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Physics of the Earth and Planetary Interiors 156 (2006) 213222 The nature of a cryptochron from a paleomagnetic study of chron
 

Summary: Physics of the Earth and Planetary Interiors 156 (2006) 213222
The nature of a cryptochron from a paleomagnetic study of chron
C4r.2r recorded in sediments off the Antarctic Peninsula
Gary Actona,, Yohan Guyodob,1, Stefanie Brachfeldc,2
a One Shields Avenue, Department of Geology, University of California, Davis, CA 95616, USA
b Laboratoire des Sciences du Climat et de l'Environnement (LSCE), Domaine du CNRS, 12 Avenue de la Terrasse,
Gif-sur-Yvette, Cedex 91198, France
c Department of Earth & Environmental Studies, Montclair State University, Montclair, NJ 07043, USA
Received 2 May 2005; received in revised form 9 September 2005; accepted 9 September 2005
Abstract
ThemagnetostratigraphyfromOceanDrillingProgram(ODP)Site1095,offthePacificmarginoftheAntarcticPeninsula,contains
an extra normal polarity event that occurs near the base of Chron 4r.2r (8.0728.699 Ma), which we interpret to be cryptochron
C4r.2r-1. Owing to the relatively high sedimentation rates (about 90 m/m.y.), this event is particularly well recorded at the site,
spanning 4.99 m of the stratigraphic section. This allows the characteristics of the cryptochron to be investigated in greater detail
than possible from marine magnetic anomalies, where it was originally identified, or from other sedimentary sections in which
it has been recorded at much lower resolution. Our observations suggest that the cryptochron is a full geomagnetic reversal, in
which both the direction and paleointensity attain levels similar to that of other normal polarity chrons at the site. Based on its
position within Chron 4r.2r, the cryptochron started at 8.622 Ma and terminated 56 k.y. later at 8.566 Ma. At the transition zones
bounding the cryptochron, the paleointensity collapses to near zero, but recovers within a few thousand years. Our results, as well
as paleomagnetic observations from other thick sedimentary units, indicate that cryptochrons are not always purely paleointensity

  

Source: Acton, Gary - Department of Geology, University of California, Davis

 

Collections: Geosciences