Jökull - 01.12.1978, Side 49

explain or correlate with other observations.
Variable thickness of unconsolidated
sediments seems to be one likely cause of this
variation.
Grain-size of sediments
Grain size of sediment samples from the
area conforms with the interpretation of the
sonographs (Fig. 5). All samples were of sand
and gravel size, and about 90% of samples
from unit 3 (sand) contain less than 10%
gravel ( > 2 mm). In unit 2, on the other hand,
the gravel content is much more variable and
reaches more than 80%. The mean size of
sediments from unit 2 is considerably coarser
than that of the unit 3 sand (Fig. 5b), whilst
the mean size of sediments from units 1 and 4
is variable.
Carbonate content
The distribution of (calcium) carbonate
(Fig. 6) is seen to form a definite pattern of
decrease in carbonate away from the central
part of the area. Samples obtained from unit 1
(rock floor) and parts of unit 2 (gravel) are
made up almost entirely of shell material
whereas minimum values of some 47% are
found in the deepest parts of the study area,
along its northern, eastern and southern
limits.
Boomer profiles
The Boomer profiles obtained covered parts
of the rock, gravel, and sand floor of map units
1, 2 and 3 (Fig. 7). Unfortunately no profiles
were obtained from the gravel of unit 4.
At least two stratigraphic divisions seem to
be present in the profiles. These are the con-
solidated sediments (rock) on the one hand,
and the younger unconsolidated sediments on
the other. The latter appear to be thin neár
rock outcrop, but form a wedge-shaped de-
posit at the eastern and northeastern borders
of the area (Fig. 8). Internal stratification seen
in the eastern profiles seems to indicate pro-
gradation to the east or into the channel
bordering the study area.
In the southern part of the study area the
Fig. 6. Carbonate distribution in the area,
expressed as percentage by weight of CaC03.
Mynd 6. Kalkinnihald lauss sets á svœðinu.
situation seems somewhat different. The few
profiles crossing this part of the area show only
a very thin cover of sediment lying on an un-
even substratum. Only in one place to the
southeast of Sydra-Hraun did the Boomer
tracks cross a sediment deposit of significant
thickness. On Fig. 7 this is tentatively joined to
the thick deposit at the eastern end of the area.
DISCUSSION
Water movements. Density distribution in
Faxaflói indicates counterclockwise flow
within the bay. On the average there is a net
flow around the tip of Gardskagi into the bay
and out of the bay again in the north. Direct
current measurements were made on August
12—13 1966 in the channel to the north of the
study area (Malmberg 1968). In the 18-hour
measurement period the current had a
maximum velocity of 18 cm/sec at 20 m depth
and 15 cm/sec at 50 m depth, towards the
northwest in both cases. These measurements
were made near neap tide and do not indicate
maximum current velocities. It should also be
pointed out that currents in the study area are
JÖKULL 28. ÁR 47