Sedimentary evolution of the Riphean-Vendian basin of southeastern Siberia

The Riphean to Vendian ( approximate to 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 younge st, the Uchur, Aimchan, Kerpyl, Lakhanda, Uy and Yudoma Groups. Group bound aries typically are regional unconformities; local angular unconformities o ccur at the base of the Aimchan and Yudoma Groups. Deposition mostly occurr ed in terrestrial to shallow marine sedimentary environments; only the Uy G roup contains evidence of deep-water sedimentation. Paleocurrent and facies trends show that provenance of the Uchur, Aimchan and most of Kerpyl Group s was from the Siberian craton to the west. This corresponds with the miner alogical and chemical composition of sandstones, which suggests continental block to recycled orogen provenance with predominance of granites in the s ource area. Sandstones from the Uy and Yudoma Groups were derived from both western (Siberian) and eastern (non-Siberian) sources. The Uy Group contai ns graywacke that implies local recycled orogen to arc orogen provenance. T race and rare earth element geochemistry suggests provenance from post-Arch ean source rocks and this is supported by U-Pb detrital zircon geochronolog y which indicates that only 3 of the 96 grains analyzed are of Archean age. Detrital zircons approximate to 2050 Ma predominate at the base of the Uch ur Group. At the base of the Kerpyl Group approximate to 2060-1880 Ma zirco ns predominate with youngest grains approximate to 1300 Ma. The latter repr esents an unknown source, as rocks younger approximate to 1700 Ma are not r eported from the basement of the Siberian platform. Zircons in the uppermos t part of the Uy Group range in age from 1500 to 1050 Ma suggesting a non-S iberian provenance, perhaps from the Grenville orogen of Laurentia. Convent ional U-Pb analysis of a few detrital zircon grains from the Yudoma Group s andstones yielded ages approximate to 2200-2000. Sedimentological and strat igraphic studies indicate that the Riphean-Vendian sedimentary basin of sou theastern Siberia initiated by rifting that subsequently failed, allowing t he development of a long-lived intracratonic sedimentary basin. Mafic magma tism and depositional features of the Uy Group suggest that there was renew ed rifting approximate to 1000 Ma, when the basin evolved into an aulacogen . Rifted arms spread to form the Verkhoyansk ocean, the margins of which we re approximately parallel to the modem margin of Siberian platform and Okho tsk massif. (C) 2001 Elsevier Science BN. All rights reserved.