Devonian (Old Red Sandstone) Sedimentation and Tectonics of Norway: ABSTRACT

Abstract

Lower and Middle Devonian continental redbeds in Norway record the deposition of coarse clastic fluvial sediments in a series of separate intramontane basins. Contemporaneous uplifting of surrounding provenance areas resulted in the deposition of breccias, conglomerates, and sandstones as thick coalescing alluvial fans and stream deposits in E-W-trending grabens and half-grabens. The largest of the structurally formed basins covers an area of approximately 2,000 sq km and has a maximum preserved continuous Devonian section of approximately 5,000 m. Devonian rocks crop out in four parts of Norway: (1) 6 basins along the west coast north of Bergen thought to contain Middle Devonian sediments; (2) several isolated areas west of Trondheim thought to be primarily Early Devonian; (3) a small outlier of very coarse Lower Devonian sediments in eastern Norway near Roragen; and (4) redbeds of probable Early Devonian age near Oslo. Fossils are scarce and include plants, crustaceans, and Crossopterygian vertebrates. The Devonian basins in western Norway developed in the former eugeosynclinal part of the Caledonian geosyncline, which underwent major orogeny and uplift during the Late Silurian and Early Devonian. This uplift resulted in the formation of a major NE-SE-SW-trending mountain system, which supplied abundant and varied detritus to the Devonian intramontane basins, including eugeosynclinal metasediments and metavolcanics, high-grade metamorphic schists, gneisses and amphibolites, and diverse mafic and felsic intrusive igneous rocks. Postdepositional folding and faulting have obscured the original basin margins; the Devonian sediments presently form a series of E-W-trending anticlines and synclines that have locally been thrust over surrounding End_Page 2498------------------------------ older rocks. The original basin margins probably were high-angle normal faults, although strike-slip faulting is suggested locally. Paleocurrent patterns suggest transport of sediment from surrounding highlands toward the central part of the basins, where larger rivers flowed parallel with the basin axes. No consistently oriented regional pattern is apparent. Stratigraphic relations, sedimentary structures, and fabrics are characteristic of fluvial deposition. The coarse intramontane sediments are very similar to Old Red Sandstone deposits in Svalbard, East Greenland, eastern Quebec, Ireland, and Scotland. End_of_Article - Last_Page 2499------------