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Russian Geology and Geophysics

2006 year, number 6


Z.N. Gnibidenko
Institute of Geophysics, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Paleomagnetic scale, magnetic minerals, orthozone, dinocysts, carpological complexes, palynocomplexes, marine and continental Paleogene, West Siberian Plate
Pages: 760-775


A complex of paleomagnetic, geologo-lithological, and paleontological data served as a base for a geomagnetic polarity scale that existed on the West Siberian Plate (WSP) in the Paleogene. The scale comprises 31 large magnetic zones (orthozones) of normal and reversed polarity. To compile the scale, we compared and correlated the Paleogene reference sections of the Kulunda, Baraba, and Tomsk lithologo-facies zones. The reliability of paleomagnetic data is controlled by the possibility to distinguish the primary component of natural remanent magnetization and structural similarity of the WSP paleomagnetic scale with the global magnetochronological scale and paleomagnetic scales of other regions. During a 34.5 Myr period, from Upper Paleocene to Lower Miocene, the Early Cenozoic geomagnetic field reconstructed from NRM vectors of the WSP Paleogene rocks experienced 31 reversals (at the rank of orthozone boundaries), with 16 and 15 regimes of normal and reversed polarity, respectively.
Comparison of the Paleogene WSP scale with the Berggren scale permitted us to demarcate Early Cenozoic series in the regional WSP stratigraphic scale in absolute chronology. The Paleocene-Eocene boundary, approximately at 55 Ma (Chron C24r), is recorded in the regional scale near the roof of the Lower Lyulin-Vor Subformation (inside Orthochron R2E1t). The Eocene-Oligocene boundary at 33.8 Ma (Chron C13r) runs in sediments near the sole of the Atlym Formation in Orthochron R8-1E2-3pr. The Oligocene-Miocene boundary at 23.8 Ma runs above the Zhuravka Formation.
The WSP Paleogene geomagnetic polarity scale is of interregional importance. Being the only Paleogene scale for northern Asia, it is a crucial link between the continental-type scale and oceanic scale compiled from bottom cores of deep-sea drilling and sea magnetic anomalies.