The Nautesund breccia contains fragments of leptite, quartzites, amphibolites, biotite gneiss, and, to a lesser extent, greenish black and dark red schists. The matrix consists mainly of quartz, but sericite, chlorite, potassium-feldspar, epidote, pyrite, and crushed rock occur in minor amounts. It is suggested that the breccia was formed by gas coring through a vent either accompanied or followed by hydrothermal activity. The schist fragments are foreign to the environment and their origin is discussed. Although the breccia is younger than Precambrian supracrustal rocks, its precise age remains a subject of speculation.
The Nautesund breccia in Sauherad, east Telemark, southern Norway