Biostratigraphy And Palaeodepositional Model Of The Sarvak Formation In The Fars Zone, Zagros, Iran

This study is scoped on biostratigraphy, and palaeodepositional analysis of the Sarvak Formation, Fars Zone, and Zagros, Iran. The biostratigraphy and microfacies of this Formation form four field sections, are discussed. The Sarvak Formation in the study area is located on Kazhdumi Formation and below the Gurpi Formation and comprise of cream to grey medium bedded to massive limestone. Seven foraminiferal assemblages have been identified from the Sarvak Formation and these assemblages form the basis of the biostratigraphy. The lower and upper parts of Sarvak Formation are lacking diagnostic microfossils and based on their stratigraphic position, Late Albian-Late Cenomanian, ages was assigned respectively. Field and microscopic data led to the identification of five facies groups; Planktonic foraminifera-dominated facies, Benthic foraminifera-dominated facies, Rudist facies, Orbitolina facies and Mudstone facies, these facies were subdivided into twelve subfacies, which were grouped into three depositional environments: inner, middle and outer shelf and overall representing a shelf setting. Facies changes during the Late Albian-Late Cenomanian were generally associated with carbonate shelf models. These containing a number of separate aspect, namely: Orbitolina conica sp.-dominated shelf with minor Orbitolina sp. during the Late Albian, a Trocholina sp. and Conicorbitolina -dominated shelf during the Late Albian, a Rudist- to algae-dominated shelf during the most of the Early Cenomanian and a pelagic and benthic foraminifera-dominated shelf during Late Cenomanian. In general, from the Kuh-e-Gadvan section to the southwest of the Fars zone (Rashtanu section), the depth of the sedimentary basin of Sarvak Formation increased.