5 47 S. K. J. Kaka Bull. Iraq nat. Hist. Mus. (2010) 11 (1): 47-56 SEDIMENTO LOGICAL STUDY OF SHIRANISH FORMATION WELL DD-1 (N-IRAQ) Sadi Kan Jan Kaka Iraq Natural History Research Center and Museum ,University of Baghdad, Bab Al-Muadhum, Baghdad, Iraq ABSTRACT Shiranish formation has been divided into two microfacies units: 1-Marly biowacke stone facies 2-Biogenic pack stone facies These microfacies reflected marine deep shelf margin in the upper part of the formation, the lower part was deeper. 238 slides were investigated depending on Mineralogical, compositional and Biological processes, which reflect deep shelf margin at upper part of the formation, but at the lower part open sea environment. The age of the formation is estimated depending on the recognized biostratigraphic zone using the index fossils to be Upper- Middle Maestrichtian. INRODUCTION Shiranish formation was first defined by Henson 1940 in (Buday et, al., 1980) from the High folded zone of northern Iraq near the village of shiranish Islam, northeast of Zakho . The formation consists of blue marls in the upper part and marly limestone and dolomite in the lower part. The present well is located in the northern part, 25 km west of Erbil city (Fig.1). The aim of the study is to identify lithology and fossil groups present in the rock. A total of 238 slides of rock cutting and core are examined for comparison purpose. The thickness of an ideal section in Shiranish formation near shiranish village in north east of zakho is about (225) m. and the average of this thickness is changed in other areas from (100) m to (400) m. (Van Bellen, etal.,1959) has described shiranish formation and divided it into two parts: bottom part that consists of marly limestone and is rich with fossils, and upper part that consists of blue marls considering the formation as an open environment. Shiranish formation has been described by (Al-Shaibani, 1973) in Asmer Area, 15 miles north Sulaimaniya and he described the formation as consisting of blue, yellow and orange marls overlapped with layers of marly limestone. ( kassab, 1973) has also studied shiranish formation in the ideal section in shiranish area to the north east of (zakho) and he has found that it consists of limestone of different shades varies from light gray to brown, leady and dark gray with marls vary from gray to blue. He has, also, limited the age of the formation to Upper-Middle Maastrichtian. (Kaddouri, 1989) has, also, studied the formation in the north west of Iraq and north east of Syria and confirms that Shiransh formation is located on the (Kometan) in the Iraqi wells. As for (Yahya Al-Shammary, 1993), he has studied Shiranish formation and (Tanjero) in Shaqlawa in north Iraq and divided the formation into four units. 48 Sediment Logical Study of Shiranish MICROFACIES The rocks of shiranish formation in the Northern Iraq, west of Erbil is divided into two micro sedimentary facies after examining (238) thin sections by polarized microscope depending on (Dunham 1962) specification which modified by (Wilson 1975) depending on litho logical component and some fossils (Fig.2 ) A sketch of distributing microfacies for sedimentary basin of the formation has been drawn according to ( Wilson model 1975 ) (Fig.3) . The sedimentary microfacies are as follows: 1- Marly biowackestone facies : This facies lies in the upper part of the formation, with thickness of ( 120 ) m and constitutes 90% of the thickness of the formation , the most important fossils: Hetrohelix glabrans , Globigerinelloides , Rugoglobigerina reichellli , Globotruncana aegyptica , Globotruncana stuarti plate(1-1) and Echinoderms plate(1-2). . The matrix composed of micrite rich in clay. The most important diagenetic process is the precipitation of cement inside shells and cracking in foraminifera,and the alteration of micritic- matrix by recrystallization in which rhombic dolomite substitute the matrix leaving the fossil chambers empty of these dolomite plate (1-3). This reflects the autogenic dolomitzation since the dolomite crystals grains magnesium ions from the same place growing on it (Fuechtbauer 1977) . This facies is similar to the (S.M.F. 3) of the facies zone (F.Z.3) which indicates to deep shelf margin 2-Biogenic pack stone facies This facies lies in the lower part of the formation with thickness of (13) m and constitute 10% of the bulk formation. The skeletal components composed of plank tonic foraminifera in the matrix-micrite like Globotruncana conica , Globotruncana duwi , globotruncana gansseri . The most important digenetic process is the alteration of micritic matrix by recrystallization in which rhombic dolomite substitute the matrix leaving the fossil chambers empty of these rhomboid. This reflects the autogenic dolomitzation since the dolomite crystals grains magnesium ions from the same place growing on it plate (2-1) (Fuechtbauer 1977). Precipitation of drossy cement was also observed in some parts of plank tonic foraminifera . These processes increase the lower part of this facies with the appearance of autogenic Pyrite (2-2) and Glauconite in the micritc- matrix) in side some shells. This facies is equivalent to standard microfacies (S.M. F.2) zone (F.Z. 2) which indicates to open sea on normal salinity. CONCLUSIONS A – Shiranish formation is divided into two micro facies 1- Marley biowacke stone facies 2- Biogenic pack stone facies B-Some autogenic minerals are present, like Glauconite accompanied with pyrite in the upper part of the formation. This means that its formation occurred in the strom wave base. C- The deposition of shiranish formation represented by packstone facies in the lower part then changed into wackestone facies in the upper part. This reflects the change in environment from high energy of low energy environment, that it means as a deepening upward cycle. 49 S. K. J. Kaka LITERATURE CITED Al-shibani,s.k.1973, Microfossils from shiranish Formation in Northeastern Iraq (Sulimania, Asmer Region), Jour.Geol. Soc..Iraq, Vol.pp 49-65. Buday, T. 1980 The regional geology of Iraq. V.1. Stratigraphy and paleography, 445pp. Dunham, R.J.1962 Classification of carbonate rocks according to depositional texture in Ham, w, w.E.(ed): Classification of carbonate rocks : AAPC Memoir 1,pp 108-121 Fluegel, E. 1982 Microfacies of limestone . Berline – Heidel berg –New York: Springer- Verlag,633pp. Fuechtbauer, H.1977 Sedimente und sedimentgestine , E. Schweizerbartsche Verlagbuch hanlung . 784 pp. Henson, F.R.S.1950 Cretaceous and tertiary reef formation, and associated sediments in Middle East. Bull .Amer . Assoc. Petrol. Geol., 238 pp. Kaddouri,N., 1989, Stratigraphy of the Mesozoic and Cenozoic Sediments in Sinjar Depression , Jour. Geol. Soc. Iraq , Vol. 22,No.2 Kassab,I.I.M. 1973, planktonic foraminifera of the shiranish Formation Type –Locality ( Northern Iraq ), jour. Geol. Soc.Iraq, Vol. 6. Wilson, J.L.1975 Carbonate facies in geologic history: Springer – Verlag, pub l . , Berlin- Heidelberg – New York, 471 pp. Yahya,N.A. and Al-Shammary, T.A., 1993, sedimentary Features and Depositional processes in the shiranish and Tanjro Formation , Shaqlawa Area Arbil , N. Iraq , Iraqi Geological Journal, Vol.26, No. 3. pp.135-154 . 50 Sediment Logical Study of Shiranish 51 S. K. J. Kaka 52 Sediment Logical Study of Shiranish Fig. 3 W ilson m odel 53 S. K. J. Kaka Plate (1) 1-Planktonic foraminifera in wackestone 40x facies 2-Echinoderms in micritic-matrix 100x 3- The chambers of Globotruncana filled with rhomboid dolomite 40x Plate (2) 1-Rhombohedral dolomite in micritic-matrix 40x 2-Autogenic pyrite is in the chamber of the plank tonic foraminifera 40x 54 Sediment Logical Study of Shiranish Plate ( 1 ) ٢ 2 1 3 55 S. K. J. Kaka Plate ( 2 ) 2 1 56 Sediment Logical Study of Shiranish Bull. Iraq nat. Hist. Mus. (2010) 11 (1): 47-56 (شمال العراق) -١-دراسة رسوبية لتكوين الشيرانش فى بئر دمرداغ كاكا سعدى خان جان ، جامعة بغداد، باب المعظم، بغداد، العراقمركز بحوث ومتحف التاريخ الطبيعى الخالصة مت تقسيم صخور تكوين الشريانش اىل وحدتني سحنية باستخدام الشرائح الرقيقة املعمول لنماذج اللباب والفتات الصخرى وذالك باالعتماد على املتحجرات املميزة باالضافة اىل نوعية النسيج الصخري والذي تتواجد فيه املتحجرات سحنة احلجر اجلريي الواكي العضوي املاريل . -١ نة احلجر اجلريي املرصوص العضوي .سح -٢ تعكس هذه السحنات ظروف بيئية حبرية عميقة يف اعلى التكوين واجلزء االسفل أكثر عمقَا يف بيئة ساحل البحر املفتوح . وقد مت حتديد عمر تكوين الشريانش يف املنطقة اليت مشلها الة ب ( املاسرتخيت) األعلى والوسطى.البحث استناداَ إىل النطاق الطبقي لتواجد املتحجرات الد