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Wyszukujesz frazę "dolomites" wg kryterium: Temat


Wyświetlanie 1-2 z 2
Tytuł:
Mesozoic remagnetization of Upper Devonian carbonates from the Česis and Skaistgirys quarries (Baltic states)
Autorzy:
Katinas, V.
Nawrocki, J.
Powiązania:
https://bibliotekanauki.pl/articles/2058838.pdf
Data publikacji:
2004
Wydawca:
Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
Tematy:
Lithuania
Latvia
Devonian
palaeomagnetism
remagnetisation
dolomites
Opis:
The palaeomagnetic properties of Frasnian and Famennian dolomites from two quarries in Latvia and Lithuania respectively are compared. Famennian dolomites from Skaistgirys quarry (N Lithuania) revealed the presence of one distinct normal polarity component (D =14 degrees Celsius, I = 53 degrees Celsius, 95 = 4.2 degrees Celsius, n = 28 specimens). The reversed polarity component predominates in Frasnian dolomites from Česis quarry (Central Latvia). Only one hand specimen from this locality contained a component with the opposite direction. The mean direction from Česis quarry (D = 198 degrees Celsius, I = -53 degrees Celsius, 95 = 4.4 degrees Celsius, n = 22 specimens) is very close to that from Skaistgirys quarry and therefore was recorded most probably during the same event of remagnetisation but at a later stage. The remagnetizations of these dolomites were caused most probably by progressive oxidation of ferric sulphides to magnetite and finaly to hematite. A comparison of the palaeomagnetic poles obtained with the stable European APWP (Apparent Polar Wander Path) indicates a Late Jurassic/Early Cretaceous age for the remagnetization event. This estimation can be useful for chronostratigraphic linking of post-Palaeozoic tectonic activity and diagenetic events, so far very poorly recognized in this part of the European plate. Our data shows also that the Late Jurassic/Early Cretaceous part of the stable European APWP may still be inaccurate.
Źródło:
Geological Quarterly; 2004, 48, 3; 293-298
1641-7291
Pojawia się w:
Geological Quarterly
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Palaeomagnetic age of remagnetizations in Silurian dolomites, Rástla quarry (Central Estonia)
Autorzy:
Plado, J.
Preeden, U.
Puura, V.
Pesonen, L. J.
Kirsimäe, K.
Pani, T.
Elbra, T.
Powiązania:
https://bibliotekanauki.pl/articles/2060209.pdf
Data publikacji:
2008
Wydawca:
Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
Tematy:
Estonia
Baltica
Silurian
palaeomagnetism
remagnetization
dolomites
Opis:
Alternating field and thermal demagnetization of dolomite samples from the Silurian (Llandovery) horizontally-bedded sequence of central Estonia reveal two secondary magnetization components (A and B) both of chemical origin. A low-coercivity (demagnetized at -50 mT) component A (D = 60.7°, I = 7.7°, alfa95 = 16.6°) with high dispersion (k = 14.2), yields a palaeopole at 18.2°N and 139.5°E that points towards the Late Devonian — Mississipian segment of the Baltica APWP (Apparent Polar WanderPath). A high-coercivity component B (D = 13.5°, I = 60.7°, k = 67.0, alfa 95 = 4.7°) carries both normal and reversed polarities. Comparing the palaeopole (71.1°N and 173.3°E) with the European APWP reveals a Cretaceous age. These two remagnetizations are linked to mineral assemblages of magnetite and maghemite (A), and hematite (B) determined from mineralogical (X-ray, SEM and optical microscopy) and rock magnetic (acquisition and thermal demagnetization of a 3-component IRM; Lowrie-test) studies. The results suggest that the first (A) Palaeozoic remagnetization was caused by low-temperature hydrothermal circulation due to the influence of the Caledonian (more likely) or Hercynian Orogeny after the diagenetic dolomitization of carbon ates. Hematite, carrying the component B, and goethite, are the latest ferromagnetic minerals that have precipitated into the existing pore space (hematite) and walls of microscopic fractures (goethite) that opened to allow ac cess for oxygen-rich fluids during the Late Mesozoic.
Źródło:
Geological Quarterly; 2008, 52, 3; 213-213
1641-7291
Pojawia się w:
Geological Quarterly
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-2 z 2

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