Revisiting the Tianjiayuanzi section - the stratotype section of the Ediacaran Doushantuo Formation, Yangtze Gorges, South China

M. Lu, M. Zhu, F. Zhao
2012 Bulletin of Geosciences  
The Ediacaran Doushantuo Formation (dating from 635 Ma to 551 Ma) of South China is composed of alternating siliciclastic and carbonate units and yields abundant extraordinarily preserved animal embryos, macroscopic multicellular algae and Ediacara-type fossils. Thus, it is critical for the chronostratigraphic calibration of the Ediacaran Period and for deciphering the evolutionary history of life during this time interval. In order to establish a high-resolution Ediacaran chronostratigraphic
more » ... ronostratigraphic framework and to clarify the correlation problem of the Doushantuo Formation, we reinvestigated the Tianjiayuanzi section, which is the stratotype section of the Doushantuo Formation. The new carbon isotope and sequence stratigraphic data, as well as the integrative correlation of the Tianjiayuanzi section with other sections in the Yangtze Gorges area demonstrate that there are four negative carbon isotope excursions (N1-N4) in the Doushantuo Formation in the Yangtze Gorges area. The N1 (CANCE) excursion occurs within the cap carbonate interval at the base of the formation. Extreme negative δ 13 C values (< -18‰) are recorded within this interval from most of the sections in the Yangtze Gorges area. The N2 (WANCE) excursion, with δ 13 C values shifting from +6‰ to -1‰, occurs in the middle of Member 2 at a major sequence boundary in the middle of the formation. The N3 excursion is situated in a horizon near the boundary between Member 2 and Member 3 of the formation and is characterized by δ 13 C values down to -6‰. The N4 (DOUNCE) excursion with a nadir of δ 13 C values as low as -9.6‰ at the top of the formation represents the most distinct negative carbon isotope excursion in the Ediacaran. New observations in the field confirm the presence of a sequence boundary at a karstic surface in the upper part of the Doushantuo Formation, which coincides with the beginning of the nadir of δ 13 C values within the DOUNCE. Additional δ 13 C data from the basal Dengying Formation indicates that the DOUNCE interval with the most negative δ 13 C values crosses entirely the black shale Member 4 at the top of the Doushantuo Formation. •
doi:10.3140/bull.geosci.1227 fatcat:wwhp24tjz5grnczka7jatdbx44