REVISION OF CARBON ISOTOPE PROFILE FOR THE EDIACARAN OF SOUTH CHINA

Large amplitude perturbation of carbon isotope during the Neoproterozoic-Cambrian transition is interpreted to reflect global carbon cycle which fundamentally links with global tectonic and biological activities, thus carbon isotope profile is widely accepted as an important chemostratigraphic tool for calibrating Neoproterozoic and Cambrian time. However, there is yet not a consensus carbon isotope profile accepted for global stratigraphic correlation, because there are arguments on synchroneity and primary signature of these carbon isotope excursions, and lacking geochronological constrains.

Here we provide a revised composite carbon isotope profile for the Ediacaran of South China based on reinvestigation of well-known sections in the Yangtze Gorges and new sections from the northern Yichang area, Hubei. A negative carbon isotope excursion (nadir of -6‰) is proved as a widely traceable excursion in the upper Member 2 of the Doushantuo Formation, except for previously recognized three excursions at the base, middle and top of the Doushantuo Formation respectively. Field investigation demonstrates that lithostratigraphic sequence at the top of the Doushantuo Formation in the sections from the west limb of the Huangling Anticline is tectonically destructed, and a positive shift of carbon isotope values within DOUNCE (nadir of -10‰; =the Shuram/Wonoka anomaly) reported previously is not original. In addition, a sequence boundary is recognized near the base of DOUNCE, the sequence boundary at the base of the black shale at the top of the Doushantuo Formation proposed previously is interpreted as a flooding surface.

Based on the composite carbon isotope profile, in combination with bio-, sequence stratigraphy and geochronological data, a new Ediacaran chronostratigraphy for South China is proposed. We suggest that the Ediacaran chronostratigraphic framework of South China can be adapted for global subdivision and correlation of the Ediacaran stratigraphy.