The stratigraphic complexity of the middle Ediacaran carbon isotopic record in the Yangtze Gorges area, South China, and its implications for the age and chemostratigraphic significance of the Shuram excursion

The middle Ediacaran Shuram excursion represents the most pronounced negative carbon isotopic shift in Earth history, and has been considered as evidence for a profound disturbance to the global carbon cycle and proposed as a key chemostratigraphic marker for Ediacaran stratigraphic subdivision and global correlation. Previous study has revealed a pronounced negative delta C-13 shift (EN3) in the upper Doushantuo Formation of South China, which has been interpreted as an equivalent of the Shuram excursion. Detailed delta C-13 investigation of multiple sections of the Ediacaran Doushantuo Formation around the Huangling Anticline, western Hubei Province, South China, indicates that the delta C-13 variation in the upper Doushantuo Formation is more complex than previously reported. In the western region of the Huangling anticline, a moderately positive delta C-13 excursion (here termed the Diaoyapo positive excursion) bisects two strongly negative delta C-13 excursions (here termed the Jiuqunao negative excursion and the younger Miaohe negative excursion), with a similar to 551 Ma ash bed capping the Miaohe negative excursion. In the central region, there is only one negative delta C-13 excursion, whereas in the eastern region, the negative delta C-13 excursion is absent. The variable stratigraphic expression of these delta C-13 excursions is most parsimoniously interpreted as reflecting local fades variation, diagenesis, and/or a cryptic unconformity. The more complete but more complex delta C-13 chemostratigraphic record in the western region of Huangling Anticline implies that, depending on how this record is correlated with the Shuram excursion, the latter may be significantly older than 551 Ma if it does represent a global chemostratigraphic marker. (C) 2016 Elsevier B.V. All rights reserved.