| 1. |
- Ahlberg, Anders, et al.
(author)
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Onshore climate change during the late triassic marine inundation of the Central European Basin
- 2002
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In: Terra Nova: the European journal of geosciences. - : Wiley. - 0954-4879. ; 14:4, s. 241-248
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Journal article (peer-reviewed)abstract
- Sedimentological, pedological and palynological evidence reveal radically increasing onshore humidity during the Rhaetian marine invasion of central Europe along the north-eastern margin of the Central European Basin (southern Sweden). Pre-Rhaetian aridity favoured the formation of Carnian redbeds with calcrete, which were succeeded by Norian hematite-cemented conglomerates, arkoses, arkosic wackestones, and smectititic mudstones deposited on braidplains and in lakes. Superimposed autochthonous coals and gleysols indicate the Rhaetian onset of year-round humidity. Chemically mature sandstones, kaolinitic mudstones and luvisols also formed at this time, influenced by a permanent vegetation cover which lowered soil pH and strongly intensified chemical weathering. The Rhaetian deposits accumulated in floodplain lakes repeatedly subjected to sediment infill, plant colonization and palaeosol development. The humidity shift resembles that contemporaneously recorded in the North Sea region.
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| 2. |
- Andréasson, Per-Gunnar, et al.
(author)
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Subduction-flip during Iapetus Ocean closure and Baltica-Laurentia collision, Scandinavian Caledonides
- 2003
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In: Terra Nova: the European journal of geosciences. - : Wiley. - 0954-4879. ; 15:6, s. 362-369
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Journal article (peer-reviewed)abstract
- Evidence is presented here from the northern Scandinavian Caledonides for development of an extensional basin of Ashgill to Mid Llandovery age along the Baltoscandian margin immediately prior to Baltica-Laurentia collision. U/Pb multigrain and ion microprobe zircon dating of plagiogranites in the Halti Igneous Complex complement previous baddeleyite and zircon dating of a dolerite dyke, and zircon dating of anatectic granite; they demonstrate that this dunite, troctolite, gabbro, sheeted-dyke complex ranges in age from c. 445 to 435 Ma. The dolerite dykes intruded and melted arkoses of inferred Neoproterozoic age. This evidence, taken together with previous documentation of ophiolites (Solund-Stavfjord), ophiolite-like associations (Sulitjelma Igneous Complex) and several other mafic suites (e.g. Rana, Artfjallet) of Ashgill to Llandovery age further south in the northern Scandinavian Caledonides, implies that Scandian collisional orogeny along this nearly 2000-km-long mountain belt was immediately preceeded by development of short-lived marginal basins. The latter developed during the final closure of the Iapetus Ocean and are inferred to be of back-arc origin, some (perhaps all) related to E-dipping subduction. Collision of the continents at c. 435 Ma is inferred to have induced a flip in subduction polarity, leading to underthrusting of Laurentia by Baltica.
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| 3. |
- Wastegard, S, et al.
(author)
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A tephra-based correlation between the Faroe Islands and the Norwegian Sea raises questions about chronological relationships during the last interglacial
- 2005
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In: Terra Nova: the European journal of geosciences. - : Wiley. - 0954-4879. ; 17:1, s. 7-12
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Journal article (peer-reviewed)abstract
- Marine ash zones from the last interglacial period have been described from cores from the North Atlantic and an ash zone from the middle part of the interglacial has been observed in connection with a major cooling event. Here we present evidence for a coeval ash zone in a terrestrial site on the Faroe Islands. The investigated sediments are correlated with the upper part of oxygen isotope stage 5e and the beginning of stage 5d. The Eemian climatic optimum is represented in the lower part of the sequence close to the first occurrence of the ash zone. A tephra-based correlation suggests that the climatic optimum was synchronous with the marine record from the Norwegian Sea, but several thousand years later than in Eemian sections of west central Europe. However, many questions on the chronological relationship between the Eemian and oxygen isotope stage 5e still remain to be answered.
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| 4. |
- Ask, Maria, et al.
(author)
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In-situ stress determination from breakouts in the Tornquist Fan, Denmark
- 1996
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In: Terra Nova. - : Wiley. - 0954-4879 .- 1365-3121. ; 8:6, s. 575-584
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Journal article (peer-reviewed)abstract
- The Tornquist Fan, a fan-shaped region in Denmark and Western Baltic, is situated in the transition zone between the Western and Northern European Stress Provinces. Breakout data from 20 wells (0.3-3.6 km) were analysed. The fan can be divided into three stress provinces: (i) The area south of the Romo Fracture Zone is part of the Western European Stress Province and has NNW-SSE orientation of the maximum horizontal stress, (ii) The sediment cover in the Norwegian-Danish Basin is dominated by ENE-WSW orientated maximum horizontal stress, (iii) The maximum horizontal stress is sub-parallel to the strike of the Sorgenfrei-Tornquist Zone. Deviations from the regional stress field were observed in wells close to faults and salt diapirs. In wells south of the Sorgenfrei-Tornquist Zone, breakout occurrence decreases with increasing age of the stratigraphic units. The downhole breakout distribution seems to correlate with lithology and thickness of the sediment layer.
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| 5. |
- Friberg, M, et al.
(author)
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Europrobe seismic reflection profiling across the eastern Middle Urals and West Siberian Basin
- 2001
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In: Terra Nova. - : Blackwell Publishing. - 0954-4879 .- 1365-3121. ; 12:6, s. 252-257
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Journal article (peer-reviewed)abstract
- New deep seismic reflection data provide images of the crust and uppermost mantle underlying the eastern Middle Urals and adjacent West Siberian Basin. Distinct truncations of reflections delineate the late-orogenic strike-slip Sisert Fault extending vertically to ∼28 km depth, and two gently E-dipping reflection zones, traceable to 15–18 km depth, probably represent normal faults associated with the opening of the West Siberian Basin. A possible remnant Palaeozoic subduction zone in the lower crust under the West Siberian Basin is visible as a gently SW-dipping zone of pronounced reflectivity truncated by the Moho. Continuity of shallow to intermediate-depth reflections suggest that Palaeozoic accreted island-arc terranes and overlying molasse sequences exposed in the hinterland of the Urals form the basement for Triassic and younger deposits in the West Siberian Basin. A highly reflective lower crust overlies a transparent mantle at about 43 km depth along the entire 100 km long seismic reflection section, suggesting that the lower crust and Moho below the eastern Middle Urals and West Siberian Basin have the same origin.
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| 6. |
- Juhlin, Christopher, et al.
(author)
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Moho imbrication in the Middle Urals
- 2007
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In: Terra Nova. - : Wiley. - 0954-4879 .- 1365-3121. ; 19:3, s. 189-194
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Journal article (peer-reviewed)abstract
- New processing of part of the Europrobe's Seismic Reflection Profiling in the Urals (ESRU) reflection seismic data in the Middle Urals shows a southwest-dipping Moho imbrication and crustal underthrusting that was not previously imaged. The area of thickening associated with it roughly coincides with a deepening of the Moho imaged by the GRANIT refraction data. This feature does not fit with the currently known Palaeozoic crustal architecture of the Uralides or with its geodynamic history. Geological data suggest that it is not related to a relict southwest-dipping subduction zone. Based on its lower crustal and Moho reflection seismic character it is presently interpreted to be a post-Uralide feature, possibly related to Mesozoic intraplate shortening in the area. Its coincidence with a locus of mild earthquake activity further suggests that it might be active today.
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| 7. |
- Lindroos, Alf, et al.
(author)
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Late-orogenic Svecofennian deformation in SW Finland constrained by pegmatite emplacement ages
- 1996
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In: Terra Nova. - : Wiley. - 0954-4879 .- 1365-3121. ; 8:6, s. 567-574
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Journal article (peer-reviewed)abstract
- Late stages of the Svecofennian orogeny in SW Finland were related to a tranpressional stress field and dextral movements along crustal scale shear zones under decreasing temperature and pressure conditions. In the Kemiö area, a minimum estimate for the time span of movements along one of these shear zones is obtained from the ages of 1840 to 1830 Myr-old microcline granite sheets, related to early ductile deformation, and by dating structurally late rare-mineral granite pegmatites, related to brittle deformation. One pegmatite was emplaced when the rheological conditions in the gabbro changed from ductile to semi-ductile and brittle. It has U-Pb ferrotapiolite ages ranging between 1807.0 ± 2.9 Myr (2 ) and 1803.1 + 2.9/ -2.0 Myr (2 ). Another pegmatite emplaced under brittle conditions has an U-Pb ferrotapiolite age of 1802.9 ± 1.3 Myr (2 ). These pegmatites were emplaced preferentially in gabbroic rocks, that showed brittle to semi-ductile deformation at a time when their more felsic host-rocks still showed ductile deformation. The age range bracketed by the microcline granite sheets and the structurally late pegmatites indicates that ductile deformation related to the transpressional Late Svecofennian tectonic regime in southwestern Finland, persisted for at least 30-40 Myr
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| 8. |
- Romer, Rolf
(author)
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Contiguous Laurentia and Baltica before the Grenvillian-Sveconorwegian orogeny?
- 1996
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In: Terra Nova. - : Wiley. - 0954-4879 .- 1365-3121. ; 8:2, s. 173-181
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Journal article (peer-reviewed)abstract
- Close geochronological correspondence of Mesoproterozoic extension-related magmatism and comparable tectonic and geochronological evolution of the Grenville and Svecononvegian orogens suggests that the Laurentian and Baltic Shields could have been joined during the Mesoproterozoic and did not separate until after the Grenvillian-Sveconorwegian orogeny. The combined Grenville-Svecononvegian orogen is here interpreted to have formed during the collision of coherent Laurentia-Baltica with an unknown craton, which is in contrast to earlier explanations that favour a late-Mesoproterozoic rotation between Laurentia and Baltica followed by collision of these two cratons with each other
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| 9. |
- Shumlyanskyy, Leonid, et al.
(author)
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U-Pb age and Hf isotope compositions of zircons from the north-western region of the Ukrainian shield : mantle melting in response to post-collision extension
- 2012
-
In: Terra Nova. - : Wiley. - 0954-4879 .- 1365-3121. ; 24:5, s. 373-379
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Journal article (peer-reviewed)abstract
- The North-Western region of the Ukrainian shield represents Palaeoproterozoic continental crust formed essentially during two orogenic events at ca. 2.1–2.05 and 2.0–1.95 Ga. At 1.8–1.74 this area was intruded by huge Korosten anorthosite–mangerite–charnockite granite complex. At least three generations of mafic dykes can be distinguished in the region. We report new U-Pb data obtained for a suite of Ni-enriched dolerite dykes and layered gabbroic intrusions. Our results indicate that the Tomashgorod dyke was formed at 1787.4 ± 6.4 Ma, the Prutivka intrusion at 1777.0 ± 4.7 Ma and the Kamenka massif at ca. 1.79 Ga. This time coincides with the collision of the Fennoscandian and Sarmatian segments of the East European craton and it is contemporaneous with the initial stages of evolution of the Korosten complex. Hf isotopic compositions of zircons indicate that these rocks originated due to melting of moderately depleted mantle material.
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| 10. |
- Wikström, A., et al.
(author)
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The Bälinge conglomerate in northern Sweden reinterpreted as a magmatic, hydraulic breccia
- 1996
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In: Terra Nova. - : Wiley. - 0954-4879 .- 1365-3121. ; 8:2, s. 166-172
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Journal article (peer-reviewed)abstract
- The Bälinge conglomerate has played a key role in the lithostratigraphy of northern Sweden. The conglomerate, with pebbles dominated by granodiorites and tonalites in a generally biotite-rich matrix, borders volcanic rocks with unclear relative age relationships. In nearby areas these volcanites have been intruded by plutonic rocks (c. 1.9 Ga) which are similar to the pebble material. On these grounds, the conglomerate has been regarded as younger than the volcanic rocks and an important marker in the geological evolution of the region. In this preliminary study, it is suggested that the features displayed by the Balinge conglomerate are not compatible with an epiclastic origin. On the contrary, they indicate that this rock represents a hydraulic breccia where the roundness of the granitoid 'pebbles' has resulted from erosion in a fluidised, heterogeneous and magmatic environment. In the actual area the 'conglomerate' must thus be dismissed as a stratigraphic marker horizon. It belongs to the early Svecofennian evolution.
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