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  • 1.
    Agić, Heda
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Moczydłowska, Małgorzata
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Yin, Leiming
    Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences.
    Diversity of organic-walled microfossils from the early Mesoproterozoic Ruyang Group, North China Craton - a window into the early eukaryote evolution2017In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, p. 101-130Article in journal (Refereed)
    Abstract [en]

    Mesoproterozoic Era was an important time for the initial diversification of eukaryotic groups and the appearance of the first complex morphologies. While eukaryotes evolved around 2.4 Ga, the first microfossils with ornamentation and sculpture occur in the 1.8-1.6 Ga successions worldwide. Shales and siltstones of the Ruyang Group, Shanxi Province, North China Craton, record a high diversity of such organic-walled microfossils. Recently, the depositional ages of this succession has been constrained to 1.75-1.40 Ga via   zircon U-Pb dating. This dating extends back the time of the first appearance of complex eukaryotic characters (e.g. processes, complex wall structure) in the fossil record. We have conducted a biostratigraphic investigation on of the samples throughout the fossiliferous Ruyang Group to provide an estimate of the early eukaryotic diversity in the Mesoproterozoic. Light- and scanning electron microscope studies have documented 26 species, including several that are reported for the first time, and some that were previously known only from younger, Neoproterozoic strata. Fossil diversity is high in the upper Baicaoping Formation, declines in the middle and reaches its peak in the upper Beidajian Formation. Novel morphologies among the unicellular Ruyang biota include a variety of processes, from tube-like extensions to hirsute spines, vesicles with velutinous outer membranes, as well as numerous specimens with internal bodies of varying sizes. We have also recorded the globally distributed Mesoproterozoic taxa Dictyosphaera, Shuiyousphaeridium, and Tappania. Key characters displayed by the Ruyang biota are consistent with reproductive structures (especially cysts among modern protists. These microfossils provide an additional evidence for the emergence of the crown group Eukarya by 1.7-1.4 Ga.

  • 2.
    Bauer, Tobias
    et al.
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Skyttä, Pietari
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Allen, Rodney
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Weihed, Pär
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Syn-extensional faulting controlling structural inversion: Insights from the Palaeoproterozoic Vargfors syncline, Skellefte mining district, Sweden2011In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 191, no 3-4, p. 166-183Article in journal (Refereed)
    Abstract [en]

    The Vargfors basin in the central Skellefte district, Sweden, is an inverted sedimentary sub-basin within a Palaeoproterozoic (1.89 Ga) marine volcanic arc. The sub-basin formed from upper-crustal extension and subsequent compression, following a period of intense marine volcanism and VMS ore formation. Detailed mapping and structural analysis reveals a pattern of SE–NW-striking normal faults and interlinked NE–SW-striking transfer faults, which define distinct fault-bound compartments, each with an individual structural geometry and stratigraphy. Constraints on the deformation style and mechanisms achieved by 2D forward modelling are in agreement with the previously inferred inversion of the early normal faults during a regional crustal shortening event. A rheologically weak carbonate-rich layer at the base of the sedimentary sequence favoured the fault inversion over more distributed shortening as the controlling deformation mechanism. Transposition of sedimentary strata into the approximately SE–NW faults led to formation of asymmetric synclines that were tightened during progressive shortening. Structural analysis infers a progressive opening of the basin towards SE and NW with time. Furthermore, it is inferred that a displacement gradient was developed along the main structural grain, with decreasing dip-slip displacements towards SE and NW, both during the extension and the structural inversion.VMS deposits in the vicinity of the contact between the volcanic and the overlying sedimentary rocks were formed along early normal faults, which reacted as fluid conduits. Subsequently, the deposits were transposed into the inverted faults during crustal shortening. Consequently, the inverted faults provide a useful tool for mineral exploration in the district.

  • 3. Be'eri-Shlevin, Yaron
    et al.
    Gee, David G.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Claesson, Stefan
    Ladenberger, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Kirkland, Chris
    Robinson, Peter
    Frei, Dirk
    Provenance of Neoproterozoic sediments in the Sarv nappes (Middle Allochthon) of the Scandinavian Caledonides: LA-ICP-MS and SIMS U-Pb dating of detrital zircons2011In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 187, no 1-2, p. 181-200Article in journal (Refereed)
    Abstract [en]

    We present U-Pb age data for detrital zircons from dike-intruded Neoproterozoic sedimentary rocks of the Caledonian Middle Allochthon in central Sweden and Norway. Detrital zircons from 11 samples from the Sarv, Saetra and upper Leksdal nappes (informally referred to as the Sarv nappes) are clustered within ca. 0.9-1.75 Ga, but display a bimodal distribution with major ca. 1.45-1.75 Ga and ca. 0.9-1.2 Ga components. An apparent increase of younger (0.9-1.2 Ga) components to the northwest reflects varying source terranes. Detrital zircons from an additional sample from the lower part of the Leksdal Nappe, of uncertain affiliation to the Sarv has a prominent 1.75-1.85 Ga component supporting previous suggestions that this part of the nappe belonged to a more proximal basin. Comparison of the Sarv age probability patterns with data from basement windows and basement slices within the Middle Allochthon in central Sweden and Norway supports the derivation of the sediments from the attenuated Baltican continental crust on which they were presumably deposited. Similar comparisons suggest that derivation from the southern segment of the Fennoscandian Shield or from eastern segments of Laurentia is less likely, mostly because they include also older components. We infer that the ca. 200 km wide belt of attenuated Baltican continental crust included northern extensions of Mesoproterozoic to early Neoproterozoic terranes exposed in the southern part of the Fennoscandian Shield and the easternmost part of Laurentia, which at ca. 900 Ma were still adjacent. Pre-1.75 Ga terranes of the Fennoscandian Shield were probably isolated from the Sarv distal basin(s) by intracratonic basins and uplifted margins associated with early development of this extended continental crust. The significantly older ages in the lower part of the Leksdal Nappe and its inferred more proximal position support this model. The proposed northern extension of Mesoproterozoic-early Neoproterozoic terranes can explain in a simpler way the occurrence of such detritus in many Caledonide-Appalachian allochthons exposed at the margins of the North Atlantic, with no need to infer large displacement along the axis of the Caledonide Orogen or to postulate selective transport of Grenville-age material from the south over large distances.One of our Sarv samples located at the Norwegian coast revealed Caledonian reworking at ca. 395 Ma. This age agrees with ages of late-tectonic amphibolite-facies metamorphism and pegmatite intrusion recorded in this part of the Caledonides.

  • 4. Bergman, S.
    et al.
    Högdahl, K.
    Nironen, M.
    Ogenhall, E.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Sjöström, H.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Lundqvist, L.
    Lahtinen, R.
    Timing of Palaeoproterozoic intra-orogenic sedimentation in the central Fennoscandian Shield; evidence from detrital zircon in metasandstone2008In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 161, no 3-4, p. 231-249Article in journal (Refereed)
    Abstract [en]

    Detrital zircon U-Pb SIMS data on quartz-rich metasandstone units presumed to belong to the upper part of the Svecofennian stratigraphy in southeastern Finland and east-central Sweden suggest the existence of clastic sedimentary basins between the two main orogenic phases at 1.89-1.86 Ga and 1.83-1.79 Ga, during a period referred to as the intra-orogenic phase (1.86-1.83 Ga). Stratigraphically below the metasandstone at Hamrange, east-central Sweden, is a metadacite with an U-Pb zircon TIMS age of 1888 +/- 6 Ma, which indicates the maximum age of sedimentation. It also indicates that an earlier proposed correlation of Hamrange metavolcanic rocks and 1.86Ga equivalents at Los to the northwest must be rejected. Instead, there is a temporal affinity to the metavolcanic rocks in the Bergslagen Province to the south or Southern Finland to the east. Quartz-rich metasandstone samples from four localities, Luukkola, Pyhantaka and Tiirismaa in Finland and Hamrange in Sweden, yield multimodal detrital zircon age distributions with main populations at 2.95-2.60 Ga, 2.10-1.95 Ga and 1.92-1.85 Ga. The groups are similar in all four samples, and they are comparable to previously reported detrital ages in this part of the Fennoscandian Shield. The oldest zircon analysed gave an age of 3.32 Ga (Tiirismaa). The maximum ages of sedimentation (and of subsequent deformation and metamorphism), indicated by the youngest detrital zircon, from the four localities are 1842 10 Ma (Luukkola), 1865 +/- 11 Ma (Pyhantaka), 1848 +/- 13 Ma (Tiirismaa), and 1855 10 Ma (Hamrange), respectively. Possible source rocks for these zircon grains are found within and around the vast Ljusdal Batholith in Sweden, and in the Arc Complexes of Western and Southern Finland. It is concluded that several intra-orogenic sedimentary basins existed during the time interval 1.86-1.83 Ga ago, between two major orogenic events in the Fermoscandian Shield.

  • 5. Bingen, B.
    et al.
    Nordgulen, O
    Sigmond, E.M.O.
    Tucker, R.
    Mansfeld, J.
    Högdahl, Karin
    Relations between 1.19-1.13 Ga continental magmatism, sedimentation and metamorphism, Sveconorwegian province, S. Norway2003In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 124, no 2-4, p. 215-241Article in journal (Refereed)
    Abstract [en]

    The Sveconorwegian and Grenville orogenic belts display widespread 1.19–1.13 Ga Early Grenvillian continental magmatism including A-type granitoids. In the Sveconorwegian province, S Norway, bimodal 1.17–1.14 Ga metavolcanic rocks of the Telemark sector are part of this magmatism. Volcanic rocks in low- to medium-metamorphic grade are interlayered with immature and locally conglomeratic clastic metasediments and covered by a thick metasedimentary sequence. Minor unconformities are reported. New zircon U–Pb data are presented and integrated in a revised stratigraphy of the Telemark supracrustal rocks. A metarhyodacite at the base of the Nore group yields a crystallisation age of 1169±9 Ma and displays 1.7–1.5 Ga inherited zircon grains (SIMS data). A metarhyolite situated below sandstone of the Heddal group yields a crystallisation age of 1159±8 Ma. In the cover sequence, a metasandstone of the Heddal group has detrital zircon grains in the intervals 2.86–2.41 and 1.94–1.11 Ga (34 analysed grains) and a metasandstone of the Kalhovd formation in the intervals 2.85–2.74 and 2.00–1.05 Ga (41 analysed grains). These metasediments were deposited after 1121±15 Ma and 1065±11 Ma, respectively and were transformed by 1.01 Ga Late Sveconorwegian deformation and metamorphism. The metasedimentary rocks contain a significant amount of regionally derived clasts. Two deformed A-type granite metaplutons yield zircon U–Pb intrusion ages of 1146±5 Ma (Eiddal) and 1153±2 Ma (Haglebu, ID–TIMS data). The 1.19–1.13 Ga magmatism is distributed in the western part of the Sveconorwegian province, in the Telemark, Bamble and Rogaland–Vest Agder sectors, indicating that these sectors were part of a single plate at that time, which is characterised by a thin lithosphere today. The A-type geochemical signature of the felsic magmatism and the continental lithosphere signature of the associated mafic volcanism point to a continental non-compressional tectonic regime. The overlap in time between widespread 1.19–1.13 Ga continental magmatism, intermontane basin formation and Early Sveconorwegian 1.15–1.12 Ga granulite-facies metamorphism recorded in the Bamble sector suggest a thermal pulse linked to upflow of asthenospheric mantle. Deposition of the cover of clastic sediments between 1.12 and 1.01 Ga possibly reflects thermal subsidence after the 1.19–1.13 Ga event and before the Late Sveconorwegian (1.03–0.95 Ga) orogenic phases. An analogy between the 1.19–1.13 Ga evolution of the Sveconorwegian province and the Cenozoic formation of the Basin and Range province in USA is discussed.

  • 6. Boskabadi, Ahmad
    et al.
    Pitcairn, Iain K.
    Stern, Robert J.
    Ayer, Mokhles K.
    Broman, Curt
    Mohamed, Fathz H.
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Carbonatite crystallization and alteration in the Tarr carbonatite–albitite complex, Sinai Peninsula, Egypt2013In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 239, p. 24-41Article in journal (Refereed)
    Abstract [en]

    Carbonate dykes occurring in the Arabian-Nubian Shield (ANS) are clearly intrusive in origin and carbonatites according to the IUGS classification, yet previous investigations refer to them as “intrusive carbonates”, due mainly to their low Sr, Ba, Nb, Y, Th and rare earth element (REE) contents. The Tarr carbonatite albitite complex (TCA) in SE Sinai, Egypt contains a series of small (<1.2 km2) albitite intrusions surrounded by small veins and dykes of carbonatite, which occur predominantly in a narrow zone of brecciation surrounding the intrusions. Fennitic alteration surrounding TCA has been reported but there is little consensus on the extent and origin of this alteration. Fennitic alteration surrounding the TCA carbonatites is not abundant. Alteration is dominated by precipitation of carbonates in the breccia zone surrounding the albitite intrusion with associated actinolite, chlorite, sericite and epidote. Geochemical compositions are consistent with addition of carbonates and associated secondary minerals because the altered rocks contain higher CaO, MgO, Fe2O3 and MnO and lower SiO2, Al2O3, Na2O and K2O compared to their less altered rocks. Fluid inclusion investigations show that the carbonatite magma contained a high-salinity H2O–CO2–NaCl–CaCl2fluid, although the lack of fennitic alteration implies that this fluid was not abundant. The crystallization conditions of the carbonatite dykes and carbonatite matrix in the breccia zones have been constrained using Zr-in-rutile thermometry and fluid inclusion microthermometry. Crystallization of the carbonatite in the dykes and in the breccia zone occurred between 565 ± 38 °C and 420–480 °C, respectively and at 0.75–1.3 kbar, which corresponds to a depth of 2.8–4.9 km. Rutile hosted within the carbonatite crystallized earlier at high temperature and the carbonate matrix crystallized later after cooling. Immiscible fluid from carbonatite magma would have altered the surrounding country rocks at lower temperature (between 400 °C and 150 °C deduced from the fluid inclusion thermometry) after the intrusion of the carbonatite melt.

  • 7. Boskabadi, Ahmad
    et al.
    Pitcairn, Iain K.
    Stern, Robert J.
    Azer, Mokhles K.
    Broman, Curt
    Mohamed, Fathy H.
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Carbonatite crystallization and alteration in the Tarr carbonatite-albitite complex, Sinai Peninsula, Egypt2013In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 239, p. 24-41Article in journal (Refereed)
    Abstract [en]

    Carbonate dykes occurring in the Arabian-Nubian Shield (ANS) are clearly intrusive in origin and carbonatites according to the IUGS classification, yet previous investigations refer to them as "intrusive carbonates", due mainly to their low Sr, Ba, Nb, Y,Th and rare earth element (REE) contents. The Tarr carbonatite albitite complex (TCA) in SE Sinai, Egypt contains a series of small (<1.2 km(2)) albitite intrusions surrounded by small veins and dykes of carbonatite, which occur predominantly in a narrow zone of brecciation surrounding the intrusions. Fennitic alteration surrounding TCA has been reported but there is little consensus on the extent and origin of this alteration. Fennitic alteration surrounding the TCA carbonatites is not abundant. Alteration is dominated by precipitation of carbonates in the breccia zone surrounding the albitite intrusion with associated actinolite, chlorite, sericite and epidote. Geochemical compositions are consistent with addition of carbonates and associated secondary minerals because the altered rocks contain higher CaO, MgO, Fe2O3 and MnO and lower SiO2, Al2O3, Na2O and K2O compared to their less altered rocks. Fluid inclusion investigations show that the carbonatite magma contained a high-salinity H2O-CO2-NaCl-CaCl2 fluid, although the lack of fennitic alteration implies that this fluid was not abundant. The crystallization conditions of the carbonatite dykes and carbonatite matrix in the breccia zones have been constrained using Zr-in-rutile thermometry and fluid inclusion microthermometry. Crystallization of the carbonatite in the dykes and in the breccia zone occurred between 565 +/- 38 degrees C and 420-480 degrees C, respectively and at 0.75-1.3 kbar, which corresponds to a depth of 2.8-4.9 km. Rutile hosted within the carbonatite crystallized earlier at high temperature and the carbonate matrix crystallized later after cooling. Immiscible fluid from carbonatite magma would have altered the surrounding country rocks at lower temperature (between 400 degrees C and 150 degrees C deduced from the fluid inclusion thermometry) after the intrusion of the carbonatite melt.

  • 8.
    Gee, David G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Andreasson, Per-Gunnar
    Lund Univ, Dept Geol, Lund, Sweden..
    Lorenz, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Frei, Dirk
    Univ Stellenbosch, Matieland, South Africa..
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, PL-30059 Krakow, Poland..
    Comments to "Detrital zircon signatures of the Baltoscandian margin along the Arctic Circle Caledonides in Sweden: The Sveconorwegian connection" by Gee et al. (2015) Reply to Ake Johansson (Precambrian Research)2016In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 276, p. 236-237Article in journal (Refereed)
  • 9.
    Gee, David Godfrey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Per-Gunnar, Andréasson
    Lund University.
    Lorenz, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Frei, Dirk
    Stellenbosch University.
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Detrital zircon signatures of the Baltoscandian margin along the Arctic Circle Caledonides in Sweden: The Sveconorwegian connection2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 265, p. 40-56Article in journal (Refereed)
    Abstract [en]

    New evidence is presented here that the Sveconorwegian Orogen continued northwards from type areas in southwestern Scandinavia along the Baltoscandian outer margin into the high Arctic. The Silver Road (Silvervägen) profile through the Scandinavian Caledonides, located in Sweden along the Arctic Circle at 66–67◦ N, provides a full section through the tectonostratigraphy of the Baltoscandian margin from the Autochthon, via the Lower Allochthon to the upperment parts of the Middle Allochthon. Metamorphic grade increases upwards through the nappes, being low greenschist facies at lowest levels and increas- ing to eclogite grade in the highest parts of the Seve Nappe Complex, the latter being related to early Ordovician subduction of the Baltoscandian outermost margin. The sedimentary rocks range in age from Neoproterozoic to Ordovician and provide evidence of the changes of environment from the Baltoscan- dian platform, westwards out over the Cryogenian rifted margin to the continent-ocean transition zone; also the Ordovician foreland basin. Twelve samples of psammites from the different tectonostratigraphic levels have yielded U/Pb detrital zircon age-signatures that reflect the changing character of their pro- venance. Autochthonous sandstones are derived from late Paleoproterozoic (1800–1950 Ma) crystalline rocks in the vicinity to the east of the thrust front. Ediacaran-early Cambrian quartzites of the Lower Allochthon also yield mainly late Paleoproterozoic zircon signatures, but with subordinate Mesopro- terozoic and late Archaean populations, whilst mid Ordovician, W-derived foreland basin turbidites are dominated by Sveconorwegian (950–1100 Ma) signatures, with subordinate older Mesoproterozoic to latest Paleoproterozoic populations. All samples from the lower parts of the Middle Allochthon (lacking dolerite dykes) have signatures that are dominated by latest Paleoproterozoic and early Mesoproterozoic ages, with subordinate populations down to Sveconorwegian ages; the latter dominate the overlying Särv nappes and also the Seve Nappe Complex, where c. 945 Ma rhyodacites have been previously reported. This evidence of Sveconorwegian source rocks in the hinterland, taken together with previously pub- lished detrital zircon data farther south and north of the Arctic Circle, clearly favours the interpretation that the Sveconorwegian Orogen, during the Neoproterozoic, extended along the entire Baltoscandian outer margin into the high Arctic.

  • 10.
    Högdahl, Karin
    et al.
    Department of Geology, Lund University, Lund, Sweden.
    Lundqvist, Th.
    Discussion on “Successive ~1.94 Ga plutonism and ~1.92 Ga deformation and metamorphism south of the Skellefte district, northern Sweden: Substantiation of the marginal basin accretion hypothesis of Svecofennian evolution” by T. Skiöld and R.W.R. Rutland, Precambrian Research 148, 181-204, 20062009In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 168, no 3-4, p. 330-334Article in journal (Refereed)
  • 11.
    Jeanneret, Pauline
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Univ Bourgogne Franche Comté, France.
    Goncalves, Philippe
    Univ Bourgogne Franche Comte, Lab Chronoenvironm UMR CNRS 6249, 16 Route Gray, F-25000 Besancon, France..
    Durand, Cyril
    Univ Lille 1, EA Lab Genie Civil & Geoenvironm 4515, F-59655 Villeneuve Dascq, France..
    Poujol, Marc
    Univ Rennes 1, UMR CNRS 6118, Geosci Rennes, OSUR, F-35042 Rennes, France..
    Trap, Pierre
    Univ Bourgogne Franche Comte, Lab Chronoenvironm UMR CNRS 6249, 16 Route Gray, F-25000 Besancon, France..
    Marquer, Didier
    Univ Bourgogne Franche Comte, Lab Chronoenvironm UMR CNRS 6249, 16 Route Gray, F-25000 Besancon, France..
    Quirt, David
    AREVA Resources Canada Inc, 817-45th St West, Saskatoon S7K 3X5, SK, Canada..
    Ledru, Patrick
    AREVA Resources Canada Inc, 817-45th St West, Saskatoon S7K 3X5, SK, Canada..
    Geochronological constraints on the trans-Hudsonian tectono-metamorphic evolution of the pre-Athabasca basement within the Wollaston-Mudjatik Transition Zone, Saskatchewan2017In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 301, p. 152-178Article in journal (Refereed)
    Abstract [en]

    The Hudsonian Pressure-Temperature-Deformation-time-(P-T-D-t) evolution of the pre-Athabasca crystalline basement (>similar to 1700 Ma) of the Wollaston-Mudjatik Transition Zone (WMTZ) highlights two major tectono-metamorphic events Ml-Dl and M2-D2. The ages of these two event have been obtained by in-situ LA-ICPMS U-Th-Pb dating of monazite from Grt-Crd bearing pelitic gneiss and U-Pb analyses performed on zircons from pegmatites, using both exposed basement and drill cores from the Wolly-McClean exploration drilling project. The M1-D1 event, interpreted as the burial of the thinned Hearne margin via southward thrusting to pressures varying from 10 to 6 kbar, occurred between ca.1840 and 1813 Ma. The M2-D2 event, producing the northeast structural trend of the WMTZ, was formed in a sinistral transpressional tectonic regime during the late stage of the Hudsonian oblique collision between ca. 1813 and 1770 Ma. Thermobarometric estimates on the M2-D2 assemblages show that the entire studied area was reequilibrated at about 5 kbar and 750-825 degrees C. trans-Hudsonian pegmatites are viewed as the main proto-ore of the uranium-rich Athabasca unconformity-type deposits. Formation, transfer and differentiation of these trans-Hudsonian pegmatites are replaced in this P-T-D-t evolution. During the 1840-1813 Ma Ml-Dl partial melting event, the first batches of melt produced in the deep crust are the most likely enriched in uranium. Then, these melts were transferred upwards to the upper crustal levels owing to the development of crustal scale steeply-dipping D2 shear zones, and finally were differentiated to form uranium-enriched pegmatites between 1813 and 1770 Ma. Some monazite and zircon grains within retrogressed migmatites recorded a later event at ca. 1720 Ma, interpreted as the terminal cooling event down to 300-400 degrees C responsible for partial retrogression of metamorphic assemblages. This age provides new insights into the timing of the onset of the Athabasca sedimentation that should therefore be at least 1710 Ma old or younger.

  • 12.
    Kampmann, Tobias C.
    et al.
    Lulea Univ Technol, Dept Civil Environm & Nat Resources Engn, Div Geosci, SE-97187 Lulea, Sweden..
    Stephens, Michael B.
    Lulea Univ Technol, Dept Civil Environm & Nat Resources Engn, Div Geosci, SE-97187 Lulea, Sweden.;Geol Survey Sweden, Box 670, SE-75128 Uppsala, Sweden..
    Ripa, Magnus
    Geol Survey Sweden, Box 670, SE-75128 Uppsala, Sweden..
    Hellstrom, Fredrik A.
    Geol Survey Sweden, Box 670, SE-75128 Uppsala, Sweden..
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Al Mickiewicza 30, PL-30059 Krakow, Poland..
    Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U-Pb geochronology on zircon and monazite2016In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 278, p. 52-68Article in journal (Refereed)
    Abstract [en]

    U-Th-Pb (zircon and monazite) ion probe data have provided constraints on the timing of emplacement and metamorphism of magmatic rocks close to the Palaeoproterozoic, Falun base metal sulphide deposit in the Bergslagen lithotectonic unit, Fennoscandian Shield, Sweden, and, thereby the timing of mineralisation. Hydrothermal alteration and mineralisation at Falun are constrained to a short interval of several million years between a Pb-207/Pb-206 weighted average age of 1894 +/- 3 Ma for a rhyolitic sub-volcanic rock in the felsic volcanic to sub-volcanic host rock suite, and a Pb-207/Pb-206 weighted average age of 1891 +/- 3 Ma for a post-sulphide, porphyritic dacite dyke. Magmatism also included the emplacement of granite plutons with igneous crystallization ages of 1894 +/- 3, 1894 +/- 2 Ma and 1893 +/- 3 Ma. The felsic sub-volcanic to volcanic activity and the emplacement of dacite dykes and granite plutons overlap in age within their respective analytical uncertainties, indicating hydrothermal alteration and sulphide mineralisation inside a narrow time span of intense magmatic activity, and burial of the supracrustal rocks. Two distinct patchy and homogeneous metamorphic monazite types in a felsic volcanic rock around and hydrothermally altered rocks at the Falun deposit yield Pb-207/Pb-206 weighted average ages of 1831 +/- 8 Ma and 1822 +/- 5 Ma, respectively. These ages fall well within the temporal range of a younger 1.84-1.81 Ga (M-2) metamorphic episode during the 2.0-1.8 Ga Svecokarelian orogeny, with the older episode (M-1) inside the Bergslagen lithotectonic unit at around 1.86 Ga. This shows the major influence of the M-2 event in the north-western part of this unit, leading to a complete resetting of the U-Th-Pb isotope system in monazite.

  • 13. Lahtinen, R.
    et al.
    Huhma, H.
    Lahaye, Y.
    Jonsson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Manninen, T.
    Lauri, L. S.
    Bergman, S.
    Hellstrom, F.
    Niiranen, T.
    Nironen, M.
    New geochronological and Sm-Nd constraints across the Pajala shear zone of northern Fennoscandia: Reactivation of a Paleoproterozoic suture2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 256, p. 102-119Article in journal (Refereed)
    Abstract [en]

    Altogether 1130 U-Pb analyses on zircons from 25 samples across the Pajala shear zone in northern Fennoscandia were performed by LA-ICPMS methodology to study the origin of the zone. The samples were also analyzed for their Sm-Nd isotope systematics and geochemically. The new data is tested with existing geological information to elaborate the provenance and maximum depositional ages, the stratigraphic position of studied samples, and finally to assess the tectonic evolution in the Pajala shear zone area. Chromium-enriched metasedimentary rocks are found within and to the east and west of the N-S trending Pajala shear zone. No material originating from Proterozoic felsic igneous (zircons) or mafic (Sm-Nd) rocks was found in these rocks and thus, only Neoarchean or very early Paleoproterozoic ages of deposition are possible. Our new results indicate that the bimodal 1.99-1.97 Ga supracrustal rocks of the Rovaniemi Supersuite cover a large area east of the Pajala shear zone. Based on the absence of Archean zircons typical of the metasedimentary rocks covering the Archean basement, it seems that the basement and its sedimentary cover were not exposed at the time of deposition of the Rovaniemi Supersuite. The metasedimentary rocks of the Uusivirka Supersuite, located within the Pajala shear zone, vary from hornblende-bearing metasedimentary rocks, metapelite, and meta-arkose to orthoquartzite. Their characteristic features include a dominant Proterozoic zircon population (65-87%), with a high proportion of analyzed grains yielding ages between 1.96 Ga and 1.91 Ga, and maximum depositional ages of 1.92-1.91 Ga. We record at least three metamorphic events; at ca. 1.92-1.90 Ga, ca. 1.85 Ga and at 1.82-1.78 Ga, of which the youngest can possibly be separated into two events at 1.83-1.82 Ga and 1.79-1.77 Ga, respectively. We propose a tectonic model in which continental breakup occurred at 2.1-2.05 Ga, followed by the development of a magmatic arc (Kittila arc) at ca. 2.0 Ga above a subduction zone. Two Archean continental units (Norrbotten and Karelia) collided at ca. 1.92-1.91 Ga, the Kittila arc was obducted upon the Karelia continent as a foreland fold and thrust belt, and the metasedimentary rocks of the Uusivirka Supersuite were emplaced as foreland deposits. The proposed tectonic model is based on the absence of 2.44 Ga layered intrusions, and especially 2.06 Ga rocks and 1.99-1.97 Ga rocks of the Rovaniemi Supersuite that are found only east of the Pajala shear zone. In our model the Pajala shear zone originated as a divergent plate boundary, and was multiply reactivated after continental collision with both lateral and vertical movements.

  • 14.
    Lundberg, Emil
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    High resolution reflection seismic imaging of the Ullared Deformation Zone, southern Sweden2011In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 190, no 1-4, p. 25-34Article in journal (Refereed)
    Abstract [en]

    The Ullared Deformation Zone (UDZ) is one of a few structures worldwide known to contain decompressed eclogite facies rocks of Precambrian age. Given the unique nature of the Ullared eclogites, a 15 km long reflection seismic profile was acquired across the UDZ in April 2007. The principal objective of the profile was to provide geometrical information on the deformation zone at depth. The profile was acquired along a crooked line which gave us the opportunity to extract strike and dip information of reflections from the data-set using non-standard seismic techniques, including a cross-dip correction. This cross-dip correction method proved to be very useful for constraining the geometry of the reflectors at depth. The most recent (from 1997) published geological interpretation of the UDZ area was based on aeromagnetic data and the UDZ was interpreted as a shear zone, or possibly a shear zone system. The seismic data and a detailed aeromagnetic analysis support the interpretation of the UDZ as a shear zone system. Based on differences in reflectivity and geometry, the UDZ can be separated into four different units. The north-easternmost unit is the only one where eclogites have been found so far. Structures of the eclogite bearing unit are interpreted to dip approximately 20-30 degrees towards northeast at depth. 

  • 15.
    Malehmir, Alireza
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tryggvason, Ari
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Lickorish, Henry
    Weihed, Pär
    Luleå University of Technology.
    Regional structural profiles in the western part of the Palaeoproterozoic Skellefte Ore District, northern Sweden2007In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 159, no 1-2, p. 1-18Article in journal (Refereed)
    Abstract [en]

    The Kristineberg mining area is situated in the western part of the Palaeoproterozoic Skellefte Ore District, northern Sweden, and is well known for its VHMS base-metal and gold deposits. This paper presents five upper crustal geological cross sections that have been constructed and mainly constrained by seismic reflection data, potential field modeling as well as geological field observations. These profiles are visualized in 3D to highlight the three dimensionality and internal consistency of structures across the region. The resulting structural model for the Skellefte volcanics and overlying metasediments comprises two thrust-sheets that expose the Skellefte volcanics in the cores of hanging-wall anticlinal structures. A shear-zone is imaged as a band of seismic reflectivity terminated by the southern Revsund granite unit. Another shear-zone, possibly a continuation of the Skellefte Shear Zone (SSZ) runs through the centre of the region and accounts for some of the structural complexity and shearing observed between the two anticlinal exposures of the volcanics. Additional smaller scale shear-zones have been identified from geological and geophysical mapping within the main structural blocks of the Skellefte volcanics. The Mala volcanic rocks in the north are separated from the Skellefte volcanics by a fault that cuts discordant to the strike of the Mala volcanics. A structural basement has been proposed to the Skellefte volcanics, constrained by seismic reflection data. Exposures of Bothnian Basin rocks south of the Revsund granite outcrops, suggest that the domain beneath the north dipping reflectivity is associated with Bothnian Basin stratigraphy. The preferred interpretation for the contact between the Skellefte volcanics and the Bothnian Basin rocks is a thrust fault that brings the felsic volcanic rocks over the metasedimentary domain. The Revsund granites are divided into two major groups based on their present day thickness and shapes. Although parts of the Viterliden intrusion are almost undeformed, it is cut by a series of shear-zones, causing the magnetic lineations seen within these rocks. The structural profiles presented demonstrate that the Kristineberg ore is situated in the northern limb of a local synformal structure. The new crustal-scale structural model demonstrates the potential of integrating geophysical and geological data when modelling structures hosting mineralization in a complex region like the Skellefte District. The structural profiles presented in this paper, have greatly improved our understanding of the 3D tectonostratigraphy and architecture of the poly-deformed ca. 1.9 Ga the Skellefte Ore District.

  • 16.
    Meinhold, Guido
    et al.
    Keele Univ, Sch Geog Geol & Environm, Keele ST5 5BG, Staffs, England;Univ Gottingen, Dept Sedimentol & Environm Geol, Goldschmidtstr 3, D-37077 Gottingen, Germany.
    Jensen, Soren
    Univ Extremadura, Area Paleontol, Fac Ciencias, Ave Fis, E-06006 Badajoz, Spain.
    Hoyberget, Magne
    Rennesveien 14, N-4513 Mandal, Norway.
    Arslan, Arzu
    Newcastle-under-Lyme, Staffordshire ST5 2ND, UK.
    Ebbestad, Jan Ove R.
    Uppsala University, Music and Museums, Museum of Evolution.
    Hogstrom, Anette E. S.
    UiT Arctic Univ Norway, Arctic Univ Museum Norway, N-9037 Tromso, Norway.
    Palacios, Teodoro
    Univ Extremadura, Area Paleontol, Fac Ciencias, Ave Fis, E-06006 Badajoz, Spain.
    Agic, Heda
    Univ Calif Santa Barbara, Dept Earth Sci, Santa Barbara, CA 93106 USA.
    Taylor, Wendy L.
    Univ Cape Town, Dept Geol Sci, Private Bag X3, ZA-7701 Rondebosch, South Africa.
    First record of carbonates with spherulites and cone-in-cone structures from the Precambrian of Arctic Norway, and their palaeoenvironmental significance2019In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 328, p. 99-110Article in journal (Refereed)
    Abstract [en]

    We report for the first time carbonates from the upper Ediacaran sedimentary succession of Finnmark, Arctic Norway. Carbonates occur as calcareous siliciclastic beds, lenses, and concretions, some with calcite spherulites and cone-in-cone (CIC) calcite, in a mudrock to fine-grained sandstone succession from approximately 3 m to 26 m above the base of the 2nd cycle of the Manndrapselva Member of the Stahpogieddi Formation (Vestertana Group). They occur c. 40 m below the Ediacaran-Cambrian boundary, which is well defined by trace fossils. Thin-section petrography and scanning micro X-ray fluorescence elemental mapping reveal a layered composition of the calcareous sedimentary rocks. In some of those, well-developed nested cones of CIC calcite form the outer layer. Thin clay coatings outline individual cones. The inner layers are composed of (1) carbonate with calcite spherulites (grainstone) and (2) thinly laminated fine-grained calcareous siliciclastics (mudstone and wackestone) indicated by elevated concentrations of Al, Si, Fe, and Ti. The inner siliciclastic layers contain framboidal pyrite and probably organic matter. Formation of calcite spherulites took place probably at the sediment-water interface either in a coastal littoral environment or in situ in the sublittoral zone under high alkaline conditions whereas CIC calcite formed during burial diagenesis and clearly in pre-Caledonian time before metamorphism and cleavage formation. This new record of carbonates with calcite spherulites and CIC structures from the Ediacaran of Arctic Norway adds to their rare occurrences in the geological record.

  • 17.
    Miao, Lanyun
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology. Chinese Acad Sci, State Key Lab Palaeobiol & Stratig, 39 East Beijing Rd, Nanjing 210008, Jiangsu, Peoples R China;Chinese Acad Sci, Ctr Excellence Life & Paleoenvironm, Nanjing Inst Geol & Palaeontol, 39 East Beijing Rd, Nanjing 210008, Jiangsu, Peoples R China;Univ Chinese Acad Sci, Coll Earth Sci, 19 Yuquan Rd, Beijing 100049, Peoples R China.
    Moczydlowska, Malgorzata
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Zhu, Shixing
    China Geol Survey, Tianjin Inst Geol & Mineral Resources, Tianjin 300170, Peoples R China.
    Zhu, Maoyan
    Chinese Acad Sci, State Key Lab Palaeobiol & Stratig, 39 East Beijing Rd, Nanjing 210008, Jiangsu, Peoples R China;Chinese Acad Sci, Ctr Excellence Life & Paleoenvironm, Nanjing Inst Geol & Palaeontol, 39 East Beijing Rd, Nanjing 210008, Jiangsu, Peoples R China;Univ Chinese Acad Sci, Coll Earth Sci, 19 Yuquan Rd, Beijing 100049, Peoples R China.
    New record of organic-walled, morphologically distinct microfossils from the late Paleoproterozoic Changcheng Group in the Yanshan Range, North China2019In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 321, p. 172-198Article in journal (Refereed)
    Abstract [en]

    Eukaryotic life has likely existed since the late Paleoproterozoic, yet little is known about its early diversity and phylogenetic relationships. Organic-walled microfossils (OWMs) with conspicuous morphology provide a unique material to investigate the deep evolution of eukaryotic and prokaryotic microbial clades. Here we report a diverse assemblage of OWMs from the lower Changcheng Group (c. 1673-1638 Ma, Changzhougou and Chuanlinggou formations) in the Yanshan Range, North China, which consists of 15 species, including 2 that are newly described. The fossil assemblage is dominated by spheromorphs with less numerous process-bearing vesicles, as are colonial and filamentous forms. Among these, 6 morphologically complex taxa (Dictyosphaera, 2 species of Germinosphaera, Pterospermopsimorpha, Simia, and Valeria) are identified as unambiguous unicellular eukaryotes. Four species (Cucumiforma, Navifusa, Schizofusa and large Leiosphaeridia) with relatively simple morphology but having large size, thick wall, and some showing median-split excystment structures, are of probable eukaryotic affinity. However, various colonial microfossils could be either eukaryotes or prokaryotes. The new record of morphologically disparate OWMs represents one of the earliest occurrences of eukaryotes in both China and the world, and indicates that the eukaryotic life was already well established in the late Paleoproterozoic and was of moderate diversity, similar to that of the Mesoproterozoic.

  • 18.
    Moczydlowska, Malgorzata
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    New records of late Ediacaran microbiota from Poland2008In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 167, no 1-2, p. 71-92Article, review/survey (Refereed)
    Abstract [en]

    New records of organic-walled microfossils, including cyanobacteria, phytoplankton (certain acritarchs) and some microbiota of unknown biological affinities, are reported from the late Ediacaran Włodawa Formation in the Łopiennik IG-1 borehole, Poland. The microfossil association consists mostly of known species, which originated prior to the Cryogenian Period, evidence that these microorganisms survived the Neoproterozoic glacial epochs. The longevity of most of the species is extended herein to ca. 545 Ma. One species is new but described as gen. et sp. indet., because only a single specimen is available. Although the microfossils represent both prokaryotic and eukaryotic groups of organisms, and benthic and planktic modes of life, all, with the exception of Valkyria, are photoautotrophic aerobes. Metabolic processes of nutrition, respiration and reproductive cycles, and ecologic habitats of these biota and the evolutionary lineages to which they belong are analyzed with respect to the basic requirements needed to survive prolonged periods of environmental perturbation.All recorded here cyanobacteria are benthic microbial mat-dwellers, requiring ample water and regular oxygen supply and sun light for their metabolism. Planktic species of Leiosphaeridia studied here are considered to be green algae (chlorophyceans), forming resting cysts and alternating sexual/vegetative generations in their life cycle. They also required habitats of well-oxygenated open water in the photic zone and periodic access to bottom sediment (to rest the cyst) in order to survive the glacial epochs, as they evidently did. It is argued that the natural habitats of all these biota must have been preserved and ecologically functional throughout the Cryogenian Period, and have been robust enough to sustain viable populations and genetic stocks of at least some evolutionary lineages known at the time. This is a primary constraint imposed by contemporaneous marine biosphere on the Earth System model, which can be accepted among hypothetical versions of the Snowball Earth hypotheses based on sedimentological, geochemical, physical and other geological records. The Slushball Earth model, or comparable, is thus favoured over strict Snowball Earth model because it reconciles the habitable conditions with other envisaged geo- and physical conditions during the period.

  • 19.
    Moczydlowska, Malgorzata
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    The Ediacaran microbiota and the survival of Snowball Earth conditions2008In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 167, no 1-2, p. 1-15Article, review/survey (Refereed)
    Abstract [en]

    Recently recovered assemblage of late Ediacaran cyanobacteria, phytoplankton and some microfossils of uncertain origin from the subsurface Włodawa Formation on the Lublin Slope in Poland, allowed to extend their stratigraphic ranges and provided a new evidence that more species survived the Cryogenian Period. Numerous other species of unicellular eukaryotes (informally called acritarchs) and prokaryotes (also coenobial and colonial) have been documented in recent years to lived-over to the Ediacaran, enlarging the global list of biota surviving the Neoproterozoic icehouse intervals. This compelling record revives the issue how marine biota could coup with the catastrophic consequences imposed by the global glaciations and/or to what extent the environmental and climatic change reduced the life habitats. For this purpose, the metabolic processes, modes of life and ecologic habitats of the biota are inferred and analyzed.

    The reviewed biota are autotrophic and aerobic: benthic cyanobacteria, which were solitary and largely colonial, living in functionally complex communities of mat-builders, and planktic and/or facultative benthic eukaryotes, which reproduced also sexually and some had advanced life cycle with alternating vegetative and reproductive generations. The environmental requirements of these microorganisms are well-oxygenated open marine waters in the photic zone, and permanent seafloor substrate for benthic and periodic access to bottom sediment for some planktic species with sexual reproduction to rest the cyst. Such natural habitats must have been preserved throughout the Cryogenian Period, and in a substantial extent (environmental “critical mass”) to sustain viable populations in the lineages that are represented by surviving species.

    Modern analogues of extraordinary adaptations of diverse biota to extreme conditions have their limitations when applied to the Cryogenian Period. Modern extreme environments (like those in Antarctica) with highly specialized organisms are maintained over relatively short time intervals (thousands of years) and may occasionally/periodically be in contact with the outside world to replenish their genetic stock. This is in a sharp contrast to the millions of years of environmental and genetic isolation invoked for the Cryogenian. The global fossil record, enlarged by recent new findings, is briefly reviewed to understand the impact of the Cryogenian glaciations on biodiversity and the rate of survival of microbiota.

    The Snowball Earth Hypothesis and its modified versions are discussed in pursuit of an environmentally plausible Earth System model consistent with the survival of biota. The radical version of the Snowball Earth Hypothesis is ruled out. An Earth System model with open marine water, ice-free shelf (at least seasonally) and access to the sea floor is obligatory for the Cryogenian in order to satisfy the living requirements of the biota that survived the period. The palaeobiological findings are entirely consistent with sedimentaological findings that require open marine water and well-functioning hydrologic cycle. The Slushball Earth model accommodates more adequately these requirements.

  • 20.
    Moczydlowska, Malgorzata
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Willman, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Ultrastructure of cell walls in ancient microfossils as a proxy to their biological affinities2009In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 173, no 1-4, p. 27-38Article, review/survey (Refereed)
    Abstract [en]

    Bacteria and protoctists dominated the biosphere in the Archean and Proterozoic, their affinities being deduced by studies of their comparative morphology, palaeoecology, biogeochemistry, and wall ultrastructure. However, exact phylogenetic relationships are uncertain for most such microfossils. Because of the limitations imposed by the simple morphology and small dimensions of such microorganisms and their little known biochemistry, new techniques in microscopy, tomography and spectroscopy are applied to examine individual microfossils at the highest attainable spatial resolution. TEM/SEM studies of the wall ultrastructure of sphaero- and acanthomorphic acritarchs have revealed complex, single to multilayered walls, having a unique texture in sub-layers and an occasionally preserved trilaminar sheath structure (TLS) of the external layer. A variety of optical characteristics, the electron density and texture of fabrics of discrete layers, and the properties of biopolymers may indicate the polyphyletic affiliations of such microfossils and/or the preservation of various stages (vegetative, resting) in their life cycle. Primarily, wall ultrastructure allows discrimination between fossilized prokaryotic and eukaryotic cells. Composite wall ultrastructure provides evidence that some Proterozoic and Cambrian leiosphaerids are of algal affinities (but not, per se, that they are referable to "Leiosphaeridia"). Certain Cambrian specimens represent chlorophyceaens, having the multilayered composite wall with TLS structure known from vegetative and resting cells in modern genera of the Chlorococcales and Volvocales. The wall ultrastructure of the studied Cambrian and Proterozoic acanthomorphs resembles the resting cysts of green microalgae, but there is no evidence to suggest a close relationship of these taxa, to dinoflagellates. It is apparent that although there is no single and direct method to recognize the precise phylogenetic relations of such microfossils, ultrastructural studies of their preserved cell walls and encompassing sheaths, combined with biochemical analyses and other advanced methods, may further elucidate their affinities to the modern biota.

  • 21.
    Moczydlowska-Vidal, Malgorzata
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Nagovitsin, Konstantin
    Ediacaran radiation of organic-walled microbiota recorded in the Ura Formation, Patom Uplift, East Siberia2012In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 198, p. 1-24Article in journal (Refereed)
    Abstract [en]

    A new assemblage of morphologically complex, ornamented and large organic-walled microfossils (acritarchs) from the Ura Formation in the Patom Uplift, East Siberia, is identified and taxonomically described as a continuation of the previous studies (0245 and 0305). Nine new species and three new genera are recognised; 10 other species are known from occurrences in the Ediacaran strata of Australia, China, the Siberian Platform (SP), and the East European Platform (EEP). The new species are morphologically advanced phenotypes, showing innovative elements of vesicle ornamentation and variable symmetry, and internal bodies within zygotic cyst-like vesicles that are indicative of the sexual reproduction stage of the microorganism. The morphological features and the preliminarily recognised cell wall ultrastructure are characteristic of phytoplankton; thus the described microfossils are identified as green microalgae. The relative age of the Ura assemblage, by comparison to microfossil records elsewhere and estimated in the regional geologic context of the Dalniaya Taiga (containing the Ura Formation) and the Zhuya (overlying) groups, is suggested to be early Ediacaran. Radiation of the Ura-type microorganisms pre-dates the records of Ediacaran microbiota from Australia (the Pertatataka association/Ediacaran Complex Acanthomorphic Palynoflora), the Siberian Platform (Khamaka-type assemblages), and the EEP (Vychegda association) but is preceded by the appearance of certain species recorded in China at the base of the Doushantuo Formation. The stratigraphic ranges of genera co-occurring in these palaeocontinents (Appendisphaera, CavaspinaCeratosphaeridiumGyalosphaeridium,LabruscasphaeridiumMultifronsphaeridiumTanarium, and Variomargosphaeridium) are extended by their lower record in the Patom Uplift and may span a major portion of the Ediacaran Period. The refined stratigraphic distribution of microfossils may provide a means for zoning the entire Ediacaran System in addition to the upper zones established in Australia.

  • 22.
    Nikkila, K.
    et al.
    Univ Helsinki, Inst Seismol, FI-00014 Helsinki, Finland..
    Korja, A.
    Univ Helsinki, Inst Seismol, FI-00014 Helsinki, Finland..
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Eklund, O.
    Abo Akad Univ, Geol & Mineral, FI-20500 Turku, Finland..
    Analog modeling of one-way gravitational spreading of hot orogens - A case study from the Svecofennian orogen, Fennoscandian Shield2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 268, p. 135-152Article in journal (Refereed)
    Abstract [en]

    Geodynamic models offer insight into deformation styles of syn- and post-collisional extensional processes. Such models often ignore the effect of lateral viscosity contrast between accreted terranes and inherited tectonic boundaries. This paper presents a set of crustal-scale analog experiments of one-way post-collisional gravitational spreading testing the effect of crustal heterogeneity by using two mechanically contrasting blocks, pre-existing cuts with varying dips, and three layers with contrasting rheologies. Two blocks represent strong, mature, and weak, juvenile crustal parts. Both blocks have three horizontal crustal layers: brittle upper, weak partially molten middle and dry strong lower layer. Cuts represent pre-existing crustal-scale shear zones and tectonic boundaries. The experiments indicated that tectonic boundaries may facilitate exhumation and increase extensional strain, when the boundaries dip opposite to the flow direction. The tectonic boundaries may also split and divide the crust into separate blocks with independent deformation signatures: shortening, elongation or rotation. The tectonic boundaries rotated along vertical axes toward the flow direction. The modeling results suggest that in areas with inherited tectonic boundaries and compositional differences the amount of extension is unevenly distributed between the different parts during the widespread unilateral gravitational spreading and that the flow has different effects on the contrasting crustal units, in both lateral and vertical directions. To validate the modeling, the results are compared to geophysical and geological data from the Paleo-proterozoic Svecofennian orogen in the Fennoscandian Shield. The comparison suggests that the orogen underwent 50% extension and was thinned by maximum of 20% via westward gravitational spreading. This spreading rotated the crustal-scale blocks, shear zones and tectonic contacts. It also brought exhumed, high grade middle crustal blocks into contact with subsided, low grade, upper crustal blocks. We suggest that results of the analog models can be used as proxies in both ancient and modern hot accreted orogens, which have undergone post-convergence continental mid-crustal weakening and have comprised of juxtaposed terranes with varying rheological compositions.

  • 23. Pease, Victoria
    et al.
    Daly, J.S.
    Elming, S-Å.
    Kumpulainen, Risto
    Moczydlowska, Malgorzata
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Puchkov, V.
    Roberts, D.
    Saintot, A.
    Stephenson, R.
    Baltica in the Cryogenian, 850-650 Ma2008In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 160, no 1-2, p. 46-65Article, review/survey (Refereed)
    Abstract [en]

    This new tectonic synthesis provides a framework for understanding the dynamic evolution of Baltica and for constraining tectonic correlations within the context of the Neoproterozoic break-up of Rodinia–Pannotia. Cryogenian Baltica is described with respect to five geographic regions: the northwest, northeast, east, south, and southwest (modern coordinates). These geographic regions define three principal Cryogenian tectonic margins: a rifting northwestern margin, a passive northeastern margin, and a poorly understood southern margin.

    The northwest region is characterized by Neoproterozoic to lower Ordovician sedimentary successions deposited on Archean to late Mesoproterozoic crystalline complexes, reworked during Caledonian orogenesis. Lare Neoproterozoic to lower Ordovician sedimentary strata record the change from an alluvial setting to a marine environment, and eventually to a partially starved (?) turbidite basin. They document rifting from the Rodinian-Pannotian supercontinent, which was unsuccessful until ca. 620–550 Ma when voluminous dikes and mafic/ultramafic complexes were intruded.

    Baltica's northeastern and eastern regions document episodic intracratonic rifting throughout the Mesoproterozoic, followed by pericontinental passive margin deposition throughout the Cryogenian. In the northeast platformal and deeper-water basin deposits are preserved, whereas the eastern region was later affected by Paleozoic rifting and preserves only shelf deposits. The northeastern and eastern regions define Baltica's Cryogenian northeastern tectonic margin, which was an ocean-facing passive margin of the Rodinia–Pannotia supercontinent. It remained a passive margin until the onset of Timanian orogenesis at ca. 615 Ma, approximately synchronous with the time of Rodinia–Pannotia rifting.

    Baltica's southern and southwestern regions remain enigmatic and controversial. Precambrian basement is generally hidden beneath thick successions of Ediacaran and younger platform sediments. Similarities between these regions exist, however, and suggest that they may share a similar tectonic evolution in the Cryogenian and therefore define the southern tectonic margin of Baltica at this time. Paleo- to Mesoproterozic basement was affected by Neoproterozoic and younger tectonism, including Cryogenian (?) and Ediacaran rifting. This was followed by Ediacaran (ca. 550 Ma) passive margin sediment deposition at the time of Rodinia–Pannotia break-up, until Early Paleozoic accretion of allochthonous terranes record the transition from rifting to a compressional regime.

    Paleomagnetic and paleontological data are consistent with Baltica and Laurentia drifting together between ca. 750 and 550 Ma, when they had similar apparent polar wander paths. Microfossil assemblages along the eastern margin of Laurentia and the western margin of Baltica (modern coordinates), suggest proximity between these two margins at this time. At ca. 550 Ma, Laurentia and Baltica separated, consistent with paleomagnetic, paleontological, and geological data, and a late break-up for Rodinia–Pannotia.

  • 24.
    Rosa, Diogo
    et al.
    GEUS Geol Survey Denmark & Greenland, Dept Petr & Econ Geol, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark..
    Majka, Jaroslaw
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Al Mickiewicza 30, PL-30059 Krakow, Poland..
    Thrane, Kristine
    GEUS Geol Survey Denmark & Greenland, Dept Petr & Econ Geol, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark..
    Guarnieri, Pierpaolo
    GEUS Geol Survey Denmark & Greenland, Dept Petr & Econ Geol, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark..
    Evidence for Timanian-age basement rocks in North Greenland as documented through U-Pb zircon dating of igneous xenoliths from the Midtkap volcanic centers2016In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 275, p. 394-405Article in journal (Refereed)
    Abstract [en]

    Igneous xenoliths have been identified within the Paleozoic Midtkap volcanic centers of North Greenland that cut through Cambrian-Ordovician deep water trough sedimentary rocks that were subsequently deformed during the south-verging Ellesmerian Orogeny. The xenoliths were characterized geochemically and their zircons dated through the U-Pb technique. This provided ages ranging from 628 to 570 Ma, for xenoliths with granitic and monzonitic compositions, the former apparently older than the latter. These ages, coupled with the geochemical signature compatible with an arc setting, provide evidence for the presence of Timanian like basement in North Greenland. The structural setting suggests that the dated xenoliths belong to an allochthonous unit emplaced during the Caledonian Orogeny and deformed during the Ellesmerian Orogeny. Furthermore, this data provides new evidence for a northwestern extension (through continuation and/or through dispersal) of the late Neoproterozoic Timanide belt, from its type locality, in the Timan-Pechora region in Russia, through Svalbard, into North Greenland, to the Pearya Terrane on Ellesmere Island.

  • 25.
    Shang, Xiaodong
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology. Chinese Acad Geol Sci, Inst Geol, Beijing 100037, Peoples R China.
    Liu, Pengju
    Chinese Acad Geol Sci, Inst Geol, Beijing 100037, Peoples R China.
    Moczydlowska, Malgorzata
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Acritarchs from the Doushantuo Formation at Liujing section in Songlin area of Guizhou Province, South China: Implications for early-middle Ediacaran biostratigraphy2019In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 334, article id 105453Article in journal (Refereed)
    Abstract [en]

    A taxonomically diverse and morphologically disparate microfossil assemblage is recovered from the upper Doushantuo Formation in the Liujing section of Songlin area, Guizhou Province, including acanthomorphic and sphaeromorphic acritarchs, multicellular algae, and filamentous cyanobacteria. Acritarch Mengeosphaera membranifera sp. nov. is newly erected and genus Cymatiosphaeroides and several species (C. forabilatus, C. kullingii, Bacatisphaera baokangensis) are emended in the systematics. The acanthomorphic species are dominated by Cymatiosphaeroides forabilatus and Mengeosphaera membranifera sp. nov. The Liujing assemblage shares many species with other Ediacaran coeval assemblages from South China, Australia, Siberia, the East European Platform, India, Mongolia and Svalbard, and indicates a significant taxonomic similarity to the global, agediagnostic assemblages. New occurrence of those known taxa in the Liujing succession documents the biodiversity of the Ediacaran acritarchs in South China. The Liujing assemblage extends the palaeogeographic distribution of the Ediacaran acritarchs and may be assigned to the Tanarium conoideum-Cavospina basiconica Assemblage Zone that was recognized in the Yangtze Gorges area of South China. Alternatively, it could be partially correlated with the barren interval between T. conoideum-C. basiconica Assemblage Zone and the overlying Tanarium pycnacanthum-Ceratosphaeridium glaberosum Assemblage Zone.

  • 26.
    Shang, Xiaodong
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Chinese Acad Geol Sci, Inst Geol, Beijing 100037, Peoples R China.
    Moczydlowska-Vidal, Malgorzata
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Liu, Pengju
    Chinese Acad Geol Sci, Inst Geol, Beijing 100037, Peoples R China.
    Liu, Lei
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Organic composition and diagenetic mineralization of microfossils in the Ediacaran Doushantuo chert nodule by Raman and petrographic analyses2018In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 314, p. 145-159Article in journal (Refereed)
    Abstract [en]

    We studied microfossils and their embedding matrix minerals from chert nodules in the Ediacaran Doushantuo Formation of the Yangtze Gorges area in South China using Raman spectroscopy as well as transmitted- and polarized light microscopy. The microfossils are composed of organic carbonaceous material with weak structural organization/ordering, which indicates a low degree of thermal maturation and alteration. Raman spectral disparity of carbonaceous material among different portions (vesicle/inclusion) of microfossils reveals some differences in organic composition and structure of their precursor biological matters. The mineral phases of silica matrix that entombs the microfossils are recognized as opal-CT, cryptocrystalline quartz, and their transitional phases. Overall, Raman spectral analyses and petrographic observations document a complete and continuous sequence of silica phase transformation from opal-CT to quartz. When reconstructing the diagenetic history of sediments and mineralization process of microfossils in a localized microenvironment, the silica in pore waters precipitated preferentially at the periphery of microorganisms in the form of opal, gradually decreasing in abundance as it transformed into more stable cryptocrystalline quartz. The recrystallization took place in cryptocrystalline quartz to form grains. Authigenic fluorapatite readily precipitated in the vicinity of some microfossils and within their degraded organic fragments. While apatite was crystallizing around organisms and their biostructures, silica precipitated in the surrounding voids, inhibiting the space of potential apatite crystallization. The silicification and phosphatization of microfossils occurred in the microbial sulfate reduction (MSR) zone of the sediment column, and both were driven by the localized pH change resulting from MSR and pyrite precipitation in the microenvironment, thus facilitating the exceptional fossil preservation in the Doushantuo chert nodules.

  • 27.
    Skyttä, Pietari
    et al.
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Bauer, Tobias
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Tavakoli, Saman
    Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Hermansson, Tobias
    Boliden Mineral AB.
    Andersson, Jenny
    Geological Survey of Sweden.
    Weihed, Pär
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Luleå tekniska universitet.
    Pre-1.87 Ga development of crustal domains overprinted by 1.87 Ga transpression in the Palaeoproterozoic Skellefte district, Sweden2012In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 206–207, p. 109-136Article in journal (Refereed)
    Abstract [en]

    The complex structural evolution within the VMS-hosting Skellefte district, Sweden, has been investigated to provide a solid structural framework for the known mineral deposits in the area. The area occurs in a transition zone between dominantly N-S to NNE-WSW striking structures in the north and approximately WNW-ESE oriented structural trends in the south. The presence of high-strain zones with both the above orientations in the Skellefte district allows constraining their mutual relationship, as well as their significance for the build-up of the Svecokarelian orogen at around 1.89 Ga and for the following tectonic overprint between 1.87-1.80 Ga. The methods used in this study include structural analysis complemented by potential field modelling and SIMS U-Pb geochronology on zircon. Based on the results of this study, the earliest deformation (D1) is constrained at 1.89–1.88 (1.87) Ga and tentatively attributed to crustal extension occurring synchronously with volcanism. Deposition of the Skellefte Group metavolcanic rocks is inferred to have occurred in a pull-apart basin developed due to dextral strike-slip shearing along approximately N-S striking regional-scale shear zones. Variations in the development of deformation fabric across the district indicate that the crust was divided into an upper, un-metamorphosed domain and a lower, strongly metamorphosed domain during D1. We further infer that the transition from the upper to lower crust was locally coupled with development of low-angle crustal-scale detachment zones during D1. The heterogenous crust was subsequently overprinted by transpressional deformation which may be explained by two alternative models. According to the first model, one single SSE-NNW transpressional event with distinct strain partitioning between the coaxially deformed upper crust and the non-coaxially deformed lower crust is largely responsible for the present-day structural geometry. A post-folding rhyolite dyke, here dated at 1871 ± 4 Ma, constrains the minimum age of this event (D2). The alternative model includes two separate transpressional events: a SW-NE one at (1.88-) 1.87 Ga, followed by SSE-NNW transpression at 1.86 Ga. Recognition of the early-orogenic detachment zones allow us to suggest that many of the major crustal-scale shear zones in the central Fennoscandian Shield have originated as 1.89-1.87 Ga crustal detachment zones, i.e. earlier than typically considered.

  • 28.
    Weihed, Pär
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Luleå tekniska universitet.
    A discussion on papers “Nature of a major tectonic discontinuity in the Svecofennian province of northern Sweden” by Rutland et al. (PR 112, 211-237, 2001) and “age of deformation episodes in the Palaeoproterozoic domain of northern Sweden, and evidence for a pre-1.9 Ga crustal layer” by Rutland et al. (PR 112, 239-259, 2001).2003In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 121, no 1-2, p. 141-147Article in journal (Refereed)
  • 29.
    Weihed, Pär
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences. Luleå tekniska universitet.
    Bergman, J.
    Uppsala University.
    Bergström, U.
    University of Gothenburg.
    Métallogeny and tectonic evolution of the early proterozoic Skellefte district, Northern Sweden1992In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 58, no 1-4, p. 143-167Article in journal (Refereed)
    Abstract [en]

    The various mineralizations in the Early Proterozoic Skellefte district are discussed and placed in a palaeotectonic context. The metallogeny, together with volcanic stratigraphy, geochemistry, isotope studies, and structural geology, favour a former destructive plate margin. At 1.89 Ga the area resembled a modern island arc environment where volcanogenic massive sulphide and gold-rich porphyry-type deposits formed. Mafic to ultramafic sills and dykes hosting Ni mineralizations intruded a greywacke sequence immediately south of the Skellefte district as a result of large scale rifting at the end of the volcanic period. Gold was emplaced 20-60 Ma later during peak metamorphism at the end of the Svecofennian orogeny. Finally at 1.80 Ga, after accretion of the island arc to the Archaean continent in the northeast, large granitoids intruded. Some of these have associated W, U, Mo, and Li mineralizations-an evidence for a crustal or cratonic influence

  • 30.
    Willman, Sebastian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Moczydłowska, Małgorzata
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Ediacaran acritarch biota from the Giles 1 drillhole, Officer Basin, Australia, and its potential for biostratigraphic correlation2008In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 162, no 3-4, p. 498-530Article, review/survey (Refereed)
    Abstract [en]

    The remarkable diversification of single-celled photosynthesising biota of algal and other as yet unknown affinities (acritarchs), followed by the diversification of metazoans, occurred during the Ediacaran Period, which is marked by extreme climatic and environmental changes. Here we describe a taxonomically diverse acritarch association from the Ediacaran part of the Giles 1 drillcore in the Officer Basin, South Australia, which documents further the Ediacaran phytoplankton radiation. The studied palynoflora comprises 21 known acritarch species belonging to 15 genera. One new monospecific genus is described (Calyxia xandaros sp. nov.) as well as one new species of Tanarium (Tanarium anozos sp. nov.). We also propose the genus Knollisphaeridium to replace the preoccupied genus Echinosphaeridium. Three stratigraphically successive assemblages that match previously observed patterns of acritarch replacement are distinguished. The present record is from slightly older strata than in previous records, thus extending the ranges of certain acanthomorphic species. The lower boundaries of three stratigraphically higher assemblage zones among the four formerly established zones, are identified by the occurrence of the index species Tanarium conoideum, Tanarium irregulare and Apodastoides verobturatus, respectively. The substantial morphological disparity of acritarchs in the Giles 1 succession suggests that they may represent a great diversity of microorganisms, not only as biological species but also representing perhaps vegetative and encysted stages in their life cycle. The reconstructed palaeogeographic distribution of several species between Australia, Siberia, Baltica (the East European Platform), and to South China, shows that acritarchs are suitable for both intra- and inter-regional correlation.

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