Jökull

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Jökull - 01.11.1998, Qupperneq 11

Jökull - 01.11.1998, Qupperneq 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 9
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