C-and Sr-isotope chemostratigraphy as a tool for verifying age of Riphean deposits in the Kama-Belaya aulacogen,the east European platform |
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| Authors: | L C Kah D C Crawford J K Bartley V I Kozlov N D Sergeeva V N Puchkov |
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| Institution: | (1) Department of Geological and Planetary Science, University of Tennessee, Knoxville, TN 37996, USA;(2) Department of Geological Science, State University of West Georgia, Carrollton, GA 30118, USA;(3) Institute of Geology, Ufimian Scientific Center, Russian Academy of Sciences, Ufa, 450000, Russia |
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| Abstract: | The Kyrpy Group of the East European platform is regarded by tradition as correlative with the Lower Riphean Burzyan Group of the Bashkirian meganticlinorium in the southern Urals. Age and correlation of the Kyrpy Group remain problematic, however, because of a limited geochronological information and controversial interpretation of paleontological materials. Data of C-and Sr-isotope chemostratigraphy contribute much to the problem solution. In the Kyrpy Group of the Kama-Belaya aulacogen, the Kaltasy Formation carbonates 1300 to 2400 m thick (boreholes 133 and 203 of the Azino-Pal’nikovo and Bedryazh areas) show 87Sr/86Sr ratios ranging around 0.7040 and narrow diapasons of δ13C values: about 0.5‰ (V-PDB) in shallow-water facies and-2.0‰ (V-PDB) in sediments of deeper origin. Despite the facies dependence of carbon isotope composition, δ13C variations not greater than ±1.0‰ are depicted in chemostratigraphic profiles of carbonate rocks characterizing separate stratigraphic intervals up to 800 m thick in the above borehole sections. Low 87Sr/86Sr ratios and almost invariant δ13C values in carbonates of the Kaltasy Formation are obviously contrasting with these parameters in the Middle and Upper Riphean deposits, being comparable with isotopic characteristics of the Lower Riphean sediments (Mesoproterozoic deposits older than 1300 Ma). Consequently, the results obtained evidence in favor of the Early Riphean age of the Kaltasy Formation and the Kyrpy Group as a whole. |
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| Keywords: | aulacogens Precambrian Kaltasy Formation carbon and strontium isotopes chemostratigraphy Lower Riphean |
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