Náttúrufræðingurinn - 1967, Side 49

NÁTTÚRUFRÆÐINGURINN
141
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SUMMARY
Some New Cx4 Datings in Iceland
by
Gudtnundur Kjartanson,
Museutn of Natural History, Deparlment of Geology and Geography,
Reykjavik.
An account of G14 datings done so far of Quaternary deposits in Iceland vvas
published by S. Thorarinsson, Th. Einarsson and the present writer in the
1964 volume of Náttúrufrœðingurinn. The present article deals only witli
later age determinations of samples submitted by the writer. Tlie age deter-
minations were all done by Dr. Ingrid U. Olsson of the Institute of Physics,
Uppsala, Sweden. The results are listed in Tablc I and their significance
discussed in the text.
Gardsendi. An age determination of a layer of peat, including stems of
Salix, which underlies a 15-metre tliick tuff layer that in turn underlies the
Helgafell Lava, indicates a maximum age of only 5000 years for this lava
flow, or about the half of previous estimates.
Thjórsárbrú. A sample taken from the base of a layer of peat, 30 cm thick,
lying' 33 m above sea level under the great Thjórsá Lava-flow, was submitted
for age determination in order to date the emersion of the spot above sea
level during the postglacial uplift of the land.
Hlidardalsshóli. Gharcoal found at the base of the great lava-flow Leita-
hraun was dated at 4530 ±100 years B.P. Thorlcilur Einarsson (1960) con-
siders the flow Ellidaárhraun in Reykjavik to be another branch of this lava-
flow. A sample of peat underlying the Ellidaárhraun and sent as early as 1950
to W. F. Libby of Ghicago for age determination was dated at 5300 ± 340
years B.P. Tlie fairly substantial difference between tlie results of that age
determination ancl the later one is not indicative of a contemporaneous origin
of the two lava branches.
Ekruhorn. The sample used for age determination was a thick shell of Mya
truncata from marine clay containing a high-arctic mollusc fauna characterised
Dy Yoldia arctica. As described by G. Bárdarson (1921) the series of strata
exposed in a long cliff, up to 20 metres high, is as lollows: At the base there
is moraine, tlien a thick layer of clay forming most of the cliff and from which
the sample for C14 age determination was collected. Near the top of the cliff
the shell fauna is still arctic, characterised by Clatnys islandicus but without
Yoldia. On the top these strata are here and there covered witli gravel con-
taning the Ivoreal species Mytilus edulis.