Jökull - 01.12.1971, Side 50

son, 1966) have assumed that crustal subsidence
followed formation of the ridge. There is addi-
tional evidence of subsidence in the Norwegian-
Greenland Sea in the case of the Jan Mayen
Ridge (Johnson and Heezen, 1967).
MAGNETICS
Fig. 2 is a total field intensity chart south-
east of Iceland. The anomalies in the southern
part of Fig. 2 strike approximately N 30° E
and are a continuation of the lineated Raff-
Mason spreading anomalies reported by Avery
et al., 1969, in their survey just to the south
of this area. These anomalies strike about N
40° E with a spreading rate of 1.13 cm/yr
(Avery et al., 1969) indicating a ten degree
northward change in strike near Iceland. (In
Fig. 1 (profile 3—6) it can be seen that ano-
malies 20—21 can be traced as far north as
profile 3.) North of profile 3 and from the
eastern end of profile 4, the high ampli-
tude short wave length anomalies of the Ice-
land—Faeroe Ridge predominate. High inten-
sity anomalies are superimposed on the (Raff-
Mason) anomalies as clearly seen on anomaly
21 (profiles 4 & 5). Between 63° N, 10-12° W
a northwest-southeast lineament is present
which appears to truncate and bend the ano-
malies to the NW. This represents the edge
of the Iceland—Faeroe Ridge. A magnetic pro-
file from the USNS Kane farther to the south
(51° 30' N) is included in Fig. 1 for comparison
with the profiles near Iceland.
In Fig. 1 (profile 1 right hand edge) as has
been previously reported by Avery et al. (1968)
Fig. 2. Total field magnetic contour chart
southeast of Iceland. Contour interval is 250
gammas. Survey lines were oriented east-west
at approximately 20 miles line spacing with
several north-east check lines; therefore the
contour lines must be considered to be pro-
visional.
Mynd 2. Kort af heildarsegulsviði suðaustur af
Islandi. Milli jafngildislina eru 250 gamma.
Mcelilínur lágu A—V með um 20 milna bili.
Auk þess voru teknar nokkrar línur með N—S
stefnu til prófunar. Jafngildislínur eru þvi ekki
nákvœmar.
lower-frequency magnetic anomalies are present
between the Faeroe and Shetland Islands in-
dicative that the basement is considerably
deeper. To the southwest, Stride et al. (1967)
ancl Bott and Staeey (1967) obtained geo-
physical data across the Faeroe bank channel
also indicating that the igneous basement occurs
at much greater depth (at least one kilometer)
in this area. The influence of the Faeroe Is-
lands can be seen in the short wave length
anomalies just to the west of the “quiet” trace
on this profile.
SEISMIC REFLECTION
As is apparent from the seismic reflection
records there is very little sediment on the
crest of the Iceland—Faeroe Ridge (Fig. 3). The
existence of strong although intermittent
bottom currents (Dietrich, 1967) carrying Nor-
wegian Sea water south over the ridge to the
Atlantic Basin, are the most likely cause of the
lack of sediment cover (Johnson and Schneider,
1969; Jones et al., 1970). Jones et al. (1970) also
speculate that the thinner sediment cover on
the southern flank of the Iceland—Faeroe Ridge
is the result of non-deposition or at least lower
sedimentation rates caused by the descending
Norwegian Sea water.
A small sediment lens which may exceed 1
kilometer in depth has apparently filled the
scarp wliich would normally act as the eastern
insular slope of Iceland (Fig. 3, profiles 1—3).
The crest of the Iceland—Faeroe Ridge is only
lightly covered by sediment and in places the
bed rock is doubtlessly exposed. Profile 5 has
the greatest sediment accumulation of about
400 rneters on the crest. It is uncertain if this
is representative of decreased bottom current
velocity with concomitant greater sedimenta-
tion rates. The sediment layers are highly
disturbed indicative of tectonism and/or sculpt-
ing by bottom currents and slumps.
Fig. 4 shows four seismic reflection lines
across the southern flank of the Iceland—
Faeroe—Shetland Ridge. The sediment cover of
up to 1.5 kilometers is apparent on the south
flank. Profiles C and D show basement appro-
aching the surface and thence rapidly dropping
off to form an escarpment. Bott, personal com-
munication, has noted similar structures in this
48 JÖKULL 21. ÁR