Late Precambrian ?Pre-Glacial? Sedimentation Stage in the Southern Siberian Platform

We present new data on the chemical composition of the late Precambrian rocks in the upper part of the regional Balaganakh stratigraphic horizon (the Nugan Formation at the Baikal segment of the Sayan-Baikal-Patom belt (SBPB) and the Bugarikhta Forma-tion of the Balaganakh Group at the Patom segment of the SBPB) and the U-Pb (LA-ICP-MS) age of detrital zircons from the Bugarikhta Formation. It has been established that the rocks of the Nugan and Bugarikhta formations resulted from the destruction of igneous and metamorphic rocks. The contents and ratios of trace and rare-earth elements in the rocks of the Nugan and Bugarikhta formations indicate a predominance of felsic igneous rocks in the provenance and the presence of rocks of mafic and intermediate compositions at the source of the terrigenous rocks of the Nugan Formation. The U-Pb age of detrital zircons from all rocks of the upper part of the regional Balaganakh Horizon is close to the age of the rocks in the basement of the southern margin of the Siberian Platform, which suggests that this basement was the main source of clastic material in the sedimentation basins. It is argued that the "pre-glacial" (pre-Marinoan) terrigenous deposits of the Nugan and Bugarikhta formations, as well as the deposits of the Ipsit Formation at the Sayan segment of the SBPB, accumulated in the Late Riphean (ca. 720-640 Ma), probably in postrift basins that formed immediately after the separation of Siberia from Laurentia at the early stages of the opening of the Paleoasian Ocean.