GeolCarp_Vol70_No5_373

GEOLOGICA CARPATHICA

, OCTOBER 2019, 70, 5, 373–385

doi: 10.2478/geoca-2019-0021

www.geologicacarpathica.com

Deep gravity data interpretation using seismic reflection

and well data: A case study of the West Gharib-Bakr area,

Eastern Desert, Egypt

AHMAD A. AZAB

Egyptian Petroleum Research Institute (EPRI), Ahmad Alzomor Str. 2, Alzohoor District, Nasr City, Cairo, Egypt; research@epri.Sci.eg

(Manuscript received June 27, 2018; accepted in revised form June 13, 2019)

Abstract: A rigorous processing and analysis of the gravity data with seismic reflection and borehole information

enabled a general view of the deep-seated regional structures in the West Gharib-Bakr area, Eastern Desert, Egypt. In this

context, several interpretational techniques were applied to learn more about the supra-basement structures and intra-

basement sources. The interpretation started with a review of the seismic data to clarify the structural elements on top of

the Miocene strata, where a number of isochronous reflection maps were constructed and had migrated into depth maps.

The Bouguer anomaly map was processed using Fast Fourier Transform filtering based on spectral analysis to separate

the gravity anomalies into its components. Gravity stripping was also performed under the seismic isopachs and density

controls. The gravity effect of each rock unit was calculated and progressively removed from the original data to obtain

a new gravity map on top of the Pre-Miocene. To ensure more reliable results, further filtering and analytical processes

were applied to the stripped map. The results of seismic analysis show simple structural configurations at the Miocene

level, with a significant increase of evaporite thickness along the Gulf of Suez coast. In contrast, analysis of the stripped

gravity map reveals a more intricate structure at the Pre-Miocene level, with increasing numbers/lengths of faults on

the basement surface. Lineament analysis shows two major peaks trending N0–20°W and N50–70°E, produced by two

main forces in NNW–SSE (compression) and ENE–WSW (tension) directions. The models confirmed a rough and

ruptured basement surface, with no evidence of any magmatic intrusions penetrating the sediments. The basement relief

map delineates five basins/sub-basins in the area which are separated from each other by ridges/saddles.

Keywords: West Bakr, Eastern Desert, Egypt, gravity stripping, applied geophysics.

Introduction

In deep basinal areas which contain excessive thickness of

evaporite (Evp) rocks, such as the Gulf of Suez (GOS) area,

the deep structural configurations are not clear enough. Seis-

mically, the reflection data has several difficulties and large

deficiencies at depths near the basement. The attenuation and

dispersion of the energy of waves within the Evp group lead to

the shortage of seismic data and bad events below the base

of the Evps. In addition, most of the seismic surveys were

acquired in the dip direction, which makes it difficult to deli-

neate locations of the transform faults. Gravitationally, this

may be attributed to the steepness of the GOS trend or to the

great gravity effect of the near-surface layers. The structural/

lithological variations of the Evps may create local anomalies

like those arisomg from the Pre-Miocene (PM) features.

All this may conceal the deeper sources and make it more dif-

ficult to determine locations of the uplifts and fault patterns.

To overcome this, an integrated interpretation was carried out

using all available geophysical data to disclose the hidden

source structures on or within basement rocks.

The work started with interpreting the seismic sections

through using the well logging information. The structural

analysis focused on the shallow features capping the tops of

the Miocene formations, where seismic lines seem to be very

good in the upper part but very bad in the lower portion.

The seismic interpretation is limited by the base of the evapo-

rites, with most basic structural interpretation next to impos-

sible. Therefore, the work has taken another way to interpret

the deep configurations depending on the Bouguer gravity

data. The interpretation is based on the fact that the gravity

anomalies can be regarded as superposition of the anomalies

reflected from the main density boundaries at varying depths.

This means that the gravity anomaly includes effects of both

shallow (residual) and deep (regional) constituents. Isolating

either of them may enhance the effect of the other. In this con-

text, two different enhancement procedures were applied to

the Bouguer anomaly map with evaluation of their effecti-

veness in characterizing the deep-seated sources/structures.

Firstly, the gravity filtering was performed using the Fast

Fourier Transform technique to separate the gravity anomalies

into residual and regional components. In fact, gravity filte-

ring results were insufficient to give details about the deep

configurations. Secondly, the layer stripping technique was

applied as a more reliable interpretation method, where gra-

vity, seismic and well data interpretation were integrated to

disclose the hidden potential sources. To do this, the gravity

effects of all shallow layers (Post-Miocene and Miocene rock

units) were calculated and subtracted from the Bouguer data.

The residue provides a stripped map on top of the PM that

374

AZAB

GEOLOGICA CARPATHICA

, 2019, 70, 5, 373–385

conforms more with the deep constituents. This approach

depends largely on the rock parameters, thickness and density

of each formation. The formation-density has been derived

from the drilled wells data, while the geometry of the forma-

tion was identified from the seismic isopach maps. Sub-

sequently the stripped map on top of the PM was subjected to

further analytical processes. The horizontal gradient filter and

Euler deconvolution method were applied on top of the PM

gravity map to map the main fault systems controlling the area.

The lineaments analysis was performed to define the structural

trends affecting the basic structure. A stress diagram and a strain

ellipse were constructed to explain the different tectonic forces

and associated shear fractures, which controlled the structural

setup. The gravity modelling was done before and after gra vity

stripping to confirm the shallower structures, and to deduce

the PM source structures. Finally, the source parameter ima-

ging method was applied to determine the approximate depths

of the basins and ridges, producing a map that more closely

resembles the geology than originally.

The potential data used is the Bouguer anomaly map con-

structed from the ground surface. Askania torsion balance was

used to construct a map with scale of 1:100,000 and contour

interval of 0.5–1 mGal, in 1976. The gravity survey was car-

ried out on the western coast of the GOS by Anglo Egyptian

Oilfield Ltd., for the Egyptian General Petroleum Corporation

(EGPC). The survey covers the area between Ras Bakr and

Ras El-Bahar on the western coast of the gulf. The seismic

data consists of fifteen seismic lines which was shot by

Geosource Limited, on sept.,1981 under the auspice of the

General Petroleum Company (GPC), for the (EGPC).

The aim of this work is to re-interpret all available geophy-

sical data, in terms of structural setting and tectonic fabric, to

shed light on deep source structures. The interpretation focuses

on the PM uplifts and cross-faults that may be helpful in loca-

ting deep prospecting. Some emphasis was also placed on

the distribution of basins and ridges in the area.

Structural considerations

The study area (Fig. 1) lies in the Eastern Desert along the

western coast of the GOS, in the middle between Suez city to

the north and Hurghada city to the south. It comprises several

onshore oilfields, which are confined between the GOS to

the east and Precambrian basement rocks of the Nubian to

the west.

Grouping of blocks or sets of blocks having the same direc-

tion of dip lead to subdivision of the GOS into three tectonic

provinces of contrasting dip attitudes, termed “Araba,

Belayim, and Amal” from north to south. Each province is

divided along major north-westerly trending faults into plates

that almost plunge in the same direction (Mostafa 1976;

Meshref 1990). The West Bakr oilfields lie in the central pro-

vince of GOS, namely the north-easterly plunging Belayim

province (Fig. 1) which is bounded from the north and south

by two major faults or “hinge zones” of a NE–SW trend.

This province was separated from the Amal province by

the “Morgan” hinge zone and from the Araba province by

the “Galala-Zenima” hinge zone. The structure and sedimen-

tology as well as the relationships between tectonics and sedi-

mentation in the active Suez-rift basin were studied by many

authors (e.g., Gupta et al. 1999; Young et al. 2002; Herkat &

Guiraud 2006; Khalil & McClay 2008; Pietrantonio 2016;

Rohais et al. 2016; Bosworth & Durocher 2017; Segev 2017;

Azab 2018).

The drillhole information in the study area indicates a thick

sedimentary section of the PM and younger rocks, unconfor-

mably overlying the basement complex (Ghanim 1972; Scotte

& Govean 1984). The sedimentary section comprises rocks of

Carboniferous, Cretaceous, Paleocene, Eocene, Miocene and

Pliocene-recent ages (Shabaan et al. 1984). The Miocene

rocks are the main source of oil-bearing rocks and they vary

from place to place. They are divided into lower clastic rocks

(Gharandal group) and upper evaporitic rocks (Ras Malsab

group). The Gharandal group includes the (Nukhul, Rudeis and

Kareem fms.) that underlie the Evps of the Ras Malaab group

(Belayim, South Gharib and Zeit fms.). The Evp rocks consist

mainly of anhydrite, gypsum, salt rocks intercalated with shale

and sandstone. The PM sediments are generally characterized

by a wide distribution and great thickness of the clastic rocks.

The crystalline basement rocks seem to be quite similar to

those cropping out to the west of the area (Mostafa 1992).

Previous works in the study area (Otsuka & Ogawa 1977;

Shabaan 1984) indicate that the west Gharib-Bakr area is

Fig. 1. Location map of West Gharib-Bakr area, with the oilfield con-

cessions (see Appendix for GPS coordinates of the wells).

375

DEEP GRAVITY DATA OF THE WEST GHARIB-BAKR AREA, EASTERN DESERT, EGYPT

GEOLOGICA CARPATHICA

, 2019, 70, 5, 373–385

charac terized by thick layers of Evps that exist in Kareem to

Zeit fms. and act as sealing rocks. The Evp group shows large

lithological variations, and consists of anhydrite (high density)

and salt-halite (low density), contaminated with shale, sands,

lime (medium density). The percentage of these rocks vary

laterally/vertically and lead to significant changes in the bulk

density from one place to another. Generally, the density of

the Miocene Evps varies widely from 1.9 to 2.9 g/cm

, based

on the percentage of anhydrite compared to other sediments.

Seismic interpretation

The structural configuration in the study area was studied

through interpreting fifteen 2D seismic lines vibrated in the NW

and NE directions. These seismic sections were carefully inspec-

ted to detect the most reliable marker horizons. The available

well velocity survey of Hashem-1 (Miocene/TD 2909 m),

EPH-1X (Cenomanian/TD 2659.98 m) and EPG-1X (Nubia/

TD 2915 m), and their composite well logs were used to faci-

litate the identification of the real reflectors in the seismic

records. The strong/continuous reflectors on the tops of the

Evp layers were easily traced along the seismic lines. The sub-

surface geological identification was done through picking

and correlation of reflection times as well as fault detection.

Analysis of the seismic sections was limited by the base

Kareem Fm., which is the deepest horizon of seismic interpre-

tation. Accordingly, several isochronous reflection maps were

established through picking the two-way times (Fig. 2).

The average velocity and isochronous reflection maps on top

of the different formations were used to convert the reflection

times into depths. The structure contour maps in terms of depth

and faulting were also constructed on the tops of the Miocene

formations (Fig. 3). Close correlation between these maps

shows that the Miocene rocks are affected by a small number

of faults that increase in number and length with depth.

The faults run mainly in the NW–SE direction (GOS trend)

while the NE–SW cross-gulf faults are absent. In addition,

the isopach maps for post-Zeit, Zeit, South Gharib, Belayim

and Kareem were constructed from the grid-data of the depth

contour maps, whilst the isopach map for the Lower-Miocene

Rudeis Fm. is constructed based on the composite logs of the

drilled wells. The isopach maps indicate presence of a large

thickness of Evp sediments in the north-east part, while Lower-

Miocene Rudeis sands increase in a south-west direction.

Seismic profiling was established to show the lateral/verti-

cal subsurface distributions more clearly. A geoseismic section

BK-1039 (Fig. 4) is displayed as an example in the NE–SW

dip direction, constructed through transforming the seismic

reflection time into depth using the well velocity data.

Generally, the seismic line seems to be very good at shallow

depths where it shows strong reflections corresponding to

the high density/velocity Evps. Noticeably, the post-Evps/

Evps decrease in their thickness towards the south-west, and

significantly increase toward the north-east before dimini-

shing over the offshore ridge (Bakr-Gharib), a fact that was

verified by well data. The seismic line shows that a small num-

ber of short fractures cut across the Miocene strata. These nor-

mal faults have small throws and do not reach the surface

where the surface layer seems to be not entirely deformed.

As expected, seismic evidence is generally very poor at large

depths, where the continuity of the seismic events is markedly

bad beneath the Kareem Fm. There is no evidence to support

the presence of faults below the Miocene Evps. If they are

present, it is rather difficult to judge whether such bad events

relate to deep fault-structures or are due to lithological varia-

tions. Generally, seismic interpretation had failed to give any

exact information about locations, orientations, magnitudes or

throws of faults below the Evp rocks. Seismic reflection is

also ineffective for locating the PM high-structures, caused by

basement uplifts.

The seismic interpretation was confirmed by a SW–NE geo-

logical cross section AA’ (Fig. 5), which extends between four

wells drilled in the study area. The cross section shows a struc-

tural uplift at the EPH-1, EPG-1 and GN-1 wells, where the

thickness of the formations is reduced and the formation tops

have less depth. Eastward, the structure exhibits a real increase

in thickness of the sedimentary section alongside the GOS

coast, especially of the Miocene and Post-Miocene sediments.

This Miocene basin is bounded from the east by an uplifted

block (Bakr-ridge), where PM rocks are shallower at Bakr-2.

Westward, the basement rocks were buried under thick sec-

tions of the PM and Lower-Miocene sediments. The Miocene

layers were affected by a number of normal faults that extend

downward and are thought to be inherited from older

tectonics.

Fig. 2. Time-depth curve and velocity analysis of Hashem-1 Well.

376

AZAB

GEOLOGICA CARPATHICA

, 2019, 70, 5, 373–385

Gravity interpretation

The Bouguer anomaly map (Fig. 6) shows dominance of

the negative gravity values from −35 to −51 mGal all over

the area, which may reflect a relatively thick sedimentary

cover. The gravity field is largely variable from east to west,

which may be associated with large lithological/structural

variations in the subsurface. Qualitatively, the map contains

a number of strong anomalous features of different amplitudes

and sizes, running nearly parallel to the GOS trend. The high

and low gravity zones are separated from each other by steep

gradients, which strike in the north-west direction. Such high

gravity gradient zones were traced on the Bouguer anomaly

map by circles of Euler solutions, which tend to cluster along

geological boundaries. The linear structures are closely asso-

ciated with locations of major bounding faults, which divided

the area into a number of gravity zones of a north-west orien-

tation. Little or no solutions tend to cluster along the trans-

form-fault traces. Generally, the gravity maxima and gravity

minima are closely linked with the major structural features in

the area. For instance, the high gravity anomaly that exists

along the offshore part corresponds to the pre-existing horst

blocks extending from Amer to Gharib. The West Bakr oil-

fields (G, H, B and K) could also be correlated with high

anomalous features. Westward, the gravity low corresponds to

a broad sedimentary basin of “Khashaba low”, while the gra-

vity maximum in the south-western corner is related to base-

ment outcrop of the Nubian Massif.

To separate the gravity anomalies into their components,

the Fast Fourier Transform matched filtering technique based

on spectral analysis was applied to the Bouguer anomaly map.

The isolation method depends mainly on the slopes of the spec-

tral analysis curve, where the frequency ranges give the most

efficient estimation of the gravity anomalies to fit the deep and

shallow constituents. The separation using the energy spec-

trum of potential field data is highly advantageous over any

other known conventional method (Sadek 1984). The poten-

tial anomalies in the space domain are transformed into

Fig. 3. Structure-depth contour map: a — on top of Zeit Formation/top Miocene section; b — on top of Rudeis Formation/base of

Miocene-evaporites.

Fig. 4. Interpreted geoseismic line BK-1039 along NE–SW direction.

Fig. 5. Geological cross section A–A', taken in the NE–SW direction,

passing through EPH-1X, EPG-1X, GN-1 and E. Bakr-2 wells.

377

DEEP GRAVITY DATA OF THE WEST GHARIB-BAKR AREA, EASTERN DESERT, EGYPT

GEOLOGICA CARPATHICA

, 2019, 70, 5, 373–385

frequency domain and the various parameters of anomaly

sources are derived from the characteristic properties of the

amplitude. Moreover, the spectral method provides the possi-

bility of doing depth measurement using gradients when no

anomalies are expressed in the profile. The theoretical assum-

ption was studied by many authors. Spector & Battacharyya

(1966) computed the energy spectrum and autocorrelation

function of FFT for the simple magnetic model. Spector

(1968) shows that the energy spectrum is greatly affected by

surface highs above the basement, the greater the high the lon-

ger the wavelengths. The anomalies and autocorrelation func-

tions associated with simple 2-D (two-dimensional) and 3-D

(three dimensional) magnetic and gravity models were subse-

quently transformed mathematically to the frequency domain

by Spector & Bhattacharyya (1966). Spector & Grant (1970)

reported some undesired effects on the calculations of the

energy spectrum which derive from processes of digitization,

quality and density of data. Dimri (1992) and Blakely (1995)

estimated the mean depth of the interfaces considering the log

of power of the Bouguer gravity spectrum as a function of

wavenumber/frequency assuming uncorrelated distribution of

sources (Spector & Grant 1970) or scaling nature of sources

(Pilkington et al. 1994; Maus & Dimri 1994, 1995, 1996).

Isolation of the gravity anomalies was carried out using

Geosoft 2007 software and the results are shown in Figure 7a.

Two linear segments of the energy decay curve with distin-

guishable slopes were used to isolate the regional and residual

components, where the regional effects are evident at larger

wavelengths and the shallow/local effects are evident in short

wavelengths. Accordingly, the energy spectrum curve invol-

ves two parts: a very steep part at low wavenumbers (0 km

−1-

< wavenumber < 0.230 km

−1

) and a less steep part at high

wavenumbers (0.230 km

−1

< wavenumber < 1.400 km

−1

The depth can be estimated by

where: (h) is depth;

(s) is slope of log (energy) spectrum. Accordingly, the slope of

the line fitted to the upper part of the spectrum curve is used to

estimate the average depth of deep sources (~24 km), and the

average depth to shallow sources (~4.5 km). The frequency

bands related to the regional and residual gravity components

on the energy spectrum were used through the band-pass fil-

tering. By bandpass, all wavenumbers between limited values

would be saved or passed while the rest would be cut, so that

the bandpass filter passes frequencies within a certain range

while rejecting frequencies outside this range.

The high-pass gravity map (Fig. 7b) shows a set of sharp

anomalous zones which are closely correlated with the shallow

components. The residual gravity field reveals improvements

of the gravity anomalies linked with near-surface con stituents,

but still lack details about deep-seated constituents. Thus, it is

Fig. 6. Bouguer anomaly map of the study area overlapped with

the Euler deconvolution solutions (SI = 0, window size = 10).

Fig. 7. a — Power spectrum of the Bouguer anomaly map, with two

linear segments of the energy decay curve with distinguishable slopes.

b — High-Pass filtered map of the Bouguer gravity data at the high

frequency and short wavelength range (230 cycle/km < wavenumber

<1400 cycle/km).

h = − s / 4π

378

AZAB

GEOLOGICA CARPATHICA

, 2019, 70, 5, 373–385

found that the filtered map does not meet the requirements for

studying the deep source structures.

Combined gravity–seismic interpretation

In fact, both seismic and gravity interpretations are unable

to reflect the deep causative source bodies due to strong

shielding of the evaporitic rocks. The large thickness of

Miocene Evps inhibits even the strong seismic energy to

refract into the deeper horizons. Likewise, gravity anomalies

are very sensitive to the thickness/density variations of the

anhydrite-salt rocks. Consequently, it is deemed necessary to

use an integration of the gravity and seismic in combination

with well information to interpret deep source structures. This

was done through applying the gravity stripping technique

based on Hammer (1963) and Otsuka & Ogawa (1977).

The gravity stripping depends on computing the gravity effect

of a certain rock unit or time-rock unit defined by its thickness

and density, then subtracting the effect from the integrated

effect of the whole sedimentary section, as has been indicated

by the Bouguer anomaly map, to get the pre-unit effect, and so

on for the other units (Parker 1973). This requires an exact

knowledge of the rock properties (geometry and density) to

get good results.

The workable equation applied for each rock unit in the

sedi mentary succession is

where Δg

is the gravity effect of a certain rock unit in mGal;

G is the international gravitational constant (6.67 × 10

-8

/g.s

);

Δρ is the density contrast between the formation density

and the basement density in g/cm

; H

is the unit thickness

in cm.

The depths to the upper and lower surfaces of each rock unit

have been seismically controlled. The thicknesses of the layers

were calculated through a number of seismic isopachs (thick-

ness-grids). The formation density was taken from the density

logs (gamma–gamma) for about eleven drilled wells, which

were checked and used to construct a set of density gradient

maps (Fig. 8). For every drilled well, the density log measure-

ments against each formation in the succession were ave raged

and used as a single value for that formation. Figure 9 is an

example for density information derived from the Bakr-2 and

Hashem-1 wells. They represent two different time intervals,

Bakr-2 Well displays densities of the PM section while

Hashem-1Well shows the densities of the Miocene section.

From the obtained thickness-grid and density-grid of each

rock unit, the gravity effect for every layer was calculated and

subtracted/removed from the observed data. The process was

repeated for all formations in the sequence from the surface to

the datum. In each case, two maps were obtained; the first map

represents the sum of gravity effects of all formations above

the datum. The second represents the gravity effect of the rock

units below the datum. At last, a stripped gravity map on top

Δg

= 2π G Δρ H

(1)

of PM was obtained which could be correlated with the

original.

Generally, the gravity effects of the Evp group are given by

The stripped gravity map on top of PM sequence can be

given by the relation

The above relations were applied using Surfer 13 Golden

Software where the outputs were calculated and contoured.

Figure 10a shows the sum of gravity effects due to sedimen-

tary section above the datum (surface layer, Miocene Evps and

Lower-Miocene clastics). The map is generally characterized

by a negative gravity effect (from −1 to −7 mGal), that

increases progressively from north-east to south-west.

Figure 10b presents the stripped gravity map on top of the PM

after removing the effects of the overlying formations from

the original data. The map shows the largest gravity effects

with negative values (from −20 to −49 mGal), which gra-

dually increase toward the south-east. This may reveal that

the gravity effect of the PM is the main source of negative

gravity present in the Bouguer map.

The correlation coefficient that measures and determines

the degree to which two variables are associated, was calcu-

lated between the gravity data before and after the stripping

process. The results in Table 1 shows a positive correlation

between the data of Bouguer and data for gravity effects on

top of the PM. Meanwhile it gives negative correlation versus

others, particularly against the Evp group (Fig. 11). The posi-

tive value may suggest that the deep causative sources have

the highest gravity effect, while the negative value may reflect

a gravity effect in the opposite direction. Accordingly, it could

be stated that, despite the large gravity effect of shallower

structures, the deeper sources are still the most effective.

The horizontal gradient method (Phillips 1998) was applied

on the stripped map (Fig. 10b) with the goal of revealing

the hidden faults. The horizontal gradient maxima delineate

the approximate locations, lengths and trends of the major

faults on/within the basement rocks. Figure 12a displays two

main trend patterns, cut cross the study area in the NNW

(Clysmic) and ENE (Syrian arc). Generally, the structure on

top of PM in Figure 12a shows dense fractures/faults if com-

pared with the Miocene structure in Figure 3. These linea-

ments were traced and statistically analysed (Affleck 1963) in

terms of number, length and direction to reveal the basic

tectonic trends. Figure 12b shows two major peaks in the

N0–30°W and N50–70°E directions. These two major peaks

demarcate two main fault systems (cross-faults) which are

predominant on the basement surface and divided the area into

segments. The structure suggests presence of a NE–SW tren-

ding shear fault zone, with a left-lateral displacement, in the

centre of the map.

Δg

evp

= 2π G ((

zeit

−

Bas

) h

zeit

+ (

−

Bas

) h

+ (

Bel

−

Bas

) h

Bel

+ (

kar

−

Bas

) h

kar

). (2)

Δg

strip

= Δg

Boug

−

(Δg

+ Δg

Δg

). (3)

379

DEEP GRAVITY DATA OF THE WEST GHARIB-BAKR AREA, EASTERN DESERT, EGYPT

GEOLOGICA CARPATHICA

, 2019, 70, 5, 373–385

Stress fields and proposed tectonic model

According to the trend analysis results shown in Figure 12b

an attempt was made to deduce the stresses and their possible

relations with the crustal deformation and plate motion which

affect the area (in-house software). Detected trends interpreted

from the gravity map after stripping were used in combination

with the idea of possible reorientation of stress (McKinstry

1953) to shed light on the direction and intensity of stresses

explaining the tectonism of the area. Figure 12c shows that

Precambrian basement is controlled by two different forces

acting on the region for long periods of time. The area was

subjected to a regional compressive stress in NNW direction,

contemporaneous with ENE extension force. The first

compressive stress is oriented N10°W. It is believed to be

associated with the collision between the African and European

plates. This principal axis of stress seems to have shifted

toward the west during different geological times, with a wide

azimuth of N0–30°W. Structurally, this stress force resulted in

two sets of primary and secondary shear fractures. The main

structural lines produced by the first stress force were formed

as primary shear fractures in a NNW–SSE direction. The ENE

folding/thrust faulting was also formed perpendicular to the

greatest principal axis of this type of stress force. Besides, the

N35°W (Clysmic) and N15°E (Aqaba) arose as secondary

strike-slip faults, where the angle between these two sets of

the sinistral and dextral fault systems is about 50° (Anderson

1951). The second force affected the area is the tensional

N85°E, which is attributed to the movement of the Arabian

plate relative to the Nubian Plate. The structural elements pro-

duced by this tectonic extension primarily take the form of the

N5°W Clysmic fault system. The N50–70°E trend is consi-

dered as a second order fault system produced by these exten-

sional forces. The rejuvenation of these tectonic trends during

different episodes may explain the high peak of N50–70°E.

The principal axis of this tensional force seems to have rotated

counter-clockwise. A reasonable model explaining the tecto-

nism in the GOS-Red Sea region was proposed by Bayoumi

(1983), to sketch the expected structural/tectonic development

during its geological history.

Deep structural elements

The Euler homogeneity relationship was used as an auto-

mated method to derive the plan location and depth estimation

of buried objects from the gridded-data. Euler’s homogeneity

equation relates the gravity field and its gradient components

Fig. 8. Formation density gradient map of the (a) Post-Miocene and Miocene evaporites, and (b) Lower-Miocene Rudeis sands.

Fig. 9. Density log of (a) Hashem-1 Well, and (b) Bakr-2 Well.

380

AZAB

GEOLOGICA CARPATHICA

, 2019, 70, 5, 373–385

to the location of the source with the degree of homogeneity

expressed as a structural index (SI; Thompson 1982).

The struc tural index is a measure of the rate of change with

distance of the field from the source (fall-off rate) and is

directly related to the source dimension. Depth and structural

index “solutions” provide information about the source of

anomalies. The advantage of the Euler Deconvolution (ED)

technique over other depth interpretation methods is that no

particular geological model is assumed, and can be directly

applied to large gridded data sets. The process reduces signifi-

cantly the time required for analysis of the data, it requires no

prior knowledge of the source of gravitation/magnetization

direction and assumes no particular interpretation model

(Barbosa et al. 1999; Hinze et al. 2013). The method can locate

or outline the confined sources, dykes and contacts with

remarkable accuracy (Reid et al. 1990). Marson & Klingele

(1993) applied it to gravity vertical gradients. Zhang et al.

(2000) applied it to gravity tensor gradient data. The Euler

deconvolution is used to confirm the modelling results,

because it is both a boundary finder and a depth estimator

(Reid et al. 2003).

The ED was applied to the stripped gravity map (Fig. 10b)

to deduce the major structural elements on top of the PM/

basement rocks. Herein, the structural insides of SI = 0 were

used to identify the rock boundaries and to estimate the depths

of their sources (Thompson 1982 and Reid et al.1990).

The calculation is running for window size (10) to obtain solu-

tions for different depths.

Figure 13 provides the best solution for the block-faults

with depths ranging from 0 to 4 km on top of the PM (without

depth of the overlying). The interpretation is based on the

linear solutions that mark the geological boundaries and divi-

ded the area into blocks. These linear features tend to occupy

zones of high gradients between anomalies. The distributions

and depths were identified using coloured circles, overlapped

on a shaded relief map. The white circles indicate shallow

depths while red circles locate deep faults. Generally, the map

reflects the complex structure on the basement surface through

a set of major faults that are bordering the main structural fea-

tures in the area. Most of these linear representations (major

faults) westerly-oriented in the NNW direction, parallel to the

axis of the GOS. The Clysmic trend is not a long-continuous

feature, but was dissected and displaced by faults oriented in

Fig. 10. Gravity effect of the sedimentary section: a — above the datum due to the Post-Miocene surface layer, Miocene evaporites and Lower

Miocene Rudeis sands; b — below the datum on top of Pre-Miocene.

Correl Coef between

Results

Boug /Pre-Miocene

0.34582

Boug /Rudeis

−0.10386

Boug /Evaporite

−0.33758

Boug /Post-Zeit

−0.03948

Table 1: Correlation coefficient results of different gravity effects

Fig. 11. Correlation coefficient between the gravity data before and

after stripping process.

381

DEEP GRAVITY DATA OF THE WEST GHARIB-BAKR AREA, EASTERN DESERT, EGYPT

GEOLOGICA CARPATHICA

, 2019, 70, 5, 373–385

an ENE direction. Some circles may be poorly-clustered,

where there is no significant density contrast, while, the large

condensation of circles may be due to dipping faults at large

depths, or upward reactivation of these trends. Generally,

the fault trends interpreted from ED in Figure 13 agree with

those shown in Figure 12. In comparison with seismic results,

the structure on top of the PM (Fig. 13) is more complicated

than that at the Miocene level (Fig. 3).

Gravity modelling

The profile B–B’ was taken on the Bouguer anomaly map

(Fig. 6) and on the stripped map (Fig. 10b) cutting across the

central part in a SW–NE direction. The profile stretches for

about 35 km, passing through four drilled wells (EPH-1X,

EPG-1X, GN-1X, AMER-8) which are considered as controls

and start points. The sedimentary layers were modelled as 2D

units, where X-axis (strike-length) is long relative to Y-axis

(depth). The sedimentary sequence consists of three main

groups with different lithological characteristics; the post-Evps

(~2200 kg/m

); Evps (~2800 kg/m

); pre-Evps (~2540 kg/m

The rock parameters were constrained by the seismic isopachs

(geometry) and by information derived from boreholes (den-

sity). The basement density was found to be 2670 kg/m

where there is no magmatic intrusion in the area (Shabaan et

al. 1984). The modelling process was done using GM-sys,

included in the Oasis Montage Package (2007).

Figure 14a presents a model for the regional subsurface

structure (shallow and deep) before doing the stripping pro-

cess. The upper part shows a good fit between the calculated

and observed gravity profiles. The lower part exhibits great

changes in the depth to the basement from the west to east,

with a regional dip regime to the west. The basement surface

is uneven/rough and loaded by thick and thin sedimentary sec-

tions that conceal beneath it more complicated structures.

Generally, topography of the basement is in harmony with

gravity anomalies where the swells and troughs are correlated

with gravity maxima and minima, respectively. The model

exhibits two deep basinal areas in both sides, these are; the PM

basin to the west (Khashaba low) in parallel to the Nubian

Massif, and Miocene basin to the east (W. Bakr basin) along-

side the GOS. These two basins are correlated with low gra-

vity anomalies, and are separated from each other by a ridge- like

form (W. Bakr high). The structure exhibits a number of major

faults separating the main topographic features. These normal

faults arise on the basement surface, grow upwards into the

PM section and mostly disappear into Miocene formations.

Figure 14b presents a sketch of the modelled profile after

doing the gravity stripping. Here, the gravity effect due to the

upper part of sedimentary cover was neglected since densities

Fig. 12. a — Maxima of horizontal gradient magnitude of the stripped

gravity map on top of Pre-Miocene. b — Rose diagram of tectonic

trends as deduced from the stripped map on top of Pre-Miocene.

c — stress-strain diagram of the study area based on statistical trend

analysis.

Fig. 13. Euler deconvolution results on top of Pre-Miocene as deduced

from the stripped map.

382

AZAB

GEOLOGICA CARPATHICA

, 2019, 70, 5, 373–385

of the Miocene and Post-Miocene were found to be zero.

The removal of the gravity effect of the shallower portion

gives a chance to better model the deeper structures. The deep

source structures were deduced through matching the observed

and calculated profiles, after fixing the parameters of the upper

portion. The top of the PM was determined through four

drilled wells which act as control points, while basement sur-

face configurations were estimated by means of iterative fit-

ting. Generally, the model nearly shows the same structural

conclusion obtained previously with some modifications on

the basement surface. The pre-Evp section was divided into

two sections; the Lower-Miocene Rudies Fm. and PM

sequence (2440 kg/m

). The structure shows a noticeable

increase in number of faults on the basement surface more

than before. The Clysmic faults originate on top of the base-

ment and vanish into the Miocene before reaching the surface.

The structure exhibits the same two basinal areas present in

south-western part (Khashaba low) and north-eastern portion

(W. Bakr basin). The uplifted area between these two basins

(W. Bakr area) is characterized by the presence of three local

sub-basins separated from each other by saddles, which

corres pond to West Bakr fields (K, H, G and B).

Basement relief

Source Parameter Imaging (SPI) function was used here as

an easy and quick powerful technique for interpreting the

gravity data to calculate the approximate depths of gravity

sources. The SPI method utilizes the relationship between

source depths and the local wavenumber (k) of the observed

field, which can be estimated for any point within gridded-data

through the horizontal/vertical gradients. The method was

carried out to determine depth to causative sources, edge

locations, source geometries and density contrast in the area

(Nabighian et al 2005). One advantage of the SPI method is

that the depths to the sources can be displayed as an image,

which makes the task of interpreting the data significantly

easier. More elaborate description of the principle, theory,

application and formulation of the method are given elsewhere

(e.g., Thompson 1982; Roest et al. 1992; Nabighian & Hansen

2001, 2002; Fedi 2005, 2007; Nabighian et al. 2005; Reeves

2005).

Practically, the automatic calculations of source depths were

done by using the SPI software included in the Oasis Montage

Package 2007. The technique computes source parameters

from gridded data of the Bouguer anomaly map based on the

complex analytic signal, where depths can be estimated with-

out assumptions about the thickness of the source bodies.

The depths to the gravity sources was determined through

a number of pre-processed grids dx, dy, and dz which were

calculated and serve as inputs for SPI processing. The first

order derivative was adhered to remove the deep crustal effect

from the original data. The upward continuation for small

height was applied because the SPI is very sensitive to noise

and interface effect (Nabighian et al. 2005). However, the SPI

has the advantages that it produces a more complete set of

coherent solution points and is easier to use. The accuracy of

SPI is about ± 20 % in comparison with the real data from

boreholes (Roest et al. 1992).

The results of the depth estimation obtained from applica-

tion of the SPI method (Fig. 15) exhibits a rough basement

surface, with great variation in depth to basement rocks which

ranges between 2.25 and 5.75 km. The map delineates three

main basinal areas corresponding to the depressions of

“Khashaba” to the west, and the “W. Bakr” toward the north-

east, and “W. Gharib” to the south-east. These large basins

were separated from each other by a broad ridge (West Bakr-

Gharib ridge) of relatively low depth. Such basement uplift is

considered a focal point in trapping oil from the adjacent

basins. Moreover, three narrow sub-basins (Hoshia, Farag and

Arta) occupy the northern portion, and are separated from

each other by structural highs/saddles. All basins/ridges are

nearly trending in the north-west to south-east direction, paral-

lel to the GOS trend. For comparison, Figure 15b displays

the approximate depths to gravity sources as deduced from

the Bouguer anomaly map (i.e., before stripping). Generally,

the map exhibits nearly the same structural conclusion that

exists in the former map, but with less details. The disparity

between these two figures could be attributed to the gravity

effect of the near-surface constituents.

Discussion

The seismic lines interpretation has shown a lack of infor-

mation that comes from the deep subsurface section, while

exhibiting a strong reflection from the relatively shallow part.

This is logical since the high reflectivity of the Evps makes

it difficult to trace any reflections at large depths, where

Fig. 14. Gravity modeling along profile B–B' taken (a) before doing

layer-stripping on Bouguer anomaly map, and (b) after doing layer-

stripping on top of Pre-Miocene.

383

DEEP GRAVITY DATA OF THE WEST GHARIB-BAKR AREA, EASTERN DESERT, EGYPT

GEOLOGICA CARPATHICA

, 2019, 70, 5, 373–385

the continuity of the seismic events became very bad beneath

the base of the Evps particularly in the north-eastern side

where the thickness of the Evps significantly increases toward

the GOS. Thus, the structural maps reveal few or no faults

penetrating the base of the Evps, which may be contrary to

the reality.

The study demonstrates how gravity interpretation can be

enhanced when integrated with seismic data and borehole

information in order to reveal the deep structural configura-

tions. The integrated interpretation has overcome the short-

coming of the filtering techniques and also seismic attenuation.

The crosschecks between the gravity, seismic and well logging

were worked out to eliminate ambiguity as well as non-unique-

ness of the gravity data interpretation.

The gravity anomalies are positively affected by the anhy-

drite of the Ras Malaab Group and/or dense limestone of

Gharandal group. Meanwhile, they are negatively influenced

by the low density halite/salt rocks, and by the Lower-Miocene

Rudeis sands. The non-linear distribution of the density with

depth makes most of the filtering methods, especially in space

domain, ambiguously interpreted when exploring the deep

prospects. So, it is found that the filtering methods applied in

this study are rather insufficient in delineating the deep struc-

tures/sources at the PM level, especially because seismic inter-

pretation is uncertain. The filtered maps provide primary

evidence for deep-seated bodies but add no details. This only

minimizes the effect of shallow bodies and somewhat enhances

the major features.

The correlation coefficient results are very variable with it

reaching the maximum (0.35) against the PM, while attaining

the minimum (−0.34) against the Evps. The positive correla-

tion suggests that most of the gravity is sourced in the deep-

seated components (PM). However, negative values confirm

that effects of these rock units act in reverse to reduce the total

gravity.

The horizontal gradient filter was able to disclose the deep

fracture systems affecting the area, which were confirmed

later by Euler deconvolution solutions that delineated loca-

tions of block-faults well. In contrast to the Miocene struc-

ture, the PM was ruptured by fractures mainly in the NNW and

ENE directions. Such cross-faults are definitely expected to

control hydrocarbon migration and accumulation at the PM

level, delineating new oilfields.

The statistical analysis of lineaments on top of the PM rocks

show that the area was affected by two tectonic trends oriented

in the N0–30°W and N50–70°E. These fracture systems are

believed to be associated with two stress phases; a compres-

sive phase (NNW–SSE) and an extension phase (ENE–WSW).

These two different tectonic forces are closely related to the

Tethyan plate tectonics. The first tectonic trend (NNW to NW)

is considered one of the oldest tectonic trends in Egypt

(Meshref 1990). The structural elements belonging to this tec-

tonic phase are believed to be predominant and most probably

developed in Precambrian compression. It was formed during

the Pan African orogeny, and rejuvenated during Tertiary–

Quaternary times due to active tensional movement of Arabia

relative to Africa (Brown & Coleman 1972). It is believed that

the ENE folding and thrust-faulting stage was primarily

formed in response to the compression force from the NNW–

SSE direction. They were developed and reactivated during

the Early to mid-Paleozoic (Caledonian cycle) by rift phases

resulting from the opening of the Paleo-Tethys under the in -

fluence of NE–SW directional tensional forces (Meshref 1990).

From the other side, the N50–70°E trend, which is genetically

related to the Syrian Arc trend, is believed to be one of the

Precambrian/Paleozoic tectonic trends that affect the Egyptian

basement and were probably reactivated with the progress of

Fig. 15. Basement relief map of the study area as deduced by source

parameters imaging (SPI): a — after gravity stripping; b — before

gravity stripping

384

AZAB

GEOLOGICA CARPATHICA

, 2019, 70, 5, 373–385

geological time (El-Emam 1990). The rejuvenation and inten-

sive deformation of this tectonic trend happened during the

Late Cretaceous, represented by the NE, ENE & E–W narrow

elongated domains of folds and faults (Sehim 1993).

In contrast to the seismic analysis, the modelling after gra-

vity stripping reveals complex structural features at the PM

level. The basement surface is uneven and contains swells,

troughs and block-faults, of different tilts and throws. The remo-

val of the gravity effects of the upper sedimentary layers, led

to the appearance of three gravity highs in the mid-area, which

are linked with three PM uplifts. It is reasonable to state that

the gravity high anomalies are closely related to basement

uplifts, while gravity lows are due to deep sources/structures

not shallower than 3 km.

The source parameter imaging method confirms that the

actual subsurface situation deduced from the stripped map is

not as simple as assumed by the Bouguer anomalies. The map

displays uneven topography of the subsurface with presence

of several basins and ridges at different depths, which are

associated with uplifted and down-faulted basement blocks.

The reversals along the sides of the basin-flank highs may give

the chance of discovering new oilfields on the PM level.

Conclusion

The results obtained from the different geophysical applica-

tions were integrated to give us a general view on the deep

source structures and shed more light on geological

conditions.

The seismic isopachs indicate that the thickness of the sur-

face layer gradually increases toward the GOS, Miocene Evps

increase excessively in the north-east direction, whereas the

Lower-Miocene Rudeis sands are well-developed in the south-

western part.

The study indicates that the structure on top of the PM is

much more complicated than that at the Miocene level.

The integrated interpretation has succeeded in delineating

several cross-faults on the basement surface which are diffi-

cult to see on the seismic sections. This indicates dominance

of the NNW-trending faults (Clysmic trend) which were

obliquely cut and displaced by ENE-trending faults (Syrian

Arc trend).

The structural inferences have depicted that faulting plays

the main role in complicating the geological setting of the

area. Lineament analysis delimits two fault systems of first

order magnitude oriented in the N0–30°W and N50–70°E

directions. These two major structural-tectonic trends are the

most widespread on the basement surface, and divide the area

into segments.

The stress-strain diagram assumes the area has been sub-

jected to two main cycles of tectonism during its geological

history; the N5°W compressional force and the N85°E ten-

sional force, producing two pairs of primary and secondary

fracture systems. The impact of such tectonic forces on the

basement surface may suggest that, although the principal

phase of opening of the GOS occurred in the Miocene age,

the forces that caused this opening are older.

The models confirm a simple structure at Miocene level in

contrast to a complex structure at the PM level. They demon-

strate a highly-fractured basement surface, overlain by a hete-

rogeneous sedimentary cover, with no indications of magmatic

intrusions penetrating into sediments. They indicate that base-

ment ridges are the source of gravity maxima while the PM

basins are the main source of gravity minima.

Acknowledgement: Author would like to express his gratitude

to three anonymous reviewers for their constructive reviews and

comments, as well as to Miroslav Bielik for editorial handling

and suggested improvements to the manuscript.

References

Affleck L. 1963: Magnetic anomaly trend and spacing patterns.

Geophysics 28, 3, 379–395.

Anderson E.M. 1951: The dynamic of faulting and dyke formation

with application to Britain. 2n

Ed. Oliver and Boyd, Edinburgh,

1–206.

Azab A.A., Ramadan M.A. & El-Sawy M.Z. 2018: An integrated

analysis of gravity and well data for deep-seated structural inter-

pretation: a case study from Ras Budran oilfield Gulf of Suez

Egypt. Journal of Petroleum Exploration and Production Tech

nology, http: //doi.org/10.1007/s13202–018–0514–8

Bayoumi A. 1983: Tectonic origin of the Gulf of Suez, Egypt, as

deduced from gravity data. CRC, Handbook of Geophysical

Explor. At Sea, 417–432.

Barbosa V., Sliva J. & Medeiros W. 1999: Stability analysis and

improvementof structural index in Euler deconvolution.

Geophysics 64, 48–60

Blakely R.J. 1995: Potential theory in gravity and magnetic applica-

tions. Cambridge Univ. Press, 1–441.

Bosworth W. & Durocher S. 2017: Present–day stress fields of the

Gulf of Suez (Egypt) based on exploratory well data: Non–uni-

form regional extension and its relation to inherited structures

and local plate motion. Journal of African Earth Sciences 136,

136–147.

Brown G.F. & Coleman R.G. 1972: The tectonic framework of the

Arabian Peninsula. 24

international Geol. Cong. Montreal,

Proc. Sect, 3. EGPC, EL Maadi, Cairo, Egypt.

Dimri V.P. 1992: Deconvolution and inverse theory. Elsevier Science

Publishers, Amsterdam London New York Tokyo.

Fedi M. 2007: DEXP: A fast method to determine the depth and the

structural index of potential field sources. Geophysics 72, 1–11.

Fedi M., Hansen P.C. & Paoletti V. 2005: Tutorial: Analysis of depth

resolution in potential-field inversion. Geophysics 70, A1–A11.

El-Emam A. 1990: The Agnes gravity/magnetic anomaly. Implica-

tions for potential field geophysics in the Western Desert of

Egypt. 10

EGPC Seminar, Cairo, Egypt, 1–13.

Ghanim M. 1972: Geology of the basement rocks north of Latit. 28

Eastern Desert, Ras Gharib Area. Ann. Geol. Survey, Cairo,

Egypt, II.

GPC 1976: General Petroleum Company, Nasr City, Cairo, Egypt.

Gupta S., Underhill J.R., Sharp I.R. & Gawthorpe R.L. 1999: Role of

fault interactions in controlling syn-rift sediment dispersal pat-

terns, Mioc, Abu Alaqa Group, Suez Rift, Sinai, Egypt. Basin

Research 11, 167–189.

Hammer S. 1963: Deep gravity interpretation by stripping. Geophysics

Xsviii, 3, 369–378.

385

DEEP GRAVITY DATA OF THE WEST GHARIB-BAKR AREA, EASTERN DESERT, EGYPT

GEOLOGICA CARPATHICA

, 2019, 70, 5, 373–385

Herkat M. & Guiraud R. 2006: The relationships between tectonics

and sedimentation in the Late Cretaceous series of the eastern

Atlasic Domain Algeria. Journal of African Earth Sciences 46,

346–370.

Hinze W.J., von Frese R.R.B. & Saad A.H. 2013: Gravity and mag-

netic exploration. Cambridge University Press, 1–525.

Keating P. & Pilkington M. 2004: Euler deconvolution of the analytic

signal and its application to magnetic interpretation. Geophys.

Prospect 52, 165–182.

Khalil S.M. & McClay K.R. 2008: Structural control on syn-rift sedi-

mentation, northwest Red Sea Margin, Egypt. Marine and Petro

leum Geology 26, 1018–1034.

Marson L. & Klingele E.E. 1993: Advantage of using the vertical gra-

dient of gravity for 3-D interpretation. Geophysics 58, 349–355.

Maus S. & Dimri V.P. 1994: Scaling properties of potential fields due

to scaling sources. Geophys. Res. Lett. 21, 891–894.

Maus S. & Dimri V.P. 1995: Potential ﬁeld power spectrum inversion

for scaling geology. J. Geophys. Res. 100, 12605–12616.

Maus S. & Dimri V.P. 1996: Depth estimation from the scaling power

spectrum of potential field. Geophys. J. Int. 124, 113–120.

McKinstry H.E. 1953: Shears of the second order. American Journal

of Science 251, 401–414.

Meshref W. M. & Hammouda H. 1990: Basement tectonic map of

northern Egypt. EGPC, 10

exploration and production Confe

rence, Cairo, 1–23.

Mostafa A.M. 1976: Block faulting in the Gulf of Suez. EGPC,

Expl. Seminar, Cairo, 1–19.

Mostafa A.M. 1992: Rifting under sediment loading in the Gulf of

Suez, Egypt. 11

Petrol, Explo. Proj. Co., Cairo, 1–15.

Nabighian M.N. 1984: Toward a three-dimensional automatic inter-

pretation of potential field data via generalized Hilbert trans-

forms: Fundamental relations. Geophysics 49 780–786.

Nabighian M.N. & Hansen R.O. 2001: Unification of Euler and

Werner deconvolution in three dimensions via the generalized

Hilbert trans form. Geophysics 66, 1805–1810.

Nabighian M.N., Grauch V.J.S., Hansen R.O., LaFehr T.R., Li Y.,

Peirce J.W., Philips J.D. & Ruder M.E. 2005: The historical de-

velopment of the magnetic method in exploration. Geophysics

70, 33–61.

Otsuka T. & Ogawa K. 1977: Combined seismic and gravity interpre-

tation in west Bakr area, Gulf of Suez, Egypt. Report of Techno

logy Research center, JPC, Tokyo, 1–6.

Parker R. L. 1973: The rapid calculation of potential anomalies.

Geophysical Journal of the Royal Astronomical Society 31,

447–455.

Phillips J.D. 1998: Processing and Interpretation of aeromagnetic

data for the Santa Cruz Basin-Patahonia Mountains area,

South-Central Arizona. U.S. Geological Survey Open

File

Report, Arizona, 02–98.

Pietrantonio G., Devoti R., Mahmoud S. & Riguzzi F. 2016: Kine-

matics of the Suez–Sinai area from combined GPS velocity

field. J. Geodyn. 102, 231–238.

Pilkington M., Gregotski M.E. & Todoeschuck J.P. 1994: Using frac-

tal crustal magnetization models in magnetic interpretation.

Geophysical Prosp. 42, 677–692.

Reid A.B., Allsop J., Granser H., Millett A.J., Somerton I.W. 1990:

Magnetic interpretation in three dimensions using Euler decon-

volution. Geophysics 55, 80–91.

Reid A., FitzGerald D. & McInerny P. 2003: Euler deconvolution of

gravity data. In: 73

Annual International Meeting Expanded

Abstracts. Society of Exploration Geophysicists, 580–583.

Reid A.B., Allsop J.M., Granser H., Millett A.J. & Somerton

Reeves C.V. 2005: Aeromagnetic Surveys, Principles, Practice

and Interpretation. Geosoft, 1–155.

Roest W.R., Verhoef J. & Pilkington 1992: Magnetic interpretation

using the 3D analytic signal. Geophysics 57,116–125.

Rohais S., Barrois A., Colletta B. & Moretti I. 2016: Pre–salt to salt

stratigraphic architecture in a rift basin: insights from a basin–

scale study of the Gulf of Suez (Egypt). Arab. J. Geosci. 9, 317,

http: //dx.doi.org/10.1007/s12517–016–2327–8.

Sadek H.S., Rashed S.M. & Blank H.R. 1984: Spectral analysis of

aeromagnetic profiles for depth estimation principles, software

and practical application. Openfile report, U. S. Geol. Survey,

Saudi Arab. Project (IR656), 1–40.

Scotte R.W. & Govean F.M. 1984: Early Depositional history of rift

basin: Miocene in the Western Sinai. EGPC. 1

Expl. Sem.,

Cairo, 1–15.

Segev A., Avni Y., Shahar J. & Wald R. 2017: Late Oligocene and

Miocene different seaways to the Red Sea–Gulf of Suez rift and

the Gulf of Aqaba–Dead Sea basins. Earth Science Reviews 171,

196–219.

Sehim A. 1993: Cretaceous tectonics in Egypt. Egypt J. Geol. 37, 1,

335–372.

Shabaan M.A., El Gindi A. & Abd El Fattah I. 1984: Contribution to

the subsurface geology of west Bakr area, Gulf of Suez, Egypt.

Bull. Fac. of Sci., Zagazig Univ., 6, 196–217.

Spector A. & Battacharyya K. 1966: Energy density spectrum and

subcorrelation function of anomalies due to some simple mag-

netic models. Geophysical Prosp. 14, 242–272.

Spector A. & Grant F.S. 1970: Statistical models for interpreting aero-

magnetic data. Geophysics 35, 293–302.

Spector A. 1968: Spectral analysis of aeromagnetic maps. Ph.D.

Thesis, Dep. Phys., Faculty of Science, Toronto Univ., 1–167.

Thompson D.T. 1982: EULDPH — A new technique for making

computer-assisted depth estimates from magnetic data.

Geophysics 47, 31–37.

Young M.J., Gawthorpe R.L. & Sharp I.R. 2002: Architecture and

evolution of syn-rift clastic depositional systems towards the tip

of a major fault segment, Suez Rift, Egypt. Basin Research 14,

1–23.

Zhang C., Mushayandebvu M.F., Reid A.B., Fairhead J.D. &

Odegard M.E. 2000: Euler deconvolution of gravity tensor gra-

dient data. Geophysics 65, 512–520.

Appendix

Well

Lat.

Long.

EPK-1x

28°21’43.3” N

55’21.9” E

EPJ-1x

22’17.9” N

52’49.8” E

Hashem-1

22’13.2” N

57’23.0” E

EPH-1x

25’21.4” N

51’42.8” E

EPG-1x

25’51.6” N

53’44.5” E

East Bakr 2

28’28.5” N

59’29.8” E

EPE-1x

29’23.2” N

53’44.7” E

EPD-1x

25’14.1” N

57’04.8” E

EGE 1

32’15.1” N

01’38.9” E

Amer 8

33’12.8” N

57’55.7” E

HH 83 1

36’36.8” N

56’50.1” E

HH 83 2

38’33.3” N

55’39.9” E