Jökull - 01.12.1963, Page 9

alternation of marine and terrestrial sediments
need not mean corresponding eustatic fluctu-
ations of sea-level but they could do so. Using
Strauch’s analysis of the sediments as a basis,
I find 25 half-periods (a rise or a fall), as
against 14 in the Breiðavík deposits, and this
shoulcl be considered as a minimum, as fluc-
tuations of small amplitude might in several
cases not have been recorded. The ratio of the
sediment thicknesses, 2,2, is similar to that of
the „period“ numbers, 1,8.
There is sofar no evidence that the fluctu-
ation in the Lower Sediments were coupled
with climatic fluctuations. But in spite of this
and the uncertainty, as to how to interprete
the series of marine and terrestrial strata in
the Lower Sediments, it seems worthwhile to
point out, in connection with the present
interpretation of the Breiðavík deposits, that
further study might reveal here a series of
eustatic and climatic fluctutions.
IV.
Drift ice frorn the Central Arctic has been
common at the northern coast of Iceland in
historic times. This should also have been so
earlier in late- and post-glacial times. Also in
interglacial times and in the uppermost Plio-
cene we might expect similar conditions.
Crystalline stones and boulders, which are
easily recognizecl as being of foreign origin,
have often been found on the shores of Ice-
land. Some of these have no doubt been trans-
portecl by the Polar drift ice. On the other
hancl, such material has also reached Iceland
as ballast, and great care is needed to distin-
guish between the two sources. Foreign material
near frequented harbours is very likely to be
ballast, and in this connection also the histori-
cal development should be kept in mind.
Thoroddsen found foreign pebbles at the shore
of Melrakkaslétta, an area much frequented
by drift ice in earlier centuries, and he as-
cribed them without hesitation to ice-tran-
sport. However, Hraunhöfn in Melrakkaslétta
was a frequented landing place for ships sai-
ling between Iceland and Norway in the early
centuries of Icelandic history. Could the for-
eign material found by Thoroddsen liave been
transported as ballast from Norway? We cannot,
without further study, exclude that possibility.
But with due care, and relying especially on
very large boulders, it ought to be possible to
collect material that could tell something about
the clistribution in space and tinie of drifted
foreign material in Iceland.
What interests us here especially is the up-
permost Pliocene. Straucli (p. 83) reports the
find of a crystalline pebble embedded in 12x
in Breiðavík and this implies ice drift then or
earlier (if the pebble stems from reworking of
an older sediment).1) During my visit to Breiða-
vík last summer I found 3 pieces (1x2x2 cm3
(granite), 2x4x4 cm3 (gneiss), and one larger
than a human head (quartzite)) in the beach
shingle on the east side of Breiðavíkurlækur.
Ballast seems in this case excluded. The peb-
bles may naturally have drifted to the shore in
later times, but it seems really more likely that
they have been washed out of the Breiðavík
marine sediments Hs—H14. If so, drifted material
may be more common in the sediments than
hitherto known, and in future research special
attention should be paid to it.
A large foreign block has for a long time
been known to lie on the beach below the cliff
formed by the Cardium Groenlandium zone.
Could it have come from these sediments?
Probably not, because these sediments are on
the whole fine-grained and erratic blocks or
cobbles in them would rnost likely have been
detected, not least in the thorough studies of
Bárðarson and Strauch. It would then seem
that drift ice did not reach Iceland that early.
The earliest probable date sofar is then the
bottom of H12, or some 2 million years B. P.
REFERENCES.
Áskelsson, J. 1934. News from Tjörnes. Report
Icel. Soc. Nat. Hist. Reykjavík, 48—50.
— 1938 Um íslenzk dýr og jurtir frá jökul-
tíma. Náttúrufræðingurinn 8, 1 — 16.
Bárðarson, G. G. 1925. A Stratigraphical Sur-
vey of the Pliocene Deposits at Tjörnes
1) The piece (micaschist to gneiss) is several
centimetres in diameter and has unworked
edges. To be careful, one should perhaps not
exclude the possibility that such a piece was
carried from Greenland to Iceland in the sto-
mach of a fish.
JOKULL 1963
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