Strontium isotope proxy of sedimentological records reveals uplift and erosion in the Southeastern Neo-Tethys ocean during the late Cretaceous

The mutual interplays between plate tectonic processes, orogenesis and continental uplift, high-flux magmatism, and high sedimentation rates can affect the geochemical signatures and composition of marine sediments. Here, we examine two major disconformities, the Cenomanian-Turonian boundary (CT-ES) and the middle Turonian (mT-ES) exposure surfaces, from the Upper Cretaceous sedimentary successions of the southeastern Neo-Tethys Ocean in the Zagros Basin (Iran). The disconformities are expressed as distinct positive peaks in rubidium (Rb) contents and ⁸⁷Sr/⁸⁶Sr isotopic ratios of carbonates. The ⁸⁷Sr/⁸⁶Sr values of samples bracketing the disconformities in seven well cores give average age ranges of 94.4-93.6 Ma for the CT-ES and 91-86 Ma for the mT-ES. These ages fall in the timespan of forearc/ophiolite formation through subduction initiation in the Neo-Tethys realm (southern margin of Eurasia), high convergence velocities between Arabia and Eurasia, and blueschist exhumation. All these processes involved buckling of the Neo-Tethyan lithosphere, initiating the Neo-Tethys closure and a high erosion rate on the Eurasian margin. The first two mechanisms exerted considerable compressional forces on the adjacent carbonate platforms, reactivated basement faults, and led to the uplift and erosion of the Arabian Plate, which provided the high contents of Rb and the high ⁸⁷Sr/⁸⁶Sr ratios in the carbonates.