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  • 1
    Electronic Resource
    Electronic Resource
    Early Proterozoic palaeomagnetic data from the Pechenga Zone (north-west Russia) and their bearing on Early Proterozoic palaeogeography (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 122 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: An Early Proterozoic palaeomagnetic signature (c. 2125 Ma), verified by a positive conglomerate test, is recorded in the Kuetsyarvi Formation, Pechenga Group (north-west Russia), but the majority of the palaeomagnetic directions observed in the Pechenga Group lithologies reflect a low-grade remagnetization event probably linked with the Late Precambrian Baikalian Orogeny which affected north-west Russia and northern Norway. Secondary pyrrhotite is the dominant remanence carrier in the uppermost formations of the Pechenga Group.Palaeomagnetic poles from the Kuetsyarvi Formation differ somewhat or partially overlap with coeval palaeomagnetic poles from other tectonomagmatic provinces in northern Fennoscandia, but it is premature at this stage to speculate on intraplate movements during the Early Proterozoic. Besides, the Kuetsyarvi Formation probably developed during an early phase of intracontinental rifting along the northern margin of Fennoscandia, similar to the present-day East African rift. Hence younger intercontinental rifting, possible seafloor-spreading and subsequent convergence would remain undetected by our palaeomagnetic data. Palaeolatitude estimates from the Kuetsyarvi Formation suggest that the Pechenga region was located in latitudes of around 20° to 30° during the 2100–2200 Ma interval. These low-latitude estimates are supported by the sedimentary record in the Pechenga region which is characterized by red beds and evaporites.Comparison of Fennoscandian palaeomagnetic poles with coeval poles from the Slave and Superior cratons (Laurentia) questions previously publicized supercontinental configurations. A close relationship between Fennoscandia and Early Proterozoic Laurentian Provinces is conceivable from palaeomagnetic data, but, given the lack of longitudinal control as well as the choice of hemisphere, such postulates are tentative at best on purely palaeomagnetic grounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb07011.x
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  • 2
    Electronic Resource
    Electronic Resource
    The Lower Palaeozoic apparent polar wander path for Baltica: palaeomagnetic data from Silurian limestones of Gotland, Sweden (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 107 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Well-dated and undeformed Silurian (Lower Wenlock) limestones from Gotland, southern Sweden, yield two stable remanence components following detailed thermal and alternating-field demagnetization studies.(1) A low blocking-temperature/coercivity magnetization, termed L, delineated below 250d̀C/10mT, is oriented parallel to the present Earth's field (Dec. 001, Inc. +67, n= 4 sites, a95= 16d̀).(2) A higher blocking-temperature/coercivity magnetization, termed H, unblocked between 250-400d̀C/10-35mT, has a NNE declination and shallow negative inclination (Dec. 025, Inc. -19, n= 5 sites, a95= 5d̀). This H component direction compares favourably with a previous result from Gotland based upon blanket cleaning.Given a lack of evidence for subsequent geological heating (Conodont Alteration Index = 1-1.5), or pervasive palaeomagnetic overprinting, the H palaeopole is regarded as reliable and primary/early diagenetic in origin (19d̀S, 352d̀E, dp/dm 3/5). The only other well-constrained Mid-Silurian pole from Baltica, that from the Ringerike Sandstone of the Oslo district, is in excellent agreement with the Gotland data. These combined poles resolve previous problems regarding the shape and time-calibration of Silurian apparent polar wander relative to Baltica.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb00832.x
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  • 3
    Electronic Resource
    Electronic Resource
    A palaeomagnetic study of the Builth Wells-Llandrindod Wells Ordovician Inlier, Wales: palaeogeographic and structural implications (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 105 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Discrepancies exist in the Southern British Ordovician palaeomagnetic data set with individual studies indicating either high southerly or temperate southerly palaeolatitudes. Although previous palaeomagnetic investigations from the Builth inlier have delineated a three-component remanence structure, doubts have been raised concerning (i) the magnetization age of the supposed ‘primary’component (P); (ii) the structural setting of the sampling area (Llanelwedd quarry) within a zone of strike-slip deformation; and (iii) whether detailed step-wise demagnetization has fully separated the various magnetization components.In addressing these problems, we present new palaeomagnetic results as follows: (i) a positive palaeomagnetic conglomerate test establishing a pre-Late Llanvirn age for component (P); (ii) an enlarged geographic sampling embracing several tectonic domains indicating that relative rotations linked to strike–slip tectonism are minor within the Builth sampling area; and (iii) evidence that component (P) is uncontaminated by overprints at some sites suggesting the resulting palaeolatitude of 35°S to be representative for the Builth inlier.We also present evidence for local syn-volcanic deformation within Llanvirn volcanics and for intrusion-related deformation of Llanvirn shales.When the revised Llanvirn pole from the inlier (3°S, 4°E) is combined with other data from Southern Britain in a statistical spline analysis, a mean palaeolatitude of 44.5°S is calculated for Builth in Llanvirn times. A palaeoreconstruction for 468–474 Ma (c. Mid-Llanvirn) is presented utilizing this analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb06727.x
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  • 4
    Electronic Resource
    Electronic Resource
    A revised Palaeozoic apparent polar wander path for Southern Britain (Eastern Avalonia) (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 104 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A revised apparent polar wander path (APWP) is presented for Palaeozoic Southern Britain. the new path, based on a structural reinterpretation of existing data combined with new data from Wales, differs significantly from previous estimates in the following ways:(1) the locus of the Ordovician path segment is extended by approximately 25 degrees of arc;(2) revised time-calibration of the APWP suggests more Ordovician APW than previously calculated; and(3) the new path implies Middle Ordovician separation across the British sector of lapetus to be greater than previous palaeomagnetic estimates based on APWP analyses (cc. 3300 km; Northern Britain cc. 15S, Southern Britain c. 45S).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb02506.x
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