Journal of Sciences, Islamic Republic of Iran 31(2): 155 - 164 (2020) http://jsciences.ut.ac.ir University of Tehran, ISSN 1016-1104

155

Early Silurian (Llandovery) Trilobite fauna from

Kopeh-Dagh, North East Iran

H. Ameri*

Department of Ecology, Institute of Science, High Technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Islamic Republic of Iran

Received: 17 February 2018 / Revised: 29 September2019 / Accepted: 13 November 2019

Abstract

The aim of this study is to analyze the assemblage of trilobites in the Silurian sequences of Iran by exploring stratigraphic section of the Silurian Niur Formation (Asadli section). Based on comprehensive field studies and laboratory investigations three Trilobite genera were identified in the study area including Calymene blumenbachii, Gravicalymene convolva, Dalmanites brevigladiolus and Calymene sp. according to this trilobite assemblage a Rhuddanian to Telychian stages (Llandovery) is suggested for deposition of the study strata. The recognized trilobite fauna will be used as a base for future geological studies on the Silurian strata in Kopeh-Dagh Basin. This is the first report of trilobites from the Silurian (Llandovery) Niur Formation in Asadli section, north- east, Iran. Keywords: Trilobite; Calymene; Biostratigraphy; Silurian; Iran.

* Corresponding author: Tel: +09131984699; Fax: +983436226617; Email: ameri.hamed@gmail.com

Introduction Calymenina were among the most dominant trilobite

groups in the Lower Paleozoic. They range from the Tremadoc into the Devonian and have world-wide occurrence. They are well-represented in Tremadoc rocks but often constitute a significant part of many Ordovician and Silurian faunas. During Llandovery times, Calymenidae underwent a dramatic increase in diversity, particularly in the shallow-water oceans covering parts of Gondwana, such as, Turkey, Poland, Kazakhstan, Japan, Italy, Sweden and Iran. The Silurian trilobites have species have been discovered in rare sites in Iran. Alas, Iranian Llandovery trilobite taxa are generally invisible in universal measurement of Silurian biostratigraphy. This article concentrated on the

Llandovery trilobite taxa of Kopeh Dagh (Asadli section).

Although Silurian strata were previously reported well from several regions of Iran, such as Kerman [1], Dajman [2], Isfahan [3], Tabas [4-6], the stratigraphy and fauna of Kopeh Dagh region remains inadequately recognized. Silurian strata were first reported from the Kopeh Dagh region by [7], done the first assessment on the Paleozoic stratigraphy of Iran. They were correlated the Silurian rocks of South East of Asia and the near East. Brice [8] briefly outlined the Silurian and Devonian stratigraphy of the area. Cocks [9] studied and described 23 taxa of brachiopods at the western Kopeh Dagh region. The Lower Paleozoic strata from Kopeh Dagh region were studied by: [10-16] and more recent surveys by Ameri et al. indicate that the Robat-e-

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Gharebil sectof this articldescription odescribe the t

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tion is also rice are to 1) pr

of the Asadli strilobites.

Figure 1.

20

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Early Silurian (Llandovery) Trilobite fauna from …

157

about 20 km. They are bounded by the Firuzeh fault at the north and the Solook fault system and Shiroyeh fault at the south. Asadli section is placed in the southwest of the Sarinow Mountain. In this area the Cambrian to Jurassic deposits cropped out. In the study area (Fig. 1), the Cambrian strata have subdivided into the Barout Formation, partly Zaigon and Lalun Formations. The Cambrian - Ordovician boundary is faulted. The Ordovician strata contained; dark sandstone, olive green shale, minor sandy limestone and volcanic (andesite to basalt), Qelli Formation (Sandbian- Hirnantian). Silurian sequence in this area comprising of more than 300 m of argillites, limestone and siltstones,

Various Ages are proposed for deposition of the Silurian Niur Formation in different areas by many authors on the basis of different fossil groups. They are: Aeronian- Sheinwoodian by conodont; in the Masuleh (western Alborz) [17], Rhuddanian to Homerian, by brachiopods and corals, [9], and as Rhuddanian to Aeronian by conodont , in Rebate Gharebil (western Kopeh Dagh region[18], Aeronian by brachiopods [14] , and as Rhuddanian to Telychian, by Acritarchs and chitinozoa in Kuh-e-Saluk [19] and as Aeronian, by brachiopods and cephalopod ,in Gerdu Valley section , [16]. The lower contact of the Niur Formation is conformable and transitional with the underlying Qelli Formation and in this section is disconformably overlain with Devonian red and white sandstone and shale of Padeha Formation.

The Asadli section

The Asadli section is located about 35 km south of Bojnord city, at 2 km south east of the Asadli village, at geographic coordinates of 37°19’38” N, 57°20’04” E (Fig. 1). More than 300 m of Silurian deposits measured that can be subdivided into four lithofacies (Fig. 2):

Member 1: comprising of more than 95 m of gray to black sandy argillite with several interbeded of graptolitic argillite and oolitic ironstone levels in the middle part.

Member 2: consisting of 35 m of bedded limestones and argillites. They contain cephalopod, trilobite and brachiopods.

Member 3: consisting of 25 m of bedded limestones intercalating with siltstone, and argillites, with no identified fossils.

Member 4: comprising of about 150 m of bedded limestones and argillites, with a level of 30 m thick, bioclastic limestone in its upper part. This member contains cephalopod, trilobite and scattered brachiopods. The Silurian deposits are overlain unconformeably by Padeha Formation (lower Devonian).

Materials and Methods The Silurian strata were studied and their trilobites

taxa, collected systematically in the Asadli section. Only the in situ fossils were collected from the study area. The taxa collected from this area are about 45 trilobite taxa. The collected trilobites are deposited in the Graduate University of Advanced Technology, [PEG].

The evoked of taxa were from marl limestone and limestone using a pneumatic pen. The trilobite samples were masked by ammonium chloride and using loop-lamp to raise the contrast. In most specimen, extra highlight from the North West quadrant was used. for The take photo of trilobites taxa were using a digital camera (Nikon D90) with a 105mm objective lens.

Results and Discussion Systematic Paleontology

Appraisement, terminology, and abbreviations are derived from [20-24] based on Ameri [24], (Fig. 3).

Family; Calymenidae Milne Edwards 1840 Subfamily; Calymeninae Milne Edwards 1840 Genus; Calymene Brongniart, 1822 Pl.1, [a-c and h], Pl.2, [a-c], Pl.3, [a, g] Type species; Calymene blumenbachii Brongniart,

1822 1950. Calymene boettneri n. sp. Harrington, p. 73-76,

pl. 1, Figs. 1-3. Material. One complete specimens, six cranidial,

and four pygidium Description: Glabella outstanding high over genal

and skeleton fine in foreside of them, frontal lobe slanting steeply onward, with 3 placenta of sidelong lobes, 1L and 2L derived by superficial linear furrows, all a partly outstanding. 2L lobes papillate; eye lobes opposite 2L glabellar lobes; Preglabellar groove narrow, profound; frontal edge equally outstanding, center of frontal lobe of central body. Thorax with 13sectors, pygidium with six perfect axial rings and six profound, pleural grooves, which develop to edge of borderless pleural zones, Pygidium is slightly minor than double as Width as length. Axis is somewhat, less than moiety the pygidial width, is strongly outstanding (sag.) has seven or 8 axial rings. All axial rings except the final determined posteriorly by full ring grooves which are weakest; last ring groove not continues; final axial segment rounded. Axial groove decidedly impressed, weakest posteriorly. Inner segment of pleural zone falls steeply from axial groove, outer part becomes vertically

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oblique. Thgrooves whicalmost reach

Figure 2. Bitrilobite taxa

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I sincere de Montpelliand advice, manuscript. (University o(Graduate Kerman) forgratefully acfor this proj

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owledgmentsDr. Raimund or the providevery helpful i grateful to

and Dr. Ebrahof Advancee reviews, ahe research f118) by Insti

e 5 (a), Dalmvolva, ( R489, 4

y Silurian (Lla

over, effaced joined to ax

s Feist (Univerd much guidain improving

Fatane Zamhim Mohammed Technoloand fieldworkfunding proviitute of Scien

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obite fauna fro

gh Technolraduate Univeran.

Hamedi M., WD., ChattertonRoss J. Cambbiostratigraphthe text). NeMonatshefte.1Alavi-Naïni M(na) (1972). Zahedi M. Étl'Iran Central)

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om …

ogy and Ersity of Advan

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égion de Djam.

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n d w n -

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