Jökull - 01.12.1994, Page 10

sun sightings, with an estimated random error of 2° in
azimuth and 1° in inclination. Most commonly, four
samples were taken from each flow, distributed later-
ally across several meters of a lava face. A 21- mm
specimen was cut from each core and measured in an
"Institut Dr. Förster" static fluxgate magnetometer
with a four-probe arrangement. Measurements were
made on the natural remenence and after altemating
field (AF) demagnetisation in a two-axis tumbler. De-
magnetisation steps for all specimens were at 10, 15,
20 and 25 mT peak field, with 30 mT also included if
necessary. Lightning effects were noted in two flows,
DG 9 and DH 9.
The remanence intensity of the lavas is similar to
that in other collections from Iceland, averaging 3.3
A/m after 10 mT AF treatment. The stability of prima-
ry remanence directions is generally very good, when
Brunhes age viscous remanence has been eliminated
(usually after 10 or 15 mT treatment). However, about
20 specimens were unstably magnetised or otherwise
anomalous, and these were discarded before statistical
analysis. As the sampling was carried out in four field
seasons, there was opportunity to resample some of
the flows which had given unsatisfactory results.
The most reliable estimate of the paleomagnetic
direction within each lava is selected as the direction
which yielded the maximum resultant from unit vec-
tors (all specimens being demagnetised at the same
alternating field). These directions and other parame-
ters are listed in Table 1. Tectonic tilt corrections,
using tilt values measured in the field, have been ap-
plied to all the directions. The tilt values are listed at
the end of Table 1.
Some flows were not accessible for coring, and
McDOUGALL el al. (19S4)
WESTERN SECTION
Fig. 8. Paleomagnetic polarity in the ísafjarðardjúp compos-
ite section constructed from twelve measured profiles DO to
DM on Ieft, along with the polarity time scale of the westem
composite section of McDougall et al. (1984). Black indi-
cates normal polarity, white indicates reverse polarity and
shaded indicates the upper portion of a prolonged period of
field instability. The latitudes of virtual geomagnetic poles
(V.G.P.) for lavas in the ísafjarðardjúp section are shown on
the right.
8. mynd. Breiddargráða sýndarsegulpóls í samsettu sniði
jarðlaga við Isafjarðardjúp. Sýnd er skörun sniðanna, kaflar
með réttri og öfugri segulstefnu, og tenging við samsvarandi
kafla í vestara sniði McDougall o.fl. (1984).
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JOKULL, No. 44