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Dating of shells and sediments related to sea fluctuation in the region of Búzios, RJ

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Monise Brito Gomes
Total Authors: 1
Document type: Master's Dissertation
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Instituto de Pesquisas Energéticas e Nucleares (IPEN/BT)
Defense date:
Examining board members:
Shigueo Watanabe; Jose Fernando Diniz Chubaci; Luiz Tomaz Filho
Advisor: Shigueo Watanabe

The formation of the Brazilian coastal plateau is mainly due to the fluctuation of the relative level of the ocean in the past. Armação dos Búzios is a municipality in the Microregion of Lagos, in the state of Rio de Janeiro. Its western limit extends to the lowland region, 2 m above the current sea level. It is part of the plateau of the Una River, a region called Pântano da Malhada and traces of shells are found in this region. In this study, shells and sediments were collected from the Pântano da Malhada region and dated, in the case of quartz crystals extracted from the sediments, the techniques of Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) were used, and for the shells, the techniques were used Electronic Paramagnetic Resonance (EPR) and C-14 dating. The annual dose rate (Dan) obtained ranged from 1.27 to 2.70 mGy / year, the accumulated dose values (Dac) were determined using the OSL regenerative dose method, using the SAR protocol \"single-aliquot regenerative dose \", And for TL and EPR the accumulated doses were determined using the MAAD protocol\" Multiple Aliquot Additive Dating \". The dating results show ages between 2480 to 5900 years. The ages of the quartz crystals obtained by OSL and TL are compatible and the ages of the shells obtained by radiocarbon and EPR are not compatible (compatibility test was performed in the respective comparisons). However, some factors may influence the comparison of the two techniques, such as the amount of sample; another factor that can affect the ages obtained from the shells in the case of the EPR method is the water content. As water is a mitigating agent, the presence of water in the place where the shells were located could protect the shell from the external irradiation of the surrounding sediments. Despite this, all of the results obtained refer to the ages of the Holocene period. This work corroborates the hypothesis of the natural presence of shells, that in the past there was a transgression of the sea in the region of Pântano da Malhada and over time the sea regressed leaving traces of mollusk shells in the region. (AU)

FAPESP's process: 17/17116-2 - Dating of shells and sediments of the Malhada marsh: correlation with the variation of the level of the ocean in the Holocene
Grantee:Monise Brito Gomes
Support Opportunities: Scholarships in Brazil - Master