Fróðskaparrit - 01.01.1979, Page 99

Marine Seismic Investigation
107
seismic penetration of the overlying sediments is 200—500 m
and the basalt drops below this depth within a few kilometres.
The contact is mostly straight and seems to follow the strati-
fication of the basalt (Fig. 4). North of 62° N the easíern
contact becomes flat and irregular. The basaltic basement thus
occurs at less than a few hundred metres depth below Nólsoy
Bank and is possibly exposed somewhere on the bank. North
and northwest of the Faeroe Islands (lines 35, 37, 39 and 60)
the outermost part of the shelf has an irregular topography
(cf. Fleischer and others 1974). The irregular zone is 10—15
km wide and seems to consist of sediments. The sediments
show little or no seismic penetration and their thickness is
unknown. However, the magnetic data suggest that the basaltic
basement occurs at shallow depth until the edge of the shelf.
Just beyond the shelf edge a wedge of transparent sediments
overlies a basement reflector and this is presumed to be basalt.
The strong reflector is lost a few kilometres downslope beneath
several hundred metres of sediments. The supposed limit of
shallow basaltic basement is shown as a stippled line on Fig.
2. Exposures of basalt reappear on the Iceland-Faeroe Ridge.
Due west of the northern Faeroe Islands shallow basaltic base-
ment extends farther to the west than the survey lines.
The sedimentary shelf
Thick sediments occur on the outer shelf east of the Faeroe
Islands. The sediments can be divided into two major strati-
graphic units.
The lower unit consists of well-bedded sediments which dip
outwards at a low angle. The oldest strata overlie the sloping
basalt-sediment contact conformably or nearly so (Fig. 4). The
lower unit is well seen along the western side of Sandoy Bank
and SuSuroy Bank and in the channel between the banks. In
this area the inclined beds apparently crop out on the sea
floor in many places. The channels (broad valleys) separating
Sandoy and Suðuroy Banks from each other and from the
basaltic inner shelf are cut down into the lower sediments.