Greinar (Vísindafélag Íslendinga) - 01.01.1976, Blaðsíða 103

101
Miocene (16-13 million years), Middle Miocene (13-9 million
years) and Upper Miocene (9-5.5 million years).1
Above the extremely monotonous layer of the Miocene plateau-
basalts lies a much more mixed volcanogenic complex, composed
both of basalts, the layers of which are much less continuous than
in the plateau-basalt formation, and of volcanic breccia and hyalo-
clastites. The age of this formation of “ancient grey basalts” is
somewhere between 5 and 1 million years and is referred by us to
the Upper Pliocene and Eopleistocene. The youngest volcanogenic
complex, Pleistocene and Holocene (the age is less than 0.7 million
years), is formed by volcanogenic rocks associated not only with
fissures, but with the central volcanoes also. The rocks of this com-
plex often have peculiar structure owing to their being the products
of sub-glacial eruptions (Moberg formation). The youngest in the
succession of Iceland (less than 10 thousand years) are the coastal,
glacial and river deposits.
The absence of considerable gaps in the formation of the succes-
sion of Iceland is indicated, for instance, by the profile from the
Borgarnes anticline on the western coast of Iceland to the vicinity
of Reykjavik (Fig. 2B). Here above the Upper Miocene basalts a
continuous rising succession of the Pliocene is observed (from 4-5
to 1.8 million years). Upwards, the whole series concordantly and
continuously passes to still younger Eopleistocene, Pleistocene and
Holocene lavas of the Reykjanes peninsula.
A practically uninterrupted succession from the Middle Miocene
to the Eopleistocene has been established in north-westem Iceland,
between the Skagi and North-Western peninsulas. The absence of
large gaps is also observed in the north-east of Iceland, where the
Pliocene and Lower Quaternary sedimentary rocks of the Tjörnes
peninsula, lying on the Miocene plateau-basalts, play in important
stratigraphical role in the section.
The apparent thickness of the Miocene plateau-basalts reaches
6-8 km, while the thickness of the Pliocene series is 3-4 km. The
thickness of the younger Quaternary formations greatly differs from
i. The upper part of this layer, younger than 9 million years, depending on the
assumed general scheme of the stratigraphic subdivision of the Neogene system,
can be referred even to the Lower Pliocene. We follow here the subdmsion
shown in Table 1.