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SUMMARY
Two early holocene tephra
layers in the Sogamýri peat
deposit, Reykjavík
, by
Magnús Á. Sigurgeirsson
National Energy Authority
Grensásvegi 9
IS-108 REYKJAVÍK
Iceland
and
Markús A. Leosson
The University of Leeds
Dep. of Earth Science
LEEDS LS2 9JT
England
Tephrochronological investigation of the
Sogamýri peat deposil in Reykjavík reveals
that at least eleven tephra layers are
preserved there (Fig. 1). The peat is
between 2 and 3 meters thick and rests
upon a blue-green clay, formed at the end
of the Weichselian glaciation. With the aid
of major element analyses, the sources for
the tephra layers can be evaluated.
According to the geochemical data, at least
five possible sources may be involved: the
Hekla, Katla, Torfajökull, Veiðivötn and
Grímsvötn or Kverkfjöll volcanic systems.
Two closely spaced tephra layers are
found near the base of the peat deposit. In
this study, special attention was paid to
these two layers, which were clearly from
early postglacial time and had not been
described in previous studies of this area.
The main objective of this paper is to
present some results obtained from geo-
chemical and textural analyses of these two
layers. Chemical analyses indicate that the
tephra layers are basaltic, of tholeiitic
composition, and that their sources may
either be in the Grímsvötn or Kverkfjöll
volcanic systems (Fig. 2). Texture analyses
indicate that the lephra layers are com-
posed of brown-coloured, angular, sparsely
vesiculated, glass shards with irregular
concave and concex surfaces. Crystals
u
136