Bull

Saadi K. Jan & Aqeel A. Al-Zubaidi

Bull. Iraq Nat. Hist. Mus.

(2014) 13 (1): 19-26

SEDIMENTARY STUDY OF SHIRANISH FORMATION AT HIJRAN

SECTION- NORTH IRAQ

Saadi K. Jan and Aqeel A. Al- Zubaidi

Natural History Research Center and Museum- University of Baghdad

ABSTRACT
Shiranish has been studied at Hijran section near Erbil city, NE Iraq. Fifty two thin-sections

were prepared to study them under polarized microscope, to determine the petrographic

component, organic content and digenetic processes. Rock units subdivided into four rock beds,

as follows: dolostone, foraminiferal biomicrite, poorly washed biomicrite and micrite. Vertical

succession of Shiranish Formation refers to off-shore quite marine environment.

INTRODUCTION
Shiranish Formation cropping out at the high- folded zone North Iraq, and also within

subsurface sections during the wells reaching Upper Cretaceous (Dunnington,1958). It’s

thickness about 225 m in type section near Shiranish Islam village north east Zako, Dahuk

Governorate and comprises blue marl and thin bedded marly limestone. It has conformable

lower contact with Beckme Limestone Formation, and upper contact with Aliji Formation that

seem to be conformable surface, but there is fossils break indicate to Cretaceous- Tertiary

boundary (Bellen, et al. 1959). Bed rocks of this formation enriched by planktonic

foraminifera that refer to off- shore depositional environment (Bellen, et al., 1959); (Buday,

1980). This study aims to determine paleoenvironment according to petrography, organic

content and diagenitic processes.

MATERIALS AND METHOD
Fifty two rock samples were collected from Shiranish Formation at Hijran section near

Shaqlawa Town, Erbil Governorate, North Iraq. Sample interval ranged from 1- 1.5 meters

(Kidwell and Holland, 1991) and thinned section (Voelkel, 1967) to study the petrography,

organic content and diagenetic processes by polarized microscope.

RESULTS AND DISCUSSION
Shiranish Formation has been subdivided to four beds according to petrography, organic

content and digenetic processes (Folk, 1974), as follow:

1- dolostone bed: this bed composed of sugary dolomite of equal sizes and similar texture

(plate 1-1), which composed by diagenetic replacement of carbonate sediments, so this bed

considers secondary origin (Schoole, 2003). Secondary dolomite indicates postdepositional

replacement of limestone or calcareous sediment by the progressive slow growth. Secondary

dolomite characterized by sugary texture may be formed at different diagenetic stages. The

boundaries of dolomite may cross original texture, thereby can't preserve depositional

interpretations (Nichols and Silbering, 2010). Dolostone bed deposits under supra tidal

environment due to organic absence and composed the lower part of Shiranish Formation

(Moore, 2001).

2- Foraminiferal biomicrite bed: it is characterized by the abundance of planktonic

foraminifera at micrite (plate 1-2), spary calcite cement filled chambers of some fossils but

Sedimentary Study Of Shiranish Formation At Hijran
rarely appeared between skeletal grains. Cement was deposits within fractures and joints

during late diagenetic processes due to tectonic uplift (Bathrust, 1975). The abundance of

planktonic foraminifera and micrite of brown to dull color refer to quite deep marine

environment (Flugel, 2010). Iron oxside has been observed in the some pores, and also

pyrite as cubic shape (Plate 1-3), and as scattered in micrite and in fossil chambers (Siesser,

1976).

3- Poorly washed biosparite bed: this bed characterized by the abundance of planktonic

foraminifera such as Globotruncana sp. (Plate 1-4) and Gobigerina sp. Chambers of most

fossils filled by micrite (Plate 2-1), while the pores of micrite filled by iron oxides (2-2).

This refers to quite deep marine environment (Wilson, 1975). This bed composed the main

component of the formation.

4- Micrite bed: this bed composed mainly of partly or completely recrystalized micrite (Plate

2-3) and transformed to microspare under newformism process and minor amount of

unidentified skeletal grains are present. The pores are filled by pyrite (Plate 2-4). Planktonic

and benthonic foraminifera are the most important fossils of this bed (Pisera, 2002).

CONCLUSIONS
Shiranish Formation at Hijran Section subdivided into four beds: dolostone bed,

foraminiferal biomicrite bed, poorly washed biosparite bed and micrite bed. Some of beds

containes planktonic foraminifera, and the main diagenetic processes are the cementation and

recrystalization. This formation deposited at quite marine environment.

REFERENCES
Al-Kassab, I.I., 1979. The genus Globotruncana Cushman from the upper Cretaceous of

Northern Iraq. Jour. Geol. Soc. Iraq. V.13, pp 27-127.

AL- Nanqib, K. M., 1959. Geology of the Southern area of Kirkuk Liwa, Iraq. Iraq petroleum

Co. Technical Pub., London. 50p.

Bathurst, R.G.C., 1975. Carbonate sediment and diagenesis, develoment in sedimentology 12,

2 anded., Elsevier pub. Co. 659 p.

Bellen, R.C.Van, Dunnington, H. V. Wetzel, W. and Morton, D. M., 1959. Lexique

Stratigraphique International, Asie, Fasc.10a, Iraq, center nat. Rech, Sci., Paris,

333p.

Buday, T.1980. The Regional Geology of Iraq. Stratigraphy and Paleography, Vol. 1.

GEOSURV, Baghdad, Iraq.

Daniel, E. j. A., 1954. Fractured reservoir of Middle East. Bull. AAPG. V.38, pp. 77- 815.

Dunnington, H. V., 1958. Generation, migration, accumulation and dissipation of oil in

northern Iraq, in week: L.G. (ed.), Habitat of oil, a symposium AAPG. Spec. pub.,

1194-1251.

Fluegel, E. 2010. Microfacies Analysis of Limestone. Springer. Berlin. 984.

Folk, L. 1974. Petrology of Sedimentary Rocks. Hemphill, Texas, 182 p.

Saadi K. Jan & Aqeel A. Al-Zubaidi

Kidwell, S. M. and Holland, S. M., 1991. Field description of coarse bioclastic fabrics. Palaios,

6, 426-454.

Moore, C., 2001. Carbonate Reservoires. Elsevier, Amsterdam, 460 p.

Nicgols, K. M. and Silberling, N. J. (2010). Eogenetic dolomitization in the Pre- Tertiary of

the Great Basin. SEPM, special publication, No. 28, 237- 246.

Pisera, A., 2002. Fossil "lithistids". In: Hooper, J. N. A. and Van Soest, R. W. M. (Eds.).

Systema Porifera. A guide to the Classification of Sponges, New York. 1, 388-

402.

Scholle, P. A. and Scholle, D.S.U., 2003. A color guide to the petrography diagenesis . AAPG

memoir 77, Tulsa, oklahama, USA, 459p.

Siesser,W. G.,1967. Authigenic pyrite and gypsum in south west African Contenental slop.

Sedimentology ,Vol. 23, pp 567.

Voelkel, H., 1967. Allgemeine ueber die Anfertigung von Dueschliffe und Anschlifften der

praeparator. Bonn. 13, 155-169.

Wilson, J. L., 1975. Carbonate Facies in Geologic History. Springer –Verlag. Berlin. 471p.

Sedimentary Study Of Shiranish Formation At Hijran

Fig. 1: Study area on the map of Iraq.

Saadi K. Jan & Aqeel A. Al-Zubaidi

Fig. 2: Lithologic section of Shiranish Formation at Hijran.

Sedimentary Study Of Shiranish Formation At Hijran

Plate-1

1- Sugary texture 100x.

2- Planktonic foraminifera in micrite 100x.

3- Cubic pyrite in foraminiferal biomicrite bed 100x.

4- Chambers of planktonic foraminifera, Glopotruncana sp. Filled by calcite 100x.

Saadi K. Jan & Aqeel A. Al-Zubaidi

Plate- 2

1- Foraminiferal chamber filled by micrite in the poorly washed biosparite bed 100x.

2-Iron oxides filled pores in micrite 100x.

3-Recrystalized micrite 100 xs.

4-Pores filled by pyrite 100x.

Sedimentary Study Of Shiranish Formation At Hijran
Bull. Iraq Nat. Hist. Mus.

(2014) 13 (1): 19-26

شمال العراق دراسة رسوبية لتكوين شيرانش في مقطع حجران

عقيل عباس الزبيدي وسعدي خان جان

جامعة بغداد –مركز بحوث ومتحف التاريخ الطبيعي

الملخص

درس تكوين شيرانش في مقطع هجران قرب مدينة اربيل، شمال شرق العراق، بعد

شريحة رقيقة ثم درست تحت المجهر المستقطب، لتحديد المكونات الصخرية، 25تحضير

: لى اربع طبقات صخرية هيوبعد ذلك قسمت ا. والمحتوى االحيائي والعمليات التحويرية

طبقة الحجر الدولومايتي، وطبقة الحجر المكرايتي الحياتي الفورامنيفري، وطبقة الحجر

اشار التتابع العمودي لطبقات صخور . الحياتي ضعيف الغسل، وطبقة الحجر المكرايتي

.تكوين شيرانش على انها مترسبة في بيئة بحرية هادئة بعيدة عن الساحل