…

30 pages

1 file

Sign up for access to the world's latest research

Gondwana Research, 1999

terranes between the Neoproterozoic to Early Cambrian break-up of Rodinia-Pannotia and the Silurian to Permian The paleogeographic evolution of the NW Proto-amalgamation of Pangea are critically reviewed. Based on Gondwana margin and the interactions of this chrono-and biostratigraphically constrained time slices supercontinent withBaltica and the extra-Baltic "European" rotational and transtensional movciiicnts of the macropla tcs the designation of the pre-Permian (pre-Pangean) Gondwana Supercontinent to "Proto-Gondwana" because the latter includes plates and terranes which during Meso-Cenozoic times were severed from "Proto-Gondwana" by the development of Te thyan and Para-Te thyan rifts.

2009

2009.04 The plate tectonic and palaeogeographic history of the late Proterozoic is a tale of two supercontinents: Rodinia and Pannotia. Rodinia formed during the Grenville Event (c. 1100 Ma) and remained intact until its collision with the Congo continent (800-750 Ma). This collision closed the southern part of the Mozambique Seaway, and triggered the break-up of Rodinia. The Panthalassic Ocean opened as the supercontinent of Rodinia split into a northern half (East Gondwana, Cathaysia and Cimmeria) and a southern half (Laurentia, Amazonia-NW Africa, Baltica, and Siberia). Over the next 150 Ma, North Rodinia rotated counter-clockwise over the North Pole, while South Rodinia rotated clockwise across the South Pole. In the latest Precambrian (650-550 Ma), the three Neoproterozoic continents--North Rodinia, South Rodinia and the Congo continents--collided during the Pan-Africa Event forming the second Neoproterozoic supercontinent, Pannotia (Greater Gondwanaland). Pan-African mountain building and the fall in sea level associated with the assembly of Pannotia may have triggered the extreme Ice House conditions that characterize the middle and late Neoproterozoic. Although the palaeogeographic maps presented here do not prohibit a Snowball Earth, the mapped extent of Neoproterozoic ice sheets favour a bipolar Ice House World with a broad expanse of ocean at the equator. Soon after it was assembled (c. 560 Ma), Pannotia broke apart into the four principal Palaeozoic continents: Laurentia (North America), Baltica (northern Europe), Siberia and Gondwana. The amalgamation and subsequent break-up of Pannotia may have triggered the "Cambrian Explosion". The first economically important accumulations of hydrocarbons are from Neoproterozoic sources. The two major source rocks of this age (Nepa of Siberia and Huqf of Oman) occur in association with massive Neoproterozoic evaporite deposits and in the warm equatorial-subtropical belt, within 30 degrees of the equator.

Geological Society, London, Special Publications, 2000

Reconstructions based on biogeography, palaeomagnetism and facies distributions indicate that, in later Palaeozoic time, there were no wide oceans separating the major continents. During the Silurian and Early Devonian time, many oceans became narrower so that only the less mobile animals and plants remained distinct. There were several continental collisions: the Tornquist Sea (between Baltica and Avalonia) closed in Late Ordovician time, the Iapetus Ocean (between Laurentia and the newly merged continents of Baltica and Avalonia) closed in Silurian time, and the Rheic Ocean (between Avalonia and Gondwana and the separate parts of the Armorican Terrane Assemblage) closed (at least partially) towards the end of Early Devonian time. Each of these closures was reflected by migrations of non-marine plants and animals as well as by contemporary deformation. New maps, based on palaeomagnetic and faunal data, indicate that Gondwana was close to Laurussia during the Devonian and Carboniferous periods, with fragments of Bohemia and other parts of the Armorican Terrane Assemblage interspersed between. It follows that, after Early Devonian time, the Variscan oceans of central Europe can never have been very wide. The tectonic evolution of Europe during Devonian and Carboniferous time was thus more comparable with the present-day Mediterranean Sea than with the Pacific Ocean. Palaeozoic palaeoeontinents During the Palaeozoic era, there were several events when major continents rifted apart and others when they collided. No continent remained as a distinct entity throughout this era; so each palaeocontinent can only be defined after consideration of its history. The major Palaeozoic continents that are represented in Europe are Laurentia, Baltica, Avalonia and Gondwana, with smaller continental fragments of the Armorican Terrane Assemblage, including Bohemia and Armorica. Laurentia, the Palaeozoic continent based on North America, did not include the Mesozoic and Cenozoic additions to the Western Cordillera, nor is it defined (Scotese & McKerrow 1990) as including the terranes accreted to the east coast in the Devonian and Carboniferous periods. Much of the northern Appalachians (eastern Newfoundland, New Brunswick, Nova Scotia and coastal New England) were parts of Avalonia until Silurian time. The Piedmont and Florida were parts of Gondwana until Carboniferous time. But Laurentia did include (as indicated by their Cambrian and Early Ordovician faunas) northwest Ireland, Scotland, Greenland, much of Svalbard, the North Slope of Alaska and the Chukotsk Peninsula of eastern Siberia (Scotese & McKerrow 1990). Palaeomagnetic data (Mac Niocaill & Smethurst 1994) and the prevalence of warm-water carbonate facies show that Laurentia remained close to the Equator throughout Palaeozoic time. Baltica consists of Scandinavia and the East European Platform, as far east as the Urals. Its southern margin extends from the North Sea to the Black Sea along the Trans-European Suture, a line much complicated by later deformation. In

Earth and Planetary Science Letters, 2000

The Rodinia reconstruction of the Neoproterozoic Supercontinent has dominated discussion of the late Precambrian Earth for the past decade and originated from correlation of sedimentary successions between western North America and eastern Australia. Subsequent developments have sited other blocks according to a distribution of V1100 Ma orogenic belts with break-up involving a putative breakout of Laurentia and rapid reassembly of continent crust to produce Gondwana by early Phanerozoic times. The Rodinia reconstruction poses several serious difficulties, including: (a) absence of palaeomagnetic correlation after V730 Ma which requires early fragmentation of continental crust although geological evidence for this event is concentrated more than 150 Ma later near the Cambrian boundary, and (b) the familiar reconstruction of Gondwana is only achieved by exceptional continental motions largely unsupported by evidence for ocean consumption. Since the geological evidence used to derive Rodinia is non-unique, palaeomagnetic data must be used to evaluate its geometrical predictions. Data for the interval V1150^500 Ma are used here to test the Rodinia model and compare it with an alternative model yielding a symmetrical crescent-shaped analogue of Pangaea (Palaeopangaea). Rodinia critically fails the test by requiring Antarctica to occupy the location of a quasi-integral Africa, whilst Australia and South America were much closer to their Gondwana configurations around Africa than implied by Rodinia. Palaeopangaea appears to satisfy palaeomagnetic constraints whilst surmounting geological difficulties posed by Rodinia. The relative motions needed to produce Gondwana are then relatively small, achieved largely by sinistral transpression, and consistent with features of Pan-African orogenesis; continental dispersal did not occur until the Neoproterozoic^Cambrian boundary. Analogies between Palaeopangaea and (Neo)pangaea imply that supercontinents are not chaotic agglomerations of continental crust but form by episodic coupling of upper and lower mantle convection leading to conformity with the geoid. ß

Gondwana Research, 2002

During the Mesoproterozoic, western Amazonia and southern Baltica both show progressive outgrowth by orogenic accretion to older cratons. Correlation of these orogenic belts indicates that Amazonia and Baltica were joined and evolved together throughout the Mesoproterozoic. Similar correlations also suggest a close relationship of Amazonia with the Labrador part of Laurentia at the same time.

Sedimentary Geology, 1998

An unresolved question in Precambrian geology is the relationship between Archean crustal fragments that are now separated by younger orogens: were they once contiguous? Williams et al. (1991) proposed the name 'Kenorland' for a speculative Neoarchean supercontinent comprising the Archean provinces in North America. Recently, a large number of ca. 2.5-2.0 Ga magmatic, metamorphic, detrital and xenocrystic ages have been reported from North America. We interpret that the wide geographic distribution and temporal spread of these ages may signify long-lived, regional-scale mantle upwelling, and anorogenic magmatic and metamorphic processes related to the protracted breakup of Kenorland. Breakup may have extended from ca. 2.5 to 2.1 Ga, culminating with dispersion of continental fragments at ca. 2.1-2.0 Ga. In North America, ca. 2.5-2.1 Ga intracratonic basin successions (e.g. Hurwitz Group) formed in the interior of Kenorland before dispersion, and passive margin sequences flanking the Superior Province (e.g. Huronian Supergroup) and the Wyoming Province (e.g. Snowy Pass Supergroup) defined the edges of Kenorland. Earliest Paleoproterozoic magmatic and sedimentary rocks, which include voluminous quartz arenites and glacigenic deposits, are consistent with a high-standing supercontinent and a mantle superplume. The Paleoproterozoic record from the Baltic and Siberian shields is similar to that of North America, suggesting inclusion in Kenorland. A slightly different record from the southern continents suggests a second, coexisting supercontinent that included the Zimbabwe, Kaapvaal, and Pilbara cratons, ('Zimvaalbara' of I.G. Stanistreet), the São Francisco Craton, and possibly, cratonic blocks in India. Attenuation of this second supercontinent started earlier than in Kenorland (ca. 2.65 Ga) and was accompanied by high sea level and deposition of vast Lake Superior-type iron formations. Immediately thereafter, both supercontinents became emergent and were subject to global cooling and glaciation.

Tectonophysics, 2004

Nature Geoscience, 2016

Precambrian supercontinents Nuna-Columbia (1.7 to 1.3 billion years ago) and Rodinia (1.1 to 0.7 billion years ago) have been proposed. However, the arrangements of crustal blocks within these supercontinents are poorly known. Huge, dominantly basaltic magmatic outpourings and intrusions, covering up to millions of square kilometres, termed Large Igneous Provinces, typically accompany (super) continent breakup, or attempted breakup and o er an important tool for reconstructing supercontinents. Here we focus on the Large Igneous Province record for Siberia and Laurentia, whose relative position in Nuna-Columbia and Rodinia reconstructions is highly controversial. We present precise geochronology-nine U-Pb and six Ar-Ar ages-on dolerite dykes and sills, along with existing dates from the literature, that constrain the timing of emplacement of Large Igneous Province magmatism in southern Siberia and northern Laurentia between 1,900 and 720 million years ago. We identify four robust age matches between the continents 1,870, 1,750, 1,350 and 720 million years ago, as well as several additional approximate age correlations that indicate southern Siberia and northern Laurentia were probably near neighbours for this 1.2-billion-year interval. Our reconstructions provide a framework for evaluating the shared geological, tectonic and metallogenic histories of these continental blocks.

Precambrian Research

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.

The break-up of Pangaea was principally facilitated by tensional plate stress acting on pre-existing suture zones. The rifting of Pangaea began during the Early Permian along the southern Tethys margin and produced the lenticular-shaped continent known as Cimmeria. A mantle-plume model is ascribed to explain the rift-related volcanism but the NW-SE oriented Cimmerian rifts do not correlate well with pre-existing suture zones or 'structural heterogeneities' but appear to have a pertinent spatial and temporal association with Late Palaeozoic glacial-interglacial cycles. Mantle potential temperature estimates of Cimmerian rift-related basalts (1410 °C ± 50 °C) are similar to ambient mantle conditions rather than an active mantle-plume rift as previously suggested. Moreover, we find that the distribution of glacial deposits shows significant temporal and spatial concurrence between the glacial retreat margins and rifting sites. We conclude that the location and timing of Cimmerian rifting resulted from the exploitation of structural heterogeneities within the crust that formed due to repeated glacial-interglacial cycles during the Late Palaeozoic. Such effects of continental deglaciation helped to create the lenticular shape of Cimmeria and Neotethys Ocean suggesting that, in some instances, climate change may directly influence the location of rifting. Crustal thinning, narrow rifting characterized by localization of strain through large boundary fault activation, and basin subsidence are the signature features of the early stages of continental break-up 1,2. Transient excess magmatic upwelling and emplacement covering the inboard portions of continental rift margins follow the early stages of rifting 2–4. Continent break-up/rifting requires tremendous amount of energy. In order to conserve energy, initial rifting sites within continental crust are often spatially associated with pre-existing 'structural het-erogeneities' such as suture zones related to ancient orogenic boundaries or regions of the crust with differential thickness 2,5–7. A given 'structural heterogeneity' may be exploited by either a mantle-plume (active extension) or a regional stress field (passive extension) associated with plate boundary forces (slab-pull) that becomes a focal point for flood basalt volcanism before developing into an ocean basin 8. Moreover, icosahedral structures with triple-junction configuration form quasi-hexagonal fractures that minimize the total boundary length and produce polyhedral plate configurations, thus minimizing the energy, area, work and stress required to brittely break plates 9,10. The amalgamation and break-up of Pangaea exemplifies the secular nature of global tectonic processes as plate stresses transitioned from compressional to extensional during the Late Carboniferous to Early Jurassic 6,10–12. There are a number tectonomagmatic models proposed to explain the break-up of Pangaea such as: post-orogenic collapse 13 , dispersal over a mantle-super plume 14 , passive rifting and self-subduction of a super-plate 11,15. However, in many cases, rifting and magmatism were initiated at old suture zones that formed during the amalgamation stage. Some of the hypotheses provide a partial explanation for the break-up of the Gondwana portion of Pangaea specifically during the Jurassic to Cretaceous but do not adequately address an earlier period of rifting 5,11. The break-up of Gondwana began during the Early Permian along a ~13,000 km long NW-SE oriented continental rift just as the Late Palaeozoic continental ice sheet retreated 16–18. The rifting of terranes from the Tethyan margin of Gondwana produced the ribbon-like continent Cimmeria and the Neotethys Ocean. The rifting of Cimmeria and accompanying magmatism are thought to be related to a regional-scale mantle-plume 19–21. However, geochemical and structural studies of the Panjal Traps (Kashmir), the single largest contiguous out-cropping of Early Permian flood basalts associated with Cimmerian rifting, suggest they are related to passive

Tectonics, 2002

PLOS One, 2011

Background: Sphaerexochinae is a speciose and widely distributed group of cheirurid trilobites. Their temporal range extends from the earliest Ordovician through the Silurian, and they survived the end Ordovician mass extinction event (the second largest mass extinction in Earth history). Prior to this study, the individual evolutionary relationships within the group had yet to be determined utilizing rigorous phylogenetic methods. Understanding these evolutionary relationships is important for producing a stable classification of the group, and will be useful in elucidating the effects the end Ordovician mass extinction had on the evolutionary and biogeographic history of the group.

Journal of Paleontology, 2010

Cladistic parsimony analysis of the subfamily Deiphoninae Raymond, 1913, was conducted to produce a hypothesis of relationship for the group. The genera Deiphon Barrande, 1850 and Onycopyge Woodward, 1880 are found to be monophyletic, while the genus Sphaerocoryphe Angelin, 1854, as it was previously defined, is paraphyletic. A modified Brooks Parsimony Analysis using the phylogenetic hypothesis reveals patterns of biogeography, in particular, vicariance and geodispersal, during the Ordovician-Silurian. The analysis yields three major conclusions about deiphonine biogeography: Eastern Laurentia and Baltica were close enough during the late Ordovician to exchange taxa via sea level rise and fall; chance dispersal occurred between Northwestern Laurentia and Australia; and deiphonine trilobites likely originated in Baltica or Eastern Laurentia.

International Geology Review, 1998

An interpretation of available paleomagnetic data from the Laurentia, Congo-Sao Francisco, Kalahari, and Amazonia cratons favors the hypothesis that these units were juxtaposed in a supercontinent by 1000 Ma. This supercontinent is similar to Hoffman's (1991) Rodinia, except for the Kalahari craton, whose 1300 to 1000 Ma Namaqua-Natal mobile belt is now juxtaposed against the correlated 1300 to 1000 Ma Grenville belt in eastern Laurentia, Our model suggests that a continuous 1300 to 1000 Ma orogenic belt, formed by the Grenville, Sunsas, Kibaride-Irumide-Lurio, Namaqua-Natal, and Dronning Maud Land-Coats Land belts, represents the suture zone between the Amazonia, Congo-Sao Francisco, Kalahari-Grunehogna, and Laurentia blocks.The formation of western Gondwana (from our Rodinia supercontinent) may be accomplished by the closure of the large Mozambique Ocean and the more restricted Adamastor Ocean, combined with some counterclockwise rotation of the Congo-Sao Francisco craton. Rotation of the Congo-Sao Francisco craton can explain the observed oblique convergence and wrench tectonics of Pan African-Brasiliano mobile belts that encircle this craton. The model is also consistent with the synchroneity between the Rodinia break-up and the assembly of Gondwana, as suggested by several authors (Laurentia began to separate from Rodinia at 625 Ma or later).

Terra Nova, 2005

The Moelv Tillite is the Late Neoproterozoic Varanger glacial deposit recorded in the Hedmark Group, SE Norway. Paired U–Pb and Lu–Hf data collected on detrital zircons in the Rendalen Formation underlying the Moelv Tillite have identified an uncommon 677 ± 15 to 620 ± 14 Ma population, that constrain the deposition of the Moelv Tillite to be younger than 620 ± 14 Ma. The youngest detrital zircons may be derived from granite magmatism related to the 616 ± 3 Ma Egersund dolerite magmatism, situated in the western part of the Sveconorwegian orogen. The Moelv Tillite, which is not overlain by a cap carbonate, possibly correlates with the c. 580 Ma Squantum-Gaskiers glacial deposits of Avalonia. Available palaeomagnetic data for the Late Neoproterozoic suggest that Baltica was located at intermediate to high latitude between 620 and 555 Ma.

Nature, 2005

Collision tectonics and the associated transformation of continental crust to high-pressure rocks (eclogites) are generally well-understood processes, but important contradictions remain between tectonothermal models and petrological-isotopic data obtained from such rocks. Here we use 40 Ar-39 Ar data coupled with a thermal model to constrain the time-integrated duration of an orogenic cycle (the burial and exhumation of a particular segment of the crust) to be less than 13 Myr. We also determine the total duration of associated metamorphic events to be ,20 kyr, and of individual heat pulses experienced by the rocks to be as short as 10 years. Such short timescales are indicative of rapid tectonic processes associated with catastrophic deformation events (earthquakes). Such events triggered transient heat advection by hot fluid along deformation (shear) zones, which cut relatively cool and dry subducted crust. In contrast to current thermal models that assume thermal equilibrium and invoke high ambient temperatures in the thickened crust, our non-steady-state cold-crust model satisfactorily explains several otherwise contradictory geological observations.

Terra Nova, 1999

Journal of The Geological Society, 2000

Felsic orthogneisses occur widely in the Ollo de Sapo Domain of the Central Iberian Zone, most of which were previously considered to represent a Precambrian basement to the Palaeozoic sequences of this domain. However, new U-Pb dating across the Berzosa-Riaza shear zone (Sierra de Guadarrama, Central Spain) indicates an Early Ordovician age for the most representative types of orthogneisses in the eastern part of the Ollo de Sapo Domain. Dated rocks include the volcaniclastic Cardoso gneiss (480 2 Ma); from the low-medium-grade hanging wall; the Riaza gneiss (468 +16 8 Ma, mylonitic granite) in the Berzosa-Riaza shear zone; three types of 'leucogneiss' (Buitrago gneiss: 488 +10 8 Ma, megacrystic granite; 482 +14 11 Ma, aplitic vein; and 482 +9 8 Ma, gneissic leucogranite); and the La Morcuera granitic augen gneiss in the high-grade footwall. The new age of the Cardoso gneiss brackets to the Mid-Late Arenig, the so-called Early Ordovician Sardic unconformity, characteristic of the Central Iberian Zone. These new ages suggest that the broadly coeval volcanism and plutonism were closely associated with the Sardic events, and that these orthogneisses were part of a felsic magmatic belt which extended along the Ollo de Sapo Domain of the Central Iberian Zone. This magmatic belt is interpreted to have been active during the Early Ordovician break-up of the peri-Gondwanan margin of the Iapetus Ocean.

Journal of The Geological Society, 2007

Study of geochemistry, examination of isotope ages of detrital minerals, palaeomagnetic analysis, and a study of the trilobites were performed to provide constraints on the palaeogeographical position of the Holy Cross Mountains in Late Ediacaran-Early Palaeozoic time. The geochemical results indicate an active continental margin or continental island arc provenance of the Ediacaran sediments. Sediments from a passive continental margin were deposited here during the Cambrian and Ordovician. The palaeomagnetic pole isolated from Cambrian rocks of the Małopolska region of the Holy Cross Mountains corresponds to the Cambrian segment of the Baltic apparent polar wander path. Isotope age estimations indicate that Cambrian sediments of the Małopolska region contain detritus not only from a latest Neoproterozoic source but also from sources with ages of c. 0.8-0.9 Ga, 1.5 Ga and 1.8 Ga. The Małopolska, Brunosilesia, Dobrugea and Moesia terranes, which originally developed near the present southern edge of Baltica and were partly involved in the Cadomian orogen, were dextrally relocated along its Trans-European Suture Zone margin. The first stage of this movement took place as early as latest Ediacaran time, while Baltica rotated anticlockwise. Anticlockwise rotation of Baltica at the Cambrian-Ordovician boundary implies further dextral movement of the Małopolska block.

GFF, 1998

Despite their Early Phanerozoic age, the Scandinavian Caledonides provide a remarkably rich record of the continental break-up and development of the continent-ocean transition as well as the ensuing subduction and imbrication of the pristine plate margin, all emplaced on land and accessible. We first organize the evidence for Baltoscandian rift basin formation and magmatism, now scattered in two major nappe complexes (and by semantics) in terms of a superterrane, the Seve-Kalak Superterrane. Extensive (1000 km) mafic dyke swarms and partly sheeted dyke complexes are interpreted as fragments of a Large Igneous Province. While attempted break-up and some tholeiitic magmatism took place already at c. 800 Ma, successful rifting occurred first in connection with intense, partly alkaline dyking and emplacement of ultramafic complexes between c. 620 and 550 Ma. This late magmatism is markedly enriched as compared to MORB, interpreted to reflect mixing between an enriched mantle source component and depleted mantle. The evidence for Early Ordovician imbrication and subduction of the rifted and intruded margin is then reviewed. In order to explain the preservation of parts of the continent-ocean transition and rift basins, we suggest early detachment and thrusting towards the foreland, by analogy with the emplacement of the Semail Ophiolite. Intercalated garnet peridotites require incorporation of subcontinental mantle fragments during imbrication. Structures and fabrics of eclogites and their host rocks suggest that extensional tectonics was important during their Early Ordovician exhumation. If so, how much of Scandian extensional tectonics is instead inherited Finnmarkian?

Geological Society, London, Memoirs, 2011

Neoproterozoic strata in southeastern Idaho and Utah include the ,766 Ma Uinta Mountain Group and Big Cottonwood Formation (Fm.) deposited in an east-trending rift basin and, to the west, the lower part of a westward-thickening rift to passivemargin succession that initiated c. 720 Ma. The latter contains a lower diamictite and volcanic succession, with a complex stratigraphic interval of Cryogenian marine glacial deposits (Pocatello and Mineral Fork formations and correlatives). This is overlain by a mostly terrigenous succession of ,667 Ma strata assigned to the upper member of the Pocatello Fm. and Brigham Group in southeastern Idaho, to the Kelley Canyon Fm. and Brigham Group in northern and western Utah, and to the McCoy Creek Group and Prospect Mountain Quartzite in adjacent Nevada. Although the Brigham Group and correlative deposits contain no direct evidence for glaciation, widely developed, though stratigraphically restricted, incised valleys, with erosional relief from a few metres to as much as 160 m, are inferred to represent subsequent times of Cryogenian glacially lowered sea level. Overall interpretations of the stratigraphy and sedimentology of these rocks have changed little in the past 10-15 years. The most important recent advances relate to U-Pb geochronology. In strata that lie unconformably below demonstrable glacial deposits, the lower Uinta Mountain Group (formerly thought to be c. 900 Ma) contains populations of detrital zircons as young as 766 + 5 Ma. Cryogenian magmatism north of the Snake River Plain in central Idaho is recognized near House Mountain, east of Boise at c. 725 + 5 Ma, in the Pioneer Mountains Core Complex at about 695 Ma, and in central and east-central Idaho at 685-650 Ma. Clasts interpreted to be from the rift-related Bannock Volcanic Member of the Pocatello Fm. are dated at 717 + 4 Ma and 701 + 4 Ma. The overlying diamictite-bearing Scout Mountain Member contains a mafic lapilli tuff near the base (686 + 4 Ma) and a reworked fallout tuff near the top (667 + 5 Ma).

Norsk Geologisk Tidsskrift, 1999

Geological Magazine, 2008

Journal of the Geological Society, 2009

Paläontologische Zeitschrift, 1998

This article reviews events during the Proterozoic/ Cambrian turnover, termed the "Cambrian explosion". The first part heralds observed stages of the organismal evolution and discusses their influence and bearing on the latest concept of the Proterozoic/Cambrian boundary. In addition, the number and extent of Cambrian fossil lagerstaetten and their meaning for the interpretation of Metazoan diversification is discussed. A third part gives a synoptic overview of the most important proposed causes and mechanisms for the Cambrian explosion.

Tectonics, 2010

Journal of Geophysical Research, 2000

The GISS GCM was used to determine if a diverse set of climate forcings, alone or in combination, could have initiated the low-latitude ice sheets of the Varanger (---600 Ma) glacial interval. The simulations use a realistic reconstruction of the paleocontinental distribution and test the following forcings, alone and in combination: 6% solar luminosity decrease, four atmospheric CO2 scenarios (1260, 315, 140, and 40 ppm), a 50% increase and a 50% decrease in ocean heat transports, and a change in obliquity to 60 ø . None of the forcings, individually, produced year-round snow accumulation on low-latitude continents, although the solar insolation decrease and 40 ppm CO2 scenarios allowed snow and ice to accumulate at high and middle latitudes. Combining forcings further cools the climate: when solar luminosity, CO2, and ocean heat transports were all decreased, annual mean freezing and snow accumulation extended across tropical continents. No simulation would have initiated low-latitude glaciation without contemporaneous glaciation at higher latitudes, a finding that matches the distribution of glacial deposits but which argues against high obliquity as a cause of the Varanger ice age. Low-level clouds increased in most scenarios, as did surface albedo, while atmospheric water vapor amounts declined; all are positive feedbacks that drive temperatures lower. In the most severe scenario, global snow and ice cover increased to 68%, compared to 12% under modern conditions, and water vapor dropped by 90%. These results do not necessarily preclude a "snowball" Earth climate scenario for the Varanger glacial interv'al. However, either more severe forcings existed or radical changes occurred in the ocean/atmosphere system which are unaccounted for by the GCM. Also, as sea ice extent increased in these experiments, snow accumulation began to decline, because of an increasingly dry atmosphere. Under snowball Earth conditions, glaciation would be impossible, since the hydrological cycle would all but cease if the atmosphere's primary moisture source were cut off. graphic relationships between, glacial deposits of each interval leave open the possibility that glaciation in various regions was diachronous [e.g., , perhaps alternating with interglacial intervals that may have been at least as warm as the present interglacial. What is especially remarkable about the Neoproterozoic glaciations is their severity; recent paleomagnetic evidence demonstrates that during both m•or glaciations at least some land regions, which were located equatorward of 20 ø latitude, were affected by continental-scale glaciation at elevations down to sea level [e.g., Schmidt and Williams, 1995; .

GFF, 2014

Detrital zircon U -Pb ages of Lower Cambrian and Middle Devonian have been determined for sandstone in Estonia through LA-ICP-MS (Nu instruments, Wrexham, UK). Both sandstones have a similar zircon age spectrum with distinct age clusters that reflect the basement geology of Baltica, i.e. 2800-2700Ma (Kola-Karelia), 1900-1700Ma (Svecofennian), 1600-1500Ma (Rapakivi) and 1200-1000Ma (Sveconorwegian). Noteworthy is a cluster at 750-550 Ma, because rocks of such age are absent within the core of Baltica. The present results suggest a possible link between Baltica and A valonia/Cadomia during the Late Neoproterozoic.

Journal of Geophysical Research, 2002

1] Paleomagnetic results from an Upper Vendian sedimentary sequence exposed along the White Sea shoreline, NW Russia are described. These classical exposures have been the subject of intense paleontological investigations due to their well-preserved Ediacara fauna, but no paleomagnetic results have as yet been published. A total of 337 hand samples and 210 oriented drill cores (35 sites) along three profiles have been collected at the locality (65.5°, 40.0°E) where a 555 ± 3 Ma U-Pb age of comagmatic zircons from volcanic ash layers has been recently obtained. Standard paleomagnetic procedures yield two main natural remanent magnetization (NRM) components: an intermediate-temperature (150°-350°C), single-polarity component (D = 121°, I = 72°, n = 232 samples, k = 46.0, a 95 = 1.3°, pole position at 40.0°N, 79.0°E, dp = 2.0°, dm = 2.3°) and a high-temperature (550°-680°C) dual-polarity component (normal polarity: D = 278°, I = 43°, n = 54 samples, k = 25.2, a 95 = 3.9°, reversed polarity: D = 101°, I = À39°n = 40, K = 23.3, a 95 = 4.8°, south pole position at 24°S, 132°E, dp = 2.3°, dm = 3.8°). This latter component, termed Z, passes reversal, stratigraphic, and consistency tests and is interpreted to reflect the direction of the Earth's magnetic field during Late Vendian times. These results put Baltica into low northern latitudes (between 10°and 35°) and the resulting pole position requires modification of the most recent Apparent Polar Wander Paths (APWP) for Baltica.

Geological Society, London, Special Publications, 2011

Our recent geological survey of the basement of central and northern Madagascar allowed us to re-evaluate the evolution of this part of the East Africa-Antarctica Orogen (EAAO). Five crustal domains are recognized, characterized by distinctive lithologies and histories of sedimentation, magmatism, deformation and metamorphism, and separated by tectonic and/or unconformable contacts. Four consist largely of Archaean metamorphic rocks (Antongil, Masora and Antananarivo Cratons, Tsaratanana Complex). The fifth (Bemarivo Belt) comprises Proterozoic meta-igneous rocks. The older rocks were intruded by plutonic suites at c. 1000 Ma, 820-760 Ma, 630-595 Ma and 560-520 Ma. The evolution of the four Archaean domains and their boundaries remains contentious, with two end-member interpretations evaluated: (1) all five crustal domains are separate tectonic elements, juxtaposed along Neoproterozoic sutures and (2) the four Archaean domains are segments of an older Archaean craton, which was sutured against the Bemarivo Belt in the Neoproterozoic. Rodinia fragmented during the early Neoproterozoic with intracratonic rifts that sometimes developed into oceanic basins. Subsequent Mid-Neoproterozoic collision of smaller cratonic blocks was followed by renewed extension and magmatism. The global 'Terminal Pan-African' event (560-490 Ma) finally stitched together the Mid-Neoproterozoic cratons to form Gondwana. Recent work has shown that while all parts of the EAAO shared a common end-Proterozoic to earliest Ordovician geological history (Meert 2003; Collins & Pisarevsky 2005; Bingen et al.

Lithosphere, 2013

The recent discovery of ultrahigh-pressure (UHP) mineral parageneses in the far-transported (greater than 400 km) Seve Nappe Complex of the Swedish Caledonides sheds new light on the subduction system that dominated the contracting Baltoscandian margin of continental Baltica during the Ordovician and culminated in collision with Laurentia in the Silurian to Early Devonian. High-grade metamorphism of this Neoproterozoic to Cambrian rifted, extended, dike-intruded outer-margin assemblage started in the Early Ordovician and may have continued, perhaps episodically, until collision of the continents at the end of this period. The recent discovery of UHP kyanite eclogite in northern Jämtland (west-central Sweden) yields evidence of metamorphism at depths of 100 km. Although UHP rocks are only locally preserved from retrogression during the long-distance transport onto the Baltoscandian platform, these high-pressure parageneses indicate that deep subduction played an important role in the tectonothermal history of the complex. Based on existing isotopic age data, this UHP metamorphism occurred in the Late Ordovician, shortly before, or during, the initial collision between the continents (Scandian orogeny). In some central parts of the complex, migmatization and hot extrusion occurred in the Early Silurian, giving way to thrust emplacement across the Baltoscandian foreland basin and platform that continued into the Early Devonian. Identifi cation of HP/UHP metamorphism at different levels within the Scandian allochthons, defi nition of their pressure-temperature-time paths, and recognition of their vast transport distances are essential for an understanding of the deeper structural levels of the orogen in the hinterland (e.g., the Western Gneiss Region), where the attenuated units were reworked together during the Early Devonian.

Journal of the Geological Society, 2009

Avalonia is the largest accreted crustal block in the Appalachian orogen and comprises a collection of late Neoproterozoic volcano-sedimentary sequences that are overlain by a Palaeozoic platformal sedimentary succession. Detrital zircons from the Conception Group are dominated by 570-620 Ma ages and contain a significant component generated by erosion of coeval igneous arc-volcanic rocks. Overlying samples from the Cuckold and Crown Hill formations are dominated by Neoproterozoic populations with ages between 600 and 650 Ma and are interpreted to be derived from the underlying calc-alkaline arc-plutonic rocks. Early Palaeozoic platform units are dominated by c. 620 Ma zircons with lesser Mesoproterozoic and Palaeoproterozoic zircons. The range of detrital zircon ages is inconsistent with a West African provenance and suggests that Avalonia originated along the Gondwanan margin of the Amazon craton. The influx of Mesoproterozoic and Palaeoproterozoic detritus in the Avalonian platform suggests a major change in tectonic regime. The prominent change in provenance is interpreted to be related to separation of Avalonia from Gondwana during the Early Ordovician opening of the Rheic Ocean. The Redmans Formation is interpreted to represent the rift-drift transition of the Rheic Ocean, which imposes important constraints on the palaeotectonic evolution of Avalonia. Supplementary material: U-Pb isotopic data of LA-ICP-MS analysis of detrital zircons are available at

Izvestiya, Physics of the Solid Earth, 2013

The new paleomagnetic data on forty dikes and two intrusive plutons of Devonian age located in different parts of the Kola Peninsula, which have not been previously covered by systematic paleomagnetic studies, are reported. We describe the results of the rock magnetic, petrographic, and microprobe investiga tions of the Devonian dikes and present their isotopic ages ( 40 Ar/ 39 Ar, stepwise heating). Within the studied area, almost all the Devonian dikes, metamorphic Archaean-Proterozoic complexes of the Fennoscandian Shield, and Proterozoic dikes have undergone low temperature hydrothermal-metasomatic alteration, which resulted in the formation of new magnetic minerals with a secondary (chemical) component of mag netization. The comparison of the paleomagnetic poles indicates the Early Jurassic age of the secondary com ponent. We suggest that regional remagnetization event was caused by endogenic activity genetically related to the formation of the Barents Sea trap province 200-170 Ma ago. On the basis of the obtained data, the preliminary Devonian paleomagnetic pole of the East European Platform is determined.

Geophysical Monograph Series, 2004

Whereas the snowball Earth hypothesis seems to account for most of the major fea tures of the Neoproterozoic glacial records, the causes that drove the Earth into a snowball state remain largely open to debate. Most of the mechanisms leading to the initiation of a snowball Earth are based on the existence of the unusual preponder ance of land masses in the tropics. However, the time of the youngest Neoprotero zoic glaciation is characterised by a rather widely distributed geography from low-to-high latitudes. In the absence of reliable knowledge of Neoproterozoic topog raphy, two series of coupled ocean-atmosphere climate model simulations were car ried out with a Late Neoproterozoic paleogeography (580 Ma) and solar luminosity reduced by 6% relative to today, the first one with flat continents and the second one with mountain ranges that mimic the Pan-African Orogen occurring at this time. Those climatic simulations coupled to the long-term carbon cycle have allowed to better constrain the atmospheric pC0 2 and the associated climate by the time of the youngest late Proterozoic glaciation. The Pan-African Orogen runs result in a snow accumulation pattern compatible with a regional-scale glaciation more less exten sive while the no relief runs do not succeed in initiating any glaciation. These results could give additional support to the inferences from many authors that some of the glacial deposits originally attributed to a snowball-like glaciation could in fact be the consequence of a more localised glaciation due to the important orogen occurring at the end of the Neoproterozoic.

Paläontologische Zeitschrift, 2011

Twelve species of Brachiopods are described from the Silurian of Gotland, six furcitellinines and six ''strophodontids.'' One is new-Strophodonta hoburgensis n. sp. The furcitellinines are moderately common and diverse in the lower part of the succession, but the last species disappears in the middle Hemse beds (*middle Ludlow). Three genera are represented: Bellimurina, Pentlandina and Katastrophomena, with the species and subspecies B. wisgoriensis, P. tartana, P. loveni, P. lewisii lewisii, K. penkillensis and K. antiquata scabrosa. Most of the taxa are confined to low energy environments, but P. loveni was evidently specialized for the high energy reef environments of the Högklint Formation. B. wisgoriensis displays environmentally induced morphological variability in developing strong, frilly growth lamellae in high-energy environments. The ''strophodontids,'' although belonging to three different families, share a common morphology consisting of denticles along the hinge line, a semi-circular outline, unequally to finely costellate ornament and, most importantly, a concavo-convex profile with both valves of the same curvature, enclosing a very small body chamber. Two leptostrophiids are generalists, occurring in both highand low-energy environments and with long stratigraphical ranges [Mesoleptostrophia filosa; latest Llandovery through the entire Ludlow. Brachyprion (Brachyprion) semiglobosa; latest Llandovery to latest Wenlock]. The third leptostrophiid (Brachyprion (Erinostrophia) walmstedti) is short ranged and occurs in low-energy environments in the latest Llandovery. The species belonging to the Strophodontidae (Strophodonta hoburgensis n. sp.) and Shaleriidae [Shaleria (Janiomya) ornatella and S. (Shaleriella) ezerensis] occur only in high-energy environments and have a short range within the late Ludlow.

Geophysical Research Letters, 1999

We calculate polar motion in models of 3-D spherical mantle convection at Rayleigh numbers up to 10 s which include internal heating, radial viscosity variations, and an endothermic phase change. Isoviscous models yield rapid polar motion of order 3ø/Myr, but a factor of 30 increase in viscosity with depth reduces the rate of polar motion to about 0.5ø/Myr due to stabilization of the large-scale pattern of convection. Avalanching due to an endothermic phase change causes pulsating inertial interchange polar excursions of order 80-110øand of duration 20-70 Myr. A layered viscosity model with an endothermic phase change yields only one inertial interchange event in 600 million years. These models show that the slow observed rate of post-Paleozoic true polar wander is not incompatible with higher rates inferred for earlier times. Van der Voo, R., True polar wander during the middle Paleozoic?, Earth Planet. Sci. Lett., 122, 239-243, 1994.

Lethaia, 2004

Journal of the Geological Society, 2004

The Brunovistulian was one of the first tectonic units of Central Europe to be defined as a 'terrane'. In spite of extensive studies, the Early Palaeozoic palaeogeographical position and provenance of this unit remains unclear. A palaeomagnetic study of the Lower Cambrian red beds and a study of the trilobite fauna were performed to provide constraints on the palaeogeographical position of the terrane in Early Cambrian time. Good quality palaeomagnetic data obtained from the Lower Cambrian red beds suggest the mixed nature of the Early Cambrian geomagnetic field and a nearly equatorial position (a palaeolatitude of c. 78) of the Brunovistulian terrane in the Early Cambrian. Comparison of this palaeolatitude with existing palaeogeographical models leads to the conclusion that at this time the Brunovistulian terrane was separated by a great distance from the Avalonian margin of Gondwana. The terrane was located within the Cadomian belt, occupying a position north of the present-day northern margin of Africa. It was coupled to the present-day southern margin of Baltica during the Cambrian, when Baltica moved along the Cadomian margin of Gondwana. Another possibility is that the Brunovistulian terrane could have remained near this margin of Baltica since Grenvillian time and was incorporated into the Cadomian orogen.

Geological Magazine, 2012

New palaeomagnetic and petrographic data are presented from Cambrian rocks of SW Svalbard to test, for the first time, Palaeozoic reconstructions of the major terranes of Svalbard. In the course of thermal demagnetization three ChRM (characteristic remanent magnetization) components were identified, which were labelled HORNL, HORNM and HORNH, respectively, on the basis of their different unblocking temperatures. The HORNM magnetization is related to the Late Ordovician–Silurian formation of the synmetamorphic S1 foliation. The HORNM palaeopole (Φ = −18.5°, Λ = 359°, Dp/Dm = 5.8°/11.4°, Plat = 6°N) matches exactly the Silurian sectors of the Baltica–Laurentia apparent polar wander paths after the closure of Iapetus (455–415 Ma). The 450 Ma 40Ar–39Ar age determination from mica ages obtained from the broad zone of mylonites along the Billefjorden Fault Zone which separates the Central and Eastern terranes, also suggests that the two terranes were eventually amalgamated by 450 Ma. The ...

Tectonics, 1999

The Ivrea crustal section exposes in map view all levels of the southern Alpine continental crust, tom ultramafic, mafic, and felsic granulite facies rocks of the deep crust (lvrea-Verbano Zone), through medium-grade basement rocks (Strona-Ceneri Zone and Val Colla Zone), to unmetamorphosed Permo-Mesozoic sediments. The oldest part of the crustal section is preserved in the medium-grade basement units, which are interpreted to be the overprinted remains of an Ordovician (440-480 Ma) magmatic arc or forearc complex. During

Journal of Geophysical Research, 2000

Minerals

During the period 750–600 Ma ago, prior to the final break-up of the supercontinent Rodinia, the crust of both the North American Craton and Baltica was intruded by significant amounts of rift-related magmas originating from the mantle. In the Proterozoic crust of Southern Norway, the 580 Ma old Fen carbonatite-ultramafic complex is a representative of this type of rocks. In this paper, we report the occurrence of an ultramafic lamprophyre dyke which possibly is linked to the Fen complex, although 40Ar/39Ar data from phenocrystic phlogopite from the dyke gave an age of 686 ± 9 Ma. The lamprophyre dyke was recently discovered in one of the Kongsberg silver mines at Vinoren, Norway. Whole rock geochemistry, geochronological and mineralogical data from the ultramafic lamprophyre dyke are presented aiming to elucidate its origin and possible geodynamic setting. From the whole-rock composition of the Vinoren dyke, the rock could be recognized as transitional between carbonatite and kimbe...

Geological Society, London, Special Publications

An updated magnetic anomaly grid of the NE Atlantic and an improved database of magnetic anomaly and fracture zone identifications allow the kinematic history of this region to be revisited. At break-up time, continental rupture occurred parallel to the Mesozoic rift axes in the south, but obliquely to the previous rifting trend in the north, probably due to the proximity of the Iceland plume at 57–54 Ma.The new oceanic lithosphere age grid is based on 30 isochrons (C) from C24n old (53.93 Ma) to C1n old (0.78 Ma), and documents ridge reorganizations in the SE Lofoten Basin, the Jan Mayen Fracture Zone region, in Iceland and offshore Faroe Islands. Updated continent–ocean boundaries, including the Jan Mayen microcontinent, and detailed kinematics of the Eocene–Present Greenland–Eurasia relative motions are included in this model.Variations in the subduction regime in the NE Pacific could have caused the sudden northwards motion of Greenland and subsequent Eurekan deformation. These ...

Geophysical Journal International, 2004

The 930-Ma Egersund-Ogna anorthosite is part of the Rogaland igneous complex of massiftype anorthosites intruded into Sveconorwegian basement of southwestern Norway. Average susceptibilities on samples from 13 sites range from 0.03 to 2.24 × 10 −3 SI and natural remanent intensities range from 0.004 to 1.54 A m −1. Corresponding Koenigsberger ratios range from 3 to 148 with a mean value of 36, indicating that magnetic field surveys will observe remanent-controlled magnetic anomalies. Optical observations indicate that haemo-ilmenite is the major oxide phase present, with lesser amounts of ilmeno-haematite and rare magnetite. Remanent directions from all samples are characterized by steeply negative inclinations with variable northwest declinations. Thermal demagnetization reveals square-shouldered demagnetization curves with little or no loss of intensity until 550 or 575 • C. Alternating field demagnetization produces a wide range of demagnetization behaviours with mean destructive fields varying from less than 5 mT to greater than 80 mT. There is little evidence for overprinting or secondary components, and all information points to a remanence acquired during initial cooling of the anorthosite at ∼ 900 Ma. Mean directional data for the 13 sites are D = 325. • 9, I = −80. • 1 and a 95 = 4. • 9. The magnetic pole calculated for Egersund-Ogna is at 42. • 1S latitude and 200. • 4 E longitude (A 95 = 9. • 0), in excellent agreement with an earlier pole determined from Egersund, and similar to other poles from Rogaland igneous complex rocks. This work supports Rodinia reconstructions that place Baltica at high (southern) latitude, ∼ 70 • , at about 900 Ma. Apparent polar wander paths for Baltica at this time are ambiguous and it is difficult to discriminate between proposed clockwise or counterclockwise loops.

Minerals

We present new whole-rock major and trace element, mineral chemistry, and U-Pb isotope data for the Ulan-Sar’dag mélange, including different lithostratigraphic units: Ophiolitic, mafic rocks and metavolcanites. The Ulan-Sar’dag mélange comprises of a seafloor and island-arc system of remnants of the Paleo-Asian Ocean. Detailed studies on the magmatic rocks led to the discovery of a rock association that possesses differing geochemical signatures within the studied area. The Ulan-Sar’dag mélange includes blocks of mantle peridotite, podiform chromitite, cumulate rocks, deep-water siliceous chert, and metavolcanic rocks of the Ilchir suite. The ophiolitic unit shows overturned pseudostratigraphy. The nappe of mantle tectonites is thrusted over the volcanic-sedimentary sequence of the Ilchir suite. The metavolcanic series consist of basic, intermediate, and alkaline rocks. The mantle peridotite and cumulate rocks formed in a supra-subduction zone environment. The mafic and metavolcani...

Canadian Journal of Earth Sciences

The Potsdam Group is a Cambrian to Lower Ordovician siliciclastic unit that crops out along the southeastern margins of the Ottawa graben. From its base upward, the Potsdam consists of the Ausable, Hannawa Falls, and Keeseville formations. In addition, the Potsdam is subdivided into three allounits: allounit 1 comprises the Ausable and Hannawa Falls, and allounits 2 and 3, respectively, the lower and upper parts of the Keeseville. Allounit 1 records Early to Middle Cambrian syn-rift arkosic fluvial sedimentation (Ausable Formation) with interfingering mudstone, arkose, and dolostone of the marine Altona Member recording transgression of the easternmost part of the Ottawa graben. Rift sedimentation was followed by a Middle Cambrian climate change resulting in local quartzose aeolian sedimentation (Hannawa Falls Formation). Allounit 1 sedimentation termination coincided with latest(?) Middle Cambrian tectonic reactivation of parts of the Ottawa graben. Allounit 2 (lower Keeseville) re...

3 Biotech, 2016

Pseudomonas, an enormously diverse genus of the c-Proteobacteria, is an important member of soil microbial communities. In this study, genetic heterogeneity and plant growth promotory property of Pseudomonas was compared within the group Pseudomonas sensu stricto isolated from the lesser explored niches of Himalayan region. A significant difference (P \ 0.001 in total Pseudomonas count) was observed among the six types of soil samples collected from oak forest, fine forest, and agricultural soil. The highest numbers of bacteria were isolated from oak forest soil followed by pine forest soil and agricultural soil. 23.52 % of the total 238 isolates were siderophore producers and were identified as Pseudomonas on the basis of PCR amplification using 16S rDNA Pseudomonas specific primer. The molecular analysis by Jaccard's similarity coefficient resulted into eight different clusters and six outlying branches. Some of the clusters include Pseudomonas from forest as well as agricultural land. Among the 51 isolates 100 % were siderophore and IAA producers, 68.62 % were phosphate solubilizers and 62.74 % HCN producers. The results reveal that isolates from lesser explored area possess beneficial properties and show genetic heterogeneity among them.

Lethaia, 2014

The history of the Iapetus Ocean in the lower Palaeozoic is well established and faunal distribution has contributed significantly to the development of this knowledge; however, lingulate brachiopods have traditionally been considered to be of little utility in assessing palaeobiogeography. The distribution of lingulate brachiopods across the Iapetus region is analysed using a number of similarity indices and other statistical measures. This analysis shows a clear palaeobiogeographic signal where lingulate faunas are sufficiently diverse, reflecting the history of the Iapetus ocean and the relative separation of Laurentia and Baltica through the Cambrian and Ordovician. Lingulate faunas on Avalonia are, however, low in diversity and show relatively high endemism; this renders them of little use in assessing the separation of Avalonia from other areas. Evidence of earlier increases in faunal similarity in lingulate faunas between continents, compared to other fossil groups, provides confirmatory evidence that Palaeozoic lingulates had long-lived planktotrophic larvae.

Ore Geology Reviews, 2022

This manuscript presents results of the newest petrographic, mineralogical and bulk chemical, as well as H, C and O stable isotope study of carbonatites and associated silicate rocks from the Tajno Massif (NE Poland). The Tajno Intrusion is a Tournaisian-Visean ultramafic-alkaline-carbonatite body emplaced within the Paleoproterozoic rocks of the East European Craton (EEC). Carbonatites of the Tajno Massif can be subdivided into the calciocarbonatite (calcite), ferrocarbonatite (ankerite), and breccias with an ankerite-fluorite matrix. Due to location at the cratonic margin and abundance in the REE, Tajno classifies (Hou et al., 2015) as the carbonatite-associated REE deposit (CARD), and more precisely as the Dalucao-Style orebody (the breccia-hosted orebody). High Fe 2 O 3 (13.8 wt%), MnO (2.1 wt%), total REE (6582 ppm), Sr (43895 ppm), Ba (6426 ppm), F (greater than10000 ppm) and CO 2 contents points for the involvement of the slabincluding pelagic metalliferous sedimentsin the carbonatites formation. Spatial relations and Sr isotope composition ((87 Sr/ 86 Sr) i = 0.7043-0.7048; Wiszniewska et al., 2020) of alkali clinopyroxenite and syenite suggest that these are products of differentiation of the magma, generated by the initial melting of the SCLM due to influx of F-rich fluids from subducted marine sediments. Carbonatites Sr isotope composition ((87 Sr/ 86 Sr) i = 0.7037-0.7038), and Ba/Th (16-20620) and Nb/Y (0.01-6.25) ratios, link their origin with a more advanced melting of the SCLM, triggered by CO 2-rich fluids from the subducted AOC and melts from sediments. The Tajno Massifand coeval mafic-alkaline intrusionsage, high potassic composition, and location along the craton margin nearly parallel the Variscan deformation front, are suggesting Variscan subduction beneath the EEC. The oxygen isotope compositions of clinopyroxene (δ 18 O value = 5.2‰) and alkali feldspar (δ 18 O value = 5.7‰), from alkali clinopyroxenite and foid syenite, respectively, are consistent with mantle-derived magmas. Isotopic compositions of carbonatites and breccias (carbonate δ 18 O = 8.7‰ to 10.7‰; δ 13 C =-4.8‰ to − 0.4‰) span from values of primary carbonatites to carbonatites affected by a fractionation or sedimentary contamination. The highest values (δ 18 O = 10.7‰; δ 13 C =-0.4‰) were reported for breccia cut by numerous veins confirming post-magmatic hydrothermal alteration. The lowest carbonate δ 18 O (9.3‰ to 10.7‰) and δ 13 C (− 5.0‰ to − 3.8‰) values are reported for veins in alkali clinopyroxenites, whereas the highest δ 18 O (11.2‰) and δ 13 C (− 1.2‰ to − 1.1‰) values are for veins in syenites and trachytes. Isotopic composition of veins suggests hydrothermal origin, and interaction with host mantle-derived rocks, as well as country rocks. In silicate rocks of the Tajno Massif, fluid influx leads to the development of Pb, Zn, Cu, Ag, Au sulfide mineralization-bearing stockwork vein system, with carbonate, silicate and fluorite infilling the veins. Bulk-rock contents of molybdenum (925 ppm), rhenium (905 ppb) and palladium (29 ppb) are notable. The Re-rich molybdenite association with galena, pyrite and Th-rich bastnäsite in carbonate veins is similar as in Mo deposits associated with carbonatites, implying the mantle source of Mo and Re.

Minerals, 2021

The U–Pb measurements of youngest, coherent group of zircons from the Mielnik IG1 dolerite at the Teisseyre-Tornquist margin (TTZ) of East European Craton (EEC) in Poland yielded age of 300 ± 4 Ma. Zircon dated an evolved portion of magma at the late stage crystallization. It is shown that this isolated dyke from the northern margin of the Lublin Podlasie basin (Podlasie Depression) and regional dyke swarms of close ages from the Swedish Scania, Bornholm and Rügen islands, Oslo rift, Norway, and the Great Whine Sill in northeastern England, were coeval. They have been controlled by the same prominent tectonic event. The Mielnik IG1 dolerite is mafic rock with Mg-number between 52 and 50 composed of the clinopyroxene, olivine-pseudomorph, plagioclase, titanite, magnetite mineral assemblage, indicating relatively evolved melt. This hypabyssal rock has been affected by postmagmatic alteration. The subalkaline basalt composition, enrichment in incompatible trace elements, progressive cr...

Terra Nova, 2002

Tectonics, 2018

Top-ESE shear is pervasive across the metamorphically zoned Caledonian nappe pile  Mylonitic fabrics indicate sustained foreland-directed general shear, causing exhumation by concurrent thrusting and vertical thinning  Back-stepping of Baltica subduction resulted in out-of-sequence propagation of orogenic wedge This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record.

Tectonics, 2002

Recent field investigations in the central East Greenland Caledonides (72°-74°N) resulted in the identification of an orogen-scale extensional fault system called the Fjord Region Detachment (FRD). Previous geochronologic constraints on this deformation indicated that the FRD was active circa 430-425 Ma, a time when the Baltica-Laurentia collision was thought to be occurring, and continued to be active for up to 80 million years. We present new 40 Ar/ 39 Ar thermochronologic data from an E-W transect that cuts across two splays of the FRD. Our data demonstrate that at least two distinct episodes of faulting were responsible for extension in the East Greenland Caledonides: an earlier phase (circa 425-423 Ma) that was synorogenic and penetrated to middle-crustal levels, followed by a post-Caledonian phase of reactivation ($414 to 380 Ma) that affected even deeper structural levels. Furthermore, we present in situ UV laser 40 Ar/ 39 Ar data for pseudotachylite collected along the deepest splay of the FRD that indicate this fault was active again as recently as $357 Ma (coeval with Devonian basin formation). Altogether, our data suggest that rather than being active continuously for 80 million years, the FRD consisted of multiple splays that were active for shorter intervals over discrete time periods separated by as much as 60 million years. Finally, our data provide evidence that young extensional deformation associated with postorogenic collapse in East Greenland was not restricted to the formation of sedimentary basins in the far eastern part of the orogen, but also resulted in deformation of the Archean-Paleozoic crystalline basement.

Tectonics, 2014

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as

GFF, 2021

The Ottfjället Dyke Swarm (ODS) is a prominent component of the Ediacaran mafic magmatism associated with opening of the Iapetus ocean, and hosted in the Särv Nappe, Middle Allochthon of the Scandinavian Caledonides. A U-Pb baddeleyite age of 596.3 ± 1.5 Ma for a thick, well preserved, plagioclase-phyric dolerite dyke in Härjedalen, Sweden, dates emplacement of the swarm. The age represents a robust, inheritance-free reference age for variably deformed and metamorphosed tholeiitic dykes in sandstone-dominated sequences of the lower part of the Middle Allochthon, representing the proximal, rifted Baltoscandian margin preceding the opening of Iapetus. The new age is within the narrow time span between 610 and 595 Ma defined by the most reliable age estimates for mafic dykes in structurally higher nappes (upper part of Middle Allochthon), representing the distal margin during the opening of Iapetus. The Ottfjället Dyke Swarm cuts the Tossåsfjället Group succession, which includes sabkha-related carbonate platform and diamictite couples, one of several correlated Neoproterozoic glaciogenic successions in Scandinavia. The intrusion age of ca. 596 Ma therefore sets a minimum age for the glaciogenic successions. It implies that Neoproterozoic glaciations in Scandinavia predate the ca. 580 Ma Gaskiers glaciation event and are probably part of the ca. 635 Ma Marinoan "Snowball-Earth"-type glaciation.

Lithosphere, 2010

The close spatial relationship between Devonian high-pressure rocks (eclogites) and Ordovician-Silurian calc-alkaline plutonic rocks, as observed in Liverpool Land, NE Greenland, is not easily explained by existing tectonic models for the Caledonide orogen. New fi eld studies and isotope dilution-thermal ionization mass spectrometry U-Pb geochronology demonstrate, however, that the association is just coincidental, because the two rock groups are located within distinct terranes separated by a composite structure. The major element is the Gubbedalen shear zone, a N-dipping shear zone dominated by a penetrative top-up-to-the-S ductile fabric. Superimposed brittle-ductile topdown-to-theN shear zones are typical of the structurally uppermost part of the shear zone. The contact against the hanging wall is the N-dipping, brittle Gubbedalen extensional detachment fault. A zircon age of 399.5 ± 0.9 Ma for an eclogite body is interpreted to represent the time of high-pressure metamorphism of the footwall. The host gneiss was migmatized between ca. 388 Ma and ca. 385 Ma, as constrained by the ages of a pegmatite predating migmatization and crosscutting granites. Coeval synkinematic granites intrude along amphibolite-grade, top-to-the-S high-strain zones in the Gubbedalen shear zone. Juxtaposition of the Ordovician-Silurian plutonic terrane (hanging wall) against the Early to mid-Devonian eclogite terrane (footwall) is best explained by a tectonic model involving early mid-Devonian buoyancy-driven exhumation followed by late mid-Devonian syncontractional extension related to thrusting on the Gubbedalen shear zone in a dextral strike-slip zone. Subsequent exhumation through the brittle-ductile transition occurred by extension on early semiductile structures and the overprinting Gubbedalen extensional detachment fault, and erosion.

Journal of Geophysical Research: Solid Earth, 2002

This paper presents new data from paleomagnetic investigations of Middle Paleozoic (Early-Middle-Late Devonian, Early Carboniferous) and Middle Jurassic geological units from the Amuria block south of the Mongol-Okhotsk suture zone. With fold tests for all localities, and two polarities for the Devonian, our new results constrain the evolution of the Mongol-Okhotsk ocean from the Devonian to the Middle Jurassic. The corresponding paleopoles lie at 21.6°N, 6.3°E (dp/dm = 5.3°/10.6°) for Early Devonian, 26.3°N, 345.3°E (dp/dm = 6.4°/12.8°) for Early-Middle Devonian, 24.6°N, 12.9°E (dp/ dm = 8.7°/16.9°) for Middle-Late Devonian, 40.5°N, 352.4°E (dp/dm = 9°/16.7°) for Late Devonian, 39.8°N, 31.6°E (dp/dm = 10°/15.5°) for Early Carboniferous, and 46°N, 37.9°E (dp/dm = 9.4°/13.4°) for Middle Jurassic. The poles confirm that the large Paleozoic Mongol-Okhotsk ocean closed during the Jurassic, ending up in the late Jurassic or early Cretaceous at the eastern end of the suture zone, as originally proposed on geological grounds. The new paleomagnetic results exhibit large tectonic rotations about local vertical axes, which we interpret as probably arising from both the collision process and left-lateral shear movement along the suture zone, related to incipient extrusion of Amuria due to indentation of India into Asia.

Earth-Science Reviews, 2021

Recent progress in plate tectonic reconstructions has seen models move beyond the classical idea of continental drift by attempting to reconstruct the full evolving configuration of tectonic plates and plate boundaries. A particular problem for the Neoproterozoic and Cambrian is that many existing interpretations of geological and palaeomagnetic data have remained disconnected from younger, better-constrained periods in Earth history. An important test of deep time reconstructions is therefore to demonstrate the continuous kinematic viability of tectonic motions across multiple supercontinent cycles. We present, for the first time, a continuous full-plate model spanning 1 Ga to the present-day, that includes a revised and improved model for the Neoproterozoic-Cambrian (1000-520 Ma) that connects with models of the Phanerozoic, thereby opening up pre-Gondwana times for quantitative analysis and further regional refinements. In this contribution, we first summarise methodological approaches to full-plate modelling and review the existing full-plate models in order to select appropriate models that produce a single continuous model. Our model is presented in a palaeomagnetic reference frame, with a newly-derived apparent polar wander path for Gondwana from 540 to 320 Ma, and a global apparent polar wander path from 320 to 0 Ma. We stress, though while we have used palaeomagnetic data when available, the model is also geologically constrained, based on preserved data from past-plate boundaries. This study is intended as a first step in the direction of a detailed and self-consistent tectonic reconstruction for the last billion years of Earth history, and our model files are released to facilitate community development.

Journal of Petroleum Geology, 2017

The Ediacaran (Upper Neoproterozoic) succession in west and SW Ukraine and Moldova rests on a Cryogenian succession or basement. The succession is exposed at the surface along the southern margin of the Ukrainian Shield and dips to the SW towards the Carpathian Overthrust; where burial depths are sufficient, it is mature for oil and gas generation. The Ediacaran succession is made up of terrigenous siliciclastics ranging from conglomerates and sandstones to siltstones and mudstones, and includes a shale interval (the Kalus Beds) which may have source rock potential. Organic matter in the Kalus shales includes Vendotenides sp. (colonial bacteria) together with amorphous OM. This paper presents a study of the Kalus Beds and is based on data from surface and core samples and thin sections, and the results of Rock‐Eval pyrolysis and reflectance analyses. TOC contents in the Kalus shales are in general <0.5 wt%, although the measured TOC was 0.89 wt% and 0.84 wt%, respectively, in sam...

Geological Society, London, Memoirs, 2011

The northwestern part of the Scandinavian Caledonides, formed by SE-to ESE-directed thrusting through the Neoproterozoic W. Baltica continental shelf, contains numerous small and often isolated outcrops of diamictite and associated strata. No precise biostratigraphic or isotopic data are available to constrain the age of these sediments, but, on the basis of their stratigraphic position, most are correlated with the Mortensnes Formation (Fm.) in E. Finnmark and also presumed to be of glaciogenic origin. The Mortensnes Fm. has been correlated with the 580 Ma Gaskiers glacial event on the basis of d 13 C isotope studies. Structurally, the deposits occur in the Autochthon (below the Torneträsk Fm.), within an external imbricate zone (Lower Allochthon), within cover successions lying unconformably on allochthonous basement (Window Allochthon) palaeogeographically derived from below or outboard of the Lower Allochthon and, more rarely, within the Middle Allochthon, derived from outboard of the Window Allochthon. Evidence for a glaciogenic origin is typically poor or lacking. Only in the Komagfjord Antiformal Stack (Window Allochthon), where an up to 40-m-thick succession of three fining upwards cycles has been mapped, are the deposits comparable in thickness and complexity to the Mortensnes Fm. Other sequences are sometimes ,1 m thick and unconformably overlain by post-'glacial' deposits. The Vakkejokk Breccia, a submarine slump in the Torneträsk area of the Autochthon closely underlies the correlative Precambrian-Cambrian lithostratigraphic boundary in E. Finnmark but overlies the first appearance of the boundary marker fossil Treptichnus pedum. Although sometimes interpreted as periglacial, this seems unlikely in view of the 30-508 palaeolatitude during deposition. Calcite nodules (,1 cm size) in the Vakkejokk Breccia have previously been interpreted as glendonite, but the microstructure and palaeolatitude makes this unlikely; they are likely a replacement of gypsum. Diamictites of uncertain origin have also been found in the Ediacaran Lower Siltstone Member of the Torneträsk Fm. and unconformably under the ?Lower Cambrian Lomvatn Fm. in the Komagfjord Antiformal Stack. This chapter primarily covers (meta-)sediments correlated with the Mortensnes Fm., the younger of the two glaciogenic units of E. Finnmark, N. Norway (cf Rice et al. 2011). Such deposits typically occur as small and isolated outcrops within both the Autochthon and nappes of the Scandinavian Caledonides, often resting unconformably on basement rocks (Kumpulainen 2011; Kumpulainen & Greiling 2011; Nystuen & Lamminen 2011) After restoration of the Caledonian nappes, these diamictite outcrops indicate that glacial deposits covered an area of some 140 000 km 2 in N. Scandinavia (including E. Finnmark). Studies in Norrbotten, Sweden, in the southernmost part of the area covered here (Fig. 58.1), led Kulling (1951) to introduce the term Varangeristiden (Varang(er)ian glaciation) to encompass both the glacial events described here and the earlier Smalfjord Fm. (Marinoan). However, for reasons summarized below, this term should no longer be used.

Geosphere, 2008

The Neoproterozoic was characterized by an extreme glaciation, but until now there has been no consensus as to whether it was a complete glaciation (snowball Earth) or a less severe glaciation (slushball Earth). We performed sensitivity experiments with an Earth model of intermediate complexity for this period of dramatic global cooling. Our simulations focus on the climate response on a cool versus a cold ocean, on a desert versus a glacier land surface, and on a lower versus a higher CO 2 concentration. All Neoproterozoic model experiments represent much colder conditions than today and widespread glaciation. In case of an initial forcing representing a snowball Earth, the model maintains its complete glaciation, and temperatures are as low as-45 °C in equatorial latitudes. At the poles, the snowball experiments demonstrate annual average temperatures of <-70 °C. If the initial model forcing is more moderate (slushball Earth), polar temperatures are <-50 °C, but temperatures in low latitudes stay well above the freezing point of water, and therefore ice-free ocean areas remain. Based on our simulations, we are able to observe that global climate reacts less sensitively to reductions of atmospheric CO 2 during times with increased glaciations. Our results suggest that the development of glaciers on land contributes signifi cantly to intense ice coverage of the oceans. Because simulations initialized without complete ice cover do not reach the global glaciation condition, we conclude that our simulations support the rather moderate scenario of a slushball Earth than the extreme snowball Earth hypothesis. The experimental design and the model might, however, limit the interpretation of our results.

International Journal of Earth Sciences, 2018

Results of a depth-to-basement study are presented for the East European Craton and the Teisseyre-Tornquist Zone (TTZ) in Poland. The terrestrial gravity data are inverted for the top of the Paleoproterozoic basement and, independently, for the top of the Ediacaran using seismic horizons from the PolandSPAN™ seismic survey and well tops as input depth measurements. The depth to the Ediacaran modelling was additionally extended to cover the Łysogóry Block and northern Małopolska Block. The results are visualised as isobath maps for the top of the Paleoproterozoic basement and top of the Ediacaran and an isopach map for the Ediacaran, supplemented with qualitative structural interpretation based on gravity and magnetic data. The results of modelling show a smooth crystalline basement slope within the TTZ with the top of the Paleoproterozoic basement uniformly descending south-westwards by 10-14 km. The thickness of the Ediacaran in SE Poland increases in the same direction to more than 10 km within the TTZ. Such a crustal architecture, in combination with the earlier documented Moho elevation of 4-6 km, reveals significant thinning of the Paleoproterozoic crust within the TTZ to form a crustal necking zone due to the Ediacaran rifting. A smooth geometry of the top of basement along with the lack of basement-rooted faults suggests a ductile mode of crustal thinning during rifting of Rodinia. Moreover, the development of the NW-SE-oriented rift, a precursor of the Tornquist Ocean, was associated with rifting in a NE-SW direction parallel to the Orsha-Volyn Rift.

Norsk Geologisk Tidsskrift, 1999

Stratigraphic information from the Neoproterozoic to Cambrian cover sequences at the Caledonian margin in central Scandinavia has been compiled from the Iiterature and our own data. Four flooding events can be recognized in the autochthonous cover rocks and parts of the eastern Caledonian Lower Allochthon: one, at the base of the Vendian at 590 Ma, two Early Cambrian events (540 and 530 Ma), and the fourth at the base of the Mid Cambrian and the alum shales (5 18 Ma). Stratigraphic successions of the western Baltica margin from northern Sweden to southem Norway are correlated using these flooding events. Based on these correlations, depth and time sections are constructed and subsidence curves calculated. Although Early Cambrian flooding events lead to temporarily higher sedimentation rates, the subsidence appears to have decreased through time. Such a decrease is consistent with models of lithospheric stretching and subsequent thermal subsidence. A review of available age data on tectonic events suggests a transition from continental rifting to ocean-floor formation off western Baltica at ca. 600 Ma ago. Accordingly, the Vendian to Cambrian evolution of the western Baltica continental margin is interpreted as a stage of post-rift subsidence showing the 'steer's head' geometry characteristic of sequences onlapping from an older wne of active rifting and of ocean-floor forrnation farther west. The gradual decrease in !herma! subsidence through Cambrian time also shows that the Baltica lithosphere was essentially thermally re-equilibrated prior to earliest Caledonian tectonic activity in Early Ordovician time.

International Journal of Earth Sciences, 2017

during Scandian metamorphism. An outcrop-scale homogenisation of the δ 13 C values reflects the local carbon isotope signature of the released metamorphic fluids that circulated channelized through the mélange unit.

Tectonics, 2018

We investigate (i) margin‐scale structural inheritance in rifts and (ii) the time scales of rift propagation and rift length establishment, using the East Greenland rift system (EGR) as an example. To investigate the controls of the underlying Caledonian structural grain on the development of the EGR, we juxtapose new age constraints on rift faulting with existing geochronological and structural evidence. Results from K‐Ar illite fault dating and syn‐rift growth strata in hangingwall basins suggest initial faulting in Mississippian times and episodes of fault activity in Middle‐Late Pennsylvanian, Middle Permian, and Middle Jurassic to Early Cretaceous times. Several lines of evidence indicate a close relationship between low‐angle late‐to‐post‐Caledonian extensional shear zones (CESZs) and younger rift structure: (i) reorientation of rift fault strike to conform with CESZs, (ii) spatial coincidence of rift‐scale transfer zones with CESZs, and (iii) close temporal coincidence betwee...

International Journal of Earth Sciences, 2020

In the supercontinent of Rodinia, Baltica occurred next to Amazonia, then the two drifted away when Rodinia broke up. By the end of the Neoproterozoic, Baltica became an independent continent. At that time, Timanide orogen developed at its modern northeastern margin. In most paleogeographical reconstructions, the opposite (SW, Tornquist) edge faced the Tornquist Ocean and remained just a passive margin till the arrival of the Gondwana-born East Avalonia in the late Ordovician. However, preliminary isotopic studies of detrital zircons from the Tornquist passive margin succession hinted that rock components of Gondwana derivation reached Baltica already in the early Cambrian. In this paper, we examine 18 drill-cores of Ediacaran-Cambrian and Ordovician siliciclastic rocks from the tectonostratigraphic units along the SW-NE transect from Upper Silesia (USB) via Małopolska (MB) and the Holy Cross Mts (HCM) to the East European Platform (EEP), SE Poland, in terms of the provenance data gained from the LA-ICP-MS and SHRIMP analyses of 32 zircon samples. Rocks from all the units revealed abundant Cadomian 0.7-0.55 Ga detrital zircons (15-50% of the total analyzed grains) and other grains that yielded peaks at 0.9-1.2, 1.4-1.6, 1.8-2.2, 2.7-3.0 Ga assignable to Baltica rather than Amazonia. Such age spectra in the USB, HCM and EEP prove the proximity of peripheral (peri-Gondwanan) fragments of the Cadomian orogen to Baltica. These fragments formed the Teissyere-Tornquist Terrane Assemblage (TTA) that obliquely docked and overrode the thinned southwestern edge of Baltica which earlier accumulated Neoproterozoic rift and passive margin deposits. Our data show that in the late Ediacaran-early Cambrian, parts of the Cadomian orogenic belt became accreted to Baltica.

Geoscience Frontiers, 2017

Geological, geochronological and isotopic data are integrated in order to present a revised model for the Neoproterozoic evolution of Western Gondwana. Although the classical geodynamic scenario assumed for the period 800e700 Ma is related to Rodinia break-up and the consequent opening of major oceanic basins, a significantly different tectonic evolution can be inferred for most Western Gondwana cratons. These cratons occupied a marginal position in the southern hemisphere with respect to Rodinia and recorded subduction with back-arc extension, island arc development and limited formation of oceanic crust in internal oceans. This period was thus characterized by increased crustal growth in Western Gondwana, resulting from addition of juvenile continental crust along convergent margins. In contrast, crustal reworking and metacratonization were dominant during the subsequent assembly of Gondwana. The Río de la Plata, Congo-São Francisco, West African and Amazonian cratons collided at ca. 630 e600 Ma along the West Gondwana Orogen. These events overlap in time with the onset of the opening of the Iapetus Ocean at ca. 610e600 Ma, which gave rise to the separation of Baltica, Laurentia and Amazonia and resulted from the final Rodinia break-up. The East African/Antarctic Orogen recorded the subsequent amalgamation of Western and Eastern Gondwana after ca. 580 Ma, contemporaneously with the beginning of subduction in the Terra Australis Orogen along the southern Gondwana margin. However, the Kalahari Craton was lately incorporated during the Late EdiacaraneEarly Cambrian. The proposed Gondwana evolution rules out the existence of Pannotia, as the final Gondwana amalgamation postdates latest connections between Laurentia and Amazonia. Additionally, a combination of introversion and extroversion is proposed for the assembly of Gondwana. The contemporaneous record of final Rodinia break-up and Gondwana assembly has major implications for the supercontinent cycle, as supercontinent amalgamation and break-up do not necessarily represent alternating episodic processes but overlap in time.

International Geology Review, 2010

Gondwana Research, 2007

The Rodinia hypothesis for the Neoproterozoic Supercontinent reconstruction is associated with five major problems: (i) The palaeomagnetic test requires continental break-up hundreds of millions of years before the geological evidence for this event is recognised near the dawn of the Cambrian. (ii) The reconstruction separates cratons with strong Late Archaean-Early Proterozoic affinities by large distances and then recombines them into Gondwana by early Phanerozoic times. (iii) The stratigraphic correlation, upon which it was originally based, incorporates successions dated ∼ 850-550 Ma during which interval palaeomagnetic data fail to predict continuity between Western North America, Australia and South China. (iv) The protracted history of break-up from 800-550 Ma is in conflict with the global subsidence record of passive margins defining initial continental break-up at ∼ 600 Ma and diverse isotopic/environmental signatures concentrated between 600-500 Ma. (v) It predicts no intrinsic link (such as a peripheral subduction zone) to large-scale mantle constraining forces. The Palaeopangean reconstruction, formulated a decade before Rodinia, was defined by correlation of ∼ 2700-600 Ma palaeomagnetic poles and predicted a quasi-rigid configuration peripherally modified by continental break-up late in the Mesoproterozoic, with a secondary quasi-rigid Neoproterozoic reconstruction surviving until ca. 600 Ma. Since Palaeopangaea addresses each of the above problems, it is re-evaluated here using the 1300-500 Ma database to March 2005, which has been greatly expanded and revised since the original proposition. Poles are shown to conform to a quasi-rigid reconstruction embracing a single APW path comprising the Gardar Track, the Keweenawan Track, the Grenville-Sveconorwegian Loop and the Franklin-Adelaide Track. The reconstruction is confirmed by sequential conformity of the high precision dated anchor poles to the APW path from 1250 Ma until 600 Ma. At this point the poles scatter and identify the geologically defined global continental break-up shortly before the dawn of the Cambrian. The key test between Rodinia and Palaeopangaea embraces the interval 800-600 Ma when all Rodinia models require differential movements between the continental blocks. The database has now expanded sufficiently to show that the poles assigned to this interval actually plot sequentially along a single APW path. Major implications of the Palaeopangaean reconstruction are: (a) continental break-up took place when the geological, geochemical and isotopic evidence predict it near the end of Neoproterozoic times; (b) The Late Archaean-Early Proterozoic cratonic nuclei of Gondwana held the proximities in Neoproterozoic times that they retained until Mesozoic times; (c) The ∼ 1100 Ma Grenville-age orogenic belts were linked as an en echelon circum-continental system conforming to the shape of the supercontinent; some were Andean in character and others were essentially intracratonic; (d) Late Neoproterozoic subduction was peripheral and focussed symmetrically within the instep between the two wings of the reconstruction; (e) Palaeopangaea possessed a symmetrical, crescent and hemispheric shape analogous to the Phanerozoic supercontinent (Neo)pangaea. Like the latter supercontinent, it appears to have been constrained by large-scale mantle convection related to the geoid form.

Tectonophysics, 2003

Palaeomagnetic data are used to study the configurations of continents during the Proterozoic. Applying stringent reliability criteria, the positions of the continents at 12 times in the 2.45- to 1.00-Ga period have been constructed. The continents lie predominantly in low to intermediate latitudes. The sedimentological indicators of palaeoclimate are generally consistent with the palaeomagnetic latitudes, with the exception of the Early Proterozoic, when low latitude glaciations took place on several continents.The Proterozoic continental configurations are generally in agreement with current geological models of the evolution of the continents. The data suggest that three large continental landmasses existed during the Proterozoic. The oldest one is the Neoarchaean Kenorland, which comprised at least Laurentia, Baltica, Australia and the Kalahari craton. The protracted breakup of Kenorland during the 2.45- to 2.10-Ga interval is manifested by mafic dykes and sedimentary rift-basins on many continents. The second ‘supercontinental’ landmass is Hudsonland (also known as Columbia). On the basis of purely palaeomagnetic data, this supercontinent consisted of Laurentia, Baltica, Ukraine, Amazonia and Australia and perhaps also Siberia, North China and Kalahari. Hudsonland existed from 1.83 to ca. 1.50–1.25 Ga. The youngest assembly is the Neoproterozoic supercontinent of Rodinia, which was formed by continent–continent collisions during ∼1.10–1.00 Ga and which involved most of the continents. A new model for its assembly and configuration is presented, which suggests that multiple Grenvillian age collisions took place during 1.10–1.00 Ga. The configurations of Kenorland, Hudsonland and Rodinia depart from each other and also from the Pangaea assembly. The tectonic styles of their amalgamation are also different reflecting probable changes in sizes and thicknesses of the cratonic blocks as well as changes in the thermal conditions of the mantle through time.

Sedimentary Geology, 2013

This review paper presents a set of revised global palaeogeographic maps for the 825-540 Ma interval using the latest palaeomagnetic data, along with lithological information for Neoproterozoic sedimentary basins. These maps form the basis for an examination of the relationships between known glacial deposits, palaeolatitude, positions of continental rifting, relative sea-level changes, and major global tectonic events such as supercontinent assembly, breakup and superplume events. This analysis reveals several fundamental palaeogeographic features that will help inform and constrain models for Earth's climatic and geodynamic evolution during the Neoproterozoic. First, glacial deposits at or near sea level appear to extend from high latitudes into the deep tropics for all three Neoproterozoic ice ages (Sturtian, Marinoan and Gaskiers), although the Gaskiers interval remains very poorly constrained in both palaeomagnetic data and global lithostratigraphic correlations. Second, continental sedimentary environments were dominant in epicratonic basins within Rodinia (>825 Ma to ca. 750 Ma), possibly resulting from both plume/superplume dynamic topography and lower sea-level due to dominantly old oceanic crust. This was also the case at ca. 540 Ma, but at that time the pattern reflects widespread mountain ranges formed during the assembly of Gondwanaland and increasing mean age of global ocean crust. Third, deep-water environments were dominant during the peak stage of Rodinia break-up between ca. 720 Ma and ca. 580 Ma, likely indicating higher sea level due to increased rate of production of newer oceanic crust, plus perhaps the effect of continents drifting away from a weakening superplume. Finally, there is no clear association between continental rifting and the distribution of glacial strata, contradicting models that restrict glacial influence to regions of continental uplift.

Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited.

Geophysical Journal International, 2011

To better constrain Baltica's position within Pangea, we conducted a palaeomagnetic study of Permo-Triassic dykes from the Oslo Graben, as a follow-up to an initial, but rather limited, study by Torsvik and colleagues in 1998. The age of these so-called Lunner dykes had previously been determined as ∼240 Ma in that study, but details in their analyses and new 40 Ar/ 39 Ar ages reveal that there may have been some argon loss in the initially dated dyke minerals and that a combined (weighted mean) age of 271 ± 2.7 (2σ ) Myr for the dykes is preferable. We find two major components of magnetization in our samples: one carried by an Fe-sulphide (likely pyrrhotite) and the other carried by low-Ti magnetite; these magnetization components may be found together (superposed) in a given sample or they may occur apart. Micronmetresized crystals of Ti-Fe oxides, observed with a scanning electron microscope (SEM) show exsolution lamellae, formed upon cooling from intrusion temperatures. Assuming that the submicronmetre-sized (Ti)-magnetite grains that carry a stable remanence are of the same generation as the observed larger grains, we interpret the magnetite remanence in the dykes as of primary, thermoremanent origin. The sulphide remanence appears to be slightly younger, as seen by the SEM observations of pyrite framboids and a Fe-sulphide grain invading a Timagnetite grain. Moreover, the sulphide mineralization is likely of region-wide hydrothermal origin. The magnetizations carried by the pyrrhotite and magnetite have nearly identical directions and so, must be nearly of the same age. For this study, we sampled 56 sites including 39 dykes, 10 baked-contact rocks and 7 host rocks removed from the immediate dyke contacts. The dykes and the contact rocks have the same SW and up directions of magnetization, and contain the Fe-sulphide or the magnetite magnetization or both, as diagnosed by their relative unblocking temperatures. However, all the sampled carbonate and igneous host rocks far away from the dykes also have the same directions. Thus, all of the 10 originally planned contact tests are inconclusive. The new palaeopoles of this study are a few degrees apart; the magnetite pole (from dykes only, N = 25) is located at 51 • N, 164 • E, K = 69, A 95 = 3.5 • , whereas the pole calculated from iron sulphide magnetic directions (all rock types, N = 20) is at 54 • N, 166 • E, K = 112, A 95 = 3.1 • . All directions are of reversed polarity, suggesting that the magnetization was acquired during the Kiaman Reversed Superchron. The palaeomagnetic mean result from the magnetite-bearing sites implies a palaeolatitude of Oslo of 23 • N, whereas the palaeolatitude calculated from the pyrrhotite magnetizations is 25-27 • N, depending on choice of host lithologies.

Geological Society, London, Special Publications, 2002

In central Europe, three crustal units, i.e. the Malopolska, the Lysog6ry and the Bruno-Silesia, can be recognized by basement data, faunas and provenance of clastic material in the Cambrian clastic rocks. They are now situated within the Trans-European Suture Zone, a tectonic collage of continental terranes bordering the Tornquist margin of the palaeocontinent of Baltica, but during the Cambrian their position in relation to each other and to Baltica was different from today. These units are exotic terranes in respect to Baltica and are interpreted as having been derived from the Cadomian margin of Gondwana. Their detachment is probably related to the final break-up of the supercontinent Rodinia at c. 550-590 Ma.

The supercontinent Pangaea dominated all aspects of Earth history for nearly 150 million years. The events in both western and eastern Pangaea document complex Wilson cycles with the opening and closing of oceans and terrane and continent collisions. The assembly of Pangaea is part of a supercontinent cycle that began in Late Proterozoic with the break-up of the previous supercontinent Rodinia. Much of the detail of earlier events is obscured by later culminating orogenies. Despite such difficulties, reasonably detailed paleogeographic reconstructions can be made of the complex events surrounding the assembly of Pangaea and both global and regional North Atlantic reconstructions are presented here. The tectonic events that culminated with the Carboniferous-Permian assembly of Pangaea can be synthesized into three general sequences. (1) In the Late Proterozoic, North America, Baltica and Siberia rifted from the supercontinent Rodinia and drifted northward leaving Gondwana straddling the South Pole. The Iapetus Ocean separated North America, Baltica and Gondwana. (2) During the Ordovician, Silurian and Devonian, North America, Baltica, Avalonia, and peri-Siberian terranes converged to form Laurussia and the Caledonian orogeny. A series of peri-Gondwanan terranes rifted from Gondwana and drifted northward to collide with Laurussia. These events left Laurussia facing a rapidly approaching Gondwana across the narrowing Rheic and paleo-Tethys Oceans.

A comparative study of the central and southern parts of the Palaeoproterozoic Svecofennian orogen in the Baltic/Fennoscandian Shield and the platform area to the east and south of the Baltic Sea indicates that at least these parts of the orogen are built up of several NW-SE trending, 100–300 km wide tectonic megadomains separated from each other and complicated by major zones of mostly dextral shearing. The generation of these zones occurred successively between 1.86 and 1.75 Ga, concomitantly with con- tinuing crustal accretion younging towards the southwest. Even considering the distorting presence of a number of microcontinents, this indicates the one-time existence and repeated episodic activity of a mas- ter subduction zone stepwise falling back to the present south-southwest. At 1.82–1.80 Ga, the oblique collision of protocontinents Volgo-Sarmatia and Fennoscandia interfered with the accretionary growth of the crust in the Svecofennian orogen. In the west, the system of Svecofennian tectonic domains and shear zones is delimited by 1.70–1.55 Ga orogenic belts marking the Laurentia-Greenland-Baltica margin of Columbia. Altogether, the available U–Pb zircon datings and studies of key rocks and structures in the South Baltic region allow more detailed Trans-Baltic correlation and the creation of new integrated models of the structural and tectonic evolution of the Svecofennian orogen in particular and northern Europe in general. The new findings will be important also in the continuing study of supercontinent formation and supercontinent cycles, and the drifting of Palaeoproterozoic protocontinents during the assembly of Columbia/Nuna.

• Explore
• Papers
• Topics

• Features
• Mentions
• Analytics
• PDF Packages
• Advanced Search
• Search Alerts

• Journals
• Academia.edu Journals
• My submissions
• Reviewer Hub
• Why publish with us
• Testimonials

• Company
• About
• Careers
• Press
• Help Center
• Terms
• Privacy
• Copyright
• Content Policy