Jökull - 01.01.2012, Blaðsíða 77

Distal tephrochronology of NW Europe
Table 1. Tephra layers from bogs and lakes in Sweden. The tephras are predominantly silicic (>63 wt% SiO2)
except the basaltic Veidivötn-1477 and the phonolitic Laacher See Tephra, from the Eifel volcanic region in
Germany. Prehistoric ages are in calendar years BP. Ages discrepancies exist for some tephras, for example the
Askja-S tephra has been dated to ca. 10,800 BP by Wohlfarth et al. (2006) and 10,500–10,350 BP by Lind and
Wastegård (2011). Persson (1966) reported unknown tephra layers in five central Swedish bogs (site 2, 8, 10
and 11) which were radiocarbon dated to between AD 500 and 1700 (Table 2). Several tephra layers have been
reported from this time interval (e.g. the AD 860 layer, Hekla-1, Hekla-1158 and Öræfajökull-1362; Hall and
Pilcher, 2002; Vorren et al., 2007) and it is possible that one or more of these also occur in Swedish bogs. –
Gjóskulög í mýrum og stöðuvötnum í Svíþjóð. Öll gjóskulögin eru súr (>63% SiO2) nema basíska gjóskan úr
Veiðivatnagosi um 1477 og fónólítíska Laacher See gjóskan frá Eifel jarðeldasvæðinu í Þýskalandi. Aldur er
í almanaksárum fyrir 1950 nema fyrir gjóskulög frá sögulegum tíma. Aldur er í flestum tilfellum úr rituðum
heimildum. Munur getur verið á tímasetningu einstakra gjóskulaga, t.d. hefur Askja-S gjóskan verið tímasett
u.þ.b. 10,800 BP af Wohlfarth o.fl. (2006) og 10,500–10,350 BP af Lind og Wastegård (2011). Persson (1966)
nefndi einnig óþekkt gjóskulög í fimm mýrum í mið-Svíþjóð (staðir 2, 8, 10, og 11). Þau voru aldursákvörðuð
með geislakolgreiningum frá um 500 til 1700 e. Kr. (tafla 2). Allmörg útbreidd gjóskulög eru þekkt frá þessu
tímabili (t.d. gjóskulag frá um 860 e. Kr., Hekla-1, Hekla-1158 og Öræfajökull-1362; sjá Hall amd Pilcher
(2002) og Vorren o.fl. (2007). Hugsanlega má einnig finna einhver þessara gjóskulaga í sænskum mýrum.
Tephra Age (AD/BP) Source volcano Sites
Askja-1875 AD 1875 Askja 1,2,3,4,5,7,8,9,10,11,13,14,15,16,19,20,21,22,24
Veidivötn-1477 AD 1477 Veidivötn 3
Stömyren* c. 2100 BP ? 12
Gullbergby c. 2700 BP Torfajökull 19
Hekla-3 c. 3000 BP Hekla 2,10,11,13,16,17,21,22,23
Sn-2/LBA-2 c. 3600 BP Snæfellsjökull 7
Hekla-S/Kebister c. 3720 BP Hekla 2,6,10,12,16,18,21,22?,23
Hekla-4 c. 4260 BP Hekla 2,13,16,22?,23,27
Lairg-A c. 6900 BP Hekla? 2
Högstorpsmossen** c. 10,200 BP Snæfellsjökull 29
Askja-S c. 10,400 BP Askja 32,34
Hässeldalen c. 11,300 BP Snæfellsjökull? 31,32,34,35
Vedde c. 12,100 BP Katla 25,26,28,29,32,33
Laacher See*** c. 12,900 BP Laacher See 30,34?
Borrobol/Penifiler? c. 14,000 BP ? 34,35
* The Stömyren can possibly be correlated with the Glen Garry tephra (e.g. Dugmore et al., 1995);
– Stömyren gjóskuna má e.t.v. tengja við Glen Garry gjóskuna (sjá t.d. Dugmore o.fl., 1995);
** The Högstorpsmossen tephra can possibly be correlated with the Sn-3 tephra (Boygle, 1999; Haflidason et al., 2000);
– Högtorpsmossen gjóskuna má e.t.v. tengja við Sn-3 gjóskuna (Boygle, 1999; Haflidason o.fl., 2000);
*** incomplete geochemistry. – Ófullgerð efnagreining.
extract tephra shards with more variable geochemical
compositions than the Vedde Ash and with different
morphological types (e.g. Blockley et al., 2005). The
rhyolitic component of the Vedde Ash has been found
in several terrestrial and uplifted marine sites in south
Sweden up to the Younger Dryas moraines (Figure 1;
e.g. Wastegård et al., 2000a; Schoning, 2002). The
basaltic component has not yet been found in Sweden.
The concentration of tephra is highest in the west-
ern sites and seems to decrease towards the south-east
where some sites have reported low or no occurrence
of the Vedde Ash (e.g. Davies et al., 2003).
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