Early cretaceous absolute geomagnetic paleointensities from Cordoba Province (Argentina)

We present here new paleointensity and geochronology results from Early Cretaceous volcanic rocks of Sierra Chica de Cordoba (Argentina). The new K-Ar isotopic ages of 5 samples range from 136 to 122 Ma. Twenty five samples from 7 individual flows yielded acceptable paleointensity estimates. The mean paleointensity values per flow are ranging from 53.0 +/- 1.9 to 25.4 +/- 2.6 mu T and the corresponding Virtual Dipole Moments (VDMs) are ranging, from 9.3 +/- 1.3 to 4.6 +/- 0.5 (10(22) Am-2). This corresponds to the mean value of 7.3 +/- 1.7 x 10(22) Am-2, which is compatible to the present geomagnetic axial dipole. Currently available selected paleointensity data from 80 to 130 Ma suggest that geomagnetic field strength frequently fluctuated before and during the Cretaceous Normal Superchron while the magnetic polarity maintained stable. The mean paleointensities derived from Cordoba lavas agree remarkably well with those obtained from the Parana Magmatic Province (133-132 Ma). This reinforces the hypothesis about the unreliability of 'Mesozoic Dipole Low'

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

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 mu T, with corresponding virtual dipole moments (VDMs) from 3.4 +/- 0.6 to 8.2 +/- 0.8 (10(22) Am-2). This corresponds to mean VDM value of 6.4 +/- 2.3 x 10(22) Am-2. Ar-40/Ar-39 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., 199