Preliminary Results of Magnetic Archaeointensity Measurements in Brazil G.A. Hartmann, M.C. Afonso, and R.I.F. Trindade 1 Introduction Variations in intensity and direction of the Earth’s magnetic field oscillate accord- ing to time scales ranging from seconds to millions of years. Variations in time period of 10 2 –10 3 years are referred to as “archaeomagnetic variations” and may be used as a dating tool due to their stochastic behavior. Archaeomagnetic dating is based on the comparison of the magnetic record of archaeological material of unknown age with master-curves for the variation of the magnetic field in a given region of the planet (e.g. Le Goff et al. 2002). Hence, archaeomagnetic dating depends on the quality of a given master-curve. Accurate curves for the last 2,000 years have been developed for Europe and Western Asia. In contrast, significantly less data is available for continents in the southern hemisphere; South America contributes with less than 1% to the world geomagnetic intensity database (or “archaeointensity” database) (Genevey et al. 2008). The possibility of providing magnetic archaeointensity data depends on the characteristics of archaeological materials. Directional and/or intensity data acqui- sitions are carried out in structures fired in situ, as kilns and hearths; intensities data acquisitions can be performed on displaced artefacts, as fragments of pottery, bricks and tiles. For this reason, intensity data are very common in comparison with directional data. The methodology for paleointensities measurements was devel- oped by Thellier and Thellier (1959), with modifications proposed by Coe (1967) and Aitken et al. (1988). The natural remanent magnetization (NRM) of archaeo- logical samples is compared with the one induced in the laboratory. These two magnetizations are acquired step by step, with progressively increasing G.A. Hartmann (*) and R.I.F. Trindade Departamento de Geofı ´sica, Instituto de Astronomia, Geofı ´sica e Cie ˆncias Atmosfe ´ricas, Universidade de Sa ˜o Paulo, Sa ˜o Paulo, Brazil e-mail: gelvam@iag.usp.br; gelvam@gmail.com M.C. Afonso Museu de Arqueologia e Etnologia, Universidade de Sa ˜o Paulo, Sa ˜o Paulo, Brazil I. Turbanti-Memmi (ed.), Proceedings of the 37 th International Symposium on Archaeometry, DOI 10.1007/978-3-642-14678-7_72, # Springer-Verlag Berlin Heidelberg 2011 495