Jökull - 01.12.2007, Blaðsíða 11

Early Pleistocene molluscan migration to Iceland
Continuation of Table 2
Torfhóll Member
Species Biogeographical Depth Salinity tolerance Torfhóll Stapavík
characteristics
NoI * % NoI * %
Macoma calcarea Arctic-boreal Changing a-mesohaline (>5‰) 92 50.6 82 30.0
(Gmelin, 1790) depth
Mya truncata Arctic-boreal Shoreface a-mesohaline (>5‰) 11 6.0 9 3.3
Linné, 1758
Mya pseudoarenaria Arctic-subarctic Shoreface? a-mesohaline (>5‰)? 3 1.1
Schlesch, 1931
Mya sp. 2 1.1 9 3.3
Cyrtodaria angusta Subarctic-boreal? Offshore ? 1 0.6
(Nyst & Westendorph, 1893)
Bivalvia sp. 23 12.6 56 20.5
*Number of Individuals 182 273
The barnacle Balanus balanus (Linné, 1758), an arctic-boreal, a-mesohaline (>5‰) species, living on the
shoreface, has been found in three specimens in Torfhóll and several hundreds of specimens in the Stapavík
samples. Furthermore, one specimen of the arctic-boreal, b-mesohaline (>15‰)? echinoid species Strongy-
locentrotus droebachiensis (Müller, 1776) has been found in Stapavík. It lives in the tidal zone as well as
offshore.
to be of the same age as the uppermost sediments and
a part of the Búlandshöfði Formation. The Búland
and Höfði Members most probably correlate with the
marine isotope stages (MIS) 32 and 31, respectively
(Shackleton et al., 1990; Chen et al., 1995).
On the north side of Snæfellsnes the sediments
and the overlying lavas become younger from Kirkju-
fell in the east to Ólafsvík and Skarðslækur in the west
(Figure 2). The lavas in Ólafsvík are normally po-
larized and apparently slightly younger than 700.000
years old (Hardarson, 1993). The sedimentation and
the volcanic activity in the area around Ólafsvík was
quite similar to that described above; the area was re-
peatedly covered with glaciers that retreated followed
by a rise in sea level and regression due to uplift. Then
the sediments were covered with basaltic lavas. Thus,
it is concluded that the sedimentary sequences near
Ólafsvík at Fossá, Innra-Klif, Arnarvarp, Tvífossa-
gil, Ólafsvíkurgil, and Skarðslækur (Figure 2) are
not contemporaneous with those in Búlandshöfði and
Stöð and they become younger toward the west. De-
tailed mapping of the lithological formation between
Kirkjufell and Skarðslækur shows that the sedimenta-
tion took place in a sedimentary basin with the deepest
part in the Búlandshöfði-Stöð area and the shallowest
at Skarðslækur in the west (Leifsdóttir, 1999; Leifs-
dóttir and Símonarson, 2005). The basin was gradu-
ally filled up with sediments, lavas, and glacial pyro-
clastic products (palagonite) from the east and south-
east so that the sediments as well as the volcanics be-
come younger towards the west (Leifsdóttir and Sím-
onarson, 2005). The infilling of the basin might have
taken at least 400.000 years. If the age estimates are
correct the oldest part of this basin is contemporane-
ous with the youngest part of the Breiðavík sedimen-
tary basin on Tjörnes, northern Iceland (see later).
JÖKULL No. 57 9