Jökull - 01.12.1984, Blaðsíða 122

Fig. 2. Composite vertical section of the Borgar-
fjördur sedimentary strata, compiled from Bárd-
arson’s (1923) data. — Mynd 2. Samsett jarðlaga-
snið er sýnir megindrætti í jarðlagaskipan setlaga í
Borgarfirði skv. athugunum Guðmundar G.
Bárðarsonar (1923).
Thoroddsen (1891, 1892) confirmed the
observations of Keilhack concerning the marine
origin of the Borgarfjördur sediments. He stated
that the sediments were deposited at the end of
the glacation because they were situated on stri-
ated bedrock and were not overlain by till. Thor-
oddsen frequently pointed out Skorradalur as a
typical ice-scoured valley (Thoroddsen 1891,
1892, 1906, 1911). He recognized a striated bed-
rock threshold barring the entrance to the valley,
and reasoned that deposits situated on the lee
side of the threshold were of glacial origin (Thor-
oddsen 1891). Pjetursson (1908) concurred with
this observation. Thoroddsen (1906) recognized a
submarine threshold barring the mouth of Hval-
fjördur, and Ashwell (1966, 1975) has observed
similar thresholds barring the entrances to most
of the Borgarfjördur tributary valleys. Thorodd-
sen (1906, 1911) summed up his observations on
marine deposits in Iceland and presented a
hypothesis on sea level changes on Iceland. He
inferred that at the end of the glaciation the
lowlands were submerged, and that sea level
stood at 80—100 m above present sea level. Later
the sea regressed to 40—50 m above present sea
level, where it persisted long enough to allow
conspicuous beaches to be formed. Later the sea
receded to its present level. This hypothesis for
sea level changes was later modified by Bárdar-
son (1923).
The investigations of Gudmundur G. Bárdarson
During the summer of 1920 the Icelandic
geologist Gudmundur G. Bárdarson carried out
both a stratigraphical investigation of the Bor-
garfjördur sediments and a palaeontological
study of their fossil fauna. Bárdarson’s (1923)
work is still considered to be the most compre-
hensive study on the sediments in the region.
Bárdarson described sections and outcrops from
many localities in the region, and distinguished
between the various beds and units on the basis
of their lithology and fossil content. He attemp-
ted to correlate the sediments in the coastal sec-
tions with morphological features indicating for-
m.a.s.l.
Fig. 3. Late Weichselian and Holocene
shore-level displacement curve from the Borgar-
fjördur region. Modified from Bárdarson (1923).
The x-axis shows time in arbitrary units. - Mynd
3. - Sjávarstöðubreytingar í Borgarfirði á síð-
jökultíma og nútíma. Stílfœrt eftir Guðmundi G.
Bárðarsyni (1923). Afstæður tími á x—ás.
120 JÖKULL 34. ÁR