Jökull - 01.12.1963, Page 8

level. In some cases a correlation between the
changes of sea-level and of climate is rather
striking. This has induced me to make the
following attempt of correlation and division
of the development into stages.
St. 1. After a period of volcanic activity
(Stangarhorn basalts) and tectonic
movement, follows a long time of ero-
sion with deposition of the river gravel
H2a. Compared with later events the
sea-level was high, and relatively warm
climate will be taken to be implied.
St. 2. Downcutting of this deposit suggests
lowering of sea-level due to increase
in glaciers and colder climate.
St. 3. Possibly a 50—60 m deep lake occupied
the area. But if H2b is marine, the
implication is a rise of sea-level by
some 50 m. Most of H2b can be con-
sidered as foreset beds, but deposition
seems to end with topset gravel, H3.
St. 4. This was at the same time the begin-
ning of a new stage: erosion, frost
heaving, cryoturbation which imply
some lowering of sea-level coupled with
a cold spell.
St. 5. Rise of sea-level and deposition of the
rather unstable clay H4, with drifted
stones. This suggests the melting of
glaciers, with warmer climate.
St. 6. A new drop of sea-level caused greater
instability of H4 and some plastic
movement. H5 is the result of very slow
deposition, possibly due to colder cli-
mate, in shallow agitated water.
St. 7. Some tectonic movement with slight
eastward tilting. Erosional period. Local
denudation of the existing hardened
sediments. Delta formation Hg/7 and
Hn. Later fluviatile transport of basalt
from a greater drainage area, as evi-
denced by H7 to Hs-
St. 8. Rise of sea-level, deposition of Hs-
Probable beginning of new volcanic
activity.
St. 9. Towards the end of Hs the deposition
became slow and the sea was cold, as
evidenced by the state and fauna of
Hg. Sea-level dropped; H9 was weath-
ered; gravel and bog-iron. It may
have been this sinking of sea-level that
made the clay in Hg unstable, with a
resulting heavy disturbance of the strata.
St. 10. Rise of sea-level; Hio with warmer sea
than in Hg. Probably change of mag-
netic polarity.
St. 11. Fall of sea-level, erosion of Hio, beach
shingle (12x). Probably Polar drift ice,
cf. below.
St. 12. Rise of sea-level, sandstone of Hi2.
Warm.
St. 13. Some fall of sea-level; beach shingle,
H13.
St. 14. Risé of sea-level; H14, warm.
St. 15. Fall of sea-level. Beginning of main vol-
canic phase of Ri.
All in all we find 7 low-level periods, more or
less clearly corresponding to relatively cold clim-
ate, and 7 high-level periods corresponding to
relatively warmer climate. Thus, the Breiðavík
deposits would seem to contain a record of a
long sucession of eustatic fluctuations of sea-
level and of climate preceding the major Pleis-
tocene fluctuations. Our dating would lead to
a duration of the order of 100 thousand years
for each period, i. e. a cold and a warm spell,
and this is at any rate comparable with the
results for the later part of Pleistocene (Emi-
liani 1958).
Finally it should be mentioned that the in-
ferred eustatic fluctuations of sea-level were
superimposed on a progressive sinking of the
area wliich amounted to about 200 m, using
Strauch’s figures for the thickness of the se-
diments above the top of H2a.
The Lower Sediments of Tjörnes indicate
still earlier fluctuations. First, the Cardium
(Serripes) Groenlandicum zone of Bárðarson (the
topmost zone of the Lower Secliments) records
the invasion into Icelandic waters of a new
rich northern fauna, and lowering of tempera-
ture. If we accept that between the normally
polarized Stangarhorn basalts and the basal
normal lavas of the Intermediate basalts there
is one reverse lava group (Tr. Einarsson 1958)
then the age of this invasion may be late N3
or perhaps something like 4 million years.
The Lower Sediments have a total thickness
of about 550 m (Strauch’s estimate) and there
is a rapid alternation of marine and terrestrial
sediments. This shows that sedimentation near-
ly kept pace with the progressive sinking. The
6
JOKULL 1963