Nitrogen isotope variations and environmental perturbations during Cenomanian-Turonian transition in the NE Tethyan realm, Koppeh-Dagh basin

The Cenomanian-Turonian Gharesu section in the east of Kopet-Dagh basin have been investigated to determine the relationship between palaeoenvironmental perturbations and nitrogen cycling across OAE2. This succession is composed of 43 m shale and marl interbedded with glauconitic sandstone and lies between Aitamir-Abderaz formations boundary. The nitrogen Isotope values fluctuate between 0‰ to +3‰ and TOC/TN ratios range from 3.5 to 20.5 in this section. The TOC/TN exhibits high ratios in the organic-rich sediments which were deposited in a low-oxygen environment because nitrogen-rich organic matter was preferably degraded in this condition. The δ15N values are also low in the organic-rich sediments which indicate a nitrogen fixation process as a consequence of greenhouse climate, enhanced productivity and expanded oxygen minimum zone during OAE2.