Jökull - 01.12.1990, Page 30

up to a maximum level, that was reached concurrently
with the culmination of the glacier extent (Kjartansson,
1958; Th. Einarsson 1985; Norðdahl and Einarsson,
1988). This pattern of sea-level changes, i.e. the inti-
mate relationship between glacial isostatic movements
and glacier extent in Iceland is explained by compar-
atively low viscosity of the asthenosphere underneath
Iceland and great deformability of a relatively thin
ocean-crust, which almost instantly reacts upon even
minor changes in the overburden load (Tr. Einarsson,
1966; Tryggvason, 1973, 1974; Norðdahl, 1983 and
Sigmundsson, 1990).
This paper follows the chronostratigraphical ter-
minology for Norden as proposed by Mangerud et al.
(1974). If not otherwise stated all 14C ages of ma-
rine organisms mentioned in this paper (Table I) have
been corrected with respect to the 13C/12C ratio and in
accordance with the apparent sea-water correction of
365 ± 2014C years for living marine organisms around
Iceland as determined by Hakansson (1983). The 14C
dates given by the Trondheim 14C laboratory (sam-
ples T-4467, 4468, 4470) were originally corrected
for sea-water influence of some 440 14C years. In this
paper, however, the Trondheim laboratory ages have
been adjusted to Hakansson’s 365 14C years sea-water
correction for Icelandic waters. In the early days of
14C dating in Iceland, geologists were unaware of the
influence of the apparent age of living marine organ-
isms and the effect of sea-water correction. Those 14C
dates marked with l> in this paper have been corrected
with respect to their respective 13C/12C ratios, but they
were not corrected for sea-water influence when orig-
inally i published. Samples showing dates marked
with 2\ have not had their 13C/12C ratios determined.
Consequently the apparent age of living marine or-
ganisms cannot be subtracted from the obtained 14C
values (Table I).
MODE OF DEGLACIATION
At the time of maximum extent of the Icelandic
inland ice sheet, the whole of Iceland with the ex-
ception of mountainous coastal areas was ice-covered
(Thoroddsen, 1905-06). Glacial striae were found at
sea-level on all major peninsulas around Iceland to
support this observation. The orientation of glacial
striae indicates, that the major part of Iceland was
covered by a single continuous ice sheet with ice-
streams and outlet glaciers flowing radially away
from ice-divides that more or less coincided with the
present water-divides in Central Iceland. At the same
time Northwest Iceland was apparently covered by
an independent ice cap with ice-streams and outlet
glaciers flowing away from an ice-divide above the
central parts of the Vestfirðir peninsula. Although
a monoglacialist, Thoroddsen (1905-06) mentioned
several end-moraines, which he found during his re-
search expeditions through Iceland at the end of the
19th century, and he was of the opinion that these
moraines had been formed at stationary ice margins
during a continuous deglaciation. On the other hand,
it is not clear whether he associated the formation
of these moraines with climatic deterioration or con-
sidered them to be a product of topographical influ-
ence during the continuous deglaciation. Thoroddsen
(1905-06) did not mention that end-moraines in dif-
ferent parts of the country might be formed by a si-
multaneous standstill or readvance of the glaciers.
The first among Icelandic geologists to realize that
the deglaciation was not only interrupted by arbitrary
standstills of the glacier margins, but in fact by read-
vances of the glaciers, was Pjeturss (1910). He sug-
gested that the end-moraines in southwestem Langa-
nes and south of Þistilfjörður in Northeast Iceland
were not formed during the maximum extent of the
glaciation but during a later advance, which he named
”Das Langanesstadium“. He correlated this advance
in Northeast Iceland with an advance and formation of
moraines on the Skagi peninsula in North Iceland, and
also with an advance and formation of a conspicuous
end-moraine in South Iceland (Pjeturss 1910).
A little later, Bárðarson (1921,1923) demonstrated
that end-moraines in the inner parts of the Breiða-
fjörður area and in the Borgarfjörður area in West
Iceland were formed when the deglaciation was inter-
rupted by standstills of the glacier margins. Subse-
quently, and further inland in these areas, less impres-
sive end-moraines were formed during a temporary
stagnation of the retreating glaciers. Bárðarson also
suggested that contemporaneous end-moraines were
to be found elsewhere in Iceland. According to the
28 JÖKULL, No. 40, 1990