Jökull - 01.11.1998, Blaðsíða 11

Table 3. Radicarbon age of carbonized moss below the Leiðólfsfell scoria deposit
Sample no. Location Lab. no. D14C d13C Age
13.07.92-03 635135N Wk-3838 -31.06.3% -23.90.2% 25060 BP
183022W
Age determination by the Radiocarbon Dating Laboratory, University of Waikato, New Zealand. The
sample material is carbonized moss and moss roots and was collected at location 2 (Figs. 1 and 4). The
1783 Laki tephra and the Leiðólfsfell scoria rest directly on the moss, which in turn includes the 1755
Katla tephra layer (see text for further discussion). The 14C depletion (D14C) is expressed in per mille
with respect to 95% NBS oxalic acid. The isotopic fractionation correction (813C) is expressed in per
mille with respect to PDB. The age is calculated using the Libby half-life of 5568 years, with isotopic
fractionation correction, 95% NBS oxalic acid as ‘modem’ with 1950 AD as the reference year, and
with the assumption of constancy in the atmospheric radiocarbon levels. Quoted errors are one standard
deviations, based on counting statistics only.
ther confirmed by C14 radiometric dating of car-
bonized moss found immediately below the deposit at
Location 2 (Fig. 4). The results give an uncorrected
radiocarbon age of 250 ± 60 years calculated from
1950 (Table 3) and the calibrated age of the moss is
~1660 + 25 AD (Stuvier, 1993). Although the age of
the moss predates the Laki eruption by ~120 years, it
shows that the Leiðólfsfell scoria is younger than
1660 AD which is consistent with the results from the
tephra stratigraphy. The moss remains collected for
analysis were ~4 cm thick and included the 1755 AD
Katla tephra layer (Fig. 4). This suggests that the sam-
pled moss was growing in the area prior to 1755,
Fig. 3. Photograph of the soil profile at location 2. The top
~ 170 cm of the profile is the Leiðólfsfell scoria deposit,
which is covered by moss and thin soil. Also indicated are
the -935 AD Eldgjá (E-935). and -870 AD Vatnaöldur (Va-
870) tephra layers. The latter tephra layer, often termed the
Settlement layer because it was deposited in the time of early
settlement in Iceland, markes the transition from prehistoric
to historic soils (Þórarinsson, 1967; Larsen, 1984). The mea-
suring stick in the center of the photograph is 62 cm long.
- Ljósmynd af jarðvegssniði 2; efst er Leiðólfsfellsgjóskan,
170 sm þykk. Jarðvegurinn undir inniheldur fjölmörg sögu-
leg og forsöguleg gjóskulög, þar á meðal gjóskulögin frá
Eldgjárgosinu ~935 e. Kr. og Vatnaöldugosinu 870 e.Kr.
Síðarnefnda gjóskulagið er jafnframt þekkt sem Landnáms-
lagið. Mælikvarðinn á miðri myndinni er 62 sm.
which may, in parts, explain the difference between
the calibrated age of the moss and the year in which it
was covered by the Leiðólfsfell scoria.
JOKULL, No. 46, 1998
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