Jökull - 01.12.2007, Blaðsíða 9

Early Pleistocene molluscan migration to Iceland
Continuation of Table 1.
Búlandshöfði-Stöð
Species Biogeographical Depth Salinity tolerance Búland Höfði
characteristics Member Member
NoI * % NoI * %
Macoma calcarea Arctic-boreal Changing a-mesohaline (>5‰) 1 0.2 17 22.7
(Gmelin, 1790) depth
Hiatella arctica Arctic-lusitanian Shoreface/ a-mesohaline (>5‰) 215 31.4 9 12.0
(Linné, 1767) offshore
Mya truncata Arctic-boreal Shoreface a-mesohaline (>5‰) 44 6.4 6 8.0
Linné, 1758
Cirripedia
Balanus balanus Arctic-boreal Shoreface? a-mesohaline (>5‰) 3 0.4 1 1.3
(Linné, 1758)
Balanus crenatus Arctic-lusitanian Shoreface a-mesohaline (>5‰) 23 3.4 4 5.3
Bruguière, 1789
Balanus sp. Subarctic-boreal? Offshore ? 35 5.1 5 6.7
Semibalanus balanoides Subarctic-lusitanian Foreshore/ b-mesohaline (>15‰) 1 1.3
(Linné, 1767) tidal zone
Chirona hameri Subarctic-boreal Offshore Polyhaline (>25‰) 13 1.9 2 2.7
(Ascanius, 1767)
Annelida
Serpulidae sp. 1 0.2
Coronula sp. 1 0.2
*Number of Individuals 684 75
lacustrine sand- and siltstones that were probably sed-
imented in a lake close to the coast and contain plant
remains, leaves and pollen of Alnus, Betula, Salix
and Erica (Áskelsson, 1939; Leifsdóttir, 1999). The
sediments of the Búlandshöfði Formation are covered
with horizontal layers of basaltic lava.
The Búlandshöfði Formation and other sedimen-
tary sequences on the north side of Snæfellsnes rest
on reversely polarized Tertiary basalts with the excep-
tion of the sediments in Kirkjufell (Figure 2), which
rest on normally polarized lava from the Gauss Chron.
Furthermore, the lava beds above the sedimentary se-
quences in Búlandshöfði and Stöð are reverse polar-
ized. Obviously the sediments and the overlying lavas
of the Búlandshöfði Formation were piled up during a
glacial stage and the beginning of the following inter-
glacial during the Matuyama Polarity Chron (Leifs-
dóttir, 1999). The overlying lava in Stöð has been
K/Ar dated to !1.12 Ma and that in Búlandshöfði to
!1.11 Ma (Albertsson, 1976; Einarsson, 1977). As
we have not found glacially striated erosional contact,
erosional unconformities, glacial sediments (diamic-
tite) or glacial pyroclastic products (palagonite) be-
tween the sediments and the overlying lavas it is con-
cluded that they were piled up during the same inter-
glacial period and therefore the lavas are considered
JÖKULL No. 57 7