Náttúrufræðingurinn - 1964, Blaðsíða 50

144
NÁTT Ú RU F RÆÐl N G U RIN N
Raised beaches are known in all parts of Iceland (Fig. 13). The evidence of
higher sealevel are old sea-cliffs, gravel terraces and bedded marine clays with
subfossil molluscs. The highest shorelines seem to be synchronous all over the
country except in eastern part of S-Iceland where they are slightly younger.
l'he varying height of the raised beaches, 110 m in southern Iceland, 80—
90 m in Borgarfjiirður, W-Iceland, and 40—50 m in western, northern ancl
eastcrn Iceland, is a result of different downwarping of Iceland caused by the
ice-sheet tluring the last glaciation, ancl of the subsequent isostatic recovery.
The radiocarbon dated molluscs (shells) were collected from marine clays
at different heights above sea level. The radiocarbon age for all of them lies
between 9580 ± 140 and 10450 ± 160. In general the molluscs from the marine
clays indicate slightly lower sea temperature than to-day.
According to former investigations the highest shorelines seem to be a little
older than the end-ntoraines of the Búdi-stage, which appear to be comparable
to the Salpausselka-Raene stage in Scandinavia, i. e. Younger Dryas. The
highest shorelines seem therefore to be of late Alleröd or Younger Dryas
age. The highest shorelines were developecl when eustatic and isostatic move-
ment were in balance. During the Búdi-stage the uplift was approximately
10—20 m in southern Iceland. The isostatic recovery was then relatively rapid
and the sea had reached the present level at 9000 B. P. (cf. radicarbon datings
in Seltjörn). The isostatic recovery slowed down and kej)t pace with eustatic
sealevel rise during the Boreal and Atlantic periods. Only at Hrútafjörður,
westernmost North-Iceland, is there evidence of an Atlantic-Sub-Boreal trans-
gression (A'i/cci/íi-transgression) witli a following regression. In Sub-Atlantic
times there has been a transgressive trend on the coasts of Iceland. In thc
Reykjavik area the subsidence seems to be about 15 cm a century.
Pollen zonation and radiocarbon datings
by Thorleifur Einarsson
University Research Instilute, Reyhjavik, Iceianil.
Moldhaugar (G)
7920 ± 170 years (H 404/370 1960)
Pollen analysis in Icelandic peat bogs reveals that most of the pollen dia-
grams can be divided into 4 pollen zones:
A. Late glacial early Holocene. In eastern N-Iceland there is a small
Betula-maximum, whereas the southern part of Iceland was Betula-lree.
B. Boreal -)- Atlanticum. The first great Beítí/n-maximum followed by a
/Je/M/a-minimum with a Sjihagnum-maximum caused by higher humidity
in Atlantic times.
C. Sub-Boreal -(- lower part of Sub-Atlanticum. Second great Betula-maxim-
um. After 2700 B. P. the climatic deterioration sets in.
D. Historical time, from A. D. 870. The influence of man is clearly re-