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Earth Planets Space, Vol. 61 (No. 1), pp. 93-100, 2009

First archeointensity results from Portuguese potteries (1550-1750 AD)

Gelvam A. Hartmann1, Ricardo I. F. Trindade1, Avto Goguitchaichvili2,3, Carlos Etchevarne4, Juan Morales2,3, and Marisa C. Afonso5

1Departamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo,Rua do Matão, 1226, 05508-090, São Paulo, Brazil
2Laboratorio de Paleomagnetismo y Geofisica Nuclear, Instituto de Geofisica, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510, México, DF, Mexico
3Laboratorio Interinstitucional de Magnetismo Natural, Instituto de Geofisica, Universidad Nacional Autónoma de México, Tzintzuntzan, 310, 58098, Morelia, Mexico
4Departamento de Antropologia, Universidade Federal da Bahia, Terreiro de Jesus, Prédio da Faculdade de Medicina, 40026-010, Salvador, Brazil
5Museu de Arqueologia e Etnologia, Universidade de São Paulo, Av. Prof. Almeida Prado, 1466, 05508-090, São Paulo, Brazil

(Received November 22, 2007; Revised February 21, 2008; Accepted February 29, 2008; Online published January 23, 2009)

Abstract: Geomagnetic field variations at archeomagnetic timescales can be obtained from well-dated heated structures and archeological potsherds. Here, we present the first archeointensity results obtained on Portuguese ceramics (1550 to 1750 AD) collected at Brazilian archeological sites. The results are compared to those obtained from Western Europe and currently available geomagnetic field models. Continuous thermomagnetic and IRM acquisitions curves indicate that Ti-poor titanomagnetite is responsible for the remanence in these ceramic fragments. Five fragments (24 samples) out of twelve analyzed yielded reliable intensity estimates. The row archeointensity data were corrected for TRM anisotropy and cooling rate effect. The mean dipole moments are obtained for three different age intervals: 1550±30 AD, 1600±30 AD and 1750±50 AD. Mean intensities vary from 37.9±4.2 μT to 54.8±7.6 μT in agreement with the previously reported data for 1550 AD and 1750 AD. Relatively weaker, but still highly dispersed, values were obtained for 1600 AD ceramics.
Key words: Archeointensity, secular variation, cooling rate correction, Portuguese pottery.


Corresponding author E-mail: gelvam@iag.usp.br


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