Twelve patterns of geomagnetic dipole behaviour are recorded in a 88 m bore-core penetrating some 3.2 Ma of shallow water carbonates in Southern Italy, around 127 Ma (Early Cretaceous). Each pattern sequence represents a complete reversal cycle that lasts for ca. 660 ka, formed of ca. 300 ka of predominantly normal polarity and ca. 330 ka of mainly reversed polarity, while virtual Geomagnetic Pole (VGP) excursions mostly last 525 ka. The succession of excursions within the reversed sequences, appears to occur as harmonics of about 20, 44 and 64 ka. These are comparable to the Earths orbital frequencies (precession and obliquity). We consider very significant for further investigations that geomagnetic behaviour predicted from 3-D computer simulations by Glatzmaier et al. (1999), based on the geophysical properties of the present-day core-mantle boundary, has very close similarities to that observed in the bore-core remanence and occurs on almost identical time-scales to those previously determined for the bore-core VGP and intensity.
Early Cretaceous geomagnetic behaviour compared to a computer model
M Iorio;
2001
Abstract
Twelve patterns of geomagnetic dipole behaviour are recorded in a 88 m bore-core penetrating some 3.2 Ma of shallow water carbonates in Southern Italy, around 127 Ma (Early Cretaceous). Each pattern sequence represents a complete reversal cycle that lasts for ca. 660 ka, formed of ca. 300 ka of predominantly normal polarity and ca. 330 ka of mainly reversed polarity, while virtual Geomagnetic Pole (VGP) excursions mostly last 525 ka. The succession of excursions within the reversed sequences, appears to occur as harmonics of about 20, 44 and 64 ka. These are comparable to the Earths orbital frequencies (precession and obliquity). We consider very significant for further investigations that geomagnetic behaviour predicted from 3-D computer simulations by Glatzmaier et al. (1999), based on the geophysical properties of the present-day core-mantle boundary, has very close similarities to that observed in the bore-core remanence and occurs on almost identical time-scales to those previously determined for the bore-core VGP and intensity.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
