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Abstract
On the island of Hisingen, 17 km to the north of Gothenburg on the west coast of Sweden, a breccia was exposed after removing 3.5 m Quaternary deposits. The breccia occupied two fissures in the Precambrian rocks. The fissures were 0.5 and 3 m wide, respectively, and the observed length approximately 6 m. They struck N 68° W and had a vertical dip. The breccia consisted of big boulders of limestone, stinkstone-concretions, sandstone, and weathered remnants of alum shale. There were also fragments of gneisses and amphibolite. The main part of the breccia material belongs to the Cambrian. The fossil content of the breccia will be treated in a separate paper by Dr. A. Martinsson, Uppsala. The big, unbroken stinkstone-concretions (c. 1 m in diametre) and the big boulders of limestone with preserved bedding indicate a short transport of the material before being deposited in the fissures.
As the northeastern wall of the big fissure is made up of rough surfaces of unweathered gneiss, it seems reasonable to regard the formation of the fissures as contemporaneous with the deposition of the breccia material. Considering the degree of diagenetisation of the Palaeozoic rocks at the moment of the formation of the breccia, a Permian age of the fissuring seems probable. This would also be the age of some doleritic dikes of WNW-ESE strike in this region. There is evidence of a later tectonisation of the breccia along its southwestern contact. Those movements took place after the cementation of the breccia.
