New absolute paleointensity results from the Parana Magmatic Province (Uruguay) and the Early Cretaceous geomagnetic paleofield

Abstract

Thellier paleointensity experiments are carried out on the Early Cretaceous Arapey Formation, which belongs to the Parana Magmatic Province (PMP) in northern Uruguay. Twenty‐seven samples out of 225 analyzed yield reliable absolute intensity determinations. For these samples the NRM fraction f used for determination ranges between 0.33 to 0.83 and the quality factor q ranges from 4.5 to 14.1, being generally greater than 5. The flow‐mean paleointensity values obtained in this study range from 16.3 ± 2.3 to 41.5 ± 3.8 μT, with corresponding virtual dipole moments (VDMs) from 3.4 ± 0.6 to 8.2 ± 0.8 (1022 Am2). This corresponds to mean VDM value of 6.4 ± 2.3 × 1022 Am2. 40Ar/39Ar dating on the PMP sequence by Feraud et al. (1999) gave a mean age of 132.2 ± 0.5 Ma. Our results in conjunction with previous studies (Kosterov et al., 1998; Goguitchaichvili et al., 2002) suggest that the paleostrength during the early Cretaceous might be as variable and strong as Brunhes data and not anomalously low as previously suggested. The scatter observed in our study is similar to recent findings by Granot et al. (2007) for the Troodos Ophiolite.

Keywords

• paleointensity
• Cretaceous
• Paraná Flood Basalts
• Arapey Formation
• Uruguay