Jökull - 01.01.2014, Side 10

Leó Kristjánsson
SY, while the tilt in profiles HT and GG was assumed
to be 2.5◦ to the southeast. The directions and vir-
tual geomagnetic pole positions derived from them are
presented in Table 1. Figure 5 shows the magnetic
polarity of each lava, along with its lithological type
based on in-situ appearance and on visual inspection
of drill cores.
Skálavík
Sampling in the profile SK south of Skálavík in 1975
(McDougall et al., 1984) ended at flow 20 due to
steepness of exposures, while the lignite sediments
occur above flow 29 or so. A new profile SY (Figures
3, 4, 5, 6) was therefore mapped and sampled about
1 km to the east-southeast from SK for a paleomag-
netic study, to improve knowledge of the stratigraphy
in the area. This profile begins in a highly porphyritic
flow SY 0 at 66◦10.484’N, 23◦29.778’W, 120 m alti-
tude; sampling reached up to the base of a thick com-
pound flow SY 22. We correlate SY 0 approximately
with SK 15, and SY 4 with SK 19. Like the other
profiles in the area described above, the lower part SY
0–10 consists mostly of reversely magnetized lavas,
with major excursions in flows 8 and 10. The lignite
sediments are thought to lie in a scree-covered inter-
val at 290–340 m a.s.l. along with at least two poorly
exposed flows SY 11 and 12 (not sampled). The ex-
cursion directions in SY 8 and the olivine tholeiite SY
10 are quite similar to those in respectively GO 23 (as
well as KE 21 and SW 11) and the olivine tholeiite
GO 25, although GO 25 seems at any rate to be above
the expected position of the lignite sediments.
Above the unexposed gap in SY we have the re-
verse flow 13, normal flows 14–17, and then a tran-
sition (also recorded by KE 34) in SY 18–20 to a re-
verse zone. This along with similarly erratic behavior
of remanence directions in lavas both just above and
just below the lignite sediments in profiles KE, SU
and GO indicates that the geomagnetic field was in
a somewhat unsettled regime when these lavas were
emplaced. Such behavior also occurs below the sed-
iments in GD/GE and SW, while it is less evident in
flows above them in the four profiles of Kristjánsson
et al. (2003) north of Ísafjarðardjúp, in GD/GF at Bol-
ungarvík, SN in Súgandafjörður, and profiles FE, FF,
TO, NE, etc. farther south.
Eyrarfjall and Súgandafjörður
Eyrarfjall, Hnífsdalur. A profile HT of 28 mostly
tholeiitic lavas was sampled at the east side of Hnífs-
dalur. We were unable to continue higher or to sam-
ple flows HT 17 and 21, because of steep exposures.
The profile starts at 66◦06.163’N, 23◦08.501’W with
a reverse to normal transition at HT 2, the flow HT 1
probably belonging to the same zone of reverse polar-
ity as flows (tested in hand samples) at sea level on
the east side of the mountain. A normal-polarity zone
HT 3–20 lies at altitudes from 150–450 m and is then
overlain by lavas of reverse polarity from HT 22 at
least up to the top of our sampling at 560 m. The same
normal-to-reverse transition occurs at about 530 m al-
titude above our profile GG (Guðmundsson, 1989; Á.
Guðmundsson, pers. comm. 2013). We are assum-
ing that it is also the same as the transition found at
about 130 m altitude between flow DO 17 and the
40 m thick reverse compound olivine tholeiite flow
DO 18, which is below a minor but conspicuous local
unconformity. This would agree roughly with Krist-
jánsson and Jóhannesson’s (1996) correlation of DO
18 with the compound flow SB 24–29 of McDougall
et al. (1984) whose base is at 700 m. It implies that
the tectonic tilt has a mean component of the order of
1–2◦ along the south-southeasterly direction between
GG and DO, within the altitude levels quoted. The
reversely magnetized feldsparphyric flows DO 19–24
may correspond to feldsparphyric flows which occur
in the sampled reverse series HT 22–28 and above it
(S. M. Hreinsdóttir, pers. comm. 2012).
Eyrarfjall, Skutulsfjörður. The profile GG starts
in a prominent gully above the Grænigarður residence
in Ísafjörður town. The position of flow GG 1 is at
66◦04.320’N, 23◦09.742’W, 150 m altitude. We have
sampled the bottom 14 lavas of profile GG, all of nor-
mal polarity. Steepness and the presence of a thick
dike in the gully prevented further sampling. An ex-
cursion of the geomagnetic pole to low latitudes in
flows GG 9–13 may correlate with excursions in flows
HT 10 and/or HT 12.
Promontory south of Súgandafjörður. A few key
flows in profile SU around the estimated level of the
lignite-bearing sediments which had given difficulties
due to poor within-flow agreement in the study by Mc-
10 JÖKULL No. 64, 2014