GRAVITY AND MAGNETIC SURVEYS TO DELINEATE SUBSURFACE STRUCTURES IN HOR AL-HUWAZAH AREA, SOUTH OF IRAQ

النسخ

1 GRAVITY AND MAGNETIC SURVEYS TO DELINEATE SUBSURFACE STRUCTURES IN HOR AL-HUWAZAH AREA, SOUTH IRAQ Ghalib F. Amin 1, Abbas M. Yass 1, Hayder A. Al-Bahadily 2 and Ahmed S. Mousa 2 Received: 05/ 09/ 2013, Accepted: 13/ 03/ 2014 Key words: Gravity, Magnetic, Hor Al-Huwaizah, Iraq ABSTRACT Gravity and magnetic surveys were carried out to study an area located between, Amara and Qurna Cities, The results of the present survey are merged with those of the previous surveys carried out exipc; using Oasis Montaj software to produce a unified database, which considered a new addition to update the gravity and magnetic field maps of Iraq. The most impressive result of the present gravity survey is the negative anomaly (A), found in the middle part of the studied area with NE SW trend. This anomaly is a completion of the more extended important negative anomaly present in the vicinity of Qalat Saleh Uzair Qurna. It is surrounded by high gravity gradient that may be related to fault and/ or contact and may reflect the occurrence of a restricted basin, or it may reflect the negative background of Zagaros root effect. It is worth to mention that most oil fields occur along the high gradient flanks of this anomaly. The expressive positive gravity anomaly (G1 and G2), are located in the upper middle part of the area with a trend of NW SE extending beyond the studied area. It may be attributed to uplift in the sedimentary cover corresponding to uplifts in the basement, as indicated in the basement relief map of exipc. This anomaly may be attributed to the presence of coral reef or anhydrite elongated body present within the sedimentary column. The magnetic map of the studied area reflects mainly the effect of the basement, but several local anomalies are also detected, some of which are related to local buried iron artifacts, which act as sources of noise. Therefore, some filters were applied to enhance the magnetic picture. مسح جذبي مغناطيسي لتحديد التراكيب تحت السطحية في منطقة هور الحويزة جنوب العراق غالب فاضل أمين عباس محمد ياس حيدر عدنان البهادلي و احمد سالم موسى المستخلص أجر ت مسوحات جذب ة ومغناط س ة ف المنطقة الواقعة ب ن مد نت العمارة والقرنة عند خط طول '00 47 الى ' وخط عرض '45 30 الى '00 32 وذلك لتحد د التراك ب تحت السطح ة باإلضافة إلى مل ء الفجوة الموجودة )منطقة( ف المسوحات الجذب ة المتوافرة ح ث كانت هذه المنطقة سابقا مغطاة بواسطة م اه هور الحو زة ماعدا الجزء الشمال من منطقة الدراسة الت ال تزال حال ا مغطاة بالم اه )هور أم النعاج(. 1 Senior Chief Geophysicist, Iraq Geological Survey 2 Assistant Chief Geophysicist, Iraq Geological Survey 95

2 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al. أجر ت الق اسات الجذب ة والمغناط س ة على طول الطرق والمسالك الغ ر معبدة المنطقة وعلى شكل مضلعات وكانت المسافة ب ن نقطة ق اس وأخرى ه واحد ك لومتر. وذلك حسب ما تقتض ه ظروف إن نتائج هذه المسوحات قد دمجت مع المسوحات السابقة الت أجر ت بواسطة شركة نفط العراق )IPC( باستخدام برنامج أو أسس مونتاج إلعداد قاعدة ب انات موحدة والت اعتبرت معلومات أضاف ة جد دة لتحد ث خرائط المجال الجذب والمغناط س للعراق. من النتائج المهمة لهذه المسوحات هو الشاذة الجذب ة السالبة )A( الت تقع ف وسط منطقة الدراسة وباتجاه شمال غرب جنوب شرق هذه الشاذة مكملة لشاذة جذب ة سالبة مهمة تمتد بالقرب من منطقة قلعة صالح العز ر القرنة وه محاطة بانحدار جذب عال ربما عود إلى صدع أو تماس أو ربما عكس تواجد حوض محدد أو ربما عكس تأث ر الخلف ة السالبة لجذر حبال زاكروس ومن الجد ر بالذكر إن معظم حقول النفط تتواجد على طول االنحدار الجذب العال لهذه الشاذة الجذب ة السالبة. من الشواذ الجذب ة المهمة أ ضا ه الشواذ )G1 و G2( والت تقع ف الجزء الوسط العلوي من منطقة الدراسة وباتجاه شمال غرب جنوب شرق وتمتد خارج منطقة الدراسة. إن هذه الشواذ ربما تعود إلى نهوض ف الغطاء الرسوب والناتج عن نهوض ف صخور القاعدة والمشار إل ه ف خر طة تضار س سطح القاعدة المعدة من قبل شركة نفط العراق إن هات ن الشاذت ن من الممكن أن تفسران كشعاب مرجان ة أو امتداد طول لجسم انها درا ت موجود ضمن العمود الرسوب. أما الخر طة المغناط س ة لمنطقة الدراسة فه تعكس بشكل أساس تأث رصخور القاعدة ومع ذلك تم تحد د عدة شواذ محل ة بعضها تعود إلى تأث ر محل ألجسام حد د ة صناع ة مدفونة والت تمثل كمصدر للضوضاء )noise( لذلك تم تطب ق عدة مرشحات لتحس ن الصورة المغناط س ة للمنطقة. كذلك أجر ت مضاهاة لمسار على طول الخط C C للمعلومات الجذب ة والمغناط س ة وذلك لتحد د الشواذ الرئ س ة ضمن المسار بواسطة تعز ز االستجابة لهذه الشواذ وبالتال جعل الشواذ سهلة التم ز والتحد د. INTRODUCTION Gravity and magnetic surveys were carried out to detect and delineate the subsurface structures at a region that extend from Amara to Qurna cities. The studied area was previously covered with marshes, especially Al-Huwaizah marsh. Both surveys were performed by 1206 stations distributed along roads and tracks present in the studied area (Fig.1). Processing and interpretation of gravity and magnetic data revealed good results complementing the gravity and magnetic data of the surrounding areas, which were achieved previously by exipc. These results are finally presented in this study using different computer techniques. The studied area (figure 4), lies within Latitude 30 45' to 32 00' N and Longitude 47 00' to 47 45' N. Scope of Work The scope of this survey is to detect and delineate the subsurface structures as well as to fill a gap in the available gravity survey. This gap in the area was previously covered by water of Hour Al-Huwaizah, except an area in the northern part of Hor Al-Huwaizah that is still filled by the water of Hor Aum Al-Na'age. Also to achieve regional geophysical mapping characteristically entails measurements on stations distributed along polygons lying along paved and unpaved roads as well as tracks (Fig.1). 06

3 Northing m Amara 78_15 78_1678_17 78_21 78_22 78_23 78_24 78_25 79_5 78_26 78_27 79_4 78_18 78_20 78_28 78_14 79_3 78_13 78_19 78_29 79_2 78_12 78_30 78_11 79_1 AMARAH BS_0 78_31 04_4 05_1 78_10 74_15 04_3 05_2 74_14 74_16 75_1575_1675_175_1875_1975_20 75_21 75_2275_2375_2475_25 75_26 76_10 75_27 75_2875_2975_3075_3175_32 05_3 78_9 04_2 74_13 74_175_14 76_9 1 05_4 2 04_1 78_8 74_18 05_505_6 74_12 75_12 75_ _8 3 78_7 4 74_11 75_11 76_7 5 05_ _1 6 05_805_9 7 07_307_407_507_6 MSHARAH 78_6 74_10 81_5 69_ _5 01_6 05_10 73_10 73_11 73_12 73_13 75_10 76_6 74_9 75_9 76_5 76_4 81_4 78_5 76_3 76_2 07_7 80_10 75_8 124A 62 69_26 01_101_201_3 01_4 01_7 05_11 81_3 78_4 74_8 07_8 73_9 75_7 76_169_25 01_801_9 05_12 74_7 75_6 02_2 07_9 05_13 81_2 80_9 78_ _24 73_8 01_10 74_6 75_5 69_23 01_1101_12 07_10 05_14 81_1 78_2 02_3 07_ _15 80_7 80_8 73_7 74_5 75_4 69_22 05_16 78_1 01_13 07_12 02_4 06_2 05_17 73_6 74_459 75_3 128A 01_14 07_13 05_18 69_19 69_20 69_21 80_4 80_580_6 73_5 74_3 75_2 02_5 07_14 06_ _19 01_15 05_20 73_4 74_2 75_1 02_6 07_15 06_4 05_21 03_1 01_16 05_2205_2305_2405_2505_2605_2705_2805_2905_305_3105_3205_33 05_34 05_35 05_36 05_37 13_6 02_7 03_203_303_4 06_5 07_16 13_5 01_17 06_6 69_11 69_12 69_13 69_14 69_1569_1669_1769_18 71_ _1 80_280_3 73_3 74_1 71_10 73_2 02_8 03_5 03_603_703_8 01_18 07_17 14_1 06_7 01_19 07_18 10_2 13_4 69_10 14_2 02_9 03_9 06_8 10_3 13_3 70_15 70_16 70_1770_1870_1970_20 70_2170_22 71_9 73_1 71_8 71_ _9 71_6 03_1003_11 01_20 02_10 03_12 08_1 14_3 70_14 03_13 01_21 10_4 13_2 69_ _ _2 14_4 02_11 10_5 70_13 69_7 71_4 03_14 08_3 13_1 69_6 10_6 14_5 02_12 03_15 08_4 12_8 12_912_1012_112_1212_1312_14 12_1512_1612_17 70_12 69_5 71_3 Kahalaa 10_7 70_11 69_4 02_13 08_5 10_8 12_5 12_612_7 70_ _ _16 10_9 69_3 21_4 02_14 08_6 70_9 71_1 15_21 03_17 10_10 15_22 15_20 21_3 12_1 12_212_312_4 70_7 09_1 11_1 68_31 69_ _8 70_6 62_1862_1962_2062_2162_22 11_2 15_19 21_2 68_30 69_1 70_5 15_18 09_2 62_15 62_1662_17 15_17 15_16 15_12 11_3 15_15 15_14 15_13 21_1 72_13 70_470_3 68_29 15_11 09_3 62_14 15_10 11_4 72_12 70_2 68_28 KAHLAA 19_1 15_9 19_2 09_4 72_11 11_5 70_1 62_13 63_1 19_3 15_8 68_2568_2668_27 09_5 11_6 09_6 11_9 72_10 68_23 68_24 62_12 63_ _4 15_7 11_8 11_7 68_22 63_3 72_9 19_5 17_1 62_11 15_6 68_21 63_4 63_563_663_763_8 19_6 17_2 72_ _10 63_963_10 19_7 15_5 17_3 68_20 63_11 63_1263_13 72_17 19_8 15_4 17_4 72_16 72_15 72_1472_7 68_18 68_19 62_9 63_1463_15 63_16 72_6 65_13 65_12 66_1 15_3 15_2 72_5 17_5 18/4 18/518/618/718/818/918/1018/11 68_16 68_ _8 65_ _2 17_6 72_4 68_15 18/3 62_7 65_10 65_9 65_865_7 66_3 67_11 67_12 17_7 68_ /2 72_3 65_665_565_465_3 66_4 67_10 68_13 17_8 16_9 18/1 62_6 65_2 66_5 72_272_1 68_12 24_13 24_1424_15 16_ _9 67_9 68_11 68_10 65_1 62_5 16_7 17_10 67_8 24_12 68_9 BS_1 16_6 16_5 17_11 67_7 68_8 77_3 77_4 77_5 62_4 24_11 16_416_3 AL MIJAR 16_217_12 77_1 16_1 67_6 68_7 77_ _3 24_10 22_14 24_9 22_1320_1 67_5 68_6 62_ _ HOR 60_660_560_460_360_2 24_8 22_12 20_2 HOR AL_HWAZAH 60_1 67_4 62_1 60_7 22_11 141A 60_8 58_6 24_7 20_3 60_9 22_10 58_5 24_624_524_424_324_224_1 22_9 20_4 55_11 55_10 60_10 58_4 23_30 22_8 20_5 45_60 58_3 23_29 22_7 55_9 23_28 20_6 22_6 61_20 61_21 61_22 61_23 61_24 61_25 61_26 61_27 61_28 61_29 68_4 68_368_2 67_3 61_30 68_1 AL-HUWAIZAH 67_2 QALAT SALIH 67_ _59 55_855_7 58_2 23_27 61_19 61_18 22_5 20_7 55_6 59_4 23_26 45_58 55_5 58_1 59_359_259_1 61_17 59_5 22_4 55_4 23_25 20_8 59_6 22_3 61_16 45_57 55_3 61_15 59_7 23_24 22_2 55_2 22_1 20_9 61_14 45_56 55_1 23_23 20_10 54_ _11 61_13 45_55 54_17 23_22 23_1 20_ _15 61_12 45_54 54_18 23_21 23_2 20_13 61_ _1 54_ _10 45_53 54_13 23_20 23_3 20_14 Almijar 56_2 61_9 45_52 56_3 54_12 64_2 64_1 23_4 20_15 23_19 45_51 56_4 AL IMAM 54_11 23_5 20_16 61_8 23_18 45_50 54_10 23_6 20_17 23_17 rr 61_7 56_5 20_18 45_49 23_16 45_45 23_7 45_46 45_44 54_9 61_61_561_4 20_19 61_361_261_145_48 45_47 23_15 23_8 20_20 45_43 54_ _14 20_21 26_1 54_7 23_9 20_22 45_ _2 23_13 23_10 20_23 26_3 57_154_6 45_41 23_12 23_11 20_24 26_4 57_2 54_5 20_34 20_33 20_25 26_34 57_3 45_40 20_32 26_5 57_4 26_35 20_31 20_26 57_5 54_4 28_12 Qalat Saleh 29 26_36 45_39 20_30 20_27 26_6 28_11 57_6 20_29 20_28 26_37 54_3 26_7 45_38 57_957_857_7 28_10 54_2 28_9 25_22 26_827 45_37 54_1 28_8 25_21 26_9 26_27 26_28 26_29 26_30 45_ _7 25_20 26_10 26_26 26_31 45_35 28_6 28_5 25_19 26_11 26_25 26_32 45_34 49_6 28_428_3 28_2 26_33 52_9 52_852_752_652_5 28_1 52_4 25_ _12 45_33 52_3 49_5 52_2 25_17 26_13 52_149_4 45_32 25_16 26_14 45_31 Auzair 49_ _15 25_ _30 49_2 25_14 26_16 26_24 45_29 53_4 49_1 53_6 53_5 25_13 26_17 53_7 53_3 53_253_1 30_330_230_1 25_125_11 25_1025_925_825_725_625_525_425_325_225_1 uzair 26_18 26_1926_2026_2126_22 45_28 53_953_8 30_4 32_6 27_1 26_23 45_27 30_5 29_17 32_5 27_2 45_26 30_6 29_16 32_4 27_3 45_25 30_7 32_3 29_ _4 45_24 30_8 32_ _14 32_1 27_5 45_23 139A 30_9 29_13 30_1130_1230_13 30_14 30_15 30_16 45_22 30_1730_1830_1930_20 27_6 48_148_248_348_448_548_6 48_7 30_10 31_ _12 45_21 27_41 27_7 31_2 30_21 30_22 30_230_2430_2530_26 29_11 27_40 27_8 45_20 31_3 29_10 27_39 27_9 45_ _4 29_9 27_38 31_5 27_10 45_ _8 27_37 31_6 27_11 45_17 BS_2 27_36 27_12 29_129_229_329_429_529_6 29_7 45_16 31_ _1 27_35 31_8 27_13 45_15 46_2 46_1 33_2 46_7 46_646_546_446_3 27_34 31_9 27_14 45_14 33_3 27_33 31_10 27_15 45_13 33_4 27_32 31_11 JWABER 27_ _5 45_12 31_12 27_31 27_17 27_19 27_18 33_6 45_11 Jwaber 27_26 27_25 27_30 27_29 27_28 31_13 27_27 27_ _21 27_20 27_23 34_1 27_22 33_7 45_10 38_4 38_538_6 39_21 34_2 33_8 45_9 39_20 34_338_1 38_238_3 51_651_751_8 33_9 rr 45_8 39_19 51_151_251_351_4 51_5 43_11 34_4 33_10 45_7 39_18 43_10 34_5 33_11 45_6 39_ _9 34_ _8 33_12 45_5 39_16 34_7 33_13 45_4 9 39_15 43_7 42_7 34_8 44_344_244_1 33_14 45_3 39_14 42_142_242_342_4 42_542_6 44_4 43_6 34_9 43_5 33_15 45_2 41_7 39_13 34_10 33_16 41_941_8 33_17 41_10 43_4 33_18 35_1 45_1 41_6 39_12 34_11 35_2 41_5 41_4 41_341_2 41_1 43_3 7 50_1 39_11 34_12 43_2 35_3 50_2 39_ _13 35_4 50_3 1 43_1 39_9 34_ _5 50_4 39_8 40_10 40_940_840_740_640_540_440_3 40_2 34_15 35_6 50_5 50_6 50_7 50_8 50_950_10 50_13 50_11 40_11 47_4 40_1 34_16 36_1 50_12 39_7 40_12 36_236_3 36_4 36_5 35_7 47_3 34_17 35_8 39_6 47_2 35_9 39_ _18 35_10 QURNAH 47_1 39_4 34_19 35_11 39_3 39_239_1 34_20 37_6 37_737_837_937_1037_1137_1237_13 35_12 37_5 34_21 37_4 35_13 37_3 3 34_ _2 35_14 37_1 34_23 35_15 34_24 35_16 35_30 Qurna 35_29 35_17 35_28 35_27 35_18 35_26 35_19 35_25 35_20 35_24 35_235_21 35_22 79_10 79_9 79_8 79_7 79_6 Msharah Location of primary gravity BS. Location of auxilary gravity BS. Location of geologic bore holes 19 Easting m. Location of oill well Ceties City or town No. of poligons Km km Fig.1: Network of gravity and magnetic stations in the studied area 06

4 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al. GENERAL GEOLOGY OF THE STUDED AREA According to Fouad, (2012) the studied area lies within the Outer Platform (Mesopotamian Fore deep) (Fig.2). No structural features observed on the surface throughout the area; however, it contains a broad subsurface syncline and narrow anticline trending predominantly NW SE (Jassim and Goff, 2006). Iraqi National Oil Company referred to the presence of subsurface structure in the study area (I.P.C., 1979) (Fig.3). Geological correlation of the drilled boreholes indicates that most part of the studied area lies within the deeper parts of the Mesopotamian Quaternary basins (syncline) (Yacoub, 1994). The studied area is completely covered by Quaternary sediments that have mainly fluvial and lacostrine origin and partly Aeolian. Marine-estuarine sediments of Quaternary age are also recognized in subsurface sedimentary sequence, the Quaternary deposits are represented by; sheet run-off sediments, flood plain sediments, shallow depression sediments and marsh sediments, (Fig.4). Fig.2: Tectonic zones of Iraq (after Fouad, 2012) shows the studied area 06

5 IRAN Buzurgan 299 Noar N AMARA Halfaya Depression Mj Q Nahr Umr km 322 Well Oil well Fault in Mesozois Mesozoic from from gravity Anticline identified identifinedfrom from Mesozoic mesozoic and locally localy from Tertiary reflector Boundary Seismic of reflectors studied meters) area (depth in Boundary from contact faulting Boundary zone from contact faulting zone Faults identified idintified from interpretation of images space photographs (landsat) Outlines of of mejor major uplifts uplifts and and depressions Boundary of the studied area Fig.3: Structural-tectonic map of Amara north part of Basrah (after I.P.C., 1972) 06

6 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al N N N N N N N N N N N N N N N N N N QUATERNARY Anthropogene sediments Sheet dep.sand,silt andclay Flood deep. Sand, silt and clay Sheet dep.sand,silt andclay Sheet Sheet dep.sand,silt andclay andclay Crevasse deep. Sand and silt Marsh dep.(active) mud Sheet Sheet deep. dep.sand,silt Silt andclay Marsh dep.(active) mud Marsh Marsh dep.(active) mud mud Depression deep. Clay and silt Marsh Marsh deep. dep.(active) mud mud Marsh deep. (dry) mud Marsh dep. (open lake) GEOLOGIC Geological contact N Gilgai soil N N Natural leaves Discontinuance sand sheet Natural leaves N Natural Natural Natural leaves leaves leaves N Abandoned river channel Crevasse splay N Abandoned Natural leaves river channel N N river channel Abandoned Abandoned river river channel channel Shallow borhole N Deep Abandoned borehole river channel N Shallow borhole Shallow Shallow Shallow borehole borhole borhole N N N TOPOGRAPHY Paved Shallow road borhole N N Paved Triangulation Paved road road point Paved Paved road road N Triangulation Triangulation point point N point N Triangulation point Town Paved Village road N Triangulation point River River N River N Valley River River Valley or stream or stream N N Bridge Valley or stream Valley or stream River Valley or stream N Ruins N International Valley or boundaries stream N N N 47.00E E E E E E 48.00E N 47.00E E E E E E 48.00E 47.00E E E E E E 47.00E 48.00E E E E E E 48.00E Fig.4: 47.00E Network E of gravity E and E magnetic E stations E superimposed 48.00E on geologic map of the studied area (Geosurv) Data Collection and Methodology The Topographic measurements were conducted using Total Station Top con 7501, 721 (with accuracy of one second) and total station Leica 405 instruments (with accuracy of five seconds). The coordinates of each station are given in UTM and geographic system using GPS GARMN-XL12 (with accuracy of ± 5 m). 06

7 The stations spacing was chosen to be 1 Km to fulfill such regional survey. The gravity survey was carried out with CG-5 (Scintrex Autograv System) gravity meter, with reading resolution of 1 µgal. The triangulation point number (43027) was chosen to be a reference basic station with absolute gravity value of mgal, proper reference. Two local auxiliary basic stations (Bs1 and Bs2) were established in the studied area and tide with the reference basic station (Fig.1). The same gravity basic stations were used as magnetic basic station to conduct the magnetic survey using Proton magnetometer (with maximum sensitivity of 1 nt) as a portable magnetometer, while ENVI PRO magnetometer, which measures and saves reading automatically with three minute interval, was used as a stationary system to monitor the diurnal variation for each workday. The mean quadratic square error (µ) in this survey is ± mgal for gravity survey and µ = ± nt for magnetic survey DATA PROCESSING Gravity Data It is necessary to apply many corrections to the raw meter readings to obtain the gravity anomalies that are the target of a survey. This is because geologically uninteresting effects are significant and must be removed. This correction comprises: Drift correction, latitude correction, free air correction, and Bouguer correction, the corrected data introduce Bouguer values, which are plotted as a map (Reynolds, 2003) (Sheriff, 2006). Magnetic Data Diurnal correction and normal field correction (Geomagnetic correction) are applied to the raw magnetic data to eliminate the effect of magnetic diurnals and the systematic increase of the magnetic field with latitude. Figure (5) shows the aeromagnetic total field map of Amara Basrah Quadrangles, which represent the surrounding of the studied area; some parts of which are not covered by C.G.G. (1974) aeromagnetic data. Figure (6) represents the geomagnetic survey as total magnetic intensity field (TMI) at the studied area, which partly has no aeromagnetic data. Comparison between Figs. (5 and 6) gives the same magnetic picture. The anomalies A, B and G have the same location and shape, as in the aeromagnetic map; this is also true for the positive anomaly E that has its negative part towards the north. Several positive and negative anomalies within the studied area are related to noise due to buried iron materials and the near occurrence of high-power lines. The reduction to the pole (RTP) filter reduces the dipolar field to a monopole field. The analytical signal calculated from the vertical integration of the magnetic field is very close to the optimum function represented by the gravity field over the anomalies (Fig.18), (Blakly and Simposn, 1986). RTP grid has been converted also to pseudogravity map (Fig.7); this map may define the relation between the gravity and magnetic anomalies in such a way that, if the magnetic and gravity anomalies are coincident, it will confirm that the gravity anomalies are related to the same deep sources. Otherwise, then it may indicate different sources or effects of remnant magnetization. The Energy Spectrum is a 2D function of energy relative to wave number and direction. The radials averaged spectrum is a function of wave number alone, and is calculated by 09

8 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al. averaging the energy for all directions for the same wave number. The above estimates can be used as a rough guide to the depth of the magnetic and gravity sources. Figures (8 and 9) that illustrate the typical reduction in energy with increasing wave number; the depth estimated from the spectrum file are statistical depth estimated to the top of the sources (Spector and Grant, 1970) N AMARA QALAT SALITH AUZAI QURNAH ±±±±± Magnetic body Boundary of the studied area ~~~~~~~~~ Magnetic discontinuity or or fault fault 9 Magnetic basement depth contour Magnetic contact or fault City km Km C.I =1 nt Fig.5: Aeromagnetic map of Amara north part of Basra Quadrangle boundary of the studied area 00

9 AMARAH QALAT SALIH AUZAI R QURNAH City C.I. = 2 nt Fig.6: TMI of the studied area after 150 m upward Continuation filter 06

10 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al. AMARAH QALAT SALIH AUZAIR QURNAH City C.I = Nt.m Fig.7: Pseudo gravity map after applying Vertical integration of RTP map 06

11 RADIALLY AVRAGED POWER SPECTRUM DEPTH ESTIMATE Fig.8: Radially averaged power spectrum of gravity field data RADIALLY AVERAGED POWER SPECTRUM DEPTH ESTIMATE Fig.9: Radially averaged power spectrum for magnetic field data 05

12 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al. DATA INTERPRETATION Gravity Data Bouguer gravity maps of Iraq and that which cover Amara north part of Basrah Quadrangle, both obtained from IPC data (Figs.10 and 11, respectively) include an area without gravity data located between latitude 30 45' 32 00' N and longitude 47 00' 48 00' E. The main aim of this study is to fill this uncovered area with land gravity survey. The gap in the area was successfully covered, except the area of Hor Aum Al-Na'age, the northern part of Hor Al-Huwaizah that is still filled with water. Figure (12) shows the same area in Fig. (10) After merging the data with the gravity data of the studied area using Oasis Montage Software. Figure (13) shows the Bouguer gravity map of the studied area deduced from the gravity surveys. Some of the inferred gravity anomalies (symboled as G, Gr and F for regional residual and fault, respectively) have the same extension and complement as that of the surrounding area, such as G1, G2, G3, G4 and the main negative anomaly within the studied area. G2 and G3 are the main two positive anomalies within the studied area, which may represent the southeastern part of Ramadi West Amara High Gravity Anomaly, which extends farther to the SE across the Iraq Iranian border (Fig.12), (Al-Bdawi et al., 2010). These two highs may be related to the same source and may represent an uplift or antiform with NW SE direction. The main negative anomaly (A) is bounded from the north and south by two gravity gradients interpreted as normal faults (F2 and F3, respectively) the anomaly F1 could be also interpreted as a normal fault because of its high gradient. It has two parts displaced from each other's by the gravity high G1, which may be interpreted as local antiform or nose imposed on the main gravity high G2, which extends almost WNW ESE direction and has a deep source. The residual positive anomaly Gr5 may be interpreted as an important anticline structure superimposed on local gravity low, which could be affected by the occurrence of salt similar to several cases, such as Zubair, Rumaila and Nahr Umar structures in the Mesopotamia foredeep. The same is true for the residual positive gravity anomaly Gr7, imposed on the main gravity low A. Another residual positive gravity anomaly (Gr8) is imposed on the regional gravity high G4, located in the southeastern part of the studied area. The latter may represent the northern part of the Kuwait Arch, where most of the hydrocarbons traps are distributed along its flank (Al-Bdaiwi et al., 2010). The same condition is right in the studied area, where the oil fields are distributed along the flank of the gravity gradient F1, F2 and F3. There is another gravity gradient represented by the anomaly F4 located in the northeastern part of the studied area, it may be interpreted as a strike slip fault according to its effect that disturbs the gravity field and affect the located gravity anomalies, within its vicinity, (Fig.13). 66

13 Fig.10: Bouguer gravity map of Iraq (after IPC, 1972) AMARAH QULAT SALIH QURNAH Fig.11: Bouguer gravity map of Amara north part of Basra Quadrangles before merging with studied area gravity data (after IPC, 1972) 66

14 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al. AMARAH QULAT SALIH QURNAH City Fig.12: Bouguer gravity map of Amara north part of Basrah (IPC, 1972) after merging it with the studied area data (C.I. = 1 mgal) 66

15 AMARAH QULAT SALIH QURNAH City Fig.13: Bouguer gravity interpretation imposed on Bouguer gravity map of the Studied area (C.I. = 0.5 mgal) 66

16 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al. AMARAH QULAT SALITH AUZAIR QURNAH City Fig.14: Bouguer gravity interpretation imposed on VDV filter of Bouguer gravity map of the studied area 66

17 AMARAH QULAT SALIH AUZAIR QURNAH City Fig.15: Bouguer gravity interpretation imposed on THD filter of Bouguer gravity map of the studied area 69

18 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al. Figure (16) shows regional gravity map after application of the third order trend surface of polynomial regression filter. The regional anomalies G1, G2 and A re still exist; G1 becomes one anomaly with negative gradient towards the east and the G2 with negative gradient towards the north, which means they have depth extent. Figure (17A) shows correlation profile along C C' between Bougure (BOUG) vertical derivative (VDV) and total horizontal derivative (THD) filters for gravity data (Figs.14 and 15 respectively) these filters were applied to ascertain the main anomalies within the profile by enhancing the response of these anomalies and make them easier to be located and recognize. These anomalies are as fallows; F1, F2 and F3 interpreted as normal faults, whereas G1, G2, Gr7 and Gr8 as a gravity highs. G1 and Gr7 are two positive gravity highs superimposed on the main gravity high and low in the studied area (G2 and A, respectively). Magnetic Data Figure (18) shows the reduction to the pole map (RTP) of the studied area; this correction simplified the complex magnetic anomalies shapes, so that they appear as positive anomalies located directly above (induced magnetized) sources; as if they were at magnetic pole. The main magnetic highs within the studied area are as fallows; M1 and M2 are located in the NW, M3 and M6 in the N, M7 in the NE, M4 and M5 are two magnetic highs superimposed on the regional magnetic low A and affect the sedimentary cover through its expression in the gravity field (Fig.13).Anomalies M8, M9 and M10 may relate to intrusions. Whereas M8 and Gr7 may relate to the same deep source affecting the sedimentary cover. The magnetic anomalies F1, F2, F3 and F4 were interpreted as normal faults. Figure (19) shows the regional RTP magnetic field at the studied area after application third order trend surface of polynomial regression filter. At northern part of the map. There is a trend of high positive gradient, while at the southern part of the map, there is a dipolar anomaly with negative pole to the north (at the middle) and positive pole to the south, and both anomalies represent deep sources. Figure (17B) shows the same correlation profile along C C' between reduction to pole (RTP), total horizontal derivative (THD) and vertical derivative (VDV) filters for RTP data. In this profile, the main interpreted anomalies are as fallows; F2 interpreted as a normal fault, whereas M1, M3 and M8 as a magnetic highs, Mr4 and Mr12 are residual magnetic highs, whereas M3 and Mr4 are two positive magnetic highs superimposed on the main magnetic low A, while Mr12 is a residual magnetic high superimposed on the magnetic low B, these anomalies have affected the sedimentary cover through its expression in the gravity field in the same localities. On the other hand, M8 is well correlated with Gr7, which is imposed on the main gravity low A indicating the possibility of salt occurrences (see Figs.13 and 18). 60

19 Nprthing (m) AMARAH N QALAT SALIH mgl City QURNAH km Easting (m) Fig.16: Regional Bouguer gravity map of the studied area (C.I. = 0.5 mgal) 66

20 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al. Correlation profile C C' of gravity data Fig.17A: Correlation between different curves resulted from different kinds of grids along cross-section C C', BOUG in mgal, VD in mgal/m, THD in mgal/m 2 (For location refer to Figs.13, 14 and 15, respectively) Correlation profile C C' of RTP data Fig.17B: Correlation between different curves resulted from different kinds of grids along cross-section C C', RTP in nt, VD in nt/m, THD in nt/m 2 (for location refer to Fig.18) 66

21 AMARAH QALAT SALIH AUZAIR QURNAH City C.I. = 3 nt Fig.18: Magnetic interpretation imposed on RTP filter of total magnetic Intensity map of the studied area 65

22 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al. AMARAH QALAT SALIH AUZAIR City C.I. = 3 nt Fig.19: Regional RTP map of the studied area after applying 5 Km upward continuation filters 66

23 DISCUSSION AND CONCLUSIONS Gravity Method It is essential to say that the Bouguer gravity map of the studied area (Fig.13) reflects mainly the structures that lie above the basement, i.e. intrasedimentary anomalies and these anomalies complete those of the surrounding map area (Fig.12). Inspection of this map may delineate several anomalies. The analytical signal calculated from the vertical integration and pseudogravity filters, (Fig.7) is very close to the optimum function represented by gravity field over the anomalies in presented Fig. (13). It's believed that the anomalies G1, G2 and G3 are parts of one extended positive anomaly, which trends NW SE; this positive anomaly has long extension outside the studied area (Al-Badawi, et al., 2010). This anomaly may be caused by uplift in sedimentary cover as indicated in the basement relief map of IPC (Fig.20). Part of this uplift occurs or may be caused by antiform structure represented by G1 that extends along the proposed fault F1 (Fig.13), or interpreted in term of coral reef or anhydrite elongated body present within the sedimentary column (Al-Badaiwi, et al., 2010). The anomaly Gr5 could be important positive anomaly imposed on a local gravity low it is related to Halfaya anticline (Fig.3), but probably the occurrence of salt has caused its negative background signature. The negative gravity anomaly A is the complementary of the negative anomaly outside the studied area. This anomaly is surrounded by high gravity gradient that may be related to presence of faults (F2 and F3). This anomaly may reflect the occurrence of a depression filled with low-density materials such as salt (Fig.3). The positive gravity anomaly G4 at the southern part of the map (Fig.13) may reflect the northern part of Nahr Umer anticline, and could represent the northern flank of the Kuwait Arch as mentioned by Al-Badaiwi et al., (2010). The positive gradient F3 could be due to the effect of fault structure bounding the negative anomaly A from the south and it may be related to Majnoon oil field. Another feature seen in the Bouguer map is the location of some oil wells, at the flanks of the high gradients of anomalies F1, F2 and F3, (Figs.13 and 14). Jassim and Goff (2006) mentioned that there are groups of buried anticlines of relatively low amplitude associated with longitudinal faults, along the Ramadi Musaiyib and the Tikrit Amara Faults Zones, These anticlines are associated with sharp gravity gradients, and the same is also seen in the studied area. 66

24 a 14.5 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al Amara 13.5 N Tigres Uzair Qurna Marshes Uplifts Uplifts of of (Hamidia)repersents represents the platform flank of Mesopotamian the platform Fordeep flank of uplifts mesopotamian and linear anticlinal zones fordeep uplifts and linear anticlinal zones Major Major transverse transvers faults faults Zone Zones of faults of faults dividing deviding the first the order first structures order styructures 13 Basement Basment depth depth (Km) km C.I.= 0.5 mgal C.I = 0.5 mgal Fig.20: Basement relief map of Amara north part of Basra Quadrangle (IPC, 1972) 66

25 Buzurgan N Halfaiah Iran Majnoon West Qurn Gravity high Lineament lineament and and fault fault Marshes and Swamps Rivers Borders Oil Field km Governorate Center Qad a Qad' a center Boundary Boundary of Studied of the studied area area Fig.21: Modified map of Amara north part of Basra Quadrangle shows the main structural axes with lineaments and oil field traces (Jassim and Goff, 2006). 66

26 Gravity and Magnetic Surveys to Delineate Subsurface Structures in Hor Al-Huwazah Area, South of Iraq Ghalib F. Amin et al. Magnetic Method The magnetic anomalies of the studied area show the same features as those of the surrounding areas surveyed eromagnetically by C.G.G. in (1975), but the most important thing is that the area is very noisy due to the occurrence of the high-power lines and different buried iron objects. The positive magnetic anomalies M1, M2 and M3 (Fig.18) may be related to the effect of the same source, represent the eastern part of the positive magnetic anomaly located at Amara city, which in turn represents the extension of the long positive anomaly South Najaf Al-Shatra anomaly, (Al-Badaiwi et al., 2010). Anomaly M8 is the main magnetic high in the studied area. This anomaly extends to the east and to the surrounding area and its complements. This anomaly is well correlated with the residual gravity anomaly Gr7, imposed on the main gravity low A, indicating the possibility of salt occurrences (see Fig.13, 17 and 18). Anomaly M11, which is located in the southern part of the studied area, could be extended farther to the south outside the studied area. The direction and location of this magnetic anomaly is well correlated with the gravity high G4: both trending NW SE. The latter may represent the north part of Kuwait Arch, where most of the hydrocarbon traps are located along its flank (Al-Bdaiwi et al., 2010). The same condition is seen in the studied area, where the same oil fields are distributed along the flank of the high gravity gradients F1, F2 and F3. REFRENCES Al-Bdaiwi, J.M., Saffo, J.K., Radhi, B.H., Abdul Qadir, S.O., Ali, A.H. and Jawad, M.B., Structural markers inferred from geophysical data. Sheet Al-Amara and AliAl-Gharbi Quadrangles, scale 1: Nos. NH-38-4 and NI GEOSURV, int. rep. no Blackly, R.J. and Simpson, R.W., Approximating edge of source bodies from magnetic or gravity anomalies: Geophysics, Vol.51, No.7, p Compni General De Géophysique (CGG), The aeromagnetic and a erospectometric survey of Iraq, Massy, France. GEOSURV, int. rep. no Fouad, S.F., Tectonic map of Iraq. Iraqi Bull. Geol. Min. Special Issue, No.4, 2011, p Iraqi National Oil Company (IPC), Basement Relief map of the republic of Iraq (south part). Iraqi national oil company (IPC), Structural- tectonic map of the republic of Iraq (south part). Jassim, S.Z. and Goff, J.C., Geology of Iraq. Dolin, and Moravian Museum, Prague, 341pp. Reynolds, J.M., An Introduction to Applied and Environmental Geophysics, John Wiley and Sons Ltd pp. Sheriff, R.E., Encyclopedic dictionary of applied geophysics, 4 th edit. 429pp. Spector, A. and Grant, F.S., Statistical model for interpreting aeromagnetic data. Geophysics, Vol.35, No.2, p Yacoub, S.Y., The geology of Al-Amara Quadrangle, sheet no. NH-38-4, scale 1: GEOSURV, Baghdad, Iraq. 66

27 About the Authors Mr. Ghalib F. Amin, graduated from University of Baghdad in 1976 and, he got M.Sc. from the same university in He joined GEOSURV in Currently he is working as Senior Chief Geophysicist in Geophysics Division, GEOSURV. His main field of interest is gravity and magnetic prospecting. He has 16 documented reports and published papers. Dr. Abbas M. Yass, graduated from University of Baghdad in 1984 with B.Sc. degree in Geology, and M.Sc. in Electrical Resistivity Method in 1989 and Ph.D. degree in gravity and magnetic methods in 2002 from the same university. He joined GEOSURV in Currently, he is working in Geophysical Division in Geology Department. He has more than 20 documented reports in GEOSURV's Library. His major field of interest is gravity, magnetic electrical resistivity and GPR methods. Mailing address: Iraq Geological Survey, P.O. Box 986, Baghdad, Iraq Mr. Hayder A. Al-Bahadily, graduated from University of Baghdad in 1994, he got M.Sc. from the same university in 1997 in geophysics and joined GEOSURV in Currently, he is working as Assistant Chief Geophysicist in the Geophysics Division, GEOSURV. His main field of interest is gravity and magnetic prospecting. He has 23 documented reports and published papers. Mr. Ahmed S. Musa, graduated from University of Baghdad in 1994, he got M.Sc. from the same university in 1997 in geophysics and joined GEOSURV in Currently, he is working as Assistant Chief Geophysicist in the Geophysics Division, GEOSURV. His main field of interest is gravity and magnetic prospecting. He has 13 documented reports and published papers. 69