ORIGIN OF LIMESTONE CONGLOMERATE IN DOKAN (Dukan) AREA, KURDISTAN REGION, NORTHEAST IRAQ
By: Kamal Haji Karim and Zardasht Ahmad Taha, University of Sulaimani
published in: Iraqi Bulletin of Geology and mining, Vol.2, No.3, p.15-24, 2012
Thick succession of limestone conglomerate (about 300m thick) is exposed on right and left sides of Dokan reservoir and covers more than 40km2 of surface area. The conglomerate does not described and shown on any geological map previously. The conglomerate is indurate and weathering resistance which mostly consists of blocks, boulders and gravel of Qamchuqa Formation with some clasts of Kometan and at the upper part rare clasts of Pila Spi Formation can be observed. It makes, in some place, angular unconformity with the Kolosh, Shiranish, Kometan formations with more than 20gderees of difference in dip. In other areas it shows, more or less equality of dip with aforementioned formations.
The paleocurrent analysis revealed southwest, south, southeast direction for lower, middle and upper part of the succession. Lithology of the succession showed that the succession is younger than Upper Eocene due to presence of the clasts of Pila Spi Formation. For finding the stratigraphic position and relation with other Tertiary unit of the succession, the surround areas are surveyed. The survey is concentrated to the south of Dokan area toward which paleocurrent directed. To the southwest of Taqtaq Town, about 40km to the south of Dokan town, the equivalent of the conglomerate is found which nearly consist of similar lithology but with finer caliber and more roundness. In this area, according to previous studies, the conglomerate is assigned as Bai Hassan (Upper Bakhtiary) Formation. Therefore, the limestone conglomerate in the Dokan Area belongs to Bai Hassan Formation too.
أصل مدملكات كلسيه في منطقة دوكان ، إقليم الكردستان ، شمال شرق العراق
كمال حاجي كريم و زةردةشت احمد طه
تظهر على السطح تتابعات سميكة ( حوالي 300متر ) من مدملكات كلسية على الجانب الأيسر و الأيمن لبحرة دوكان وتغطي حوالي 40كم مربعا من المنطقة. لم توصف و لم توضع هذه المدملكات على الخارطة سابقا. يمتاز بتماسك جيد حيث تظهر بشكل جروف عالية و مقاومة لتجوية حيث تتكون من كتل و جلاميد و حصوات كلسيه و غالبيتها ترجع الى تكوين القمجوقة و قليل من قطع ترجع إلى تكوين كومتان و بلاسبي في الجزء العلوي. تقف هذه تتابعات ، في بعض أمكنة ، فوق تكوين كولوش و تانجرو و شرانش و كومتان بشكل عدم توافقا زاويا ذات فرقا زاويا بميل تقدر بحوالي 20 درجة. و لكن في أمكنة أخرى يمتاز بتساوي تقريبي في الميل مع التكاوين الذكورة. ظهر من خلال تحليل اتجاه تراكب الجلاميد و الحصوات بان اتجاه التيار القديم كان إلى جنوب الغربي و الجنوب و جنوب الشرقي للجزء السفلي و والوسطي والعلوي على التوالي. ظهر بان عمر المدملكات احدث من الايوسين المتأخر بسب احتوائها على قطع من تكوين البلاسبي. من اجل إيجاد موقع الطباقي للمدملكات مع وحدات العصر الثلاثي الأخرى تم مسح المناطق المجاورة و المسح ركزت باتجاه الجنوب مدينة دوكان(اتجاه نقل الترسبات خلال البلايوسين). في جنوب المدينة طقطق(40كم إلى جنوب مدينة دوكان) تم أجاد نوع من مدملكات داخل تكوين باي حسن ( البختياري الأعلى) ما يكافئ مدلمكات المنطقة دوكان بصورة تقريبية.هذه المدملكات تشبه مدملكات دوكان و يختلف فقط في حجم حبيبات انعم و تكور أعلى. لذلك ترجع المدملكات المدروسة في منطقة دوكان إلى تكوين باي حسن أيضا.
The aim of this study is mapping, description and finding stratigraphic relation of a thick succession of limestone conglomerate for the first time at Dokan area. This conglomerate is called “Dokan Conglomerate” in this study. The study also includes the paleocurrent analysis and paleogeographic reconstructions of the area. Dokan area is located in the High Folded Zone in the Northeastern Iraq. The area includes Dokan reservoir and Dokan town in addition to Bingird, Khidran and Khalakan town at the northeast, northwest and southeast respectively (Fig.1 and 2).
The conglomerate is mainly exposed as four separated outcrops around Dokan Lake. Two of them, the largest, are located to the west of the lake, the large one is called Kostrat outcrop and exposed long the northwestern limbs of Kostrat anticline while the other one called Kani watman outcrop which located on the northwestern plunge of the later anticline. The other two outcrops are located to the east of the lake, the large one is cropping out to the south of Bingird town (called Bingird outcrop) and other one is called Qarasard outcrop and exposed along the northwestern limb of the Qarasard anticlines (Fig.1). This conglomerate didn’t mentioned and mapped by Buday (1980), and Stevanovic and Markovic (2004). This later authors mapped the area and put the Kometan Formation on distribution of the conglomerate on the surface.
Characteristics of the conglomerate
The conglomerate consist of thick succession of tough and concrete like rocks which form high mountains such as Buko Zawa and Kani Zard mountains (about 1050m high). The thickness is variable but it reaches more than 300m in some place (Fig.3 and 4). This thickness appears as massive beds long cliffs and each bed has the thickness of 1-5m. Therefore, they appear, at a distance of few kilometers as Qamchuqa or Bekhme formations. Lithologically it is very coarse and consisted of blocks, boulders and granules of the limestone. About 80 percent of the limestone clasts belong to Qamchuqa Formation and the rest belong to Kometan Formation. In some place the conglomerate contain rare boulders of Pila Spi Formation in the upper part. In the two places some blocks of the Qamchuqa Formation is more than one meter in diameter (Fig.5). The clasts of Qamchuqa Formation can be distinguished when the study of Ameen (2008) is considered. The clasts contain radiolitid rudist, stromatolite and orbitoids forams. The cement material consists of calcite and the clasts are sub angular to well rounded with badly sorting. The clasts show well developed imbricated pebbles which show different paleocurrent direction such as south, southwest or southeast (Fig6 and 7).
Stratigraphically, the conglomerate rest on Kolosh, Tanjero Shiranish, and Kometan formations and it make angular unconformity. In Kani Watman area, and northeast of Khalakan town, the angular difference of tilting with these formations reaches about 20 degrees (Fig.1A). The dip angles are also variable which range from horizontal to about 60 degrees which can be seen in the outcrops of Kani Watman and Kostrat respectively. Along the northeastern limb of the Kosrat anticline the conglomerate has nearly the same dip (15-60 degrees) of the underlying formation (Kometan and Qamchuqa Formations). In some place, the conglomerate folded in the form of domal anticlines which can be seen to the southeast of Kani Binaw, Mewza and Chinara villages (Fig.7).
Fig.3: outcrop section of the Limestone conglomerate (Dokan Conglomerate), a) at northwest of Khalakan Town N: 36o 3– 11.44= , E: 44o 44– 8= which rests unconformably on Tanjero Formation with tilt angle of about 30 degrees( Making an angular unconformity) . B) At northeastern limb of Kosrat anticline, overlying Kometan Formation with dip amount of about 35 degrees. It is exposed between the two arrows (about 3Kms). And the Dokan Lake can be seen at the background.
Origin of the conglomerate
As the succession barren from the indigenous fossils, three of the aforementioned characteristics are important for the indication of the relative age and origin of the conglomerate. The first one is the relatively high degree of tilting and folding (in some place) which is evidence that the succession is not belong to Quaternary (Recent and Pleistocene). The second is high degree of lithification by which it appears in the form of high cliffs and mountains due to its weathering resistance. These three properties are not known for the Quaternary sediments. Therefore, it is clear that the succession is younger than Pleistocene. For knowing the stratigraphic relation with the pre-Pleistocene rocks, the area to the south, southwest and southeast of the outcrops are surveyed in the Low Folded zone in the Kirkuk and Erbil Governorate.
In the survey, the direction of the paleocurrent direction is considered. All the conglomerate and sandstone are inspected for finding the time equivalent of the conglomerate. For this the basal conglomerate at the base of Pila Spi and Fat,ha (Former Lower Fars) formations are studied. These two conglomerates (as studied by Ameen, 2006 and Ameen, 2008) are different which contain no clasts of Qamchuqa Formation. When the survey is further shifted toward south, an equivalent conglomerate is found inside the Bai Hassan (Upper Bakhtiary) Formation which called (Taqtaq Conglomerate) in this study. This conglomerate consist of three bed (each about 4m thick) and located at 3kilometers to the southwest of Taqtaq town directly to the west of the paved road that lead to Kirkuk City (Fig.7). As the Dokan conglomerate, the Taqtaq conglomerate is mainly consist of clasts (rounded boulders and gravels) of limestone of Qamchuqa Formation with about 15 % of igneous and chert clasts (Fig.8). This minor difference in the lithology can be justified and discussed as comes below. The Taqtaq conglomerate is located in the distal area as compared to the Dokan Conglomerate which is located in the proximal area. The distal area can be the locus of deposition from different source areas and several stream meet in it. Therefore, it is possible that the chert and igneous clasts derived from Mawat and Chuwarta areas which contain ophiolite and chert source area. The clasts are transported by smaller stream and mixed with main stream or fan. Therefore, the Dokan conglomerate is equivalent to Bai Hassan (Upper Bakhtiary) Formation and can be regarded as part of it.
Fig.8: Google Earth Satellite image showing the studied area and the paleocurrent direction (sediment transport direction) of lower and upper parts of the Dokan Conglomerate in addition to paleocurrent direction of the thrust zone which was either to east or west.
Fig.9: A) Alternation of Limestone conglomerate with red clatstone of Bai Hassan Formation at southwest of Taqtaq town. It is the only coglomerate that is high resemble the Dokan conglomerate. B) Closeup photo of the the conglomerate which only contains rare igneous clasts as indicated by black arrow at the upper left corner.
In the geologic record of Iraq, three major conglomerates are recorded. The first is the 500 meter thick conglomerate that is located at the lower part of Tanjero Formation (Maastrichtian) which made of boulders and pebbles of chert and limestone. According to Karim (2006) and Karim and Surdashy (2005), this conglomerate is deposited in the low stand fan delta environment (Alluvial Fan that was connected to sea).
The second major conglomerate is that of the Red Bed Series which according to (Barzinjy, 2005 and Karim et al, 2007), about 1500m thick and mostly deposited fan delta environments too. The third one is that of present study (Dokan Conglomerate) which about 300meter thick. As that of Maastrichtian, Dokan conglomerate is deposited in alluvial fan environment. This fan was deposited inland far away from the sea which constituted the most proximal part of the fan and most probably belongs to the sediments of the fan apex of one of the large fans that was covering the mountains fronts during Pliocene.
As known the typical Bakhtiary Formation contains chert and igneous boulders and Pebbles in areas of its occurrence such as Dilla, Sulaimanyia, Kirkuk, Erbil and Dohuk Areas. From this, a question is arising: Why does the Dokan Conglomerate is composed only of limestone clasts. For answering this question, the source area must be known. Now, the source areas (as inferred from lithology of the clasts) are located at north, northeast and northwest of the studied areas and consist of two types. The first is nearby source and the second one is remote source area. The first one is located inside present High and Imbricate Zone. This source area most possibly consisted, during Pliocene, of Qamchuqa, Dokan and Kometan formations. The second type (far away source areas) a is located inside Thrust Zone inside Iraq and Northwestern Iran which is consisted of Radiolarian Chert (Qulqula Radiolarite Formation) and ophiolite with Qandil Metamorphic Group. It is clear that Dokan Conglomerate is received only sediments from the first type (nearby one) (Fig.8).
The absence of second type clasts (chert and ophiolite clasts) are most possibly attributed to the presence of a barrier that prevented the influx of the sediments of the second type to move toward south or southwest. This barrier consisted of limbs of the anticlines that composed of about 600m of hard limestone of the Qamchuqa Formation. The evidence for this is that there are, in the type one source area, many northwest-southeast anticlines. The crests and cores of these anticlines are removed during Pliocene and supplied limestone clasts to studied area forming the Dokan conglomerate.
It is possible that during Quaternary, gates (routes) are opened for little Zab River to transport sediment to studied area from second type of source areas. But during Pliocene the second type is drained to the east or west away from studied area and then toward south in Sulaimanyia and Erbil areas (Fig.8).
1-Thick succession of limestone conglomerate (about 300m thick) described and mapped for the first time on right and left sides of Dokan dam and covers more than 40km2 of surface area.
2-The conglomerate is indurated and weathering resistance which mostly consists of blocks, boulders and gravel of Qamchuqa Formation with some clasts of Kometan and at the upper part rare clasts of Pila Spi Formation can be observed.
3-It makes, in some place, angular unconformity with the Kolosh, Shiranish, Kometan formations with more than 20gderees of difference in dip. In other areas it shows, more or less equality of dip with aforementioned formations.
4-The paleocurrent analysis revealed southwest, south, southeast direction for lower, middle and upper part of the succession. Lithology of the succession showed that the succession is younger than Upper Eocene due to presence of the clasts of Pila Spi Formation
4- Field study showed that the limestone conglomerate in the Dokan Area belongs to Bai Hassan Formation.
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