3 39 S. K. Jan Bull. Iraq nat. Hist. Mus. (2004) 10 (2): 39-47 MICROFACIE STUDY OF SUBSURFACE SECTION OF BEKHME FORMATION(NORTH IRAQ) Sadi Kan Jan Iraq Natural History Museum University of Baghdad Baghdad , Iraq ABSTRACT Bekhme formation, Dernir Dagh well -1 has been divided into two facies units using core sample slides and depending on sedimentary structures and diagenetic processes .The facies reflect the environment of the foreslope.This work proves the absence of Bekhme formation in Dernir Dagh Well- 1 as a tongue as reported by the Oil Exploration Company. Some species and genera of bentonic foraminifera were identified. The age of Bekhme formation was estimated depending on the recognized index fossils to be lower Maastrichtian. INRODUCTION Bekhme limestone formation was first defined and described by wetzel (1950) in a gorge of the greater Zab river in the high folded zone. Bellen et al . ( 1959) mentioned that the Bekhme Formation in its upper division composed of bituminous secondaryT dolomites, replacing organic detrital limestone; in its middle division as reef detrital limestone ,alternating with reef shoal limestone and its lower division as basal breccia conglomerates. The studied area situated 25 km west of Arbil City, north of Iraq (fig. 1) .The aim of the present study is the identification of the sedimentary facies of Bekiune formation and to know the litholoicain nature and the fossil groups present in the rocks to determine the environment of Bekhme Formation. A total of 41 thin section slides were examined. BIOSTRTIGRAPHY Most of the fossils present in Bekhme Formation are Rudists and species of bentonic foraminifera as Cosinella sp. Cuneolina cytcylindrica , Dictyoconella Complanata, Ephidicella multiscissuriata, Dicyclina schumbergeri. In addition, fragments of echinoid spines, ostracods and mussel shells, are present. MICROFACIES Bekhme formation was divided, depending on sedimentary structures and diagenetic processes, into diagenetic and non diagenetic sedimentary facies as descrided by wilson (1975) and fluegel (1982). 1. Bioclast packstone with Rudists -Echinodermis fragments facies : Thickness of this facies 95 ft and represents 56 . 5% of the total thickens of the formation. It contains a high Ration of rudists and broken fragments of echindenns , ostracods and mollusca shells, the extraclast presents in a small ratio This facies is affected by cementation of some shells especially ostracods filled with cement -B. In the upper part of the formation with thickness of 24 ft , the authogenic dolomite scattered in a micritic matrix . The 40 Microfacie Study of Subsurface Section authogenic glauconite is also observed . This facies represents the standard microfacies (SMF-3)of the facies zone (FZ-3) fore slope. 2. Recrystallized Rudists - Echinoderms fragments : The thikness of this facies is 73 ft and represents 43.5% of the total thickness of the formation . it contains broken fragments of rudists echinoderms . and some bentonic foraminifera and mollusca. This facies composed of recrystallized microsparite as it appeared in some indefinite fossils because of filling their chambers with sparite. This facies characterized -with presence of Authigenic minerals as glauconite which increased in ratio with the depth until it become 5% in the bottom of the formation . The presence of glauconite indicates a marine environment with a very slow deposition. There is also pyrite spreaded in all of the formation parts filling cracks as inoldic pyrite. The stylolite is also observed in the formation bottom ,it intersects minerals initiated after diagenetic processes like calcite cement and secondary dolomite. This facies represents the standart microfacies (SMF-4) of the facies zone (FZ-4) fore slope,fig.2.shows the distribution of microfacies in the well. CONCLUSIONS 1. The Bekhme formation in Demir Dagh well-i is not present as tongue as it reported by the Oil Exploration Company. 2. The separation limit between Bekhme formation and shiranish formation is estimated at the depth 5540 ft; and between Bekhme formation and kometan formation at the depth of 5708 ft. 3. The Bekhrne formation is divided into two facies ;a-Bioclast packstone with Pudisten- Echinoderms fragments, b-Recrystallized Rudisten-Echinoderms packstone. 4. The stylolite present in the bottom of the formation filled with pyrite was formed after solidification since the stylolite intersects minerals formed after the diagenetic processes like cacite-cement and secondary dolomite. 5. The most important diagenetic processes is the affection of micritic matrix by the recrystallization. The dolomite rhompoides appear to replace mnicritic matrix, and the fossil chambers remain empty of these rhomboides This indicate authigenic dolornization since dolomitetcrystals extracted Magnesium ions from the same place growing on. 6. The age of the Bekhme formation , depending on index fossils, is estimated to be lower Maasrichtian.. LITERATURE CITED Bellen, V. R. 0. 1959 Lexique Stratigraphiqua International . paris .333 pp. Buday,T. 1980 The regional geology of Iraq Nol. 1 stratigraphy and paleography 7445 pp. Dunham,R.T. 1962 Classification of carbonate rocks according to depositional texture. In Ham p.108- 121. Dunnington,H.V .1955 Micropaleontology. Vol.1 ,no.3, Dept. Micropaleontology-NY,2 l9pp. Dunnington,H V.1954 Stylolite development , Vol.24, no.1, journal of sedimentary petrology,Iraq petroleum Company .pp49 Engelhardt,W.V. 1973 die Bildung von sedimente und sedimentgesteinen.Berlin-Heidelberg. 41 S. K. Jan Flugel,E. 1982 Microfacies analysis of limestone .Berlin-Hei’delberg-New york; Spriger Verlag,633pp. Fuechtbauer, H. 1977 S edi inente und sedi mentgestei nen . E. Scheizerbartsche. verlagsbuchhandlung, 784pp. Krurnbein,W.C.,Sloss,L.L. 1963 Stratigraphy and sedimentation .2..Aufl., San Francisco- London 660pp. Stehli,F.G. ,Hower,j. 1961 Mineralogy and early diagenetic of Carbonate sediments.Tulsa 371 pp. Wilson,J.L 1975 Carbonate facies in geologic history; Springer Verlag pub.,Berlin Heidelberg-New york, 471 pp. Wetzel,R. 1950 Stratigraphy of the Amadiya region .MPC.Report ,INOC Library,No. TR/RW 12, Bagdad. 42 Microfacie Study of Subsurface Section 43 S. K. Jan 44 Microfacie Study of Subsurface Section 45 S. K. Jan 46 Microfacie Study of Subsurface Section Plate 1: 1. Recrystalliaed echinoderms packstone 20X 2. J3iociast Packitone with )ctraclat 20X Plate 2 : 1. Moc).atic Paokstone with Rudists.-Echinoderms fragment and glauconite grains 20Z 2. Sty)olith in IL:5critio ma’c 20X 47 S. K. Jan Bull. Iraq nat. Hist. Mus. (2004) 10 (2): 39-47 قطع خمة ف م ن لب كوي ري لت جه م ت ل حنا س س ا ي درا ت طح راق(تح ل ا ع ما )ش خا جان سعد ي خ ال بيع ري ف ال ا ح مت داد ة بغ جامع ة ص الخال دام ال رائح الرقي ة حنيت با ت س ني ىل وح ت رداغ ا م يف بئ مة خ ور ال خ م ص سي مت تق العمولة لنماذج اللباب الصخري وذلك باالعتماد على نوعية الريب الصخري والعمليات .التحويرية لقد امكن من اثبات عدم تواجد تكوين البخمة يف بئر دمرداغ على شكل لسان كما هو وارد يف تقرير احلفر النهائي لشركة االستكشافات النفطية، لقد امكن من متييز عدد من انواع واجناس اسرتخيت الفورامينغريا العلمية، ومت تقدير عمر تكوين البخمة يف املنطقة اليت مشلها البحث اىل امل .االسفل