Nitrogen isotope chemostratigraphy of the Ediacaran and Early Cambrian platform sequence at Three Gorges, South China

Marine redox variations and nitrogen cycle of the early Cambrian southern margin of the Yangtze Platform, South China: Evidence from nitrogen and organic carbon isotopes

“…3). Upward, the ␦ 13 C org curve exhibits positive excursions in the Dahai Member of the Zhujiaqing Formation, Yunnan and in the upper Yanjiahe Formation, Three Gorges area (Cremonese et al, , 2014Kikumoto et al, 2014) (Fig. 3b), which are typical of early Cambrian Stage 2, consistent with the appearance of the third SSF biozone (Fig.…”

“…8a), indicating relatively normal marine productivity conditions on the shallow platform , which could have benefited the bloom of small shelly fossils (SSFs) there. However, in the Three Gorges area, lower ␦ 15 N bulk values between 0‰ and +3‰ could reflect a stronger contribution from N 2 -fixation, and that waters in the outer-shelf area were less oxic than the shallow platform during this time interval (Cremonese et al, 2014;Kikumoto et al, 2014) (Fig. 8b).…”

“…At Yuanjia section, the PrecambrianCambrian boundary could be placed at the negative ␦ 13 C org excursion in the upper Liuchapo Formation (Guo et al, 2013) because this excursion may correlate with the ␦ 13 C carb and/or ␦ 13 C org negative excursions in the Daibu Member of the Zhujiaqing Formation at Xiaotan section, Yunnan Province Li et al, 2013a;Zhou et al, 1997) and in the lower part of the Yanjiahe Formation at Wuhe section, Three Gorges area (Cremonese et al, 2014;Ishikawa et al, 2008;Kikumoto et al, 2014) (Fig. 3b).…”

“…To further reconstruct the spatiotemporal variability of marine redox conditions along the southern margin of the Yangtze platform, we correlate ␦ 15 N data from this study and published data from Xiaotan section in Yunnan Province and Wuhe section in the Three Gorges area (Cremonese et al, 2014;Kikumoto et al, 2014), which are located in the shallow platform and transitional zone, respectively (Fig. 8).…”

“…Given that the nitrogen cycle is not only closely related to marine environmental conditions and biological metabolism, but also reflects the ocean redox structure, an increasing number of studies have been conducted on the nitrogen isotope systematics of Ediacaran -early Cambrian marine sediments (Ader et al, 2014;Cremonese et al, 2013Cremonese et al, , 2014Kikumoto et al, 2014;Wang et al, 2013). However, these studies mainly focused on the shallow platform realm.…”