Geology of Åland
The geology of Åland includes Jotnian age sediments from the Proterozoic, such as sandstone, siltstone, arkose, conglomerate, rapakivi granite and shale. The islands are underlain by plutonic rocks common of the Svecofennian Domain.[1][2]
Geological history
[edit]Precambrian
[edit]Archaean eon
[edit]The rapakivi granite on Åland was formed during the Archaean around 1640–1540 Mya by anorogenic tectonic settings.[3][4]
Proterozoic eon
[edit]The Jotnian age sediments were formed during the Proterozoic. Jotnian sediments are usually assigned to the Riphean Stage of the Mesoproterozoic Era.[5][6] Jotnian sediments were deposited approximately 1600–1260 Mya. Some Jotnian sediments are, however, younger than the diabases, meaning they can be younger than 1260 Mya.[5] Lumparn would be formed during the Proterozoic by a meteorite.
Modern Åland would be part of Baltica, a paleocontinent that formed in the Paleoproterozoic. Baltica formed at c. 2000–1700 Mya by the collision of three Archaean-Proterozoic continental blocks: Fennoscandia (including the exposed Baltic Shield), Sarmatia (Ukrainian Shield and Voronezh Massif), and Volgo-Uralia (covered by younger deposits). Sarmatia and Volgo-Uralia formed a proto-craton at c. 2000 Mya which collided with Fennoscandia c. 1800–1700 Mya. The sutures between these three blocks were reactivated during the Mesoproterozoic and Neoproterozoic.
Phanerozoic
[edit]Ordovician
[edit]Between Pleistocene sediments and crushed rapakivi granite bedrock there is a layer of Ordovician limestones. This makes Lumparn one of the few places in Finland where fossils have been found. Fossils of mainly invertebrates have been found, mainly trilobites, various mollusks, and crinoid fossils.[7]
Quaternary
[edit]Around 18,000 BC, during the Weichselian glaciation, a thick cover of ice stretched over Scandinavia,[8] which eventually receded from the islands around 9000 BC.[9] Around 8000 BC the highest peaks of the then submerged archipelago rose from the Baltic Sea.[10] The sea levels would alternate in the Baltic Sea,[11] but a land bridge to Åland never formed.
Due to the post-glacial rebound after the icecaps melted, the area around Åland is still rising several millimeters per year, marginally expanding the archipelago's surface.[12]
Geological features
[edit]Lumparn
[edit]A impact structure from the Proterozoic from around 1000 Mya.[13] The remains of the crater are filled with sediments. Between Pleistocene sediments and crushed rapakivi granite bedrock there is a layer of Paleozoic limestones. This makes Lumparn one of the few places in Finland where fossils have been found. Long shatter cones have been discovered in the southwestern part of the bay.
Orrdalsklint
[edit]Orrdalsklint, at 129.1 metres (423.6 ft) above sea level, is the highest point on Åland. Orrdalsklint would be one of the first parts of Åland to rise out of the sea 10,000 years ago.
References
[edit]- ^ Vaasjoki, M.; Korsman, K.; Koistinen, T. (2005). "Overview". Precambrian Geology of Finland Key to the Evolution of the Fennoscandian Shield. Developments in Precambrian Geology. Vol. 14. pp. 1–17. doi:10.1016/S0166-2635(05)80002-7. ISBN 978-0-444-51421-9.
- ^ Salminen, Johanna; Lehtonen, Elina; Mertanen, Satu; Pesonen, Lauri J.; Elming, Sten-Åke; Luoto, Toni (2021). "The Precambrian drift history and paleogeography of Baltica". Ancient Supercontinents and the Paleogeography of Earth. pp. 155–205. doi:10.1016/B978-0-12-818533-9.00015-1. ISBN 978-0-12-818533-9. S2CID 244982213.
- ^ Rämö, Osmo Tapani; Haapala, Ilmari Johannes. "One hundred years of Rapakivi Granite". University of Helsinki.
- ^ A. M. Larin. "Rapakivi granites in the geological history of the Earth. Part 1. Magnetic associations with rapakivi granites: age, geochemistry, and tectonic setting". ResearchGate.
- ^ a b Amantov, A.; Laitakari, I.; Poroshin, Ye (1996). "Jotnian and Postjotnian: Sandstones and diabases in the surroundings of the Gulf of Finland". Geological Survey of Finland, Special Paper. 21: 99–113. Retrieved 27 July 2015.
- ^ "Jotnian Series". The Great Soviet Encyclopedia. 1979.
- ^ Johnson, Markes (17 November 2023). "Stepping Ashore the Fennoscandian Shield in the Åland Archipelago". Columbia University Press blog. Columbia University.
- ^ NASA. (2014, June 4). Åland Islands. Earthobservatory.Nasa.Gov. https://earthobservatory.nasa.gov/images/52174/aland-islands Retrieved 25 August 2021.
- ^ Mörner, N. A. (1995). The Baltic Ice Lake-Yoldia Sea transition. Quaternary International, 27, 95-98.
- ^ Stone Age Åland. Retrieved 29 August 2006. (in Swedish)
- ^ Andrén, T., Björck, S., Andrén, E., Conley, D., Zillén, L., & Anjar, J. (2011). The development of the Baltic Sea Basin during the last 130 ka. In The Baltic Sea Basin (pp. 75-97). Springer, Berlin, Heidelberg.
- ^ "December 2006, Anne-Maj Lahdenperä Pöyry Environment Oy, Working Report 2006-111, Literature Review on Future Development of the Baltic Sea and Recommendations for Safety Modelling" (PDF). Archived from the original (PDF) on 2016-03-04. Retrieved 2014-09-29.
- ^ "Lumparn". Earth Impact Database. Planetary and Space Science Centre University of New Brunswick Fredericton. Retrieved 2009-08-15.
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