Vi. Shul'Diner et al., The late Karelian in the stratigraphic scale of Russia: Determination of its lower boundary and regional units in the stratotype area, STRATI GEOL, 8(6), 2000, pp. 544-556
The U-Pb zircon age is determined for stratigraphically important Upper Kar
elian structures of the northern Ladoga region. The age of the Sortavala Gr
oup volcanics is assumed to be 1.97-1.95 Ga that coincides with age of the
Outokumpu and Jormua ophiolites in Finland. The Sortavala and coeval Suisar
groups are recommended to be distinguish as the Livvian, the initial regio
nal unit of the upper Karelian, which, along with ophiolites of Finland, ma
rks the opening stage of the Svecofennian belt. The overlying Ladoga Group
is a stratotype of the early Ladogian marking the mature evolutionary stage
of Svecofennides. The upper boundary of the Ladoga Group is established on
the basis of gabbroid intrusions intersecting the group and dated back to
1.88-1.89 Ga. The subsequent late Ladogian interval (up to 1.80 Ga) that ch
aracterizes an intense volcanism in the region is missing from the successi
ons.