Geological and petrographical investigations in the Kongsberg-Bamble formation.

Abstract

The rocks of the Kongsberg-Bamble Formation are Pre-Cambrian and belong to the deeper parts of an ancient mountain range (the Sveco-Fennides). The main geological features appear from Table 11. In comparison with the stratigraphical scheme of the Sørland and Modum District the scheme for the Kongsberg District is given. The Kongsberg District is probably the area least changed by metamorphism and migmatization in the Kongsberg-Bamble Formation, and the stratigraphy is well known after the detailed description of C. Bugge. In the writers opinion the quartzites, micaschists, marbles, and banded gneisses belong to the oldest geosynclinal formations in the Kongsberg-Bamble Formation. They are included in the Old Complex which comprises rocks formed before the culmination of the revolutionary phase. The quartzites, micaschists, and marbles are interpreted as metamorphic sedimentary rocks. Although true sedimentary structures have not yet been found, both the wide distribution and the mode of occurrences of the rocks are in accordance with a sedimentary origin. But during a late phase of the migmatization period large part of the Kongsberg-Bamble Formation have been subjected to a regional influence of circulating solutions, giving rise to hydrothermal quartz- and calcite dikes. The material of these solutions was, in all probability, leached from the adjacent rocks.