Jökull - 01.12.1980, Side 3

JOKULL
30. Ár 1980 No. 30
JÖKLARANNSÖKNAFÉLAG (SLANDS JARÐFRÆÐAFÉLAG ÍSLANDS
Tjörnes, North Iceland: A Bibliographical Review
of the Geological Research History
JÓN EIRÍKSSON
Science Institute, University of Iceland,
Jarðfrœðahús Háskólans, 101 Reykjavík
ABSTRACT
The Tjörnes sequence spans Late Tertiary and
Quaternary lava flows and fossiliferous sedimentary
rocks. The great thickness of the sediments is unusual
in Iceland which consists mainly of volcanic rocks.
The sequence is unique in the North Atlantic area in
its lithological character and long Quaternary record.
The Tjörnes sequence combines lithological and
palaeontological evidence about past temperature con-
ditions and climate. The present paper is a review of
the geologtcal research hislory of the Tjörnes area.
The earliest contributions deal mainly with the fossil
matenal. While the palaeontological research has
contmued up to the present, studies combining strati-
graphical, palaeontological, and sedimenlological
aspects of the sequence became more frequent in the
20th century. During the last two decades the main
emphasis has been on palaeomagnetic stratigraphy,
K/Ar dating, and lithostratigraphy of the upper part
of the Tjörnes sequence, where lithological evidence
and changes in mollusc assemblages indicate the onset
of recurrent glaciations.
INTRODUCTION
Tjörnes has been frequented by geologists
for over a century. This is reflected by the
wealth of literature concerning the area. Two
features set the Tjörnes sequence apart from
other exposed sequences in Iceland. Firstly, it
contains thick marine sediments of Pliocene
and Pleistocene age. Secondly, Tjörnes (Fig. I)
represents a horst structure bounded in the
east by a subsiding volcanic zone (Thoroddsen
1902, Th. Einarsson et al. 1967, Sæmundsson
1974). The presence of up to 5Ö0 m .thick,
predominantly marine sediments in this
uplifted segment has obvious implications
about the nature of the nearby shelf area.
Clearly, the study of the Tjörnes sequence is of
local importance in evaluating offshore data
in the Tjörnes area. Ever since Pjetursson
(1905b) found glacial signs in the Tjörnes
sequence in the Bay of Breiðavík, the con-
troversy about the Pliocene/Pleistocene
boundary in Iceland has involved the Tjörnes
sequence. On the basis of the fossil evidence,
the sequence has been used to define that
boundary in Iceland (Th. Einarsson 1968). Th.
Einarsson et al. (1967) reported ten glacial
horizons in the upper Tjörnes sequence and
attempted a correlation with the palaeomag-
netic time scale. The investigation of the
sequence is thus of importance for the local
stratigraphy of Iceland, and for the evaluation
of the climatic evolution before and during
the Late Cainozoic ice age in the North
Atlantic area.
JÖKULL 30. ÁR 1