首页|Nitrogen isotope evidence for oxygenated upper ocean during the Cryogenian interglacial period

Nitrogen isotope evidence for oxygenated upper ocean during the Cryogenian interglacial period

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  • NSTL
  • Elsevier
The Cryogenian interglacial period have witnessed dramatic changes in dim ate, oceanic environment and biological evolution. The nitrogen isotopic composition, as an important biogeochemical proxy, has the potential to track both the nutrient cycling and redox conditions in the past. However, nitrogen isotopic data during this interglacial time is rather limited. Here, we present integrated data for nitrogen isotopes (delta N-15), as well as organic carbon isotopes (delta(13)Corg), iron (Fe) speciation, pyrite morphology and trace elements from the Cryogenian interglacial Datangpo Formation derived from a drill core from South China to figure out the nitrogen cycling and coeval redox states. The results reveal a gradual oxygenation bottom waters along with deepening O-2-H2S chemocline from euxinic black shale in the lower unit (LU), to oxic siltstone in the upper unit (UU), which is consistent with the redox variation inferred in previous studies. Sedimentary delta N-15 values constantly remain positive (mean value> + 4 parts per thousand) throughout the Datangpo Formation and display an increase from the LU to the UU. We interpreted the positive delta N-15 values in the LU as a result of denitrification related to the development of euxinic conditions. The further increase towards the UU associated with limited nutrient supply may indicate the existence of a stable nitrate reservoir in the upper water column, which was consistent with an increased oxygenation during the interglacial time. The elevated O-2 levels and bioavailable nitrogen in seawater may have further contributed to the appearance of the earliest metazoan. In addition, our data lay good foundation for further global delta N-15 correlations among other interglacial successions.

CryogenianDatangpo FormationNitrogen isotopeDenitrificationInterglacial periodBASAL DATANGPO FORMATIONSANTA-BARBARA BASINSOUTH CHINAREDOX CONDITIONSYANGTZE PLATFORMNANHUA BASINNEOPROTEROZOIC GLACIATIONSORGANIC-MATTERMETASEDIMENTARY ROCKSDOUSHANTUO FORMATION

Li, Tingting、Wang, Pengju、Zhu, Guangyou、Zhao, Kun、Song, Haijun、Zhang, Zhiyao、Yan, Huihui、Song, Huyue

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PetroChina

China Univ Geosci

2022

10.1016/j.chemgeo.2022.120929

Chemical geology

Chemical geology

EISCI
ISSN：0009-2541
年,卷(期)：2022.604
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