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Rapid directional changes associated with a 6.5kyr-long Blake geomagnetic excursion at the Blake–Bahama Outer Ridge

Rapid directional changes associated with a 6.5kyr-long Blake geomagnetic excursion at the Blake–Bahama Outer Ridge
Rapid directional changes associated with a 6.5kyr-long Blake geomagnetic excursion at the Blake–Bahama Outer Ridge
Geomagnetic excursions are recognized as intrinsic features of the Earth's magnetic field. High-resolution records of field behaviour, captured in marine sedimentary cores, present an opportunity to determine the temporal and geometric character of the field during geomagnetic excursions and provide constraints on the mechanisms producing field variability. We present here the highest resolution record yet published of the Blake geomagnetic excursion (View the MathML source) measured in three cores from Ocean Drilling Program (ODP) Site 1062 on the Blake–Bahama Outer Ridge. The Blake excursion has a controversial structure and timing but these cores have a sufficiently high sedimentation rate (View the MathML source) to allow detailed reconstruction of the field behaviour at this site during the excursion. Palaeomagnetic measurements of the cores reveal rapid transitions (View the MathML source) between the contemporary stable normal polarity and a completely reversed state of long duration which spans a stratigraphic interval of 0.7 m. We determine the duration of the reversed state during the Blake excursion using oxygen isotope stratigraphy, combined with 230Th excess measurements to assess variations in the sedimentation rates through the sections of interest. This provides an age and duration for the Blake excursion with greater accuracy and with constrained uncertainty. We date the directional excursion as falling between 129 and 122 ka with a duration for the deviation of 6.5±1.3 kyr. The long duration of this interval and the fully reversed field suggest the existence of a pseudo-stable, reversed dipole field component during the excursion and challenge the idea that excursions are always of short duration.
palaeomagnetism, geomagnetism, geomagnetic excursion, blake, 230Th, ODP (Ocean Drilling Program)
0012-821X
21-34
Bourne, Mark
e4e48e93-7612-40fa-b01d-4bf8510cee41
Mac Niocaill, Conall
67169dfb-3ae5-434b-8893-ee8410b16443
Thomas, Alex L.
d0eef8d7-3dd9-49cd-a128-7d53018d4eaa
Knudsen, Mads Faurschou
82265238-80cb-4f15-894c-4fed31efe50f
Henderson, Gideon M.
8b14c275-d7ff-47f7-ad8f-7189b6d2e152
Bourne, Mark
e4e48e93-7612-40fa-b01d-4bf8510cee41
Mac Niocaill, Conall
67169dfb-3ae5-434b-8893-ee8410b16443
Thomas, Alex L.
d0eef8d7-3dd9-49cd-a128-7d53018d4eaa
Knudsen, Mads Faurschou
82265238-80cb-4f15-894c-4fed31efe50f
Henderson, Gideon M.
8b14c275-d7ff-47f7-ad8f-7189b6d2e152

Bourne, Mark, Mac Niocaill, Conall, Thomas, Alex L., Knudsen, Mads Faurschou and Henderson, Gideon M. (2012) Rapid directional changes associated with a 6.5kyr-long Blake geomagnetic excursion at the Blake–Bahama Outer Ridge. Earth and Planetary Science Letters, 333-334, 21-34. (doi:10.1016/j.epsl.2012.04.017).

Record type: Article

Abstract

Geomagnetic excursions are recognized as intrinsic features of the Earth's magnetic field. High-resolution records of field behaviour, captured in marine sedimentary cores, present an opportunity to determine the temporal and geometric character of the field during geomagnetic excursions and provide constraints on the mechanisms producing field variability. We present here the highest resolution record yet published of the Blake geomagnetic excursion (View the MathML source) measured in three cores from Ocean Drilling Program (ODP) Site 1062 on the Blake–Bahama Outer Ridge. The Blake excursion has a controversial structure and timing but these cores have a sufficiently high sedimentation rate (View the MathML source) to allow detailed reconstruction of the field behaviour at this site during the excursion. Palaeomagnetic measurements of the cores reveal rapid transitions (View the MathML source) between the contemporary stable normal polarity and a completely reversed state of long duration which spans a stratigraphic interval of 0.7 m. We determine the duration of the reversed state during the Blake excursion using oxygen isotope stratigraphy, combined with 230Th excess measurements to assess variations in the sedimentation rates through the sections of interest. This provides an age and duration for the Blake excursion with greater accuracy and with constrained uncertainty. We date the directional excursion as falling between 129 and 122 ka with a duration for the deviation of 6.5±1.3 kyr. The long duration of this interval and the fully reversed field suggest the existence of a pseudo-stable, reversed dipole field component during the excursion and challenge the idea that excursions are always of short duration.

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More information

Published date: 1 June 2012
Keywords: palaeomagnetism, geomagnetism, geomagnetic excursion, blake, 230Th, ODP (Ocean Drilling Program)
Organisations: Paleooceanography & Palaeoclimate

Identifiers

Local EPrints ID: 360291
URI: https://eprints.soton.ac.uk/id/eprint/360291
ISSN: 0012-821X
PURE UUID: db89a815-beee-41d4-96e9-1243814d371e

Catalogue record

Date deposited: 04 Dec 2013 10:02
Last modified: 18 Jul 2017 03:13

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