Jökull - 01.01.2016, Blaðsíða 89

The Kleifakot geomagnetic instability event in NW-Iceland
profiles) it was not certain where in the time sequence
they belong. The excursion zone is underlain by the
normal-polarity zone DD 3–20 of Kristjánsson and
Jóhannesson (1996).
New sampling in Ísafjörður, 2014–2016
As a test of the persistence of Kleifakot-event se-
quences in the lava pile, additional sampling for pa-
leomagnetic studies was carried out in 2014-2016 in
profiles on the coasts of Ísafjörður (Figure 2b). The
main one was DW near the Álftagrófará stream (Fig-
ure 3), with flow DW 0 at sea level. Also sampled
were DQ along the old road across mt. Eyrarfjall, and
DI at the Eyrargil gully, flows number 1 in all these
profiles being just above the present road. Flow DI
2 could be followed northeast to the stream Laugará
where it was sampled at road level as site DP 1.
In this continuation, 6 to 8 core samples were
initially drilled at each site and oriented in azimuth
using sun shots, sightings on distant geographic ob-
jects, and/or sightings on nearby objects with posi-
tions known from GPS measurements. Additional
samples were subsequently collected when deemed
necessary, cf. the preceding section. The measure-
ments were made in an Institut Dr. Förster static flux-
gate magnetometer setup, as in previous projects. AF
demagnetization was carried out in a Molspin tumbler
demagnetizer at the peak-field steps listed above.
Site-average results are shown in Table 1. Very
similar remanence directions are sometimes found in
some successive sites, such as DW 5 and 5A having
visually different lithology. Sites DQ 0 and 1 which
were sampled below and above the coastal road re-
spectively, also have identical directions. Site DF 0
was cored at sea level 700 m northeast of DF 1, where
sampled above the road in 1983. In the latter cases,
these sites may each belong to one flow of over 20
m thickness. The directions obviously have excellent
internal consistency, with all the α-angles except in
DF 0 being smaller than 3.5◦. Values of the precision
constant k mostly lie in the range 350–1100. All the
samples collected are used in computing average re-
manence intensities (after 10 mT AF treatment) which
are generally low relative to the overall mean values
of 3–4 Am−1 for lava collections in Iceland outside
the volcanic zones (Kristjánsson, 2013, 2015).
Table 1. Paleomagnetic results from Ísafjörður lava
sites, 2014–2016. – Niðurstöður nýlegra bergsegul-
mælinga á kjarnasýnum úr Ísafirði.
SITE N n Dec Inc Lon Lat Alf J10 POL
DW Álftagrófará – Ísafjörður East
DW 0 15 11 156 +70 354 +31 2 0.97 NT
DW 1 14 10 110 +18 46 +1 3 1.00 E
DW 2 7 7 80 +14 74 +11 3 1.14 NT
DW 3 Inaccessible
DW 4 10 10 64 +41 82 +32 3 0.91 NT
DW 5 13 6 204 -38 306 -43 3 0.62 R
DW 5A 7 7 206 -40 304 -44 3 1.53 R
DW 6 7 7 173 +31 344 -7 2 2.44 E
DW 7 7 7 176 +42 341 +0 3 0.63 E
DW 8 8 8 261 +62 276 +35 2 7.91 NT
DW 9 6 6 32 +59 107 +59 3 1.19 N
DQ Eyrarfjall road – Ísafjörður West
DQ 0 7 7 69 -7 88 +5 3 1.33 E
DQ 1 8 6 71 -3 86 +6 3 0.63 E
DQ 2 7 5 233 -53 266 -45 3 1.07 R
DQ 3 8 8 354 +49 166 +54 3 0.31 N
DI Eyrargil – Ísafjörður West
DI 1 7 7 73 -4 84 +5 2 1.07 E
DI 2 6 6 239 -55 259 -44 3 0.52 R
DI 3 7 7 4 +28 152 +39 2 0.75 NT
DI 4 7 7 354 +63 169 +68 3 0.32 N
DP Laugará – Ísafjörður West
DP 1 8 7 226 -50 276 -45 2 1.05 R
DF Kleifakotsmúli – Ísafjörður East
DF 0 7 7 295 +44 236 +34 7 0.58 NT
N = number of core samples collected. n = number of sam-
ples used in averaging of remanence directions. Dec = dec-
lination, inc = inclination, lon = VGP longitude, lat = VGP
latitude, alf = 95% confidence angle (α95) for the average
direction, all in degrees. J10 = mean remanence intensity
(all samples) after demagnetization at 10 mT peak field,
Am−1. Pol = polarity (N = normal, R = reverse, T = VGP
latitude below 40◦, E = VGP latitude below 10◦). – n er
fjöldi nothæfra sýna af þeim N sem safnað var. Dec, inc
lýsa segulstefnunni, lon, lat og pol lýsa staðsetningu sýnd-
ar-segulskauts, alf er 95% óvissuhorn segulstefnunnar, J10
er meðalstyrkur segulmögnunar sýnanna.
JÖKULL No. 66, 2016 89