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Paleomagnetic constraints on the age of the Botucatu Formation in Rio Grande do Sul, southern Brazil

Author(s): Tamrat Endale | Ernesto Marcia

Journal: Anais da Academia Brasileira de Ciências
ISSN 0001-3765

Volume: 78;
Issue: 3;
Start page: 591;
Date: 2006;
Original page

Keywords: paleomagnetism | Botucatu Formation | magnetostratigraphy | magnetic anisotropy | Late Jurassic

Paleomagnetic and rockmagnetic data are reported for the aeolian Botucatu Formation, in the southern Brazilian State of Rio Grande do Sul. Oriented samples were taken from a section located between the cities of Jaguari and Santiago. After thermal and alternating field demagnetization, both normal and reversed characteristic remanent magnetizations were found. These results yielded 13 reversed and 5 normal polarity sites, composing a magnetostratigraphic column displaying a sequence of reversed-normal-reversed polarity events. The paleomagnetic pole calculated for 18 sites is located at 114.7ºE, 78.5ºS (dp=8.1º; dm=1.2º), after restoring the strata to the paleohorizontal. This paleomagnetic pole indicates a Late Jurassic-Early Cretaceous age to the Botucatu Formation in the investigated area, and places the sampling sites at paleolatitudes as low as 21ºS.

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