Fróðskaparrit - 01.01.1979, Page 98

Fróðskaparrit - 01.01.1979, Page 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
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