Jökull - 01.01.2014, Page 4

Leó Kristjánsson
The progression of K-Ar ages obtained by Mc-
Dougall et al. (1984) harmonized broadly with the
stratigraphical mapping, and yielded ages from 14 Ma
above the oldest lignite sediments south of Súganda-
fjörður to just less than 12 Ma at the south coast.
The pattern of polarities in their 4-km thick western
composite section is shown as the right-hand column
of Figure 2. The inferred average rate of buildup
there was about 1.8 km/M.y., somewhat higher than
in East Iceland (see above). McDougall et al. (1984)
also sampled the lava pile at some distance below
the lignite sediments in their profile SK in Skálavík,
and their profiles SU, SN south of Súgandafjörður
crossed these sediments (Figures 2, 3). There is a
slight southeasterly dip (around 1◦ on average) along
Súgandafjörður. In profile SU the sediments are ex-
pected to lie between flows 33 and 34 in a thick zone
of reverse polarity (flows SU 8 to 49). Samples from
flows 32 and 33 had unstable magnetization. In con-
trast, the lignite sediments in the other profile SN
some 9 km downdip (also sampled by Kristjánsson,
1968) are overlain by ten normal-polarity flows. Ex-
planations may include a general down-dip thickening
of lava series (cf. Walker, 1959).
Figure 2. Simplified columns of polarities in two com-
posite sections (Figure 1) through the lava pile of North-
west Iceland. Left: section along the tributary fjords
south of Ísafjarðardjúp, from Kristjánsson and Jóhann-
esson (1996). Right: section from Skálavik to the south
coast of the Northwest peninsula, from McDougall et
al. (1984). Both columns include additions at the base
from profiles sampled by Kristjánsson et al. (2003), as
well from new profiles (in bold). Further information
on the profiles is given in the three papers and in the
text below. The short bars on some of the vertical lines
indicate which portion of that profile was used in the
construction of the respective column. Black is normal
polarity, hatching denotes an episode of unstable geo-
magnetic field whose existence has been recently con-
firmed (Kristjánsson, 2015). The thicknesses of the po-
larity zones should not be taken to be precise; they vary
from place to place. Many thin polarity zones and ex-
cursions have been left out. Tentative correlations are
shown, from bottom to top: Lignite sediments – com-
pound flows in profiles DO and SB – top of thick norm-
al-polarity zone – field instability – Brjánslækur sed-
iments. – Helstu syrpur af réttum og öfugum segul-
stefnum í hraunlagasúlum úr þversniðunum á 1. mynd,
ásamt tengingum milli þeirra. Byggt er á gögnum úr
fyrri greinum nema í feitletruðu sniðunum neðst.
4 JÖKULL No. 64, 2014