Facies analysis and depositional environment of a late Cambrian mixed carbonate-siliciclastic ramp from the Zard Kuh Mountain (Zagros Basin, south-western Iran)

Mixed carbonate-siliciclastic rocks were particularly widespread during the Furongian (late Cambrian), a critical time interval marked by biotic turnovers, extinction events and carbon cycle perturbations. In this context, the Zagros Basin (SW Iran) is a key area for the study of this time interval due to the well-exposed mixed carbonate-siliciclastic successions. Nevertheless, these are still poorly constrained from a sedimentological point of view. The current study aims to contribute to the palaeoenvironmental reconstruction of the Zagros Basin during the Furongian through high-resolution facies and microfacies analysis of the Tang-e-Ilbeyk section. The latter includes, in ascending order, the upper Mila C Member and Ilbeyk Formation. The facies and microfacies analysis recognized six facies associations, representing different settings of a mixed carbonate-siliciclastic ramp at the north-eastern Gondwanan margin. The vertical stacking pattern of these facies associations revealed five medium-scale Transgressive-Regressive cycles, superimposed by larger-scale sequences. In particular, during the latest Miaolingian (formerly late middle Cambrian) to early Furongian, a climate change from arid to humid conditions caused a major regressive event with the progradation of clastic shorelines and the following pollution and drowning of the Mila C Member's carbonate factory. The latter was replaced by a storm -dominated siliciclastic shelf (Ilbeyk Formation) that, throughout middle/late Furongian, experienced a large-scale transgressive event, culminating with a maximum flooding interval. A significant forced regression occurred in the latest Furongian when shallow water conditions were re-established (uppermost Ilbeyk Formation). The palaeoenvironmental reconstruction of this study allowed correlation with other coeval depositional events at re-gional (Arabian plate) and global (Laurentia and Baltica) scales, contributing to new constraints for the lower Palaeozoic evolution of north-eastern Gondwana.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

This study contributes to the reconstruction of the palaeoenvironment of the Zagros Basin during the Furongian period through high-resolution facies and microfacies analysis. The analysis identified six facies associations representing different settings of a mixed carbonate-siliciclastic ramp and revealed five medium-scale transgressive-regressive cycles and larger-scale sequences. The findings provide new constraints for the lower Palaeozoic evolution of the north-eastern Gondwana.