Jökull - 01.12.1985, Síða 16

Late glacial oscillations and final deglaciation.
During the late glacial period, in a wide and, as
regards Hornstrandir, not absolutely dated sense, but
roughly comprising the Late Weichselian - Early Flan-
drian of Mangerud et al. (1974), the glaciers retreated
and finally disappeared. In Haelavík and Adalvík there
are clear indications of an early retreat on to presently
dry land, followed by a renewed glacial advance, and
then by the final deglaciation. The local evidence is as
follows:
Haelavík: High up on Haelavíkurbjarg (Fig. 7),
around or above the 200 m level, lie three poorly
developed cirques facing the bay. The uppermost rec-
ognizable lateral deposits laid down by the glacier com-
ing from the valley inside Haelavík are met with around
the 150 m level. There is another, very distinct lateral
terrace at about 55 m. It has a low gradient and ends
with a northwardly convex terminus about 500 m inside
the west end of Haelavíkurbjarg.
Along the coast in Haelavík there are three cliff
sections, kept open by the present marine erosion. They
are numbered 1, 2 and 3 on Fig. 7. The stratigraphy of
section 1 is shown in Fig. 8. The lower part of it consists
of 5 m of compact, silty till, rich in boulders. In the
upper part of this till is a concentration of boulders in
the silty matrix (Fig. 9), interpreted as waterlain clasts.
Then follows 3 m of silt, completely barren as regards
both mollusc shells and foraminifera. The silt has been
Fig. 5. The absolute maximum extent
of glaciers during the Weichselian.
The 100 m depth curve of today, de-
limiting the shallower part of the
shelf, runs at least 10 km beyond the
indicated glacier terminus in the west
and some 25 km beyond it off the
northern coast. Black areas indicate
high plateaux which protruded above
the general ice surface. To a large
extent these plateaux were probably
covered by thin inactive and/or cold
based icefields. 5. mynd. Hámarksút-
breiðsla jökla á síðasta jökulskeiði
(Weichsel). Svörtu svœðin eru háslétt-
ur sem hafa staðið upp úr meginísn-
um, þótt trúlega hafi verið þar þunn
ísþekja.
contorted by an overriding glacier, which deposited
about 5 m of compact, silty and boulder rich till, very
similar to that in the lower part of the section. The
upper till was later abraded by the sea which then,
according to the altitude of the abrasion terrace inland
from this section and the border between abraded and
non-abraded areas around it, reached 26—27 m above
present sea level.
Sections 2 and 3 (Figs. 7 and 10) show that some time,
probably rather a short time after the final deglaciation
(the last glacier here is represented by a sandy and
gravelly supraglacial till), sea level had regressed down
to or below its present level. This is indicated (section 3)
by the deposition of laminated lacustrine/fluvial silt with
a distinctly non-marine lacustrine/fluvial diatom
spectra, below 1 m above present sea level. It was
parallelled by the deposition of lacustrine sand and silt
at section 2, containing lacustrine/fluvial-type diatoms.
All this probably took place in what was then a system
of kettleholes. Contemporaneously with the lacustrine/
fluvial deposition at section 3 a sudden and heavy influx
of tephra took place. This tephra, hereafter named the
Haelavík tephra and further discussed below, was
deposited in the lacustrine environment at section 3
(with about 1 m of silt with a slight gyttja content on its
top; Figs. 10 and 12), but as an eolian sediment at
section 2. This shows that the water at section 2 had
disappeared when there was still water up to the same
14 JÖKULL 35. ÁR