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Abstract: Biogeochemical and Tectonic Events Across the Mesoproterozoic-Neoproterozoic Transition in Siberia

BARTLEY, JULIE K., Geology Department, State University of West Georgia, Carrollton, GA; ALAN J. KAUFMAN, Department of Geology, University of Maryland, College Park; ANDREW H. KNOLL, Botanical Museum, Harvard University Cambridge, MA; MIKHAIL A. SEMIKHATOV, Geological Institute, Russian Academy of Sciences, Moscow, Russia; STEIN B. JACOBSEN, Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138

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