Study of Proterozoic (Jatulian) facies in Central Karelia

Jatulian (middle Proterozoic) deposits in Karelia form isolated synclinoria, trending northwest and surrounded by blocks of granitic rocks and schists. Individual zones are 70-250 km long by 5-130 km wide. They have been traced 600 km from south to north. Jatulian deposits consist of metamorphosed sedimentary and volcanic rocks. Sedimentary rocks in central Karelia consist of polymictic conglomerates, sericitic sandstones and carbonate-bearing sandstones. Facies change gradually away from the central parts of Jatulian troughs from lacustrine to shallow-water shore facies and then to those of streams and mountain slopes. The intervals thin in the same basins. The lateral facies sequence is repeated vertically. Variations in thickness and facies were determined by contemporaneous Jatulian tectonic activity. There resulted a system of relatively narrow zones with different rates of subsidence, sedimentation and uplift.—C. G. Tillman.