Carbonate rocks of Karelia: geochemistry and carbon-oxygen isotope systematics in the Jatulian stratotype and potential for magnesite deposits
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Closely spaced samples (73 in number) of shallow water, red, stromatolitic dolomite and magnesite from the Palaeoproterozoic (1980 +-27 Ma as a minimum age) Tulomozerskaya Formation in a distal portion of the Onega palaeobasin, Russian Karelia, have been analysed for Q13Ccarb, Q18Ocarb, trace and major elements. The 800 m-thick terrigeneous-carbonate succession is interpreted to be formed in lacustrine evaporitic settings prograding to sabkha, and then to marine environment. The carbonate rocks (essentially stromatolitic dolo- stones with minor magnesites), despite their depositional settings, exhibit throughout isotopically heavy carbon.