Because the C and Sr isotopic compositions of seawater respond to major evolutionary and tectonic events, their long-term secular variations, recorded in carbonate rocks, provide a powerful tool for assessing global change. Where global reference curves exist, such as in the latter part of the Neoproterozoic (ca 850 Ma to 543 Ma) and in the Phanerozoic, temporal change in d¹³C and ⁸⁷Sr/⁸⁶Sr permits correlation of successions worldwide. The less studied early Neoproterozoic and Mesoproterozoic interval has been cited as a time of muted d¹³C and potentially large ⁸⁷Sr/⁸⁶Sr change. Recent studies in Siberia, including the Uchur-Maya region in the east and the Turukhansk Uplift in the northwest suggest a first-order shift in d¹³C from values near 0o/oo in the early Mesoproterozoic (> ca. 1300 Ma) to values near +3 to +4o/oo in late Mesoproterozoic and early Neoproterozoic sediments. These variations are consistent with isotopic data from other continents across this critical transition.

Combined lithologic, biostratigraphic, and geochemical data sets allow us to refine correlations between the two successions in Siberia and represent a significant step toward construction of global C and Sr isotopic reference curves. Available data are consistent with a decrease in ⁸⁷Sr/⁸⁶Sr values over the interval where d¹³C values rise. These first-order variations in C and Sr isotopic composition likely record the impact of the assembly of a Rodinian supercontinent (ca 1300-1150 Ma) on both the crustal and biogeochemical cycles.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah