Fróðskaparrit - 01.01.1998, Síða 211

MANNAÁRIN í TJØRNUVÍK f FØROYUM
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(Zielinski et al., 1997). However, a chemi-
cally distinct tephra with a calendar age of
AD 860 ± 20 has been described from Irish
peat (Pilcher et ai, 1995). The geochemi-
cal analyses of the glass shards from Ire-
land, which are based on 25 reference
points, show it to be distinct from that of
the ‘Landnám’ tephra layer, and so could
not have originated from the Vatnaoldur
eruption despite the fact that its calibrated
age overlaps the ice core age for that event
(Zielinski et al., 1997). Furthermore, Zie-
linski et al. (1994) and Zielinski (1995)
report another eruption recorded in the
summit ice core which covers a two year
period, and gives a calibrated age from AD
822 to 823. The source area of this layer is
presently unknown, but is thought to be
Icelandic (Zielinski, pers. comm. April,
1998).
Numerous eruptions have been de-
scribed in the written records since the first
settlement on Iceland (Hallsdóttir, 1987;
Hafliðason et al., 1992,) and many of these
tephra horizons may be present in the Faroe
Islands. Volcanic ash layers have been
identified by the refractive indices of the
glass shards from peat deposits in the Faroe
Islands by Persson (1968; 1971). At one of
the sites, Mýramar on the island of Streym-
oy, a tephra layer is bulk radiocarbon dated
to the calibrated age of AD 850 -1050
(Persson 1968; 1971) and a correlation sug-
gested to the Landnám tephra. A further
aim of this work was to see if this could be
identified in the sediment sequence exam-
ined, in order to increase the dating preci-
sion of the settlement horizon. We began by
using a new technique for extracting rhy-
olitic microtephra from minerogenic de-
posits, developed by Turney (1998).
Methods
Tjørnuvík was chosen as the prime target
for investigation, as it was here that Jóhan-
sen (1971; 1985) had described palaeo-
botanical evidence for early settlement. At
the time of his investigations, the total
depth of the peat was unknown, as sam-
pling stopped at 250 cm. A series of new
probes were made across the peat deposit in
the autumn of 1994 to determine the maxi-
mum depth. Preliminary pollen samples
were taken every 5 cm and counts of c. 500
pollen grains were made at each level. The
annulus diameter, pore diameter, M+
(largest diameter of a pollen grain), and M-
(diameter at a right angle to M+) of all
Gramineae pollen grains with an annulus
diameter of >8 pm were measured, to sepa-
rate cereal type pollen taxa from those of
large, wild grasses (Andersen, 1979).
Once the area covering the settlement
horizon had been identified, a 30 cm sec-
tion of the core was cut out of the main pro-
flle and frozen. This was then sliced while
frozen at between 3 and 4 mm intervals us-
ing an electric meat slicer. The slices were
placed in individual plastic bags and put
back in the freezer. Before samples were
taken for pollen preparation, the slices were
carefully scraped on both sides while
frozen, to remove any possible contamina-
tion. Pollen samples were prepared for
every sample over the settlement horizon,
in order to pinpoint for dating purposes, the
first instance of cereal pollen.
Plant macrofossils were picked from