Rit (Vísindafélag Íslendinga) - 01.07.1962, Blaðsíða 133

131
13) Renewed erosion of cliffs at the present lake level. The
hardness of the scree 12) suggests that it must be older
than post-glacial.
Tentatively we put the erosion 13) into the post-glacial; the
scree formation 12) into the Wurm glaciation, assuming that
it did not leave other evidence here. The sea-level must then
have been lower than now in relation to the Reykjanes penin-
sula and this might explain the low level of the lake. The
breccia 10) would have been formed early in the Riss-Wurm
interglacial. To create the cliffs in this hard breccia we need
the interglacial unless the cliffs were formed by a glacier,
say Wurm II, while the scree was due to less glaciation in
Wurm III, leaving the striae to Wiirm I. In this case we have
the Riss-Wúrm interglacial for the bench formation at the
high level, and, after tectonism, much erosion at the low level.
Thus the Sveifluháls tuffs and the uplift can hardly be young-
er than lower Riss-Wurm interglacial.
The essence of this study is that in the Kleifarvatn area
we are dealing with the youngest tuff-breccia rocks in SW-
Iceland and we are able to show that nevertheless they range
far back into the Pleistocene. We have found here a long and
varied history since the dolerite-capped tuff-breccia blocks
were uplifted, and one result is that in this area there were
ice-free places at least during the last glaciation.
We seem compelled to think that the dolerites range at
least back to the Middle Pleistocene. An upper age limit
is given by the normal polarity, as far as this goes. For
this reason the dolerites may not range farther back than
into the Lower Mindel-Riss interglacial. The uplift of the
block mountains, and depressions in some places, might then
be put somewhat later into the same interglacial.
This dating also most likely refers to the tectonic phase of
the whole stretch from Geitahlíð over Hengill to the Thing-
vellir-Laugarvatnsfjöll area (Ármannsfell, Hrafnabjörg,
Kálfstindar, Laugarvatnsfjall etc.).