| 1. |
- Andreasson, Per Gunnar, et al.
(författare)
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Magmatism during late Ordovician-early Silurian accretion of the Caledonides of Arctic Scandinavia : the Halti-Guolasjavri area revisited
- 2023
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Ingår i: Norwegian Journal of Geology. - : Geological Society of Norway. - 2387-5852 .- 2387-5844. ; 103:2
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Tidskriftsartikel (refereegranskat)abstract
- In the Scandinavian Caledonides, evidence of syn-collisional magmatism related to extensional basin development immediately prior to late Silurian Baltica-Laurentia collision was considered restricted to exotic terranes until late Silurian ages were obtained from the Halti Igneous Complex (HIC), hosted by a thrust sheet (Corrovarre Nappe, CN) of continental affinity. Various orogenic models for the extension and magmatism, a. o. subduction flip, slab roll-back, and ridge subduction have been proposed. Crucial factors include the affinity (Baltican or exotic) of the CN, and the nature of the debated unconformity at the base of the overlying exotic Vaddas Nappe (Koli). This study reexamines a critical tectonostratigraphic section and reports U-Pb zircon ages (441-436 Ma) of palingenetic granitic dykes generated by the HIC. We reinterpret the CN as a slice of the continental margin and accreted with some other nappes of the Seve Nappe Complex (SNC) which decoupled from the continent-ocean transition (COT) at an early stage of subduction of the margin. The lower part of the bipartite Vaddas Nappe, composed of a very dense dolerite dyke swarm with screens of quartzite, marble and subordinate black schist, is reinterpreted as a continuation northwards of the uppermost nappe of the SNC in Indre Troms, derived from the Ediacaran outermost continental margin. The contact with the overlying telescoped succession of conglomerates, marbles, volcanics and turbidites of the Vaddas Nappe is tentatively interpreted as a tectonised unconformity. To a classical model of back-arc spreading outboard of Laurentia during closure of the Iapetus Ocean, we add the arrival of Baltica, with a prism of decoupled slices of the COT and exhumed/exhuming UHP nappes. The spreading centre of the basin provides a plausible setting for gabbros and pillow lavas of the Vaddas Nappe, and the shores of the basin for a Seve-Koli unconformity. Future PTt studies are required in order to be able to relate the proposed shallow, syn-exhumation HIC magmatism to the tectonometamorphic evolution of the HP-UHP nappes of the SNC.
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| 2. |
- Anjar, Johanna, et al.
(författare)
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OSL dating of Weichselian ice-free periods at Skorgenes, western Norway
- 2018
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Ingår i: Norwegian Journal of Geology. - : Geological Society of Norway. - 2387-5852 .- 2387-5844. ; 98:3, s. 301-313
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Tidskriftsartikel (refereegranskat)abstract
- During recent years, many sites with sediments pre-dating the Last Glacial Maximum have been identified in formerly glaciated areas. As more and better dates are presented from these sites, the dynamic behaviour of the Scandinavian Ice Sheet is becoming increasingly clear. In this study, we revisited the site Skorgenes in western Norway. Here, sediments from two ice-free periods are found below and interbedded with glacial diamicts. We present an updated chronology for the site, based on ten new Optically Stimulated Luminescence (OSL) dates, and discuss possible correlations. The samples had poor OSL properties but still provide a substantial improvement of the existing chronology. The oldest sediments identified at Skorgenes were deposited in a proglacial subaqueous setting at some point between 21 and 42 ka. This period was followed by a glacial advance and, during the subsequent ice retreat, a delta or subaqueous fan formed at Skorgenes. OSL ages from the foreset beds indicate deposition at some point between 17 and 30 ka, implying that the ice-front retreated east of Skorgenes at least once during the Late Weichselian. A substantial ice advance followed this retreat. The youngest sediments, forming a proglacial delta succession, were deposited during the final deglaciation of the site.
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| 3. |
- Bingen, B., et al.
(författare)
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Geochronology of the Palaeoproterozoic Kautokeino Greenstone Belt, Finnmark, Norway: Tectonic implications in a Fennoscandia context.
- 2015
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Ingår i: Norwegian Journal of Geology. - : Geological Society of Norway. - 2387-5844 .- 2387-5852. ; 95, s. 365-396
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Tidskriftsartikel (refereegranskat)abstract
- Zircon U–Pb geochronological data in 18 samples from Finnmarksvidda and one sample from the Repparfjord Tectonic Window, northern Norway, constrain the evolution of the Palaeoproterozoic Kautokeino Greenstone Belt and neighbouring units in a Fennoscandia context. The Jergul Complex is an Archaean cratonic block of Karelian affinity, made of variably gneissic, tonalite–trondhjemite–granodiorite–granite plutonic rocks formed between 2975 ± 10 and 2776 ± 6 Ma. It is associated with the Archaean Goldenvárri greenstone–schist formation. At the base of the Kautokeino Greenstone Belt, the Masi Formation is a typical Jatulian quartzite, hosting a Haaskalehto-type, albite–magnetite-rich, mafic sill dated at 2220 ± 7 Ma. The Likčá and Čáskejas formations represent the main event of basaltic magmatism. A synvolcanic metagabbro dates this magmatism at 2137 ± 5 Ma. The geochemical and Nd isotopic signature of the Čáskejas Formation (eNd = +2.2 ± 1.7) is remarkably similar to coeval dykes intruding the Archaean Karelian Craton in Finland and Russia (eNd = +2.5 ± 1.0). The Čáskejas Formation can be correlated with the Kvenvik Formation in the Alta–Kvænangen Tectonic Window. Two large granite plutons yield ages of 1888 ± 7 and 1865 ± 8 Ma, and provide a maximum age for shearing along two prominent NNW–SSE-oriented shear zones recording Svecokarelian transpression. The Bidjovagge Au–Cu deposit formed around 1886 to 1837 Ma and is also related to this NNW–SSE-oriented shear system. The Ráiseatnu Complex is mainly composed of granitic gneisses formed between 1868 ± 13 and 1828 ± 5 Ma, and containing metasediment rafts and zircon xenocrysts ranging from c. 3100 to 2437 Ma. The Kautokeino Greenstone Belt and Ráiseatnu Complex are interpreted as Palaeoproterozoic, pericontinental, lithospheric domains formed during rifting between Archaean cratonic domains. They accommodated oblique convergence between the Karelian and the Norrbotten Archaean cratons during the Svecokarelian orogeny.
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| 4. |
- Bremer, Oskar, 1985-, et al.
(författare)
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Silurian vertebrate remains from the Oslo Region, Norway, and their implications for regional biostratigraphy
- 2019
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Ingår i: Norsk Geologisk Tidsskrift. - : GEOLOGICAL SOC NORWAY. - 0029-196X .- 1502-5322. ; 99:1, s. 129-155
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Tidskriftsartikel (refereegranskat)abstract
- Several vertebrate assemblages are described from the Silurian of the Oslo Region, Norway, based on the review and revision of previous reports of microremains, as well as unpublished material from museum collections. Articulated thelodont specimens from the Rudstangen Fauna, Ringerike Group, are also described here for the first time, revealing a seemingly monogeneric loganelliid assemblage. The oldest assemblage (mid-Llandovery) only contains the thelodont Loganellia cf. aldridgei, while a single sample from upper Llandovery strata produced four Thelodus sp. scales. These scales share features with those from younger Thelodus taxa and give additional support to an early appearance of this genus. The mid-Wenlock faunas consist of thelodonts Loganellia grossi, Loganellia einari and Thelodus laevis. These are joined by the thelodont Paralogania martinssoni, anaspids Rhyncholepis parvula and cf. Pterygolepis nitida, as well as the osteostracans cf. Tyriaspis whitei and Osteostraci gen. et sp. indet. in late Wenlock and earliest Ludlow faunas. These complement the previously described anaspids and osteostracans of the Rudstangen Fauna based on articulated specimens. The faunas of a number of calcarenite samples collectively contain the thelodonts L. grossi, L. einari, P. martinssoni and T. laevis, and are most likely of early Ludlow age. When the vertebrate-producing samples are put in the proposed stratigraphical framework for the Oslo Region that has been refined in recent decades, the faunas fit well into the vertebrate biozonation established for the Silurian, contrary to previous claims. The earliest faunas in the area show similarities to the Llandovery of Britain, whereas thelodonts and anaspids, but not osteostracans, from late Wenlock and early Ludlow are more closely related to Baltic forms. Additional sampling of the area may assist in refining the biostratigraphy and provide insights into Silurian vertebrate distributions in Norway and related regions.
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| 5. |
- Hall, Adrian Malcolm
(författare)
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Phanerozoic denudation across the Kola Peninsula, northwest Russia : implications for long term stability of Precambrian shield margins
- 2015
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Ingår i: Norsk Geologisk Tidsskrift. - : Geological Society of Norway. - 0029-196X. ; 95:2, s. 153-169
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Tidskriftsartikel (refereegranskat)abstract
- Contrasting views exist on the stability of the Earth’s shield regions over the last 1 Ga that have major implications for reconstructing erosion patterns on shields and the supply of sediment to intra-cratonic and marginal basins. This paper explores Phanerozoic denudation rates and patterns on the northern part of the Fennoscandian Shield in the Kola Peninsula, Northwest Russia. This shield region was intruded by magmatic rocks of the Kola Alkaline Province (KAP) in the Devonian and Early Carboniferous. The KAP comprises a varied suite of alkali–ultramafic plutonic and hypabyssal intrusions, diatremes and dykes that was emplaced at various depths in the crust and allows assessment of depths and rates of erosion during and since the KAP magmatic episode. Further evidence of long-term denudation is provided by Mesoproterozoic and Neoproterozoic cover rocks found around the margins of the Kola Peninsula and in the White Sea. The burial and exhumation history is compared to available Apatite Fission Track (AFT) data for the Kola Peninsula and adjacent areas. Post-Devonian denudation rates on the shield rocks of the Kola Peninsula have varied in space and time. Around the periphery of the Kola Peninsula, low long-term denudation of shield rocks is indicated by the survival of Riphean cover rocks and Late Devonian lavas, kimberlite crater facies and near-surface emplacement of dykes. In contrast, in the main belts of KAP intrusions, 4–6 km of rock was removed in response to doming between 460 and 360 Ma. Deep denudation is indicated by the emplacement depths of alkaline intrusions and Phoscorite–Carbonatite pipes (PCPs). Erosion on the Kola Peninsula since 360 Ma has been far more limited. Extensive, shallow, late-stage magmatism associated with PCPs, dykes and the large alkaline intrusions in the KAP indicates that erosion depths nowhere exceeded 2 km. Post-Devonian denudation has removed <1 km of rock from the margins of the Kola Peninsula and from the backslope of the Saariselkä–Karelia scarp in northern Finland. AFT data point to an important phase of erosion in the early Mesozoic but depths of unroofing of 3–5 km based on AFT cooling ages for this later phase are in conflict with the evidence of lesser erosion provided by the late-stage KAP intrusions and also require unrealistic depths of former Devonian to Triassic cover rocks. Mean denudation rates were greatest (up to 40 m/Myr) during the KAP magmatic phase. Post-Devonian rates across the Kola Peninsula and adjacent shield areas were much lower (<3–6 m/Myr) and are compatible with low long-term denudation rates for other cratons. Further resolution of longterm denudation patterns and rates on the Kola Peninsula requires the application of low-temperature thermochronometry, detailed examination of the regional geomorphology and firmer dating of ancient weathering episodes.
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| 6. |
- Høyberget, Magne, et al.
(författare)
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Re-evaluation of the stratigraphically important olenellid trilobite Holmia cf. mobergi from the Cambrian Series 2, Stage 3 and its implications for the lower Cambrian stratigraphy in the Mjøsa area, Norway
- 2019
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Ingår i: Norsk Geologisk Tidsskrift. - : Geological Society of Norway. - 0029-196X .- 1502-5322. ; 99:1, s. 63-92
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Tidskriftsartikel (refereegranskat)abstract
- The olenellid trilobite Holmia cf. mobergi, known from a single cephalon in the upper lower Cambrian strata from a river section in Flagstadelva, Hamar, has played a significant stratigraphic role in interpreting the lower Cambrian informal Series 2, Stage 3 in the Mjøsa area, Norway, sinceits discovery in the early 1950s. It was considered one of the oldest trilobite taxa in the lower Cambrian of Scandinavia, but the stratigraphic leveland biozonation of the cephalon were problematic and a matter of discussion for decades. Moreover, organic-walled microfossil biostratigraphyquestioned the supposed age of the trilobite. New specimens of this taxon collected from the type locality show that the species occurs at a differentstratigraphic level than first reported, prompting a new description of the species and a re-evaluation of the taxon’s biostratigraphic significance.Holmia cf. mobergi is compared with new and well-preserved topotype material of Holmia inusitata, a very rare taxon hitherto known from onesingle outcrop in an autochthonous setting in Norway. Holmia cf. mobergi and Holmia inusitata are here considered conspecific.
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| 7. |
- Briner, Jason P., et al.
(författare)
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Configuration of the Scandinavian Ice Sheet in southwestern Norway during the Younger Dryas
- 2023
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Ingår i: Norwegian Journal of Geology. - 2387-5844. ; 103
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Tidskriftsartikel (refereegranskat)abstract
- The extent of the Scandinavian Ice Sheet in southwestern Norway is precisely located during the well-characterized Younger Dryas re-advance. However, the thickness of the ice sheet is less well constrained inland from the terminal position. Some exceptions include lateral moraines traced inland and up to 1000 m a.s.l. along Hardangerfjorden. Here, we apply 10Be dating in two areas: (1) bedrock and boulders in the high-relief landscapes near the Younger Dryas margin around the Bergen urban area, and (2) boulders from an upland 1600 m a.s.l. much farther (120 km) inland. We find that coastal summits ranging from ~400 to ~680 m a.s.l. and located only ~10–15 km up-flow from the ice margin, were covered by the Scandinavian Ice Sheet during the Younger Dryas. The scatter in the 10Be age population of 22 boulder samples is best explained by isotopic inheritance owing to inefficient subglacial erosion during the foregoing glaciation. Most of the 11 bedrock samples also exhibit inheritance, pointing to the source of inheritance in boulders and implying inefficient subglacial erosion during the last glaciation even in valley-bottoms near Bergen. Regional glacial striae compilations suggest that ice flow during maximum Younger Dryas ice-sheet configurations was for the most part cross-valley, with potentially low basal slip rates. Five new 10Be ages from the inland site help to constrain ice height far inland. We combine these new results with prior information to generate a cross profile of the Younger Dryas ice sheet in southern Norway.
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