725–729) is positive, corresponding to Type B with γ = 8.7° and γ0 = 3.7°. , View all references Classification of the reversal test in paleomagnetism: Geophysical Journal International, v. Classification of the reversal test in paleomagnetism: Geophysical Journal International, 103: 725–729. The reversal test as defined by McFadden and McElhinny (199035. The mean palaeomagnetic direction of normal polarity sites give I = −41.8°, D = 4.9°, k = 112, and α95 = 4.9°, whereas reversely magnetized sites give I = 37.1°, D = 181.4°, k = 23, and α95 = 11.1°. Nine sites display normal polarity magnetization, whereas nine others are reversely magnetized and the remaining eight sites yield intermediate palaeodirections. No palaeodirections were determined for two sites because of a very complex and erratic behaviour of the remanence during the palaeomagnetic treatments. We precisely determined the palaeofield direction for 26 sites for which the characteristic remanent magnetizations exhibit small within-site dispersion and high directional stability. The initial aims of our study were to (i) document variability of the Earth's magnetic field during the time interval sampled, (ii) obtain a new Early Cretaceous palaeomagnetic pole (PP) for stable South America, and (iii) estimate the extrusion rate of the Paraná magma. We report a detailed palaeomagnetic investigation of 28 lava flows (221 standard palaeomagnetic cores) collected from the Paraguayan part of the Paraná flood basalts (the Alto Paraguay Formation). Keywordspaleosecular variation–Early Cretaceous–paleomagnetic poles–Paraná Magmatic Province–Argentina–Posadas Formation Reported for Early Cretaceous, which are consistent with some inferences from computer simulations previously published. These intensities agree with the relatively high values already This correspond to a mean value of 7.7 ± 2.1 × 1022 Am2 which is 96% of the present day geomagnetic field strength. The virtual dipole moments (VDMs) range from 4.8 to 9.9 × 1022 Am2. Only 15 samples from 5 individual basaltic lava flows, yielded acceptable paleointensity estimates. The pole position suggested by fixed hotspot reconstructions, which may be due to true polar wander or the hotspot motion Both paleomagnetic poles and average VGP paths are significantly different from Published Paraná Magmatic Province poles. Interestingly, the axialĪverage VGP path traces an almost complete cycle around the geographical pole and passes near the location of all previously Were used to analyze the sequential variation of virtual geomagnetic pole’s (VGP) axial positions. 23 sites yielded normal polarity magnetization and only 3 are reversely magnetized. Five sites show evidences for the self-reversal of thermoremanent Small within-site dispersion and high directional stability. ![]() The average paleofield direction is precisely determined from 26 sites, which show Posadas) in order to contribute to the study of PSV during the early Cretaceous and to obtain precise Cretaceous paleomagnetic We report here a detailed rock-magnetic, paleomagnetic and paleointensity investigationįrom 28 lava flows (331 standard paleomagnetic cores) collected in the Argentinean part of the Parana Flood Basalts (Formation Unsolved problems are related to the mode of paleosecular variation (PSV) of the Earth’s magnetic field before and during The Early Cretaceous may be considered a key period for understanding the evolution of the Earth’s magnetic field.
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