Keywords: Asmari Formation, Larger benthic foraminifera, Biostratigraphy, Paleoenvironment, Zagros Basin, Iran.

Transcription

1 Stratigraphy and Sedimentology Researches 26 th year, Vol. 40, No. 3, Autumn 2010 Received: 2010/6/14 Accepted: 2010/10/25 pp Biostratigraphy and paleoenvironment of the larger benthic foraminifera in wells sections of the Asmari Formation from the Rag-e-Safid oil field, Zagros Basin, southwest Iran M. Amirshahkarami, Assistant Professor, Department of Geology Payame Noor University, Tehran A. Ghabishavi, National Iranian South Oil Company (NISOC) A. Rahmani, National Iranian South Oil Company (NISOC) Abstract Based on the stratigraphical distribution of the larger benthic foraminifera in the subsurface sedimentary successions of the Asmari Formation (Oligocene Miocene) from the Rag-e-Safid oil field four assemblage zones have been recognized. Assemblage zone I suggests a Rupelian age and includes Nummulites fichteli, Nummulites vascus, Eulepidina, Nephrolepidina, Austrotrillina paucialveolata, Heterostegina assilinoides, Praerhapydionina delicate, Pseudolituonella reicheli; Assemblage zone II represents a Chattian age and is introduced by association of Archaias, Austrotrillina, Amphistegina, Miogypsinoides complanatus; Assemblage zone III suggests an Aquitanian age and consists of Miogypsinoides deharti, Miogypsina sp. and peneropelidae; Assemblage zone IV refers to Burdigalian age and is recognized by the first appearance of Borelis melo and Borelis curdica. The paleoecology and biofacies of the larger benthic foraminifera suggest four depositional settings included open marine; ooids shoals; lagoon and tidal flat. These sedimentary settings correspond to the inner and middle parts of a carbonate ramp. Keywords: Asmari Formation, Larger benthic foraminifera, Biostratigraphy, Paleoenvironment, Zagros Basin, Iran. Correspondent Author: [email protected]

2 64 Stratigraphy and Sedimentology Researches 26 th year, Vol. 40, No. 3, Autumn Introduction The Oligocene Miocene Asmari Formation is famous as the most prolific oil producing sequences in the Zagoros Basin in the southwest of Iran. The Zagros Mountains of Iran are divided into the three principal tectonic units (Stocklin 1968; Jong 1982). It is divided into three zones included the Zagros fold-thrust zone, the imbricated zone and the Urumieh Dokhtar magmatic zone (Alavi 2004). The Asmari Formation has been deposited in the flanking shelves of the Zagros foredeep and is composed of light-coloured and shallow marine limestone (Ziegler 2001). The type section of the Asmari Formation was measured in the Tang-e- Gele Torsh in Khuzestan province by Richardson (1924). It is consists of 314 m of limestones, dolomitic limestones and argillaceous limestones at the type locality (Motiei 1993). In the most places of the Zagros Basin, included Lurestan, Khuzestan and some parts of the Coastal Fars and Interior Fars provinces the Asmari Formation lies conformably on the deeper facies of the Pabdeh Formation (Paleocene Oligocene). The Upper contact of the Asmari Formation with the Gachsaran Formation is marked by an unconformity in most places (Fig. 1). Figure 1. Cenozoic stratigraphic correlation chart of the Iranian Sector of the Zagros Basin, adopted from James and Wynd (1965). The Oligocene Miocene marine carbonates of the Asmari Formation are an excellent example of the larger benthic foraminiferal limestones on a broad scale. The particular abundance and radiation of these fauna is in time of Eocene Oligocene. The main objective of this research is biostratigraphy and paleoecology of the Asmari Formation based on the biofacies pattern of the larger benthic foraminifera, in the wells sections at the Rag-e-Safid oil Field. This provides useful tools for the chronostratigrapgy and paleoenvironmental reconstruction of the Asmari Formation on both of the outcrop sections and subsurface sedimentary successions. 2. Regional setting The study area is located at the Rag-e-Safid oil Field with an anticlinal structure, in the fold thrust zone of the Zagros Baisn in southwest of Iran (Fig. 2). This oil Field is about 150 Km southeast of Ahvaz (Fig. 3). It is measured in detail at to N, 49.4 to E at surface. This study involves two well sections of the Asmari Formation from the Rag-e-Safid oil Field. The well number 13 is 2576 m deep and the well number 21 is 2702 m deep (Fig. 4).

3 Biostratigraphy and paleoenvironment of the larger benthic 65. Figure 2. Subdivisions of the Zagros orogenic belt: OL, Oman line; UDMA, Urumieh-Dokhtar magmatic arc; ZDF, Zagros deformational front; ZFTB, Zagros fold-thrust belt; ZIZ, Zagros imbricate zone; ZS, Zagros Suture (After Alavi 2004) Figure 3. Location of the study area at the Rag-e-Safid oil field in southwest of Iran.

4 66 Stratigraphy and Sedimentology Researches 26 th year, Vol. 40, No. 3, Autumn 2010 Figure 4. Location of the wells numbers 13 and 21 from the Rag-e-Safid oil field Because of the incomplete drilling in the wells, there are not any cores from the undrilled lower part of the Asmari Formation at the Rag-e-Safid oil field. Therefore, the lower contact of the Asmari Formation with the Pabdeh Formation (Paleocene Oligocene) cannot be discussed. The upper contact is overlain by the Gachsaran Formation (Miocene). 3. Material and Methods This paper is the first report on the biostratigraphy and paleoecology of the Asmari Formation at the Rag-e-Safid oil field. This study involves the wells numbers 13 and 21 from this oil field. For this research, more than 3000 thin sections of the cores were analyzed for description of biofacies characterizes. The most samples contain wellpreserved and abundant larger benthic foraminifera. The foraminiferal assemblages of the Asmari Formation consist of various imperforate and

5 Biostratigraphy and paleoenvironment of the larger benthic 67. perforate forms. This fauna is a good tool for biofacies analysis, recognition of the paleoecology and biostratigraphy. Biostratigraphic data of the Asmari Formation was established by Wynd (1965) and reviewed by Adams and Bourgeois (1967) in unpublished reports. Adams and Bourgeois (1967) designed four assemblage zones for the Asmari Formation (Table I). Table 1. Biozonation of the Asmari Formation in the Zagros Basin, in south west Iran (Adopted from Adams and Bourgeois, 1967). Ehrenberg et al. (2007) applied the method of strontium isotope stratigraphy to date the Asmari Formation in some localities in the southwest of Iran. The defined assemblage zones at the study area accommodated the biozonation of the Upper Oligocene Lower Miocene sediments (Table 2) by Laursen et al. (2009). Table 2. Biozonation of the Upper Oligocene Lower Miocene sediments by distribution of larger benthic foraminifera (Laursen et al. 2009).

6 68 Stratigraphy and Sedimentology Researches 26 th year, Vol. 40, No. 3, Autumn Previous work The fundamental biostratigraphy of the Asmari Formation was outlined by Thomas ( ). The biostratigraphic criteria of the Asmari Formation were studied by James and Wynd (1965), Adams and Bourgeois (1967), Wells (1967), Seyrafian (1981), Kalantari (1986), Jalali (1987). More recent studies in the paleoecology, biostratigraphy and sequence stratigraphy characterizes of the Asmari Formation were carried out by Seyrafian et al. (1996), Hamedani et al. (1997), Seyrafian and Hamedani (1998, 2003), Seyrafian (2000), Seyrafian and Mojikhalifeh (2005), Vaziri-Moghaddam et al. (2006), Amirshahkarami (2007), Amirshahkarami et al. (2007a-b), Amirshahkarami (2008), Sadeghi et al. (2009), Rahmani et al. (2009) and Vaziri- Moghaddam et al. (2010). Ehrenberg et al. (2007) and Laursen et al. (2009) have applied the method of strontium stratigraphy to date the Asmari Formation. While many full field investigations of the Asmari Reservoir in the Rag-e-Safid oil field (Shirmohammadi et al. 1974; Wiley and Habibi 1978; Petresim Integrated Technologies Ltd Co. 1993; Kish Petroleum Engineering Co. 2003; Zahrabzadeh 2007) a few detailed studies on biostratigraphical and paleoecological aspect have been attempted. 5. Assemblage biozones description The biostratigraphic zonation of the Asmari Formation has been studied by the paleontological analysis in cored sections of the wells numbers 13 and 21 from the Rag-e-Safid oil field. In this research, four assemblage zones have been recognized by distribution of the larger benthic foraminifera in the well sections of the Asmari Formation (Figs. 5-6) Assemblage zone I Assemblage I is characterized by an association of Nummulites fichteli, Nummulites vascu, Eulepidina dilitata, Neprolepidina sp., Eulepidina sp., Heterostegina assilinoides, Praerhapydionina delicate, Pseudolituonella reicheli and Austrotrillina paucialveolata (Plates 1, 4, 5). This microfauna corresponds to the Nummulites vascus- Nummulites fichteli assemblage zone of Laursen et al. (2009) and suggests a Rupelian (Oligocene) age for the lower part of the Asmari Formation. This associated fauna represents Eulepidina-Nephrolepidina-Nummulites biozone of Adams and Bourgeois (1967) Assemblage zone II This assemblage is determined by the presence of Archaias kirkukensis; Archaias hensoni; Archaias operculiniformis; Archaias asmaricus; Borelis pygmaea; Austrotrillina asmariensis; Austrotrillina howchini and Austrotrillina striata (Plates 4, 5). The faunal assemblage of this zone corresponds to Archaias asmaricus - A. hensoni - Miogypsinoides complanatus assemblage zone of Laursen et al. (2009) and represents a Chattian age. This assemblage zone includes lower parts of the Miogypsinoides-Archaias-Valvulinid biozone of Adams and Bourgeois (1967) Assemblage zone III This assemblage is defined by the concurrence of Amphistegina bohdanowiczi, Miogypsinoides deharti, Miogypsina sp., Amphistegin aff. Radiat, Peneroplis thomasi, Peneroplis evolutus, Meandropsina anahensis; Triloculina tricarinata; Dendritina ranji, Bigenerina sp., Eouvigerina sp., Pyrgo sp., Elphidium sp. and Valvulinid sp. (Plates 2, 3, 4, 5). This fauna assemblage zone is correlated with Miogypsina-Elphidium sp Peneroplis farsenensis assemblage Zone of Laursen et al. (2009) and suggests an Aquitanian age.

7 Biostratigraphy and paleoenvironment of the larger benthic Barren zone There is a very fossil poor limestone unit with about 30m thickness, in between the assemblage zone III and the topmost assemblage zone IV. The fauna only consists of miliolids and Dendritina rangi. This sedimentary unit is called barren zone (Figs. 5-6). This zone usually is composed of mudstone or bioclastic wackestone microfacies at the sedimentation setting of lagoon (Amirshahkarami et al. 2007a, b). It has been named the Indeterminate Zone by Laursen et al This sedimentary unit is mainly associated with the Aquitanian age (Amirshahkarami 2007; Laursen et al. 2009) Assemblage zone IV This assemblage zone is recognized in the upper part of the Asmari Formation and is marked by the first appearance of Borelis melo and Borelis curdica in the upper part of the Asmari Formation (Plate 5). These microfauna correspond to Borelis melo curdica - B. melo melo assemblage zone of Laursen et al. (2009) and Borelis melo- Meandopsina iranica biozone of Adams and Bourgeois (1967) and indicate a Burdigalian age. Based on the distribution of the larger benthic foraminifera, four foraminiferal assemblage zones was introduced in the subsurface depositions of the Asmari Formation at the Rag-e-Safid oil Field. These assemblage fauna correspond to the biozonation pattern of Laursen et al. (2009). Correlation of the biostratigraphical characterizes in the wells numbers 13 and 21 from Rag-e-Safid oil Field (Fig. 7) indicates to the following explanations: Because of the incomplete drilling in the wells of the Rag-e-Safid oil Field, the cores of the Asmari Formation contact with the underlying Pabdeh Formation (Paleocene-Oligocene) are not available. Therefore fauna analysis of the lowermost subsurface layers of the Asmari Formation cannot be discussed in these wells sections. In the well number 13, three assemblage zones included biozones I-III have been recognized. In this well, the fauna analysis of the Burdigalian upper Asmari layers (assemblage zone IV) and its upper contact with Gachsaran Formation cannot be defined because their cored sections are not available. 6. Biostratigraphical correlation

8 70 Stratigraphy and Sedimentology Researches 26 th year, Vol. 40, No. 3, Autumn 2010 Figure 5. Biostratigraphy column of the Asmari Formation at the Rag-e-Safid oil field, well no. 13, (Zagros Basin, SW Iran). SGR: Sum Gamma Rays, API: antecedent precipitation index by the American Petroleum Institute. (For lithology symbols see Fig. 6).

9 Biostratigraphy and paleoenvironment of the larger benthic 71. Figure 6. Biostratigraphy column of the Asmari Formation at the Rag-e-Safid oil field, well no. 21, (Zagros Basin, SW Iran) SGR: Sum Gamma Rays, API: antecedent precipitation index by the American Petroleum Institute.

10 72 Stratigraphy and Sedimentology Researches 26 th year, Vol. 40, No. 3, Autumn 2010 In the well number 21, the biozonation of the lower Asmari beds (assemblage zone I) and its contact with underlying Pabdeh Formation cannot be discussed because these layers have been undrilled. - The upper contact of the Asmari Formation with Gachsaran Formation is conformable in the well section 21 (Fig. 7).? Figure 7. Biostratigraphic correlation of the Asmari Formation in the Chaman-Bolbol and Tang-e-Gurgdan outcrops sections and the wells numbers 13 (RS#13) and 21 (RS#21) from Rag-e-Safid oil field, Zagros Basin, SW Iran.

11 Biostratigraphy and paleoenvironment of the larger benthic 73. The correlation of the identified biozones of the Asmari Formation in various outcrop and subsurface sections, indicate to variant numbers of biozones (Fig. 7). For example, at the Chaman- Bolbol and Tang-e-Gurgdan outcrops sections, five assemblage zones have been recognized in the Oligocene-Miocene Asmari Formation (Amirshahkarami et al. 2010; Amirshahkarami 2007). In others sections such as Khaviz and Lali outcrop sections (Kimiagari 2006; Vaziri- Moghaddam et al. 2006), a biofacies of planktonic foraminifera was identified in a Rupelian age in the lower part of the Asmari Formation. Based on the chronostratigraphy and correlation of the many sections, variant thickness and species distribution in the Asmari formation is due to various paleoenvironmental conditions (Amirshahkarami 2007). 7- Paleoenvironment Larger benthic foraminifera are an important tool for the paleoecology recognition of the Cenozoic carbonate platforms. The paleoenvironmental distribution of foraminiferal assemblages depends on intrabasinal conditions including: nutrient, temperature, salinity, depth, light, substrate and water energy (Geel 2000; Hottinger, 1983). According to Hottinger (1983) gradient of the light is the most important factors in distribution of species because it is effective on symbioses and nutrient. Size, degree flatness and wall of the larger foraminifera test, can also provide environmental information (Hallock and Gleen 1986; Langer and Hottinger 2000; Geel 2000). Larger and flatter individuals become more common as the lower limit of the euphotic zone. For example lepidocyclinidae and large and flat nummlitidae occur in the lower photic zone of an open marine but small medium sized and lens shape nummulites lived together alveolina in the uppe part of photic zone in an interior platform. The occurrence of a large number of imperforate foraminifera (e.g. miliolids) is generally taken as evidence for restricted lagoon or relatively nutrient-rich with slightly hypersaline habitat. Perforate foraminifera with symbiotic algae (e.g. lepidocyclinidae, large and flat nummlitidae) occur in the shallow water of the open marine conditions. Planktonic foraminifera are indicative individuals of open marine conditions with slope and basin facies (Geel 2000). In this research the identification of the paleoecology condition of the Asmari Formation is based on the study of the microfacies in thin sections of the cores as following explanations: The recognition of the medium-high energy shallow water in open marine conditions is supported by the abundance of large and flat Nummulitidae and Lepidocyclinidae in facies of Bioclastic Nummulitidae lepidocyclinidae packstone-grainstone (Fig. 8A). The presence of this fauna in comparison with analogues in the modern platform (Hottinger 1983; Hohenegger 1996; Hohenegger et al. 1999; Reiss and Hottinger 1984; Leutenegger, 1984; Hottinger, 1997) indicates that this facies has been deposited in the lower photic zone. The facies of Bioclastic miliolids ooid packstone-grainstone (Figure 8B) suggests the ooids shoals and submarine mobile sandy bars setting (Flügel 2004). The co-occurrence of perforate benthic foraminifera (small Nummulitidae, Miogypsinidae, Amphistegina and Neorotalia) and imperforate foraminifera (miliolids, Borelis and Austrotrillina) in facies of bioclastic perforate foraminifera miliolids wackestonepackstone (Fig. 8C) indicate the semirestricted and open lagoon depositional setting. The small Nummulitidae was reported from open marine conditions by Romero et al. (2002). Miogypsinoids lived in shallow water of normal salinity (Geel 2000) and recent Amphistegina and Neorotalia live in photic zone of shallow water (Romero et al. 2002). According to Taheri et al. (2008) this depositional setting is characterized by microfacies types that include mixed open marine bioclasts and protected environment bioclasts. The depositional setting of a shelf lagoon facies was recognized as bioclastic imperforate foraminifera packstone-grainstone facies (Fig. 8D) with high diversity and abundant of imperforate foraminifera including: miliolids, peneroplids, alveolinids and soritids. Acording to Romero et al. (2002) imperforate foraminifera lived in protected environment. A similar facies was also reported from shelf lagoon by Vaziri-Moghaddam et al. 2006, 2010; Amirshahkarami et al. 2007a-b and Rahmani et al

12 74 Stratigraphy and Sedimentology Researches 26 th year, Vol. 40, No. 3, Autumn 2010 The low diversity of foraminifera and the paucity of fauna in Mudstone facies (Fig. 8E) suggest a restricted lagoon with quiet water conditions. The input of the terrigenous materials into the carbonate environment can take place by erosion of the underlying sediments in a tidal zone (Flügel 2004). Therefore microfacies of Quartz mudstone (Fig. 8F) suggests the tidal flat sediments. By comparing the textures and biofacies with those of recent settings and owing to the similar depositional profile of shelf system, a very low gradient homoclinal carbonate ramp model is suggested for the Asmari Formation in the Rag-e- Safid oil field. Figure 8. Microfacies of the Asmari Formation in Rag-e-Safid oil field, Southeast Ahavaz. (A) Bioclastic Nummulitidae Lepidocyclinidae packstone-grainstone; Well no. 13 (Sample no. 8117'). (B) Bioclastic miliolids, ooid packstone-grainstone; Well no. 21 (Sample no. 8252'). (C) Bioclastic Amphistegina miliolids packstone; Well no. 21 (Sample no. 8390). (D) Bioclastic miliolids Peneroplidae, packstone-grainstone; Well no. 21 (Sample no. 8727). (E) Mudstone;Well no. 13 (Sample no. 7209'). (F) Quartz mudstone; Well no. 21 (Sample no. 8670).

13 Biostratigraphy and paleoenvironment of the larger benthic 75. The paleoenvironmental recognition of the Asamri Formation based on the biofacies analysis suggests the various depositional settings in variant sections. For example, at the Chaman- Bolbol outcrop section four depositional settings including: tidal flat, lagoon, barrier, and open marine were recognized (Amirshahkarami et al. 2007a). At the Lali outcrop section five depositional settings including: tidal flat, shelf lagoon, shoal, slope and basin environmental were recognized (Vaziri-Moghaddam et al. 2006). Anyway, based on the various researches, the Oligocene-Miocene Asmari Formation was deposited as a ramp type carbonate platform at the margin of the Zagros Basin (Vaziri-Moghaddam et al ; Amirshahkarami et al. 2007a-b; Rahmani et al. 2009). Conclusions 1. Based on the distribution of the larger benthic foraminifera, four assemblage biozones have been recorded from the sedimentary cores of the Rag-e- Safid oil field. 2. The most important species are Nummulites fichteli, Eulepidina dilitata; Eulepidina sp., Eulepidina dilitata, Archaias asmarienis, Archaias kirkukensis, Archaias hensoni, Miogypsinoides dehaartii, Austrotrillina asmariensis, Austrotrillina howchini; Peneroplis thomasi, Peneroplis evolutus, Borelis melo and Borelis curdica. The analysis of the vertical distribution of these foraminifera refers to Oligocene (Rupelian) to Early Miocene (Burdigalian) age. 3- There is a barren zone with poorly fossil layers in Aquitanian age. These beds are in the base of the assemblage zone IV (Burdigalian). 4- The paleoenvironment and biofacies of the larger benthic foraminifera suggest four depositional settings included open marine; ooids shoals; lagoon (shelf lagoon and restricted lagoon) and tidal flat. These sedimentary settings correspond to the inner and middle parts of a ramp type carbonate platform. Acknowledgments The authors appreciate National Iranian South Oil Company for cored sections. The authors are grateful to the Payame Noor University of Isfahan for providing financial support and would also like to thank Dr. Naser Arzani and the reviewers for their helpful comments. References 1. Adams, C.G. and E., Bourgeois, 1967, Asmari biostratigraphy: Geological and Exploration Division: Iranian Oil Offshore Company, 1074, (unpublished). 2. Alavi, M., 2004, Regional stratigraphy of the Zagros fold-thrust belt of Iran and its proforeland evolution: American Journal of Science, p. 304, Amirshahkarami, M., 2007, Biostratigraphy, Microfacies and sequence stratigraphy of the Asmari Formation in the Tang-e-Gurgdan (north Gachsaran) and Chaman-Bolbol (north west Fahlian): Ph.D. Thesis, Isfahan University, Isfahan, Iran, 148p., (in Persian). 4. Amirshahkarami, M., 2008, Distribution of Miogypsinoides in the Zagros Basin, Southwest of Iran: Historical Biology, v. 20(3), p Amirshahkarami, M., H., Vaziri Moghaddam, and A., Taheri, 2007a, Sedimentary facies and sequence stratigraphy of the Asmari Formation at Chaman-Bolbol, Zagros Basin, Iran: Journal of Asian Earth Science, v.29, p Amirshahkarami, M., H., Vaziri Moghaddam, and A., Taheri, 2007b, Paleoenvironmental model

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15 Biostratigraphy and paleoenvironment of the larger benthic Hottinger, L., 1983, Processes determining the distribution of larger foraminifera in space and time: Utrecht Micropaleont. Bull. 30, p Hottinger, L., 1997, Shallow bentihic foraminiferal assembelages as signals for depth of their deposition and their limitations: Bull. Soc. Geol. France, v. 168(4), p Jalali, M.R., 1987, Stratigraphy of Zagros Basin: National Iranian Oil Company, Exploration and Production Division Report 1249, Jong K.A. de, 1982, Tectonics of the Persian Gulf, Gulf of Oman and southern Pakistan region, in: Narin, A.E.M., Stehli, F.G., (Eds.), The ocean basins and margins, vol. 6, The Indian Ocean. Elsevier, Amesterdam. p James, G.A., and J.G., Wynd, 1965, Stratigraphic nomenclature of Iranian oil consortium agreement area: American Association of Petroleum Geologists Bulletin, v. 49, no.12, p Kalantari, A., 1986, Microfacies of carbonate rocks of Iran: National Iranian Oil Company, Geological Laboratory Publication, Tehran, v. 11, 520 p. 26. Kimiagari, M., 2006, Biostratigraphy, microfacies and sequence stratigraphy of the Asmari Formation in the Gurpi Anticline (Lali area) to Khaviz Mountain (Behbahan area), PhD. Thesis, Isfahan University, 220p., (In Persian). 27. Kish Petroleum Engineering Co. 2003, Rag-e- Safid Full Field Study and Preparation of Master Development Plan: Contract No: Me01, Tehran, Iran, p Langer, M., and L. Hottinger, 2000, Biostratigraphy of selected larger foraminifera: Micropaleontology, no. 46, p Laursen, G.V., S. Monibi, T.L. Allan, N.A.H. Pickard, A. Hosseiney, B. Vincent, Y. Hamon, F.S.P. van Buchem, A. Moallemi and G. Druillion, 2009, The Asmari Formation Revisited: Changed Stratigraphic Allocation and New Biozonation: First International Petroleum Conference & Exhibition Shiraz, Iran, B Leutenegger, S., 1984, Symbiosis in benthic foraminifera, specificity and host adaptations: Journal of Foraminifera Research, no.14, p Michelotti, G., 1841, Saggio storico die Rizopodi carratteristici dei terreni sopracretacei: Mem., Soc. Ital. Sci. Modena, v. 22, p Michelotti, G. 1861, Etudes sur le Miocene inferieur del Italie septentrionale: Nat. Ver., Holland Maatsch. Wetensch. Haarlem, Ser.2, v. 15, p Montfort de, P., and de, Denys 1808, Conchyliologie Systmatique et Classification Methodique des Coquilles: F. Schoell, Paris, no Motiei, H., 1993, Stratigraphy of Zagros. In: Treatisie of Geology of Iran, 1. Iran Geol. Surv., Publ., p Orbigny, A.D.d., 1826, Tableau methodique de la classe des. Céphalopods: Annales des Sciences Naturelles, Paris, v. 7, no.1, p Petresim Integrated Technologies (Ltd Co.), 1993, Rag-e-Safid Full Field Study: Contract No ,Calgary, Canada, p.1-48, 3543p., NISDC, Ahwaz, P Rahmania, A., H., Vaziri-Moghaddam, A., Taheri, and A., Ghabeishavi, 2009, A model for the paleoenvironmental distribution of larger foraminifera of Oligocene Miocene carbonates rocks at Khaviz Anticline, Zagros Basin, SW Iran: Historical Biology, v. 21, p Reichel, M., 1937, Étude sur les Alveolines: Schweizerische Paläontologische Abhandlungen, v. 59, no(3), p

16 78 Stratigraphy and Sedimentology Researches 26 th year, Vol. 40, No. 3, Autumn Richardson, R.K., 1924, The geology and oil measures of southwest Persia: Journal Institute Petroleum Technology, v. 10, p Reiss, Z., and L., Hottinger, 1984, The Gulf of Aqaba: Ecological Micropaleontology: Berlin Springer. 354p. 41. Romero, J., E., Caus and J., Rossel, 2002, A model for the palaeoenvironmental distribution of larger foraminifera based on Late Middle Eocene deposits on the margin of the south Pyrenean basin: Palaeogeography, Palaeoclimatology, Palaeoecology, no.179, p Sadeghi, R., H., Vaziri-Moghaddam, and A., Taheri, 2009, Biostratigraphy and Palaeoecology of the Oligo-Miocene succession in Fars and Khuzestan areas (Zagros Basin, SW Iran): Historical Biology, v. 21, p Seyrafian, A., 1981, Geological study of the Siah Makan Field (Asmari Formation): National Iranian Oil Company, Report, 37 45, unpublished. 44. Seyrafian, A., 2000, Microfacies and depositional environments of the Asmari Formation, at Dehdes area (A correlation across Central Zagros Basin): Carbonates and Evaporites, v. 15, p Seyrafian, A., H., Vaziri-Moghaddam, H., Torabi, 1996, Biostratigraphy of the Asmari formation. Burujen area, Iran: Journal of Science, v. 7, p Seyrafian, A. and A., Hamedani, 1998, Microfacies and depositional environment of the Upper Asmari Formation (Burdigalian), northcentral Zagros Basin, Iran: Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, v. 210, no(2), p Seyrafian, A., and A., Hamedani, 2003, Microfacies and palaeoenvironmental interpretation of the lower Asmari Formation (Oligocene), North-Central Zagros Basin, Iran: N. Jb. Geol. Palaont. Mh. v. 3, p Seyrafian, A., and A.R., Mojikhalifeh, 2005, Biostratigraphy of the Late Paleogene-Early Neogene succession, north-central border of Persian Gulf, Iran: Carbonates and Evaporites, v. 20 (1), p Shirmohammadi, N., P., Verstfelt, J.,Wiley, 1974, Geology study of Asmari Reservoir in Rage-Safid Field: Report p- 2451, Nisoc, Ahwaz, 90p. 50. Smouth, A. H., and F. E., Eames, 1958, The genus Archaias (Foraminifera) and its stratigraphical distribution: Palaeontology, v. 1, p Stocklin J., 1968, Structural history and tectonics of Iran: A review: American Association Petroleum Geologists Bulletin, v. 52, p Thomas, A.N., 1950, Haplophragmium slingeri sp. Nov., and some new species of Zeauvigerina Finaly from Southwest Iran: Annalus and Magazine of Natural History, v. 12, no. 3, p Thomas, A.N., 1952, Facies variation in Asmari Limestone (with discussion): International Geology Congress 18 th London, Rept. v. 10, p Vaziri-Moghaddam, H., M., Kimiagari, and A., Taheri, 2006, Depositional environment and sequence stratigraphy of the Oligocene-Miocene Asmari Formation in SW Iran, Lali Area: Facies, Springer-Verlag, New York, v. 52(1), p Vaziri-Moghaddam, H., A., Seyrafian, A., Taheri and H. Motiei, 2010, Oligocene-Miocene ramp system (Asmari Formation) in the NW of the Zagros basin, Iran: Microfacies,

17 Biostratigraphy and paleoenvironment of the larger benthic 79. paleoenvironmental and depositional sequence: Revista Mexicana de Ciencias Geolόgicas, v. 27(1), p Vlerk, I.M.van der, 1924, Miogypsina dehaartii, nov. species de larat (Moluques): Eclogae Geologia Helvetiae, v.18, no. (3), p Wells, A.J., 1967, Lithofacies and geological History of Lower Tertiary sediments in southwest Iran: IOOC Report Wiley, J., and F. Habibi, 1978, Geology study of Asmari Reservoir in Rag-e-Safid Field report, unpublished. 59. Wynd, T., 1965, Biofacies of Iranian oil consortium agreement area: Iranian Oil Offshore Company: Report, no. 1082, Unpubl. 60. Zahrabzadeh, M., 2007, Geology studying of the Asmari Reservoir in the Rag-e-Safid Oil Field: Iranian Oil Offshore Company, Report 5954, Unpubl, (In Persian). 61. Ziegler, M.A., 2001, Late Permian to Holocene paleofacies evolution of the Arabian plate and its hydrocarbon occurrence: GeoArabia, v. 6 (3), p

18 80 Stratigraphy and Sedimentology Researches 26 th year, Vol. 40, No. 3, Autumn 2010 Plate 1: Fig. 1: Neprolepidina sp., Oligo.-Miocene, Axial section, Rage Sefid field, Well 13, Iran, Sample no Fig. 2: Eulepidina sp., Oligo.-Miocene, Axial section, Rage Sefid field, Well 13, Iran, Sample no. 8124'6''. Fig. 3: Eulepidina dilitata (MICHELOTTI) 1861; Late Oligocene, Axial section, Rage Sefid field, Well 13, Iran, Sample no. 8105'6''. Fig. 4: Eulepidina dilitata (MICHELOTTI) 1861; Late Oligocene, Axial sections,, Rage Sefid field, Well 13, Iran, Sample no. 8117'. Fig.5: Nummulites vascus JOLY & LEYMERIE 1848; Late Oligocene (Chattian), Axial section, Rage Sefid field, Well 13, Iran, Sample no. 8305'6''. Fig. 6: Heterostegina assilinoides BLANCKENHORN 1890, Late Oligocene, Axial section, Rage Sefid field, Well 13, Iran, Sample no.8311'6''. Fig.7: Nummulites fichteli (MICHELOTTI) 1841; Late Oligocene (Chattian), Axial section, Rage Sefid field, Well 13, Iran, Sample no. 8308'6''. Fig.8: Nummulites fichteli (MICHELOTTI) 1841; Late Oligocene (Chattian), Axial section, Rage Sefid field, Well 13, Iran, Sample no. 8117'.

19 Biostratigraphy and paleoenvironment of the larger benthic 81. Plate 2: Fig.1: Triloculina tricarinata D ORBIGNY 1826; Oligocen Early Miocene, Equatorial section, Rage Sefid field, Well 21, Iran, Sample no ''. Fig.2: Dendritina ranji D ORBIGNY 1826; Oligo.-Early Miocene, Equatorial section, Rage Sefid field, Well 21, Iran, Sample no Fig.3: Valvulinid sp. Oligo.-Miocene; Subequatorial section, Rage Sefid field, Well 21, Iran, Sample no Fig.4: Elphidium sp. DE MONTFORT 1808; Oligocene - Early Miocene, Equatorial section, Rage Sefid field, Well 21, Iran, Sample no Fig.5: Reussella sp.; Oligocene - Miocene, Axial section, Rage Sefid field, Well 21, Iran, Sample no Fig.6: Bigenerina sp. D ORBIGNY 1826;Oligocene - Miocene, Subaxial section, Rage Sefid field, Well 21, Iran, Sample no Fig.7: Pyrgo sp. DEFRANCE 1844; Oligo.- Miocene, Axial section, Rage Sefid field, Well 21, Iran, Sample no ''.

20 82 Stratigraphy and Sedimentology Researches 26 th year, Vol. 40, No. 3, Autumn 2010 Plate 3: Fig. 1: Amphistegin aff. radiat FICHTEL and MOLL, 1949; Late Oligocen Early Miocene, Subaxial section, Rage Sefid field, Well 21, Iran, Sample no Fig. 2: Peneroplis sp., HENSON 1950;Late Oligocene - Early Miocene, Subaxial section, Rage Sefid field, Well 21, Iran, Sample no Fig. 3: Peneroplis evolutus HENSON 1950; Late Oligocene - Early Miocene, Axial section, Rage Sefid field, Well 21, Iran, Sample no Fig. 4: Miogypsina sp., Subaxial section, Miocene (Aquitanian), Rage Sefid field, Well 21, Iran, Sample no. 8252'. Fig. 5: Peneroplis evolutus HENSON 1950; Late Oligocene - Early Miocene, Subequatorial section, Rage Sefid field, Well 21, Iran, Sample no Fig. 6: Amphistegina bohdanowiczi BIEDA 1936; Late Oligocen Early Miocene, Axial section, Rage Sefid field, Well 21, Iran, Sample no Fig. 7: Miogypsinoides deharti (VAN DER VLERK) 1924; Early Miocene (Aquitanian), Subequatorial section, Iran, Sample no

21 Biostratigraphy and paleoenvironment of the larger benthic 83. Plate 4: Fig. 1: Archaias asmaricus SMOUT and EAMES 1958; Late Oligocene, Axial section, Rage Sefid field, Well 21, Iran, Sample no. 8545'. Fig. 2: Archaias operculiniformis HENSON 1950; Upper Oligocene; Equatorial section, Rage Sefid field, Well 13, Iran, Sample no. 8204'6''. Fig. 3: Austrotrillina howchini SCHLUMBERGER, 1942; Late Oligocen, Equatorial section, Rage Sefid field, Well 21, Iran, Sample no Fig. 4: Meandropsina anahensis HENSON 1950; Late Oligocene - Early Miocene, Oblique section, Rage Sefid field, Well 21, Iran, Sample no. 8388'6''. Fig. 5: Meandropsina anahensis HENSON 1950; Late Oligocene - Early Miocene, Oblique section, Rage Sefid field, Well 21, Iran, Sample no Fig. 6: Austrotrillina asmariensis ADAMS 1966; Late Oligocen, Equatorial section, Rage Sefid field, Well 21, Iran, Sample no Fig. 7: Austrotrillina asmariensis ADAMS 1966; Late Oligocen, Equatorial section, Rage Sefid field, Well 21, Iran, Sample no Fig. 8: Austrotrillina paucialveolata GRIMSDALE 1952; Oligocene, Subequatorial section, Rage Sefid field, Well 13, Iran, Sample no Fig. 9: Austrotrillina striata TODD and POST 1954; Late Oligocene, Subequatorial section, Rage Sefid field, Well 21, Iran, Sample no Fig. 10: Archaias hensoni SMOUT and EAMES 1958; Upper Oligocene, Oblique section, Rage Sefid field, Well 13, Iran, Sample no Fig. 11: Peneroplis thomasi HENSON 1950;Late Oligocene - Early Miocene, Subequatorial section, Rage Sefid field, Well 21, Iran, Sample no

22 84 Stratigraphy and Sedimentology Researches 26 th year, Vol. 40, No. 3, Autumn 2010 Plate 5: Fig. 1: Archaias hensoni SMOUT and EAMES 1958; Late Oligocene, Subaxial section, Rage Sefid field, Well 21, Iran, Sample no ''. Fig. 2: Archaias sp., SMOUT and EAMES 1958; Late Oligocene, Obliqueequatorial section, Rage Sefid field, Well 21, Iran, Sample no ''. Fig. 3: Archaias sp., HENSON 1950; Late Oligocene, Equatorial section, Rage Sefid field, Well 21, Iran, Sample no Fig. 4: Archaias operculiniformis HENSON 1950; Late Oligocene; Axial section, Rage Sefid field, Well 21, Iran, Sample no Fig. 5: Archaias operculiniformis HENSON 1950; Late Oligocene; Oblique-equatorial, Rage Sefid field, Well 21, Iran, Sample no Fig. 6: Borelis pygmaea HANZAWA 1930; Oligo.-Miocene, Oblique section, Rage Sefid field, Well 21, Iran, Sample no Fig. 7: Borelis melo (FICHTEL and MOLL) 1798; Early Miocene (Burdigalian), Equatorial section Rage Sefid field, Well 21, Iran, Sample no. 8075' 6''. Fig. 8: Borelis pygmaea HANZAWA 1930; Oligo.- Miocene, Axial section, Rage Sefid field, Well 21, Iran, Sample no. 8735'. Fig. 9: Borelis curdica (REICHEL) 1937; Early Miocene (Burdigalian), Subequatorial section, Rage Sefid field, Well 21, Iran, Sample no Fig. 10: Praerhapydionina delicata HENSON, 1950; Oligocene, Axial section; Rage Sefid field, Well 13, Iran, Sample no. 8271'. Fig. 11: Pseudolituonella reicheli MARIE 1954; Olig.-Miocene, Axial sections, Rage Sefid field, Well 13, Iran, Sample no. 8201'. Fig. 12: Praerhapydionina delicata HENSON, 1950; Upper Oligocene - Early Miocene, Equatorial section of a septum near the center; Rage Sefid field, Well 13, Iran, Sample no Fig. 13: Elphidium sp. DE MONTFORT 1808; Upper Oligocene - Early Miocene, Equatorial section, Rage Sefid field, Well 13, Iran, Sample no. 8193'6''.