Abstract

New high-resolution δ13C data through the Lower Cambrian of Siberia reveal multiple, positive excursions coincident with phases in the "explosion" of invertebrate phyla (Nemakit-Daldynian to middle Botomian stages). Comparison of the δ18O and trace element (Mg, Fe, Mu, Sr) chemistry indicate that six new δ13C cycles are primary rather than diagenetic features, with potential for global correlation. Positive δ13C excursions up to +3‰ indicate that fractional organic carbon burial rates were high but variable through the Cambrian explosion. Values for δ13C dropped sharply from around +2.2‰ to -1.6‰ in Botomian time, coincident with mass extinction of the archaeocyathan reef biota. The rapid fluctuation of the δ13C signal and the temporal coincidence of the pronounced negative shift with the extinction event hint that the δ13C record may record productivity variations during the Early Cambrian radiation.

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