Paleoenvironmental significance of the carbon isotope record across the Cenomanian-Turonian transition and the Oceanic Anoxic Event 2 (OAE2) in the southeastern Neotethys, Zagros, Iran

A high-resolution carbon isotope record of pelagic carbonates (813Ccarb) from the Zagros Mountains, Iran, documents a 1.8%o positive carbon isotope excursion (CIE) in the southeastern Neotethys during the Cenomanian-Turonian transition, corresponding to Ocean Anoxic Event (OAE2). The succession is controlled by biostratigraphy that includes the Rotalipora cushmani, Whiteinella archaeocretacea, and Helvetoglobotruncana helvetica biozones. The CIE is characterized by a positive shift culminating in a first positive peak (at 3.3%o), followed by a 1%o negative excursion, accompanied by the highest 818Ocarb values that can be interpreted as the result of a short-lived global cooling, the Plenus Cold Event. A subsequent second positive peak and a plateau of higher 818Ocarb values are followed by relatively low values in the earliest Turonian akin to pre-excursion values. The biostratigraphic positions of the three diagnostic maximum points, referred to as peaks A, B, and C, within the generally positive CIE indicate a syn-chronous 813Ccarb variability worldwide. The average 813Ccarb values in southeastern Neotethys are generally lower compared to the open-ocean records of the same period. We attribute this offset to a substantial regional regression combined with recycling of isotopically light organic carbon. The dia-chronous deposition of black shales/mudstones after the onset of positive CIE suggests that its formation strongly depends on local paleogeography and paleoenvironmental factors.& COPY; 2023 Elsevier Ltd. All rights reserved.