La position stratigraphique déterminée paléomagnétiquement de sédiments carbonifères de Minudie Point, Nouvelle Ecosse : à propos de l'horizon repère magnétique du Carbonifère

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Abstract
Chemical, thermal, and alternating field cleaning treatments indicate that the Minudie Point sedimentary beds acquired their initial magnetization slowly and progressively during a lengthy process that lasted from deposition to lithification. The magnetization carried by the pigment is separated vectorially from the magnetization acquired during the early phases and its direction is shown to be a reliable indicator of the direction of the magnetic field during lithification. The agreement between the directions of the magnetizations acquired at the beginning (175°, +15°; α95 = 6°; pole 122° E, 36° N) and at the end (172°, +20°; α95 = 5°; pole 125° E, 33° N) of the process indicates that the direction (irrespective of the sign) of the magnetic field remained virtually unchanged during the magnetization process. Slicing of specimens shows that certain apparently aberrant directions are in reality the directions of the resultant vectors of two magnetizations of opposite polarities.The recording of a normal polarity during the early phase of magnetization places these sediments below (and perhaps immediately below) the magnetic horizon marker at the base of the Permo – Upper Carboniferous interval of reversed polarity. This indicates that these beds which on geological evidence could be of Pictou or Riversdale age belong to the Riversdale Group. This result contributes to the pin-pointing of the stratigraphic position of the Carboniferous magnetic horizon marker which can be most useful for the study of the tectonic history of the ancient Carboniferous basin of eastern Canada. The study shows that this magnetic horizon marker is a valuable stratigraphic tool which can be used most effectively for global correlation of Carboniferous units.

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