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Integrated chronostratigraphy of Proterozoic-Cambrian boundary beds in the western Anabar region, northern SiberiaCarbonate-rich sedimentary rocks of the western Anabar region, northern Siberia, preserve an exceptional record of evolutionary and biogeochemical events near the Proterozoic/Cambrian boundary. Sedimentologically, the boundary succession can be divided into three sequences representing successive episodes of late transgressive to early highstand deposition; four parasequences are recognized in the sequence corresponding lithostratigraphically to the Manykal Formation. Small shelly fossils are abundant and include many taxa that also occur in standard sections of southeastern Siberia. Despite this coincidence of faunal elements, biostratigraphic correlations between the two regions have been controversial because numerous species that first appear at or immediately above the basal Tommotian boundary in southeastern sections have first appearances scattered through more than thirty metres of section in the western Anabar. Carbon- and Sr-isotopic data on petrographically and geochemically screened samples collected at one- to two-metre intervals in a section along the Kotuikan River, favour correlation of the Staraya Reckha Formation and most of the overlying Manykai Formation with sub-Tommotian carbonates in southeastern Siberia. In contrast, isotopic data suggest that the uppermost Manykai Formation and the basal 26 m of the unconformably overlying Medvezhya Formation may have no equivalent in the southeast; they appear to provide a sedimentary and palaeontological record of an evolutionarily significant time interval represented in southeastern Siberia only by the sub-Tommotian unconformity. Correlations with radiometrically dated horizons in the Olenek and Kharaulakh regions of northern Siberia suggest that this interval lasted approximately three to six million years, during which essentially all 'basal Tommotian' small shelly fossils evolved.
Document ID
20040089280
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
Authors
Kaufman, A. J.
(Botanical Museum, Harvard University Cambridge, MA 02138, United States)
Knoll, A. H.
Semikhatov, M. A.
Grotzinger, J. P.
Jacobsen, S. B.
Adams, W.
Date Acquired
August 21, 2013
Publication Date
January 1, 1996
Publication Information
Publication: Geological magazine
Volume: 133
Issue: 5
ISSN: 0016-7568
Subject Category
Geosciences (General)
Funding Number(s)
CONTRACT_GRANT: EAR-9086119
CONTRACT_GRANT: EAR-9118628
CONTRACT_GRANT: NAGW-893
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
NASA Discipline Exobiology

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