Jökull - 01.01.2010, Page 153

Paleomagnetic observations in SW- and S-Iceland
Figure 2. Location of the surroundings of profile WB, with flows 1–8 in the Þórisgil gully and 9–18 along the
same stream to the slopes of Botnssúlur. – Lega jarðlagasniðs WB í Þórisgili og ánni upp af því.
The profile was subsequently sampled by Wilson et
al. (1972) who named it WB. Wilson et al. (1972, p.
460) sketch the altitudes of flow boundaries, both as
obtained by Einarsson and as derived from observa-
tions during the sampling. Their results which do not
agree very well, are not reproduced here. The R2-N2
boundary in these sketches occurs at respectively 380
and 440 m.
The present author has resampled the R2-series as
well as the four lowest lavas of the N2. The strati-
graphic column in Figure 3 is based on his notes. Al-
titudes were measured with a handheld GPS receiver,
to an accuracy of some 5 m. The mean primary re-
manence directions and intensities obtained are listed
in Appendix 1. The directions have been corrected for
tectonic tilt which is estimated to decrease from 6◦ at
the base to 3◦ at the top, with a downdip direction of
130◦ east.
Successive directions are found to be grouped to
a considerable extent. Thus they are very similar in
flows WB 1 and 2, also almost constant in flows 6–11,
and again very similar in flows 12–13. This probably
is due to episodes of rapid buildup. Flow WB 6 is of
unusual appearance and has unusual magnetic prop-
erties with very low remanence intensity and suscep-
tibility, pointing to the presence of a highly oxidized
magnetic mineral component. This flow (along with
flows WB 1 and 8) also had a high coercivity of rema-
nence, the median destructive field of the remanence
in its samples being 50 mT or more while in the other
lavas in this study it mostly ranged from less than 10
to 35 mT.
There do not seem to be any lava flows of in-
termediate directions present at the reverse-to-normal
boundary which coincides with a thick intermittently
exposed layer of tuff and hyaloclastite. Einarsson
(1962, Fig. 32) describes a series of some 11 N2 "flow
units" above a tillite which presumably overlies the
lava numbered WB 18 here; this series was not sam-
pled by Wilson et al. (1972) or in the present survey.
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