Paleomagnetism of early cretaceous arapey formation (Northern Uruguay) |
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| Authors: | Miguel Cervantes Solano Avto Goguitchaichvili Leda Sánchez Bettucci Ruben Cejudo Ruiz Manuel Calvo-Rathert Vicente Carlos Ruiz-Martinez Ruth Soto Luis M Alva-Valdivia |
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| Institution: | 1.Laboratorio Interinstitucional de Magnetismo Natural, Instituto de Geofísica — Sede Michoacán,Universidad Nacional Autónoma de México,Morelia,Mexico;2.Departamento de Geología, Area Geofísica-Geotectónica, Facultad de Ciencias,Universidad de la República,Montevideo,Uruguay;3.Laboratorio de Paleomagnetismo, Departamento de Física, Escuela Politécnica Superior,Universidad de Burgos,Burgos,Spain;4.Departamento de Física de la Tierra, Astronomía y Astrofísica I,Universidad Complutense de Madrid,Madrid,Spain;5.Instituto Geológico y Minero de Espa`na (IGME),Zaragoza,Spain;6.Laboratorio de Paleomagnetismo, Instituto de Geofísica,Universidad Nacional Autónoma de México,México DF,Mexico |
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| Abstract: | We report detailed rock-magnetic and paleomagnetic directional data from 35 lava flows (302 standard paleomagnetic cores)
sampled in the Central-Northern region of Uruguay in order to contribute to the study of the paleosecular variation of the
Earth’s magnetic field during early Cretaceous and to obtain precise Cretaceous paleomagnetic pole positions for stable South
America. The average unit direction is rather precisely determined from 29 out of 35 sites. All A95 confidence angles are less than 8°, which points to small within-site dispersion and high directional stability. Normal polarity
magnetizations are revealed for 19 sites and 10 are reversely magnetized. Two other sites yield well defined intermediate
polarities. The mean direction, supported by a positive reversal test is in reasonably good agreement with the expected paleodirection
for Early Cretaceous stable South America and in disagreement with a 10° clockwise rotation found in the previous studies.
On the other hand, paleomagnetic poles are significantly different from the pole position suggested by hotspot reconstructions,
which may be due to true polar wander or the hotspot motion. Our data suggest a different style of secular variation during
(and just before) the Cretaceous Normal Superchron and the last 5 Ma, supporting a link between paleosecular variation and
reversal frequency. |
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