COMMISSION GEOLOGIOUE - Arkisto.gsf.fi

80 Bulletin de la Commission geologique de Finlande N: 0 212.
The stratigraphy of the area of supracrustal rocks south of Tervola is
described by Härme (1949), who notes that the lowermost member in the
sequence of these rocks is quartzite. It is overlain by basic volcanics which
graduaIly pass over upwards into slates. The quartzite is current bedded,
and the stratified volcanics as weIl as the slates exhibit graded bedding.
The dolomite occurs as intercalations partly in the upper section of the
quartzite and mainly in the transition zone between the stratified volcanics
and the slates. The occurrenee of the stromatolite structures in the dolomite
gives an idea of the eonditions that prevailed during the sedimentation of
the Karelidie dolomites.
The age of the supraerustal formation of that area is an open question,
for no radiometrie age determinations of the supracrustal roeks exist. The
age of the biotite eontained in an interseeting granodiorite oeeurring in the
neighborhood (Nosa, Alatornio parish) has been determined (Wetherill,
Kouvo, Tilton and Gast 1962) by the Rb-Sr-method, and the figure is 1780
millions of years.