EGU2020-1814
https://doi.org/10.5194/egusphere-egu2020-1814
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Evaluating nitrogen isotopes as proxies for depositional redox conditions in shales: A case study from the Chang 7 Shale in the Ordos basin, North China.

Ruiqian Chen and Guangdi Liu
Ruiqian Chen and Guangdi Liu
  • China University of Petroleum-Beijing, College of Geosciences, Department of Petroleum Geology, China (richen@cup.edu.cn)

Bulk sedimentary nitrogen isotopes (δ15N) have been used as an accurate redox proxy in well-preserved sedimentary systems, however, fewer studies of N-isotope have been performed in lacustrine shales.  In this paper, we report the first δ15N data from the Chang 7 Shale from a core drilled in the Ordos Basin. Bulk δ15N values are significantly higher in Zone A (the Chang 73 and the lower part of the Chang 72 submembers, average = 9.4 ± 1.3‰) than in Zone B (the upper part of the Chang 72 and the Chang 71 submembers, average = 5.4 ± 1.5‰). Given the lithological characteristics and previous geochemical measurements, we suggest that sediments within Zone A of the Chang 7 Shale were mainly deposited under suboxic bottom water conditions, whereas Zone B sediments show evidence of deposition under oxic deep water regimes. Additionally, organic carbon isotopes (δ13Corg) and total nitrogen (TN) values were measured to characterize any processes that might control alteration of the bulk δ15N signal, including changes in organic matter source and post-depositional processes. Our results show that there is no significant difference in the organic carbon isotopes (δ13Corg) and total nitrogen (TN) values between the two zones. In conclusion, we suggest that the difference in δ15N values through the Chang 7 Shale primarily reflects differences in the depositional redox conditions and δ15N values of shale can provide important details regarding the depositional history of unconventional resource plays.

How to cite: Chen, R. and Liu, G.: Evaluating nitrogen isotopes as proxies for depositional redox conditions in shales: A case study from the Chang 7 Shale in the Ordos basin, North China., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1814, https://doi.org/10.5194/egusphere-egu2020-1814, 2019