Carbonate rocks of Karelia: geochemistry and carbon-oxygen isotope systematics in the Jatulian stratotype and potential for magnesite deposits

Abstract

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.