Jökull - 01.12.1963, Qupperneq 3

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JOKULL
Á R S R I T
JÖKLARAN NSÓKNAFÉLAGS ÍSLANDS
III 13. ÁR REYKJAVÍK 1963
Some new Observations of the
Breiðavík Deposits in Tjörnes
BY
TRAUSTI EINARSSON
FACULTY OF ENGINEERING, UNIVERSITY OF ICELAND
The Breiðavík deposits constitute the upper-
most part of the Upper Pliocene deposits on
Tjörnes in Northern Iceland; they are separa-
tecl from the main bulk, or Lower Sediments,
by the Intermediate Basalts ancl are again cove-
red by basalts which fall into two groups of
reversely and normally magnetized basalts, re-
spectively. The Breiðavik deposits indicate
cooler climate and sea-temperature than the
Lower Sediments. In age they range from about
2 million years to about 2i/2-3 million years
before present, as concluded below on the
basis of paleomagnetism. The sediments seem
to reflect a series of fluctuations of sea-level
which may be due to eustatic changes of clima-
tic origin. Polar drift ice appears to have reach-
ed the area at least towards the end of sedi-
mentation. Thus the Breiðavík deposits are a
record of general climatic development in a
transition period between the Pliocene and the
Pleistocene.
The Breiðavik deposits liave been studied
by Pjeturss (1905), Bárðarson (1925), Áskelsson
(1934, 1938), Tr. Einarsson (1958), and Strauch
(1963). These studies did not lead to a fully
satisfactory picture, as several stratigraphical
JÖKULL 1963
questions remained unsolved. Tliese questions
were the object of new observations last summ-
cr which are described below.
I.
In the following discussion of the Breiðavik
deposits we shall proceed from the bottom up-
wards, giving a short description of such strata
which seern to have been satisfactorily described
in the earlier works, while the main attention
will be paid to the hitherto doubtful points.
The lowest liorizon Hi (using Strauch’s
notation, instead of Noi etc. as formerly done)
is íormed by the basalt lavas of Stangarhorn,
the top of the Intermediate Basalts. On these
rests unconformably the conglomerate H^a
which represents the load of one or more strong
rivers and originally has most probably for-
med a more extensive sheet, over 60 m thick.
I consider it to represent a considerable erosio-
nal interval. In my former study (Tr. Einars-
son 1958) I emphasized the fluviatile origin
of this material as against glacial origin. Strauch
claims littoral-estuarine environment for the
outcrop area. In that connection it may be
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ÍSLÁNLiS
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