Authors: Akhmet A Galeev V M Vinokurov F A Mouraviev Yu N Osin
Publish Date: 2009/07/03
Volume: 35, Issue: 3, Pages: 473-479
Abstract
Lower Permian 280 to 300 Ma evaporite dolomite rocks from the western part of the East European platform were studied by optical microscopy scanning electron microscopy with microprobe analysis and Xband electron paramagnetic resonance EPR Microscopic studies showed that many dolomite grains consist of an aggregation of submicron dolomite crystals 02–2 μm as a spheroidal nucleus which is overgrown by a larger dolomite rhombohedron 5–20 μm The EPR spectrum of a raw rock sample is mainly determined by thermally unstable radiation centers and Mn2+ ions substituted at Ca and Mg sites in the dolomite crystal structure The presence of dispersed organic matter at low concentrations was revealed from the backscattered electron images with a microprobe analysis of carbonenriched areas on cleaved surfaces and the registration of the carboncentered free organic radical signal in EPR spectra of heattreated samples A model of two successive growing stages for dolomite grains is suggested the dolomite or dolomite precursor nucleation and aggregation in the colloidal stage to form suspended organomineral particles before the gravitational settling and early diagenetic overgrowth at lower temperature and more stable environment of the marine bottom to form a dolomite rhombohedron The observation of both growing stages for dolomite grains indicates that there was no recrystallization in the later stages of the rock history
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