed in aragonite shells collected from different layers of Sambaqui Santa Marta II, starting from the base to the center of the Sambaqui. Radiocarbon analysis by Accelerator Mass Spectrometry (AMS) at Beta Analytic laboratory were also performed for comparison with ESR results. Before measurements, shells were chemically etched, after drying, were pulverized and sieved. The sediments were separated into small portions which were irradiated with gamma radiation from a 60Co source with doses from 5 up to 120 Gy. Ages around 2,000 to 4,000 years have been obtained. The results obtained are consistent with the dates of others Sambaquis of the region, possibly were built at the same time

Electron Spin Resonance and Thermoluminescence dating of shells and sediments from Sambaqui (shell mound) Santa Marta II, Brazil

In Tupi, the word Sambaqui means “mound of shells”. These archaeological sites are cultural vestiges left by the prehistoric occupation of the Brazilian coast from five to six thousand years ago. Mollusks, fishes, and other marine edible foods were important for the survival of this population. The remains of foods, mainly shells, were heaped up, giving a mound of different proportions, which became part of the landscape of the Brazilian coastal plain. Due to the large number of Sambaquis in Brazil and considering that Sambaqui Santa Marta II, Laguna, SC, has not yet been dated, Electron Spin Resonance (ESR) measurements were performed in aragonite shells collected from different layers of Sambaqui Santa Marta II, starting from the base to the center of the Sambaqui. Radiocarbon analysis by Accelerator Mass Spectrometry (AMS) at Beta Analytic laboratory were also performed for comparison with ESR results. Before measurements, shells were chemically etched, after drying, were pulverized and sieved. The sediments were separated into small portions which were irradiated with gamma radiation from a 60Co source with doses from 5 up to 120 Gy. Ages around 2,000 to 4,000 years have been obtained. The results obtained are consistent with the dates of others Sambaquis of the region, possibly were built at the same time

Dating of Brazilian shells through electron paramagnetic resonance

In the present work we report dating procedure of these shells by using the electron paramagnetic resonance. The first step of the analysis was the definition of the optimal procedure for sample preparation. At this aim the analysis of the sample composition was carried out by X-ray fluorescence (XRF) measurements and an accurate analysis was study on the effect of the chemical etching with varying typology and concentration of acid to be used for removing the external layer of shells which are affected by alpha particles