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  • 1. Bingen, B.
    et al.
    Corfu, F.
    Stein, H.J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    U-Pb geochronology of the syn-orogenic Knaben molybdenum deposits, Sveconorwegian orogen, Norway2015In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 152, p. 537-556Article in journal (Refereed)
    Abstract [en]

    Paired isotope dilution – thermal ionization mass spectrometry (ID-TIMS) and secondary ion mass spectrometry (SIMS) zircon U–Pb data elucidate geochronological relations in the historically important Knaben molybdenum mining district, Sveconorwegian Orogen, south Norway. This polyphase district provided c. 8.5 Mt of ore with a grade of 0.2%. It consists of mineralized quartz veins, silica-rich gneiss, pegmatites and aplites associated with a heterogeneous, locally sulphide-bearing, amphibolites facies gneiss called Knaben Gneiss, and hosted in a regional-scale monotonous, commonly weakly foliated, granitic gneiss. An augen gneiss at the Knaben I deposit yields a 1257±6 Ma magmatic zircon age, dating the pre-Sveconorwegian protolith of the Knaben Gneiss. Mineralized and non-mineralized granitic gneiss samples at the Knaben II and Kvina deposits contain some 1488–1164 Ma inherited zircon and yield consistent intrusion ages of 1032±4, 1034±6 and 1036±6 Ma. This age links magmatism in the district to the regional 1050–1020 Ma Sirdal I-type granite suite, corresponding to voluminous crustal melting during the Sveconorwegian orogeny. A high-U, low-Th/U zircon rim is present in all samples. It defines several age clusters between 1039±6 and 1009±7 Ma, peaking at c. 1016 Ma and overlapping with a monazite age of 1013±5 Ma. The rim records protracted hydrothermal activity, which started during the main magmatic event and outlasted it. This process was coeval with regional high-grade Sveconorwegian metamorphism. Molybdenum deposition probably started during this event when silica-rich mineralizing fluids or hydrous magmas were released from granite magma batches. An analogy between the Knaben district and shallow, short-lived porphyry Mo deposits is inappropriate.

  • 2.
    Dahlin, Peter
    et al.
    Uppsala Universitet.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    Andersson, Ulf Bertil
    LKAB.
    Source character, mixing, fractionation and alkali metasomatism in Palaeoproterozoic greenstone dykes, Dannemora area, NE Bergslagen region, Sweden2014In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 151, no 4, p. 573-590Article in journal (Refereed)
    Abstract [en]

    The geochemical and isotopic characteristics of metamorphosed Svecofennian mafic dykes from the Dannemora area in the NE part of the Bergslagen region in central Sweden were investigated and compared to mafic intrusive rocks in their vicinity. The dykes, with an inferred age of c. 1860–1870 Ma, are calc-alkaline, sub-alkaline and basaltic in composition and have a mixed subduction and within-plate geochemical affinity. They are the result of mixing of at least three mantle source components with similar basaltic major element composition, but different concentrations of incompatible trace elements. Magma M1 is strongly enriched both in Rare Earth Elements (REE) and High-Field-Strength Elements (HFSE); magma M2 is highly enriched in Large-Ion Lithophile Elements (LILE, except Sr) with only moderate enrichment in HFSE and REE (particularly low in Heavy Rare Earth Elements); and magma M3 is enriched in Sr and has a flat REE profile. Magma M3 also has a somewhat more positive (depleted) initial εNd value of +1.8, compared to +0.4 to +0.5 for magmas M1 and M2. The magma evolution was controlled by a mixture of fractionation (mainly affecting the compatible elements) and mixing, best seen in the incompatible element concentrations and the Nd isotope data. The basaltic overall composition indicates little or no wholesale contamination by upper continental crust, but the dykes have undergone later metasomatic changes mainly affecting the alkali elements.

  • 3. Devaere, Lea
    et al.
    Skovsted, Christian
    Swedish Museum of Natural History, Department of Paleobiology.
    New early Cambrian sclerites of Lapworthella schodakensis from NE Greenland: advancements in knowledge of lapworthellid taxonomy, sclerite growth and scleritome organization2017In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 154, no 5, p. 1061-1072Article in journal (Refereed)
    Abstract [en]

    The Cambrian Stage 4 upper Bastion Formation of Albert Heim Bjerge and CH Ostenfeld Nunatak, NE Greenland, yielded 34 excellently preserved sclerites of Lapworthella schodackensis among other small shelly fossils. Lapworthellids have been interpreted as members of the camenellans,a basal tommotiid group. Little is known about this group although the morphological andultrastructural features of their sclerites allow a potential reconstruction of a lophophorate body plan.The exquisite material from Greenland provides significant new data for the revision of the species taxonomy, but also for the comprehension of the scleritome structure of lapworthellids and the modeof formation of their sclerites. Two morphotypes of L. schodackensis sclerites are identified: one with asimple apex, occurring in sinistral and dextral forms; and one bilaterally symmetrical sclerite with twoapices. All bear a similar ornamentation constructed of repeated growth sets consisting of a reticulate inter-rib groove with tubercles, a densely denticulate rib and a striated sub-rib area. The new data onthe ornamentation and observations of the laminar shell microstructure of L. schodackensis enable us to improve the reconstruction of growth in lapworthellids. Finally, the morphological features of the two types of sclerites provide new information for the reconstruction of the bilaterally symmetrical multi-component lapworthellid scleritome with evidence of the fusion of adjacent sclerites duringearly ontogeny.

  • 4.
    Edirisooriya, Geetha
    et al.
    Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka.
    Dharmagunawardhane, H.A.
    Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka.
    McLoughlin, Stephen
    Swedish Museum of Natural History, Department of Paleobiology.
    The first record of the Permian Glossopteris flora from Sri Lanka: implications for hydrocarbon source rocks in the Mannar Basin2018In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 155, p. 907-920Article in journal (Refereed)
    Abstract [en]

    Strata exposed near Tabbowa Tank, Tabbowa Basin, western Sri Lanka have yielded the

    first representatives of the distinctive Permian Glossopteris flora from that country. The assemblage

    includes gymnosperm foliage attributable to Glossopteris raniganjensis, roots referable to Vertebraria

    australis, seeds assigned to Samaropsis sp., sphenophyte axes (Paracalamites australis) and

    foliage (Sphenophyllum emarginatum), and fern foliage (Dichotomopteris lindleyi). This small macroflora

    is interpreted to be of probable Lopingian (late Permian) age based on comparisons with the

    fossil floras of Peninsula India. Several Glossopteris leaves in the assemblage bear evidence of terrestrial

    arthropod interactions including hole feeding, margin feeding, possible lamina skeletonization,

    piercing-and-sucking damage and oviposition scarring. The newly identified onshore Permian strata

    necessitate re-evaluation of current models explaining the evolution of the adjacent offshore Mannar

    Basin. Previously considered to have begun subsiding and accumulating sediment during Jurassic

    time, we propose that the Mannar Basin may have initiated as part of a pan-Gondwanan extensional

    phase during late Palaeozoic – Triassic time. We interpret the basal, as yet unsampled, seismically

    reflective strata of this basin to be probable organic-rich continental strata of Lopingian age, equivalent

    to those recorded in the Tabbowa Basin, and similar to the Permian coal-bearing successions

    in the rift basins of eastern India and Antarctica. Such continental fossiliferous strata are particularly

    significant as potential source rocks for recently identified natural gas resources in the Mannar

    Basin.

  • 5. Jacquet, Sarah, M.
    et al.
    Brougham, Thomas
    Skovsted, Christian
    Swedish Museum of Natural History, Department of Paleobiology.
    Jago, James, B.
    Laurie, John, R.
    Betts, Marissa, J.
    Topper, Timothy, P.
    Brock, Glenn, A.
    Watsonella crosbyi from the lower Cambrian (Terreneuvian, Stage 2) Normanville Group in South Australia2016In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, p. 1-17Article in journal (Refereed)
    Abstract [en]

    Correlation of lower Cambrian strata is often confounded by provincialism of key fauna. The widespread occurrence of themicromollusc Watsonella crosbyi Grabau, 1900 is therefore an important biostratigraphic signpost with potential for international correlation of lower Cambrian successions. Previous correlations of W. crosbyi from Australia (Normanville Group) suggested an Atdabanian- to Botoman-equivalent age. However, in the upper part of the Mount Terrible Formation, stratigraphic ranges of W. crosbyi and Aldanella sp. cf. golubevi overlap prior to the incoming of vertically burrowed ‘piperock’, which is indicative of an age no earlier than Cambrian Stage 2. The stratigraphic range of W. crosbyi in the Normanville Group, South Australia correlates with the ranges of the taxon in China, France, Mongolia and Siberia (though not Newfoundland). The new Australian data add further support for considering the first occurrence of W. crosbyi a good potential candidate for defining the base of Cambrian Stage 2. The stratigraphic range of W. crosbyi through the lower Cambrian Normanville Group has been determined based on collections from measured sections. Although rare, W. crosbyi is part of an assemblage of micromolluscs including Bemella sp., Parailsanella sp. cf. murenica and a sinistral form of Aldanella (A. sp. cf. A. golubevi). Other fauna present include Australohalkieria sp., Eremactis mawsoni, chancelloriids and Cupitheca sp.

  • 6.
    Jagt, John
    et al.
    Natuurhistorisch Museum Maastricht.
    Thuy, Ben
    Geoscience Centre, University of Göttingen.
    Donovan, Stephen K.
    Naturalis Biodiversity Centre, Leiden.
    Stöhr, Sabine
    Swedish Museum of Natural History, Department of Zoology.
    Portell, Roger W.
    Pickerill, Ron K.
    Harper, David A. T.
    Lindsay, William
    Jackson, Trevor A.
    A starfish bed in the Middle Miocene Grand Bay Formation of Carriacou, The Grenadines (West Indies)2014In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 151, no 3, p. 381-393Article in journal (Refereed)
  • 7.
    Kenny, Gavin
    et al.
    Swedish Museum of Natural History, Department of Geology.
    O'Sullivan, Gary
    Department of Geology, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland.
    Alexander, Stephen
    Department of Geology, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland.
    Simms, Michael
    Department of Natural Sciences, National Museums Northern Ireland, Cultra, BT18 0EU Northern Ireland, UK.
    Chew, David
    Department of Geology, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland.
    Kamber, Balz
    School of Earth, Environmental and Biological Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4001, Australia.
    On the track of a Scottish impact structure: a detrital zircon and apatite provenance study of the Stac Fada Member and wider Stoer Group, northwest Scotland2019In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 156, p. 1863-1876Article in journal (Refereed)
  • 8.
    Li, Liqin
    et al.
    State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China.
    Wang, Yongdong
    State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China.
    Vajda, Vivi
    Swedish Museum of Natural History, Department of Paleobiology. Department of Geology, Lund University, Sweden.
    Liu, Zhaosheng
    State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China.
    Late Triassic ecosystem variations inferred by palynological records from Hechuan, southern Sichuan Basin, China2018In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 155, p. 1793-1810Article in journal (Refereed)
    Abstract [en]

    The Late Triassic deposits of the Sichuan Basin, southwestern China are significant for hosting abundant and diverse fossil assemblages including plants (containing spores and pollen), bivalves and insects. However, the Late Triassic palaeoecological variations are still poorly documented in this region. Here we present results from a palynological study from the Upper Triassic Xujiahe Formation in Hechuan of Chongqing, southern Sichuan Basin. The palynological analysis revealed a well-preserved terrestrial palynoflora of high diversity, comprising 184 species in 75 genera of spores and pollen. Three palynological assemblages were recognized, reflecting terrestrial successions throughout the entire interval with significant changes in the vegetation. Cycads/bennettites/ginkgophytes and conifers show an increasing trend into younger deposits, while ferns and lycopsids decrease in relative abundance. The Late Triassic vegetation underwent changes from lowland fern forest to a mixed forest with more canopy trees. We applied the Spore-pollen Morphological Group (SMG) method and Sporomorph EcoGroup (SEG) model to interpret the palaeoclimate features. The results reveal that the lower part of the Xujiahe Formation was deposited under relatively warm and humid conditions with an overall cooling and drying trend from latest Norian to Rhaetian time, accompanied by a general decrease of ferns and simultaneous increase of gymnosperms, and a decline in diversity of miospores. This study presents data on variations within the terrestrial ecosystem prior to the end-Triassic extinction event in the Sichuan Basin, and therefore provides important information for understanding the changes in the vegetation preceding the end-Triassic event.

  • 9. Walczak, Katarzyna
    et al.
    Cuthbert, Simon
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology.
    Majka, Jarosław
    Smit, Matthijs A.
    U–Pb zircon age dating of diamond-bearing gneiss from Fjørtoft reveals repeated burial of the Baltoscandian margin during the Caledonian Orogeny2019In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 156, no 11Article in journal (Refereed)
    Abstract [en]

    The first find of microdiamond in the Nordøyane ultra-high-pressure (UHP) domain of the Western Gneiss Region (WGR) of the Scandinavian Caledonides reshaped tectonic models for the region. Nevertheless, in spite of much progress regarding the meaning and significance of this find, the history of rock that the diamonds were found in is complex and still largely ambiguous. To investigate this, we report U–Pb zircon ages obtained from the exact crushed sample material in which metamorphic diamond was first found. The grains exhibit complicated internal zoning with distinct detrital cores overgrown by metamorphic rims. The cores yielded a range of ages from the Archaean to the late Neoproterozoic / early Cambrian. This detrital zircon age spectrum is broadly similar to detrital signatures recorded by metasedimentary rocks of the Lower and Middle allochthons elsewhere within the orogen. Thus, our dating results support the previously proposed affinity of the studied gneiss to the Seve–Blåhø Nappe of the Middle Allochthon. Metamorphic rims yielded a well-defined peak at 447 ± 2 Ma and a broad population that ranges between c. 437 and 423 Ma. The data reveal a prolonged metamorphic history of the Fjørtoft gneiss that is far more complex then would be expected for a UHP rock that has seen a single burial and exhumation cycle. The data are consistent with a model involving multiple such cycles, which would provide renewed support for the dunk tectonics model that has been postulated for the region.

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