C-isotope variations and paleoceanographic changes during the late Neoproterozoic on the Yangtze Platform, China

This study reports delta C-13 measurements on the well-preserved and continuous marine carbonate strata of the Donglongtan Formation (late terminal Proterozoic) from southwestern China. Geochemical criteria including Mn/Sr ratios have been used to assess the alteration of depositional delta C-13 values. The C-isotope measurements reveal a previously unrecognized positive rise from - 0.5 parts per thousand to + 4.4 parts per thousand in the carbonate strata of late terminal Proterozoic, considered to reflect a similar change in the isotopic composition of coeval seawater. The composite C-isotope chemostratigraphy of the late Neoproterozoic on the Yangtze Platform is consistent with that of well-dated Neoproterozoic successions elsewhere, and provides a tentative scenario of paleoceanographic changes before the 'Cambrian explosion'. (C) 2002 Elsevier Science B.V. All rights reserved.