Biostratigraphic Studies of the Lower Cretaceous (Upper Barremian ...

ISSN 08695938, Stratigraphy and Geological Correlation, 2011, Vol. 19, No. 2, pp. 188–204. © Pleiades Publishing, Ltd., 2011.

Biostratigraphic Studies of the Lower Cretaceous (Upper Barremian—Lower Aptian) Sarcheshmeh and Sanganeh Formations in the Kopet Dagh Basin, NE Iran: an Integration of Calcareous Nannofossil and Ammonite Stratigraphies1 S. N. Raisossadata and M. H. Shokrib a

Geology Department, Faculty of Sciences, Birjand University, Birjand, Iran b Exploration Directorate, National Iranian Oil Company, Tehran, Iran email: [email protected] email: [email protected] email: [email protected] Received June 18, 2009; in final form, February 18, 2010

Abstract—Lower Cretaceous sediments of the northwestern part of the Kopet Dagh sedimentary basin have been sampled with the purpose to study stratigraphic distribution of calcareous nannofossils. A total of 87 samples from the 1900mthick marly limestones, shales and siltstones of the Sarcheshmeh and Sanganeh Formations (late Barremian–early Aptian) displayed diverse nannofossil assemblages. Representative species of the following genera were recorded from the Sarcheshmeh Fm.: Braarudosphaera, Calcicalathina, Calcio solenia, Chiastozygus, Conusphaera, Cretarhabdus, Cyclagelosphaera, Eprolithus, Haqius, Hayesites, Lithraphidites, Manivitella, Micrantholithus, Nannoconus, Radiolithus, Retecapsa, Rhagodiscus, Rucinolithus, Watznaueria, and Zeugrhabdotus. In the Sanganeh Formation, Biscutum, Broinsonia, Cribrosphaerella, Cru cicribrum, Cyclagellosphaera, Diazomatolithus, Discorhabdus, Eiffellithus, Lithraphidites, Nannoconus, Pre discosphaera, Rhagodiscus, Tranolithus, and Watznaueria were found. The identified nannofossil assemblages enabled the recognition of NC5–NC7A zones in the studied part of the section. Paleoecologically, these nan nofossil assemblages are typical for the Lower Cretaceous of the Tethyan realm and indicate warm surface water conditions. Keywords: Lower Cretaceous, Barremian, Aptian, nannofossils, ammonites, Kopet Dagh, Iran. DOI: 10.1134/S0869593811020109 1

INTRODUCTION

The Kopet Dagh (Koppeh Dagh) sedimentary basin is situated in the northeastern Iran and southern Turkmenistan. The Iranian part of the Kopet Dagh Basin is geographically located between 54°00′ to 61°14′E and 36°00′ to 38°16′N (Fig. 1). The Kopet Dagh Basin was formed as an intracon tinental basin in the northeastern Iran after the closure of Hercynian Ocean that followed Early Kimmerian orogeny (Berberian and King, 1981). From the Juras sic through Eocene, relatively continuous sedimentary succession forms five major transgressive–regressive sequences in the eastern Kopet Dagh (AfsharHarb, 1979, 1983). A faultcontrolled subsidence of the Kopet Dagh Basin started in the late midJurassic (AfsharHarb, 1979; SeyedEmami and AlaviNaini, 1990; SeyedEmami et al., 1994, 1996) and termi nated in the Oligocene causing the deposition of up to 1 The article is published in the original.

10kmthick sedimentary succession (Berberian and King, 1981) (Fig. 2). The Cretaceous deposits are divided into nine for mations in the Kopet Dagh Mts. (Fig. 3). A single megasequence in the Kopet Dagh Basin embraces the whole Lower Cretaceous succession which is made up of conglomerates and sandstones of the Shurijeh Fm. in the lower part and of dark grey shales and siltstones of the Sanganeh Fm. in the upper part (Fig. 3). Detailed geological studies were conducted by geologists of the National Iranian Oil Company (NIOC) during the 1960s and 1970s. The most impor tant publications were made by AfsharHarb (1969, 1979) on general geology and petroleum geology, Kal antari (1969) on the Jurassic and Cretaceous foramin ifers, and by Hubber (1976) and AfsharHarb (1982, 1983) as to geological mapping. Despite recent lithostratigraphic, biostratigraphic and paleontological studies of the Sarcheshmeh and Sanganeh Fms. in the Kopet Dagh Basin (Dehghan, 2002; Hadavi and Shokri, 2001, 2006; Hadavi and

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BIOSTRATIGRAPHIC STUDIES OF THE LOWER CRETACEOUS 53°

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Fig. 1. Geographical names and their position. Location of the measured sections and gas reservoirs are shown by circles and ovals, respectively.

Badaghi, 2006; Immel et al., 1997; Raisossadat, 1999, 2000, 2001, 2002, 2003a, 2003b, 2004, 2006; Raisos sadat and MoussaviHarami, 1993, 2000; Raisossadat et al., 1998; Shokri, 2001), the research in many fields needs to be continued. For instance, foraminifers and ammonites have been studied in more detail, whereas other fossil groups like calcareous nannofossils have not been considered up to now. In this paper, calcare ous nannofossils from the Lower Cretaceous Sanga neh Fm. are reported for the first time and the nanno fossil biostratigraphy and paleoecology of the Sarcheshmeh and Sanganeh Fms. are discussed. MATERIALS AND METHODS Two stratigraphic sections have been studied and sampled during the fieldwork in summer 1998 and 1999. Smearslides were prepared from 100 samples using gravity settling methods (Bown and Young, 1998). Lightmicroscope images were carried out from smearslides using OLYMPUS DP10 digital camera. Scanning electronic microscopy (SEM) images were made on a LEO Gemini 1530 at the Ruhr University, Bochum. The smearslides are stored in Geology Department of Birjand University, Iran. Bibliographic references for identified taxa are given in Perch Nielsen (1985) and Bown et al. (1998). STRATIGRAPHY AND GEOLOGICAL CORRELATION

STRATIGRAPHY Sarcheshmeh Formation Sarcheshmeh village is situated in the central Kopet Dagh, 14 km east of the Bojnord town. Afshar Harb (1979) proposed to consider a succession exposed in the Khur valley along the MashhadKalat road as a type section of the Sarcheshmeh Fm. It is one of the most complete and best outcropped successions of the area (Fig. 1). Normally, the Sarcheshmeh Fm. consists of two informal members: the lower marly and the upper shaly member. In the type section, the lower member is represented by a 178mthick uniform light green ishgrey to bluishgrey marl with pencil weathering. A 20cmthick bed rich in oyster coquina occurs at the top of this member. The upper member includes a 98mthick dark bluishgrey calcareous shale weathered to light greyishgreen color in the lower part, overlain by the 34mthick sequence of alternating bluishgrey shale and thinly bedded limestones (AfsharHarb, 1979; Raisossadat and MoussaviHarami, 1993) (Figs. 4 and 5). The sediments are moderately weathered and form a distinct grey rock succession disposed between the underlying ridgeforming brownweathered Tir Vol. 19

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RAISOSSADAT, SHOKRI Azerbaijan

Turkmenistan Kopet Dagh

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Fig. 2. Iranian major tectonosedimentary units (redrawn from Berberian and King, 1981): (1) Stable area, Arabian Precambrian platform in southwest and Turanian Hercynian Plate in northeast; (2) Zagros, including Zagros foredeep, main sector of the mar ginal active fold belt peripheral to stable area and High Zagros; (3) Alborz Mountains; (4) Central Iran lying between the two mar ginal active fold belts; (5) Talesh, Armenian Late Hercynian belt with a possible continuation to Iranian Talesh Mountain; (6) ZabolBaluch and Makran postophiolite flysch trough; (7) Kopet Dagh folded belt and foredeep. STRATIGRAPHY AND GEOLOGICAL CORRELATION

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Fig. 3. General stratigraphic column of the Cretaceous of the eastern Kopet Dagh Basin (modified from Kalantari, 1987 and Immel et al., 1997).

STRATIGRAPHY AND GEOLOGICAL CORRELATION

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gan Fm. and the overlying dark grey to black Sanganeh Fm. Kalantari (1969) and Raisossadat and Moussavi Harami (1993) suggested the Aptian age for the Sarcheshmeh Fm. on the basis of foraminifer study. The ammonite fauna found in this formation indicates the late Barremian–early Aptian age (Immel et al., 1997; Raisossadat, 2002, 2003a, 2004). It should be emphasized that the formation shows younger age eastward. Sanganeh Formation Fig. 4. Weathered pencil marl of the lower part of the Sarcheshmeh Formation, Sanganeh section, near the Kalat Road section.

Top Sarcheshmeh Fm.

Sanganeh Fm.

Fig. 5. The Sarcheshmeh–Sanganeh formations’ bound ary near the Kalat Road section, dark to black shales of the Sanganeh Formation overlying light grey shales and fossil iferous limestones of the Sarcheshmeh Formation, looking north.

The name is derived from the village of Sanganeh, 70 km northeastward from the town of Mashhad (Fig. 1). The Sanganeh Fm. consists of dark grey to black weathered shales, includes few thin siltstone beds in some areas, and contains abundant septarian nodules and coneincone structures (Raisossadat and MoussaviHarami, 1993; AfsharHarb, 1994). It dif fers from the underlying Sarcheshmeh limestone bed and the overlying ridgeforming Aitamir Sandstone by a dark colour and highly weathered shale. In addition, the Sanganeh Fm. contains fewer limestone intercala tions than the upper shale member of the Sarchesh meh Formation and mostly forms a badland topogra phy. The thickness of this formation in the type section is about 770 m (AfsharHarb, 1979) (Figs. 5 and 6). The Albian age was suggested for the Sanganeh Fm. based on foraminifer studies (Kalantari, 1969; Raisossadat and MoussaviHarami, 1993). However, Immel et al. (1997) and Raisossadat (2002, 2003b, 2006) have reinterpreted the age of the formation as midAptian to early Albian on the basis of ammonite fauna results. The formation is diachronous with the age getting younger eastward. STUDIED SECTIONS

Fig. 6. Concretion nodule in the Sanganeh Formation.

Two thickest sections were studied in the Takal Kuh area. The Sarcheshmeh and Sanganeh formations contain numerous ammonitebearing beds. The Takal Kuh section is situated northwest of Ashkhaneh and 55 km from Ashkhaneh along the road to Shahrabad (Fig. 1). To access to the sections, a track passable by car is used for roughly 15 kilometres. The Takal Kuh 1 and Takal Kuh 2 sections are located close to each other at 37°43′N and 56°10′E, and 37°43′N and 56°7′E, respectively. Calcareous nannofossils were mainly investigated from the Takal Kuh 1 section, and few samples from the Takal Kuh 2 section were studied as well. In addition, we studied nannofossils from the Sarcheshmeh and Sanganeh Formations sampled in the eastern part of the basin at Kalat road (60°03′N, 36°33′E).


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Takal Kuh Sections Sarcheshmeh Formation. The thickness of the for mation is 1150 m at the Takal Kuh 1 section and 1220 m at the Takal Kuh 2 section. The lower basal marly limestone beds of the Sarcheshmeh Fm. overlay conformably the uppermost fossiliferous limestone bed of the Tirgan Fm. At this locality, the Sarchesh meh Fm. cannot be distinctly divided into two mem bers clearly visible in the type section. The lower part of the Sarcheshmeh Fm. mostly consists of grey marly limestone with a few shaly limestone beds. The follow ing calcareous nannofossils are found in this part of the section: Braarudosphaera sp., Cretarhabdus conicus, Lithraphidites cf. bollii, Watznaueria barnesiae, W. biporta, W. fossacincta, and Zeugrhabdotus erectus (Figs. 7–9). Additionally, these beds contain ammo nites Argvethites sp., Barremites cf. difficilis, Martelites securiformis, M. sp. 1, Heteroceras sp. 1, Imerites spar sicostatus, Paraimerites sp., Toxoceratoides sp., Turk meniceras cf. tumidum, and Turkmeniceras multicos tatum (Fig. 10) (Raisossadat, 2002, 2003a). An upper Barremian age is suggested for this interval. Thinbedded grey shaly member (300–800m thick) includes thin limy marl and shaly limestone with intercalations of fossiliferous limestones in the middle part. These beds contain calcareous nannofos sils Cyclagelosphaera margerelli, Hayesites irregularis, and Lithraphidites carniolensis (Fig. 11). Few ammonite specimens of Deshayesites oglan lensis, D. cf. tuarkyricus, D. cf. weissiformis, D. sp. 1, and Ancyloceras cf. manteli were previously reported (Raisossadat, 2002). Based on these ammonites and those recently described, the BarremianAptian boundary should be placed between Sample 22 and Sample 24 where the last Turkmeniceras and the first Deshayesites were found, respectively (Raisossadat 2002, 2004). The upper part of the Sarcheshmeh Fm. (800– 1150 m) consists of thin to mediumbedded grey marly limestone, marl and calcareous marl, grey lam inated shale with light grey to yellow grey medium bedded sandy fossiliferous limestone intercalations. Few calcareous nannofossil species are identified in this part: Calciosolenia fossillis, Micrantholithus obtusus, Rhagodiscus asper, and Watznaueria britan nica (Fig. 11). This part of the section contains ammonites Aconeceras haugi, Cheloniceras sp., Deshayesites dechyi, Deshayesites deshayesi, D. cf. euglyphus, D. cf. involutes, D. luppovi, D. cf. involutes, D. oglanlensis, D. cf. planus, D. weissi, Deshayesites sp. 2, Deshayesites sp. 3, Melchiorites aff. melchioris, Phylloceras sp., and Phyllopachyceras sp. (Fig. 12) (Raisossadat, 2002, 2004). The late Barremian to early Aptian age is sug gested for the Sarcheshmeh Fm. on the basis of calcar eous nannofossil and ammonite assemblages. Sanganeh Formation. In the Takal Kuh area, the formation is about 730 m thick. Dark grey, thinbed STRATIGRAPHY AND GEOLOGICAL CORRELATION

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ded, strongly weathered shales of the Sanganeh Fm. conformably overlie the Sarcheshmeh Fm. (Fig. 3). A shale sequence of about 200 m thick forms the lower most part of the Sanganeh Fm. where calcareous nan nofossils Discorhabdus sp., Lithraphidites sp., Rhago discus splendens, and Watznaueria barnesiae are recorded (Fig. 12). The preservation of calcareous nannofossils is poor to moderate. The sediments also yield Aconeceras haugi, Cheloniceras sp., Deshayesites deshayesi, Melchiorites aff. melchioris, Pseudosaynella sp., and Tonohamites sp. (Raisossadat, 2002, 2003b) ammonites. These beds are overlain by a shale sequence with alternated marly limestone, shaly limestone, and marl. The differential weathering of these rocks forms small ridges among strongly weathered badland topography of the Sanganeh shales. Few silty shale and sandy fos siliferous limestone beds can be seen in the upper part of the formation. Calcareous nannofossils of the upper part of the section are well preserved and the following species were found in two samples (TK83, TK84): Bis cutum constans, Broinsonia sp., Cyclagelosphaera rein hardtii, C. rotaclypeata, Discorhabdus rotatorius, Epro lithus floralis, Haqius circumradiatus, Lithraphidites carniolensis, Micrantholithus hoschulzii, M. obtusus, Nannoconus circularis, Nannoconus sp. 1, Nannoconus sp. 2, Rhagodiscus angustus, R. asper, Staurolithites sp., Tranolithus sp., Watznaueria barnesiae, W. biporta, W. fossacincta, W. ovata, Zeugrhabdotus diplogrammus, and Z. embergeri (Figs. 7, 9, 11, 13). This assemblage is associated with ammonites Aconeceras haugi, Deshayesites cf. planus, D. cf. conso brinoides, D. cf. multicostatus, Melchiorites aff. mel chioris, Australiceras sp., and Tonohamites sp. (Fig. 12) (Raisossadat, 2002). The fossil remains recorded in the Sanganeh Fm. suggest its midearly Aptian age. Another section (720 m thick) is situated approxi mately 4 km westward of Sect. 1. The lithology of both sections is very similar showing minor lateral changes in some beds. The ammonite Dufrenoyia sp. recorded in the Takal Kuh 1 section, was found in the upper most part of the Takal Kuh 2 section (Raisossadat, 2002). The reported assemblage indicates the early Aptian age for the Sanganeh Fm. in this section as well. The boundary of the Sanganeh Fm. with the overlying Kalat Fm. (Maastrichtian) is marked by an angular unconformity. Nannofossil assemblage including Braaru dosphaera regularis, Calcicalathina oblongata, Chias tozygus litterarius, Conusphaera mexicana, Cretarhab dus conicus, C. striatus, Cyclagelosphaera margerelli, Eprolithus floralis, E. antiquus, Haqius circumradiatus, Lithraphidites bollii, Lithraphidites carniolensis, Manivitella pemmatoidea, Micrantholithus hoschulzii, M. obtusus, Nannoconus broennimannii, N. colomi, N. truitti frequens, N. truitti truitti, N. wassalii, Radi olithus planus, Retecapsa sp., Rhagodiscus angustus, R. asper, R. splendens, Rucinolithus sp., Watznaueria Vol. 19

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Fig. 7. Nannofossil range chart of the Sarcheshmeh and Sanganeh formations in Takal Kuh section (1), (P = present).

NC7A

covered probably shale

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87

NC5

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Biozones

Sample number Biscutum constans Broinsonia sp. Braarudosphaera sp. Calciosolenia fossils Cretarhabdus conicus Cyclagelosphaera reinhardtii Cyclagelosphaera margerelii Discorhabdus sp. D. rotatorius Eprolithus floralis Haqius circumradiatus Hayesites irregularis Lithraphidites cf. bollii Lithraphidites carniolensis Lithraphidites sp. Micrantholithus hoschulzii Micrantholithus obtusus Nannoconus circularis Nannoconus spp. Rhagodiscus asper Rhagodiscus splendens Staurolithites sp. Tranolithus sp. Watznaueria barnesiae Watznaueria biporta Watznaueria fossacincta Watznaueria britannica Watznaueria manivitiae Watznaueria ovata Zeugrhabdotus diplogrammus Zeugrhabdotus embergeri Zeugrhabdotus erectus

Thickness, m

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(Roth, 1978)

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Dufrenoyia sp.

Maast. Kalat Fm.

Reboulet et al., 2009

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Deshayesites deshayesi

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D. weissi (47)

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D. cf. planus (46)

Micrantholithus obtusus

Deshayesites oglanlensis

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D. oglanlensis (33)

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Martelites securiformis

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Deshayesites sp. 1 (24)

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Martelites securiformis (14) Watznaueria barnesiae Watznaueria fossacincta

Heteroceras sp.

Fig. 8. Nannofossil and ammonite integration of the Sarcheshmeh and Sanganeh formations in the Takal Kuh. STRATIGRAPHY AND GEOLOGICAL CORRELATION

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B

C

D

E

F

G

H

I

J

K

A

0.002 mm

Fig. 9. Calcareous nannofossils of the Sanganeh Formation; (A) Broinsonia sp., (B) Nannoconus sp., (C) Watzanaria barnesiae, (D) Tranolithus sp., (E) Triscutum bearminsternsis, (F) Discorhabdus rotatorius, (G) Nannoconus sp., (H) Zeugrhabdotus erectus, (I) Lithraphidites carniolernsis, (J) Biscutum constans (distal side), (K) Biscutum constans (proximal side).

barnesiae, W. biporta, W. britannica, W. fossacincta, Zeugrhabdotus diplogrammus, Z. embergeri, and Z. xenotus (Dehghan, 2002) was recognized in another outcrop near the type locality of the Sarcheshmeh Fm. along the Kalat road.

part of the Sanganeh Fm. Eiffelithus sp. 1, Eiffelithus sp. 2, Nannoconus elongatus, N. vocontienis, N. was salii, Prediscosphaera columnata, P. cretacea, P. spi nosa, and Tranolithus orionatus were found (Dehghan, 2002).

In the Sanganeh Fm. some nannofossil taxa persist from the Sarcheshmeh Fm. In addition, some new genera and species such as Cribrosphaerella ehren bergii, Crucicribrum anglicum, Cyclosphaera deflan drei, Diazomatolithus lehmanii, Lithraphidites alatus, and Nannoconus vocontienis are recorded. In the upper

Immel et al. (1997) and Raisossadat (2002) reported the following ammonites from the Kalat road section: Acanthohoplites cf. aschiltaensis, A. cf. big oureti, A. sp., Beudanticeras sp. ex gr. newtoni, Che loniceras (Epicheloniceras) sp., Colombiceras sp., Dou villeiceras aff. mammillatum, D. sp. ex gr. monile,


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C(×0.5)

A

B(×0.5)

E(×2) F G D

H

I

K J L(×0.5)

Fig. 10. Ammonite fauna of the Sarcheshmeh and Sanganeh formations: (A, C) Turkmeniceras multicostatum, Sarcheshmeh For mation; (B) Turkmeniceras cf. tumidum, Sarcheshmeh Formation; (D) Heteroceras cf. colchicus, Sarcheshmeh Formation; (E) Aconeceras haugi, Sanganeh Formation; (F) Martelites securiformis, Sarcheshmeh Formation; (G) Argvethites sp., Sarchesh meh Formation; (H) Deshayesites weissi, Sarcheshmeh Formation; (I) Deshayesites cf. weissiformis, Sarcheshmeh Formation; (J) Deshayesites oglanlensis, Sarcheshmeh Formation; (K) Deshayesites deshayesi, Sarcheshmeh Formation; (L) Deshayesites cf. multicostatus, Sanganeh Formation.

Hypacanthoplites shepherdi, H. clavatus, H. uhligi, Leymeriella (Neoleymeriella) regularis, Parahoplites sp. ex. gr. Melchioris, P. cf. campichii, and Uhligella sp.

the age of the formation to the Aptian in the eastern part of the basin, for example in the Kalat road sec tion.

Based on the ammonites and nannofossils docu mented in the Takal Kuh sections, the late Barremian to early Aptian age is suggested for the Sarcheshmeh Fm. However, both ammonite (Raisossadat, 2002) and nannofossil assemblages indicate a restriction of

The beds of the Sanganeh Formation are younger eastward from the Raz road. The presence of Acantho hoplites, Parahoplites, and Hypacanthoplites in the central and eastern sections suggests mid to late Aptian age for the Sanganeh Fm. in these areas. At the


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A

0.005 mm

B

C

D

E

F

G

H

I

J

K

L

Fig. 11. Calcareous nannofossils of the Sanganeh and Sarcheshmeh formations: (A) Watzanueria fossacinta, Sanganeh Forma tion; (B) Rhagodiscus asper, Sanganeh Formation; (C) Watzanueria cf. barnesiae, Sanganeh Formation; (D) Cyclogelosphaera margelli, Sanganeh Formation; (E) Watzanueria biporta, Sanganeh Formation; (F) Watzanueria barnesiae, Sanganeh Formation; (G) Watzanueria fossacinta, Sanganeh Formation; (H) Micrantholithus obtusus, Sanganeh Formation; (I) Cretarhabdus conicus, Sanganeh Formation; (J) Micrantholithus hoschulzii, Sarcheshmeh Formation; (K) Eprolithus floralis, Sanganeh Formation; (L) Hayesites irregularis, Sarcheshmeh Formation.

same time, based on Immel et al. (1997), Raisossadat (2002), and the results of nannofossil study, the early Aptian to early Albian age is assumed for the Sanganeh Fm. in the eastern part of the basin. CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY Several nannofossil zonal scales were proposed for the Lower Cretaceous interval (Thierstein, 1973, 1976; Sissingh, 1977; Bralower et al., 1994; Erba, 1996; Bown et al., 1998). The Thierstein’s biozonation for the Tethys realm is followed by other researchers with some changes in range of nannofossil index spe cies (Figs. 7 and 8). According to Thierstein (1971, 1976), the Aptian stage can be subdivided into two zones, Chiastozygus litterarius and Parhabdolithus (Rhagodiscus) angustus. Bralower et al. (1993) introduced the Chiastozygus tenuis Zone and Rhagodiscus angustus Zone for the Aptian. They used C. tenuis as a marker species because C. litterarius continues into the early Maas

trichtian. This biozonation was applied for the Aptian stratotype in southeastern France (Bergen, 2000). Calcareous nannofossil assemblages from the Kopet Dagh are similar to those recorded in Europe (table) including representative species of the genera Braarudosphaera, Biscutum, Calcicalathina, Chias tozygus, Cretarhabdus, Cribrosphaerella, Crucicribrum, Cyclagelosphaera, Discorhabdus, Eiffellithus, Eproli thus, Haqius, Hayesites, Lithraphidites, Manivitella, Micrantholithus, Nannoconus, Prediscosphaera, Rha godiscus, Rucinolithus, Tranolithus, Staurolithites, Watznaueria, and Zeugrhabdotus (see Aguado et al., 1999; Bergen, 2000; Bischoff and Mutterlose, 1998; Mutterlose, 1987; Thierstein, 1973). In the lower part of the Sarcheshmeh Fm. the assemblage includes Braarudosphaera sp., Braaru dosphaera regularis, Calcicalathina oblongata, Cretar habdus conicus, C. striatus, Lithraphidites bollii, Micrantholithus hoschulzii, N. colomii, N. wassalii, Watznaueria barnesiae, W. biporta, W. fossacincta, and Zeugrhabdotus erectus (table). This assemblage is sim ilar to those documented in the Tethys realm (Thier


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B(×0.5)

F

A E

C D G

Fig. 12. Ammonite fauna of the Sarcheshmeh and Sanganeh formations: (A) Deshayesites luppovi, Sarcheshmeh Formation; (B) Deshayesites cf. involutes, Sarcheshmeh Formation; (C) Deshayesites dechyi, Sarcheshmeh Formation; (D) Deshayesites cf. weissiformis, Sarcheshmeh Formation; (E) Deshayesites cf. planus, Sanganeh Formation; (F) Dufrenoyia sp., Sanganeh Forma tion; (G) Deshayesites cf. consobrinoides, Sanganeh Formation.

stein, 1973) and could be correlated with the Micran tholithus hoschulzii Zone (Thierstein, 1973; Perch Nielsen, 1985), upper part of CC5 and CC6 nannofos sil zones (Sissingh, 1977), upper part of the Flabellites oblongus Zone, and Micrantholithus obtusus Subzone (Roth, 1978). STRATIGRAPHY AND GEOLOGICAL CORRELATION

Moreover, the ammonite fauna confirms the late Barremian age for the lower part of the Sarcheshmeh Fm. In the middle and upper parts of the Sarcheshmeh Fm., calcareous nannofossil assemblage includes Cal ciosolenia fossilis, Chiastozygus litterarius, Conusphaera Vol. 19

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A

B

C

D

E

F

G

H

I

J

K

L

0.005 mm

Fig. 13. Calcareous nannofossils of the Sanganeh and Sarcheshmeh formations: (A, B) Calsiosolena fossils, Sarcheshmeh Forma tion (in XPL and PPL); (C) Discorhabdus sp., Sanganeh Formation; (D) Microantholithus obtusus, Sanganeh Formation; (E, F) Nannoconus circularis, Sanganeh Formation (in XPL and PPL); (G) Nannoconus sp., Sarcheshmeh Formation; (H) Lithraphid ites bolli, Sarcheshmeh Formation; (I) Cyclogelosphaera margelli, Sarcheshmeh Formation; (J) Rhagodiscus splendens, Sanganeh Formation; (K) Zeagrhabdotus erectus, Sarcheshmeh Formation; (L) Watznaueria britannica, Sarcheshmeh Formation.

mexicana, Cyclagelosphaera margerellii, Discorhabdus sp., Haqius circumradiatus, Hayesites irregularis, Lithraphidites carniolensis, N. wassalii, Micran tholithus obtusus, Retecapsa sp., Rhagodiscus asper, Staurolithites sp., Tranolithus sp., Watznaueria britan nica, Zeugrhabdotus diplogrammus, Z. embergeri, and Z. xenotus. This assemblage could be correlated with the lower part of the Chiastozygus tenuis Zone (Thier stein, 1973), the lower part of the CC7 zone (Sissingh, 1977), and lower part of NC6A (Bralower et al., 1993)

and CC7A (PerchNielsen, 1985) zones (Fig. 8). The occurrence of Hayesites irregularis and Rhagodiscus asper are reliable indicators for the early Aptian. This assemblage also corresponds to the Deshayesites oglan lensis and Deshayesites weissi ammonite zones. Calcareous nannofossil assemblage of the Sanga neh Fm. includes Biscutum constans, Broinsonia sp., Diazomatolithus lehmanii, Discorhabdus rotatorius, Discorhabdus sp., Eprolithus floralis, Lithraphidites alatus, Lithraphidites sp., Manivitella pemmatoidea,


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Upper Barremian–Lower Albian calcareous nannofossil biozonation and the proposed biozonation for the Kopet Dagh ba sin Bralower et al., 1993

Perch Nielsen, 1985

Roth, 1978

Sissingh, 1977

Thier stein, 1973

Stage

Assemblage flora in Takal Kuh and Kalat Road sections

Micrantholithus hoschulzii Zone

NC5 partly

CC6 partly

Micrantholithus hoschulzii Zone

Upper Barremian

Micrantholithus Eprolithus floralis Conusphaera mexicana subzone obtusus subzone subzone Flabellites oblongus Rhagodiscus Chiastozygus angustus Zone tenuis Zone Zone (partly)

NC6, NC7,

CC7

Prediscosphaera Chiastozygus columnata litterarius Zone

NC8

CC8

Aptian

Parhabdolithus Chiastozygus angustus litterarius Zone

Albian

Cribrosphaerella ehrenbergii, Cyclosphaera deflandrei, Crucicribrum anglicum, Eiffelithus sp. 1, Eiffelithus sp. 2, Nannoconus elongatus, Prediscosphaera colum nata, P. cretacea, P. spinosa, Tranolithus orionatus

Biscutum constants, Broinsonia sp., Discorhabdus rotatorius, Diazomatolithus le hmanii, Discorhabdus sp., Eprolithus floralis, E. antiquus, Lithraphidites alatus, Lithraphidites sp., Manivitella pemmatoidea, Nannoconus broennimannii, N. cir cularis, N. truitti frequens, N. truitti truitti, N. vocontienis, Nannoconus sp. 1, Nannoconus sp. 2, Radiolithus planus, Rhagodiscus angustus, R. splendens, Tra nolithus sp. and Watznaueria barnesiae, W. ovata Calciosolenia fossils, Chiastozygus litterarius, Conusphaera mexicana, Cretarhab dus striatus, Cyclagelosphaera margerelli, Discorhabdus sp., Haqius circumradi atus, Hayesites irregularis, Lithraphidites carniolensis, N. wassalii, Micran tholithus obtusus, Retecapsa sp., Rhagodiscus asper, Staurolithites sp., Trano lithus sp., Watznaueria britannica, Zeugrhabdotus diplogrammus, Z. embergeri, Z. xenotus Braarudosphaera regularis, Braarudosphaera sp., Calcicalathina oblongata, Cre tarhabdus conicus, Lithraphidites bollii, Micrantholithus hoschulzii, N. colomi, N. wassalii, Watznaueria barnesiae, W. biporta, W. fossacincta and Zeugrhabdot us erectus

Nannoconus cf. broennimannii, N. circularis, N. truitti frequens, N. truitti truitti, Nannoconus sp. 1, Nannoco nus sp. 2, Radiolithus planus, Rhagodiscus angustus, R. splendens, Tranolithus sp., Watznaueria barnesiae, and W. ovata. The assemblage could be correlated with the upper part of the Chiastozygus litterarius Zone (Thierstein, 1973; PerchNielsen, 1985), upper part of CC7 Zone (Sissingh, 1977), and upper part of NC6 and NC7 zones (Roth, 1978). The Chiastozygus litterarius Zone has been confined to the lower and middle part of the Aptian and the Rhagodiscus angustus Zone was sug gested for the rest of the Aptian (Larson et al., 1993). Bischoff and Mutterlose (1998) correlated the Chias tozygus litterarius Zone with the uppermost part of the sarasini, tuarkyricus, weissi and lower part of deshayesi ammonite zones. In the Kopet Dagh basin the above assemblage is correlated with the deshayesi and the lower part of the furcata ammonite zones. In the uppermost part of the Sanganeh Fm. in the Kalat road section the following assemblage is identi fied: Cribrosphaerella ehrenbergii, Cyclosphaera deflandrei, Crucicribrum anglicum, Eiffellithus sp. 1, Eiffellithus sp. 2, Nannoconus elongatus, N. vocontie nis, N. wassalii, Prediscosphaera columnata, P. creta STRATIGRAPHY AND GEOLOGICAL CORRELATION

cea, P. spinosa, and Tranolithus orionatus. The assem blage can be correlated with the lower part of the Par habdolithus angustus Zone (Thierstein, 1973), lower part of CC8 Zone (Sissingh, 1977), lower part of NC8 Zone (Roth, 1978), and the Prediscosphaera colum nata Zone (PerchNielsen, 1985) that implies differ ent age of the uppermost Sanganeh Fm. Bown et al. (1998) introduced a nannofossil biozo nation for the Boreal realm. They suggested the Bis cutum constans Zone for the upper Barremian and Watznaueria britannica, Farhania varolii, Lithraphid ites morayfirthensis, and Rhagodiscus asper zones for the lower Aptian. Watznaueria britannica occurs within the oglanlensis Zone in the Takal Kuh 1 section which can be correlated with the same level that Bown et al. (1998) reported. Rhagodiscus asper is also recorded in the Kopet Dagh basin. Its occurrence is within the weissi Zone that is earlier than its occur rence mentioned by Bown et al. (1998) from the Boreal realm. Few seaways connecting Tethys and Boreal realm existed in the early Cretaceous. It can be hypothesized that some calcareous nannofossils migrated from the Tethyan to Boreal realm. Vol. 19

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PALEOECOLOGY As mentioned above, to better understand the pale oecological characteristics of the Sarcheshmeh and Sanganeh Fms., it is necessary to make more thorough sampling and estimate relative abundance of nanno fossil genera and species. However, even based on the data available by now, it is possible to suggest paleoecological interpretation of the calcareous nannofossil assemblages studied. Diagenesis effects the preservation of calcareous nan nofossils and, consequently, limits their use for pale oenvironmental interpretation. Paleoecology of the identified genera and species will be discussed below. The Nannoconus group is typical for the Lower Cretaceous of the Tethys. However, this does not con tradict its sporadic occurrence in the Boreal realm (Mutterlose, 1987; Mutterlose and Bockel, 1998). This group has been considered as characteristic of warm surface water (Mutterlose, 1991). A global nan noconid crisis has been documented in the early Aptian (Erba, 1993, 1994, 1995; Bralower et al., 1994). It preceded the Oceanic Anoxic Event 1a (OAE 1a) in the late early Aptian (Herrle and Mutterlose, 2003; Erba, 2004). Erba (1993, 1994) suggested that a nutri cline shallowing during the early Aptian restricted the Nannoconus production in the deep photic zone and led to this global crisis. Black shale in the lower part of the Sanganeh Fm. can be correlated with the early Aptian OAE 1a. Organic carbon in the Sanganeh Fm. accounts for up to 3.7% (AfsharHarb, 1979). It reaches up to 1% in the Takal Kuh section (Mahanipour, personal com munication). Moreover, carbon and oxygen isotope analysis showed significant changes at this level (Rai sossadat et al., in press). Nannoconus is recorded in the upper part of the Sanganeh Fm. in the Takal Kuh sec tion, where the age of formation is defined as late early Aptian. The Watznaueria group including W. barnesiae, W. britannica, and W. ovata is believed to be the most resistant to diagenesis (Bischoff and Mutterlose, 1998; Roth and Bralower, 1981). W. barnesiae was shown to be an indicator of low fertility during the midCreta ceous (Roth and Krumbach, 1986). Watznaueria bar nesiae and Cyclagelosphaera margerelli are known as the shallow water or epicontinental sea indicators (Thierstein, 1973). Watznaueria is abundant in the lower part of the studied interval, where organic detri tal and oolitic shallowwater limestones of Tirgan Fm. change into marly and shaly limestones of the Sarcheshmeh Fm. The Biscutum group is recorded in the Chiastozygus tenuis, Flabellites oblongus, and Eprolithus floralis zones of northwestern Europe (Bischoff and Mutter lose, 1998). The Biscutum and some species of Zeugrhabdotus were considered as Cretaceous indica tors of high surfaces water fertility (Bergen, 2000; Roth, 1986; Roth and Bralower, 1981; Roth and

Krumbach, 1986; Watkins, 1989). Zeugrhabdotus appears in the lower part of the Sarcheshmeh Fm. and Biscutum is recorded in the upper part of the Sanganeh Fm. The Rhagodiscus group including R. angustus and R. asper is thought to be indicative of warm surface water (Bischoff and Mutterlose, 1998; Mutterlose, 1991). They occur in the upper part of the Sarchesh meh and lower part of the Sanganeh Fms. Assuming equal effect of diagenesis in both formations and con sidering that the nannofossil assemblage in the Sanga neh Fm. is more diverse than in the Sarcheshmeh Fm., we infer more favourable environmental condi tions in the middle and upper parts of the Sanganeh Fm. CONCLUSIONS The representative species of the Biscutum, Braaru dosphaera, Broinsonia, Calcicalathina, Calciosolenia, Cretarhabdus, Cyclagelosphaera, Discorhabdus, Epro lithus, Haqius, Hayesites, Lithraphidites, Micran tholithus, Nannoconus, Rhagodiscus, Staurolithites, Tranolithus, Watznaueria, and Zeugrhabdotus genera are recorded in the Sarcheshmeh and Sanganeh Fms. exposed in the Takal Kuh sections. The assemblage is characteristic of the Tethyan realm. The nannofossil assemblage of the Sarcheshmeh Fm. corresponds to the upper part of CC5 to lower part of CC7 or lower part of the NC6 nannofossil zones that implies its late Barremian to early Aptian age. The calcareous nannofossil assemblage in the San ganeh Fm. can be correlated with the middle part of CC7 or upper part of NC6 zone suggesting its late early Aptian and, possibly, earliest late Aptian age. The identified assemblages are typical for the Early Cretaceous of the Tethys and indicate warm surface water. High abundance of Watznaueria group can be the result of both diagenetic impact and surface water oligotrophy during the midCretaceous. At the same time, sporadic occurrence of Biscutum and Zeugrhab dotus spp. at individual levels suggests increased sur faces water fertility during certain intervals. ACKNOWLEDGMENTS The authors thank Professor J. Mutterlose (Bochum), Dr. Sudeep Kanungo (Utah University, USA), Dr. Jackie Lees (University College London), and Dr. Anoshirvan Kani (Shaheed Beheshti Univer sity, Iran) for helpful discussions of the specimens. A part of images (especially SEM images) was taken in the Bochum University. We are grateful to Dr. E.A. Shcherbinina and Dr. A.B. Herman (Geo logical Institute, Russian Academy of Sciences), who acted as referees, for their useful suggestion. Logistical support for field works and laboratory facilities was partly financed by the Birjand University and the


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Department of Geological Sciences at UCL. Thanks go to Iranian friends for their help in the field. Reviewers E.A. Shcherbinina and A.B. Herman REFERENCES AfsharHarb, A., A Brief History of Geological Exploration and Geology of the Sarakhs Area and the Khangiran Field, Bull. Iran. Petrol. Inst., 1969, no. 37, pp. 86⎯93. AfsharHarb, A., The Stratigraphy, Tectonics and Petro leum Geology of the Kopet Dagh Region, Northern Iran, PhD Thesis, London: Imperial College of Science and Technology, 1979. AfsharHarb, A., Geological Quadrangle Map of Darreh Gaz, 1 : 250000 Scale (One Sheet), Tehran: Exploration and Pro duction, National Iranian Oil Company (N.I.O.C.), 1982. AfsharHarb, A., Geological Quadrangle Map of Sarakhs, 1 : 250000 Scale (One Sheet), Tehran: Exploration and Pro duction, N.I.O.C., 1983. AfsharHarb, A., Geology of Kopet Dagh, in Treatise on the Geology of Iran, Hushmandzadeh, A., Ed., Tehran: Geolog ical Survey of Iran, 1994) [In Persian]. Aguado, R., Castro, J.M., Company, M., and De Gea, G.A., Aptian BioEvents and Integrated Biostratigraphic Analysis of the Almadich Formation, Inner Prebetic Domain, SE Spain, Cretaceous Res., 1999, vol. 20, pp. 663⎯683. Berberian, M. and King, G.C.P., Toward a Palaeogeogra phy and Tectonic Evolution of Iran, Can. J. Earth Sci., 1981, vol. 18, pp. 210⎯265. Bergen, J.A., Calcareous Nannofossils from the Lower Aptian Historical Stratotype at CassisLa Bédoule (SE France), Géologie Méditerraneenne, 2000, vol. 25, nos. 3⎯4, pp. 227⎯255. Bischoff, G. and Mutterlose, J., Calcareous Nannofossils of the Barremian/Aptian Boundary Interval in NW Europe: Biostratigraphic and Palaeontologic Implications of a High Resolution Study, Cretaceous Res., 1998, vol. 19, pp. 635⎯ 661. Bown, P.R., Rutledge, D.C., Crux, J.A., and Gallagher, L.T., Lower Cretaceous, in Calcareous Nannofossil Biostratigra phy, Bown, P.R., Ed., London: Chapman and Hall, 1998, pp. 86⎯131. Bown, P.R. and Young, J.R., Techniques, in Calcareous Nannofossil Biostratigraphy, Bown, P.R., Ed., London: Chapman and Hall, 1998, pp. 86⎯131. Bralower, T.J., Sliter, W.V., Arthur, M.A., et al., Dys oxic/Anoxic Episodes in the AptianAlbian (Early Creta ceous). The Mesozoic Pacific: Geology, Tectonics and Vol canism, Geophys. Monograph., 1993, vol. 77, pp. 5⎯37. Bralower, T.J., Arthur, M.A., Leckie, R.M., et al., Timing and Paleoceanography of Oceanic DyoxiaAnoxia in the Late Barremian to Early Aptian (Early Cretaceous), Palaios, 1994, vol. 9, pp. 335⎯369. Dehghan, F., Biostratigraphy of Sarcheshmeh Formation Based on Calcareous Nannoplanktons in Type Section (Koppeh Dagh), MSc Thesis, Shaheed Beheshti University, 2002. Erba, E., Calcareous Nannofossils Distribution in Pelagic Rhythmic Sediments (AptianAlbian Piobbico Core, Cen tral Italy), Rivista Italiana di Paleontologia e Stratigrafia, 1991, vol. 94, pp. 249⎯284. STRATIGRAPHY AND GEOLOGICAL CORRELATION

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Vol. 19

No. 2

2011