High-resolution record of the Upper Olduvai transition from Po Valley (Italy) sediments: support for dipolar transition geometry? - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Physics of the Earth and Planetary Interiors Année : 1991

High-resolution record of the Upper Olduvai transition from Po Valley (Italy) sediments: support for dipolar transition geometry?

Résumé

A detailed record of the Upper Olduvai polarity transition, composed of > 100 transitional directions, has been obtained from the Crostolo section in northern Italy. A careful examination of the rock magnetic properties of the sediments using standard paleomagnetic techniques, thermomagnetic, scanning electron microscopy, microprobe, X-ray diffraction and Mdssbauer analysis, shows that greigite is the main magnetic carrier of the remanence. The correlation of a shift in the magnetic record to a small-scale sedimentary feature observed in the section indicates that themagnetization was acquired at deposition, or very shortly after. The virtual geomagnetic pole (VGP) path is largely confined along a great circle over North and South America — 90° west of the site and consists ofthree stages: first, the VGP moves to southern mid-latitudes, then, after a period ofstandstill, it comes back to almost true north, and, finally, the south pole is reached in a third step. Although different from a record from the southern Indian Ocean, this path is virtually identical to those obtained for the same transition from North Pacific deep-sea cores, and partly coincides with a North Atlantic record, which suggests that a dipolar component may be present in the transitional field during the Upper Olduvas reversal. A review of the recently obtained records of various transitions shows that in more than two-thirds ofthe cases the VGP paths are similarly confined along a meridian over the Americas or antipodal to them, irrespective ofthe sampling site and ofthe sense of the transition. Although not deterministic, this tendency suggests that a similar dipolar component might be present in the transitional fields of other reversals of different ages.

Dates et versions

hal-03583548 , version 1 (21-02-2022)

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Citer

Emmanuel Tric, Carlo Laj, Célestine Jéhanno, Jean-Pierre Valet, Catherine Kissel, et al.. High-resolution record of the Upper Olduvai transition from Po Valley (Italy) sediments: support for dipolar transition geometry?. Physics of the Earth and Planetary Interiors, 1991, 65 (3-5), pp.319-336. ⟨10.1016/0031-9201(91)90138-8⟩. ⟨hal-03583548⟩

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