Fróðskaparrit - 01.01.1998, Síða 194

200
HOLOCENE TEPHRA LAYERS IN THE FAROEISLANDS
Figure 2
O
<u
16
14
12
10 -
8 -
6
4
2 -
&
• Saksunarvatn Tephra
□ Layer L 3574
0 40
45
50
55 60
wt % SiO,
Fig. 2 . Selected major element
datafrom Saksunarvatn
showing the Saksunarvatn
tephra and the L 3574 tephra
(full data in Tables 2 and 3).
The basaltic Saksunarvatn
tephra is more homogeneous
than the silicic layer L3574. All
data is also available at
http://www.geo. ed. ac. uk/tephra/
tbasehom.html
Mynd 2. Úrvaldar upplýsingar
um høvuðsfrumevni úr
Saksunarvatni, sum vísa
Saksunarvatnstefruna og ‘L
3574-tefruna’ (fullfíggjaðar
upplýsingar á talvu 2 og 3).
Saksunarvatnstefran úr basalti
er meira einsháttað enn
kisilflógvin L 3574. Alt tilfarið
er eisini til taks á
http://www.geo.ed.ac.uk/tephra/
tbasehom.html.
ence core from Saksunarvatn (Jóhansen,
1981). Here it is provisionally named L
3574 (Table 3, Fig. 2). While it forms a cm-
scale layer in Saksunarvatn, the well-devel-
oped sediment focusing in this lake basin
(>30 m of accumulation in 9,000 years)
means that its thickness in the core is likely
to be exaggerated (Jóhansen, 1977). The
actual thickness of the fallout is likely to be
on the mm or sub-mm scale, but this should
still form a recognisable isochrone across
Faroe and neighbouring areas of the North
Atlantic.
Conclusions
At least six Holocene tephras layers are
present in the Faroe Islands. Five are silicic
and one is basaltic in composition. Two
silicic tephras have been positively identi-
fied on the basis of new geochemical analy-
ses. They are H-S (3500 BP) and H-4 (3800
BP).
Historical records, and the identification
of Icelandic tephras of historical age in the
British Isles suggest that at least five other
recent tephras may be present in the Faroe
islands, but this has yet to be confirmed by
physical evidence.
There is a considerable, and largely un-
realised, potential for tephrochronology on
Faroes. Tephras exist both as visible, cm-
scale layers and as microscopic horizons.
The development of an effective chronolo-
gy will require the geochemical characteri-
sation of all the tephras present that will
permit the effective correlation to type se-
quences in Iceland.
Key reference profiles for tephrochrono-