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

• Published in: Physics of the Earth and Planetary Interiors
• Main Authors: Tric, Emmanuel, Laj, Carlo, Jéhanno, Célestine, Valet, Jean-Pierre, Kissel, Catherine, Mazaud, Alain, Iaccarino, Silvia
• Other Authors: Centre des Faibles Radioactivités, Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS), Università degli studi di Parma = University of Parma (UNIPR)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 1991
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; Geomagnetic Pole; North Atlantic; South pole
• Online Access: https://hal.science/hal-03583548; https://doi.org/10.1016/0031-9201(91)90138-8

International audience A detailed record of the Upper Olduvai polarity transition, composed of > 100 transitional directions, has been obtainedfrom the Crostolo section in northern Italy. A careful examination of the rock magnetic properties of the sediments usingstandard paleomagnetic techniques, thermomagnetic, scanning electron microscopy, microprobe, X-ray diffraction andMdssbauer analysis, shows that greigite is the main magnetic carrier of the remanence. The correlation of a shift in themagnetic record to a small-scale sedimentary feature observed in the section indicates that themagnetization was acquired atdeposition, or very shortly after. The virtual geomagnetic pole (VGP) path is largely confined along a great circle over Northand 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. Althoughdifferent from a record from the southern Indian Ocean, this path is virtually identical to those obtained for the sametransition from North Pacific deep-sea cores, and partly coincides with a North Atlantic record, which suggests that a dipolarcomponent may be present in the transitional field during the Upper Olduvas reversal. A review of the recently obtainedrecords of various transitions shows that in more than two-thirds ofthe cases the VGP paths are similarly confined along ameridian over the Americas or antipodal to them, irrespective ofthe sampling site and ofthe sense of the transition. Althoughnot deterministic, this tendency suggests that a similar dipolar component might be present in the transitional fields of otherreversals of different ages.