Abstract
Paleomagnetic directional data were obtained from fourteen 0 to 2 Ma old lava flows at Basse-Terre Island (Guadeloupe, French West Indies). Five reversed polarity flows are consistent with their Matuyama age between 1.6–1.5 Ma and 875–790 ka while the ages of the other nine normal polarity units tie them to the Olduvai subchron and the Brunhes Chron. These directions have been combined with previous results obtained from Basse-Terre Island. The overall mean direction (D = −1.2°, I = 31.4°, α95 = 3.3°) obtained from the 39 non-transitional flows from Basse-Terre Island is indistinguishable from the expected geocentric axial dipole value (D = 0°, I = 29.8°). The dispersion measured from the angular standard deviation of the Virtual Geomagnetic Poles (VGPs) was found to be close to, but smaller than the predictions of geomagnetic models. Together with further directions from the nearby Martinique Island, the 45 directions obtained within the Brunhes chron provide the most robust estimate of the statistical distribution of paleosecular variation (PSV) at this latitude. The sequence of directions shows episodes of high amplitude secular variation that are coeval with several geomagnetic events including the last reversal documented by five transitional directions. Finally, three lava flows have recorded a transitional behavior which could be link to two excursions, the Laguna del Sello (at ~340 ka) and the Pringle Falls (at ~210 ka) events.
Highlights
When averaged over a long enough time interval the Earth’s magnetic field is predicted to be mostly that of a geocentric axial dipole[1,2]
Forty per cent of samples carried a secondary magnetization component that was removed by a 15 mT a.f. or after heating at 300 °C
The Virtual Geomagnetic Poles (VGPs) dispersion (Sb) of 10.2° and 9.6°, for the all Basse-Terre flows and only those restricted to the Brunhes chron, respectively, is lower than in paleosecular variation (PSV) models (e.g. TK0361, C18)
Summary
When averaged over a long enough time interval the Earth’s magnetic field is predicted to be mostly that of a geocentric axial dipole[1,2]. Carlut et al.[13] previously studied 0–1 Ma old flows from the Basse-Terre island (Guadeloupe) These authors calculated a mean paleomagnetic pole in agreement with the geocentric axial dipole (GAD) field direction and inferred that no significant persistent second-order features were present at Basse-Terre over the last million years. Tanty et al.[21] found a mean paleomagnetic direction at Martinique island that is indistinguishable from the GAD field though the observed dispersion was higher than the PSV model predictions In these two studies, slightly different mean inclinations were reported for the 700–400 ka and 400–0 ka periods, respectively, questioning the statistical significance of the offset[13,21]. The compilation of former paleomagnetic studies[13], added to new K-Ar radiometric ages[19,20] provide an integrated paleomagnetic dataset for the eastern Caribbean that constrains the time-averaged field in this area
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