HR: 14:55h
AN: GP32A-06    [PDF]
TI: Non-Uniform Occurrence of Short-Term Polarity Excursions in the Geomagnetic Field?
AU: * Krijgsman, W
EM: krijgsma@geo.uu.nl
AF: Paleomagnetic Lab. Fort Hoofddijk Utrecht University, Budapestlaan 17, Utrecht, 3584 CD Netherlands
AU: Kent, D
EM: dvk@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964 United States
AB: We will present new magnetostratigraphic results from DSDP Site 608 in the North Atlantic that reveal the presence of nine short-term polarity excursions in the middle to late Miocene. These polarity excursions do not correspond to subchrons in the most recent GPTS. Four of them correspond to cryptochrons. IRM component analysis suggests that these polarity excursions represent true fluctuations of the geomagnetic field. Comparison with published results from ODP Sites 845 and 1092, and from the continental Orera Composite Section, shows that all nine polarity excursions have been observed in more than one record. A refined criterion for a short-term polarity excursion to qualify as polarity subchron defines five new subchrons in the late Miocene: C4r.2r-1n, C4Ar.1r-1n, C5r.2r-1n, C5r.2r-2n, and C5r.3r-1n. The three events within C5n and the one in C5An.2n qualify better as polarity excursions and are most likely associated with decreases in paleointensity of the geomagnetic field. These results imply that the occurrence of short-term polarity excursions in the geomagnetic field is non-uniformly distributed through time - for example, being relatively more common in the early Late Miocene and the Pleistocene but virtually absent in the latest Miocene and Pliocene - but it remains uncertain if this is related to real behavior of the geodynamo.
DE: 1513 Geomagnetic excursions
DE: 1520 Magnetostratigraphy
DE: 1560 Time variations--secular and long term
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting