Nannostratigraphy of the Pliocene deposits in Kharchang section (Eastern Paratethys of South Caspian Sea)

Document Type : مقالات پژوهشی

Authors

• Adel Barari otaghsara
• Fatemeh Hadavi

Ferdowsi University of Mashhad

10.22067/sed.facies.v10i1.20813

Abstract

Introduction
In this research, Calcareous Nannofossils of the Kharchang section have been studied. The area under study is located in the eastern Paratethys and the section with 260 meters thickness is located 10 kilometers far in south of Sari city and in the north of the Kharchang village. The lithology of the deposits consists of soft, yellow fine grained sandstones, gray, blue and yellow sandstone, and yellow and brown sandy claystone.
 
Material and Methods
In this study, 35 samples from the Kharchang section have been studied. Samples were prepared as smear slide method. In order to study of the thin sections and the prepared slides, Olympus Optical Microscope (BH2) with an object lens with a magnification of 100 was used and the gypsum plate was used for distinguishing certain species. In general, 23 genera and 43 species of the calcareous nannofossils have been recognized in this section.
 
Discussion Nannofossils are suitable for biostratigraphical studies since they are abundant, planktonic, rapidly evolving and largely cosmopolitan. These fossils are found abundantly in the section and they are well preserved, especially Discoasters, which are protected from excess growth and dissolution and have a fairly large variety of species. The coccoliths in this section have relatively high diversity and good preservation. The biostratigraphic studies are done based on Martini (1971) zoning. In this zonation, the NN abbreviation represents Neogene nanoplanktons (Nannoplankton Neogene).
Based on the identified nannofossils, age of the lower part of this section is Early Pliocene (Zanclean) corresponding to NN14 (Martini, 1971).
In the known fossil assemblage, a number of reworked  Mesozoic fossils are seen such as Braarudosphaera bigelowii, Calculites obscurus, Calculites ovalis, Eiffellithus gorkae, Eiffellithus turriseiffelii, Micula concava, Watznaueria barnesae and Watznaueria biporta and some Palaeogene species such as Chiasmolithus bidens, Chiasmolithus nitidus, Coccolithus pelagicus, Cribrocenrum martini, Cruciplacolithus tenuis, Discoaster deflandrei, Discoaster kuepperi, Discoaster kugleri, Ellipsolithus lajollaensis, Ericsonia staerkeri, Fasciculithus tympaniformis, Helicosphaera reticulata, Helicosphaera seminulum, Neochiastozygus concinnus, Neochistozygus imbriei, Prinsius martini, Sphenolithus ciperoensis, Sphenolithus radians and Triquetrorhabdulus carinatus present and species commonly associated with the Neogene are Catinaster coalitus, Helicosphaera ampliaperta, Helicosphaera sellii, Pseudoemiliania lacunosa, Reticulofenestra pseudoumbilica, Sphenolithus belemnos and Sphenolithus heteromorphus.
The age that have been suggested for the studied section are introduced as follows:
DISCOASTER ASYMMETRICUS ZONE (NN14)
Definition: From the first occurrence of Discoaster asymmetricus to the last occurrence of Amaurolithus tricorniculatus
Author: Gartner (1969)
Age range: Early Pliocene (Zanclean)
The mentioned zone is 28 meters thick in the Kharchang section and the biozone was identified in the base of the section.
Considerations: Because the species belonging to the mentioned genera are present in almost all specimens, their attribution to Neogene is ascertained. For example, the species Sphenolithus belemnos, Sphenolithus heteromorphus, Amaurolithus tricorniculatus , Ceratolithus acutus, Discoaster brouweri, Discoaster calcaris, Discoaster druggii, Discoaster exilis, Discoaster kugleri, Discoaster pentaradiatus, Discoaster surculus and Discoaster asymmetricus were observed. It should be noted that due to the presence of the Amaurolithus and Ceratolithus genera in the Late Miocene and the presence of the Amaurolithus tricorniculatus species in the first specimen, which is present at the basis of the studied deposits, it is indicative of the absence of deposits older than Late Miocene, but the Discoaster asymmetricus species appearing in the Lower Pliocene and at the base of the studied thickness indicates the age of Pliocene is the beginning of this sedimentary sequence. Since the species has been present throughout the studied section, the age of these deposits can be attributed to the Early Pliocene, which is compatible with the NN14 zone of the Standard Zoning of Martini (1971). Regarding the fact that the NN15 biozone begins with the last occurrence of Amaurolithus tricorniculatus, and the species is found in the last sample, unfortunately we cannot currently determine the age of the top of these deposits.
 
Conclusion
In this research, Calcareous Nannofossils of the Kharchang section have been studied. The section with 260 meters thickness consists of soft, yellow fine grained sandstones, gray, blue and yellow sandstone, and yellow and brown sandy claystone. Based on the current studies, 23 genera and 43 species have been identified in the 35 studied samples and the age of these deposits is the Early Pliocene, which corresponds with the NN14 zone of the standard zoning of Martini (1971)..
 
Keywords: Paratethys; Caspian Sea; Kharchang; calcareous nannofossils.
 
References
Gartner, S., 1969. Correlation of Neogene planktonic foraminifera and calcareous nannofossil zones. Transactions of the Gulf Coast Association of Geological Societies, 19: 585-599.
Martini, E., 1971. Standard Tertiary and Quaternary calcareous nannoplankton zonation. Proceeding Planktonic Conference, 739-785.

Keywords

• Paratethys
• Caspian Sea
• Kharchang
• Calcareous Nannofossils

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