Evolution of the Early Proterozoic (Ludikovian) riftogenic basin of the southwestern margin of the Karelian Craton (Baltic Shield)

Abstract

The geological structure and stratigraphic sections of typical areas of Ludikovian sediments on the northeast coast of the Lake Ladoga (Republic of Karelia) were studied. The formation of these strata is associated with the development in the Ludikovian time period of the extensive sedimentary basin, which was formed on the Archean crystalline basement of the Karelian craton. Variations in the composition and thickness of these metamorphosed Lower Proterozoic sedimentary and volcanic-sedimentary complexes, both laterally and in section, suggest a very disjointed bottom relief of the Ludikovian paleobasin and changing sedimentation conditions during the development of this structure. The reconstruction of the primary composition of metamorphosed volcanogenic and sedimentary rocks of Ludikovian rocks was carried out based on petrochemical and petrographic characteristics. The protolith of the rocks lying at the base of the Ludikovian strata was mainly carbonate and partly terrigenous sandy-clay sediments; the central part of the section is composed of metabasalts; ash, carbonate and clay sedimentary material with partly siliceous matter most likely associated with post-volcanic underwater exhalations and hydrothermal activity served as the protolith of metamorphosed volcanic-sedimentary rocks of the upper part of the section. Various environments of sedimentation in the Ludikovian paleobasin were designated: a complex of graphite-containing rocks was formed in deep-water paleodepressions of the bottom of the sea basin with oxygen deficiency; carbonate and clay sediments accumulated in the zones of free hydrodynamics. According to the results of the analysis of the contents of rare-earth elements, the complexes of “continental” and “oceanic” metabasalts, spatially combined as a result of the overthrust tectonics of the accretion-collision stage of development of the territory, were identified. We propose a scheme of the evolution of the Ludikovian paleobasin formed in the conditions of the developing riftogenesis, in transition from continental to oceanic environments, with the formation of sediments of the “Red Sea” type.