The problems of radiolarian-based dating of Jurassic-Cretaceous siliceous rocks from accretionary complexes,the Russian East |
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| Authors: | V S Vishnevskaya |
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| Institution: | (1) Department of Geosciences, University of Oslo, NO-0316 Oslo, Norway;(2) Geological Survey of Norway, NO-7491 Trondheim, Norway;(3) SINTEF Petroleum Research, Trondheim, Norway;(4) Department of Geology and Mineral Resources Engineering, NTNU, NO-7491 Trondheim, Norway;(5) Eni Norge AS, NO-4064 Stavanger, Norway |
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| Abstract: | Radiolarians, which represent the most widespread fossil faunal group in jaspers and cherts, are the best tool for determining
the geological age of Jurassic-Cretaceous volcanogenic-siliceous sequences in the Pacific margin of Russia, because they meet
all the conditions required for orthostratigraphic groups, i.e., demonstrate rapid evolutionary changes of their assemblages,
completeness of their record through the geological section, and a wide lateral distribution. The selection of biostratigraphic
scales for determining the age of radiolarian assemblages is of principal significance. The significant difficulty in correlating
Tethyan and Pacific assemblages is similar to that appearing in the case of the correlation between the Tethyan and Boreal
ammonite standards. The existing discrepancies are explained by the different life spans of some guide species that determine
the stratigraphic range of particular zones in their geographic type areas and may be different in other paleobiogeographic
regions and provinces. The program of scientific studies should include the search for and thorough analysis of Jurassic-Cretaceous
sections in Russia that contain simultaneously radiolarians, buchians, and ammonites. Such sections might provide the possibility
for developing a single scale for the transitional sections and outlining ways for correlating the Tethyan and Pacific assemblages. |
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