Coupled evolution of nitrogen cycling and redoxcline dynamics on the Yangtze Block across the Ediacaran-Cambrian transition

Feedback Between Carbon and Nitrogen Cycles During the Ediacaran Shuram Excursion

“…This negative δ 15 N excursion was interpreted as evidence for an increased nitrate pool which may have resulted in the partial assimilation of NO 3 − (Kikumoto et al, 2014;Nishizawa et al, 2019). Nitrogen isotope data have also been reported from the other Ediacaran sections in South China and other continents (e.g., Ader et al, 2014;Spangenberg et al, 2014;Wang et al, 2017;Chen et al, 2019;Lan et al, 2019;Nishizawa et al, 2019), but the Shuram excursion is poorly developed or missing in these sections. In this contribution, we report high resolution δ 15 N and δ 13 C org data from the upper Doushantuo Formation in two sections (Jiulongwan and Xiangerwan) in the Yangtze Gorges area, South China, where the Shuram-EN3 excursion is well recorded (Jiang et al, 2007;An et al, 2015;Zhou et al, 2017).…”

“…More data are needed to confirm this variation. Chen et al (2019) reported δ 15 N data from the Doushantuo Formation in an upper slope drill core section (zk 2012) in the Daotuo area, northeastern Guizhou Province. A conspicuous decline in δ 15 N was observed in the upper Doushantuo Formation (Figure 6E; Chen et al, 2019).…”

“…Chen et al (2019) reported δ 15 N data from the Doushantuo Formation in an upper slope drill core section (zk 2012) in the Daotuo area, northeastern Guizhou Province. A conspicuous decline in δ 15 N was observed in the upper Doushantuo Formation (Figure 6E; Chen et al, 2019). Although no δ 13 C carb data were reported in zk 2012, the δ 13 C carb profile from an adjacent drill core verifies the presence of the Shuram-EN3 excursion in the upper Doushantuo Formation (Wei et al, 2019).…”

“…Modeled results indicate that δ 15 N data from the Ediacaran Doushantuo Formation show contrasting distributions before and during the Shuram excursion (Figure 7). High δ 15 N values from the lower-middle Doushantuo Formation prior to the Shuram excursion have been attributed to incomplete denitrification that preferentially removed light 14 N from the ocean (Kikumoto et al, 2014;Ader et al, 2014;Wang et al, 2017Wang et al, , 2018Chen et al, 2019;Lan et al, 2019;Xu et al, 2020). The decrease of δ 15 N associated with the Shuram excursion was previously interpreted as partial assimilation of NO 3 − from an expanding nitrate pool in response to a rise of oxygen levels in the ocean-atmosphere system, implying that dissolved P rather than N was the limiting nutrient during the excursion interval (Kikumoto et al, 2014;Nishizawa et al, 2019).…”

“…750 Ma to 570 Ma, spanning from the Tonian through the Cryogenian to the middle Ediacaran (Ader et al, 2014). Particularly, after the deglaciation of the Marinoan Snowball Earth, which represented a global sea level rise, δ 15 N remains high for at least 60 Myr or even longer until the onset of the Shuram excursion (Xiang et al, 2018;Chen et al, 2019;Xu et al, 2020). Further, from the Ediacaran to early Cambrian the ocean was characterized by predominately anoxic environments with multiple short-term oxygenation events (Sahoo et al, 2016;Li et al, 2018).…”