Fróðskaparrit - 01.01.1998, Síða 218

224
HUMAN IMPACT AT TJØRNUVÍKIN THE FAROEISLANDS
Source Thingvallavatn3 (n = 5) GISP2b (n = 6) Litlidalurc (n = 10) Tjømuvík (n
Mean 1 o Mean 1.0 Mean 1 o
Si02 49.94 0.87 52.0 1.4 49.89 0.75 48.78
Ti02 1.86 0.29 1.5 0.4 2.00 0.33 1.83
ai2o3 13.15 0.44 13.8 0.4 13.20 0.25 13.32
FeOtot 12.79 0.49 14.0 1.3 12.54 0.39 12.46
MnO 0.24 0.04 - - 0.21 0.04 0.24
MgO 6.53 0.24 6.1 0.4 6.40 0.38 7.32
CaO 11.59 0.24 11.0 0.6 10.65 0.53 11.02
Na20 2.38 0.16 1.1 0.3 2.63 0.16 2.66
k2o 0.17 0.15 0.4 0.1 0.31 0.05 0.21
Total (%) 98.87 99.9 97.84 97.84
a Hafliðason et al. (1992, Table 2)
b Zielinski et al. (1997).
c Boygle (1994, data from Tephrabase, http://www.geo.ed.ac.uk/tephra/tbasehom.html)
Table 4. The chemical composition ofthe basaltic phase ofthe Landnám Tephra from Iceland
and Tjørnuvík, determined by electron microprobe. All analyses are expressed as wt%.
Talva 4. Tann evnafrøðiliga samansetingin av basaltskiftinum í Landnámstefruni úr íslandi og
Tjørnuvík, fastsett við elektroniskari mikrosondu. Allar greiningar eru endurgivnar sum wt%.
1240 and therefore does not include the
tephras in the AD 800s, geochemically de-
fined by Hafliðason et al., (1992), Gron-
vold et al., (1995), Pilcher et al., (1995) or
Zielinski et al., (1997). Table 2 gives the
details of sample size, original (published)
radiocarbon years BP, the original calibrat-
ed estimation and the re-calibration using
CALIB vers. 3.0.3 (Stuiver and Pearson,
1993).
Discussion
The palaeobotanical investigations at the
site of Tjørnuvík are now complete, and the
settlement layer identified by a series of
techniques and dated (Table 1; Figure 1).
This horizon had to be pinpointed micro-
scopically, as the sediment changes associ-
ated with settlement were not clear in the
fteld. The evidence is threefold: (1) There
is a significant increase in macrofossils of
weed species such as Montia fontana, Sag-
ina procumbens and Stellaria media that
rarely set seed in their native habitats unless
repeatedly disturbed (Bloch, 1980) (2)
Palaeobotanical analyses revealed a shift in
local vegetation conditions from a wet
meadow community with tall herbs includ-
ing Cyperaceae, Succisa, Potentilla, Al-
chemilla, Epilobium, Filipendula, Ranun-
culus flammula, Menyanthes trifoliata, Hy-
pericum pulchrum and Equisetum palustre
together with shrubs such as Juniperus,
Calluna and Salix, to a dry grassland with
associated macrofossil weed species in-
cluding Stellaria media, Montia fontana,