چكيده لاتين :
Introduction
The rugose corals described in this paper were collected from the Ozbak-kuh Mountains of East-Central Iran. These mountains are located in the Northern part of the Tabas Block, the main block of the Central Iran Microcontinents. The Tabas Block is considered a failed rift basin, related to the Paleotethys margin, which was separated along with the rest of the Cimmerian plate from Northern Gondwana during the Permian (Bagheri and Stampfli, 2008). Carboniferous succession of Iran is mostly represented by Lower Carboniferous deposits. The Late Carboniferous age only exists in some parts of Central Iran (Leven et al., 2006; Sohrabi, 2005). The main deposits of Late Carboniferous belongs to the Tabas area sequence (St?cklin et al., 1968; Stepanov, 1971; Kehler 1974; Leven, Taheri, 2003; Wendt et al., 2005). Sardar formation predominantly consists of Early - Late Carboniferous sandy-shaly facies; however, from South to the North of Tabas Block the amount of carbonate rocks increases (Khanehbad, 2012).
Flügel (1974,1975,1994) underlined the most unique features of the coral associations from the Sardar Formation in the Central Iran. Since then very few researches were conducted on Pennsylvanian corals (e.g. Badpa et al., 2011, 2009; Gorgij and Boomeri, 2010), since the rocks of this age are not widespread in Iran and just have a few outcrops in central Iran.
The main aim of this paper is to re-describe and illustrate the Bashkirian coral fauna from Zaladu Section in Ozbak-kuh Mountains based on systematic study. This is first report of Late Carboniferous paleobiogeography based on coral fauna in the Iran. The Bashkirian age assignment for our corals was derived from associated foraminiferal faunas first identified by Leven et. al.(2006). This age was confirmed by subsequent conodonta and foraminiferal studies by Sohrabi(2005). These layers consist of fossiliferous limestone beds, belonging to carbonate shelf (homoclinal ramp),(Khanehbad, 2012).
The Ozbak-kuh Mountains are located approximately 140 km north of Tabas city. Zaladu Section is located on the northern side of the Zaladu Valley, at N: and E: geographic coordination.
Material & Methods
For study of corals in the studies section more than 200 thin sections of coral fossils from varied samples were prepared with 20 rock samples were collected from the area for more detailed studies. Before the preparation of thin sections, samples had been put in cold water for one week, and after numbering and providing description for samples. General features of every sample were noted such as: external morphology like general body plan, length, maximum diameter, existence of transverse and longitudinal bands, coral wall preservation, rejuvenation, columella and basal plate. Then, from coral fossils longitudinal, transverse and serial thin sections were provided. these thin sections, used 4 standard size lams have been selected based on coral sizes on 70 ×90, 45 ×60, 30 ×45, 25 ×70 that under binocular microscope. PP light should be used. During the study of thin sections some points should be noticed such as: coral diameter, tabularium diameter, dissepimentarium thickness and dissepiment rows, their size and slope, and also dissepiment types, presence or absence of central structure, its type, shap and thickness of septa, existence of small septa , total septa and also their types(Alar septa, cardinal septa, and …), existence of carinae, granul, fossula and their types, biform tabularium, tabulae rows in each cm, type of wall, its thickness and surface ornamentsm central structure diameter, decelopment of middle lamellae and septotheca.
Discussions of result & conclusions
The coral assemblage of Bashkirian from the Sardar formation in Zaladu section the Ozbak kuh Mountains were described. These fauna exist in 2 units. The first corals member is composed of just fasciculate rugose coral(Fomichevella uralica(Dobroliobova, 1936). The second corals member consist of Fomichevella uralica (Dobroliobova, 1936), Fomichevella holtedahli (Heritsch, 1939), Fomichevella orientalis (Stuckenberg, 1885), Heintzella sp. 1., Heintzella sp. 2., Paraheritschioides antoni minor (Flügel, 1994), Klepatrina (Porfirivella) bashkirica (Flügel, 1994), Minatoa bulla (Flügel, 1974), Minatoa alternata (Flügel, 1974), Minatoa infirma (Flügel, 1974), Michelinia escobari (Wilson, 1990), Multithecopora hypatiae (Wilson, 1963).
In this study, one genus [Heintzella (Fedorowski, 1967)] , and 4 specimens[Multithecopora hypatiae (Wilson, 1963), Michelinia escobari(Wilson, 1990), Fomichevella orientals (Stuckenberg, 1885), Fomichevella holtedahli (Heritsch, 1939), Multithecopora hypatiae (Wilson, 1963), Michelinia escobari(Wilson, 1990), Fomichevella orientals (Stuckenberg, 1885), Fomichevella holtedahli (Heritsch, 1939) are introduced for the first time in Iran.
First Coral member based on Eostaffellina paraprotvae- Endothyra bashkirica foraminiferal zone and Idiognathodus sinuatus- I. primulus / I. corrugates- I. sulcatus conodont zone(Sohrabi, 2005) is Early Bashkirian (Namurian B,C; Late Chokerian – Alpotian). Also second corals member Based on Pseudostaffella compressa- Pseudostaffella antique- Eostaffella amabilis foraminiferal zone and Idiognathodus sulcatus parva conodont zone(Sohrabi, 2005) is Middle Bashkirian (Kinderscoutian-Yeadonian to to Late(?) Bashkirian; Early Westphalian A= Longsettian). Thus this fauna are assemblage zone of Early-Middle Bashkirian (Late Chokerian – Kinderscoutian-Yeadonian (?).
specimens of Fomichevella uralica, Paraheritschioides antoni minor, Klepatrina (Porfirivella) bashkirica, Minatoa Spp. Just described from (Early-Middle?) Bashkirian.
In this unit, based on abundance these fauna is common: Fomichevella, Heintzalla, Minatoa, Multithecopora, Paraheritschioides, Kleopatriana, Michelinia. Also, based on the high diversity, these corals are common: Fomichevella(3 species), Minatoa(3 species), Heintzalla(2 species), Multithecopora, Paraheritschioides, Kleopatriana, Michelinia(1 species). As a result, in this community Fomichevella(Fedorowski, 1975) has highest abundant and diversity, too Michelinia(de konink, 1841), has least abundant and diversity. all of these fauna consist of colony corals that has fasciculate and cerioid shapes. Rugose corals belongs to Kleopatrinidae and Durhaminidae families. In this community Kleopatrinidae family by 4 genus and 7 species has highest abundant and diversity. Durhaminidae family has 1 genus and 3 species. There are 1 species of families of Michelinidaea and Multithecoporidaea.
This fauna Indicative of Early-Middle Bashkirian assemblage zone in the Sardar Formation.
Fedorowski et al.(2012), described of the oldest known Carboniferous rugose coral fauna in the Canadian Arctic Islands, he belived that upper? Bashkirian specimen of Paraheritschioides, is the oldest known representative of that genus. Based on Fedorowski et al.(2012), all other Carboniferous species included by Fedorowski et al. (2007) in that genus are Moscovian or younger. But we have many sample of Paraheritschioides that actually belonging to Late Serpukhovian to Middle Bashkirian. This age assignment for our corals was derived from associated foraminiferal faunas first identified by Leven et. al.(2006). This age was confirmed by subsequent conodonta and foraminiferal studies by Sohrabi(2005). Iranian Paraheritschioides are oldest known representative of that genus.
Bashkirian specimens from the Ozbak-Kuh Mountains, described by Gorgij & Boomeri(2010), don’t include Fomichevella because they has weakly developed and strongly interrupted axial structure at maturity in longitudinal section and that is feature of Heintzella. thus Fomichevella specimens of Gorgij & Boomeri(2010), (Plate III, fig A-D) exclude from Fomichevella.
Specimens of Actinocyathus floriformis Gorgij et al. (2001), from Visean of Sardar Fm. in the Ozbak-Kuh shows features of the family durhaminidae and exclude from Actinocyathus, Gorgij et al. (2001), samples have Dibunophyllum-type, axial structure which is not bounded by tabulae walls. lonsdaleid dissepiments and cerioid growth of corallites are the main features in this genera. We believe that these specimens belonging to Bashkirian genus of Minatoa that is abundant in this area.
Based on Paleobiogeographical study, some of the genera are widespread (Fomichevella, Heintzella, Multithecopora, Michelinia), one genera is endemic during the Bashkirian of Iran (Minatoa), and some genera have irregular and limited distribution(Paraheritschioides, Klepatrina (Porfirivella)). These fauna exist in the southern subprovince of )Mediterranean province( Tethys sea in the Bashkirian.
Keywords: Carboniferous, Bashkirian, Coral, Ozbak-kuh, Sardar Formation, Paleobiogeography
