Jökull - 01.12.1963, Blaðsíða 5

the latter. To explain the gradual encroach-
ment of H5 on H4 it is here suggested that the
deposition was very slow, and agitation in the
water swept the fine material into deeper
water, keeping pace with the deposition.
Whether these strata are marine or lacustrine
is uncertain, as no fossils have been found.
He/7 is a coarse deposit containing much
material derived from Hr, and deeper sediments,
even traces of the Lower Sediments on western
Tjörnes (Bárdarson, Strauch). The deposit
no doubt corresponds to a major erosional
interval. The previous deposits were now til-
ted slightly to the east, and to the west of
Breiðavík they were subjected to erosion, per-
haps completely wiped out, so that the Lower
Sediments were laid bare. But as east- or north-
eastward tilting and erosion also occurred later,
the exact position of the earlier erosional sur-
face is difficult to reconstruct.
The lowest layers in Hg/7, just east of Foss-
gil, have steep northeast dip (20°) but the dip
decreases gradually upwards and eastwards, and
blocks and pebbles of basalt become more pre-
dominant. Towards the top, material derived
from the brown sediments is nearly absent.
This change in composition, which has not
been noticed earlier, will be seen to be of
stratigraphic value.
H7 was distinguished from H6 by Péturss and
Bárðarson by its content of large boulders and
greyish colour, which suggested glacial influ-
ence. But the two members are in other re-
spects difficult to distinguish from each other,
whence Strauch combines them into He/7. But
also a sandstone resting on H7 is difficult to
distinguish from it. Near the top of the cliff
a conglomerate bank is prominent by its resi-
stence to weathering. On the E—W section
seen, it has only a very slight eastward dip.
At the west end this bank is hardly distinguish-
able from H7 while at the east end it rests in
part on the sandstone while also it ends against
a wall of the liigher part of the sandstone. This
is apparently not a fault, it may be slumping
or a temporary sea cliff, but this is not too
clear; for a detailed study in the steep cliff,
working in ropes would be necessary. What is
clear is that the conglomerate bank rests on
the sandstone and the latter seems to be a
direct continuation of H7, although it is per-
haps not excluded that during a short lowering
of sea-level H7 was eroded a little before a new
submergence that brought the sandstone. These
strata are cut by a fault, on the east side of
which is found the thick layer Hs- This is a
muddy sandstone with some pebble bands at
the base. Althougli it is not possible to see
directly the sense of the movement at the fault,
it seems most likely that the east side was
thrown down and that the base of Hg is re-
presented by the finer sediments in the upper
part of the wall on the west side of the fault,
whence these are also marked IL in the dia-
gram. In my former study I also discussed an-
other possibility but this can now be dropped
on the basis of new observations at Svarthamar,
farther east.
Svarthamar is an isolated mass of conglomer-
ate whose stratigraphic position lias formerly
not been ascertained. Bárðarson put it as No.
11 in his section, while he, Áskelsson and Ein-
arsson suspected some lower position, and
Strauch identified Svarthamar with H2a. There
can now be no doubt that Svarthamar belongs
to H6/ 7. The Svarthamar conglomerate is a
delta consisting of stratified, well-worn river
gravel, with a dip of 20—30° NNE. Most com-
mon are pebbles of 2—3 cm diam. but blocks
of 30—40 cm occur, and a part is sandy. The
pebbles consist very largely of brown sandstone
to siltstone. According to my estimate such
pebbles are at least 50—60% of the total
volume.
North of the centre of Svarthamar we can
observe liow IIs rests on the conglomerate.
There is no sharp limit, the gravel becomes
grádually finer and the dip decreases as we
come higher, and the percentage of the brown
sediment material decreases at the same time.
This is the same relationship as is found in
Hö—H7—Hg, and the composition of Svartham-
ar sliows very clearly that, like He/7, it was
formed during a breaking down of the sedi-
ments Hg to Hatl. Strauch mistakenly states
that brown sediment pebbles are nearly absent
from Svarthamar. Perhaps he only saw the con-
glomerate in a wet state, when the sediment
pebbles look rather similar to basalt.
Cementation in Svarthamar is the same as
noted for H2a and He/7. Pieces of peat and
carbonized wood chips are found occasionally
in Svarthamar.
We see now that the coarse material of He/7
JÖKULL 1963
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