Biostratigraphy of the Gurpi Formation with emphasis on Calcareous Nannofossils in the Evaz section, southeast of Shiraz

One of the most extensive Cretaceous deposits in Zagros is the marine sediments of Gurpi Formation in southeast Shiraz, which was studied based on stratigraphic and paleontology. Type section of the Gurpi Formation is located in Tang-e Pabdeh (Jams & Wynd, 1965). One of the most important achievement obtained from the Gurpi Formation can be related to study of calcareous nannofossils which is used for determination of precise age and biostratigraphy. In the southeast of Shiraz, Gurpi Formation consists of 95 m thickness which consists mainly of marl, marly limestone and shale, which is gradually overlain by Tarbur Formation.
Materials &

In this study, 42 samples from Gurpi Formation have been studied. Samples were prepared following standard smear slide method (Bown & Young 1998). The nomenclature of calcareous nannofossil follows the taxonomic schemes of Perch-Nielsen (1985), Bown (1998) and Burnett (1998).

In order to study the biostratigraphy of Gurpi Formation in southeast of Shiraz, the Evaz section was selected. In this section, the Gurpi Formation is mainly composed of marl, shale, and argillaceous limestone. Calcareous nannofossils recorded in the Mesozoic strata are an appropriate tool for biostratigraphic studies. The nannofossil zonation used in the present study is based on the Nannofossils Cretaceous zonation of Sissingh (1977), Roth (1978) and Burnett (1998). According to the first and last occurrence of index species the following bio zones are identified:Aspidolithus parcus parcus zone (CC18/ UC14/NC18)
This bio zone is recorded from the FO Aspidolithus parcus to the LO of Marthasterites furcatus. The age of this zone is Early Campanian.
Calculites ovalis Zone (CC19/ UC15/NC18)
This bio zone is recorded from the LO Marthasterites furcatus to the FO of Ceratolithoides aculeus. The age of this zone is late Early Campanian.
Ceratolithoides aculeus Zone (CC20/UC15/ NC19)
This zone spans the interval from the FO of Ceratolithoides aculeus to the FO of Uniplanarius sissinghii. The age of this zone is late Early Campanian.
Quadrum sissinghii Zone (CC21/ UC15/NC19)
The next nannofossil unit recorded in this study is the CC21. This zone spans the interval from the FO of Uniplanarius sissinghii to the FO of Quadrum trifidum. The age of this zone is late Early Campanian-early Late Campanian.
Quadrum trifidum Zone (CC22/UC15/ NC20)
This zone spans the interval from the FO of Quadrum trifidum to the LO of Reinhardtites anthophorus. The age of this zone is late Late Campanian.
Tranolithus phacelosus Zone (CC23/UC15-UC18/ NC20-NC21)
This zone spans the interval from the LO of Reinhardtites anthophorus to the LO of Tranolithus orionatus. The age of this zone is late Late Campanian-Early Maastrichtian.
Reinhardtites levis Zone (CC24/ UC18/NC21)
This zone spans the interval from the LO of Tranolithus phacelosus to the LO of Reinhardtites levis. The age of this zone is late Early Maastrichtian.

As a result of this study, 22 genera and 33 species of calcareous nannofossils have been recognized. Based on distribution of index species of calcareous nannofossils, biozones of the zonation of Sissingh (1977) have been recognized, including Aspidolithu sparcus zone, Calculites ovalis zone, Ceratolithoides aculeus zone, Quadrum sissinghii zone, Quadrum trifidum zone, Tranolithus phacelosus zone and Reinhardtites levis zone, that corresponding to lower part of NC18 to lower part of NC21of the zonation of Roth (1978) and UC14-UC18 Nannofossil Zone of the zonation of Burnett (1998). According to the identified biozones, the age of the Gurpi Formation is Early Campanian to late Early Maastrichtian. The study of the Evaz section shows that sediments of Gurpi Formation deposited in the shalloer depth of sedimentary basin during the late Early Maastrichtian, as conformable and suddenly led to the limestone formation of Tarbur Formation.