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   زیست چینه نگاری، ریز رخساره‌ها و محیط رسوب‌گذاری سازند آسماری در یکی از چاه‌های میدان نفتی مارون و مقایسه آن با سایر نواحی زاگرس  
   
نویسنده گودرزی محمد ,وحیدی‌نیا محمد ,امیری بختیار حسن ,نورایی نژاد محمد رضا
منبع رخساره هاي رسوبي - 1398 - دوره : 12 - شماره : 2 - صفحه:226 -253
چکیده    این مطالعه با هدف زیست چینه نگاری سازند آسماری و مقایسه آن با برش ‌های ماله کوه، چاه میدان نفتی قلعه نار، برش مشکان و برش فیروزآباد و نیز شناسایی ریز رخساره ‌ها و محیط‌ ‌های رسوبی آن در یکی از چاه ‌های میدان نفتی مارون در پهنه فروافتادگی دزفول انجام شده است. ضخامت سازند آسماری در چاه مورد مطالعه 370/5 متر بوده وعمدتاً از سنگ آهک، دولومیت، سنگ آهک دولومیتی، ماسه سنگ و شیل آهکی تشکیل شده است. مرز زیرین سازند آسماری در این چاه با سازند پابده و مرز بالایی آن با سازند گچساران به صورت پیوسته می‌ باشد. پس از مطالعه 150 مقطع نازک میکروسکپی تعداد 43 جنس و 61 گونه شناسایی و بر اساس پخش و پراکندگی آنها شش زیست‌زون تجمعی (پنج زیست‌زون و یک زون مبهم) مورد شناسایی قرار گرفت. زیست‌زون‌های شناسایی شده در چاه مورد مطالعه شامل globigerina spp. turborotalia cerroazulensis hantkenina assemblage zone ، lepidocyclina operculina ditrupa assemblage zone، archaias asmaricus archaias hensoni – miogypsinoides compalanatus assemblage zone، miogypsina elphidium sp.14 – peneroplis farsensis assemblage zone، indeterminate zone و borelis melo curdica borelis melo melo assemblage zone? هستند. بر مبنای مجموعه فسیلی و زیست‌زون‌های شناسایی شده سن سازند آسماری در چاه مورد مطالعه روپلین، شاتین بوردیگالین؟ تعیین شده است. مطالعات انجام شده به شناسایی تعداد 12 ریزرخساره متعلق به محیط ‌های رمپ خارجی، رمپ میانی (بخش دیستال و پروکسیمال)، شول و رمپ داخلی (ریف کومه ای، لاگون نیمه محصور، لاگون محصور و پهنه جزر و مدی) منجر شده است. تبدیل تدریجی رخساره‌ ها به هم، نبود ساخت ‌های ریزشی و لغزشی و نبود دانه ‌های پوشش ‌دار شواهدی از رسوب‌گذاری در یک رمپ کربناته از نوع هموکلینال می‌ باشند.
کلیدواژه زاگرس، الیگومیوسن، میدان نفتی مارون، فروافتادگی دزفو، زیست چینه نگاری، ریزرخساره، رمپ هموکلینال
آدرس دانشگاه فردوسی مشهد, دانشکده علوم, گروه زمین شناسی, ایران, دانشگاه فردوسی مشهد, دانشکده علوم, گروه زمین شناسی, ایران, شرکت ملی نفت مناطق نفت خیز جنوب, ایران, شرکت ملی نفت مناطق نفت خیز جنوب, ایران
 
   Biostratigraphy, microfacies and depositional environment of Asmari Formation in one of the Marun oil field wells and comparison with other Zagros area  
   
Authors Amiri Bakhtiar Hasan ,Goodarzi Mohammad ,Vahidinia Mohammad ,Noraii Nejad Mohammad Reza
Abstract    IntroductionThis study was aimed at the biostratigraphy and sedimentary environments reconstruction in one of the wells in Maroun oilfield at Dezful embayment zone. We also compared the studied subsurface section with the equal intervals in MalaKuh, GhaleNar oilfield, Moshkan section, and Firouzabad section. The thickness of Asmari Formation in the studied well is 370.5 m and consists mainly of limestone, dolomite, dolomitic limestone, sandstone and argillaceous limestone. In this well, the lower boundary of the Asmari Formation with Pabdeh Formation and its upper boundary with Gachsaran Formation is continuous.Method and MaterialsFor this study, 150 thin sections (mainly drilled cores) were studied in detail for paleontology, biostratigraphy, allochems identification, and microfacies determination. References such as Loeblich and Tappan (1980), BoudagherFadel, (2008), Adams Bourgeois (1967), and other related articles were used to identify the available microfossils. We used the biozonation scheme of Laursen et al. (2009) and Van Buchem et al. (2010) to define and correlate the biozones. Classification of rock types was done according to Dunham (1962) and Embry Klovan (1971), and microfacies identification and interpretation were carried out based on Wilson (1975), Buxton Pedley (1989), Geel (2000), and Flugel (2010),Results and DiscussionBased on paleontological studies, 43 genera and 61 species of benthic and planktonic foraminifera were identified. They have been classified into six zones (five assemblage zones and one indeterminate zone) as follows:1 Globigerina spp.Turborotalia cerroazulensisHantkenina Assemblage ZoneThis biozone is 76 meters thick and lies between the depths of 3706.5 to 3630.5 m. It corresponds to the upper part of the Pabdeh Formation. In this biozone with Oligocene (Rupelian) age, Globigerina spp. are abundant, and the extinction of Turborotalia cerroazulensis occurs in this biozone.2 LepidocyclinaOperculinaDitrupa Assemblage ZoneThis biozone is 129.5 meters thick and lies between 3630.5 to 3501 m. The beginning of this biozone is based on the first occurrence of the Lepidocyclina sp. and Operculina complanata. Its end is marked by the first appearance of the Miogypsinoides compalanatus and Spiroclypeous blankenhorni. This biozone belongs to the ChattianRupellian age.3 Archaias asmaricusArchaias hensoniMiogypsinoides compalanatus Assemblage ZoneThe thickness of this biozone is 80 meters and lies between 3501 to 3421 meters deep. The onset of this biozone is marked by the first occurrence of Miogypsinoides compalanatus and Spiroclypeous blankenhorni. The first occurrence of Elphidium sp.14, Peneroplis farsensis and disappearance of Archaias distinguish the end of the biozone. The age of this biozone is Chattian.4 Elphidium sp.14 – Peneroplis farsensis Assemblage ZoneThis Assemblage zone is 83 meters thick and lies between 3421 to 3338 meters deep. The age of this biozone is Aquitanian. The onset of this biozone is determined by the occurrence of the Elphidium sp.14, Peneroplis farsensis, and the end of this biozone is characterized by a decrease in the fossil fauna assemblage known as the Ambiguous Zone.5Indeterminate ZoneWith 70.44 meters thickness, this zone lies between the depths of 3338 to 3267.57 meters. A decrease in fossil assemblages characterizes this interval. According to its stratigraphic locality, this indeterminate zone is related to Aquitanian (Laursen et al., 2009). The fossils present in this biozone are very sparse and consist mainly of porcelaneous and indeterminate milliolids.6 Borelis melo curdicaBorelis melo melo Assemblage Zone?This biozone is related to the uppermost part of the Asmari Formation. The beginning of this biozone is defined based on the occurrence of the Borelis spp., continues to the end of the Asmari Formation. This biozone is 7.56 meters thick and lies between 3267.56 to 3260 meters deep. The age of this biozone is cautiously Burdigalian.Based on the mentioned biozones, the age of Asmari Formation in the studied well is Rupelian – Chattian –?Burdigalian.According to sedimentary texture, sedimentary structures, skeletal and nonskeletal elements in the microscopic studies if the provided thin section, 12 microfacies related to the outer ramp, middle ramp (distal and proximal parts), shoal and inner ramp environments (patch reef, lagoon (semirestricted and restricted( and tidal flat were identified in the studied well. Gradual changes of facies to each other, the lack of coated structures, and the absence of coated grains are the main evidence suggesting deposition in a homoclinic carbonate ramp. Microfacies analysis shows that planktonic foraminifera in the upper part of the Pabdeh Formation belongs to the outer ramp. Due to the presence of large hyaline foraminifera, the lower part of the Asmari Formation is deposited in the distal part of the middle ramp, while the presence of lenticular foraminifera demonstrates the proximal ramp environment. A highenergy, shallowshoal environment with the presence of thickwalled lenticular foraminifera, cementation, and grainstone textures characterize the boundary between the middle and the inner ramp. Inner ramp environment is considered by the presence of patchy corals (patch reef) and imperforate foraminifera (Archaias, Peneroplis, milliolids) of the lagoon (semirestricted and restricted lagoon) and tidal flat zones.ReferencesAdams, T.D., Bourgeois, F., 1967. Asmari biostratigraphy. Iranian Oil Operating Companies. Geological and Exploration Division, Report 1074: 137. (Unpublished)BoudagherFadel, M.K., 2008. Evolution and Geological Significance of Larger BenthicForaminifera. Developments in Paleontology and Stratigraphy, 21. Elsevier, Amsterdam, p. 544.Buxton, M.W.N., Pedley, H.M., 1989. A standardized model for Tethyan Tertiary carbonates ramps. Journal of the Geological Society, London, 146: 746748.Dunham, R.J., 1962. Classification of carbonate rocks according to depositional texture. In: Ham, W.E., (ed.), Classification of carbonate rocks. American Association of Petroleum Geologists Memoir, 1: 108121.Embry, A.F., Klovan, J.E., 1971. A Late Devonian reef tract on northeastern Banks Islands, Northwest Territories. Bulletin of Canadian Petroleum Geology, 19: 730781.Flügel, E., 2010. Microfacies of Carbonate Rocks, Analysis Interpretation and Application. SpringerVerlage, Berline, Heidelberg. 984 p.Geel, T., 2000. Recognition of stratigraphic sequences in carbonate platform and slope deposits: empirical models based on microfacies analysis of Paleogene deposits in southeastern Spain. Paleogeography, Palaeoclimatology, Palaeoecology, 155: 211238.Laursen, G.V, Monibi, S., Allan, T.L., Pickard, N.A.H., Hosseiney, A., Vincent, B., Hamon, Y., Van Buchem, F.S.H., Moallemi, A., Driullion, G., 2009. The Asmari Formation revisited: Changed stratigraphic allocation and new biozonation, First international petroleum conference exhibition, Shiraz, Iran.Loeblich, A.R.Jr., Tappan, E., 1988. Foraminiferal genera and their classification. Van Nostrand Reinhold Campany, New York, 1970.Van Buchem, F.S.P., Allan, T.L., Laursen, G.V., Lotfpour, M., Moallemi, A., Monibi, S., Motiei, H., Pickard, N.A.H., Tahmasbi, A.R., Vedrenne, V., Vincent, B., 2010. Regional stratigraphic architecture and reservoir types of the OligoMiocene deposits in the Dezful Embayment (Asmari and Pabdeh Formations), SW Iran. Geological Society, London, Special Publications, 329 (1): 219263.Wilson, J.L., 1975. Carbonate facies in geologic history. 1st edition, SpringerVerlag, New York, 1471.
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