<p>Bulk sedimentary nitrogen isotopes (&#948;<sup>15</sup>N) 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.&#160; In this paper, we report the first &#948;<sup>15</sup>N data from the Chang 7 Shale from a core drilled in the Ordos Basin. Bulk &#948;<sup>15</sup>N values are significantly higher in Zone A (the Chang 7<sub>3</sub> and the lower part of the Chang 7<sub>2</sub> submembers, average = 9.4 &#177; 1.3&#8240;) than in Zone B (the upper part of the Chang 7<sub>2</sub> and the Chang 7<sub>1</sub> submembers, average = 5.4 &#177; 1.5&#8240;). 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 (&#948;<sup>13</sup>C<sub>org</sub>) and total nitrogen (TN) values were measured to characterize any processes that might control alteration of the bulk &#948;<sup>15</sup>N 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 (&#948;<sup>13</sup>C<sub>org</sub>) and total nitrogen (TN) values between the two zones. In conclusion, we suggest that the difference in &#948;<sup>15</sup>N values through the Chang 7 Shale primarily reflects differences in the depositional redox conditions and &#948;<sup>15</sup>N values of shale can provide important details regarding the depositional history of unconventional resource plays.</p>
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
