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| Titel |
A Comparison of two Brunhes Chron Geomagnetic Excursions Recorded by Neighbouring North Atlantic Sites (ODP Sites 1062 and 1063) |
| VerfasserIn |
M. Bourne, C. Mac Niocaill, M. F. Knudsen, A. L. Thomas, G. M. Henderson |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065924
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| Zusammenfassung |
| A full picture of geomagnetic field behaviour during the Blake excursion is currently limited
by a paucity of robust, high-resolution records of this ambiguous event. Some records seem to
point towards a ’double-excursion’ character whilst others fail to record the Blake excursion
at all. We present here a high-resolution record of the Blake excursion obtained from Ocean
Drilling Program (ODP) Site 1062 on the Blake Outer Ridge (ODP Leg 172). Palaeomagnetic
measurements in three cores reveal a single excursional feature associated with a
broad palaeointensity low, characterised by rapid transitions (less than 500 years)
between a stable normal polarity and a fully-reversed, pseudo-stable polarity. A
relatively high sedimentation rate (~10 cm kyr-1) allows the determination of
transitional field behaviour during the excursion. Rather than assuming a constant
sedimentation rate between assigned age tie-points, we employ measurements of
230Thxs concentrations in the sediment to assess variations in the sedimentation
rates through the core sections of interest. This allows us to determine an age and
duration for the two excursions with greater accuracy and known uncertainty. Our
new age model gives an age of 127 ka for the midpoint of the Blake event at Site
1062. The age model also gives a duration for the directional excursion of 7.1±1.6
kyr.
This duration is similar to that previously reported for the Iceland Basin Excursion (~185
ka) from the nearby Bermuda Rise (ODP Site 1063), which recorded a ~7-8 kyr event.
Similarly, a high sedimentation rate (10-15 cm kyr-1) at this site allows a high-resolution
reconstruction of the geomagnetic field behaviour during the Iceland Basin Excursion. The
Site 1063 palaeomagnetic record suggests more complicated behaviour than that of the Blake
excursion at Site 1062. Instead, transitional VGP paths are characterised by stop-and-go
behaviour between VGP clusters that may be related to long-standing thermo-dynamic
features of the core–mantle system. The long duration of fully reversed directions at the two
sites is somewhat longer than that typically assumed for excursions and appears to
suggest that there may be a degree of stability associated with the two excursional
events.
We will present a comparison of the geomagnetic field behaviour of the two excursions as
recorded at these two sites. |
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