Jökull - 01.12.1963, Síða 4

noted that the conglomerate does not contain,
in any significant amount, material derived
form the Lower Sediments, although these
would probably have been exposed to sea-
attack, if H2a was mainly littoral. The pebbles
of the conglomerate consist nearly exclusively
of basalt ancl this would point in the main to
an inland source and fluviatile transport. The
essential absence of sediment pebbles will also
be seen to be significant when we come to a com-
parison with the very much different conglomer-
ate of Svarthamar, Hn, whose stratigraphic
position has hitherto been incorrectly under-
stood.
It is of some interest also to note the appar-
ent absence of rhyolite pebbles in H2a, as well
as in all the higher Breiðavik strata, as such
pebbles seem to have sorne stratigraphic value
within the Upper Tertiary rocks in Iceland
(Tr. Einarsson 1962). As far as this evidence
goes, it suggests that the Breiðavik deposits are
younger than the topmost plateau basalts on
the west side of Bárðardalur.
We also remark that the original spaces in
H2a are largely filled with onyx-like pink silica
with nearly horizontal internal stratification,
and in this way a practically dense rock has
been produced. Such infillings are also of
similar quantity in the conglomerates H(j, H7
and Hn, which suggests that the main process
of diagenese was relatively late — possibly after
the tilting movements, although this point has
not been studied sufficiently.
After some early consolidation of H2a, the
sheet was much dissected and at least 50 m
deep valleys were formecl. Then these were
filled and H2a was covered with the brown
sand- and siltstone H2l) which contains trans-
ported peat and twigs whose pollen content
was analyzed by Schwarzbach and Pflug (1957).
Strauch assumes a lacustrine-fluviatile origin
of this layer. Perhaps even in that case, but
especially if it is marine, it would indicate a
higher sea-level than that of the preceding time
of valley erosion. For the following cf. Fig. 1.
H2b is covered with a 2-3 m thick laver of
blocks and clay of somewhat morainic appea-
rance, H3, whose origin and relation to Hob
has not been clear. Bárðarson speaks of a resem-
blance with a moraine „both from the appear-
ance of the stones and from the fact that they
seem to be irregularly tumbled together in the
stratum“. Slightly scratched blocks may be
found but neither Bárðarson nor Tr. Einars-
son were convinced of a glacial origin of the
stratum. Strauch says that H2[) and H3 cannot
be sharply separated and „H3 is partly re-
presented by the sandstones of H2b.“ Further:
in the higher part of Hob, sanclstones predomi-
nate with „final local blocksheets (H3)“. Fin-
ally Strauch remarks that single blocks, such
as are found in H3, occur within H2b.
Below the waterfall in Fossá I founcl that
the uppermost i/2 m oí H2b is broken up,
probably by frost action, ancl weathered; on this
weathered zone rests H3. Further the strati-
fication of H2b is in part apparently discord-
ant with H3, but the contact is not clear. The
actual relationship may be that of foreset to
topset beds. From these observations it is
concluded that H3 in part corresponds to coarse
topset beds but that in part it is a residuum
of blocks left on the surface of H2b after con-
siderable weathering in which frost action
played a part. Cryoturbation is then thought to
account for the morainic appearance of H3.
In any case, a lowering of water- or sea-level
from H2b to H3 is inferred.
A new submergence of the area led to the
deposition of H4 and H5. The former is a
greyish brown sandstone to siltstone of fine
lamination with an occasional boulder of basalt
t:p to 1 m in diam. that must have been tran-
sported by floating ice. Also a clrifted piece of
peat was founcl. During deposition there was
slight plastic movement and formation of an
occasional pocket that was again filled up by
deposition, so that its trace is not found in
the base of Hg. Moreover, some greater slump-
ing occurred in the encl, for it is on the step-
formecl surface of H4 that H5 was deposited.
That these steps are of erosional nature, as
assumed by Strauch, is not statisfactory; on
the lowest step no trace of erosion between H4
and Hg was found. On this step both layers are
fully concordant.
The layers of the stratified, coarsely bankecl
sandstone Hfl encroached gradually upon the
steps of the already stabilized H4. Thus, the
bottom layer of Hg on the second step (shown
by broken line in Fig. 1) lies 6—7 m above the
bottom on the first step. The main difference
between H4 and H5 is that muddy glacial
material is included in the former but not in
2
JÖKULL 1963