A pronounced negative δ13C excursion in an Ediacaran succession of western Yangtze Platform: A possible equivalent to the Shuram event and its implication for chemostratigraphic correlation in South China

A pronounced negative delta C-13 shift that can be potentially correlated with the Shuram excursion has been reported from middle Ediacaran strata in the Yangtze Gorges area of South China. Whether it represents a perturbation to the ocean carbon cycle or a record of post-depositional alteration is still open to debate. Resolving this controversy will help clarify if delta C-13 variations can be used for chemostratigraphic correlation of Ediacaran successions. To further understand the regional pattern of Ediacaran carbon isotopic excursions in the Yangtze platform, we carried out a detailed delta C-13 analysis of the Lianghong section in the western part of the Yangtze platform. The Ediacaran System at Lianghong is overlain by the Maidiping Formation yielding early Cambrian small shelly fossils and underlain by the Cryogenian Lieguliu Formation diamictite and tuffaceous siltstones. It comprises the Guanyinya and Hongchunping formations, which have been traditionally correlated with the Doushantuo and Dengying formations, respectively, in the Yangtze Gorges area. Two negative delta C-13 excursions occur in the Lianghong section. The lower one at the uppermost Guanyinya Formation, with a nadir at -8.6 parts per thousand, may be correlated with the pronounced negative delta C-13 shift (EN3) in the uppermost Doushantuo Formation in the Yangtze Gorges area and possibly with the well known Shuram event in Oman. The upper negative delta C-13 excursion occurs in the upper Hongchunping Formation and may be correlated with negative excursions (EN4) near the Ediacaran/Cambrian boundary. Other negative delta C-13 excursions (e.g., EN1 and EN2) are not expressed in the Lianghong section because the lower Guanyinya Formation is dominated by siliciclastic rocks. Combined with previously published Ediacaran delta C-13 profiles, our results indicate that the EN3 excursion (likely a Shuram equivalent) may occur widely in South China and can be a useful chemostratigraphic feature for regional and global stratigraphic correlation. (C) 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.