Geochemistry of isotopes ( delta super(13)C, delta super(18)O) and formation conditions of lower-middle permian rocks in the Soyana River region (Arkhangel'sk district)

The results of study of the isotopic-lithological compositions of carbonate and terrigenous-carbonate rocks in the Soyana River section (northern East European Platform, Arkhangel'sk district) are presented. The results make it possible to identify 10 main lithotypes and show a wide variation range of delta super(13)C (from -2.2 to +3.6ppt, PDB) and delta super(18)O (from 22.5 to 30.5ppt, SMOW). These lithological features and isotopic compositions suggest that the rocks were formed in a shallow-marine setting characterized by rapidly changing sedimentation conditions in various facies (and/or paleoecological) zones: inlets, lagoons, supralittoral, littoral, and shoals. Periods of aridization and humidization are recorded. The results also indicate numerous synsedimentary short-term hiatuses and stages of increased continental runoff-episodic pulsatory input of clastic material with the continental paleoflows.