Jökull - 01.01.2010, Page 157

Paleomagnetic observations in SW- and S-Iceland
mate are also abundant, and so is evidence of land-
scapes formed by erosion. This along with complex
tectonics (Khodayar and Franzson, 2004, 2007) and a
scarcity of radiometric age determinations has made
it difficult to reconstruct the geological history of the
Hreppar region. Kristjánsson et al. (1998) review pre-
vious research within the region by Einarsson (1962,
p. 132–142), Friðleifsson et al. (1980) and others.
They also describe their study of stratigraphy and pa-
leomagnetic polarities in several short sampling pro-
files along the Þjórsá river (roughly in the area Þ of
Figure 1). From the polarities and K-Ar age determi-
nations on four lava flows, Kristjánsson et al. (1998)
concluded that a composite section of some 500–600
m thickness made up from these profiles covers the
age interval from 2.2 Ma to less than 0.8 Ma. The
youngest outcrops sampled may be 0.2 Ma old.
A paleomagnetic survey to supplement the results
of Kristjánsson et al. (1998) was carried out in two ad-
jacent and overlapping profiles HR and FO (Figure 7)
near the Fossnes farm in Þjórsárdalur, totalling some
500 m in thickness. The work took place in conjunc-
tion with geological mapping of the surrounding area
by Á. Geirsdóttir and Th. Thordarson (ms. in prepa-
ration) which focused both on the volcanic stratigra-
phy of this area, and on clastic sedimentary deposits
(Geirsdóttir et al., 1993, 1994). Sampling was also
undertaken in nearby hills (Núpsfjall, Þjórsárholts-
Figure 7. Approximate location of profiles
HR and FO. The lava units HR 5A to 5I
were sampled from the road at Þjórsá to
just beyond the tributary Þverá as shown.
The series HR 5L to 5V, 7, 9 and 11 were
sampled successively along the west bank
of Þverá up to near the top of the map.
Lavas FO 20 to 40 were sampled along the
east bank of Þverá, from near HR 5V to
the top of the map. – Lauslegt kort af stað-
setningu sniðanna HR og FO við Fossnes
í Þjórsárdal.
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