Ordovician of the Siberian Platform

The Ordovician of the Siberian Platform exhibits a wide range of shallow-water facies in thick, normal marine and lagoonal carbonate-clastic sequences. It is illustrated herein by two west-east geological profiles across the Siberian Platform. Stratigraphic and paleontologic studies in this area led to subdivision of the Ordovician into 12 regional stages. Their boundaries correspond to changes in sedimentology and in taxonomic composition of a benthic fauna dominated by brachiopods and ostracodes. In most cases the precise correlation of regional with global stages is difficult, mainly because of the endemic character and sparse distribution of the East Siberian fauna in shallow-water facies, as well as the sporadic occurrences of graptolites. Two important events at the beginning of the Volginian (the Hustedograptus teretiusculus Zone) and Chertovskian (Nemagraptus gracilis Zone) are documented in the Ordovician of the East Siberian Basin. They include large-scale transgressions and significant biotic changes, and are used as the most reliable levels for correlation in the vast area of the Siberian Platform and the Verkhoyano-Chukotka region. The distribution of lithofacies and dominant members of faunal communities are figured on three maps for the Nyaian (Early Ordovician), Volginian (Middle Ordovician), and Baksanian (Late Ordovician). Comparative analysis of the Ordovician benthic faunas of the Siberian Platform, Taimyr, Novosibirsk Islands, and the Verkhoyano-Chukotka region shows that they all belong to the Kolymo-Siberian paleobiogeographic province. Available data confirm the location of the Siberian paleocontinent in the Southern Hemisphere during most of the Ordovician and an inverted orientation relative to its present position. © 2010 The Geological Society of America. All rights reserved.