THE MIDDLE ORDOVICIAN LITHO- AND BIOSTRATIGRAPHY OF NORTHEASTERN GORNYI ALTAI
E.V. Bukolova
A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Ordovician, graptolites, zonal stratigraphy, Gornyi Altai
Pages: 979-990
Abstract
The structure of the Lower-Middle Ordovician Tuloi and Karasinka Formations, which occur widely in northeastern Gornyi Altai, has been studied. A bed-by-bed description of a new section of the boundary sediments between these stratigraphic units has been given. The graptolite, trilobite, and brachiopod assemblages typical of the Tuloi and Karasinka Formations have been analyzed. Graptolite zones and subzones have been recognized, which permit correlating the stratotype and key sections of these local stratigraphic units with the stages of the International Stratigraphic Chart (ISC). The Karasa Formation occupies a considerably larger stratigraphic volume than presumed: It spans the late Arenig and the entire Llanvirn (including the Llandeilo) of the British standard, which is used in Russia (= Upper Dapingian-Darriwilian of the new Ordovician standard in the ISC). Finally, the paper discusses the suggested changes in the names of regional units (horizons) in the Ordovician stratigraphic chart of the western Altai-Sayan fold belt.
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