Jökull - 01.01.2014, Blaðsíða 5

Paleomagnetic studies, Northwest Iceland
Figure 3. Locations of paleomagnetic sampling profiles SK, SU, SN, SB of McDougall et al. (1984), DO of
Kristjánsson and Jóhannesson (1996), KE, SW, GD, GE, GF, GO, FF, FE, TO and NC/ND/NE of Kristjánsson
et al. (2003) and the new profiles SY, HT and GG (in bold). – Staðsetningar sýnasöfnunarsniða í fyrri greinum,
auk þriggja nýrra úr Töflu 1 hér.
K-Ar dating by McDougall et al. (1984) included
a determination of a single flow below the oldest lig-
nite sediments, namely SU 10 at 50 m a.s.l. It yielded
an age of 15.3 Ma with a small error margin. One
should note however, that it is an olivine tholeiite, a
type of basalt which is both low in potassium (SU 10
has just about the lowest K-content of all the samples
dated in the 1984 paper) and is in general more sus-
ceptible to hydrothermal alteration than olivine-free
tholeiites. The possibility of systematic error in age
here is demonstrated by the fact that the age deter-
mined for the flow SU 37 (340 m a.s.l.) is almost 0.9
M.y. younger than that for SU 70 (630 m a.s.l.). Both
lie above the lignite sediments and have about four
times the potassium content of SU 10. It is there-
fore doubtful whether the age difference of 2.4 M.y.
between SU 10 and SU 37 does reflect any lengthy
hiatus at the lignite sediments.
Research in 1985–2000
Guðmundsson (1989) mapped sections through the
lava pile of the area between Bolungarvík, Álftafjörð-
ur and Önundarfjörður at numerous locations. This
mapping which also involved the interpretation of
many core logs from drill holes, was commissioned
by the Public Roads Administration (Vegagerð ríkis-
ins) as a fundamental part of preparations for the
construction of road tunnels from Skutulsfjörður to
Önundarfjörður and Súgandafjörður. Guðmundsson
(1989) divided the pile above the lignite-bearing sedi-
ments into 5–7 main stratigraphic series. These in turn
were divided into sub-series which are more or less of
lithologically distinct character and of uniform mag-
JÖKULL No. 64, 2014 5