Oligocene-Miocene Ramp System (Asmari Formation) in the NW of the Zagros Basin, Iran: Microfacies, Paleoenvironment and Depositional Sequence

56 Vaziri-MoghaddamRevista Mexicana et al. de Ciencias Geológicas, v. 27, núm. 1, 2010, p. 56-71

Oligocene-Miocene ramp system (Asmari Formation) in the NW of the Zagros basin, Iran: Microfacies, paleoenvironment and depositional sequence

Hossein Vaziri-Moghaddam1,*, Ali Seyrafian1, Azizolah Taheri2, and Homayoon Motiei3

1 Department of Geology, Faculty of Sciences, University of Isfahan, Isfahan, Iran, 81746-73441. 2 Geology Department, Faculty of Earth Science, Shahrood University of Technology, Shahroud, Iran. 3 National Iranian Oil Company Research and Development Division, Tehran, Iran. * [email protected]

ABSTRACT

The Asmari Formation deposited in the Zagros foreland basin during the Oligocene-Miocene. Four different measured sections were studied in this area in order to interpret the facies, depositional environment and sequence stratigraphy of the Asmari Formation. In this study, thirteen different microfacies types have been recognized, which can be grouped into six depositional environments: tidal flat, restricted lagoon, open lagoon, shoal, slope and basin. The Asmari Formation represents sedimentation on a carbonate ramp. Four third-order sequences are identified, on the basis of deepening and shallowing patterns in the microfacies and the distribution of the Oligocene-Miocene foraminifers. The depositional sequences 1, 2 and 3 were observed in Dehluran and Kabirkuh-Darrehshahr areas, and are synchronous with a period of either erosion or non-deposition represented by unconformities in Mamulan and Sepid Dasht areas.

Key words: microfacies, paleoenvironment, ramp, Asmari Formation, Zagros basin, Iran.

RESUMEN

La Formación Asmari se depositó en el antepaís de la cuenca Zagros durante el Oligoceno-Mioceno. Se estudiaron y midieron cuatro secciones diferentes en esta área para interpretar las facies, ambiente de depósito y la secuencia estratigráfica de la Formación Asmari. En este estudio, trece tipos diferentes de microfacies han sido reconocidos, los cuales pueden ser agrupados en seis ambientes de depósito: planicie de marea, laguna restringida, laguna abierta, mar somero (bancos de arena), pendiente marina y cuenca. La Formación Asmari representa sedimentación en una rampa carbonatada. Cuatro secuencias de tercer orden se identificaron, según patrones de profundidad y superficialidad de las microfacies y la distribución de los foraminíferos del Oligoceno-Mioceno. Las secuencias de depósito 1, 2 y 3 se observaron en las áreas de Dehluran y Kabirkuh-Darrehshahr, y son sincrónicas con un período de erosión o bien de no depósito, representado por discordancias en las áreas de Mamulan y Sepid Dasht.

Palabras clave: microfacies, paleoambiente, rampa, Formación Asmari, cuenca Zagros, Irán.

Vaziri-Moghaddam, H., Seyrafian, A., Taheri, A., Motiei, H., 2010, Oligocene-Miocene ramp system (Asmari Formation) in the NW of the Zagros basin, Iran: Microfacies, paleoenvironment and depositional sequence: Revista Mexicana de Ciencias Geológicas, v. 27, núm. 1, p. 56-71. Asmari Formation: Microfacies, paleoenvironment and depositional sequence 57 Introduction in the study area mainly based on the distribution of the foraminifera. This paper deals with the Asmari Formation, an Oligocene-Miocene carbonate succession in the northwestern Zagros basin, southwest Iran (Figure 1). The area is GEOLOGICAL SETTING excellent to establish the geometrical relationship between sedimentary facies and sequence stratigraphy of a carbon- Based on the sedimentary sequence, magmatism, ate platform. metamorphism, structural setting and intensity of defor- The Asmari Formation, a thick carbonate sequence of mation, the Iranian Plateau has been subdivided into eight the Oligocene-Miocene, is one of the best known carbonate continental fragments, including Zagros, Sanandaj-Syrjan, reservoirs in the world. It is present in most of the Zagros Urumieh-Dokhtar, Central Iran, Alborz, Kopeh-Dagh, Lut, basin. Lithologically, the Asmari Formation consists of and Makran (Heydari et al, 2003; Figure 2). The study area limestone, dolomitic limestone, dolomite and marly lime- is located in the northwestern part of the Zagros basin and in- stone. Some anhydrite (Kalhur Member) and lithic and limy clude four sections: 1) Dehluran, 2) Kabirkuh-Darrehshahr, sandstones (Ahwaz Member) also occur within the Asmari 3) Mamulam and 4) Sepid Dasht (Figure 1). Formation (Motiei, 1993). The Zagros basin is composed of a thick sedimentary The Asmari Formation was originally defined in pri- sequence that covers the Precambrian basement formed mary works by Busk and Mayo (1918), Richardson (1924), during the Pan-African orogeny (Al-Husseini, 2000). Van Boeck et al. (1929), and Thomas (1948). Later, James The total thickness of the sedimentary column depos- and Wynd (1965), Wynd (1965), Adams and Bourgeois ited above the Neoproterozoic Hormuz salt before the (1967), Kalantary (1986), and Jalali (1987) introduced Neogene Zagros folding can reach over 8 to 10 km (Alavi, the microfaunal characteristics and assemblage zones for 2004; Sherkati and Letouzey, 2004). The Zagros basin has the Asmari Formation. More recent studies of the Asmari evolved through a number of different tectonic settings Formation have been conducted on biostratigraphic criteria since the end of Precambrian. The basin was part of the (Seyrafian et al., 1996; Seyrafian and Mojikhalifeh, 2005; stable Gondwana supercontinent in the Paleozoic, a passive Hakimzadeh and Seyrafian, 2008; Laursen et al., 2009), margin in the Mesozoic, and became a convergent orogen microfacies and depositional environments (Seyrafian in the Cenozoic. and Hamedani, 1998, 2003; Seyrafian, 2000) and depo- During the Palaeozoic, Iran, Turkey and the Arabian sitional environment and sequence stratigraphy (Vaziri- plate (which now has the Zagros belt situated along its Moghaddam et al., 2006; Amirshahkarami et al., 2007a, northeastern border) together with Afghanistan and India, 2007b; Ehrenberg et al., 2007). made up the long, very wide and stable passive margin of This paper reports on a sedimentological study of Gondwana, which borderered the Paleo-Tethys Ocean to Asmari Fm. outcrops, whose results could contribute to a the north (Berberian and King, 1981). better understanding of the subsurface Asmari Formation in By the Late Triassic, the Neo-Tethys ocean had opened adjacent oilfield areas. The main objectives of this reseach up between Arabia (which included the present Zagros re- were foused on (1) a description of the facies and their gion as its northeastern margin) and Iran, with two different distribution on the Oligocene-Miocene carbonate platform, sedimentary basins on both sides of the ocean (Berberian (2) the palaeoenvironmental reconstruction of the carbonate and King, 1981). platform, and (3) the origin of sequences that developed The closure of the Neo-Tethys basin, mostly during

Figure 1. Map showing the location of the study areas in northwest Zagros. Dehluran (Section 1), Kabirkuh-Darrehshahr (Section 2), Mamulan (Section 3) and Sepid Dasht (Section 4). 58 Vaziri-Moghaddam et al. basin axis (Motiei, 1993). During the Oligocene-Miocene this basin was gradually narrowed and the Asmari Formation was deposited. Different facies, including lithic sandstone (Ahwaz Member) and evaporites (Kalhur Member) were deposited during late Oligocene-early Miocene times (Ahmadhadi et al., 2007). In the southwestern part of the Zagros basin, the Asmari Formation overlies the Pabdeh Formation, whereas in the Fars and Lurestan regions it covers the Jahrum and Shahbazan formations (Figure 3). Although the lower part of the Asmari Formation interfin- gers with the Pabdeh Formation in the Dezful Embayment (Motiei, 1993), its upper part covers the entire Zagros basin. The maximum thickness of the Asmari Formation is found in the northeastern corner of the Dezful Embayment.

Methods and study area

Four sections of the Asmari Formation were measured bed by bed, and sampled in four areas (Dehluran, 180; Kabirkuh-Darrehshahr, 260; Mamulan, 69/5; and Sepid Dasht, 82/5 m thick; Figures 1 and 4), and sedimentologi- cally investigated. The sections were described in the field, including their weathering profiles, facies and bedding surfaces. Fossils and facies characteristics were described in thin sections from 408 samples. Test shapes of the largest benthic foraminifera were taken into account for the facies interpretation, as their differences depend on the environment (Hottinger, 1980, 1983; Reiss and Hottinger,1984; Leutenegger, 1984; Hohenegger, 1996; Hallock, 1999; Figure 2. Subdivisions of the Zagros orogenic belt (adopted from Heydari Hohenegger et al., 1999; Geel, 2000; Brandano and Corda, et al., 2003). 2002; Corda and Brandano, 2003; Barattolo et al., 2007). The lithology and the microfacies types were described the Late Cretaceous, was due to the convergence and north- according to the schemes porposed by Dunham (1962) and east subduction of the Arabian plate beneath the Iranian Embry and Klovan (1971). Also, the same 408 samples were sub-plate (Berberian and King, 1981; Stoneley, 1981; used for sequence stratigraphy analyses. Beydoun et al., 1992; Berberian, 1995). The closure led to the emplacement of pieces of the Neo-Tethyan oceanic lithosphere (i.e., ophiolites) onto the northeastern margin BIOSTRATIGRAPHY of the Afro-Arabian plate (e.g., Babaie et al., 2001; Babaei et al., 2005; Babaie et al., 2006). Biozonation and age determinations are based on Continent-continent collision starting in the Cenozoic strontium isotope stratigraphy recently established for the has led to the formation of the Zagros fold-and-thrust belt, Asmari Formation by Laursen et al. (2009). Results from continued shortening of the mountain range, and creation of the foraminifera data are summarized in Table 1. the Zagros foreland basin. The Late Cretaceous to Miocene Three assemblages of foraminifera were recognized rocks represent deposits of the foreland basin prior to the in the studied areas and were discussed in ascending strati- Zagros orogeny, and subsequent incorporation into the graphic order as follows: colliding rock sequences. This sequence unconformably Assemblage 1. This assemblage occurs only at overlies Jurassic to Upper Cretaceous rocks. Kabirkuh-Darrehshahr area (Section 2). The most impor- Compressional folding began during or soon after the tant foraminifera are: Eulepidina sp., Eulepidina dilatata, deposition of the Oligocene-Miocene Asmari Formation Eulepidina elephantine, Lepidocyclina sp., Nephrolepidina (Mapstone, 1978; Sepehr and Cosgrove, 2004). sp., Operculina sp., Operculina complanata, Austrotrillina During the Palaeocene and Eocene, the Pabdeh (pe- howchini, Austrotrillina asmaricus, Peneroplis sp., lagic marls and argillaceous limestones) and the Jahrum Triloculina trigonula, Spiroclypeus blanckenhorni, mili- (shallow marine carbonates) formations were, respectively, olids and globigerinids. This assemblage is correlated deposited in the middle part and on both sides of the Zagros with Lepidocyclina-Operculina-Ditrupa assemblage zone Asmari Formation: Microfacies, paleoenvironment and depositional sequence 59

Figure 3. Schematic section showing the stratigraphic position of the Asmari Formation within the Cenozoic rocks of southwestern Iran (Motiei, 2001). of Laursen et al. (2009) (Table 1) and is attributed to the components and textures. The general environmental inter- Chattian time. pretations of the microfacies are discussed in the following Assemblage 2. This assemblage is present in paragraphs. Dehluran (Section 1) and Kabirkuh-Darrehshahr (section 2) areas. The most diagnostic species in both studied sections include: Miogypsina sp., Elphidium sp. 14, Microfacies A. Stromatolitic boundstone (Figure 5.1) Lepidocyclina sp., Operculina complanata, Austrotrillina sp., Austrotrillina asmaricus, Peneroplis sp., Peneroplis This microfacies, with finely or moderately crinkled thomasi , Triloculina trigonula, Miogypsinoides sp., Borelis horizontal lamination, consists of alternating calcilutitic sp., Meandropsina iranica, Meandropsina anahensis, laminae and calcisiltic bioclastic laminae. Microfacies A is Dendritina rangi, Amphistegina sp., miliolids, Discorbis only present at Dehluran area (Section 1) and intercalates sp., Valvulinid sp. and Neorotalia viennoti. This assem- with mudstone facies. blage corresponds to the Miogypsina–Elphidium sp. 14- Interpretation. This facies type is common in tidal Peneroplis farsensis assemblage zone of Laursen et al. flat sediments (Flügel, 2004; Hardie, 1986; Steinhauff and (2009) (Table 1). The assemblage is considered to be Walker, 1996; Lasemi, 1995; Hernández-Romano, 1999; Aquitanian in age. Aguilera-Franco and Hernández-Romano, 2004). Today, Assemblage 3. This assemblage is recordable in flat laminated structures of microbial origin are found in all studied sections and consists of Borelis melo curdica, intertidal settings. In regions with an arid climate (e.g., Borelis sp., Peneroplis sp., Neorotalia sp., Elphidium sp., Persian Gulf or Shark Bay) stromatolites with smooth mats Meandropsina iranica, Dendritina rangi, Dendritina sp., are located in the lower intertidal zone (Davies, 1970a, miliolids, Discorbis sp. and globigerinids. The assemblage 1970b; Kinsman and Park, 1976; Hoffman, 1976). represents the Borelis melo curdica-Borelis melo melo assemblage zone of Burdigalian age (Laursen et al., 2009). Microfacies B. Fenestrate mudstone (Figure 5.2)

MICROFACIES ANALYSIS This facies consists of fine grained microcrystalline limestone. Bioclasts are lacking and the fenestrate struc- Facies analysis of the Asmari Formation in the study tures are well developed. Microfacies B was identified at areas resulted in the definition of thirteen facies types Kabirkuh-Darrehshahr area (Section 2) and mostly occurs (Figure 5), which characterize platform development. Each with quartz mudstone. of the microfacies exhibits typical skeletal and non-skeletal Interpretation. Fenestrate structures are typical prod- 60 Vaziri-Moghaddam et al.

Figure 4. Outcrop photographs of three of the studied sections. Stratigraphic sections related to these outcrops are shown in Figure 13. a: Dehluran section (Pabdeh, Asmari and Gachsaran formations). b: Dehluran section (Pabdeh Formation, lower and upper Kalhur Member and Asmari Formation). c: Kabirkuh-Darreshahr section (Pabdeh, Asmari and Gachsaran formations). d: Mamulan section (Shahbazan, Asmari and Gachsaran formations).

ucts of shrinkage and expansion, gas bubbles, and air escape Microfacies C. Mudstone (Figures 5.3 and 5.4) during flooding, or may even result from burrowing activity of worms or insects. Shinn (1983) considered similar facies This microfacies is composed of dense lime mud- representative of a tidal flat environment, where trapped air stones. Sediments also contain sparse unidentified fauna. In between irregularly-shaped deposits leads to the develop- some samples, subordinate amounts of detrital quartz grains ment of birdseyes. and gypsum are also present. This facies occurs in middle Asmari Formation: Microfacies, paleoenvironment and depositional sequence 61 and upper parts of the Asmari Formation. Microfacies C Table 1. Distribution of foraminiferal assemblages in the Asmari Formation occurs at Dehluran (Section 1), Kabirkuh-Darrehshahr (refer to Figure 1 for locations). (Section 2) and Mamulan (Section 3) areas. It is either next Biozones Age/Epoch Sec. 1 Sec. 2 Sec. 3 Sec. 4 to anhydrite or intercalates with lagoonal facies. (Laursen et al., 2009) Interpretation. Lime mudstone, with gypsum blades Borelis melo curdica- Burdigalian ● ● ● ● and small quartz grains and no evidence of subaerial expo- Borelis melo melo Ass. sure, was deposited in a restricted shelf lagoon. This facies Zone indicates hypersaline conditions within a shelf lagoon. Miogypsina- Elphidium sp. Aquitanian ● ● 14 - Peneroplis farsensis Ass. Zone Microfacies D. Anhydrite (Figure 5.5) Lepidocyclina- Chattian ● Operculina- Ditrupa Ass. Zone Anhydrite facies have been observed in the upper part of the Pabdeh Formation and in the lower part of the Asmari Formation. The first anhydrite deposit is surrounded by and soft muddy substrate (Geel, 2000; Romero et al., 2002; marly limestones containing pelagic fauna. There is a sharp Corda and Brandano, 2003; Vaziri-Moghaddam et al., 2006; contact with the carbonates above and below. The second Bassi et al., 2007). anhydrite deposit is intercalated between shallow water carbonates. Microfacies D is only present at Dehluran area (Section 1) and mostly associates with mudstone facies. Microfacies F. Bioclastic rotaliids miliolids bioclast Interpretation. Considering the thickness of the anhy- wackestone-packstone (Figure 5.7) drite deposits, their vertical stacking and lateral continuity, it is assumed that they are submarine deposits formed in an Skeletal grains consist of diverse fauna, includ- isolated saline basin. The deposition of anhydrite implicates ing benthic foraminifera (miliolids, rotaliids), echinoid, that the depositional environment became isolated from the corallinacean and bivalve fragments. Texture varies from open ocean at that time, which allowed for the concentration wackestone to packstone. Microfacies F was identified at and submarine precipitation of salt. An eustatic sea level Dehluran (Section 1), Kabirkuh-Darrehshahr (Section 2) drop is invoked as the most likely cause. This event took and Mamulan (Section 3) areas. place around the Oligocene-Miocene boundary. Ehrenberg Interpretation. The co-occurrence of normal marine et al. (2007) noted that strontium dates obtained from anhydrite in the Asmari Formation were close to the expected biota such as rotaliids, corallinaceans and echinoids with depositional ages and suggested that the anhydrite formed lagoonal biota such as miliolids, indicates that sedimentation as an evaporate rather than as a later diagenetic product. took place in an open shelf lagoon. A similar facies with imperforate foraminifers and perforate foraminifers was reported from the inner ramp of the Oligocene-Miocene Microfacies E. Dendritina miliolids peloids sediments of the Zagros basin (Vaziri-Moghaddam et al., wackestone-packstone-grainstone (Figure 5.6) 2006).

Identifiable components of this facies include benthic imperforate foraminifera (Dendritina and miliolids) and Microfacies G. Bioclastic miliolids coral floatstone- peloids. Borelis, bivalves and gastropods (whole shell and rudstone (Figure 5.8) broken fragments) are less common. The grains are poorly to medium sorted, are fine-to medium size and vary from This facies is predominantly composed of miliolids sub-angular to semi-rounded. Textures are dominantly pack- and corallite fragments or fragments of coral colonies. stone, but range from wackestone to grainstone. In some Additional components are echinoderm fragments, recrys- samples, the predominant non-skeletal carbonate grains tallized bivalve fragments and small benthic foraminifers are intraclasts. Microfacies E is present in all sections and (Austratrillina and Dendritina). Grains are poorly sorted and mostly intercalates with open lagoonal facies. are medium to coarse sand to granule in size. Microfacies Interpretation. This facies was deposited in a restricted G is present at Kabirkuh-Darrehshahr (Section 2) and shelf lagoon. The restricted condition is suggested by the Mamulan (Section 3) areas. rare to absent normal marine biota and abundant skeletal Interpretation. Co-occurrence of normal marine components of restricted biota (imperforate foraminifera (perforate foraminifera and corals) and platform-interior such as miliolids and Dendritina). The subtidal origin is (imperforate foraminifera) components in facies F and G supported by the lack of subaerial exposure and stratigraphic suggests the absence of an effective barrier. Restricted shelf position. This microfacies represents the shallowest upper organisms are effectively separated from the normal marine part of the photic zone, with very light, highly translucent environment by barriers. 62 Vaziri-Moghaddam et al.

Figure 5. Microfacies types of the Asmari Formation. 1: Stromatolitic boundstone, microfacies A (Sample No. O37, Dehluran section). 2: Fenestrate mudstone, microfacies B (Sample No. M 122, Kabirkuh-Darreshahr section). 3: Mudstone, microfacies C (Sample No. M119, Kabirkuh-Darreshahr section). 4: Mudstone with gypsum, microfacies C (Sample No. O79, Dehluran section), G: gypsum. 5: Anhydrite, microfacies D (Sample No. O20, Dehluran section). 6: Dentritina miliolid peloid grainstone, microfacies E (Sample No. M73, Kabirkuh-Darreshahr section). M: miliolids, P: peloid, D: Dendritina and G: gastropod. 7: Rotaliids miliolids bioclast packstone, microfacies F (Sample No. O40, Dehluran section), R: rotaliids, M: miliolids, B: bivalve and E: echinoid. 8: Miliolids coral bioclast rudstone, microfacies G (Sample No. M82, Kabirkuh-Darreshahr section), C: coral, B: bivalve, M: miliolids, and CR: corallinacea.

Microfacies H. Bioclastic ooids packstone-grainstone and within the storm wave base. Open marine, well-oxygen- (Figure 5.9) ated conditions are indicated by the diverse fauna. A similar microfacies was reported by Wilson (1975), Longman The predominant grain types are skeletal fragments (1981), Flügel (1982), Riding et al. (1991), and Melim and and ooids. Biotic grain types include echinid and gastropods. Scholle (1995). Ooid nuclei consist of recrystallized bivalve fragments, miliolids and rotaliids, with oval, circular or elongate outlines. Grains are fine- to coarse-sand size and sorting is moderate. Microfacies J. Bioclastic Miogypsina corallinacean Microfacies H was only identified at Kabirkuh-Darrehshahr wackestone-packstone (Figures 5.12 and 5.13) area (Section 2) and mostly intercalates with imperforated coral rudstone to bioclastic Miogypsina corallinacea pack- A diverse assemblage of poorly to moderately sorted, stone facies. fragmented and whole fossils in lime mud is characteristic Interpretation. The features of this facies indicate of this microfacies. Miogypsina and corallinacean fragments moderate to high energy shallow waters with much move- are the dominant bioclasts. Less common bioclasts include ment and reworking of bioclasts and the production of ooids. bryozoan and fragments of recrystallized bivalves and echi- Sediments are interpreted to have been deposited in sand noderm. In a few samples with increasing nummulitids, the shoal (Wilson, 1975; Flügel, 2004). name of this microfacies changes to bioclast nummulitids corallinacean wackestone-packstone. Microfacies J was identified at Dehluran (Section 1), Kabirkuh-Darrehshahr Microfacies I. Bioclastic corallinacean coral (Section 2) and Sepid Dasht (Section 4) areas and interca- floatstone-rudstone (Figures 5.10 and 11) lates with open marine facies. Interpretation. The presence of high diverse steno- The main characteristic of this microfacies is abundant haline fauna such as red algae, bryozoan, echinoid and fragments of corallinacean and corals. Echinoid and bryo- larger foraminifera (Miogypsina and nummulitids) indi- zoan fragments are also present. The fragments are coarse cate that the sedimentary environment was situated in the sand to granule in size. Due to changes in the type of fauna oligophotic zone in a shallow open marine environment or in some samples, the name of this facies changes to bio- near a fair-water wave base on the proximal middle shelf clastic Miogypsina coral floatstone-rudstone. Microfacies (Pomar, 2001a, 2001b; Brandano and Corda, 2002; Corda I referred to Sepid Dasht (Section 4) and mostly interca- and Brandano, 2003; Cosovic et al., 2004). In open marine, lates with bioclastic Miogypsina foraminifera corallinacea shallow waters, foraminifera produce robust, ovate tests wackestone-packstone. with thick walls, as a protection against photo inhibition of Interpretation. This facies is interpreted as an open symbiotic algae inside the test in bright sunlight, and/or as marine facies that formed seaward of the platform margin a protection against test damage in turbulent water. Asmari Formation: Microfacies, paleoenvironment and depositional sequence 63

Figure 5 (continued). 9: Bioclastic ooids packstone-grainstone, microfacies H (Sample No. M78, Kabirkuh-Darreshahr section), O: ooid and S: shell fragment. 10: Corallinacean coral bioclast floatstone, microfacies I (Samples No. T26, Sepid-Dasht section), CR: corallinacea and C: coral. 11: Miogypsina coral bioclast floatstone-rudstone, microfacies I, (Sample No. T75, Sepid-Dasht section), M:Miogypsina , C: coral. 12: Miogypsina corallinacean bioclast packstone, microfacies J (Samples No. M61, Kabirkuh-Darreshahr section), M: Miogypsina, S: shell fragment, and CR: corallinacea. 13: Bioclast nummulitids corallinacean, Microfacies J, (Sample No. O10, Dehluran section), N: nummulitids and CR: corallinacea. 14: Lepidocyclinids nummulitids bioclast wackestone-packstone, microfacies K (Sample No. M48, Kabirkuh-Darreshahr section), L: lepidocyclinids, N: nummulitids 15: Planktonic foraminifera lepidocyclinids bioclast packstone, microfacies L (Sample No. M5, Kabirkuh-Darreshahr section), P: planktonic foraminifera and L: lepidocyclinids. 16: Bioclastic planktonic foraminifera wackestone, microfacies M (Sample No. O3, Dehluran section), P: planktonic foraminifera and E: echinoid.

Microfacies K. Bioclastic lepidocyclinids nummulitids entire tests of planktonic foraminifers. Bioclasts are angular wackestone-packstone (Figure 5.14) to rounded and size ranges from silt to granule. Bioclastic planktonic foraminifera nummulitids wackestone-packstone The main components are bioclasts and large perfo- and bioclastic planktonic foraminifera Miogypsina wacke- rate foraminifera. Bioclasts include bivalve, corallinacean stone-packstone are similar to the microfacies described (including articulated and crustose fragments), echinoderm above in overall character, but differ from each other by and bryozoan fragments. The foraminifera are character- their larger foraminifera. Microfacies L occurs at Kabirkuh- ized by a relatively diverse assemblage of nummulitids Darrehshahr (Section 2) and Sepid Dasht (Section 4) areas (Operculina, Hetorestegina and Spiroclypeus) and lepidocy- and intercalates with bioclastic planktonic foraminifera clinids (Eulepidina and Nephrolepidina). This facies is most wackestone facies. prominent in lower parts of the Asmari Formation. Grains Interpretation. In general, the observed higher faunal are coarse sand to granule in size and are in a fine-grained diversity and the associated benthic foraminifers (lepido- carbonate matrix. Fragmentation of larger foraminifera is cyclinids, nummulitids and Miogypsina) and planktonic rare. In a few samples, Amphistegina are more or less equal foraminifers, as well as bioclasts, indicate an open marine to lepidocyclinids in abundance, therefore, the name of the environment. Poorly washed matrix and mud-supported microfacies changes to bioclast Amphistegina nummulitids textures suggest environments below wave-base influenced wackestone-packstone. Microfacies K referred to Kabirkuh- by bottom-currents (Geel, 2000; Vaziri-Moghaddam et al., Darrehshahr (Section 2), Mamulan (Section 3) and Sepid 2006; Amirshahkarami et al., 2007a). Dasht (Section 4) areas. Interpretation. The presence of large flat lepidocyclinids and nummulitids indicate that sedimentation took place Microfacies M. Bioclastic planktonic foraminifera in relatively deep water. Flatter test and thinner walls with wackestone (Figure 5.16) increasing water depth reflect the decreased light levels at greater depths (Geel, 2000; Beavington and Racey, 2004; In this microfacies, planktonic foraminifera are the Nebelsick et al., 2005; Bassi et al., 2007; Barattolo et al., dominant biotic components, but fine fragments of bryozoan 2007). and echinoid are also present. The planktonic foraminifers include non-keeled globorotalids and globigerinids. Some planktonic tests are filled with sparry cement. This facies Microfacies L. Bioclastic planktonic foraminifera occurs mostly in lower parts of the Asmari Formaton in lepidocyclinids wackestone-packstone (Figure 5.15) most sections; however, it is recorded in the upper part of the formation at Sepid-Dasht area. Microfacies M is present The most frequent skeletal components of this mi- at Dehluran (Section 1), Kabirkuh-Darrehshahr (Section 2) crofacies are test fragments of echinoids, bryozoan, coral- and Sepid Dasht (Section 4) areas. linacean, larger benthic foraminifera (lepidocyclinids) and Interpretation. The general lack of sedimentary struc- 64 Vaziri-Moghaddam et al. tures, the fine-grained character, and the presence of undis- open lagoon and protected lagoon. In the restricted lagoon turbed whole fossils from planktonic foraminifera suggest environment, the faunal diversity is low and the normal that this facies was deposited in calm, deep, normal-salin- marine fauna are lacking, except for imperforate benthic ity water (Buxton and Pedley, 1989; Cosovic et al., 2004; foraminifera (miliolids, Dendritina, borelisids), which Flügel, 2004). indicates quiet, sheltered conditions. A large number of por- cellaneous imperforate foraminifera points to the presence of slightly hypersaline waters (Geel, 2000). Open lagoonal SEDIMENTARY MODEL conditions are characterized by mixed open marine fauna (such as red algae, echinoids and perforate foraminifera) The recognized microfacies have allowed the and protected environment fauna (such as miliolids). The differentiation of several carbonate marine system shallow subtidal environment above the fair-weather wave environments including tidal flat, restricted lagoon, open base is characterized by the presence of a facies associa- lagoon, shoal, slope and basin. These six depositional tion showing signs of long-term water agitation (packing, environments of the Oligocene-Miocene in the study area sorting, poor taphonomic preservation and ooids). Such are similar to those found in many modern carbonate high-energy deposits are typically associated with carbonate depositional settings (Read, 1985; Jones and Desrochers, shoals on carbonate platforms (Figure 6). 1992). Of these, the Persian Gulf is perhaps the best modern During the Chattian, outer ramp facies (Pabdeh analogue for inference of ancient water depths, because it Formation) was predominant at the Dehluran area (Section shares many similarities with the Zagros foreland basin 1, Figure 7). Simultaneously, outer to middle ramp condi- during the Oligocene-Miocene. Therefore, sedimentological tions occurred at the Kabirkuh-Darrehshahr area (Section and paleontological studies show that a ramp type carbonate 2). The Dehluran area was experiencing outer-middle ramp platform sedimentary model can be fully applied to these conditions during the Early Aquitanian. At the same time, ancient carbonate deposits (Read, 1982; Tucker, 1985; sedimentation at the Kabirkuh-Drarrehshahr area took placed Tucker and Wright, 1990). According to Burchette and in the middle and inner ramp environments. These areas Wright (1992), carbonate ramp environments are separated experienced inner ramp (mostly lagoon sub-environment) into inner ramp, middle ramp and outer ramp. Outer ramp condition during the Late Aquitanian (Figure 7). Eastern facies are characterized by marl and marly limestone parts of the study area (Mamulan and Sepid Dasht were lithologies. Wackestones predominate with abundant sites of non-deposition or erosion during Chattian through planktonic foraminifera. The presence of mud-supported Aquitanian. In Mamulan area (section 3), middle and inner textures and the apparent absence of wave and current ramp environments prevailed through Burdigalian, whereas structures suggest a low energy environment below storm middle and outer ramp conditions were predominant in Sepid wave base (Burchette and Wright, 1992). Dasht area (section 4) during the Burdigalian (Figure 7). Larger perforate foraminifera are abundant biogenic components of the shallow water carbonate succession in the Asmari Formation. A proliferation of perforate SEQUENCE STRATIGRAPHY foraminifera is indicative of normal marine conditions (Geel, 2000). The lack of abrasion of the foraminifera The studied succession can be framed in a sequence indicates autochthonous accumulations, thus wackestone- stratigraphic context. As a guide, we used the principal se- packstone with lepidocyclinids and nummulitids were quence stratigraphic concepts developed by many workers deposited under low energy conditions, below fair weather (e.g., Sarg, 1988, Posamentier et al., 1988; Van Wagoner et wave base (FWWB) and above storm wave base (SWB) al., 1988, 1990, Read and Hrbury, 1993; Emery and Myers, in the middle ramp setting. The variation in the shape 1996; Coe and Church, 2003; Catuneanu, 2006) to recognize of the test reflects the differences in water depth. The TST (transgressive systems tract), mfs (maximum flood- sediments with perforate robust and ovate specimens reflect ing surface), HST (highstand systems tract) and sequence the presence of shallower water than those containing boundaries. large and flat lepidocyclinids and nummulitids. Larger Based on the distribution of planktonic and benthonic foraminifera are limited geographically to temperate to foraminifera, and on the detailed sedimentological and strati- tropical/subtropical environments (Hohenegger et al., 2000; graphical study, we defined four third-order sequences. Langer and Hottinger, 2000). The common association of symbiotic algae with perforate foraminifera implies that light is a main factor in Sequence 1 determining the depth distribution (Hansen and Buchardet, 1977; Hallock, 1979, 1981; Bignot, 1985; Hallock and The depositional sequence 1 is present in sections 1 Glenn, 1986). (Dehluran, 17 m thick) and 2 (Kabirkuh-Darrehshahr, 60 Inner ramp deposits represent a wider spectrum of m thick) of the study area (Figures 8 and 9). The sediments marginal marine deposits, indicating high-energy shoal, of sequence 1 are Chattian in age. Sequence 1 includes Asmari Formation: Microfacies, paleoenvironment and depositional sequence 65

Figure 6. Depositional model for the carbonate platform of the Asmari Formation at the northwest of Zagros basin. Interpretation adopted from Hottinger (1997), Pomar (2001b) and Rasser and Nebelsick (2003). FWWB: Fair weather wave base; SWB: Storm wave base; A-M: facies defined in Figures 8-11. the upper part of the Pabdeh Formation at Dehluran area, planktonic foraminifera and document a deep-subtidal, low whereas at Kabirkuh-Darrehshahr area it encompasses the energy environment during the TST. The maximum flood- upper part of the Pabdeh Formation and the lower part of the ing surface (mfs) coincides with the boundary between the Asmari Formation. At Dehluran area, TST and HST could Pabdeh and Asmari formations. The highstand systems tract not be differentiated because the relatively uniform deep (HST) comprises the lower part of the Asmari Formation. sub-tidal succession is composed of planktonic foramin- The early HST was characterized by constant shallow open ifera wackestone without distinct changes in microfacies. marine environmental conditions (wackestone-packstone TST was clearly recognized at Kabirkuh-Darrehshahr area. with perforate foraminifera). The late HST shows a trend Shale and marly limestone of the TST contain abundant toward more protected sediments (wackestone-packstone der or d : (Dehluran) r iime Unit sequence 3 T Darreshahr) Duration (M.a.) Section 2: (Kabirkuh - Section 1 Section 3: (Mamulan) Section 4: (Sepid Dasht)

2.0 4

BURDIGALIAN m.

V V V V

1.3 3 V i F i ANIAN ......

M I O C E N ......

V V V

AQUIT 2.4 2 V

V V V V As m a r a m As TTIAN A IGOCENE 2.6 1 B CHA OL P a b d e h F m. S h a h b a z a n F m.

3583000 3583000 888000 Sequence Stratigraphy Asmari Formation

1000 Faunal Assemblages 61 A Agg Aggradation: Ramp Tehran I R A N Khoramabad : Borelis melo group - Meandropsina iranica T TST : Transgressive systems tract Inner Outer Middle L LST : Lowstand systems tract 3 : Elphidium sp. 14 - Miogypsina

SB SB : Sequence boundary Anhydrite 4 Non deposition LH 2 Pabdeh Formation A: Eulepidina - Nephrolepidina - Nummulites

LHST : Late highstand systems tract Bar Shahbazan Formation Open idal-flat HST 888000 Marine Lagoon T

EH EHST : Early highstand systems tract V 1 V . . B: Globigerina spp.

1000 V .

. .

61 V . . mfs mfs : maximum flooding surface . . 0 20 50 km . . 3773000 3773000 Figure 7. Chronostratigraphic scheme for the Asmari Formation across the northwestern part of the Zagros basin. Correlation of depositional environments, biozones and third-order sequences across the study area is shown (see text for explanations). Deposition of the Asmari Formation started earlier in the southwest, in a deeper environment (over the Pabdeh Formation) and continued in a relatively shallower environment. The Asmari Formation is younger to the east. 66 Vaziri-Moghaddam et al. with imperforate foraminifera), expressing a filling of the accommodation space. The sequence boundary is charac- LITHOLOGY Microfacies terized by abrupt facies changes from subtidal-lagoonal to

ime Units tidal flat environments. Such changes reflect a significant Formation T Tidal

Sequence Open Biozones flat Lagoon decrease in water depth (Figures 8 and 9). Stratigraphy marine Sample No. Age

Epoch

V V A C D E F J M

O102 V V O101 Gachsaran O100 O99 SB1 O 98 O97 O96 Sequence 2 O95

O94

O93 O92

O91 O90 The depositional sequence 2 formed during the late elis melo O89 O88 Chattian-early Aquitanian transgression. At Dehluran area,

O87 O86

U p p e r e p p U O85 dica - Bor O84 this sequence is 21 m thick, (Figure 8), and begins with 9 O83 O82 O81 O80 assemblage zone O79 m-thick sediments of the anhydrite facies. These are inter- O78 ~ ~ 77 B u r d i g a l i a n a i l a g i d r u B O O76 75

elis melo cur O ~ preted as the lowstand systems tract (LST) of this sequence. ~ ~ O74 Bor O73 O72 The contact between the LST and the basinal deposits with O71 O70 O69 O68

R I R pelagic fauna (Pabdeh Formation) below is sharp. At this O67 O66 section, the TST and HST comprise an 11 m-thick, monoto- O65 ~ ~ ~ O64 nous succession of open marine deposits, demonstrating O63 A O62 O61 ~ ~ ~ that prograding shallow-water sediments did not reach far O60

O59 A O58 west. At Kabirkuh-Darrehshahr area, 130/5 m thick (Figure

O57 O56

O55 9), the vertical variations in the facies during the transgres- ~ ~ ~ O54

assemblage zone assemblage O53 O52 sion are different from those described in sequence 1. An O51 . . . . O50 O49 increase in third-order accommodation space is indicated O48 O47 ~ ~ O46 by shallow lagoonal facies overlain by shallow-open marine ~ ~

oplis farsensis oplis O45 ~ ~ O44 facies. Wackestone with abundant planktonic foraminifers O43

M i d d l e l d d i M O42

- Pener - O41

q u i t a n i a n a i n a t i u q represent deep-water facies; this is, therefore, interpreted as

O40 V

V A

M I O C E N E N E C O I M O39 ~

38 V O V

sp.14 ~ ~ the mfs. An upward-shallowing facies trend (HST) is indi- V

O37 ~V SSBB2

S M S ~ ~

V O36 V ~ ~

O35 cated by shallow open marine gradational facies, overlain O34

V O33 V

O32 ~ V

O31 ~ ~

V by shallow-lagoonal facies (Figures 8 and 9). V

O30 ~ ~V ~ O29 A

~ ~

O28 V

V O27 V

O26

V V

A O25

Miogypsina - Elphidium - Miogypsina V

O24 V

V V

O23 V Sequence 3

O22 V

V V

V L

O21 V

V V

O20 V

V V V

O19 V This sequence is late Aquitanian in age and is pres-

V V O18 ~ ~ ent in Dehluran area (48/5 m thick) and in Kabirkuh- O17 ~

16 V

O V SB2 O15 ~ ~ O14 ~ ~ Darrehshahr area (14/5 m thick). At Dehluran (Figure O13 ~ ~ O12 ~ ~ ~ A O11 ~ 8), the lowstand deposits of this sequence consist of a

~ ~

V O10 V

O9 V V

V well developed anhydrite. A temporary isolation of the

O8 V L V

O7 V V sedimentary environment would be necessary in order to be O6 ~ SB2 ass. zone ass. ~ ~ O5 ~ ~ ~ ~ able to precipitate the anhydrite. At the base, the anhydrite O4 ~ ~ 10 m ~ Pabdeh ~ ~ O3 I G O C E N E N E C O G I ~ ~ ~ is homogenous, but passes up into a more heterogenous C h a t t i a n a i t t a h C O2 T ~ ~

O1 Globigerina

O L O ~ ~ ~ composition and interdigitates with shallow water carbon- ~ 0 ~ ates. The sea level transgression caused the deposition of Lithology

Limestone Dolomitic limestone shallow subtidal facies within an aggradational staking

V V

Calcareous dolomite V Anhydrite/gypsum Sequence Stratigraphy pattern in Dehluran and Kabirkuh-Darrehshahr areas. The V

V ~ ~ ~

V ~ ~ Anhydritic limestone ~ ~ Marl A Agg Aggradation:

V sequence boundary is characterized at the top by stromato- V

V Anhydritic dolomite Dolomite T TST : Transgressive systems tract Argillaceous limestone Shale litic boundstone (Dehluran area) and mudstone with quartz LST : Lowstand systems tract L SB : Sequence boundary (Kabirkuh-Darrehshahr area), which marks the end of a Facies SB LH LHST : Late highstand systems tract A. Stromatolitic boundstone HST shallowing-upward trend (Figures 8 and 9). C. Mudstone EH EHST : Early highstand systems tract D. Anhydrite The development of a long, narrow, evaporitic in- E. Dendritina miliolids peloid wackestone-packstone-grainstone mfs mfs : maximum flooding surface F. Bioclastic rotaliids miliolids wackestone-packstone tra-basin, during the latest Oligocene-earliest Miocene J. Bioclastic nummulitidae corallinacean wackestone-packstone M. Bioclastic pelagic foraminifera wackestone (Chattian-Aquitanian) likely indicates an abrupt facies change (both laterally and vertically), which seems to Figure 8. Microfacies and sequence stratigraphy of the Asmari Formation at Dehluran area (Section 1). TST: transgressive systems tract; LST: lowstand be difficult to interpret simply by eustasy or any sedi- systems tract; Agg: aggradation; SB1 and SB2: sequence boundaries. mentological process alone, without any tectonic control (Ahmadhadi et al., 2007). An abrupt facies change from Asmari Formation: Microfacies, paleoenvironment and depositional sequence 67 marls to evaporites suggests a direct relationship between out. Ahmadhadi et al. (2007), suggest that the genesis of this this restricted intra-basin lagoon and the deep-seated base- sub-basin has been, at least, partly tectonically controlled. ment faults. Nevertheless, eustatic control cannot be ruled

Sequence 4

LITHOLOGY Microfacies The sequence 4 is present in all sections (Dehluran,

ime Units 117/5; Kabirkuh-Darrehshahr, 55; Mamulan, 69/5; and Formation

T Lagoon - Open

Bar Sequence

Biozones Tidal flat marine Stratigraphy

Sample No. Sepid Dasht, 82/5 m thick). Age

Epoch B C E F G H J K L M V

V The lower boundary of Sequence 4 in Dehluran and

V V

Gachsaran V M 126 SB1 M 125

dica - 124 Kabirkuh-Darrehshahr areas is characterized by a type 2 M

M 123

M 122

ass. zone Upper B. melo M 121

B. melo cur Burdigalian M 120 sequence boundary (Figures 8 and 9), whereas in Mamulan,

M 119

M 118 (section 3) and Sepid Dasht, (section 4) areas it is defined M 117

M 116 M 115 M 114 M 113 by a type 1 sequence boundary (Figures 10 and 11). A long M 112 A M 111

M 110 period of lagoonal conditions reflecting a balanced situation

M 109

M 108

M 107 between accommodation and sedimentation characterizes

M 106

M 105 M 104 the sequence 4 in Dehluran and Kabirkuh-Darrehshahr M 103 M 102 SSBB2 M 101 M 100 99

oplis farsensis M

M 98 R I R M 97 A ~ ~ M 96 ~ ~ ~ ~

Pener M SSBB2 M 94

M 93 M 92 M 91 sp.14 - M 90 M 89 ~ ~ ~ ~ M 88 ~ M 87 Microfacies M 86 M 85 ~ ~ LITHOLOGY ~

A M 84

M 83 assemblage zone

M 82 M I O C E N E N E C O I M

M i d d l e l d d i M M 81

M 80 q u i t a n i a n a i n a t i u q M 79

M 78 ime Units

M 77 Formation T M 76

M 75 A

M 74 ~ ~ ~ Sequence M 73 Biozones M 72 Open Sample No. Stratigraphy Lagoon M 71 M 70 marine

M 69

M 68 Age M 67 M 66 Epoch C E F G K Miogypsina - Elphidium

M 65 ~ ~ M 64 ~

~ V

M 63 Gachsaran V ~ ~

M 62 V ~

V ~ V M 61 M 60 M 59 L113 SB M 58 1 M 57 L112 M 56 L111 M 55

S M S L110 M 54 M 53 L109 M 52 L108 H M 51 L107 M 50 L106 M 49 L105 M 48 M 47 L104 M 46 L103 M 45 mfs ~ ~ L102 ~ ~ ~ 101 ~ L Covered~ ~ L100 ~ ~ ~ ~ ~ ~ L99 M 44 ~ ~ ~ mfs A 98 ~ ~ L ~ ~

~ I R

M 43 elis melo L97

M 42 A L96

M 41 M 40 T L95 M 39 L94 ~ ~ ~ L93 M 38 ~ ~ ~ L92 M 37 M S

dica - Bor M I O C E N E N E C O I M 91 T M 36 L

M 35 SB2 A U p p e r e p p U L90 M 34 ~ Covered ~ assemblage zone ~ L89 M 33 M 32 culina - Ditrupa L88 M 31

M 30 B u r d i g a l i a n a i l a g i d r u B M 29 L87 M 28 M 27 M 26 Covered~ ~ L86 ~ ~ ~ ~ M 25 LH L85 elis melo cur 24 84 o w e r e w o M L ~

~ ~ ~ L83 L

assemblage zone ~ Covered~ ~ Bor I G O C E N E N E C O G I ~ L82 M 23 L81 M 22 ~ Covered~ ~ ~ ~ L80 M 21 L79 M 20 C h a t t i a n a i t t a h C L78 M 19 L77 SB 1 M 18 EH M 17

Lepidocyclina - Oper 76 O L O L M 16

M 15 N M 14 ~ ~ L75 M 13 M 12 74 A L M 11 ~ ~ ~ M 10 73

Z L M 9 10 m L72 M 8

M 7 A L71 M 5, 6 L70 M 1, 2, 3, 4 ~ ~ ~ mfs 69 ~ ~ L ~

~ B H Pabdeh ~ ~ 0 T L68

L67

A E O C E N E N E C O E Lithology L66 10 m

L65 S H S Limestone Dolomitic limestone L64 L63 Sequence Stratigraphy L62

Calcareous dolomite Dolomite L61 S L60 ~ L59 ~ ~ Agg Aggradation: 0 ~ ~ A L58 Sandy limestone ~ ~ Marl Argillaceous limestone Shale T TST : Transgressive systems tract Lithology LST : Lowstand systems tract Sequence Stratigraphy Facies L Limestone

SB SB : Sequence boundary Dolomitic limestone Agg Aggradation:

V A

B. Mudstone with birdeye fabric V

V LH V C. Quartz mudstone LHST : Late highstand systems tract Calcareous dolomite Anhydrite / gypsum E. Dendritina miliolids peloid wackestone-packstone-grainstone HST EH EHST : Early highstand systems tract T TST : Transgressive systems tract F. Bioclastic rotaliids miliolids wackestone-packstone Dolomite G. Bioclastic miliolids coral rudstone LST : Lowstand systems tract mfs mfs : maximum flooding surface L SB : Sequence boundary H. Bioclastic ooid packstone-grainstone Facies SB J. Bioclastic Miogypsina corallinacean packstone C. Mudstone LH LHST : Late highstand systems tract K. Bioclastic Lepidocyclinidae nummulitidae packstone HST L. Bioclastic pelagic foraminifera lepidocyclinidae packstone E. Dendritina miliolids wackestone-packstone EH EHST : Early highstand systems tract M. Bioclastic pelagic foraminifera wackestone F. Bioclastic rotaliids miliolids wackestone-packstone G. Bioclastic miliolids coral rudstone mfs mfs : maximum flooding surface K. Bioclastic Amphistegina wackestone Figure 9. Microfacies and sequence stratigraphy of the Asmari Formation at Kabirkuh-Darreshahr area (Section 2). TST: transgressive systems Figure 10. Microfacies and sequence stratigraphy of the Asmari Formation tract; EHST; early highstand systems tract; LHST; late highstand systems at Mamulan area (Section 3). TST: transgressive systems tract; HST; tract; mfs: maximum flooding surface; Agg: aggradation; SB1 and SB2: highstand systems tract; mfs: maximum flooding surface; SB1 and SB2: sequence boundaries. sequence boundaries. 68 Vaziri-Moghaddam et al. facies with a rich planktonic foraminifera, perforate larger LITHOLOGY Microfacies benthic foraminifera, corallinacean and coral fragments. These sediments were characterized by constant open ime Units Formation T marine environmental conditions, representing constant

Biozones Sequence Sample No. Stratigraphy Open marine

Lagoon accommodation at Sepid Dasht area. Age Epoch E I J K L M Ehrenberg et al. (2007) recognized some surfaces in ~. ~ . . ~ .~ . RAZAK ~ well sections from the Bibi Hakimeh, Marun, and Ahwaz ~ . ~ . T77 SB 1

T76 S S

S oilfields and interpreted them as sequence boundaries (Ch T75

T74 S 20 SB, Ch 30 SB, Aq 10 SB, intra-Aq10 SB, Aq20/Bu10

S S T73 SB, Bu 20 SB). Because these sequence boundaries were T72 S not recognized in the study area, the sequence stratigraphy T71

T70 T69 S T68 of Ehrenberg et al. (2007) can not be confidently applied T67

T66

S R I R

T65 S T64 to these sections. T63 T62

T61 S T60 On the basis of facies changes (Figures 8 and 9), in T59

58 T S both sections (1 and 2), sequence boundaries recognized T57

T56

T55 in the upper part of the Chattian and the middle part of the S

T54 A T53 Aquitanian, may be associated with the Aq 10 and Aq20/Bu10 T52 elis melo T51 S sequence boundaries recognized by Ehrenberg et al. (2007).

T50 U p p e r e p p U T49

M I O C E N E N E C O I M T48 B u r d i g a l i a n a i l a g i d r u B The depositional sequences 1, 2 and 3 were observed T47

T46 T dica - Bor in Dehluran and Kabirkuh-Darrehshahr areas (sections 1 and T45

T44 T43 2), and are synchronous with a period of either erosion or T42

assemblage zone S T41 S T40 non-deposition represented by unconformities in Mamulan T39 T38 T37 T36 T35 elis melo cur and Sepid Dasht areas (sections 3 and 4) (Figures 7-12). T34 T33 S 32 T31T Bor T30

T29

T28 S M S

T27 CONCLUSIONS

T26

T25 S The Oligocene–Miocene Asmari Formation of the

T24

A Zagros basin is a thick sequence of shallow water carbon- T23

T22 S SB 1 ate. The outcrops of the Asmari Formation in northwest of T21 the Zagros (Dehluran, Kabirkuh- Darreshahr, Sepid Dasht T20

T19 and Mamulan areas) allow the recognition of different 10 m T18 depositional environments, on the basis of sedimentological

T17 E O C E N E N E C O E SHAHBAZAN T16 analysis, distribution of foraminifera and microfacies stud- T15 0 ies. These depositional environments correspond to inner, Lithology Sequence Stratigraphy middle and outer ramp. In the inner ramp, the most abundant

Dolomitic limestone Limestone V

V A Agg Aggradation: V V V Anhydrite / gypsum Dolomite lithofacies are medium-grained wackestone–packstone with ~ ~ ~ Marly limestone ~ T TST : Transgressive systems tract imperforated foraminifera. The middle ramp is represented LST : Lowstand systems tract Facies L SB : Sequence boundary E. Dendritina miliolids wackestone-packstone-grainstone SB by packstone–grainstone to floatstone with a diverse as- LH LHST : Late highstand systems tract I. Bioclastic corallinacean coral floatstone-rudstone HST J. Bioclastic Miogypsina corallinacean wackestone-packstone EH EHST : Early highstand systems tract semblage of larger foraminifera with perforate wall, red K. Bioclastic nummulitidae Amphistegina packstone L. Bioclastic pelagic foraminifera Miogypsina wackestone mfs mfs : maximum flooding surface algae, bryozoa, and echinoids. The outer ramp is dominated M. Bioclastic pelagic foraminifera wackestone by argillaceous wackestone characterized by planktonic Figure 11. Microfacies and sequence stratigraphy scheme of the Asmari Formation at Sepid-Dasht area (Section 4). TST: transgressive systems foraminifera and large and flat nummulitidae and lepido- tract; SB1 and SB2: sequence boundaries. cyclinidae. Four third-order sequences are identified on the basis of deepening and shallowing microfacies patterns and on the distribution of Oligocene-Miocene foraminifers. areas. Following the very shallow subtidal deposition of the uppermost part of the sequence 4 at Mamulan area, a clearly marine deepening occurred and led to the deposition ACKNOWLEDGMENTS of shallow lagoonal facies, forming a TST. The overlying wackestone-packstone with diverse fauna reflects a mfs, The authors wish to thank the National Iranian Oil and the beginning of deposition of a HST. The overlying Company Research and Development Management for their mfs, rich in imperforate foraminifera, have been deposited financial support and permission to publish this work. We in a calm and shallow-lagoonal environment; this part is also thank Dr. Mohammad Ali Emadi for his support and interpreted as a HST. Above type 1 sequence boundary thoughtful comments. The authors appreciate the National at Sepid Dasht area, there are limestones of open marine Iranian Oil Company Exploration Division for provid- Asmari Formation: Microfacies, paleoenvironment and depositional sequence 69

Section 1: (Dehluran) Section 2: (Kabirkuh- Darreshahr) Section 3: (Mamulan) Section 4: (Sepid Dasht)

LITHOLOGY LITHOLOGY LITHOLOGY LITHOLOGY ime Units ime Units ime Units ime Units Formation Formation Formation Formation

T T T T

Sequence

Stratigraphy

Stratigraphy Stratigraphy Age Age Age Age Epoch Epoch Epoch

Epoch

V V V

V ~

V ~. .

V ~

V ~ V ~ . ~

Gachsaran ~ .~ . V Gachsaran V SB Gachsaran ~ ~ ~

1 RAZAK . .

SB1 V ~ ~ ~ V

~ V SB 1

S S

SB 1 S

Upper Burdigalian

H S

S S

mfs S

S U p p e r e p p U

R I R S A

~ ~ S

I B u r d i g a l i a n a i l a g i d r u B

~ ~ ~

S M I O C E N E N E C O I M

R T

SSBB2

S M S

S U p p e r e p p U

R A

A A ~ ~ ~ ~

~ ~ I

SSBB2 S B u r d i g a l i a n a i l a g i d r u B

~ ~ r e p p U

~ M I O C E N E N E C O I M A n a i l a g i d r u B

~ ~ ~ ~ ~

A T ~ ~ ~ SB 1

~ ~ ~

M i d d l e l d d i M

q u i t a n i a n a i n a t i u q M I O C E N E N E C O I M ~ ~ ~

A ~ ~ ~ 10 m S . . . . M

SHAHBAZAN

E O C E N E N E C O E S M I O C E N E N E C O I M ~ ~ 0 ~ ~ M

~ ~

V V

M i d d l e l d d i M ~ V

~ V

~ A V

Aq u i t a n i a n a i n a t i u Aq ~V SSBB2

S ~ ~

V V ~ ~

S SB 1

V V

~ S V ~ ~

V ~ ~ V

~ ~V ~ ~ ~ ~ A ~ Covered~ ~ ~ ~

V ~ ~

V ~ V ~

V ~ ~ 10 m ~ ~ ~ mfs ~

V ~ ~ V ~

V V E N E C O E

SHAHBAZAN V

V T 0

V V

L A ~ ~ ~ V

V V ~ ~

V V V

V SB

V 2 V ~

Covered

V ~

V ~ V ~ ~

V SB2 Lithology Sequence Stratigraphy ~ ~ ~ ~ Covered~ ~ ~ ~ ~ ~ ~ ~ LH ~ ~ A Agg Aggradation:

~ r e w o A ~

~ ~ ~ ~ Conglomerate Limestone Dolomitic limestone

~ ~ L

V V

Covered~ V V

V ~ ~

~ V

V V

V V V L T ~

I G O C E N E N E C O G I Covered~ Sandstone Calcareous dolomite Anhydrite/gypsum

V TST : Transgressive systems tract

~ ~ ~

V V V n a i t t a h C ~ ~

V L LST : Lowstand systems tract ~ SB2 ~ ~ ~ EH Dolomite Anhydritic limestone ~ ~ Marl SB SB : Sequence boundary

~ ~ ~ V ~

~ ~ LH

V ~ ~ 10 m V ~ ~ LHST : Late highstand systems tract ~ ~ L O ~ ~ Anhydritic dolomite Sandy limestone Siltstone HST Pabdeh ~ ~ ~ 10 m I G O C E N E N E C O G I T EH EHST : Early highstand systems tract

~ ~ C h a t t i a n a i t t a h C ~ Sandy dolomite Argillaceous limestone Shale ~ ~ ~ ~ ~ mfs ~ ~ mfs : maximum flooding surface O L O ~ 0 ~ mfs ~ ~ Pabdeh ~ ~ 0 T

Figure 12. Sequence stratigraphy scheme for the Asmari Formation across northwest of the Zagros basin. Four third-order sequences in the Dehluran and Kabirkuh-Darrehshahr (Sections 1 and 2) and one third-order sequence in the Mamulan and Sepid Dasht (Sections 3 and 4) areas are shown. ing surface geological maps. Also we thanks the Revista Paleoenvironmental model and sequence stratigraphy of the Mexicana de Ciencias Geológicas reviewers for their con- Asmari Formation in southwest Iran: Historical Biology, 19(2), 173-183. structive comments. Amirshahkarami, M., Vaziri-Moghaddam, H., Taheri, A., 2007b, Sedimentary facies and sequence stratigraphy of the Asmari Formation at Chaman-Bolbol, Zagros Basin Iran: Journal of Asian Earth Sciences, 29(5-6), 947-959. REFERENCES Babaie, H.A., Ghazi, A.M., Babaei, A., La Tour, T.E., Hassanipak, A.A., 2001, Geochemistry of arc volcanic rocks of the Zagros crust zone, Adams, T.D., Bourgeois, F., 1967, Asmari biostratigraphy: Iranian Oil Neyriz, Iran: Journal of Asian Earth Sciences, 19(1-2), 61-76. Operating Companies, Geological and Exploration Division, Babaei, A., Babaie, H.A., Arvin, M., 2005, Tectonic evolution of the Report 1074. Neyriz ophiolite, Iran: an accretionary prism model: Ofioliti, Aguilera-Franco, N., Hernández-Romano, U., 2004, Cenomanian-Turonian 30(2), 65-74. facies succession in the Guerrero-Morelos Basin, Southern Babaie, H.A., Babaei, A., Ghazi, A.M., Arvin, M., 2006, Geochemical, Mexico: Sedimentary Geology, 170(3-4), 135–162. 40Ar/39Ar age, and isotopic data for crustal rocks of the Neyriz Ahmadhadi, F., Lacombe, O., Marc Daniel, J., 2007, Early reactivation ophiolite, Iran: Canadian Journal of Earth Sciences, 43(1), of basement faults in central Zagros (SW Iran), Evidence from 57-70. pre-folding fracture populations in Asmari Formation and Lower Barattolo, F., Bassi, D., Romero, R., 2007, Upper Eocene larger Tertiary paleogeography, in Lacombe, O., Lave, J., Roure, F., foraminiferal-coralline algal facies from the Klokova Mountain Verges, J., (eds.), Thrust Belts and Foreland Basins: Berlin, (south continental Greece): Facies, 53(3), 361-375. Springer, 205-228. Bassi, D., Hottinger, L. Nebelsick, H., 2007, Larger Foraminifera from Alavi, M., 2004, Regional stratigraphy of the Zagros fold-thrust belt of the Upper Oligocene of the Venetian area, northeast Italy: Iran and its proforeland evolution: American Journal of Sciences, Palaeontology, 5(4), 845-868. 304, 1-20. Beavington-Penney, S.J., Racey, A., 2004, Ecology of extant nummulitids Al-Husseini, M.I., 2000. Origin of the Arabian Plate structures: Amar and other larger benthic foraminifera. applications in Collision and Najd Rift: Geo Arabia, 5(4), 527-542. Paleoenvironmental analysis: Earth Science Review, 67(3-4), Amirshahkarami, M., Vaziri-Moghaddam, H., Taheri, A., 2007a, 219-265. 70 Vaziri-Moghaddam et al.

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