I. MisaghMaghfouri Mirzaei Moghadam et al. / Iranianet al. / Iranian Journal Journal of Earth of Sciences Earth Sciences 6 (2014) 6 (2014)/ 1-11 / 51-62 51

Microbiostratigraphy of the Formation in South and Islamic Azad University Mashhad Branch West of Tafresh, Central

I. Maghfouri Moghadam1*, S. Borji2, E. Amini2, S. Azadbakht3 and M. Taherpour Khalil Abad4

1. Department of Geology, Faculty of Science, Lorestan University, Khorram-Abad, Iran 2. Department of Geology, Branch, Islamic Azad University, Ashtian, Iran 3. Payame Noor University, Khorram-Abad, Iran 4. Young Researchers Club and elites, Mashhad Branch, Islamic Azad University, Mashhad, Iran Received 14 November 2013; accepted 14 April 2014

Abstract

The Qom Formation, a series of shales, sandstones and carbonate deposits, is the last transgression of the sea in Central Iran sedimentary basin. Foraminifera are one of the most important and numerous fossil groups present in the Qom Formation. In this study, the micropaleontology of the Qom Formation in three measured stratigraphic sections in south and west of Tafresh (Rakin, Band-e-Ali Naghi Beig and Hezar Abad) are discussed. Except of the Rakin stratigraphic section, the lower and upper boundaries of the Qom Formation with Lower and Upper Red formations are conformable from the stratigraphy point of view. But, there is no outcrop in the upper boundary of the Rakin stratigraphic section. The study of 78 samples which were taken from the studied sections led to the identification of 34 genera and 39 species of benthonic foraminifera, 2 genera and 2 species of planktonic foraminifera, 4 genera of red algae and 3 genera of bryozoan. Based on the recognized foraminifera such as Lepidocyclina (Nephrolepidina), Miogypsioides sp., Meandropsina anahensis, Ammonia beccarii the age of the Qom Formation in the Rakin stratigraphic section is determined as Chatian-Aquitanian and in the Band-e-Ali Naghi Beig stratigraphic section as well as the Hezar Abad stratigraphic section is determined as Aquitanian.

Keywords: Qom Formation, Iran, Tafresh, Foraminifera, Oligocene, Miocene.

Introduction bryozoan fragments, miliolids, textularids, rotalids and Scutella. The Qom Formation, a series of shales, sandstones ▪ Member b (149-319 m): marls, sandy marls and and carbonate deposits (Oligocene-Miocene), is the last sandstones, partly glauconitic contain Miogypsinoides transgression of the sea in Central Iran zone (Reuter et complanata, Miogypsina sp., Rotalia viennoti, al., 2007). The Qom Formation was introduced by Globorotalia opima opima. Loftus (1855) as Nummulitic series with Oligocene ▪ Member c1 (130-380 m): alternating organodetrital age. After oil was discovered in 1934 [1], this limestones and marls, the latter increasing top ward; formation was in the fouls of scientific research, such this member is rich in microfauna such as: as Gansser [2], Furrer and Suder [3], Abaie et al. [4], Miogypsinoides complanata, Miogypsina sp., Rotalia Bozorgnia [5], Rosenberg [6], Khaksar and Maghfouri- viennoti, Anomalinella rostrata, Discorbis magna Moghadam [7] and Daneshian and Ramezani Dana [8]. aquitanica, Eulepidina elephantine, Operculina cf. Furrer and Suder [3] divided the Qom Formation complanata, Heterostegina antillea, Amphistegina cf. into five members (a-f members) and introduced the lessonii, Nephrolepidina sp., Globigerina mountains in the vicinities of the Qom city as type ouachitaensis ciperoensis, G. praebulloides, G. locality. Later, Abaie et al. [4] divided c member into angustiumbilicata, Globigerinoides triloba immature, four sub-members (c1-c4) (Fig. 1). They introduced G. triloba triloba. This assemblage is replaced in the another evaporate member (e Member). Also, uppermost part of the member by a brackish water Bozorgnia [5] considered in Kashan area, an unnamed fauna with Ammonia beccarii, Elphidium sp., member at the base of the Qom Formation. Ilyocypris bradyi, etc. As it is mentioned above, the Qom Formation is ▪ Member c2 (6-150 m; locally in a partial volcanic divided into 9 members, which from the base to the top facies up to 300 m): red and grey shales, sandstones, are as follows: gypsum, locally with lava and pyroclastic beds; ▪ Member a (basal limestone, 34-80 m): brown, brackish to fresh water ostracods. massive and thick-bedded organodetrital limestone, ▪ Member c3 (30-70 m): bryozoan limestone having a sandy in lowermost part; these deposits contain corals, persistent oolithic bed at the base and contain Lepidocyclina (Eulepidina) sp., Lepidocyclina ------(Nephrolepidina) sp., Amphistegina lessonii, bryozoan *Corresponding author. fragments. E-mail address (es): [email protected] ▪ Member c4 (about 30 m): mostly marls, but in places

52 I. MaghfouriMisagh Mirzaei Moghadam et al. et / al.Iranian / Iranian Journal Journal of Earth of Earth Sciences Sciences 6 (2014) 6 (2014) / 1-11 / 51-62

passing laterally into calcareous shales and reefal were used for washing and micropaleontological limestones contain Globigerinita stainforthi, G. studies. In addition, 37 additional thin sections were unicava, Globigerina ouachitaensis ciperoensis, G. made from isolated larger foraminifera. Systematical praebulloides, Globigerinoides triloba triloba. determinations of foraminifera mainly follow the ▪ Member d (20-40 m): gypsum with some red shale, description of Leoblich-Tappan [10]. Planktonic barren. foraminifera are rare in the studied sections, therefore, ▪ Member e (80-650 m): green marls, partly making the correlation with the standard planktonic gypsiferous, with few intercalation of argillaceous zonation is difficult. Biostratigraphic zonation is limestone contain Globigerina ouachitaensis, G. therefore based on the larger foraminifera which are angyustiumbilicata, G. praebulloides, Globigerinoides abundant. Considerable similarity is observed between triloba triloba, G. triloba n. subsp., G. sacculifera, G. the foraminifera from the Qom and the Asmari bisphaerica, Robulus calcar, R. vertex, Cibicides formations (in Zagros basin, SW Iran). The correlation ungerianus, C. dutemplei, C. floridanus, between the Qom and the Asmari formations has been Globigerinatella insueta. done by various authors such as Daneshian and ▪ Member f (top limestone, 180-320 m): whitish- Ramezani Dana [8]. yellow limestone, interfingering with green marls of Larger foraminifera are the main means for the the e-Member contain Neoalveolina melo curdica, stratigraphic zonation of carbonate sediments. The Peneroplis evolutus, Dendritina rangii, Meandropsina biostratigraphical contents of the Asmari Formation anahensis, Acervulina sp., Archaias sp., bryozoan and were described by Wynd (1965) and reviewed by gastropods. Adams and Bourgeois [11]. Therefore, we apply the Aims biozonation of Adams and Bourgeois [11] which The present paper aims to clarify stratigraphic comprises an Oligocene-Miocene carbonate sequences setting of the Qom Formation in south and west of for the bio-correlation of the Qom Formation. Adams Tafresh based on recorded foraminifera assemblages. and Bourgeois [11] divided the Asmari Formation into three biozones and correlated these zones with Material and methods lithostratigraphic subdivisions of Less [12] (Fig. 2). Recently, results of Sr-isotope measurements clearly In this research three stratigraphic sections (Rakin, show that the zonation of Adams and Bourgeois [11] is Band-e-Ali Naghi Beig and Hezar Abad) in south and fairly robust and the marker species are more west of Tafresh city in were studied stratigraphicaly restrained [13-15]. The age assignment (Fig.4). Each section was measured and logged. From of the Archias asmaricus–Archias hensoni Assemblage the Rakin stratigraphic section 27 samples are taken at subzone previously assigned to Aquitanian by Adams less than 3 meters interval. Also, 26 samples are and Bourgeois [11] is changed into Chattian [16] (Fig. collected from the Band-e-Ali Naghi Beig stratigraphic 3). section at the 3 to 4 meters intervals and 23 samples are collected from the Hezar Abad stratigraphic Rakin stratigraphic section section. The outcrop of the Qom Formation is exposed at Geological setting and Micropaleontological the north-northeast of Farmahin city; 25 km west of studies Tafresh city. The exposures of the Qom Formation at this location is 121.4 m thick and is Light-gray in The basal parts of Cenozoic rocks in Tafresh area colour and from the microfaices point of view, it belong to Eocene age. The Karaj Formation consists of contains benthic foraminifera packstone, bryozoan, turbiditic and pyroclastic rocks exposed around the corallinacea packstone and rudstone. Particles of area and belongs to the Urumieh–Bazman volcanic belt spongia and pelecypoda are also associated (Fig.7). (figs. 5 & 6). Orogenic movement in the Late Eocene- The interval from base of section to 63 m belongs to Early Oligocene results in the creation of lagoon to Assemblage Zone 56 of Wynd (1967) and to continental sedimentary regime characterized by Assemblage Zone no.3 of Adams and Bourgeois [11] detritus sediments of the Lower Red Formation. as well. From the 63 m to 121.4 m interval, the upper Carbonates of the Qom Formation represent marine part of section belongs to Assemblage Zone 59 of transgressions in this area, with calcareous marl Wynd (1967) and Assemblage zone no.2a of Adams sedimentation. During this period andesitic volcanism and Bourgeous [11] also. The lowest occurrence of occurred locally. In the Late Miocene, thick lagoon complex benthic foraminifera is 17 m above the continental deposits of Upper Red Formation were section. The boundary between Chattian and replaced by the marine depositions of the Qom Aquitanian stages is marked by the first occurrence of Formation [9]. Miogypsina sp. and last occurrence of Lepidocyclina The basis of this study was a micropaleontology (Nephrolepidina). The Assebblage Zone 56 contains analysis of 76 thin sections. Four marly shale samples microfauna such as: