Rit (Vísindafélag Íslendinga) - 01.06.1967, Blaðsíða 177

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Kárasker in Breidamerkurjökull, at Kvísker in the SE, and
Skaftafellsfjöll NW of the Öraefajökull stratovolcano mas-
siv, and in Núpsstadaskógur-valley at the westem edge of
Skeidarárjökull. It seems that geological studies in the area
have been concentrated on the great stratovolcano Öraefa-
jökull and the glaciers but the studies of the Tertiary rocks
neglected. This volcano has mainly heen built up during late
Quatemary time (the Brunhes geomagnetic epoch), hut it
rests almost certainly on a Tertiary basement. This means
that the southeastern margin of the Quaternary zone lies at
least 40—50 km further west than assumed up to now.
Another assumption which has been repeatedly made in
the geological literature on Iceland is that there are no Ter-
tiary rocks exposed in the so-called “central grahen” of Ice-
land. It should be stressed, that there are at least two areas
within this zone where Tertiary rocks outcrop, i.e. in the
Thjórsárdalur area in southern Iceland and Tjörnes in north-
em Iceland (see Fig. 1).
The Tertiary rocks on Tjörnes have been known for a long
time (cf. Thoroddsen 1906). Between the TPB, which dips
10—20° NW, and the overlying Tjörnes heds of Upper Plio-
cene age which dip 5° NW, is a distinct dip discordance.
Erosion has peneplained the TPB, Tjömes beds (their upper
part is of Lower Pleistocene age), the Höskuldsvík hasalt
lavas, the Furuvík sediments and the Stangarhorn basalt lavas.
The Breidavík glacial and interglacial sedimentary sequence,
containing some marine sediments, was deposited trangres-
sively on top of the underlying rock sequence. The Breidavík
sediments were deposited mainly during the Matuyama geo-
magnetic epoch, i.e. 2,4—0,7 m. y. ago. Since that time the
Tjörnes area has been uplifted and tilted to the NW. The
uplift in the southern part of Tjörnes amounts to 630 m.
This uplift has taken place in the last million years and is
still going on (Thorleifur Einarsson et al., 1967).
In the Hreppar area, hetween the rivers Thjórsá and Hvítá,
in S.-Iceland a gentle anticline is found, whose axis runs