Jökull - 01.12.1963, Page 6

to the west o£ Breiðavíkurlækur can be con-
sidered as an early stage in the development
of a delta that later advanced at least 1 km
farther NNE to Svarthamar. The lack of traces
of heavy surf in Svarthamar then seems to
throw some doubt on tlie correctness of
Strauch’s interpretation that He/r was formed
under the influence of heavy surf. But even if
such an agency has played some part locally,
it is now clear that He/r and Hn represent an
erosional period during which, first, the sedi-
ments below Hg were broken down (to the
west of Breiðavík), but later predominantly
basaltic material was carried, no doubt by a
river, front a greater distance to the Breiðavík
area, to cover the lower sediments and their
detritus.
This period ends with further submergence
and deposition of Hs- The material of Hs is
largely stratified sand and silt but in the west
deposition started with fine gravel. The gradual
change from the Svarthamar conglomerate to
the finer Hs material has been mentioned.
To the southwest of Svarthamar the upper-
most 15 m or so of Hs are seen. In the lower
part of the exposure. we have brown silty sand
with occasional pieces of peat, and there is
considerable resemblance to Hob. Higher up,
gravel predominates and one is reminded of
H3; there are scattered blocks of up to 50—70
cm in diam.; sedimentary blocks or pebbles are
in the main lacking. Finally, there is again finer
material, recalling H4. If to this we add the
dark banks o£ H9, the resemblance to the group
H2b-H5 is rather striking. It is only when the
Svarthamar conglomerate is seen to be younger
than H5 that real correspondence is excluded.
But a remarkable repetation of events, one
might perliaps speak of two large cycles, is
suggested. Strauch found examples of Macoma
and Nucula in Hg, probably in the lower acces-
sible part of the exposure, ancl by analogy it
is then perhaps not excluded that Hob is rnarine,
although Strauch favoured lacustrine environ-
ment.
The sediments above Hs are all marine. H9
consists mainly of dark clay and is at most 2.5
m thick, according to Strauch. It should in
reality be considered as the topmost part of Hg,
only distinguished through fine, compact and
hard material and dark brown colour, and
probably clue to very slow deposition. It cor-
responds very likely to a short interval of time.
Strauch has described vestiges of plastic
movements in Hs and H9. But the main dis-
tortion took place after depositions of H9, as
the tracing of H9 from Breiðavíkurlækur north-
eastwards beyond Svarthamar clearly shows.
Tracing this layer eastwards from Breiðavíkur-
lækur it falls gently to a bend where it divides
into 3 separate dark banks, the bend being most
marked in the lowest bank. After a new rise, it
breaks finally up into separate lumps that fall
stepwise to the east and disappear in the shore.
Some distance farther northeast the layer reap-
pears in a small bend ancl here it contains bands
of gravel, and a few cobbles are found here just
above H9. Coming closer to Svarthamar, H9
suddenly appears in a nearly horizontal and
undistorted position 15—20 m up in the cliff.
The depression on tlie southwest side of this
high-lying block is occupied by the Macoma
mudstone Hi0. The southwest slope on Hs,
on which Hio was deposited, is covered with a
layer of conglomerate in which red stain and
bog iron is found.
From this it is seen that after deposition of
Ha, the layers were disturbed and laid dry and
subjectecl to weathering. This is also borne out
by an observation by Strauch, that on the
northeast side of Svarthamar Hg disintegrates
into a string of somewhat rounded blocks.
After a new submergence the depression was
filled up with the lower part of Hi0, while no
sedimentation took place on the surface of
the higher northeastern block. For this reason
one may get the false impression that H0
extends out into Hi0. Strauch thus concludes
mistakenly that H9 divides into two parts, the
one running down the slope at the base of
Hi0 and the other running with slight dip
southwest into Hi0.
On Hi0 rests the Cyprina deposit Hi2. At
the base, northeast of Svarthamar, is a lens of
gravel, rich in broken shells (12x in Bárðar-
son); this seems to be beach shingle. Submer-
gence then led to deposition of the sandstone,
the main part of Hi2. The surface of this is
eroded, as noticed by Strauch, and the basal
1/2 m or so of the hanging gravel layer Hi3,
which is very rich in shell fragments, is a re-
working of the shelly sandstone. In the higher
part of the conglomerate there is additional
gravel material, beach shingle or river gravel,
JÖKULL 1963
4