Fróðskaparrit - 01.01.1998, Blaðsíða 212

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HUMAN IMPACT AT TJØRNUVÍKIN THE FAROEISLANDS
each sediment slice after sub-sampling for
pollen and washed with distilled water
through individual plastic netting (sieve
size 180 pm). Determinations were made
based on the plant macrofossil collection at
the Department of Quaternary Geology in
Lund and the first author’s own reference
collection. After identification, terrestrial
plant macrofossils to be used for dating
were immediately dried at 50°C ovemight
in aluminium foil, to eliminate contamina-
tion sources arising from being left in dis-
tilled water (Wohlfarth et al., 1998). AMS
dating was carried out by Steinar Gulliksen
at the Laboratory for Radiological Dating,
Trondheim, Norway.
Preparation for the density separation
technique for concentrating rhyolitic mi-
crotephra (25 - 80 pm) from minerogenic
deposits followed the procedures as out-
lined by Turney (1998). The advantage of
this new method is that less extensive
tephra horizons may be discovered. The
study concentrated on invisible tephra hori-
zons from the period before and after the
first settlement as identified by pollen
analysis. A density of between 2.3 and 2.5
g/cnr’ was chosen, which should pick up
most rhyolitic glass shards (Turney et al.,
1997).
The percentage weight loss on ignition
was carried out at 1 cm intervals at 105°C
and 550°C to determine the water and or-
ganic content of the sediment. Re-calibra-
tion of the bulk radiocarbon dates from
Jóhansen (1971; 1985) and Persson
(1968; 1971) were carried out using the
CALIB vers. 3.0.3 (Stuiver and Pearson,
1993). Quantitative microcharcoal count-
ing followed the techniques described by
Clark (1982).
Results
Sediments
The maximum sediment depth was 357 cm,
and the deepest section beside the flat area
where the present village and hayfields
now lie. The new sediment profile, taken
with a Russian Corer, produced a complete
core of 335 cm, of which the section be-
tween 165 and 250 cm is shown here. The
sediments were mainly peat with much
sand. The massive increase of inorganic
sediment described in the literature as re-
flecting Norse Landnám (Buckland, 1990)
was not clear in the field in the present
study. A layer of almost pure moss, identi-
fied as Calliergon giganteum and dated to
880±100 BP (AD 1028-1276; 1 <y varia-
tion; CALIB vers. 3.0.3; Stuiver and Pear-
son, 1993) in Jóhansens original study, was
visible between 193 and 195 cm, along
with a thick, unsorted gravel layer between
233.5 and 245 cm also identified by
Jóhansen (1971; 1985). Other thinner lay-
ers of sorted material were also visible, and
are thought to have been deposited by the
small river in the centre of the flat area in
times of flood. While slicing the core sec-
tion between 205 and 235 cm, a change was
noticed in the nature of the sediment be-
tween 223 and 224.3 cm which again had
not been visible in the field. The sediment
became much more gritty in texture and the
pollen concentration was too low to allow a
pollen count. There was a marked increase
in organic matter above 217 cm, rising from
11.9% to 20.7%. Microcharcoal was first