Fróðskaparrit - 01.01.1979, Qupperneq 98

106
Marine Seismic Investigation
SM50 sounder. The local morphology of the sea bottom was
investigated by side-scan sonar (Edo Western 515T/606). The
side-scan system was operative only on the last day of the
survey. The magnetic field was measured by a proton magneto-
meter (Geometrics G803). Position was determined by an inte-
grated satellite navigator sonar doppler system (Magnavox).
The positional accuracy is well within 200 m when the system
is working properly but in many cases the navigator system
caused troubles. A description of such marine investigations is
given by, e.g. McQuillin and Ardus (1976).
Results
Tbe basaltic shelf
Most of the wide shelf around the Faeroe Islands consists
of basalt like the Faeroe Islands themselves. The submerged
basalt area is characterized by strong, short-waved magnetic
anomalies and lack of seismic penetration. The eroded basalt
flows often form inclined steps clearly visible on bathymetric
and seismic profiles and side-scan records (Fig. 3). The incli-
nation of such steps and of rare internal reflections in the
basalts suggest that the flows are dipping towards the limit
of the basalts east and west of the islands (Fig. 4).
Also the top of Faeroe Bank to the southwest consists of
basalt.
Young sediments partly fill shallow depressions on top of
the basalt but rarely exceed a thickness of 50 m. Glacial over-
deepened depressions occur in the fiords between the islands
and may be empty (e.g. Skopunarfjørður) or filled with 50—
150 m of sediment (e.g. Nólsoyarfjørður, Djúpini).
The limit of the basaltic shelf
The basalt disappears below sediments on the outer shelf or
slope around the Faeroe Islands (Fig. 2). The basalt contact
towards the sediments varies in character. To the southeast,
south and southwest the top of the basalt falls 2—10°, seldom
more, beneath the sediment sequence. The estimated depth of