Ecological changes and depositional sequences during Cenomanian/Turonian platform evolution in the Zagros Basin, SW Iran; an interplay between tectonics and aquifer-eustasy

Abstract

This study focuses on the facies associations and depositional sequences of a Cenomanian/Turonian (C/T) outcrop, spanning the upper part of the Sarvak Formation in the Izeh zone, Zagros basin, Iran. The significant variations in sedimentary facies of the studied succession suggest an evolution from a late Cenomanian open-shelf to an early Turonian ramp system. This change is believed to be response of transition in the tectonic regime of Arabian plate from a passive to an active margin during the late Cretaceous. Two partial and one complete third-order depositional sequences and also several fourth-order sequences and small-scale cycles were recognized in the studied section. The global correlation of the third-order sequences suggests that they were eustatically-driven. However, local tectonic activities overprint the eustatic signature from the latest Cenomanian. The association of transgressions with cooling and regressions with warming during the fourth-order sequences support the aquifer-eustasy model as a controlling factor for the sea-level fluctuations under C/T supergreenhouse conditions.