Calcareous nannofossil biostratigraphy in the Gurpi Formation Aghar anticline section located in SW Shiraz

One of the most extensive Cretaceous strata is the marine strata of the Gurpi Formation in Zagros, which was studied based on paleontology studies. The Gurpi Formation type section is located in Tang-e Pabdeh, North of Masjed Soleyman city (James & Wynd, 1965). One of the most important achievements obtained from the Gurpi Formation is the evaluation of stage boundary and biostratigraphy of it. In this section, the Gurpi Formation consists of 143 m thick which mainly consists of marl and marly limestone.

In this study, 73 samples from the Gurpi Formation interval have been studied. Samples were prepared following the standard smear slide method (Bown & Young 1998). All the slides were examined under the polarized light microscope at ×1000 magnification. The nomenclature of calcareous nannofossil follows the taxonomic schemes of Perch-Nielsen (1985) and Burnett (1998).

To study biostratigraphy based on calcareous nannofossils, the Gurpi Formation succession in the southwest of the Aghar anticline, SW Shiraz, was selected. In this section, the Gurpi Formation with 143 m thickness mainly consists of marly limestones and marl. For introducing index species, calcareous nannofossil assemblages, and bio-zones, slides have been studied at the Gurpi Formation, which led to the determination of 40 species and 21 genera of calcareous nannofossils. In this study, ten biozones were recognized in the Gurpi Formation. Bio-zones including Lucianorhabdus cayeuxii Zone (CC16), Calculites obscurus Zone (CC17), Aspidolithus parcus Zone (CC18), Calculites ovalis Zone (CC19), Ceratolithoides aculeus Zone (CC20), Quadrum sissinghii Zone (CC21), Quadrum trifidum Zone (CC22), Tranolithus phacelosus Zone (CC23), Reinhardtites levis Zone (CC24) and Arkhangelsiella cymbiformis Zone (CC25) with Late Santonian - middle Maastrichtian in age. According to the first and last occurrence of index species the following bio-zones are identified