Late Cretaceous Biostratigraphy Planktonic Foraminifera of the Farokhi Formation , Iran

The Farokhi Formation is one of the informal Central Iran formations, which is located in the NW Tabas township. The Tabas area is a part of the Central Iran sedimentary basin which is located in the Yazd Province. The Farokhi stratigraphic section is located 7 km northwest from Farokhi village (33 ̊54' 9''N and 54 ̊52'48''E). The Bazyab, Debarso, Haftoman and Choopanan formations are well-exposed in the studied area. In this study, the Farokhi Formation is investigated in the Farokhi stratigraphic section with regard to planktonic foraminifera. The Farokhi Formation is mainly composed of thickbedded limestones with ammonoids, thin-bedded limestone with silicified echinoids and ichnofossils, marls with nodular cherts, spherical corals and bivalves. Biostratigraphy of the Farokhi Formation at type section has been concentrated in view of planktonic foraminifera. Thickness of this formation is 251 meters. The lower and upper contacts of studied formation with Haftoman and Choopanan formations are respectively conform and inconsistent. In view of late research, it has been identified that 28 planktonic foraminifera species have a place with 9 genera in edge of 6 biozones, for example: 1) Globotruncanita elevata Partial Range Zone. 2) Globotruncana ventricosa Interval Zone. 3) Globotruncanita stuartiformis Partial Range Zone. 4) Globotruncana aegyptiaca Interval Zone. 5) Gansserina gansseri Interval Zone. 6) Contu-sotruncana contusa Interval Zone. Finally based on this research, Early Campanian-Late Maastrichtian ages for the Farokhi Formation at type locality have been determined.


Introduction
Central Iran continents have been divided into three parts such as Loot, Tabas How to cite this paper: Allameh, M. and Nejad, R.R.Y. (2017) Late Cretaceous Biostratigraphy Planktonic Foraminifera of the and Yazd from east toward the west [1] [2].The Farokhi Formation has been consisted of light grey limestone with chert and some echinoids and bivalves with high frequency.Lower parts of this formation were composed of marl and sandstone with 45 to 120 meters thickness.This formation has out crop in Tabas Province.The studied section was placed at the west of Farokhi village.Farokhi Formation at type section has 65 -180 meters thickness with light gray lime stone and chert with echinoids and bivalves with the high frequency and also based on brachiopoda, bivalves and echinoids, Late Senonian-Danian ages have been detected.[3] [4] studied Echinoids in Farokhi Formation and introduced Echinocorys ex.gr scutata.[5], for the first time studied Dinocyst in the Farrokhi Formation.Also [6] investigated Farokhi Formation at khoor section, based on planktonic foraminifera and proposed Early-Late Maastrichtian.[7] has found Porosphaera globularis (kind of sponge).[8], based on benthic and planktonic foraminifera proposed Early Maastrichtian-Paleocene for the mentioned formation.[9] proposed Late Senonian-Paleocene for the studied formation based on Brachiopoda and Echinoids.

Geological Setting
The Tabas area is a part of the Central Iran sedimentary basin which is located in the Yazd Province.The Farokhi stratigraphic section is located 7 km northwest from Farokhi village (33˚54'9''N and 54˚52'48''E).The Bazyab, Debarso, Haftoman and Choopanan formations are well-exposed in the studied area.In this study, the Farokhi Formation is investigated in the Farrokhi stratigraphic section with regard to echinoids (Figure 1).The Farokhi Formation is mainly composed of thick-bedded limestones with Ammonoids, thin-bedded limestone with silicified echinoids and ichnofossils, marls with nodular cherts, spherical corals and bivalves.

Method
Totally twenty three samples were collected from studied area .Depending on their lithology, the samples were washed in two methods.The shale and marl samples were put in H 2 O 2 10% for a day after being crushed into small pieces.The re-Figure 1. Location of the studied section in NE Iran.sidues were then washed with water on the screeners assigned with 125 and 63 µm meshes [10].
Limestones were grid and boiled in Na 2 So 4 solution then washed with water on the screeners assigned with the above mentioned meshes [11].
First, all of samples were chopped to a crashed sediment and then took in H 2 O 2 (10% molar) for 12 hours and then washed all of these sediments on the various number of sieves, respectively 63 µm and 125 µm (reframe).Finally, for separation of sediment and fossils, all of washed samples stayed in Ultrasonic Cleaner for 15 min and then they were washed again.
Ultimately, all sample residues remaining on mentioned sieves were studied and picked and then taken picture by Scanning Electron Microscope (SEM) in central laboratory of Ferdowsi University of Mashhad.All of SEM pictures in this manuscript were arranged in 4 plates as Appendix (Plates 1-4).

Lithostratigraphy of the Farokhi Formation at Type Section
Lithostratigraphy of the Farokhi Formation is in the study area.The upper and lower boundaries of the Farokhi Formation in the studied stratigraphic section are not observable because of the wide-spreading of formation in the area.From the lithological point of view, the Farokhi Formation in the studied area is mainly composed of the units as followed (Figure 2): Thick-bedded, pinky limestone with fossil debris in some parts (50.50 m); Thin-bedded limestone with great amount of cherty echinoids and ichnofossils

Conclusion
Foraminifera, Latin, meaning hole bearers, (informally called "forams") are mem-  has allowed an impressively detailed picture of species inter-relationships to be developed on the basis of fossils, in many cases subsequently validated independently through molecular genetic studies on extant specimens.

Biozonation of Farokhi Formation
Diverse planktonic Foraminifera possessing wide stratigraphic range occur in abundance in most samples of the Farokhi Formation in the studied area.Nine genera and twenty eight species of planktonic Foraminifera were recognized.
The biozonation is as follows:

Globotruncanita Elevate Partial Range Zone
Definition: Interval from last occurrence of Dicarinella asymetrica to first occurrence of Globotruncana ventricosa.
Age: Early Campanian.Partial range of the nominate taxon from the last appearance of Dicarinella asymetrica to the first appearance of Globotruncana ventricosa defines the zone.This Biozone was defined for the first time by Postuma (1971).The biozone is 11.5 meter thick and consists of grey dark, greyish to green and blue shale.

Globotruncana ventricosa Interval Zone
Definition: Interval from first occurrence of Globotruncana ventricosa to first occurrence of Radotruncana calcarata.
The biozone is 24 meter thick and it consists of grey to green shale, grey to light blue marl, and grey to dark blue marl.This zone was defined by Dalbiez, (1955) as the range of the nominate taxon between its first appearance to the first occurrence of Radotruncana calcarata.
Partial range of the nominate taxon from the last appearance of Globotruncana ventricosa to the first appearance of Globotruncana aegyptiaca defines the zone.This Biozone was defined for the first time by [30].The biozone is 22.5 meter thick and consists of grey dark, greyish to green and blue shale.

Globotruncana aegyptiaca Interval Zone
Definition: Interval from first occurrence of Globotruncana aegyptica to first occurrence of Ganserina gansseri.
The biozone is 15.5 meter thick and it consists of grey to light green shale and grey to light green silty shale.The range of this biozone was introduced by Bronnimann in 1952 from the first occurrence of Globotruncana aegyptica to first occurrence of Gansserina gansseri.This biozone has late Campanian age.
The biozone is 14 meter thick and it consists of grey to light green shale and grey to light green silty shale.The range of this biozone was introduced by Bronnimann in 1952 from the first occurrence of Ganserina gansserito and first occurrence of Contusotruncana contusa.This biozone has late Campanian age.

Contusotruncana contusa
At last in view of late research, Early Campanian-Late Maastrichtian ages for this formation have been recorded.
Based on this research Early Campanian-Maastrichtian ages were detected of mentioned studied section.Finally all of realized biozones in this research have been compared with main Tyetyan biozonation scheme in the world and all of zones which were identified for Farokhi Formation at type section resembles with [17] biozonation.
bers of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm that among other things is used for catching food, and commonly by an external shell or "test" made of various materials and constructed in diverse forms.All but perhaps a very few are aquatic and most are marine, the majority of which live on or within the seafloor sediment (i.e., are benthic) while a smaller variety are floaters in the water column at various depths (i.e., are

Figure 2 .
Figure 2. Stratigraphic column of the Farokhi Formation in the studied area.

Figure 3 .
Figure 3. Distribution and planktonic foraminiferal zonation of the Farokhi Formation at type section.

Figure 4 .
Figure 4. Correlation of the proposed biostratigraphic zonal scheme at this study with other accepted standard biozones of other parts of the world.

Interval Zone (Premoli Silva & Bolli, 1973)
Age: Early-Late Maastrichtian.The biozone is 7.5 meter thick and it consists of grey to light green shale and grey to light green silty shale.The range of this biozone was introduced by Bronnimann in 1952 from the first occurrence of Ganserina gansserito first occurrence of Contusotruncana contusa.This biozone has late Campanian age.Main fossils are recognized in this zone are: