T Akbari; L Bakhshandeh
Abstract
Based on stratigraphic value of calcareous nannoplanktons in determing the age of sedimentary layers, they have been used for biostratigraphic studies of Surgah Formation in sadd Ilam (Ilam damp) section ,Kabir –Kuh of Ilam. This formation is composed mainly ot dark gray shales. In Type section ...
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Based on stratigraphic value of calcareous nannoplanktons in determing the age of sedimentary layers, they have been used for biostratigraphic studies of Surgah Formation in sadd Ilam (Ilam damp) section ,Kabir –Kuh of Ilam. This formation is composed mainly ot dark gray shales. In Type section , the thickness of the Surgah Formation is 153.7 m. 109 samples were taken from shaly layers and for the first time their calcareous nannofossils were studied.The result of taxonomic studies lead to identification of 16 family , 44 genera and 80 species. Based of first occurrence of the index species and the assemblages zones is nannofossil Zones CC13-CC15 or Uc 8- Uc 12 of standard pattern. Based on biozone,the Upper Cretaceous sediments in the study area are of the Turonian through Early Santonian ages.
L Bakhshandeh; T Mohtat; H Bakhshandeh; S Senmari
Abstract
The Ilam Formation, cropping out in the ZagrosMountain, consists of 195m of cream-colored limestones in the type section, south of Ilam city. This formation has conformable and continuous contacts with the lower Surgah and the upper Gurpi formations. In the present study, 35 foraminifera planktonic species ...
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The Ilam Formation, cropping out in the ZagrosMountain, consists of 195m of cream-colored limestones in the type section, south of Ilam city. This formation has conformable and continuous contacts with the lower Surgah and the upper Gurpi formations. In the present study, 35 foraminifera planktonic species of 17 genus have been identified. The Ilam formation was divided into 4 cosmopolitan biozones on the basis of the planktonic foraminifera which, consist of: Biozone 1-Marginotruncana sigali -Dicarinella primitiva Partial Zone, Biozone 2- Dicarinella concavata Interval Zone, Biozone 3- Dicarinella asymetrica Total -range zone, and Biozone 4- Globotruncanita elevata Partial- range zone. According to these biozones, the Ilam formation was deposited from the late middle Turonian to the early Campanian.
A. Ghaderi; A. Aghanabati; B. Hamdi; J. F. Miller
Abstract
The Shirgesht Formation is one of the fossiliferous units of Central Iran which in the type section is defined (informally) in the terms of 3 members. This formation is mainly composed of limestone, marl, siltstone, shale and dolomite, conformably overlay on the upper part of the Derenjal Formation with ...
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The Shirgesht Formation is one of the fossiliferous units of Central Iran which in the type section is defined (informally) in the terms of 3 members. This formation is mainly composed of limestone, marl, siltstone, shale and dolomite, conformably overlay on the upper part of the Derenjal Formation with a gradual contact, composed of brachiopods limestone bearing (Billingsella limestone). The Shirgesht Formation is overlain by sandy limestone and volcanic rocks of the Niur Formation.
To do biostratigraphy studies on the first and second members of Shirgesht Formation in the type section, totally 99 rock samples were selected. The conodont fauna of lower part of its first member contain some species of Westergaardodina, Furnishina and prooneotodus which show an age of late Cambrian. Several species of Cordylodus, Oistodus, Drepanodus, Proconodontus and Paroistodus in distance of middle part of the lower member to the end of the second member represent an age of Tremadocian – Arenigian. According to conodont content of the first and second members of Shirgesht Formation, 7 conodont assemblage zones were determined in the type section which show an age of Late Cambrian – Early Ordovician. The recognized biozones are as follow:
1. Furnishina - Westergaardodina Assemblage Zone.
2. Proconodontus - Oneotodus Assemblage Zone.
3. Cordylodus proavus - Cordylodus oklahomensis Assemblage Zone.
4. Cordylodus lindstromi Assemblage Zone.
5. Cordylodus angulatus Assemblage Zone.
6. Drepanodus - Paltodus deltifer Assemblage Zone.
7.Paroistodus proteus Assemblage Zone.
The mentioned conodont assemblage zones are equivalent to Cordylodus spp., Deltiferand Proteus global standard conodont biozone. In contrast with the previous reports, the Cambrian – Ordovician boundary is located in the first member of the Shirgesht Formation. Thus, the Shirgesht Formation in type section is diachronous formation.
F. Hadavi; A. Pouresmaeil
Abstract
Nannofossils are suitable for biostratigraphical studied since they are aboundant, planktonic, rapidly evolving and largly cosmopolitan, especially in Late Cretaceous. ...
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Nannofossils are suitable for biostratigraphical studied since they are aboundant, planktonic, rapidly evolving and largly cosmopolitan, especially in Late Cretaceous.
According to this, due to the lack of any precise Paleontological study, the nannofossils of Neyzar Formation has been investigated in type locality. This formation consists of thick- bedded glauconitic sandstone,shale and a sandy limestone bed in the upper part. The Neyzar Formation conformably overlies the Abtalkh Formation and is itself conformably overlained by the Kalat formation. As a result of this study, for the first time, 22 genera and 42 species of nannofossils have been identified. Based on these obtained nannofossils, the section is Late Maasrichtian in age, corresponding to CC25- CC26 (Sissingh,1977) (equivalent to CC25c-CC26a-b, Perch- Nielsen,1985).