CLASSIFICATION OF THE ALLUVIAL FANS IN IRAQ
Varoujan K. Sissakian
Consultant Geologist, Iraqi Kurdistan Region, Erbil, Ainkawa
Mawahib F. Abdul Jab'bar
Assistant Chief Geologist, Iraq Geological Survey, P.O. Box 986, Baghdad, Iraq
Iraqi Bulletin of Geology and Mining, Vol.10, No.3, 2014 , pp 43 - 67
Abstract
The Iraqi territory exhibits diverse topography in its different parts; from the extreme southeast, where the coastal area along the Arabian Gulf, passing northwards to the Mesopotamia Plain, and more north and northeast to hilly, low mountainous and high mountainous areas, respectively. Whilst towards west, the plateau of the Southern and Western Deserts exist and in the northwestern part is the Jazira Plain. This diversity in the topography with climatic changes has caused development of different systems of alluvial fans, with different ages, stages, shapes, sizes and constituents.
This study aims to establish a classification of alluvial fans developed in Iraq depending mainly on the stages, for the main types and the size, shape and covering constituents for the types and sub-types. Consequently, two main types were found: Single Stage and Multi Stage Alluvial Fans. Furthermore, each main type is classified into many types, depending on the size, shape and top covering materials. The age is not included in the classification, because almost all the existing alluvial fans in Iraq have the same age range (Pleistocene – Holocene). Moreover, no accurate dating is available to use for the fan classification. The constituent factor is not used, because it depends on the type of the exposed rocks in the source area. Examples are given for each type and sub-type from different parts of Iraq. Some of the examples have fan names, used in other studies.
Keywords: Alluvial fans, Bajada, Pleistocene, Iraq
تصنيف المراوح الفيضية في العراق
فاروجان خاجيك سيساكيان
مواهب فاضل عبد الجبار
مجلة الجيولوجيا والتعدين العراقية - وزارة الصناعة والمعادن - المجلد 10 - العدد 3 - 2014 - ص ص 43 - 67
هناك اختلاف كبير في طوبوغرافية سطح العراق، فمن ساحل البحر المطل على الخليج العربي في أقصى الجنوب، ومن ثم مروراً بالسهل الرسوبي لنهري دجلة والفرات باتجاه الشمال، وبعد ذلك الى المناطق الجبلية الواطئة ثم مناطق الجبال العالية، تباعاً باتجاه الشمال والشمال الشرقي. أما باتجاه الغرب، فتوجد هضبة الصحراء الجنوبية والصحراء الغربية، وفي اقصى الشمال الغربي يوجد سهل الجزيرة. إن هذا التنوع في الطوبوغرافية، إضافةً الى الاختلافات المناخية قد أدت الى تكون مجاميع من المراوح الفيضية المختلفة، مع اختلافات في العمر والمراحل والشكل والحجم والرسوبيات.
أن هذه الدراسة تهدف الى اعداد تصنيف للمراوح الفيضية في العراق. اعتماداً على المراحل، تم تصنيف المراوح الى صنفين رئيسيين، ومن ثم تم تصنيفهما الى صنوف وصنوف ثانوية اعتماداً على الحجم والشكل وأنواع الرسوبيات التي تغطي سطح المراوح. وعليه تم تصنيف المراوح الى صنفين رئيسيين هما: المرواح الفيضية ذات المرحلة الواحدة والمراوح الفيضية ذات المراحل المتعددة. كما تم تصنيف الصنفين الرئيسيين الى صنوف ومن ثم الى صنوف ثانوية. ولم يعتمد العمر في التصنيف لان غالبية المراوح لها نفس المدى العمري وهو البلايستوسين – الهولوسين، كما انه لا يتوفر في العراق امكانية تحديد العمر بشكل دقيق.ولم يتخذ كذلك عامل المكونات الرسوبية للمراوح، لان ذلك يعتمد على الصخور المتكشفة في منطقة المصدر. وقد ذكرت امثلة عن كل صنف رئيسي وصنف وصنف ثانوي ومن مختلف مناطق العراق. وان لبعض المراوح اسماء وقد ذكرت وكما جاءت في الدراسات السابقة المتوفرة عن وصف المراوح الفيضية.
INTRODUCTION
An alluvial fan is a fan- or cone-shaped deposit of sediment crossed and built by streams. If a fan is built up by debris flows it is properly called a debris cone or colluvial fan. These flows come from a single point source at the apex of the fan, and over time move to occupy many positions on the fan surface. Fans are typically found where a canyon draining from mountainous terrain emerges out onto a flatter plain, and especially along fault-bounded mountain fronts. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a Bajada, or compound alluvial fan (A.G.I., 1962).
In Iraq, alluvial fans are developed almost in all physiographic provinces, but with different types, shapes, sizes and constituent materials. However, few of them are presented on the geological maps, especially those, which have considerable areas. Google Earth and satellite images show very clearly the occurrence of the alluvial fans. Alluvial fans are apronlike deposits of granular debris that extend from the base of a mountain front to the low land below. Each fan radiates from a single source channel, and has fan-like shape in plain view. Its transverse profile is arched, and the longitudinal profile is slightly concave. Slopes are usually less than 10°. The fans are best developed in semiarid terrains, where elongate mountain ranges that are tectonically active (basin-and-range topography) and lack protective vegetation cover, are subjected to erosion by episodic heavy rain precipitation (Bull, 1991).
The aim of this study is to establish a classification, which deals with the present alluvial fans in different parts of Iraq, which have different characteristics; as to the number of stages, sizes, shapes and cover materials. The classification can be applied on the existing alluvial fans, in Iraq.
The geological and topographical maps with the Google Earth and Satellite images were used to recognize the present alluvial fans in different parts of Iraq. GIS techniques were used to calculate the coverage area and other geometrical parameters of the main large alluvial fans. Field description points in different geological reports and relevant published articles were reviewed to indicate the number of the stages, shape, sizes, covering materials and constituents of the existing alluvial fans. Geological maps (GEOSURV, 1992 – 2012, and Sissakian and Fouad, 2012a) were reviewed to indicate the relation between the exposed geological formations and the present alluvial fans. Some already existing classifications, worldwide were used, directly or indirectly to establish the basics of this introduced classification.
The geological and topographical maps with the Google Earth and Satellite images were used to recognize the present alluvial fans in different parts of Iraq. GIS techniques were used to calculate the coverage area and other geometrical parameters of the main large alluvial fans. Field description points in different geological reports and relevant published articles were reviewed to indicate the number of the stages, shape, sizes, covering materials and constituents of the existing alluvial fans. Geological maps (GEOSURV, 1992 – 2012, and Sissakian and Fouad, 2012a) were reviewed to indicate the relation between the exposed geological formations and the present alluvial fans. Some already existing classifications, worldwide were used, directly or indirectly to establish the basics of this introduced classification.
Fig.1: Physiographic Map of Iraq (after Sissakian and Fouad, 2012a)
Fig.2: Google Earth image of the Qara Chough Alluvial Fan of Single Stage Medium
type, surrounded by Single Stage Small type alluvial fans, forming Bajada
Fig.3: Single Stage Small alluvial fan derived from slid mass of a landslide (A), which is
originally a Single Stage Medium alluvial fan, top covered by calcrete (B)
in Qara Dagh Mountain
Fig.4: Landsat 7 image of a Single Stage Fan of Medium type derived from
Pera Magroon Mountain (Ziwi Fan)
Fig.5: Google Earth image of a Single Stage Fan of Medium type around
Darbandi Khan Lake
Fig.6: Landsat 7 image of a Single Stage Fan of Large type;
the Karbala – Najaf Plateau, top covered
by gypcrete
Fig.7: Landsat 7 image of a Single Stage Fan of Large type,
Daqooq (Tawuq) Fan, top covered by soil
Fig.8: Google Earth image of a Single Stage Fan of Large type,
Kifri Fan, top covered by soil
Fig.9: Google Earth image of Al-Breem Alluvial Fan of Single Stage Large type;
Soil covered sub-type, in the Iraqi Western Desert
Fig.10: Google Earth image of Two Stage Fans type, with Fine Clastics
sub-type, along the southern rim of Al-Ga'ara Depression
Fig.11: Geological Map of Sinjar anticline, note the concentric contour lines radiating from
one single outlet, forming the first stage alluvial fans (after Sissakian, 2011)
Fig.12: Google Earth image showing the location of the four stages of the Sinjar alluvial fans;
at the northern limb of the anticline
The red lines are the location of subsurface faults (after Sissakian, 2011)
Fig.13: Google Earth image of Multi Stages Alluvial Fan in Zurbatiya vicinity,
note the tone differences in different stages, as well in different parts
Fig.14: Google Earth image showing two big alluvial fans, Al-Teeb to the left and Al-Fak'ka
to the right, between Kumait and Amara, the fans are most probably partly inactive; due to
uplifting of Buzurgan (B) and Halfaya (H) subsurface anticlines
Fig.15: Landsat 7 image of Two Stages alluvial fans, along the southern limb of Sinjar anticline, compare with Fig. (12) concerning the number of the stages
CONCLUSIONS This study has the following conclusions.
The established classification of the alluvial fans includes 21 main types, types and subtypes.
Within the established classification, 2 main types, 6 types and 13 sub-types of alluvial fans are introduced.
The classification depends on the number of the stages for dividing the fans into two main types, whereas the types and sub-types are divided according to the shape, size, top cover materials and partly based on genesis, and number of the stages, too.
The established classification is applicable in different parts of Iraq, as far as the existing alluvial fans are concerned.
The age is excluded from the classification, because almost all the fans are within Pleistocene – Holocene age.
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