Sistema de rampa del Oligoceno–Mioceno (Formación Asmari) en el NW de la cuenca de Zagros, Irán: microfacies, paleoambiente y secuencia de depósito

Hossein Vaziri–Moghaddam^1,*, Ali Seyrafian¹, Azizolah Taheri², and Homayoon Motiei³

¹ Department of Geology, Faculty of Sciences, University of Isfahan, Isfahan, Iran, 81746–73441. *E–mail: avaziri7304@gmail.com.

² Geology Department, Faculty of Earth Science, Shahrood University of Technology, Shahroud, Iran.

³ National Iranian Oil Company Research and Development Division, Tehran, Iran.

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.

INTRODUCTION

This paper deals with the Asmari Formation, an Oligocene–Miocene carbonate succession in the northwestern Zagros basin, southwest Iran (Figure 1). The area is excellent to establish the geometrical relationship between sedimentary facies and sequence stratigraphy of a carbonate platform.

The Asmari Formation, a thick carbonate sequence of the Oligocene–Miocene, is one of the best known carbonate reservoirs in the world. It is present in most of the Zagros basin. Lithologically, the Asmari Formation consists of limestone, dolomitic limestone, dolomite and marly limestone. Some anhydrite (Kalhur Member) and lithic and limy sandstones (Ahwaz Member) also occur within the Asmari Formation (Motiei, 1993).

The Asmari Formation was originally defined in primary works by Busk and Mayo (1918), Richardson (1924), Van Boeck et al. (1929), and Thomas (1948). Later, James and Wynd (1965), Wynd (1965), Adams and Bourgeois (1967), Kalantary (1986), and Jalali (1987) introduced the microfaunal characteristics and assemblage zones for the Asmari Formation. More recent studies of the Asmari Formation have been conducted on biostratigraphic criteria (Seyrafian et al., 1996; Seyrafian and Mojikhalifeh, 2005; Hakimzadeh and Seyrafian, 2008; Laursen et al., 2009), microfacies and depositional environments (Seyrafian and Hamedani, 1998, 2003; Seyrafian, 2000) and depositional environment and sequence stratigraphy (Vaziri–Moghaddam et al., 2006; Amirshahkarami et al., 2007a, 2007b; Ehrenberg et al., 2007).

This paper reports on a sedimentological study of Asmari Fm. outcrops, whose results could contribute to a better understanding of the subsurface Asmari Formation in adjacent oilfield areas. The main objectives of this reseach were foused on (1) a description of the facies and their distribution on the Oligocene–Miocene carbonate platform, (2) the palaeoenvironmental reconstruction of the carbonate platform, and (3) the origin of sequences that developed in the study area mainly based on the distribution of the foraminifera.

GEOLOGICAL SETTING

Based on the sedimentary sequence, magmatism, metamorphism, structural setting and intensity of deformation, the Iranian Plateau has been subdivided into eight continental fragments, including Zagros, Sanandaj–Syrjan, Urumieh–Dokhtar, Central Iran, Alborz, Kopeh–Dagh, Lut, and Makran (Heydari et al, 2003; Figure 2). The study area is located in the northwestern part of the Zagros basin and include four sections: 1) Dehluran, 2) Kabirkuh–Darrehshahr, 3) Mamulam and 4) Sepid Dasht (Figure 1).

The Zagros basin is composed of a thick sedimentary sequence that covers the Precambrian basement formed during the Pan–African orogeny (Al–Husseini, 2000). The total thickness of the sedimentary column deposited above the Neoproterozoic Hormuz salt before the Neogene Zagros folding can reach over 8 to 10 km (Alavi, 2004; Sherkati and Letouzey, 2004). The Zagros basin has evolved through a number of different tectonic settings since the end of Precambrian. The basin was part of the stable Gondwana supercontinent in the Paleozoic, a passive margin in the Mesozoic, and became a convergent orogen in the Cenozoic.

During the Palaeozoic, Iran, Turkey and the Arabian plate (which now has the Zagros belt situated along its northeastern border) together with Afghanistan and India, made up the long, very wide and stable passive margin of Gondwana, which borderered the Paleo–Tethys Ocean to the north (Berberian and King, 1981).

By the Late Triassic, the Neo–Tethys ocean had opened up between Arabia (which included the present Zagros region as its northeastern margin) and Iran, with two different sedimentary basins on both sides of the ocean (Berberian and King, 1981).

The closure of the Neo–Tethys basin, mostly during the Late Cretaceous, was due to the convergence and northeast subduction of the Arabian plate beneath the Iranian sub–plate (Berberian and King, 1981; Stoneley, 1981; 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 of the Afro–Arabian plate (e.g., Babaie et al., 2001; Babaei et al., 2005; Babaie et al., 2006).

Continent–continent collision starting in the Cenozoic has led to the formation of the Zagros fold–and–thrust belt, continued shortening of the mountain range, and creation of the Zagros foreland basin. The Late Cretaceous to Miocene rocks represent deposits of the foreland basin prior to the Zagros orogeny, and subsequent incorporation into the colliding rock sequences. This sequence unconformably overlies Jurassic to Upper Cretaceous rocks.

Compressional folding began during or soon after the deposition of the Oligocene–Miocene Asmari Formation (Mapstone, 1978; Sepehr and Cosgrove, 2004).

During the Palaeocene and Eocene, the Pabdeh (pelagic marls and argillaceous limestones) and the Jahrum (shallow marine carbonates) formations were, respectively, deposited in the middle part and on both sides of the Zagros 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 interfingers 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.

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 sedimentologically 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; Hohenegger et al., 1999; Geel, 2000; Brandano and Corda, 2002; Corda and Brandano, 2003; Barattolo et al., 2007). The lithology and the microfacies types were described according to the schemes porposed by Dunham (1962) and Embry and Klovan (1971). Also, the same 408 samples were used for sequence stratigraphy analyses.

BIOSTRATIGRAPHY

Biozonation and age determinations are based on strontium isotope stratigraphy recently established for the Asmari Formation by Laursen et al. (2009). Results from the foraminifera data are summarized in Table 1.

Three assemblages of foraminifera were recognized in the studied areas and were discussed in ascending stratigraphic order as follows:

Assemblage 1. This assemblage occurs only at Kabirkuh–Darrehshahr area (Section 2). The most important foraminifera are: Eulepidina sp., Eulepidina dilatata, Eulepidina elephantine, Lepidocyclina sp., Nephrolepidina sp., Operculina sp., Operculina complanata, Austrotrillina howchini, Austrotrillina asmaricus, Peneroplis sp., Triloculina trigonula, Spiroclypeus blanckenhorni, miliolids and globigerinids. This assemblage is correlated with Lepidocyclina–Operculina–Ditrupa assemblage zone of Laursen et al. (2009) (Table 1) and is attributed to the Chattian time.

Assemblage 2. This assemblage is present in Dehluran (Section 1) and Kabirkuh–Darrehshahr (section 2) areas. The most diagnostic species in both studied sections include: Miogypsina sp., Elphidium sp. 14, Lepidocyclina sp., Operculina complanata, Austrotrillina sp., Austrotrillina asmaricus, Peneroplis sp., Peneroplis thomasi , Triloculina trigonula, Miogypsinoides sp., Borelis sp., Meandropsina iranica, Meandropsina anahensis, Dendritina rangi, Amphistegina sp., miliolids, Discorbis sp., Valvulinid sp. and Neorotalia viennoti. This assemblage corresponds to the Miogypsina–Elphidium sp. 14– Peneroplis farsensis assemblage zone of Laursen et al. (2009) (Table 1). The assemblage is considered to be Aquitanian in age.

MICROFACIES ANALYSIS

Facies analysis of the Asmari Formation in the study areas resulted in the definition of thirteen facies types (Figure 5), which characterize platform development. Each of the microfacies exhibits typical skeletal and non–skeletal components and textures. The general environmental interpretations of the microfacies are discussed in the following paragraphs.

Microfacies A. Stromatolitic boundstone (Figure 5.1)

This microfacies, with finely or moderately crinkled horizontal lamination, consists of alternating calcilutitic laminae and calcisiltic bioclastic laminae. Microfacies A is only present at Dehluran area (Section 1) and intercalates with mudstone facies.

Interpretation. This facies type is common in tidal flat sediments (Flügel, 2004; Hardie, 1986; Steinhauff and Walker, 1996; Lasemi, 1995; Hernández–Romano, 1999; Aguilera–Franco and Hernández–Romano, 2004). Today, flat laminated structures of microbial origin are found in intertidal settings. In regions with an arid climate (e.g., Persian Gulf or Shark Bay) stromatolites with smooth mats are located in the lower intertidal zone (Davies, 1970a, 1970b; Kinsman and Park, 1976; Hoffman, 1976).

Microfacies B. Fenestrate mudstone (Figure 5.2)

This facies consists of fine grained microcrystalline limestone. Bioclasts are lacking and the fenestrate structures are well developed. Microfacies B was identified at Kabirkuh–Darrehshahr area (Section 2) and mostly occurs with quartz mudstone.

Interpretation. Fenestrate structures are typical products of shrinkage and expansion, gas bubbles, and air escape during flooding, or may even result from burrowing activity of worms or insects. Shinn (1983) considered similar facies representative of a tidal flat environment, where trapped air between irregularly–shaped deposits leads to the development of birdseyes.

This microfacies is composed of dense lime mudstones. Sediments also contain sparse unidentified fauna. In some samples, subordinate amounts of detrital quartz grains and gypsum are also present. This facies occurs in middle and upper parts of the Asmari Formation. Microfacies C occurs at Dehluran (Section 1), Kabirkuh–Darrehshahr (Section 2) and Mamulan (Section 3) areas. It is either next to anhydrite or intercalates with lagoonal facies.

Interpretation. Lime mudstone, with gypsum blades and small quartz grains and no evidence of subaerial exposure, was deposited in a restricted shelf lagoon. This facies indicates hypersaline conditions within a shelf lagoon.

Microfacies D. Anhydrite (Figure 5.5)

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 marly limestones containing pelagic fauna. There is a sharp contact with the carbonates above and below. The second anhydrite deposit is intercalated between shallow water carbonates. Microfacies D is only present at Dehluran area (Section 1) and mostly associates with mudstone facies.

Interpretation. Considering the thickness of the anhydrite deposits, their vertical stacking and lateral continuity, it is assumed that they are submarine deposits formed in an isolated saline basin. The deposition of anhydrite implicates that the depositional environment became isolated from the open ocean at that time, which allowed for the concentration and submarine precipitation of salt. An eustatic sea level drop is invoked as the most likely cause. This event took place around the Oligocene–Miocene boundary. Ehrenberg et al. (2007) noted that strontium dates obtained from anhydrite in the Asmari Formation were close to the expected depositional ages and suggested that the anhydrite formed as an evaporate rather than as a later diagenetic product.

Microfacies E. Dendritina miliolids peloids wackestone–packstone–grainstone (Figure 5.6)

Identifiable components of this facies include benthic imperforate foraminifera (Dendritina and miliolids) and peloids. Borelis, bivalves and gastropods (whole shell and broken fragments) are less common. The grains are poorly to medium sorted, are fine–to medium size and vary from sub–angular to semi–rounded. Textures are dominantly packstone, but range from wackestone to grainstone. In some samples, the predominant non–skeletal carbonate grains are intraclasts. Microfacies E is present in all sections and mostly intercalates with open lagoonal facies.

Interpretation. This facies was deposited in a restricted shelf lagoon. The restricted condition is suggested by the rare to absent normal marine biota and abundant skeletal components of restricted biota (imperforate foraminifera such as miliolids and Dendritina). The subtidal origin is supported by the lack of subaerial exposure and stratigraphic position. This microfacies represents the shallowest upper part of the photic zone, with very light, highly translucent and soft muddy substrate (Geel, 2000; Romero et al., 2002; Corda and Brandano, 2003; Vaziri–Moghaddam et al., 2006; Bassi et al., 2007).

Microfacies F. Bioclastic rotaliids miliolids bioclast wackestone–packstone (Figure 5.7)

Interpretation. The co–occurrence of normal marine biota such as rotaliids, corallinaceans and echinoids with lagoonal biota such as miliolids, indicates that sedimentation 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 sediments of the Zagros basin (Vaziri–Moghaddam et al., 2006).

Microfacies G. Bioclastic miliolids coral floatstone–rudstone (Figure 5.8)

This facies is predominantly composed of miliolids and corallite fragments or fragments of coral colonies. Additional components are echinoderm fragments, recrystallized bivalve fragments and small benthic foraminifers (Austratrillina and Dendritina). Grains are poorly sorted and are medium to coarse sand to granule in size. Microfacies G is present at Kabirkuh–Darrehshahr (Section 2) and Mamulan (Section 3) areas.

Interpretation. Co–occurrence of normal marine (perforate foraminifera and corals) and platform–interior (imperforate foraminifera) components in facies F and G suggests the absence of an effective barrier. Restricted shelf organisms are effectively separated from the normal marine environment by barriers.

Microfacies H. Bioclastic ooids packstone–grainstone (Figure 5.9)

The predominant grain types are skeletal fragments and ooids. Biotic grain types include echinid and gastropods. 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 H was only identified at Kabirkuh–Darrehshahr area (Section 2) and mostly intercalates with imperforated coral rudstone to bioclastic Miogypsina corallinacea packstone facies.

Interpretation. The features of this facies indicate moderate to high energy shallow waters with much movement and reworking of bioclasts and the production of ooids. Sediments are interpreted to have been deposited in sand shoal (Wilson, 1975; Flügel, 2004).

Microfacies I. Bioclastic corallinacean coral floatstone–rudstone (Figures 5.10 and 11)

The main characteristic of this microfacies is abundant fragments of corallinacean and corals. Echinoid and bryozoan fragments are also present. The fragments are coarse sand to granule in size. Due to changes in the type of fauna in some samples, the name of this facies changes to bioclastic Miogypsina coral floatstone–rudstone. Microfacies I referred to Sepid Dasht (Section 4) and mostly intercalates with bioclastic Miogypsina foraminifera corallinacea wackestone–packstone.

Microfacies J. Bioclastic Miogypsina corallinacean wackestone–packstone (Figures 5.12 and 5.13)

A diverse assemblage of poorly to moderately sorted, fragmented and whole fossils in lime mud is characteristic of this microfacies. Miogypsina and corallinacean fragments are the dominant bioclasts. Less common bioclasts include bryozoan and fragments of recrystallized bivalves and echinoderm. In a few samples with increasing nummulitids, the name of this microfacies changes to bioclast nummulitids corallinacean wackestone–packstone. Microfacies J was identified at Dehluran (Section 1), Kabirkuh–Darrehshahr (Section 2) and Sepid Dasht (Section 4) areas and intercalates with open marine facies.

Interpretation. The presence of high diverse stenohaline fauna such as red algae, bryozoan, echinoid and larger foraminifera (Miogypsina and nummulitids) indicate that the sedimentary environment was situated in the oligophotic zone in a shallow open marine environment or near a fair–water wave base on the proximal middle shelf (Pomar, 2001a, 2001b; Brandano and Corda, 2002; Corda and Brandano, 2003; Cosovic et al., 2004). In open marine, shallow waters, foraminifera produce robust, ovate tests with thick walls, as a protection against photo inhibition of symbiotic algae inside the test in bright sunlight, and/or as a protection against test damage in turbulent water.

Microfacies K. Bioclastic lepidocyclinids nummulitids wackestone–packstone (Figure 5.14)

The main components are bioclasts and large perforate foraminifera. Bioclasts include bivalve, corallinacean (including articulated and crustose fragments), echinoderm and bryozoan fragments. The foraminifera are characterized by a relatively diverse assemblage of nummulitids (Operculina, Hetorestegina and Spiroclypeus) and lepidocyclinids (Eulepidina and Nephrolepidina). This facies is most prominent in lower parts of the Asmari Formation. Grains are coarse sand to granule in size and are in a fine–grained carbonate matrix. Fragmentation of larger foraminifera is rare. In a few samples, Amphistegina are more or less equal to lepidocyclinids in abundance, therefore, the name of the microfacies changes to bioclast Amphistegina nummulitids wackestone–packstone. Microfacies K referred to Kabirkuh–Darrehshahr (Section 2), Mamulan (Section 3) and Sepid Dasht (Section 4) areas.

Interpretation. The presence of large flat lepidocyclinids and nummulitids indicate that sedimentation took place in relatively deep water. Flatter test and thinner walls with increasing water depth reflect the decreased light levels at greater depths (Geel, 2000; Beavington and Racey, 2004; Nebelsick et al., 2005; Bassi et al., 2007; Barattolo et al., 2007).

Microfacies L. Bioclastic planktonic foraminifera lepidocyclinids wackestone–packstone (Figure 5.15)

The most frequent skeletal components of this microfacies are test fragments of echinoids, bryozoan, corallinacean, larger benthic foraminifera (lepidocyclinids) and entire tests of planktonic foraminifers. Bioclasts are angular to rounded and size ranges from silt to granule. Bioclastic planktonic foraminifera nummulitids wackestone–packstone and bioclastic planktonic foraminifera Miogypsina wackestone–packstone are similar to the microfacies described above in overall character, but differ from each other by their larger foraminifera. Microfacies L occurs at Kabirkuh–Darrehshahr (Section 2) and Sepid Dasht (Section 4) areas and intercalates with bioclastic planktonic foraminifera wackestone facies.

Interpretation. In general, the observed higher faunal diversity and the associated benthic foraminifers (lepidocyclinids, nummulitids and Miogypsina) and planktonic foraminifers, as well as bioclasts, indicate an open marine environment. Poorly washed matrix and mud–supported textures suggest environments below wave–base influenced by bottom–currents (Geel, 2000; Vaziri–Moghaddam et al., 2006; Amirshahkarami et al., 2007a).

In this microfacies, planktonic foraminifera are the dominant biotic components, but fine fragments of bryozoan and echinoid are also present. The planktonic foraminifers include non–keeled globorotalids and globigerinids. Some planktonic tests are filled with sparry cement. This facies occurs mostly in lower parts of the Asmari Formaton in most sections; however, it is recorded in the upper part of the formation at Sepid–Dasht area. Microfacies M is present at Dehluran (Section 1), Kabirkuh–Darrehshahr (Section 2) and Sepid Dasht (Section 4) areas.

Interpretation. The general lack of sedimentary structures, the fine–grained character, and the presence of undisturbed whole fossils from planktonic foraminifera suggest that this facies was deposited in calm, deep, normal–salinity water (Buxton and Pedley, 1989; Cosovic et al., 2004; Flügel, 2004).

SEDIMENTARY MODEL

The recognized microfacies have allowed the differentiation of several carbonate marine system environments including tidal flat, restricted lagoon, open lagoon, shoal, slope and basin. These six depositional environments of the Oligocene–Miocene in the study area are similar to those found in many modern carbonate depositional settings (Read, 1985; Jones and Desrochers, 1992). Of these, the Persian Gulf is perhaps the best modern analogue for inference of ancient water depths, because it shares many similarities with the Zagros foreland basin during the Oligocene–Miocene. Therefore, sedimentological and paleontological studies show that a ramp type carbonate platform sedimentary model can be fully applied to these ancient carbonate deposits (Read, 1982; Tucker, 1985; Tucker and Wright, 1990). According to Burchette and Wright (1992), carbonate ramp environments are separated into inner ramp, middle ramp and outer ramp. Outer ramp facies are characterized by marl and marly limestone lithologies. Wackestones predominate with abundant planktonic foraminifera. The presence of mud–supported textures and the apparent absence of wave and current structures suggest a low energy environment below storm wave base (Burchette and Wright, 1992).

Larger perforate foraminifera are abundant biogenic components of the shallow water carbonate succession in the Asmari Formation. A proliferation of perforate foraminifera is indicative of normal marine conditions (Geel, 2000). The lack of abrasion of the foraminifera indicates autochthonous accumulations, thus wackestone–packstone with lepidocyclinids and nummulitids were deposited under low energy conditions, below fair weather wave base (FWWB) and above storm wave base (SWB) in the middle ramp setting. The variation in the shape of the test reflects the differences in water depth. The sediments with perforate robust and ovate specimens reflect the presence of shallower water than those containing large and flat lepidocyclinids and nummulitids. Larger foraminifera are limited geographically to temperate to tropical/subtropical environments (Hohenegger et al., 2000; Langer and Hottinger, 2000).

The common association of symbiotic algae with perforate foraminifera implies that light is a main factor in determining the depth distribution (Hansen and Buchardet, 1977; Hallock, 1979, 1981; Bignot, 1985; Hallock and Glenn, 1986).

Inner ramp deposits represent a wider spectrum of marginal marine deposits, indicating high–energy shoal, open lagoon and protected lagoon. In the restricted lagoon environment, the faunal diversity is low and the normal marine fauna are lacking, except for imperforate benthic foraminifera (miliolids, Dendritina, borelisids), which indicates quiet, sheltered conditions. A large number of porcellaneous imperforate foraminifera points to the presence of slightly hypersaline waters (Geel, 2000). Open lagoonal conditions are characterized by mixed open marine fauna (such as red algae, echinoids and perforate foraminifera) and protected environment fauna (such as miliolids). The shallow subtidal environment above the fair–weather wave base is characterized by the presence of a facies association showing signs of long–term water agitation (packing, sorting, poor taphonomic preservation and ooids). Such high–energy deposits are typically associated with carbonate shoals on carbonate platforms (Figure 6).

During the Chattian, outer ramp facies (Pabdeh Formation) was predominant at the Dehluran area (Section 1, Figure 7). Simultaneously, outer to middle ramp conditions occurred at the Kabirkuh–Darrehshahr area (Section 2). The Dehluran area was experiencing outer–middle ramp conditions during the Early Aquitanian. At the same time, sedimentation at the Kabirkuh–Drarrehshahr area took placed in the middle and inner ramp environments. These areas experienced inner ramp (mostly lagoon sub–environment) condition during the Late Aquitanian (Figure 7). Eastern parts of the study area (Mamulan and Sepid Dasht were sites of non–deposition or erosion during Chattian through Aquitanian. In Mamulan area (section 3), middle and inner ramp environments prevailed through Burdigalian, whereas middle and outer ramp conditions were predominant in Sepid Dasht area (section 4) during the Burdigalian (Figure 7).

SEQUENCE STRATIGRAPHY

The studied succession can be framed in a sequence stratigraphic context. As a guide, we used the principal sequence stratigraphic concepts developed by many workers (e.g., Sarg, 1988, Posamentier et al., 1988; Van Wagoner et al., 1988, 1990, Read and Hrbury, 1993; Emery and Myers, 1996; Coe and Church, 2003; Catuneanu, 2006) to recognize TST (transgressive systems tract), mfs (maximum flooding surface), HST (highstand systems tract) and sequence boundaries.

Based on the distribution of planktonic and benthonic foraminifera, and on the detailed sedimentological and stratigraphical study, we defined four third–order sequences.

Sequence 1

The depositional sequence 1 is present in sections 1 (Dehluran, 17 m thick) and 2 (Kabirkuh–Darrehshahr, 60 m thick) of the study area (Figures 8 and 9). The sediments of sequence 1 are Chattian in age. Sequence 1 includes the upper part of the Pabdeh Formation at Dehluran area, whereas at Kabirkuh–Darrehshahr area it encompasses the upper part of the Pabdeh Formation and the lower part of the Asmari Formation. At Dehluran area, TST and HST could not be differentiated because the relatively uniform deep sub–tidal succession is composed of planktonic foraminifera wackestone without distinct changes in microfacies. TST was clearly recognized at Kabirkuh–Darrehshahr area. Shale and marly limestone of the TST contain abundant planktonic foraminifera and document a deep–subtidal, low energy environment during the TST. The maximum flooding surface (mfs) coincides with the boundary between the Pabdeh and Asmari formations. The highstand systems tract (HST) comprises the lower part of the Asmari Formation. The early HST was characterized by constant shallow open marine environmental conditions (wackestone–packstone with perforate foraminifera). The late HST shows a trend toward more protected sediments (wackestone–packstone with imperforate foraminifera), expressing a filling of the accommodation space. The sequence boundary is characterized by abrupt facies changes from subtidal–lagoonal to tidal flat environments. Such changes reflect a significant decrease in water depth (Figures 8 and 9).

Sequence 2

The depositional sequence 2 formed during the late Chattian–early Aquitanian transgression. At Dehluran area, this sequence is 21 m thick, (Figure 8), and begins with 9 m–thick sediments of the anhydrite facies. These are interpreted as the lowstand systems tract (LST) of this sequence. The contact between the LST and the basinal deposits with pelagic fauna (Pabdeh Formation) below is sharp. At this section, the TST and HST comprise an 11 m–thick, monotonous succession of open marine deposits, demonstrating that prograding shallow–water sediments did not reach far west. At Kabirkuh–Darrehshahr area, 130/5 m thick (Figure 9), the vertical variations in the facies during the transgression are different from those described in sequence 1. An increase in third–order accommodation space is indicated by shallow lagoonal facies overlain by shallow–open marine facies. Wackestone with abundant planktonic foraminifers represent deep–water facies; this is, therefore, interpreted as the mfs. An upward–shallowing facies trend (HST) is indicated by shallow open marine gradational facies, overlain by shallow–lagoonal facies (Figures 8 and 9).

Sequence 3

This sequence is late Aquitanian in age and is present in Dehluran area (48/5 m thick) and in Kabirkuh–Darrehshahr area (14/5 m thick). At Dehluran (Figure 8), the lowstand deposits of this sequence consist of a well developed anhydrite. A temporary isolation of the sedimentary environment would be necessary in order to be able to precipitate the anhydrite. At the base, the anhydrite is homogenous, but passes up into a more heterogenous composition and interdigitates with shallow water carbonates. The sea level transgression caused the deposition of shallow subtidal facies within an aggradational staking pattern in Dehluran and Kabirkuh–Darrehshahr areas. The sequence boundary is characterized at the top by stromatolitic boundstone (Dehluran area) and mudstone with quartz (Kabirkuh–Darrehshahr area), which marks the end of a shallowing–upward trend (Figures 8 and 9).

Sequence 4

The sequence 4 is present in all sections (Dehluran, 117/5; Kabirkuh–Darrehshahr, 55; Mamulan, 69/5; and Sepid Dasht, 82/5 m thick).

The lower boundary of Sequence 4 in Dehluran and Kabirkuh–Darrehshahr areas is characterized by a type 2 sequence boundary (Figures 8 and 9), whereas in Mamulan, (section 3) and Sepid Dasht, (section 4) areas it is defined by a type 1 sequence boundary (Figures 10 and 11). A long period of lagoonal conditions reflecting a balanced situation between accommodation and sedimentation characterizes the sequence 4 in Dehluran and Kabirkuh–Darrehshahr 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 of shallow lagoonal facies, forming a TST. The overlying wackestone–packstone with diverse fauna reflects a mfs, and the beginning of deposition of a HST. The overlying mfs, rich in imperforate foraminifera, have been deposited in a calm and shallow–lagoonal environment; this part is interpreted as a HST. Above type 1 sequence boundary at Sepid Dasht area, there are limestones of open marine facies with a rich planktonic foraminifera, perforate larger benthic foraminifera, corallinacean and coral fragments. These sediments were characterized by constant open marine environmental conditions, representing constant accommodation at Sepid Dasht area.

Ehrenberg et al. (2007) recognized some surfaces in well sections from the Bibi Hakimeh, Marun, and Ahwaz oilfields and interpreted them as sequence boundaries (Ch 20 SB, Ch 30 SB, Aq 10 SB, intra–Aq10 SB, Aq20/Bu10 SB, Bu 20 SB). Because these sequence boundaries were not recognized in the study area, the sequence stratigraphy of Ehrenberg et al. (2007) can not be confidently applied to these sections.

On the basis of facies changes (Figures 8 and 9), in both sections (1 and 2), sequence boundaries recognized in the upper part of the Chattian and the middle part of the Aquitanian, may be associated with the Aq 10 and Aq20/Bu10 sequence boundaries recognized by Ehrenberg et al. (2007).

The depositional sequences 1, 2 and 3 were observed in Dehluran and Kabirkuh–Darrehshahr areas (sections 1 and 2), and are synchronous with a period of either erosion or non–deposition represented by unconformities in Mamulan and Sepid Dasht areas (sections 3 and 4) (Figures 7,–12).

CONCLUSIONS

The Oligocene–Miocene Asmari Formation of the Zagros basin is a thick sequence of shallow water carbonate. The outcrops of the Asmari Formation in northwest of the Zagros (Dehluran, Kabirkuh– Darreshahr, Sepid Dasht and Mamulan areas) allow the recognition of different depositional environments, on the basis of sedimentological analysis, distribution of foraminifera and microfacies studies. These depositional environments correspond to inner, middle and outer ramp. In the inner ramp, the most abundant lithofacies are medium–grained wackestone–packstone with imperforated foraminifera. The middle ramp is represented by packstone–grainstone to floatstone with a diverse assemblage of larger foraminifera with perforate wall, red algae, bryozoa, and echinoids. The outer ramp is dominated by argillaceous wackestone characterized by planktonic foraminifera and large and flat nummulitidae and lepidocyclinidae. Four third–order sequences are identified on the basis of deepening and shallowing microfacies patterns and on the distribution of Oligocene–Miocene foraminifers.

ACKNOWLEDGMENTS

The authors wish to thank the National Iranian Oil Company Research and Development Management for their financial support and permission to publish this work. We also thank Dr. Mohammad Ali Emadi for his support and thoughtful comments. The authors appreciate the National Iranian Oil Company Exploration Division for providing surface geological maps. Also we thanks the Revista Mexicana de Ciencias Geológicas reviewers for their constructive comments.

REFERENCES

Adams, T.D., Bourgeois, F., 1967, Asmari biostratigraphy: Iranian Oil Operating Companies, Geological and Exploration Division, Report 1074.        [ Links ]

Aguilera–Franco, N., Hernández–Romano, U., 2004, Cenomanian–Turonian facies succession in the Guerrero–Morelos Basin, Southern Mexico: Sedimentary Geology, 170(3–4), 135–162.        [ Links ]

Ahmadhadi, F., Lacombe, O., Marc Daniel, J., 2007, Early reactivation of basement faults in central Zagros (SW Iran), Evidence from pre–folding fracture populations in Asmari Formation and Lower Tertiary paleogeography, in Lacombe, O., Lave, J., Roure, F., Verges, J., (eds.), Thrust Belts and Foreland Basins: Berlin, Springer, 205–228.        [ Links ]

Alavi, M., 2004, Regional stratigraphy of the Zagros fold–thrust belt of Iran and its proforeland evolution: American Journal of Sciences, 304, 1–20.        [ Links ]

Al–Husseini, M.I., 2000. Origin of the Arabian Plate structures: Amar Collision and Najd Rift: Geo Arabia, 5(4), 527–542.        [ Links ]

Amirshahkarami, M., Vaziri–Moghaddam, H., Taheri, A., 2007a, Paleoenvironmental model and sequence stratigraphy of the Asmari Formation in southwest Iran: Historical Biology, 19(2), 173–183.        [ Links ]

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.        [ Links ]

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, Neyriz, Iran: Journal of Asian Earth Sciences, 19(1–2), 61–76.        [ Links ]

Babaei, A., Babaie, H.A., Arvin, M., 2005, Tectonic evolution of the Neyriz ophiolite, Iran: an accretionary prism model: Ofioliti, 30(2), 65–74.        [ Links ]

Babaie, H.A., Babaei, A., Ghazi, A.M., Arvin, M., 2006, Geochemical, 40Ar/39Ar age, and isotopic data for crustal rocks of the Neyriz ophiolite, Iran: Canadian Journal of Earth Sciences, 43(1), 57–70.        [ Links ]

Barattolo, F., Bassi, D., Romero, R., 2007, Upper Eocene larger foraminiferal–coralline algal facies from the Klokova Mountain (south continental Greece): Facies, 53(3), 361–375.        [ Links ]

Bassi, D., Hottinger, L. Nebelsick, H., 2007, Larger Foraminifera from the Upper Oligocene of the Venetian area, northeast Italy: Palaeontology, 5(4), 845–868.        [ Links ]

Beavington–Penney, S.J., Racey, A., 2004, Ecology of extant nummulitids and other larger benthic foraminifera. applications in Paleoenvironmental analysis: Earth Science Review, 67(3–4), 219–265.        [ Links ]

Berberian, M., 1995, Master "blind" thrust faults hidden under the Zagros folds: active basement tectonics and surface morphotectonics: Tectonophysics, 241(3–4), 193–224.        [ Links ]

Berberian, M., King, G.C.P., 1981, Towards a paleogeography and tectonic evolution of Iran: Canadian Journal of Earth Sciences, 18, 210–265.        [ Links ]

Beydoun, Z.R., Hughes Clarke, M.W., Stoneley, R., 1992, Petroleum in the Zagros basin: a late Tertiary foreland basin overprinted onto the outer edge of a vast hydrocarbon–rich Paleozoic–Mesozoic passive margin shelf, in Macqueen, R.W., Leckie, D.A., (eds.), Foreland basins and fold belts: American Association of Petroleum Geologists Memoir, 55, 309–339.        [ Links ]

Bignot, G., 1985, Elements of Micropaleontology: London, Graham and Totman Limited, Sterling House, 217 pp.        [ Links ]

Brandano, M., Corda, L., 2002, Nutrients, sea level and tectonics constraints for the facies architecture of a Miocene carbonate ramp in central Italy: Terra Nova, 14(4), 257–262.        [ Links ]

Burchette, T.P., Wright, V.P., 1992, Carbonate ramp depositional systems: Sedimentary Geology, 79(1–4), 3–57.        [ Links ]

Busk, H.G., Mayo, H.T., 1918, Some notes on the geology of the Persian Oilfields: Journal Institute Petroleum Technology, 5, 5–26.        [ Links ]

Buxton, M.W.N., Pedley, H.M., 1989, Short paper: a standardized model for Tethyan Tertiary carbonates ramps: Journal of the Geological Society, London, 146(5), 746–748.        [ Links ]

Catuneanu, O., 2006, Principles of sequence stratigraphy: New York, Elsevier, 386 pp.        [ Links ]

Coe, A.L., Church, K.D., 2003, Sequence stratigraphy, in Coe, A.L. (ed.), The Sedimentary Record of Sea–level Change: Cambridge, Cambridge University Press, 57–98.        [ Links ]

Corda, L., Brandano, M., 2003, Aphotic zone carbonate production on a Miocene ramp, Central Apennines, Italy: Sedimentary Geology, 161(1–2), 55–70.        [ Links ]

Cosovic, V., Drobne, K., Moro, A., 2004, Paleoenvironmental model for Eocene foraminiferal limestones of the Adriatic carbonate platform (Istrian Peninsula): Facies, 50(1), 61–75.        [ Links ]

Davies, R.G., 1970a, Carbonate bank sedimentation, Eastern Shark Bay, Western Australia, in Logan, B.V., Davies, R.G., Read, J.F.,Cebulski, D.E. (eds.), Carbonate Sedimentation and Environments Shark Bay, Western Australia: American Association of Petroleum Geologists Bulletin, 13, 85–168.        [ Links ]

Davies, R.G., 1970b, Algal–laminated sediments, Western Australia environments, Shark Bay, Western Australia: American Association of Petroleum Geological Memoir, 13, 169–205.        [ Links ]

Dunham, R.J., 1962, Classification of carbonate rocks according to depositional texture: American Association of Petroleum Geologists Memoir, 1, 108–121.        [ Links ]

Ehrenberg, S.N., Pickard, N.A.H., Laursen, G.V., Monibi, S., Mossadegh, Z.K., Svana, T.A., Aqrawi, A.A.M., McArthur, J.M., Thirlwall, M.F., 2007, Strontium isotope stratigraphy of the Asmari Formation (Oligocene – Lower Miocene), SW Iran: Journal of Petroleum Geology, 30(2), 107–128.        [ Links ]

Embry, A.F., Klovan, J.E., 1971, A Late Devonian reef tract on Northeastern Banks Island, NWT: Canadian Petroleum Geology Bulletin, 19(4), 730–781.         [ Links ]

Emery, D., Myers, K.J., 1996, Sequence Stratigraphy: Oxford, Blackwell Science, 297 pp.         [ Links ]

Flügel, E., 1982, Microfacies analysis of limestones: Berlin – Heidelberg, New York, Springer, 633 pp.        [ Links ]

Flügel, E., 2004, Microfacies analysis of limestones, analysis interpretation and application: Berlin, Springer–Verlag, 976 pp.        [ Links ]

Geel, T., 2000, Recognition of stratigraphic sequence in carbonate platform and slope: empirical models based on microfacies analysis of Paleogene deposits in southeastern Spain: Palaeogeography, Palaeoclimatology, Palaeoecology, 155(3), 211–238.        [ Links ]

Hakimzadeh, S., Seyrafian, A., 2008, Late Oligocene–Early Miocene benthic foraminifera and biostratigraphy of the Asmari Formation, south Yasuj, north–central Zagros basin, Iran: Carbonates and Evaporites, 23(1), 1–10.        [ Links ]

Hallock, P., 1979, Trends in test shape with depth in large symbiont–bearing foraminifera: Journal of Foraminiferal Research, 9(1), 61–69.        [ Links ]

Hallock, P., 1981, Light dependence in Amphistegina: Journal of Foraminiferal Research, 11(1), 40–46.        [ Links ]

Hallock, P., 1999, Symbiont bearing foraminifera, in Sen Gupta, B.K., (ed.) Modern Foraminifera: Dordrecht, Kluwer, 123–139.        [ Links ]

Hallock, P., Glenn, E.C., 1986, Larger foraminifera: a tool for paleoenvironmental analysis of Cenozoic depositional facies: Palaios, 1(1), 55–64.        [ Links ]

Hansen, H.J., Buchardet, B., 1977, Depth distribution of Amphistegina in the Gulf of Elat, Israel: Utrecht Micropaleontological Bulletin, 15, 205–224.        [ Links ]

Hardie, L.A., 1986, Ancient carbonate tidal flat deposits: Quarterly Journal of the Colorado School of Mines, 81, 37–57.        [ Links ]

Hernández–Romano, U., 1999, Facies stratigraphy and diagenesis of the Cenomanian–_Turonian of the Guerrero–Morelos Platform, southern Mexico: United Kingdom, University of Reading, Postgraduate Research Institute for Sedimentology, Ph.D. Thesis, 322 pp.        [ Links ]

Heydari, E., Hassanzadeh, J., Wade, W.J., Ghazi, A.M., 2003, Permian–Triassic boundary interval in the Abadeh section of Iran with implications for mass extinction, Part 1–Sedimentology: Paleogeography, Paleoclimatology, Paleoecology, 193(3), 405–423.        [ Links ]

Hoffman, P., 1976, Stromatolite morphogenesis in Shark Bay, Western Australia, in Walter, M.R. (ed.), Stromatolites: Development in Sedimentology, 20, 381–388.        [ Links ]

Hohenegger, J., 1996, Remarks on the distribution of larger foraminifera (Protozoa) from Palau (western Carolines), in Aoyama, T., (ed.), The progress report of the 1995 survey of the research project, Man and the environment in Micronesia: Kagoshima University Research Center for the Pacific Islands, Occasional Papers, 32, 19–45.        [ Links ]

Hohenegger, J., Yordanova, E., Tatzreiter, Y., 1999, Habitats of larger foraminifera on the upper reef slope of Sesko Island, Okinawa: Marine Micropaleontology, 36(2), 109–168.        [ Links ]

Hohenegger, J., Yordanova, E., Hatta, A., 2000, Remarks on West Pacific Nummulitidae (Foraminifera): Journal of Foraminiferal Research, 30(1), 3–28.        [ Links ]

Hottinger, L., 1980, Répartition comparée des grands foraminifères de la mer Rouge et de l'Océan Indien: Annali dell'Università di Ferrara, 6, 35–51.        [ Links ]

Hottinger, L., 1983, Processes determining the distribution of larger foraminifera in space and time, in Meulenkamp, J.E. (ed.), Reconstruction of marine paleoenvironments: Utrecht Micropaleontological Bulletin, 30, 239–253.        [ Links ]

Hottinger, L., 1997, Shallow benthic foraminiferal assembelages as signals for depth of their deposition and their limitation: Bulletin de la Societé Géologique de France, 168(4), 491–505.        [ Links ]

Jalali, M.R., 1987, Stratigraphy of Zagros Basin: National Iranian Oil Company, Exploration and Production Division, Report, 1249, 1072.        [ Links ]

James, G.A., Wynd, J.C., 1965, Stratigraphic nomenclature of Iranian oil consortium agreement area: American Association of Petroleum Geologists Bulletin, 49(2), 94–156.        [ Links ]

Jones, B., Desrochers, A., 1992, Shallow platform carbonates, in Walker, R.G., James, N.P. (eds.), Facies models, Response to sea level change: St John's, Newfoundland, Geological Association of Canada, 277–303.        [ Links ]

Kalantary, A., 1986, Microfacies of carbonate rocks of Iran: National Iranian Oil Company, Geological Laboratory Publication, Tehran, 520 pp.        [ Links ]

Kinsman, D.J.J., Park, R.K., 1976, Algal belt and coastal sabkha evolution, Trucial Coast, Persian Gulf, in Walter, M.R. (ed.), Stromatolites: Development in Sedimentology, 20, 421–433.        [ Links ]

Langer, M., Hottinger, L., 2000, Biogeography of selected 'larger' foraminifera: Micropaleontology, 46(1), 105–126.        [ Links ]

Lasemi, Y., 1995, Platform carbonates of the Upper Jurassic Mozduran Formation in the Kopet Dagh Basin, NE Iran–facies, palaeoenvironments and sequences: Sedimentary Geology, 99(3–4), 151–164.        [ Links ]

Laursen, G.V., Monibi, S., Allan, T.L., Pickard, N.A., Hosseiney, A., Vincent, B., Hamon, Y., Van–Buchem, F.S.P., Moallemi, A., Druillion, G., 2009, The Asmari Formation revisited: changed stratigraphic allocation and new biozonation: Shiraz, First International Petroleum Conference & Exhibition, European Association of Geoscientists and Engineers.        [ Links ]

Leutenegger, S., 1984, Symbiosis in benthic foraminifera, specificity and host adaptations: Journal of Foraminiferal Research, 14(1), 16–35.        [ Links ]

Longman, M.W., 1981, A process approach to recognizing facies of reef complex, in Toomey, D.F. (ed.), European Fossil Reef Models: Society of Economic Paleontologists and Mineralogists, Special Publication, 30, 9–40.        [ Links ]

Mapstone, N.B., 1978, Structural geology of structures of Dezful (north) Embayment: Oil Service Company of Iran (OSCO), internal report, Technical note.        [ Links ]

Melim, L.A., Scholle, P.A., 1995, The forereef facies of the Permian Capitan formation, The role of sediment supply versus sea–level changes: Journal of Sedimentary Research, 65(1b), 107–119.        [ Links ]

Motiei, H., 1993, Stratigraphy of Zagros: Geological Survey of Iran, 583 pp.        [ Links ]

Motiei, H., 2001, Simplified table of rock units in southwest Iran: Tehran, Keyhan Exploration and Production Services.         [ Links ]

Nebelsick J.H., Rasser, M. Bassi, D., 2005, Facies dynamic in Eocene to Oligocene Circumalpine carbonates: Facies, 51(4), 197–216.        [ Links ]

Pomar, L., 2001a, Types of carbonate platforms: a genetic approach: Basin Research, 13, 313–334.        [ Links ]

Pomar, L., 2001b, Ecological control at sedimentary accommodation: evolution from a carbonate ramp to rimmed shelf, Upper Miocene, Balearic Island: Palaeogeography, Palaeoclimatology, Palaeoecology, 175(1), 249–272.        [ Links ]

Posamentier, H.W., Jerevy, M.T., Vail, P.R., 1988, Eustatic controls on clastic depositions I– conceptual framework in Wilgus C.K., Hastings B.S., Kendall C.G.St.C., Posamentier H.W., Ross C.A., Van Wagoner J.C., (eds.), Sea–Level Changes: An integrated approach: Society of Economic Paleontologists and Mineralogists Special Publication, 42, 109–124.        [ Links ]

Rasser, M.W., Nebelsick, J.H., 2003, Provenance analysis of Oligocene autochthonous and allochthonous coralline algae: a quantitative approach towards reconstructing transported assemblages: Palaeogeography, Palaeoclimatology, Palaeoecology, 201(1), 89–111.        [ Links ]

Read, J.F., 1982, Carbonate margins of passive (extensional) continental margins: types, characteristics and evolution: Tectonophysics, 81, 195–212.        [ Links ]

Read, J.F., 1985, Carbonate platform facies models: American Association of Petroleum Geologists, 69(1), 1–21.        [ Links ]

Read, J.F., Horbury, A.D., 1993, Diagenesis and porosity evolution associated with metre scale disconformities and sequence bounding unconformities, in Horbury, A.D., Robinson, A.G., (eds.), Diagenesis and basin development: American Association of Petroleum Geologists, Studies in Geology, 36, 155–197.        [ Links ]

Reiss, Z., Hottinger, L., 1984, The Gulf of Aqaba: Ecological Micropaleontology, 50, 354 pp.         [ Links ]

Richardson, P.K., 1924, The geology and oil measures of southwest Persia: Journal Institute Petroleum Technology, 10, 256–283.        [ Links ]

Riding, R., Martin, T.M., Braga, T.C., 1991, Coral–stromatolite reef framework, Upper Miocene, Almeria, Spain: Sedimentology, 38(5), 799–818.        [ Links ]

Romero, J., Caus, E., Rosell, J., 2002, A model for the palaeoenvironmental distribution of larger foraminifera based on late Middle Eocene deposits on the margin of the South Pyrenean basin (NE Spain): Palaeogeography, Palaeoclimatology, Palaeoecology, 179(1), 43–56.        [ Links ]

Sarg, J.F., 1988, Carbonate sequence stratigraphy, in Wilgus, C.K., Hastings, B.S., Kendall, C.G.St.C., Posamentier, H.W., Ross, C.A., Van Wagoner, J.C. (eds.), Sea–Level Changes: An integrated approach: Society for Sedimentary Geology, Special Publication, 43, 155–181.        [ Links ]

Sepehr, M., Cosgrove, J.W., 2004, Structural framework of the Zagros Fold–Thrust belt, Iran: Marine and Petroleum Geology, 21(7), 829–843.        [ Links ]

Seyrafian, A., 2000, Microfacies and depositional environment of the Asmari Formation, at Dehdez area (A correlation across Central Zagros Basin): Carbonates and Evaporites 15(2), 121–129.        [ Links ]

Seyrafian, A., Hamedani, A., 1998, Microfacies and depositional environment of the upper Asmari Formation (Burdigalian), north–central Zagros Basin, Iran: Neues Jahrbuch für Geologie und Paläontology, Abhandlungen, 21, 129–141.        [ Links ]

Seyrafian, A., Hamedani, A., 2003, Microfacies and paleoenvironmental interpretation of the lower Asmari Formation, (Oligocene), North Central Zagros Basin, Iran: Neues Jahrbuch für Geologie und Palaeontologie, Monatshefte, 3, 164–174.        [ Links ]

Seyrafian, A., Mojikhalifeh, A.R., 2005, Biostratigraphy of the Late Paleogene–Early Neogene succession, north–central border of Persian Gulf: Carbonates and Evaporites, 20(1), 91–97.        [ Links ]

Seyrafian, A., Vaziri–Moghaddam, H., Torabi, H., 1996, Biostrtigraphy of the Asmari Formation, Borujen area, Iran: Journal of Sciences, 7(1), 31–47.        [ Links ]

Sherkati, S., Letouzey, J., 2004, Variation of structural style and basin evolution in the central Zagros (Izeh zone and Dezful Embayment), Iran: Marine and Petroleum Geology, 21(5), 535–554.        [ Links ]

Shinn, E., 1983, Tidal flats, in Scholle, P.A., Bebout, D. G., Moore, C.H. (eds.), Carbonate Depositional Environments: American Association of Petroleum Geologists Memoir, 33, 171–210.        [ Links ]

Steinhauff, D.M., Walker, K.R., 1996, Sequence stratigraphy of an apparently non–cyclic carbonate succession: recognizing subaerial exposure in a largely subtidal, Middle Ordovician stratigraphic sequence in eastern Tennessee, in Witzke, G.A., Ludvingson, J.E., Day, B.J. (eds.), Paleozoic Sequence Stratigraphy, Views from the North American Craton: Geological Society of America, Special Paper, 306, 87–115.        [ Links ]

Stoneley, R., 1981, The Geology of the Kuh–e Dalneshin Area of Southern Iran, and Its Bearing on the Evolution of Southern Tethys: Journal of the Geological Society, London, 138, 509–526.        [ Links ]

Thomas, N.A., 1948, The Asmari Limestone of southwest Iran: National Iranian Oil Company, Report 706, unpublished.        [ Links ]

Tucker, M.E., 1985, Shallow marine carbonate facies and facies models, in Brenchley P.J., Williams B.P.J. (eds.), Sedimentology, recent development and applied aspects: Geological Society of London, Special Publication, 18, 139–161.        [ Links ]

Tucker, M.E., Wright, V.P., 1990, Carbonate sedimentology: Oxford, Blackwell Scientific Publications, 425 pp.        [ Links ]

Van Boeckh, H. D.E., Lees, G.M., Richardson, F.D.S., 1929, Contribution to the stratigraphy and tectonics of the Iranian ranges, in Gregory, J.W. (ed.), The Structure of Asia.: London, Methuen and Co., 58–177.        [ Links ]

Van Wagoner, J.C., Posamentier, H.W., Mitchum, R.M.J.R., 1988, An overview of the fundamentals of sequence stratigraphy and key definition, in Wilgus, C.K., Hastings, B.S., Kendall, C.G.St.C., Posamentier, H.W., Ross, C.A., Van Wagoner, J.C. (eds.), Sea–Level Changes: An integrated approach: Society for Sedimentary Geology, Special Publication, 42, 39–45.        [ Links ]

Van Wagoner, J.C., Mitchum, R.M., Campion, K.M., Rahmanian, V.D., 1990, Siliciclastic sequence stratigraphy in well logs, cores and outcrop: concepts for high resolution correlation of time and facies: American Association of Petroleum Geologists Methods in Exploration Series, 7, 55.        [ Links ]

Vaziri–Moghaddam, H., Kimiagari, M. Taheri, A., 2006, Depositional environment and sequence stratigraphy of the Oligo–Miocene Asmari Formation in SW Iran: Facies, 52(1), 41–51.        [ Links ]

Wilson, J.L., 1975, Carbonate facies in geological history: New York, Springer, 471 pp.        [ Links ]

Wynd, J., 1965, Biofacies of Iranian oil consortium agreement area: Iranian Oil Offshore Company Report 1082, unpublished.        [ Links ] ]]> 1967 1074 2004 170 3-4 3-4 135-162 2007 205-228 2004 304 1-20 2000 5 4 4 527-542 2007 19 2 2 173-183 2007 29 5-6 5-6 947-959 2001 19 1-2 1-2 61-76 2005 30 2 2 65-74 2006 43 1 1 57-70 2007 53 3 3 361-375 2007 5 4 4 845-868 2004 67 3-4 3-4 219-265 1995 241 3-4 3-4 193-224 1981 18 210-265 1992 55 309-339 1985 217 2002 14 4 4 257-262 1992 79 1-4 1-4 3-57 1918 5 5-26 1989 146 5 5 746-748 2006 386 2003 57-98 2003 161 1-2 1-2 55-70 2004 50 1 1 61-75 1970 13 85-168 1970 b 13 169-205 1962 1 108-121 2007 30 2 2 107-128 1971 19 4 4 730-781 1996 297 1982 633 2004 976 2000 155 3 3 211-238 2008 23 1 1 1-10 1979 9 1 1 61-69 1981 11 1 1 40-46 1999 123-139 1986 1 1 1 55-64 1977 15 205-224 1986 81 37-57 1999 322 2003 Paleoclimatology, Paleoecology, 193 3 3 405-423 1976 20 381-388 1996 32 19-45 1999 36 2 2 109-168 2000 30 1 1 3-28 1980 6 35-51 1983 30 239-253 1997 168 4 4 491-505 1987 1249 1072 1965 49 2 2 94-156 1992 277-303 1986 520 1976 20 421-433 2000 46 1 1 105-126 1995 99 3-4 3-4 151-164 2009 1984 14 1 1 16-35 1981 30 9-40 1978 1995 65 1b 1b 107-119 1993 583 2001 2005 51 4 4 197-216 2001 13 313-334 2001 175 1 1 249-272 1988 42 109-124 2003 201 1 1 89-111 1982 81 195-212 1985 69 1 1 1-21 1993 36 155-197 1984 50 354 pp 1924 10 256-283 1991 38 5 5 799-818 2002 179 1 1 43-56 1988 43 155-181 2004 21 7 7 829-843 2000 15 2 2 121-129 1998 21 129-141 2003 3 164-174 2005 20 1 1 91-97 1996 7 1 1 31-47 2004 21 5 5 535-554 1983 33 171-210 1996 306 87-115 1981 London 138, 509-526 1948 706 1985 18 139-161 1990 425 1929 58-177 1988 42 39-45 1990 7 55 2006 52 1 1 41-51 1975 471 1965 1082