Rb-Sr geochronology of Vendian shales,the Staraya Rechka Formation,Anabar Massif,northern Siberia |
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| Authors: | I M Gorokhov M A Semikhatov T L Turchenko P Yu Petrov N N Mel’nikov G V Konstantinova E P Kutyavin |
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| Institution: | 1.Institute of Precambrian Geology and Geochronology (IGGD),Russian Academy of Sciences,St. Petersburg,Russia;2.Geological Institute,Russian Academy of Sciences,Moscow,Russia |
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| Abstract: | Fine-grained clayey subfractions (SF) with particle sizes of 1–2, 0.6–1.0, 0.3–0.6, 0.2–0.3, 0.1–0.2, and <0.1 μm were extracted
from shales of the Vendian Staraya Rechka Formation in the Anabar Massif and studied by XRD and Rb-Sr methods. All the clayey
subfractions are represented by illite with high crystallinity indices, which are characteristic of the low-temperature diagenesis/catagenesis
zone and grow with the decrease of the particle size. The Rb-Sr systematics in clayey subfractions combined with mineralogical
data provide grounds for the conclusion that illite from clayey rocks of the Staraya Rechka Formation was forming during two
periods: approximately 560 and 391–413 Ma ago. The first illite generation was likely formed in the course of lithostatic
subsidence of the Staraya Rechka sediments and the second one, during the Devonian lithogenesis stage. It is assumed that
age of the first generation (∼560 Ma) is close to that of the Staraya Rechka Formation. This inference is consistent with
biostratigraphic, chemostratigraphic, and geochronological data obtained for both rocks of the Anabar Massif and Vendian sediments
from other regions of Siberia. |
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