SEDIMENTARY EVOLUTION OF THE RIPHEAN-VENDIAN BASIN OF SOUTHEASTERN SIBERIA

Abstract

The Riphean to Vendian ( ≈1600–540 Ma) sedimentary succession of the southeastern margin of the Siberian platform is 12–14 km thick and consists of terrigenous-carbonate successions termed, from oldest to youngest, the Uchur, Aimchan, Kerpyl, Lakhanda, Uy and Yudoma Groups. Group boundaries typically are regional unconformities; local angular unconformities occur at the base of the Aimchan and Yudoma Groups. Deposition mostly occurred in terrestrial to shallow marine sedimentary environments; only the Uy Group contains evidence of deep-water sedimentation. Paleocurrent and facies trends show that provenance of the Uchur, Aimchan and most of Kerpyl Groups was from the Siberian craton to the west. This corresponds with the mineralogical and chemical composition of sandstones, which suggests continental block to recycled orogen provenance with predominance of granites in the source area. Sandstones from the Uy and Yudoma Groups were derived from both western (Siberian) and eastern (non-Siberian) sources. The Uy Group contains graywacke that implies local recycled orogen to arc orogen provenance. Trace and rare earth element geochemistry suggests provenance from post-Archean source rocks and this is supported by U–Pb detrital zircon geochronology which indicates that only 3 of the 96 grains analyzed are of Archean age. Detrital zircons ≈2050 Ma predominate at the base of the Uchur Group. At the base of the Kerpyl Group ≈2060–1880 Ma zircons predominate with youngest grains ≈1300 Ma. The latter represents an unknown source, as rocks younger ≈1700 Ma are not reported from the basement of the Siberian platform. Zircons in the uppermost part of the Uy Group range in age from 1500 to 1050 Ma suggesting a non-Siberian provenance, perhaps from the Grenville orogen of Laurentia. Conventional U–Pb analysis of a few detrital zircon grains from the Yudoma Group sandstones yielded ages ≈2200–2000. Sedimentological and stratigraphic studies indicate that the Riphean–Vendian sedimentary basin of southeastern Siberia initiated by rifting that subsequently failed, allowing the development of a long-lived intracratonic sedimentary basin. Mafic magmatism and depositional features of the Uy Group suggest that there was renewed rifting ≈1000 Ma, when the basin evolved into an aulacogen. Rifted arms spread to form the Verkhoyansk ocean, the margins of which were approximately parallel to the modern margin of Siberian platform and Okhotsk massif.