Dating of dune-barriers between Cabo Frio and Arraial do Cabo, State of Rio de Janeiro

• Grant number: 17/13842-0
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: October 01, 2017
• End date: September 30, 2018
• Field of knowledge: Physical Sciences and Mathematics - Physics - Condensed Matter Physics
• Principal Investigator: Shigueo Watanabe
• Grantee: Rafaela de Jesus Silva
• Host Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 14/03085-0 - Quaternary geochronology of Southeastern and Southern coast of Brazil, AP.TEM

Abstract

The Sea coast in the region of towns of Cabo Frio, Armação dos Búzios and Arraial do Cabo, state of Rio de Janeiro, is characterized by dune-barriers. Geologists say that these dunes are due, in past the relative sea level fluctuation in these place 5000 to 6000 years in the past. Some dunes are called actives and their positions change with wind; others are established with vegetables developed. As first step in this work, sediments from dunes are collected. As samples preparations for the so called accumulated dose (or paleodose) mesurements necessary amount of sediments are washed in solutions of H2O2, HCl and HF. After that portions of samples are sieved retaining grains size between 0,080 mm and 0,180 mm size. They then are irradiated with gamma rays and their TL are read out. The curve of TL intensity in function of dose is extrapolated and the intersession with dose-axis gives the quantily called accumulated dose (or paleodose), Dac. The original sediment is than used to find the concentration of Th(232), U(238) and K(40) using techniques like mass spectrometes ICP-MS or gamma-spectrometes. From the concentrations of Th, U and K one can estimate the annual dose rate, Dan, of the soil that induced TL in the sediments. Finally, Age = Dac/Dan. As final work an analyses is carried out to see evolution of dunes in time. (AU)