Document Type : Original Article
Authors
Assistant Professor, Department of Geology, Payame Noor University, Tehran, Iran
Abstract
This research have sampled and studied the Late Triassic sequences in south of Natanz, (Donbi area). 13 genera and 20 species of Late Triassic of Foraminifers recognized in Nayband Formation (Dunbi area). They included:
Ophthalmidium spp., Ophthalmidium lucidum Trifonova, Palaeolituonella cf. minima He & Wang, Glomospira sp., Angulodiscus gaschei gaschei Koehn-Zaninetti & Brönnimann, Planiinvoluta carinata Leischner, Planiinvoluta sp., Nodosaria nitidana Brand, Nodosaria ordinata Trifonova, Nodosaria spp., Lenticulina acutiangulata Terquem, Lenticulina varians Brönniman, Lenticulina sp., Galeanella tollmanni Kristan, Galeanella? Laticarinata Al-Shaibani, Carter and Zaninetti, Glomospirella minima Michalk, Jendrejakova et Borza, Endothyra sp., Aglutisolena conica Senowbari-Darian,
Turrispirillina? licia variabilis Blau, Involutina planidiscoides Oberhauser.
Also, 5 genera and 6 species of scleractinian corals were identified from the studied patch reefs:
Retiophyllia clathrata Emmrich, Retiophyllia norica Frech, Crassistella juvavica Frech, Stylophyllopsis rudis Emmrich, Pamirophyllum iranicum Melnikova, Pamiroseris rectilamellosa Winkler. Due to the appearance and extinction of these foraminifera and scleractinian corals, the age of Nayband formation in the Dunbi (south of Natanz) is considered Norian- Rhaetian. Porcelaneous foraminifers (Galeanella, Ophthalmidium and Planiinvoluta) and microgranular and agglutinated foraminifers (Glomospira, Glomospirella, Palaeolituonella, Endothyra) can be evidence of the reef environment. Porcelaneous foraminifers have the highest frequency in the studied area, which indicates the reef environment. The presence of Nodosaria and Glomospirella in the studied sedimentary layers indicates on fore-reef environment. According to the field evidence and based on the presence of foraminifera and scleracetina corals, the water depth of the Late Triassic Sea in the region was not very high (more than 150 meters). The abundance of foraminifera in the studied area is very similar to the foraminifera of the southern part of Tethys and the Alps.
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