Jökull - 01.12.1980, Blaðsíða 10

Tjörnes sequence is divided into Series (Table
1). Old Quaternary age is assigned to the
Breiðavík Series with reference to Askelsson’s
work.
Voice of a sceptic — early
palaeomagnetic studies
A tone of scepticism towards Pjetursson’s
glacial history was struck by T. Einarsson
(1940a, 1940b, 1946), who interpreted many
of Pjetursson’s moraines (“grey conglomer-
ates”) as being entirely of volcanic origin,
being mudflow deposits either directly
erupted by volcanic vents or formed as a
secondary product of certain eruptions. Ear-
lier, Hawkes (1938) had studied some of
Pjetursson’s localities, including Tjörnes, and
rejected a glacial origin of the conglomerates
in question. T. Emarsson’s investigations on
Tjörnes began in 1939 and continued until the
early sixties. In the first instance he dealt
mainly with the stratigraphy and structure of
the peninsula, but the origin of the sediments
and the palaeomagnetism of the lava flows
were also investigated (71 Einarsson 1957a,
1957b, 1958). The study of palaeomagnetism
on Tjörnes had been initiated by Hospers
(1953, 1954). T. Einarsson (1957b) found that
the youngest rocks on Tjörnes consisted of
two groups of lava flows separeded by a
“moraine-like” conglomerate, an upper nor-
mally magnetized group, and a lower rever-
sely magnetized one that rested conformably
on the Breiðavík sediments (cf. Fig. 3). The
upper part of these in turn consisted of an old
Quaternary sequence (of presumed Villa-
franchian age). In this paper T. Einarsson
stated that the Tertiary/Quaternary boun-
dary should be drawn at the base of R1 (the
Quaternary thus spanning the two youngest
polarity groups). T. Einarsson (1958) presented
the first detailed survey of the interior of
Tjörnes peninsula, and identified angular un-
conformities within the sequence. He defined
stratigraphical units for the Tjörnes sequence
(Table 1). Tectonic aspects and age relation-
ships were again discussed in later papers
(Thorarinsson et al. 1959, T. Einarsson 1960).
While eariier authors had generally assumed
an unconformity beneath the “Lower
sediments”, T. Einarsson (1958) c.oncluded that
they were conformable with and partly of the
same age as the “Basal Basalts” at Kaldakvísl.
He visualized the early Pliocene Tjörnes as a
subsiding area of low relief, the subsidence
amounting to 700—800 m during the
Pliocene. After an emergence (still within the
Pliocene, at which time he suggested a
regional uplift of some 300 m predating the
Breiðavík sediments) the area was covered by
lavas. T. Einarsson pointed out that Tjörnes is
cut off from the area south of Húsavík village
by a fault running from Húsavík to the
southeast. To the north of the fault, the “Basal
Basalts” have been uplifted to an altitude of
700 m, while they cannot be seen to the south
of the fault. T. Einarsson suggested that the
fault was of Pleistocene age.
T. Einarsson collected pollen samples from
lignite horizons and terrestrial sediments in
the Tjörnes sequence. The palynological
results were discussed along with the problem
of provenance of rhyolitic pebbles in his work
on Upper Tertiary and Pleistocene rocks in
Iceland, and in later papers (71 Einarsson 1962,
1963a, 1963b, 1964). The results of his study of
palaeomagnetism on Tjörnes were compiled
on a map in a paper where 71 Einarsson (1965)
also delt with lavas resting on fossiliferous
shale to the south of Húsavík. The strati-
graphy and sedimentological aspects of the
Tjörnes sequence were briefly dealt with in 71
Einarsson’s (1972) textbook on geology. In a
recent paper he emphasized a Pliocene age of
the Breiðavík beds on Tjörnes and emphati-
cally rejected the interpretation that interca-
lated glacial signs were produced by
Pleistocene ice caps. Instead, he suggested,
they were in many cases formed in the vicinity
of high ice capped volcanoes (71 Einarsson
1977).
Climatic evidence examined
In his study of the climatic history of Ice-
land, Schwarzbach (1955) examined the
climatic evidence of the Tjörnes beds and
8 JÖKULL 30. ÁR