GEOLOGICA BALCANICA, 41. 1–3, Sofia, Dec. 2012, p. 21–37. Integrated biostratigraphy of the Upper Cretaceous Abderaz Formation of the East Kopet Dagh Basin (NE Iran) Meysam Shafiee Ardestani1, Mohammad Vahidinia1, Abbas Sadeghi2, José Antonio Arz3, Docho Dochev4 1 Faculty of Science, Department of Geology, Ferdowsi University of Mashhad, Mashhad, Iran; e-mail: [email protected] 2 Department of Geology, Faculty of Science, University of Shahid Beheshti, Tehran, Iran 3 Departamento de Ciencias de la Tierra (Paleontología) e Instituto de Investigación en Ciencias Ambientales (IUCA), Universidad de Zaragoza, C/ Pedro Cerbuna 12, E-50009 Zaragoza, Spain 4 Department of Geology, Paleontology and Fossil Fuels, Faculty of Geology and Geography, Sofia University “St. Kliment Ohridski”, Sofia, Bulgaria (Accepted in revised form: November2012) Abstract. Based on planktonic foraminifera, inoceramids and echinoids, we present a detailed biostratigraphic analysis of the Abderaz Formation at the 606 m thick Padeha section, NE Iran. This sequence consists mainly of gray shales and marls with four levels of chalky limestones intercalated. The lower boundary of the Abderaz Formation with the Aitamir Formation is a paraconformity, while the upper boundary with the Abtalkh Formation represents a gradual transition. Fifty four species of planktonic foraminifera from 15 genera were identified, and five zones were recognized, namely: Whiteinella archaeocretacea (Bolli) Partial-Range- Zone; Helvetoglobotruncana helvetica (Sigal) Total-Range-Zone; Marginotruncana schneegansi (Dalbiez) Interval-Range-Zone; Dicarinella concavata (Brotzen) Interval-Range-Zone; and Dicarinella asymetrica (Sigal) Total-Range-Zone. Based on these data, the age of the Abderaz Formation is determined as earli- est Turonian to earliest Campanian. Inoceramid bivalves Cremnoceramus walterdorfensis walterdorfensis (Andert) and Cremnoceramus deformis deformis (Meek) were identified in the uppermost Turonian and in the middle part of the early Coniacian, respectively. Echinocorys ex. gr. scutata and Cordiceramus sp. were recorded near the Coniacian/Santonian boundary. Shafiee Ardestani, M., Vahidinia, M., Sadeghi, A., Arz, J.A., Dochev, D. 2012. Integrated biostratigraphy of the Upper Cretaceous Abderaz Formation of the East Kopet Dagh Basin (NE Iran). Geologica Balcanica 40(1–3), 21–37. Key words: Upper Cretaceous, Abderaz Formation, Biostratigraphy, Planktonic foraminiferal zonation, Inoceramids, NE Iran. INTRODUCTION region; all formations are conformable, except for a few disconformities within the Cretaceous succession. These The Kopet Dagh sedimentary basin was formed after the can be related to epeirogenic movements in the basin. All Middle Triassic orogeny in northeast Iran (Afshar-Harb, formations thin out from north-west to south-east. They 1969). The basin was framed due to the faulting activ- were folded during the Late Alpine Orogeny and formed ity with approximately NW–SE trend. Four of these ma- the structural traps of the Khangiran and Gonbadli gas jor active basement faults have been recognized in the fields (Raisossadat and Moussavi-Harami, 2000). The central and western part of the basin. Sedimentation was Cretaceous sediments in the Kopet Dagh Basin are di- more or less continuous throughout the Middle Jurassic vided into nine different formations, composed mainly to Oligocene interval in the eastern part of the basin, of sandstones, conglomerates, mudstones, limestones where five major transgressive-regressive sequences and dolostones with subordinate evaporites. The thick- have been identified. Moussavi-Harami and Brenner ness of these sediments is normally more than 4000 m, (1992) concluded that subsidence in the eastern part of showing a prominent decrease to 2500 m in the eastern the basin was predominantly a result of sediment load- part of the basin (Shafiee Ardestani et al., 2011). The ing. There is no evidence of major tectonic activity in this Abderaz Formation is the major lithostratigraphic unit of 21 Late Cretaceous age in the Kopet Dagh Basin. It includes 6) Thick bedded white chalky limestones, 20 m thick. highly diverse and abundant micro- and macrofossils. 5) Thin bedded light gray shales, 44 m thick. Planktonic foraminiferal biostratigraphic analyses, 4) White chalky limestones, 7 m thick. together with the identification of invertebrate (mainly 3) Thin bedded light gray shales, 79 m thick. inoceramid) bio-events were conducted in order to pre- 2) White chalky limestones, 20 m thick. cise the age of the Abderaz Formation. It is based on 1) Thin bedded yellowish to gray marls, 40 m thick. the study of the Padeha section (Mashhad Province, NE The lower boundary of the Abderaz Formation with Iran), since this section was found to be well exposed and the Aitamir Formation is a paraconformity. Upwards, the containing enough micro- and macrofossils of high bios- Abderaz Formation passes gradually into the Abtalkh tratigraphic value to give a reliable age determination. Formation. The rocks contain common inoceramids, fre- quent echinoids, and some ammonites. Abundant plank- tonic foraminifers occur, especially in the chalky lime- LITHOSTRATIGRAPHY stones. The total thickness of the section is 606 m. The Padeha section is located southeast of Mashhad. It crops out along the Mashhad-Sarakhs road, 25 kilo- METHODOLOGY meters east of type locality of the Abderaz Formation, and 2 kilometers from the Padeha rural road, near the The sampling density at the Padeha section was 3 me- Rakhshani region. The geographical position of the sec- ters, thus a total of 200 samples was collected. Samples tion is 60°44'39.6" E and 36°06'23.7" N (Fig. 1). were soaked in water with diluted hydrogen peroxide, The Abderaz Formation at Padeha section consists of and washed through 63 μm, 150 μm and 250 μm sieves. 11 lithological packets from top to bottom, namely (Fig. 2): About 200–300 foraminiferal specimenss were picked up 11) Thin bedded light gray shales, 28 m thick. from each sample in two size fractions (63–150 μm and 10) White chalk limestones, 18 m thick. >150 μm), determined, and mounted on microslides for 9) Thin bedded light gray marls, 300 m thick. permanent record and future revisions. 8) Thin bedded gray marls, 10 m thick. The most representative and the best preserved fora- 7) Thin bedded light gray shales, 40 m thick. miniferal specimens were selected for scanning electron Fig. 1. Geological and geographical sketch-maps of the area of Padeha section (NE Iran) 22 microscopy (SEM), using a JEOL JSM 6400 SEM at of Ferdowsi University of Mashhad. Taxonomy is based the Microscopy Service of the Universidad de Zaragoza on Bolli (1957), Postuma (1971), Robaszynski and (Spain). They are illustrated in Figures 3–6. We also Caron (1979, 1995), Caron (1985), Loeblich and Tappan studied planktonic foraminiferal collection from the (1988), Nederbragt (1990), Ellis and Messina (1999), Abderaz Formation deposited at the National Museum and Premoli Silva and Verga (2004). FORAMINIFERAL BIOSTRATIGRAPHY The planktonic foraminiferal zonation here used is com- pared with other Tethyan biozonations (Fig. 7) (Barr, 1972; Premoli-Silva and Bolli, 1973; Vaptzarova, 1976; Sigal, 1977; Wonders 1980; Salaj, 1980, 1997; Robaszynski et al. 1984; Caron, 1985; Sliter, 1989; Abdel-Kireem et al., 1995; Robaszynski and Caron 1995; Premoli-Silva and Verga, 2004; Dimitrova and Valchev, 2007; Takashima et al., 2010). This zonation is similar to that of Robaszynski and Caron (1995). In this study, 54 species belonging to 15 genera of planktonic foraminifera, and 11 invertebrate species (8 inoceramids, 2 echinoids and 1 ammonite), were recognized in the Abderaz Formation (Fig. 8). The Padeha section has been correlated with other sec- tions of the Abderaz Formation from West and East Kopet-Dagh Basin, which were previously studied by Shafiee Ardestani et al. (2012) (Fig. 9). These are the Hajgelichkhan section (Lowermost Turonian- Lowermost Santonian), Qarehso section (Lowermost Turonian-Late Santonian), Abderaz section (Early Turonian-Lowermost Cam panian), Muz­­duran type section (Middle Turonian-Lowermost Campanian), and Shorab section (Lowermost Turonian-Lowermost Campanian) (Fig 9). Di. asymetrica Zone is of greater thickness than the others (Fig. 9). Rates of sedimenta- tion in all studied sections are different. Planktonic foraminiferal biostratigraphy indicates early Turonian to earliest Campanian age of the Abderaz Formation. Five successive zones are described below. Whiteinella archaeocretacea Partial-Range-Zone Bolli, 1966 Definition. Interval with Whiteinella archaeocretacea between the last occurrence data (LOD) of Rotalipora cushmani and the first occurrence data (FOD) of Helvetoglobotruncana helvetica. Planktonic foraminifera assemblage: Dicarinella cana liculata (Reuss, 1854), Di. hagni (Scheibnerova, 1962), Heterohelix globulosa (Ehrenberg, 1840), H. more mani (Cushman, 1938), H. reussi (Cushman, 1938), Macroglobigerinelloides bollii (Pessagno, 1967), M. ca seyi (Bolli, Loeblich and Tappan, 1957), M. ultra- micra (Subbotina, 1949), Muricohedbergella delrioensis (Carsey, 1926), M. simplex (Morrow, 1934), Whiteinella aprica (Loeblich and Tappan, 1961), W. baltica Douglas and Rankin, 1969, W. brittonensis (Loeblich and Tappan, 1961), W. paradubia (Sigal, 1952), and W. praehelvetica (Trujillo, 1960). Remarks. The base of this zone coincides with the bound- ary between the Aitamir and the Abderaz Formation, Fig. 2. Lithological column of the Abderaz Formation at Padeha