STRONTIUM ISOTOPIC EVIDENCE FOR SUPERCONTINENTAL BREAKUP AND FORMATION IN THE RIPHEAN: WESTERN MARGIN OF THE SIBERIAN CRATON

Abstract

Sr isotopic composition in carbonate rocks of the Baikit anteclise and Yenisei Ridge, western margin of the Siberian craton, has been analyzed. These rocks were formed between 1500-1450 and 850 Ma. Carbonate deposits of the Baikit anteclise are featured by low Sr isotopic ratios that increase gradually form 0.70404 to 0.7052 up the stratigraphy. Riphean carbonate rocks of the Yenisei Ridge exhibit a wide scatter of 87Sr/86Sr (0.7050-0.7095 or higher). High Sr isotopic ratios are coupled chiefly with considerable postdepositional changes of the rocks. Comparing 87Sr/86Sr trends and rocks assemblages formed at different positions of the relative sea-level shows that lows on the 87Sr/86Sr curve correlate well with transgressions and relative sea level highstands, while high Sr isotopic ratios correspond to sea-level drops.