Behavior of Abu-Jir Fault Zone in Al-Thirthar Valley and Near Habbaniya Lake Areas – Comparative Study Using Seismic Reflection Sections
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J. of University of Anbar for pure science : Vol.11:NO.1: 2017 ISSN: 1991-8941 Behavior of Abu-Jir Fault Zone in Al-Thirthar Valley and near Habbaniya Lake Areas – Comparative Study Using Seismic Reflection Sections Abdulkhaleq A. Alhadithi Emad A. M. Salih College of Science, Al-Anbar University. Abstract A comparative study of behavior of Abu-Jir fault zone in Al-Thirthar Valley and near Al-Habbaniya Lake areas has been carried out using seismic reflection sections. Interpretation of the seismic sections showed some similarities and differences in behavior of Abu-Jir Fault Zones in both areas. The seismic sections exhibit simple flower structure in the fault zone of both Al-Thirthar Valley and near Habbaniya Lake but the flower structure in later is simpler than the former. The fault zone in Al- Thirthar Valley behaves as blind fault, whereas it reaches to the Earth's surface near Habbaniya Lake. Abu-Jir Fault Zone near Habbaniya Lake is wider than that in Thirthar Valley area. Syn-rifting due to faulting and slightly thickening has begun within both areas; occur between Alan and Hartha reflectors in Thirthar area and between Alan and Dammam reflectors near Habbaniya Lake. Abu-Jir Fault Zone near Habbaniya Lake suffered to strike slip movement less than that in Thirthar Valley because it is far from the collision suture zone between Arabian plate and Turkish and Iranian plates. Key words: Abu-Jir, Behavior, Habbaniya, Thirthar, Flower structure, Seismic section. Introduction counterclockwise of Arabian plate included Abu-Jir Fault Zone forms an expressive linear wide scale strike slip movement along the feature across the Iraqi territory for about 600 older faults [9]. km that is clearly visible from satellite images. This work aims to compare behavior of Abu- This zone consists of several NW-SE trending Jir Fault zones in Al-Thirthar Valley and near faults that extend from Anah Graben, across Habbaniya Lake area using the available the Euphrates River valley to Hit, Awasil, seismic sections, Figure 2. Abu-Jir, Shithatha, along the western side of Geological Setting the Euphrates River through Kerbala, Najaf Stratigraphically, many formations are and Samawa to meet Al-Batin lineament west exposed through the study area, wide spread Basrah and northwest Kuwait [1]. Many Euphrates, Nfayil, Fatha and Injana formations researchers used Abu-Jir Fault Zone as a and many deposits of Quaternary, Figure 3. boundary between stable and unstable shelves, Euphrates formation (Early Miocene) consists but they differed in determining whether the of three units. Lower Unit of basal fault beyond Hit city continues northwards, conglomerate followed by recrystallized, following Al-Thirthar valley to meet Makhul- fossiliferous limestone changing to coralline Hamrin range, where it dies out just south of limestone. Middle Unit consists of alternation Sinjar area [2, 3 and 4] or westward to meet of hard limestone and pseudoolitic limestone. Anah Grabin [1 and 5] Figure 1. Northeast Upper Member consists of alternation of grey passive margin of Arabian plate has suffered limestone with green marl [10]. Nfayil extension, continental rift, due to opening Neo- Formation (Middle Miocene) is widely Tethys Ocean during Mesozoic Era [3, 4 and cropped out west of Habbaniya and Razzazah 6]. Many subsurface structural features have Lakes but covers by thin veneer of gypcrete. It developed in central, east and north of Iraq involves two members; Lower Member territory [6, 7 and 8]. The irregularity in consists of three cycles of green marl and grey margin of the Arabian, Iranian and Turkish fossiliferous limestone. Upper Member plates at the subduction zones with the consists of cyclic deposits of reddish brown 47 J. of University of Anbar for pure science : Vol.11:NO.1: 2017 claystone, siltstone and sandstone with thin direction of major fault while the minor faults, limestone horizons [11]. antithetic, dipping opposite of the major fault. In Al-Jazira Area Fatha Formation (Middle Generally flower structure occurs within the Miocene) includes two members; Lower seismic section in either strike slip movement Member consists of limestone – gypsum cycles or as dip-slip inversion [16 and 17]. Evidences and Upper member is characterized by of dip slip inversion are missing in this seismic limestone and red mudstone and claystone section. Strike slip movement can be with some gypsum horizons [12]. developed in either positive or negative flower Injana Formation (Late Miocene) consists of structure [16 and 17]. Strike slip fault in this red, brown and grey claystone, siltstone and seismic section forms simple flower sandstone [12]. architecture. It tightly clustered fault strands Structurally, according to locations of the that dip steeply to upward spreading fault seismic sections, the northern part of the study arrays that show extensional displacements area is located within Mesopotamian Foredeep with uplifting in lower part of the major fault. of outer platform and cut the boundary Negative flower structure is formed. between Mesopotamian Foredeep and Low Opening of the Red Sea and Gulf of Adan and Folded Zone and the southern part cuts the the collision between Arabian and Anatolian boundary of Inner and Outer Platforms [5]. plates develop stresses that affects to the pre- Surface structural features are missing but existing fault (graben strucuture) as strike slip there are many subsurface extensional movement that form Negative Flower structures through the area [6 and 9]. Abu Jir Structure. Fault Zone is the most important subsurface Interpretation of seismic section WT-36 shows structure. It formed many geomorphological that interval time of Shuaiba and Mauddud features through Abu Jir vicinity such as reflectors are variable with presence of the Awasil, Al-Jabha, Al-Mudowar and Abu Jir onlap stratigraphy features inside the main Sag ponds [13]. The strata are almost graben area, this refers to an increase in horizontal. The slop is gentle southward thickness of sediments, while the interval time through Al-Thirthar Valley [14] and is a gently in the shoulder areas is almost fixed. Slight sloping with a gradient of 5 m/Km towards thickening is occurred during extension phase east and northeast in Abu Jir vicinity [15]. of northeast passive margin of Arabian plate. Interpretation of Seismic Sections Stratigraphic sequence between Alan and Two seismic reflection sections were Hartha reflectors represent syn-rift. It employed to investigate behavior of Abu-Jir continues from Late Liassic to Late Fault Zone in the study area. Reflection Campanian- Early Maastrichtian. The interval seismic section WT-36 crosses Al-Thirthar time of Kurra chine and Alan reflectors is valley west of Makhul Anticline was used to almost fixed and equitable both inside main study behavior of the fault zone in Al-Thirthar graben and shoulders area. Fixed thickening of Valley, Figure 4, while the reflection seismic the sequence is from Alan reflector downward section AR-38 used to investigate behavior of that represents pre-rift. According to seismic Abu-Jir Fault Zone near Habbaniya Lake, interpretation indicators and well data, this Figure 5. type of normal faults develops due to increase Seismic section WT-36 in weight (thickness) of sediments which are According to analysis of synthetic variety at the head of the hanging wall seismograms of some oil wells, six reflectors comparing with thickness at footwall where it were picked, Figure 4. These reflectors include almost constant and thinner [18]. Neither the following formation from the oldest to the thickening nor faulting through the sequence youngest: Kurra chine (Late Triassic), Alan from Hartha reflector upward therefore has it (Late Liassic), Shuaiba (Aptian), Mouddud represented post-rift. (Albian), Hartha (Late Campanian- Early Seismic Section AR-38 Maastrichtian) and Jeribe (Middle Miocene). Seismic section AR-38 is used by [13] Figure Discontinuity of the good reflectors shows 5. It reveals five major faults. The first one clear image of the main fault in the middle of (F1) is steeply dipping northeastward which the seismic section. The fault zone has width has two synthetic minor faults dip approximately 3 km measured on Hartha northeastward and one antithetic minor fault reflector. It consists of major fault that dips dips southwestward. Fault (1) is suffered to steeply toward northeast. The fault zone strike slip movement that develop negative includes several steeply dipping normal faults flower structure. that divergent upward. Two sets of minor Graben structure is developed in the central of faults dipping toward each other. The minor the seismic section. F2 and F3 are southwest faults, synthetic, are dipping in a same and northeast normal faults of the graben - 48 - J. of University of Anbar for pure science : Vol.11:NO.1: 2017 respectively. F2 dips northeast and F3 dips Fault Zone in Al-Thirthar valley is reached to southwest. Another graben is formed. F4 and Hartha reflector (Late Campanian-Early F5 are southwest and northeast normal faults Maastrichtian) Figure 4. It is continues inactive of the graben respectively. F4 dips northeast from Maastrichtian upward. Seismic section and F5 dips southwest. There is slight AR-38 reveals Abu Jir Fault Zone cuts all thickening between Dammam and Hartha stratigraphic sequence of the basin. The reflectors. Seismic sections AR-50 and AR-22, in area Comparison of Abu-Jir fault zone near Habbaniya Lake, appear Abu Jir Fault There are similarities and differences between Zone reaches to earth’s surface [19]. Abu Jir the behaviors of the fault zone in area of Al- Fault Zone sometime appears on the earth’s Thirthar Valley and near Habbaniya Lake surface especially in area west of Al-Razzazah areas. The characteristics of the fault zone may Lake [4 and6] and very clear in view of digital be summarized as; images between Najaf and Hit cities. Many • Abu Jir Fault Zone in seismic section AR-38 geological features related to faulting along reaches to earth’s surface, cutting Dammam Abu Jir fault Zone are showed by optical reflector, whereas in seismic section WT-36 viewing of aerial photograph or satellite image.