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Abstract: The DOUNCE (Doushantuo negative carbon isotope excursion), characterized by a large shift in δ13Ccarb from +5‰ down to −12‰ in the upper part of the Ediacaran Doushantuo Formation, was previously known only from a few sections mainly in the Yangtze Gorges area, western Hubei, South China. As a consequence, it remains uncertain whether the DOUNCE is of diagenetic origin, of local significance only, or corresponds to the worldwide mid-Ediacaran Shuram–Wonoka anomaly. Here we report the widespread occurrence of the DOUNCE in nine sections from various depositional settings ranging from coastal shallow basin, offshore intra-shelf basin to deepwater slope on the Yangtze platform. The results indicate that the DOUNCE starts in the upper part of Doushantuo Sequence 2 and ends at the base of the Dengying Formation. The variable appearance of the DOUNCE is facies dependent and any absence of the DOUNCE is shown to be the result of stratigraphic hiatus. The fall and recovery of δ13Ccarb values that bracket the DOUNCE occur over a relatively short stratigraphic interval and were possibly of shorter duration than the nadir of δ13Ccarb values which remain stable for a much longer interval from the transgressive systems tract to the condensed portion of the sedimentary sequence. Both the fall and the recovery of δ13Ccarb values are gradual and independent of lithology, suggesting a non-diagenetic origin for the DOUNCE which is further supported by the lack of any systematic diagenetic positive covariation between δ13Ccarb and δ18Ocarb data, and systematic differences in absolute isotope values between dolostone and limestone units. Field investigations and sedimentary analysis suggests the occurrence of a major sequence boundary at the basal part of the DOUNCE and reveals that previous reports of an interval of positive δ13C values within the DOUNCE resulted from either post-depositional sliding or faulting. Similarities between the evolutionary pattern and stratigraphic occurrence of the DOUNCE and global Shuram–Wonoka anomalies demonstrate that the DOUNCE represents a global change in seawater chemistry during the mid-Ediacaran which was closely related to the evolution of macroscopic metazoans. [Copyright &y& Elsevier]

Abstract: The Doushantuo Formation of South China, consisting of intercalated siliciclastic and carbonate rocks which exhibit considerable variation in thickness and sedimentary facies, is one of the key sedimentary units in the world for understanding Ediacaran geobiological processes. However, stratigraphic correlation and sedimentary facies evolution of the Doushantuo Formation remain controversial. Sedimentary facies analysis of the well-known sections of the Yangtze Gorges area and new sections in northern Yichang, western Hubei indicate that the Doushantuo succession in the Yangtze Gorges area was deposited in an offshore intra-shelf basin within the Yangtze platform. In contrast, the Doushantuo Formation in the northern Yichang area which is characterized by one or a few phosphate-rich horizons represents deposition on the subtidal or intertidal shelf, and so is similar to the succession in the Weng’an area (central Guizhou Province). The carbon isotope profiles of the different sections exhibit significant variation, which is interpreted to result from facies differences. Sequence and high-resolution carbon isotope stratigraphy have clarified problematic correlations and the temporal relationship between fossil assemblages of the Doushantuo Formation on the Yangtze platform. The results confirm that a prominent negative δ 13Ccarb excursion (BAINCE, nadir down to −5‰) in the middle portion of the second sequence of the Doushantuo Formation is a widely traceable event. BAINCE together with three other δ 13Ccarb excursions, namely CANCE at the base, WANCE near the first sequence boundary near the middle, and DOUNCE at the top of the Doushantuo Formation, constitute a complete carbon isotope profile for the Doushantuo Formation that reflects contemporaneous seawater and so serves as a reference chemostratigraphic profile for global stratigraphic correlation and for evaluating the chemical evolution of seawater during the Ediacaran Period. [Copyright &y& Elsevier]