Jökull - 01.12.1990, Side 32

sea-level, which reached its highest relative position
(70-80 m a.s.l.) concurrently with the formation of
end-moraines. Secondly, further development of sea-
level changes was mainly characterized by a contin-
uous regression of relative sea-level, which finally
fell below present sea-level. Furthermore, Bárðarson
(1923) implied a possible transgression of relative sea-
level up to an intermediate position (40-50 m a.s.l.)
in the Borgarfjörður area.
Having studied the faunal assemblages collected
from raised marine sediments in the Breiðafjörður
area, Bárðarson (1921) concluded that high Arctic
conditions must have prevailed in the sea at the be-
ginning of the deglaciation period. Consequently the
marine environmental conditions shifted from Arctic
towards increased Boreal.
SINGLE ADVANCE DEGLACIATION
(SAD) MODEL
The next phase in the development of deglacia-
tion models in Iceland was the appearance of a model
which contained one widespread glacier advance that
interrupted the otherwise continuous deglaciation of
Iceland. The first geologist to be mentioned in this
context is Guðmundur Kjartansson. His studies in
South Iceland enabled him to map an apparently
continuous end-moraine complex, the Búði moraine
(Fig. 1) from Vatnsdalsfjall in the southeastern part
of the area and across the South Icelandic lowlands
to Efstadalsfjall (Kjartansson, 1943; 1958). Conse-
quently the advance leading to the Búði moraine was
termed the Búði advance. Later, Kjartansson (1964a)
argued that the Búði moraine could be traced from
Efstadalsfjall to Kjölur in the central highlands, thus
indicating an ice-flow from an easterly direction in
that area.
According to Kjartansson (1943) the Búði moraine
was formed in subaquatic position during a readvance
of the inland ice sheet and a concurrent transgression
of relative sea level, which ultimately reached about
110 m a.s.l. Near the end of the Búði stage relative
sea level had retreated to 90-100 m a.s.l. and at about
8,100 B.P. (8,065 ± 400 , W-482; 8,170 ± 300 , W-
913) it had fallen below present sea-level (Kjartansson,
1958; 1964b).
On the basis of his studies of glacial striae,
Kjartansson (1955) modified Thoroddsen’s (1905-06)
pattern of ice-flow and located the main ice-divide in
the area south of the present water-divide in Central
Iceland. The orientation of glacial striae in this area
shows, that during the retreat of the ice sheet ice-flow
became more and more influenced by the local to-
pography, and that the direction of ice-flow and, thus,
the position of the ice-divide, had successively been
shifted towards the south. Furthermore, the direc-
tions of glacial striae on Melrakkaslétta in Northeast
Iceland strongly indicate the existence of a former
north - south orientated ice-divide above the penin-
sula (Kjartansson, 1955).
A comparable glacier readvance was demonstrated
in North Iceland when Thorarinsson (1951) interpreted
the huge sediment formations on the northem side of
Mývatn — the Reykjahlíð moraine as ”a complex of
terminal moraines and ice-marginal fluvioglacial de-
posits", which he correlated with ”terminal moraines
and kames“ at Breiðamýri and Laugar in Reykjadalur
west of Mývatn and with ”terminal moraines of heavy
boulders (Hauksstaðahólar)“ in Jökuldalur in East Ice-
land (Fig. 1). Thorarinsson was of the opinion that
these moraines were formed during the Hólkot stage.
Gravel terraces at the mouth of Laxárgljúfur, about
27 km north-northwest of Mývatn, were formed when
relative sea-level stood about 50 m a.s.l. This trans-
gression of relative sea-level coincided with the ad-
vance of the inland ice sheet during the Hólkot stage
(Thorarinsson, 1951).
Kjartansson (1940) and Thorarinsson (1951) were
both of the opinion that the Búði and Hólkot moraines
had been formed by a climatically induced glacier
readvance. They individually suggested that this ad-
vance and the coinciding transgression of relative sea-
level up to the marine limit in South and North Iceland
probably was equivalent with the Salpausselka - Ra
stage of Fennoscandia.
A correlation between Kjartansson’s (1964a) Búði
moraine in Kjölur and Thorarinsson’s (1951) Hólkot
moraine was first proposed by Th. Einarsson (1960,
1964) when he showed a hypothetical position of an
ice sheet margin across the area between Kjölur in
30 JÖKULL,No. 40, 1990