User:Mikenorton/Hornelen Basin
| Hornelen Basin | |
|---|---|
| Coordinates | 61°45′N 5°27′E / 61.75°N 5.45°E |
| Etymology | Hornelen |
| Region | Sogn og Fjordane |
| Country | Norway |
| Characteristics | |
| On/Offshore | Onshore |
| Area | 15,000 km2 (5,800 sq mi) |
| Geology | |
| Basin type | Extensional |
| Age | Devonian |
| Faults | Nordfjord-Sogn Detachment |
The Hornelen Basin is a sedimentary basin containing an estimated 25 km stratigraphic thickness of coarse clastic sedimentary rocks of Devonian age. It forms part of a group of basins of similar age along the west coast of Norway between Sognefjord and Nordfjord, related to movement on the Nordfjord-Sogn Detachment. It formed a a result of extensional tectonics as part of the post-orogenic collapse of crust that was thickened during the Caledonian Orogeny towards the end of the Silurian period. It is named for the mountain Hornelen on the northern margin of the basin.
Basin fill
[edit]The dominant lithology is sandstone, which is organised into a series of coarsening-upward cycles, laid down by a west-draining axial river system. At the basin margins the sandstones interfinger with conglomerates deposited by alluvial fans. The northern conglomerates were deposited by mainly debris flow fans, while those to the south are mainly streamflow in type. Near the northern margin there is a zone where siltstone is developed, forming the finest-grained sediments in the basin.
Origin
[edit]The Hornelen sequence, in common with other Old Red Sandstone sequences in Norway, Scotland and Greenland was originally described as deposited in an intermontane depression with most faulting being post-depositional.[1] The first tectonic model for the basin was developed in 1964, with an eastward migrating depocentre proposed in a downthrown basin between two high-angle normal faults with sedimentation keeping pace with eastward propagation of the faults.[2] In 1977 a strike-slip pull-apart basin model was proposed, by analogy with basins developed along the San Andreas Fault system, with the cyclicity explained as a result of periodic fault activity.[3] In 1984 another extensional model was proposed[4] and this was supported in 1986 by the recognition of the underlying Nordfjord-Sogn Detachment, a major extensional structure with tens of kms of displacement.[5]
References
[edit]- ^ Friend, P.F. (1969). "Tectonic Features of Old Red Sedimentation in North Atlantic Borders: Chapter 51: Late Orogenic Stratigraphy and Structure". In Kay, M. (ed.). North Atlantic Geology and Continental Drift. AAPG Memoir. Vol. 12. American Association of Petroleum Geologists.
- ^ Bryhni, I. (1964). "Migrating Basins on the Old Red Continent". Nature. 202: 384–385. doi:10.1038/202384b0.
- ^ Steel, R.J.; Maehle, S.; Nilsen, H.; Røe, S.L.; Spinnanger, Å (1977). "Coarsening-upward cycles in the alluvium of Hornelen Basin (Devonian) Norway: Sedimentary response to tectonic events" (PDF). Bulletin of the Geological Society of America. 88 (8): 1124–1134. doi:10.1130/0016-7606(1977)88<1124:CCITAO>2.0.CO;2.
- ^ Hossack, J.R. (1984). "The geometry of listric growth faults in the Devonian basins of Sunnfjord, W Norway". Journal of the Geological Society. 141: 629–637. doi:10.1144/gsjgs.141.4.0629.
- ^ Norton, M.G. (1986). "Late Caledonide Extension in western Norway: A response to extreme crustal thickening". Tectonics. 5 (2): 195–204. doi:10.1029/TC005i002p00195.