Jökull - 01.12.1978, Blaðsíða 103

25 m and 8 m approximately. These are des-
cribed.
Supposing that contemporaneous shoreli-
nes increase in heights towards the inland, as is
known from the Reykjavík area, the 25 m
shoreline corresponds to the highest shoreline
in Reykjavík, the age of which is about 11.000
years. The 8 m shoreline corresponds to the
transgression known from Raudhóll, near
Hafnarfjördur. The age is somewhere between
9.000 and 11.000 years. The highest shoreline
at Vogastapi corresponds to a 110 m shoreline
in Akrafjall. This shoreline is contempo-
raneous to or older than the advance of the
“Alftanes glacier” which covered the Reykja-
vík area during Older Dryas Stadial.
The shorelines have not been disturbed by
tectonic activity in the Reykjanes fissure
swarm.
LITHIFIED ICE-CONTACT SEDIMENTS
IN BREIDAVÍK, NE-ICELAND
Jón Eiríksson,
University of Iceland
Irregularly shaped conglomerate bodies
within the upper part of the Pliocene—
Pleistocene Tjörnes sequence, NE-Iceland, are
interpreted as ice-contact sediments. A
genetic classification of stratified ice-contact
sediments is based on originally supraglacial,
englacial or subglacial deposition. Penecon-
temporaneous deformation and faulting of
primary structures are taken to suggest supra-
glacial deposition and subsequent sagging and
partial collapse as the underlying ice melted.
Subglacial or ice-walled deposition is inferred,
when internal bedding is intact and faulting
and slumping are confined to margins.
Lithified kames and/or eskers occur above
three tillite horizons in Breidavík Bay, a
fourth tillite is succeeded by glacio-lacustrine
siltstone. The upper part of the Tjörnes
sequence is characterized by a cyclic recur-
rence of beds reflecting Late-Cenozoic
climatic fluctuations.
ON THE CONTROL OF MAGMA
CHEMISTRY ON PILLOW
DIMENSIONS
Ingvar Birgir Fridleifsson, National Energy
Authority, Harald Furnes, Bergen University, Brian
Atkins, Oxford University
Measurements were made on the axial
dimensions of 822 pillows with composition
varying from olivine tholeiite to andesite in
Plio-Pleistocene subglacial volcanics in S- and
W-Iceland. The average diameter of the pil-
lows is found to decrease by 50% from olivine
tholeiite to basaltic andesite but with further
increase in silica content the pillow diameter
increases again. The primary porosity of the
pillows also decreases significantly from
olivine tholeiite to basaltic andesite. The
primary porosity of a pillow lava pile is of two
types; a) the interspace between individual
pillows, which is large because of the geome-
tric shape of the pillows, and b) the pore space
within individual pillows. Both factors are
affected by the chemical composition. The
above results suggest higher porosity and
effective permeability in pillow lava sequences
of olivine tholeiite composition formed in vol-
canic fissure swarms than in pillow lava
sequences associated with central volcanoes
characterized by intermediate and acid vol-
canics.
ACER ASKELSSONI N. SP. BIG
NEOGENE SAMARAS FROM ICELAND
Walter L. Friedrich, Árhus Universitet, Denmark,
Leifur A. Símonarson, Science Institute, University
of Iceland
Acer-samaras have been found in the
Hredavatn area, West-Iceland. They are dis-
tinguishable from recent and fossil forms by
their big locules. We name them Acer
askelssoni n. sp. The winged fruit can be
compared with A. saccharinum from North-
JÖKULL 28. ÁR 101