Microfacies, Sedimentary Environment and Sequence Stratigraphy of Gadvan and Darian Formations in the Zagros Basin, South of Semirom, Iran

摘要

Gadvan and Darian formations are in the upper part of Khami group that has been deposited in the highland Zagros zone and the southern Margin of Neotethys. These formations outcrop in the south of Semirom (Agh-Dagh Mountain) consist of Orbitolina limestones and marly limestones with a Late Barremian-Aptian age and thickness of 520 meters. Based on field characteristics, petrographic and texture of facies, these rocks consist of Oregonian facies (Urgonian facies) with 12 carbonate microfacies which are deposited in Lagoon, barrier and shallow open marine. The absence of loss and flows of turbidities indicates that carbonate platform of Gadvan and Darian formations in the studied area are (Hmoklinal) platform type. Abundance of rudist (bivalves) and Peloid markers show that there is a Photozoan collection in tropical climates. In the above sedimentary succession, from a sequence stratigraphic perspective, three sedimentary cycles were recognized which deposited in a platform model. The Gadvan Formation overlies on Fahliyan Formation disconformable and is covered by Darian Formation gradual with reducing the amount of marl and increase of limestone. The Kazhdumi Formation is exposed disconformably with hematite nodules and oxidized sediments over the Darian Formation. On the basis of petrographic studies, diagenetic process of Gadvan and Darian formations in the study area includes cementation, the physical and chemical density and replacement processes such as pyritation, ironies and silica. Porosity observed in the study area is mainly inter-granular porosity type, modular and vaggy.