Jökull - 01.12.1979, Síða 47

Fig. 1. Location of the
fossiliferous deposits men-
tioned in the text.
SELARDALUR
GERPIR
SKAMMIDALUR
North Iceland. In the Lower Pliocene also the first
tillites appear. The Lower Pliocene climate was
probably similar to that in coastal Europe today
where the mean temperature for the coldest month
is close to 0°C.
The water temperature (annual mean tempera-
ture) in the Tjörnes area during the Lower
Pliocene, when the marine Tapes and Mactra Zones
were deposited, was at least 10°C, or about 5°C
higher than the present one, as indicated by the
presence of Glycimeris glycimeris (Linné), Abra alba
(Wood) and other warmth-loving mollusc species.
Plio-Pleistocene and Upper Pleistocene climate
Stratigraphical studies in Iceland indicate at
least 10 glaciations during the Upper Pliocene
and about as many during the Pleistocene. At the
beginningof the Plio-Pleistocene, about 3 m.y. ago,
a climatic deterioration took place, affecting the
flora as well as the marine fauna. The temperate
conifers and deciduous trees became extinct during
the Plio-Pleistocene (3.1—0.7 m.y.) and could not
reach Iceland again during interglacials, probably
because it was already an island. The most
prominent constituents of the Plio-Pleistocene flo-
ras were Alnus, Betula, Salix and grasses, as indicated
by the interglacial floras in Bakkabrúnir, North
Iceland (between 2 and 1 m.y.), and Stöd, West
Iceland (slightly older than 1 m.y.).
The Pleistocene floras became more and more
similar to the present one, which is clearly of
European affinity. Pinus became extinct about 1
m.y. ago after the deposition of the 2—1 m.y. old
interglacial sediments in Breidavik, Tjörnes Penin-
sula, North Iceland, and the sediments in Stöd,
West Iceland. Alnus was still living in Iceland dur-
ing the third last interglacial when the fresh-water
sediments at Svínafell, southeastern Iceland, were
deposited, whereas it is unknown in deposits from
the last two interglacial stages. Apparently the first
interglacials were milder than the later ones and
probably the first glaciations were not so severe. On
the other hand, the third last and the second last
glaciations seem to have been extremely severe.
The climate during the later interglacial stages
was probably similar to the present one, but during
the glaciations the annual mean temperature was
at least 5—10°C lower than today and the snow-
line was about 1000 m lower. During the last
glaciation Iceland was almost completely covered
with ice, but the main accumulation was south of
the present water shed, which indicates that the
precipitation was mainly brought by southerly
winds, as is the case today.
The Plio-Pleistocene marine faunas reveal a
similar trend. The Upper Pliocene marine fauna in
Skammidalur, South Iceland, comprises warmth-
loving species as Chamelea (= Venus) gallina (Linné),
Scrobicularia plana (da Costa), and Abra alba (Wood).
These are not found in younger Pleistocene
deposits and do not live in Iceland now. This indi-
cates a water temperature 2—4°C higher than the
present one. In the Tjörnes area the thermophilic
species disappeared before the deposition of the
Upper Pliocene Serripes groenlandicus Zone. How-
ever, the change in the marine Tjörnes fauna is
JÖKULL 29. ÁR 45