CONTINUATION OF THE CALEDONIDES NORTH OF NORWAY - SEISMIC REFLECTORS WITHIN THE BASEMENT BENEATH THE SOUTHERN BARENTS SEA

The offshore continuation of the Caledonides to the north of Norway is poorly understood, and the seismic signature of these rocks is unknown. Indeed, the seismic signature of basement rocks is in general poorly documented from conventional seismic data. This paper discusses an area in the southern Barents Sea - the 'Gjesvaer low' - where inferred Caledonian basement rocks have been studied from conventional seismic data. The Gjesvaer low, which has not been described previously as a separate structural element, is defined on image-processed gravity data. The main processing steps were directional filtering and principal component analysis. The interpretation of the low as a feature within the inferred basement rocks is based on well data, the calculated depth to magnetic basement, seismic signature and velocities. In addition, two-dimensional gravity modelling shows that density variations within the basement rocks may explain the observed gravity anomaly. Although the following model may be simplistic, distinct seismic reflectors within the low may be interpreted as originating from tectonic boundaries within a thrust system. In the most likely evolutionary scenario, the Gjesvaer low and the south-western part of the Nordkapp Basin are interpreted as having been formed as continuous Caledonian structures whose continuity has survived until the present. Subsequent Late Palaeozoic erosion may have removed more than 10 km of Caledonian rocks in the area of the low. Carboniferous rifting reactivated the Caledonian structures and the south-western Nordkapp Basin was formed. The Nordkapp Basin, which was decoupled from the Gjesvaer low in Carboniferous times, subsided while the low was again eroded.