The Oceanic Anoxic Events such as Cenomanian‐Turonian boundary event (OAE2), which is generally coeval with widespread deposition of organic-rich sediments, can be investigated through geochemical and chemostratigraphic studies. The carbon isotope curve for both organic and carbonate carbons (δ13Corg ،δ13Ccarb) in Gharesu section (east of Kopet-Dagh basin) show a similar trend to the globally documented Cenomanian/Turonian positive excursion that was resulted by burial of isotopically depleted organic carbon. Climate proxy data (δ18O and Δ13C) indicate a long term global warming and high sea surface temperatures in the C-T transition. Also high burial rates of organic carbon were likely sufficient to significantly draw down atmospheric CO2 and cause transient cooling periods of the global climate. The δ15N depletion in the high TOC sediments is another characteristic of this interval, which indicates enhanced nitrogen fixation due to expansion of oxygen minimum zone.

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