Spatio-temporal carbon isotope variation during the Ediacaran period in South China and its impact on bio-evolution

Abstract

The Ediacaran period is characterized by the extremely negative carbon isotope anomalies and great biotic evolution in Earth history. At least four negative carbon isotope anomalies have been reported from this interval in South China so far. It is traditionally argued that the isotope variations can be used as a useful tool for global correlation of Ediacaran succession; however, more and more researches argued against this idea. We reviewed the previously published carbon isotope data in South China, and distributed the mean values of a certain time to the paleogeographic maps. The results show that the carbon isotope values (δ 13 C) vary greatly in different environments, but a clear tendency of becoming lighter from shallow platform to deep basin, with a maximum variation up to 11‰. Moreover, the important changes in Ediacaran biota, marked by the introducing of new taxa or ecologic groups, seemed to always postdate the negative anomalies but coincide with the positive shift. If the negative excursions represented the oxidation of a large dissolved organic carbon (DOC) reservoir in the ocean, the diverse Ediacaran organisms and the carbon isotope anomalies may suggest totally different environments: oxic and anoxic/euxinic. We also suggest that the elimination of euxinic state through precipitation of pyrites is one of the important environment factors in prompting the Ediacaran bio-evolution.

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

“…Previously published Ediacaran δ 13 C chemostratigraphic data have shown a strong δ 13 C gradient from shallow-water platform to deepwater basin environments in South China (Jiang et al, 2007Wang and Shi, 2009), but Ediacaran δ 13 C chemostratigraphic profiles are consistent among shallow-water platform successions Zhu et al, 2007). Composite δ 13 C profiles for the Ediacaran System in shallow-water platform in South China have been constructed using litho-and biostratigraphic markers as independent calibrations Zhu et al, 2007).…”

Astronomical time scale for the lower Doushantuo Formation of early Ediacaran, South China

“…Notably, enhanced carbonate precipitation during that transition may have resulted from the combination of rising sea levels, and of high carbon-dioxide levels, intense chemical weathering, and associated flux of calcium and other ions would have raised marine alkalinity and promoted enhanced carbonate precipitation [8]. Nevertheless, there are many changes in the surface climate and sedimentary environment, in weathering prior to Snowball Earth [8][9][10][11], release of methane hydrates [11,12] and in oxidation of super-sized dissolved organic carbon (DOC) reservoirs in the early Ediacaran Ocean [13][14][15]. A key challenge that would help address this issue is to gain knowledge of the rates and durations of cap carbonate formation in different places.…”