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| Titel |
Regional 10Be production rate calibration for the past 12 ka deduced from two radiocarbon-dated rock avalanches at 69° N, Norway |
| VerfasserIn |
Cassandra R. Fenton, Reginald Hermanns, Lars Blikra, Peter W. Kubik, Charlotte Bryant, Samuel Niedermann, Anette Meixner, Mirjam Goethals |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041987
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| Zusammenfassung |
| Cosmogenic 10Be is an ideal nuclide to use for surface-exposure age-dating in
natural-hazards and climate-change research in northern Norway, particularly because many
landslides and glacial landforms in the region contain quartz-rich lithologies. Here, we
present data establishing the first regional 10Be production rate calibration for northern
Norway, in the Troms county region. Systematic natural-calibration of production rates of
different terrestrial cosmogenic nuclides, including 10Be, was one of the main goals
set by the CRONUS-EU research network, and was the driving force behind this
project.
Two rock avalanches in Troms County –the Grøtlandsura and Russenes – were
selected as CRONUS-EU natural cosmogenic 10Be production-rate calibration sites
because they (a) preserve large boulders that have been continuously exposed to
cosmic irradiation since their emplacement; (b) contain boulders with abundant
quartz phenocrysts and veins with low concentrations of naturally-occurring 9Be
(typically < 1.5 ppb); and (c) have reliable radiocarbon ages of 11424 ± 108 yr BP
and 10942 ± 77 yr BP (1-sigma; Oxcal 4.1), respectively. BP is by convention
regarded as years prior to 1950, and the radiocarbon ages are thus corrected to 2006 –
the sampling year – for the purposes of calculating 10Be production rates in our
study. Quartz samples (n=6) from these two sites contained between 4.41x104 and
5.10x104 at 10Be/g when normalized to the ETH’s S555 standard and scaled with Lal
(1991)/Stone (2000) in CosmoCalc (Vermeesch, 2007). Determination of these 10Be
concentrations accounts for isostatic rebound and shielding from snow and moss cover.
Using the 10Be half-lives of (1) 1.36 Myr (Nishiizumi et al., 2007), (2) 1.387 Myr
(Chmeleff et al., 2009; Korschinek et al., 2009), and (3) 1.51 Myr (Hofmann et al.,
1987), we calculate preliminary weighted mean total 10Be production rates of (1)
4.07±0.31, (2) 4.16±0.32, and (3) 4.52±0.34 at/g/yr (2-sigma), respectively. These are in
agreement within uncertainty with other 10Be production rates in the literature,
but are nominally lower than previous average global 10Be production rates. Like
other studies, our research concludes that regional cosmogenic production rates
should be used for determining exposure ages of landforms in order to increase the
accuracy of those ages. As such, using the total 10Be production rate from our
study calculated with the 1.387 Myr 10Be half-life, we determine a weighted mean
surface-exposure age of a third rock avalanche in Troms County (the Hølen avalanche) to be
7.5±0.4 kyr. This age suggests that the avalanche occurred shortly after the 8.2
kyr cooling event, just as the radiocarbon ages of the Grøtlandsura and Russenes
avalanches confirm field evidence that those rock-slope failures occurred shortly after
deglaciation. |
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