Biostratigraphy, microfacies, sedimentary environments of the Gurpi and Amiran formations in the Gerdbisheh section, High Zagros

Biostratigraphy, microfacies and depositional environments of the Upper Cretaceous deposits (Gurpi and Amiran formations) were carried out in the Gerdbisheh section. The Gurpi Formation predominantly consists of shales interbedded with some argillaceous limestone layers. This formation disconformably overlies the Sarvak Formation and gradually underlies the Amiran Formation. The Amiran Formation is represented by grey to greenish shales, siltstones and sandstone intercalations which underlay the informal siliciclastic-carbonate unit 1. Planktonic foraminiferal assemblages have led to the recognition of six zones that reveal the late Coniacian?–early Maastrichtian age for the Gurpi Formation. Radiolaria and scattered planktonic foraminifera are the two main fossil groups present in the Amiran Formation. Therefore, based on the precence of the index planktonic foraminfera and the stratigraphic position the early-middle? Maastrichtian age is proposed for the Amiran Formation. We determined two microfacies in the interval of the Gurpi Formation and three petrofacies in the Amiran Formation. According to the obtained data the Gurpi Formation was deposited in the basinal setting, whereas the Amiran Formation is deposited as submarine fans on the slope part of a carbonate shelf under the control of turbidity currents.