| 1. |
- Agić, Heda, 1989-, et al.
(författare)
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Reproductive cyst and operculum formation in the Cambrian-Ordovician galeate-plexus microfossils
- 2016
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 138:2, s. 278-294
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Tidskriftsartikel (refereegranskat)abstract
- Unicellular organic-walled microfossils from the Cambrian-Ordovician transition in Estonia (ca. 490-480 million years ago) exhibit rare characters reflecting their function as reproductive algal cysts. The studied assemblages record the evolutionary history of phytoplankton in the early Paleozoic Era: novel morphologies appearing through the Cambrian and subsequently diversifying in the Ordovician. Well preserved specimens were extracted following a standard palynological method and studied by light transmitted microscopy. The galeate plexus acritarchs Caldariola, Priscogalea and Stelliferidium have revealed exceptionally preserved morphological elements and a rare structure among both fossil and extant protists – an opening with operculum (lid) in reproductive cysts, in addition to lavish vesicle ornamentation and sculpture. Analogous morphology is observed in the living dasycladalean alga Acetabularia (Chlorophyta), which possesses an intrinsic lid-forming apparatus used during organism’s reproductive stage. Based on the observations on the fossil material and studies on the Acetabularia lid-formation, we propose a model of operculum formation in the galeate plexus microorganisms. Due to strong morphological and ecological similarities between galeate fossils and dasycladalean cysts, and the antiquity of this algal order, galeates may be positioned within green algae, more specifically Dasycladales. Unique morphology of the operculum-bearing microbiota would have required a high degree of intracellular complexity for its development, suggesting that advanced intracellular machinery was present already in the early Paleozoic phytoplankton. Additionally, minute prasinophyte microfossils Reticella corrugata are reported for the first time in the Upper Cambrian strata.
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| 2. |
- Ahlberg, Anders, et al.
(författare)
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Enigmatic Late Cretaceous high palaeo-latitude lonestones in Chukotka, northeasternmost Asia
- 2002
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Ingår i: GFF. - : Informa UK Limited. - 2000-0863 .- 1103-5897. ; 124:4, s. 197-199
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Tidskriftsartikel (refereegranskat)abstract
- Well-rounded cobbles were encountered within a low-energy restricted marine organic-rich deposit of latest Cretaceous age in Chukotka, NE Asia. The clasts are hydrodynamically incompatible with the inferred quiet depositional environment of the host sediment. Driftwood capable of tree-rafting, glacial striations, gastrolith clast clustering, and disrupting clast impact impressions typical of volcanic ejecta were absent, as were signs of traction currents. If indeed ice-rafting is responsible, this supports recent climate models and palaeobotanical data which favour seasonal marine ice cover of high northern latitudes over a wide span of boundary conditions.
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| 3. |
- Ahlberg, Per, et al.
(författare)
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Cambrian stratigraphy of the Tomten-1 drill core, Västergötland, Sweden
- 2016
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 138:4, s. 490-501
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Tidskriftsartikel (refereegranskat)abstract
- The Tomten-1 drilling at Torbjörntorp in Västergötland, southern Sweden, penetrated 29.85 m of Cambrian Series 2, Cambrian Series 3, Furongian, and Lower–Middle Ordovician strata. Lithostratigraphically, the succession includes the File Haidar, Borgholm and Alum Shale formations, and the Latorp and Lanna limestones. The drill core succession is described herein for the first time, with special focus on the biostratigraphy of the Cambrian Alum Shale Formation. In the Cambrian Series 3, through Furongian Alum Shale Formation, agnostoids and trilobites have been identified to species level and the succession is subdivided into nine biozones (in ascending order): the Ptychagnostus gibbus, Ptychagnostus atavus, Lejopyge laevigata, Agnostus pisiformis, Olenus gibbosus, Parabolina spinulosa, Ctenopyge tumida, Ctenopyge bisulcata and Ctenopyge linnarssoni zones. The succession is interrupted by numerous stratigraphic gaps of variable magnitudes, as is evident from the biostratigraphy and conspicuous unconformities.
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| 4. |
- Alebouyeh Semami, Farnaz, et al.
(författare)
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New U–Pb geochronologic and palaeomagnetic constraints on the late Palaeoproterozoic Hartley magmatic event : evidence for a potential large igneous province in the Kaapvaal Craton during Kalahari assembly, South Africa
- 2016
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 138:1, s. 164-182
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Tidskriftsartikel (refereegranskat)abstract
- The volcanic Hartley Formation (part of the Olifantshoek Supergroup, which is dominated by red bed successions) in South Africa recorded depositional and tectonic conditions along the western Kaapvaal Craton during the late Palaeoproterozoic. It formed in association with red bed deposition elsewhere in the cratonic hinterland and along the craton’s northern margin. However, the exact correlation of the Olifantshoek Supergroup with these other red-bed successions is hindered by poor geochronological constraints. Herein, we refine the age and palaeopole of the Hartley Formation, and provide geochronological constraints for large-scale 1.93–1.91 Ga bimodal magmatism on the Kaapvaal Craton (herein named the Hartley large igneous province). We present new age constraints for the mafic and felsic phases of this event at 1923 ± 6 Ma and 1920 ± 4 Ma, respectively, which includes the first reported age dating of the Tsineng Dyke Swarm that has been linked to Hartley volcanism. A mean 1.93–1.91 Ga palaeomagnetic pole for the Hartley large igneous province at 22.7°N, 328.6°E with A95 = 11.7° represents a significant improvement on a previously published virtual geomagnetic pole. This improved pole is used to refine the late Palaeoproterozoic apparent polar wander path of the Kaapvaal Craton. This can assist in correlation of red-bed successions in southern Africa.
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| 5. |
- Alexanderson, Helena, et al.
(författare)
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Late glacial and Holocene sand drift in south-central Sweden: sediments and ages
- 2019
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Ingår i: GFF. - : Informa UK Limited. - 2000-0863 .- 1103-5897. ; 141:2, s. 84-105
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Tidskriftsartikel (refereegranskat)abstract
- The aeolian deposits of Sweden have received modest attention, despite their usefulness as a palaeoenvironmental archive. Here we present sedimentological information and optically stimulated luminescence (OSL) ages from inland sand dunes in the lowlands of south-central Sweden. Three main lithofacies, each with two subfacies, were identified in the deposits: massive sand, laminated sand and crossbedded sand. Massive sand was most common and present at all sites, and is largely due to secondary bioturbation when found close to the surface. Other prevalent depositional processes are wind-ripple migrationand grain flow. Secondary features include animal burrows and tracks, root traces, infiltration structures and soil profiles. The luminescence ages plot in two different groups, centred in the early and late Holocene, respectively. The primary dune-forming phase occurred in the early Holocene, after local deglaciation and uplift above sea/lake level. However, at some sites, OSL ages suggest a prolonged phase of sand drift, or repeated reworking, long after deglaciation due to locally beneficial conditions. The late Holocene wasdominated by reactivation events and sheet sand deposition, which led to the formation of an aeolian mantle.
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| 6. |
- Alexanderson, Helena
(författare)
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Sub-till glaciofluvial sediments at Hultsfred, South Swedish Upland
- 2010
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 132:3&4, s. 153-159
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Tidskriftsartikel (refereegranskat)abstract
- In a gravel pit near Hultsfred, at the eastern margin of the South Swedish Upland, gravelly, sandy and silty-sandy beds covered by a thick, strati?ed gravelly diamicton are exposed. Large folds and shear-planes indicate post-depositional deformation of the sorted sediments, which according to OSL dating have a maximum Middle Weichselian (,60 ka) age. The sand and gravel are interpreted as glacio?uvial sediments that were deposited laterally during a Middle Weichselian deglaciation, or possibly subglacially during the Late Weichselian. The large-scale deformation was due to glaciotectonics, caused by an overriding wet-based ice sheet during the last deglaciation. The subglacial hydrostatical pressure was high and led to the formation of downward-injected clastic dykes. A basal till, which forms the cover moraine in the area, caps the succession. The fairly frequent occurrence of sub-till sediments on the South Swedish Upland demonstrates the limited effect of glacial erosion in parts of this area. During the Last Glacial Maximum, the South Swedish Upland was an ‘island’ of slow-moving, polythermal and at least partly non-erosive ice, surrounded by faster ice-streams in the Baltic and in the Skagerrak. The ice sheet may have left its main impact on the landscape during short periods during advance and deglaciation only.
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| 7. |
- Andersson, Stefan, et al.
(författare)
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Metamorphism and deformation of a Palaeoproterozoic polymetallic sulphide-oxide mineralisation : Hornkullen, Bergslagen, Sweden
- 2016
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 138:3, s. 410-423
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Tidskriftsartikel (refereegranskat)abstract
- The Hornkullen mineralisation is situated in the westernmost part of the Bergslagen ore province, south-central Sweden. Here, polymetallic sulphides and oxides are hosted by an inlier of Svecofennian, c. 1.9Ga skarn-bearing metavolcanic units, enclosed in the c. 1.8Ga Filipstad granite belonging to the Transscandinavian Igneous Belt. The Ag- and Au-bearing mineralisation is dominated by veins and impregnations of magnetite, pyrrhotite, galena, chalcopyrite and arsenopyrite with subordinate pyrite, sphalerite, ilmenite, lollingite, Pb-Fe-Ag-Cu-Sb sulphosalts and rare gudmundite, pentlandite and molybdenite. Overall, a detailed textural and mineralogical study of the ore assemblages suggests significant deformation and remobilisation at high temperature, which is corroborated by sulphide geothermobarometry. The arsenopyrite geothermometer yields an average temperature of c. 525 degrees C, which is likely to be the result of metamorphic re-equilibration. Sphalerite geobarometry gives peak pressures of c. 300-400MPa, albeit with caveats. The combined observations suggest that the present mineralogical and textural nature of the ore assemblages at Hornkullen is primarily related to remobilisation during Svecokarelian regional metamorphism of a pre-existing, most likely syn-volcanic mineralisation. This scenario is likely to be applicable to many other Svecofennian metasupracrustal-hosted deposits in the Bergslagen ore province.
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| 8. |
- Andersson, Ulf Bertil, et al.
(författare)
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Emendment to the term complex in: “Guide for geological nomenclature in Sweden” (Kumpulainen 2016)
- 2022
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Ingår i: GFF. - : Taylor & Francis. - 1103-5897 .- 2000-0863. ; 144:3-4, s. 151-151
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Since the publication of Kumpulainen (2016), the Committeehave been alerted by the investigation and subsequent changesto the North American Stratigraphic Code concerning thelithodemic unit“complex”(Easton et al.2016; North Ameri-can Commission on Stratigraphic Nomenclature (NACSN)2017). These changes concern the introduction of the nomen-clature unit“Intrusive Complex”. In the original version(NACSN1983), as well as in the Swedish Guide for nomencla-ture (Kumpulainen2016), the unit“complex”is defined ascontaining at least two genetic classes of rocks, i.e., igneous,sedimentary, or metamorphic.
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| 9. |
- Andréasson, Per Gunnar, et al.
(författare)
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Seve terranes of the Kebnekaise Mts., Swedish Caledonides, and their amalgamation, accretion and affinity
- 2018
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 140:3, s. 264-291
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Tidskriftsartikel (refereegranskat)abstract
- A major allochthon of the Scandinavian Caledonides, the Seve belt has traditionally been considered to be derived from the rifted margin and continent-ocean transition (COT) of Baltica. However, geochronological results obtained from its inferred northern equivalent, the Kalak Nappe Complex (KNC), have been taken to indicate an exotic affinity of this complex and of also Seve terranes, an interpretation adopted in recent palaeogeographic models. In the Kebnekaise Mts., the COT is represented by the Kebnekaise terrane composed of amphibolitized dykes of gabbro and dolerite of depleted magma source and rare felsic and ultramafic rocks. Coronitic dolerite and gabbro with abundant rutile suggest high pressures before or during amalgamation with the underlying Mårma terrane, composed of quartzofeldspathic gneisses intruded by mafic and granitic rocks, the latter including a previously dated c. 845 Ma-old granite. The granite mingled with mildly alkaline dolerites chemically similar to transitional basalts of continental rifts. Following emplacement at shallow (andalusite stability) crustal levels, the igneous complex and host rocks underwent extensive deformation, metamorphism within the sillimanite-kyanite stability field and local migmatization. The Kebnekaise and Mårma terranes amalgamated in early Ordovician as indicated by the U-Pb age of 487±7 Ma obtained from titanite fabrics of deformed granite in thrust vicinity, and by 40Ar-39Ar results. The pressure increase in both terranes suggests that amalgamation occurred during initial subduction and imbrication. Correlation of the Mårma terrane with the KNC is discussed. Results obtained in this study give no reason to ascribe an exotic affinity to the Seve terranes of the Kebnekaise Mts.
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| 10. |
- Andréasson, Per Gunnar
(författare)
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The continent-ocean (Seve-Köli) boundary in the Sarek-Padjelanta Mts. revisited : Swedish Caledonides
- 2020
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 142:2, s. 125-138
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Tidskriftsartikel (refereegranskat)abstract
- In the Swedish Caledonides, the continent-ocean boundary is represented by the basal thrust of the Iapetus-derived Köli Nappe Complex (KNC) which overlies the Seve Nappe Complex (SNC) derived from the outer rifted margin of Baltica and the continent-ocean transition (COT). Current maps and literature subdivide the Seve teconostratigraphy in northern Sweden (Sarek-Padjelanta region) into three mega-lenses, the lowest of which (Vaimok lens) is composed of quartz-feldspathic gneisses and subordinate marble, all hosting eclogites. It is overlain by the Sarek lens composed of a COT dyke complex and, along its western margin, a narrow belt of phyllites, schists, quartzite, marbles and greenschists. Overlying this belt is Tsäkkok lens of the same composition as the Vaimok lens. The situation with an intermediate-pressure and often excellently preserved sheeted-dyke complex intercalated between two lenses of complexly deformed high-pressure rocks invited to intricate models of accretion, including out-of-sequence stacking of slices of the continental margin during early Ordovician subduction. Based on a detailed study of a select area and examination of the evolution of previous concepts, this study reinterprets the narrow belt along the western margin of the Sarek Lens as typical of the lower KNC. The favoured explanation of the presence of intermediate-pressure Köli rocks below high-pressure Seve rocks is recumbent folding and/or mega-sheath folding of the Seve-Köli nappe sequence during Scandian (Siluro-Devonian) accretion, by analogy with the situation in places in the central Swedish Caledonides. Previous models of early out-of-sequence stacking during subduction of the continental margin need reconsideration.
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