This study focuses on Paleoproterozoic polymictic conglomerates recognized within the Koikary and Elmus domains of the Vedlozero-Segozero greenstone belt (VSGB), Karelian Craton. The detrital material was differentiated into dominant groups according to petrographic and petrochemical characteristics, and then the clasts were matched with the rock complexes composing this territory. It was found that the composition of the clastic material and cement of the polymictic conglomerates was significantly influenced by the underlying rocks: rock associations of the Mesoarchean volcanogenic-sedimentary complex of the VSGB, Paleoproterozoic (Sumian) andesibasalt associations and granitoids of the Elmus domain. Geochronological studies of detrital zircons from conglomerate cement were carried out. New records date the formation of polymictic conglomerates of the Koikary domain to 2408 ± 9 Ma and of the Elmus domain to 2428 ± 19 Ma, while the Koikary domain is dominated by clastic zircon aged ca. 2810 ± 12 and 2880 ± 12 Ma, and conglomerates of the Elmus domain are dominated by zircons aged 2620 ± 24 – 2650 ± 27 and 2580 ± 27 Ma. The lower time limit for the formation of sedimentary sections is the age of the underlying Sumian volcanics (~2450 Ma). Based on the morphological characteristics of coarse-grained sediments and the comparative analysis of clasts against rock complexes of the Koikary and Elmus domains, the sedimentary basins are recognized as Paleoproterozoic molassoid complexes formed in pull-apart basins during the proto-platform stage in the evolution of the Karelian craton.