Fróðskaparrit - 01.01.1998, Side 217

MANNAÁRIN í TJØRNUVÍK í FØROYUM
223
LT Tjørnuvík A Tephra Tjørnuvík B Tephra
Sample 1 2 3 4 5 6 7 8 9 10 11 12 13
SiO, 48.78 74.60 73.50 73.45 72.16 68.21 67.20 65.57 65.26 65.15 63.63 63.52 63.09
Ti02 1.83 0.09 0.13 0.14 0.09 0.26 0.45 0.47 0.39 0.38 1.52 1.44 1.42
ai2o3 13.32 13.04 13.09 12.99 12.86 14.31 15.00 14.66 14.47 13.85 13.86 13.66 13.89
FeOtot 12.46 2.10 2.07 1.93 2.03 4.25 5.62 5.35 5.48 6.50 6.13 5.99 6.37
MnO 0.24 0.10 0.10 0.10 0.09 0.15 0.20 0.15 0.21 0.21 0.19 0.22 0.22
MgO 7.32 0.09 0.08 0.08 0.03 0.24 0.58 0.52 0.56 0.24 1.51 1.52 1.45
CaO 11.02 1.31 1.34 1.36 1.14 2.73 3.26 3.09 2.97 3.58 3.56 3.42 3.49
Na20 2.66 4.00 3.97 4.26 4.21 4.25 4.41 4.10 4.11 3.51 4.28 3.80 4.53
K20 0.21 2.80 2.82 2.92 2.74 2.29 2.01 1.90 2.07 1.99 2.65 2.56 2.55
Total (%) 97.84 98.13 97.10 97.23 95.35 96.69 98.73 95.81 95.52 95.41 97.33 96.13 97.01
Table 3. The chemical composition of individual glass shards from Tjørnuvík, 207.4 cm,
determined by electron microprobe. Only analyses with totals above 95% are shown. The
preparation for microprobe analysis and subsequent analytical procedures follow Dugmore et al.
(1995).
Talva 3. Tann evnafrøðiliga samansetingin av einstøkum glasbrotum í Tjørnuvík, 207,4 cm,
fastsett við elektroniskari mikrosondu. Einans greiningar við heildarúrsliti oman fyri 95% verða
vístar. Fyrireikingin til mikrosondugreiningina og eftirfylgjandi arbeiðsháttur fylgja Dugmore et
al. (1995).
Tephra and the subordinate population the
Tjørnuvík B Tephra. None of the tephra
horizons were visible to the naked eye, and
were concentrated by the new technique for
extracting rhyolitic microtephra from
minerogenic sediments (Turney, 1998).
Re-calibration of bulk
radiocarbon dates
The re-calibrated bulk radiocarbon dates
from Tjørnuvík which are illustrated on
Figure 2 and tabulated on Table 2, came
from three separate proftles, A, B and C, to-
gether with the AMS date from the present
study. The purpose of this figure is to illus-
trate the consistency in the dating results to
the late AD 600s, early 700s. The initial
date taken from Profile A, was a 10 cm bulk
sediment sample. The results were of such
significance, that at a later stage, two fur-
ther profiles were dated: the first of which
(Profile B) consisted of a 4 cm, and the sec-
ond (Profile C), a 2 cm bulk sediment sam-
ple. In each case, the settlement horizon
had been identified in the middle of the sec-
tion and the dating results of Profile A were
repeated. The AMS radiocarbon date car-
ried out in the present study of terrestrial
plant macrofossils extracted from a 3 mm
sample, is the most stratigraphically pre-
cise. It confirmed the consistent results
from the original work (Jóhansen, 1971;
1985).
The result for the re-calibration of the
tephra layer to cover this time period from
the peat deposit at Mýrarnar on Streymoy
(Persson,1968; 1971), reveals that the cal-
endar age of this layer is from AD 1020 -