Evidence of Mid-Cretaceous carbon cycle perturbations and OAE2 recorded in Cenomanian to middle Campanian carbonates of the Zagros fold–thrust belt basin, Iran

Abstract

The Cenomanian to middle Campanian succession of the Zagros fold-thrust belt basin in Iran was investigated to evaluate the sedimentologic and geochemical response to Oceanic Anoxic Event 2 (OAE2), the Cenomanian–Turonian Boundary Event (CTBE) and Mid Cenomanian Event I (MCEI). The succession was examined at the Chenareh anticline locality, which is situated between the two main tectonic zones of the Zagros fold-thrust belt basin. Petrographic analysis led us to define 10 carbonate microfacies and a shale petrofacies that were deposited in four facies belts: tidal flat, lagoon, shoal, and open marine within a larger platform ramp environment. Carbon isotope and trace element data indicate that the Coniacian to middle Campanian Ilam Formation formed within anoxic to dysoxic settings, with lower amounts of water/rock interaction compared to the underlying Sarvak Formation. Carbon isotope chemostratigraphy allows the CTBE and MCEI evidence to be distinguished within the Zagros Basin, however, values measured by this study are depleted compared to other published chemostratigraphic records of the event. The results, therefore, demonstrate that diagenesis or a local CTB hiatus affected the record of these global events in the study area at the Zagros Basin.