A CARBON-ISOTOPE REFERENCE SCALE FOR THE LOWER CAMBRIAN SUCCESSION INSIBERIA - REPORT OF IGCP PROJECT-303

Four sections from the mid-Atdabanian to lowest Toyonian (middle Cambr ian) along the Lena River of Siberia were sampled for carbon isotope s tratigraphy. These show a mainly heavy but highly oscillatory delta(13 )C signature for the Atdabanian to mid-Botomian interval, coincident w ith the major phase of invertebrate innovation. A prolonged interval o f negative delta(13)C followed until late Toyonian times, coincident w ith Botomian-Toyonian mass extinctions. Eleven carbon isotope cycles a re identified through the lower Cambrian, which should now be tested f or their utility in global correlation and relationship to bioevents i n the Cambrian explosion.