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High-resolution record of the Laschamp geomagnetic excursion at the Blake-Bahama Outer Ridge

High-resolution record of the Laschamp geomagnetic excursion at the Blake-Bahama Outer Ridge
High-resolution record of the Laschamp geomagnetic excursion at the Blake-Bahama Outer Ridge
Geomagnetic excursions are brief deviations of the geomagnetic field from behaviour expected during ‘normal secular’ variation. The Laschamp excursion at ?41?ka was one such deviation. Previously published records suggest rapid changes in field direction and a concurrent substantial decrease in field intensity associated with this excursion. Accurate dating of excursions, and determination of their durations from multiple locations, is vital to our understanding of global field behaviour during these deviations. We present here high-resolution palaeomagnetic records of the Laschamp excursion obtained from two Ocean Drilling Program (ODP) Sites, 1061 and 1062 on the Blake-Bahama Outer Ridge (ODP Leg 172). High sedimentation rates (?30–40?cm?kyr?1) at these locations allow determination of transitional field behaviour during the excursion. Palaeomagnetic measurements of discrete samples from four cores reveal a single excursional feature, across an interval of 30?cm, associated with a broader palaeointensity low. We determine the age and duration of the Laschamp excursion using a stratigraphy linked to the ?18O record from the Greenland ice cores. This chronology dates the Laschamp excursion at the Blake Ridge to 41.3?ka. The excursion is characterized by rapid transitions (less than 200?yr) between stable normal polarity and a partially reversed polarity state. The palaeointensity record is in good agreement between the two sites, revealing two prominent minima. The first minimum is associated with the Laschamp excursion at 41?ka and the second corresponds to the Mono Lake excursion at ?35.5?ka. We determine that the directional excursion during the Laschamp at this location was no longer than ?400?yr, occurring within a palaeointensity minimum that lasted 2000?yr. The Laschamp excursion at this location is much shorter in duration than the Blake and Iceland Basin excursions.
0956-540X
1519-1533
Bourne, M.D.
fa227921-13da-4380-bf75-8d12e150bd0f
Mac Niocaill, C.
2b02026b-66c9-4a6a-b6da-244d969f8250
Thomas, A.L.
3c3c7ab1-ca34-49bb-8cbe-a3c45c3f1e22
Henderson, G.M.
1a310365-c407-4667-a617-b8473505a536
Bourne, M.D.
fa227921-13da-4380-bf75-8d12e150bd0f
Mac Niocaill, C.
2b02026b-66c9-4a6a-b6da-244d969f8250
Thomas, A.L.
3c3c7ab1-ca34-49bb-8cbe-a3c45c3f1e22
Henderson, G.M.
1a310365-c407-4667-a617-b8473505a536

Bourne, M.D., Mac Niocaill, C., Thomas, A.L. and Henderson, G.M. (2013) High-resolution record of the Laschamp geomagnetic excursion at the Blake-Bahama Outer Ridge. Geophysical Journal International, 195 (3), 1519-1533. (doi:10.1093/gji/ggt327).

Record type: Article

Abstract

Geomagnetic excursions are brief deviations of the geomagnetic field from behaviour expected during ‘normal secular’ variation. The Laschamp excursion at ?41?ka was one such deviation. Previously published records suggest rapid changes in field direction and a concurrent substantial decrease in field intensity associated with this excursion. Accurate dating of excursions, and determination of their durations from multiple locations, is vital to our understanding of global field behaviour during these deviations. We present here high-resolution palaeomagnetic records of the Laschamp excursion obtained from two Ocean Drilling Program (ODP) Sites, 1061 and 1062 on the Blake-Bahama Outer Ridge (ODP Leg 172). High sedimentation rates (?30–40?cm?kyr?1) at these locations allow determination of transitional field behaviour during the excursion. Palaeomagnetic measurements of discrete samples from four cores reveal a single excursional feature, across an interval of 30?cm, associated with a broader palaeointensity low. We determine the age and duration of the Laschamp excursion using a stratigraphy linked to the ?18O record from the Greenland ice cores. This chronology dates the Laschamp excursion at the Blake Ridge to 41.3?ka. The excursion is characterized by rapid transitions (less than 200?yr) between stable normal polarity and a partially reversed polarity state. The palaeointensity record is in good agreement between the two sites, revealing two prominent minima. The first minimum is associated with the Laschamp excursion at 41?ka and the second corresponds to the Mono Lake excursion at ?35.5?ka. We determine that the directional excursion during the Laschamp at this location was no longer than ?400?yr, occurring within a palaeointensity minimum that lasted 2000?yr. The Laschamp excursion at this location is much shorter in duration than the Blake and Iceland Basin excursions.

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Published date: December 2013
Organisations: Paleooceanography & Palaeoclimate

Identifiers

Local EPrints ID: 360289
URI: https://eprints.soton.ac.uk/id/eprint/360289
ISSN: 0956-540X
PURE UUID: ec06e9fe-5291-4057-970a-b7020dc2229c

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Date deposited: 04 Dec 2013 09:58
Last modified: 18 Jul 2017 03:13

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