Greinar (Vísindafélag Íslendinga) - 01.01.1977, Page 41

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In the upper Miocene the peninsula is clear but too short to
hamper the Gulf Stream in any way. This is in good agreement
with a warm climate in the lands bordering on the northern
North Atlantic.
The same state still prevails in the Lower Pliocene. But in
the Upper Pliocene the Straits of Florida have become clearly
narrower, and this is in accordance with cooler climate in the
northern North Atlantic area. Finally, the further narrowing
of the Straits, leads to the succession of the Pleistocene Ice
Ages.
On this basis and on direct evidence, we must conclude that
in the late Upper Pliocene, the Gulf Stream was no stronger
than today, and that the conditions in the Arctic Ocean were
about the same as now. This means that a North Pacific fauna
could not possibly migrate from the Bering Strait into Atlantic
waters along an Arctic route. This could only have happened
in the Lower Pliocene or earlier, when the Straits of Florida
were open enough, not to hamper the flow of the Gulf Stream
(29). And there is unquestioned evidence (27) that such Paci-
fic fauna as is found in the uppermost division of the Tjörnes
deposits proper, the Cardium Groenlandicum zone, did migrate
via the northern route, from Bering Strait to Europe, as early
as the Upper Miocene or earliest Pliocene. We do not see a
reason for introducing a much later final migrational step to
Tjörnes, as seems to be left open as a possibility in (27). There-
fore, we seem justified to accept a Lower Pliocene or possibly
Upper Miocene age for those Tjörnes marine strata which con-
tain Pacific species (32 species of invertebrates according to
(27)).
Later in this chapter we shall deal with the occurence of Ter-
tiary glacial deposits in Iceland, and point out that they are
due to special mountain glaciations. It does, therefore, not af-
fect the obtained Tertiary age for the Tjörnes deposits, that
10 glacial horizons are reported in (28) within the uppermost
Tjörnes deposits. The lower divisions show clearly warmer
sea, so that we should not be surprised to find that they reach,
in fact, down to the Oligocene, although the corresponding