Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 184

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Adding these to the 5 magnetic groups in Hreppar we then
find at least 11 magnetic groups overlying the oldest cold
climate vestiges in Iceland. Only the 2 youngest groups are
considered to be Pleistocene, i.e. no indication is found in
Iceland that more than two magnetic periods correspond to
the Pleistocene time, with sea-level at or below 100 m.
A major gap in the paleomagnetic record must he assumed
to correspond to the period of peneplanation of the Young
Plateau Basalts, partly above the group N2 of Westem Ice-
land and partly helow it.
With the strandplane stage, a following eustatic drop of
sea-level during the Pleistocene, relatively slight further mo-
delling of the landscape, and a little volcanic activity at a
few places (mouth of Skagafjörður) the story comes to an
end for us in the northem and northwestem parts of the
area here studied.
But in Southwestern Iceland there was further tectonic
and volcanic development. This refers mainly to the active
area between the Esja—Súlur complex in the west and the
Hreppar basalts in the east, i.e. in a depression between hlocks
of the Plateau Basalts.
We shall first mention the late development here: 1) For-
mation of an extensive sheet of grey basalts (dolerites) co-
vering a low plain extending from Faxaflói to Hvítá. 2) After
a glaciation the dolerites were covered in the Grafningur area
by a roughly 100 m thick layer of breccias. This was follow-
ed by 3) Early uplift of Laugardalsfjöll, Grafningsfjöll—Ing-
ólfsfjall, Hestfjall and more blocks. 4) Late uplift, especially
represented in the Reykjanes mountain ridge, from Hengill
to Kleifarvatn. Some basins were formed by subsidence at
the same time, Thingvallavatn and the Kleifarvatn area he-
ing the main ones.
Near Reykjavík the dolerites covered a 60 m high strand-
plane and an outlier flowed into the low pass Stíflisdalur to-
wards Kjós. Together with the normal polarity of the lavas
this indicates that they are younger than Lowest Pleistocene,