GEOLOGY OF EGYPT

INTRODUCTION

This course tends to present a general geological framework of Egypt; its litho-and bio-stratigraphy, structural setting, geological history and main economic resources.

Geographic Location

Egypt located in NE corner of Africa; approximately between Lat. 25ْ and 31ْ 20َ N, and Long. 25ْ and 34ْ 30َ E. It covers an area of about one million square kilometers, and is bordered from north by the Mediterranean Sea, from south by Sudan, from west by Libya and from east by the Red Sea, Gulf of Aqaba and Palestine.

Climatic Conditions

Egypt lies in the arid belt, which extends from the Atlantic Ocean from west, crossing North Africa and further eastwards to Saudi Arabia, Arab Gulf, Iran and Pakistan. The climate is characterized by high temperature in summer (up to 40 ْ) and mild (above 0 ْ) in winter. Rainfall precipitation is generally rare except the northern coastal stretch where the precipitation ranges between 15 to 25 mm per a year in winter. Occasionally heavy rainfall and flash floods do happen on Sinai and Eastern Desert Mountains destroying roads, cultivated lands and villages.

Geomorphological Features

Physiographically, Egypt is classified into four main geographic provinces:

Western Desert

Nile Valley , Nile Delta and Fayum Depression

Eastern Desert and Red Sea mountains

Sinai peninsula

1- Western Desert

It covers an area of about 610.000 square kilometers, lies between Libyan border and Nile Valley and Delta from west and east, respectively, and is bounded from north by the Mediterranean Sea and Sudanese border from south. Geomorphologically, Western Desert is characterized by:

1 Arid climate with very rare rainfall and seasonally windy weather

2 #9; Absence of high relief mountainous areas and prominent wades except Gabal Uweinat at its southwestern corner

3 presence of internal drainage lines

4 Sandy wind is the principal geomorphic agent that accentuated its characteristic landforms.

5 Presence of large number of depressions and oases (e.g. Siwa, Qattara, Moghra, Fayum, Bahariya, Farafra, Dakhla, Kharga, Kurkur and Dungul)

6 Presence of several sands dune belts and sand sea (Ex. Abu Moharik Sand Dune, Ghorabi Sand Dune, El Hussein Sand Dune and Qazzun Sand Dune).

7 Peoples (inhabitants) live and plant the oases of the depressions depending upon the underground water and springs.

8 The vast desert land of the Western Desert comprises six main geomorphic units being from south to north:

1.1 Gabal Uweinat

It lies at the southwestern corner of the Western Desert, and extends in Libya, Sudan and Chad. The mountain attains a height of about 1934 m above sea level (a.b.s.), and is built up of Precambrian igneous and metamorphic rocks. East-and northwards, that high mountain descends gradually forming more or less sandy plain of low relief with scattered hills and hillocks. This vast sandy plain area (~ 250 square Km.) is subjected since nineties to development programs for cultivation based on the underground water and known as East Qweinat- Darb El Arbin project to establish a new human being community.

1.2 El Gilf El Kebir Plateau

El Gilf El Kebir Plateau attains height oh about 1000-m (a.s.l), and is formed of Nubian sandstone ranging in age from Paleozoic to Cretaceous. It receives no rainfall, and of high summer- and low winter- temperatures. At the west and north the Great Sand Sea covers it, while natural glass sands cover its eastern side.

1.3 Oases Land

The Gilf El Kebir Plateau slopes northeastwards to the well-known Kharga, Dakhla and Farafra Depressions, which have different geomorphic shapes and landforms. During sixties the Egyptian Government made a great effort to establish a new large human community called the New Valley at Kharga and Dakhla Depressions.

1.4 The Eocene Plateau

This plateau has an elevation of about 500 m (a.s.l), and is made up of Eocene carbonates with scarps consisting of Cretaceous and Paleocene clastics and carbonates. The plateau delimits from north the southern the Western desert Depressions (refers to Kharga, Dakhla, Farafra, Kurkur and Dungul), while the Bahariya depression was carved within it.

1.5 The Marmarica (Miocene Plateau)

The Eocene plateau merges northwards into another plateau with an elevation up to 200-m (a.s.l) Known as Marmarica Plateau. This plateau is made up of Oligo-Miocene clastic scarps capped with Miocene carbonates forming the plateau surface. At the southern margin of the plateau exist the Qattara, Siwa and Moghra depressions. The Qattara Depression is huge sized depression reaching a depth of about – 134 m (b.s.l) with steep to wall like scarps, and its floor is covered with loose sands, mud and sabkha. The Qattara depression was studied geologically and hydrogoelogically for evaluating the possibility of generating electricity through connecting the Mediterranean water to fall in the depression.

1.6 Mediterranean coastal stretch

This land stretch forms the Mediterranean coast, with an average width of about 1 Km. It is characterized by beautiful beaches and bays, and is mainly built by Pliocene and Pleistocene sandy carbonates forming coastal ridges.

2. Eastern Desert

Eastern Desert lies between Nile Valley and Delta from west and the Red Sea and Gulf of Suez from east. Due north and south is bounded by the Mediterranean Sea and Sudanese border, respectively. Geomorphologically, Eastern Desert is characterized by:

1 It is a mountainous desert and rocky plateau land with high relief.

2 Arid climate with winter rainfall.

3 Presence of high relief mountainous areas with external drainage and prominent wades debauching either in the Gulf of Suez, Red Sea and Nile Valley (e.g. Wadi Araba, Wadi Abu Had, Wadi El Tarfa, Wadi Qena, Wadi Assuiti, Wadi Shait, Wadi Kharit and Wadi Allaqi).

4 Rainfall, flash floods and wind are the principal geomorphic agents that accentuated its characteristic landforms.

5 Absence of depressions and oases.

6 Peoples (inhabitants) live in the great wades depending upon the heavy seasonal rainfall.

7 The vast desert land of the Western Desert comprises four main geomorphic units being from south to north:

2.1 Red Sea Mountains

They form a prominent triangular shape geomorphic unit; its base is at the Egyptian- Sudanese border, and its apex occurs few tens of kilometers north of Ras Gharib. The mountains have rough and rugged serrated topography, of which the highest one (Gabal El Shayeb) attains about 2187-m (a.s.l.). Gabal Gharib, Gabal Hamata and Gabal Nugrus are of the most famous examples of these high relief mountains. This mountainous chain represents the oldest Egyptian rocks and formed of Precamrian igneous and metamorphic rocks.

2.2 Eocene Plateau

The Eocene Plateau extends westwards from the Red Sea Mountains to the Nile Valley where it forms its eastern bank. It is formed of Eocene carbonates and marls and is dissected by a number of deep and long wades. Northwards, approximately, north of El Sheikh Fadl- Gharib road, this Eocene plateau is dissected into three distinct small plateaus or questas, known from south to north: South Galala Plateau, North Galala Plateau and Gabal Ataqa. They are separated from each others by prominent wades and are formed of Paleozoic and Mesozoic rocks constituting scarps capped by Eocene Carbonates.

2.3 Miocene Plateau

It extends approximately from Cairo -Suez road to the northeastern border of the Nile Delta. It is characterized by low relief desert land with isolated structurally controlled hills as Gabal Shabrawit, and Gabal Owiebid, Gabal Homier.

3. Nile Valley, Nile Delta and Fayum Depression

3.1 #9; Nile Valley

The Nile River is one of the longest rivers in the world (6825 km, in length); its basin measures an area of about 50.000 square kilometers with annual discharge being about 86 billion cubic meter/ year.

The Nile enters Egypt at Adindan Village in Wadi Halfa (at Egyptian -Sudanese border), and flows northward without receiving any tributaries until debauching its load in the Mediterranean via Rosseta and Damietta branches.

The Nile has a meander pass with several islands; its valley has different widths and is drained by many large wadies (e.g. Wadi Kalabsha, Wadi Alaqi, Wadi Kharit, Wadi Shait, Wadi Assuti, Wadi Qena, and Wadi Tarfa). The valley is embanked with different rocks from place to another.

- From Adeindan to Aswan, the Nile course is itself the Nile Valley, and cuts in the Cretaceous sandstone and shale rocks of the Nubia Group.

- At Kalabsha and Aswan, the Nile cuts through the Precambrian granites covered with thin sandstone beds. Isolated blocks of granites obstruct the Nile course forming cataracts (e.g. Aswan cataract)

-North Aswan, steep scarps of Nubian sandstone rise, extends N-S, and borders the Nile from both sides. These scarps host the economic iron ore of Aswan.

- At Kom Ombo town (N. of Aswan) the Nubian sandstone cliffs turn and extend east- westward, where the Nile forms the widest part of its valley known as Kom Ombo plain. The E-W Kom Ombo plain has a flat surface and is about 20-25 m above the Nile water, and is structurally graben.

- Going downstream, from Idfu to Luxor, the Nile Valley is banked by the Upper Cretaceous rocks capped by the Lower Eocene Carbonates.

- At Qena, the Nile forms its famous bend (Qena bend), and from there to Cairo, it is bordered from both sides by the Eocene carbonates, which build the Mokattam and Giza Pyramid plateaus overlooking Cairo.

3.2The Nile Delta

The Nile Delta covers a triangular area of about 21.000 sq. Km; its apex is at north of Cairo (at El Kanater El Khairia) where the Nile bifurcates into Rosetta and Damietta branches. These branches are the remnant of pre-existing six branches that crossed the Delta with the beginning of the Holocene and in historic times. The famous old branch is the Pellusia branch that drained its load in Lake Manzala and in the Mediterranean Sea. Beside Lake Manzala, other lakes as Lake Burullos, Lake Idku and Lake Marut, exist along the northern margin of the Nile Delta.

3.3The Fayum and Wad Rayan Depressions

The Faytum and Rayan depression are dealt with the Nile Valley and Delta geomorphic unit because they are close to the Nile Valley, and the Fayum is connected with the Nile by the water channel "Bahr Youssif".

The Fayum depression has a total area of about 1700 sq. km; Birket Qarun (-45 m, below sea level) occupies its northern part, and is delimited from the north by an elongate scarp of Gabal Qatrani trending generally east- west. The Lake Qarun occupied much area in old times (pre-historic) proved by the presence of old raised beaches containing relics of ancient man (implements), and was known as Lake "Moeris".

Due to the south of Fayum depression lies Wadi El Rayan depression being over -60 m below sea level. Now, it is connected with the Fayum depression by subsurface canal in order to get rid of the drainage water of the cultivated lands of the Fayum instead of drain this water into Birket Qarun.

4- Sinai Peninsula

Sinai lies at the northeast corner of Egypt. It has a triangular shape covering an area of about 61.000 sq. km. It possesses geomorphologic features as same as the Eastern Desert. It is divided into the following geomorphologic units:

4.1. The southern Sinai mountainous unit

This unit occupies the southern triangle of Sinai overlooking the Red Sea. It is built up of Precambrian igneous and metamorphic rocks forming very high serrated peaked mountains (e.g. Gabal Kathrina, G. Musa, G. Um Shumar, G. Serbal and G. Abu Banat). This geomorpic unit serves as a water divide at its central part leading to the development of major wades draining into the Gulf of Suez and Gulf of Aqaba (e.g. Wadi Feiran, Wadi Taratir and W. Kid).

4.2 The Egma- Tih Plateau unit

This unit occupies central Sinai. The Egma plateau is built up of Cretaceous limestone and marls overlying pre-Cenomanian clastics, and capped by Paleocene shale and Lower Eocene limestone (Egma Limestone Formation). The top surface of this plateau is flat to undulated, and is dissected by many wades and numerous faults with minor drag folds.

The Tih plateau encircles the Egma plateau, and both slope due north. It is formed of Upper Cretaceous rocks capped with Egma limestone. Wadi El Arish is the longest wadi in central and north Sinai, and collects its water from the Tih Plateau.

4.3 The north folded geomorphic unit

This unit extends in NE – SW direction north of the Egma – Tih Plateau unit. It is characterized by high hills, hillocks and small plateaus separated from each other by wide plains and wide wades (e.g., W. El Arish, Wadi El Hassana). The hills of this unit belong to the well-known Syrian Arc structural system consisting of numerous anticlines and synclines (e.g. G. El Maghara, G. Halal, G. Yelleg, and G. Aref El Naqa). A vast plain exists to the NW of these anticlinal hills, and is covered by sand sheets, sand dunes and playa deposits.

4.4- The northern coastal plain

This coastal unit extends from Rafa in the east to Suez Canal in the west. It has an average width of 20 km but that width increases remarkably in the direction of Lake Bardawil and further to the west to sahl El Tinah. This unit is veneered by sand dunes, sand sheets, wadi deposits and sabkhas.

 

 

2- TECTONIC FRAMEWRK OF EGYPT

The general tectonic megapicture of Egypt is formed of a persistent nuclear Arabo-Nubian shield or Massive of Precambrian igneous and metamorphic rocks surrounded and covered by platform sedimentary deposits. The latter was accumulated via shallow seas invaded Arabian shield during Phanerozoic Era.

Tectonically there is a general agreement that Egypt can be divided into 6 distinctive tectonic units; each one possesses a characteristic structural features and geological history. These tectonic units include:

Arabo-Nubian shield

Stable shelf

Unstable shelf

Red Sea and Gulf of Suez Rift

Gulf of Aqaba

Delta hinge Zone

Arabo-Nubian Shield

This massive includes the Precambrian rocks of Eastern Desert (Red Sea Mountains), south Western Desert (G. Uweinat), Southern Sinai Mountains, west Saudi Arabia and northeast Sudan.

The shield is formed of highly deformed igneous and metamorphic rocks with extensive folds, thrusts, shears, extensional fractures and dykes. The main lineament dissecting these rocks trends due N-S and E-W.

The shield rocks host in different localities different magmatic mineral wealth comprising: gold, copper, banded iron ore, barite, talc, lead, and zinc, asbestos and ornamental stones.

Stable Shelf

Stable shelf constitutes the southern and middle portions of both Eastern and Western Dessert as well as mid Sinai. It is characterized by:

1. Thin sedimentary cover, ranging, in thickness, from ~400 m in south to 1000 m in north and, in age, from Paleozoic to Middle Eocene. However, isolated basins containing a thick pile of sediments reaching to 4000 m are recently recorded, firstly via aeromagnetic survey and later documented by drilling (e.g. Kom Ombo basin and Kharit basin at the southern Nile Valley and Eastern Desert). The sedimentary cover of the stable shelf is divided into lower clastic unit (Paleozoic- Cretaceous), and upper shale and carbonate unit (Cretaceous- Eocene).

2. Structurally, this shelf is less deformed than the unstable shelf. It is mainly affected by faulting with minor role of folding.

2.1 . Faulting: four main trends of faults dissect the stable shelf; these included:

E-W (Mediterranean or Tethyan) fault trend; these faults are old and deep-seated fractures inherited from Precambrian tectonics, and rejuvenated during Phanerozoic times. These faults are common in the southern landstreach of the Western Desert. The most prominent example of them is the Kalabsha fault, Abu Bayann fault, Mid Sinai fault and Raqabet El Naam dyke. The first (Kalabsha) is strike slip fault trending E-W, and represents an active fault where recent earthquake that happened few tens of years ago was centered along its plane.

N – S (east African) fault trend: this trend is also inherited from Precambrian tectonics; the best example of which, the Wadi Qena fault and Kharga fault.

NW- SE (Clysmic) fault trend: these faults are parallel to the Gulf of Suez, and are of normal type with different throws. They are common in the Eocene plateau, east of the Nile Valley, and were considered to control the pass of the Nile at many sectors, particularly Qena- Samalut sector.

NE- SW (Aqba) fault trend: they are less prominent in the stable shelf, and were considered to control the Nile Pass at north Samalut sector.

2.2 . Folding: folds in the stable shelf are subordinate, and comprise three types:

ý Rolls: they are gentle folds with very great amplitude and gentle dip (2° 4°), with trend being almost N-S; examples: Kharga anticlinal roll, Nile Valley synclinal roll, Wadi Qena anticlinal roll.

ý Drag folds: they are small double plunging anticlines and synclines formed due to dragging along movement of major faults; Examples: anticlines and synclines arranged along Abu Bayann fault; south Kharga depression and the anticlines and synclines developed along the mid Sinai dextral fault

Unstable Shelf

It covers the northern belt of Egypt, and is characterized by:

Thick stratigraphic succession that range, in age, from Cambrian to Holocene, and in thickness from 4 km in some subsurface basins in the north Western Desert (e.g. Abu Gharadiq basin) to more than 2 km in some surface sections (as in Gabal El Maghara) in north Sinai.

The thick sedimentary cover of the unstable shelf is simply divided into three main units, from top to base:

v Upper clastic- carbonate unit (Late Eocene- Holocene)

v Middle carbonate dominated unit (Late Cretaceous- Middle Eocene)

v Lower clastic dominated unit (Cambrian to Early Cretaceous)

Structurally; folding and faulting intensively deformed the unstable shelf. The most pronounced structural feature of the unstable shelf is the Syrian Arc fold system. This fold system started, probably with the end of the Cenomanian, and was intensively active and vigorous during Turonian-Santonian time interval, and probably culminated with local rejuvenation during the Eocene. The system consists of a series of anticlines and synclines that are characterized by:

¨ They are double plunging folds

¨ They are asymmetrical folds with its southern flanks are almost steeper reaching in some folds to be vertical or even overturned.

¨ They trend due to NE- SW or ENE-WSW.

¨ They are brachy-anticlines and synclines with their cores are mostly eroded.

¨ They are almost dissected by normal and reverse faults; the latter are almost parallel to its fold axes, while the former extend mostly perpendicular or oblique to its axes.

¨ They are almost related to shear movement along master wrench faults that trend generally due ENE.

¨ They commonly display an echelon array along the associated master wrench fault.

¨ These folds arrange in series of nearly parallel lines, examples:

El Bahariya - Abu Roash – Shabrawit line

El Maghara - Minsherah line

Yelleg- Libni- Halal line

Aref El Naga line

4- Gulf of Suez / Red Sea Rift

The Gulf of Suez is northwest trending intracratonic basin that is separated from the Red Sea by the Aqaba- trending transfer fault. It is bounded on the east by the Sinai Massif and on the west by the Red Sea Mountains of the Eastern Desert. The Gulf extends in N30W for a distance of about 350-km, from Suez to Hurghada, with breadth is 25-100 km and maximum depth of about 80 m.. The Suez rift has a great interest not from the stratigraphical and structural points of view, but also due to its oil potentiality, where about 80% of Egyptian oil production comes from the Gulf of Suez (onshore and offshore).

The Suez rift is considered as one of the most faulted areas in the world. A series of major faults extend along the rift and bound it from both sides. These faults, which trend generally due NW, N-S, and locally NE, dissect the Gulf area into a large number of faulted blocks with different attitudes and throws. These faulted blocks are built up of Pre-rift rock succession (Precambrian-Eocene) that unconformably covered by the syn-rift and post-rift deposits.

The Gulf rift basin is divided into three distinct provinces based on the location of the master faults and the attitude of the faulted blocks in each province. These three provinces are assigned; northern sector, central sector and the southern sector. In both northern and southern sectors there is a series of major faults throwing due east and exist along the western boundary of the rift. Meanwhile, in the same sectors, there is only a single major fault throwing due west and bounds the rift from the east. Thus it is expected that the combined throws of the major series of downthrown-east faults will be more than the throw of the downthrown-west fault. This fact will result in regional southwest dip of the tilted fault blocks in both the northern and southern provinces. On the other hand, the central province is bounded from the east by a series of downthrown-west faults and from the west by a single downthrown-east fault. Accordingly it is expected that the central province will have a regional northeast dip. It is also interesting to note that two major accommodations (transfer) zones (faults) bound and separate the central province from both northern and southern provinces of regionally southwest dip regime.

Close examination of the Gulf structural configuration shows the great similarity between its style and the dogleg model proposed by Harding (1984).

The Gulf of Suez is considered to be originated along a major NW shear fracture that complements a major NE (Aqaba) shear fracture. Both of the two complementary shear fractures (NW, NE) were resulted from a northwesterly horizontal compression. This compressive force is believed to have started in Late Eocene times as a result of the northward motion of Africa toward Laurasia, which destroyed Tethys II and resulted in the Mediterranean Sea. With the beginning of Oligocene a movement and opening along the NW (Suez) shear component of the two complementary trends was occurred resulting in a more highly developed Gulf of Suez-Red Sea trend rather than opening along the NE (Aqaba) trend. This priority of opening along NW trend may be attributed to the fact that the northwest trend was an old Precambrian tectonic trend and that it has just rejuvenated in Oligocene time.

Two possible primary dynamic forces that could initiate the opening of the NW trend and form the Gulf of Suez rift. They either are a right lateral coupled force along the shear plane or a regional extension across that NW shear. A rifting due to right lateral shear as that proposed for the Western North America almost resulted in basins and horsts of northeast trend, which is totally opposite to that of the Gulf of Suez rift. Accordingly, the possibility of initiation of the Suez rift by right lateral shear is completely excluded and the regional extension in a direction approximately perpendicular to it is generally accepted. Such extension began in early Oligocene time by normal faulting and dyke injection, resulting in tilted fault blocks in the form of half grabens. The main bounding normal faults for the tilted blocks show an original dip angle of 60°. With active horizontal extension, more thinning of the earth crust took place due to the rotation of blocks; this resulted in decreasing the dip angle of the main bounding faults down to 40. With continued regional extension during the Early and Middle Miocene more tilting and faulting of the larger blocks took place.

Red Sea rift is considered as an embryonic ocean occupies an elongate escarpment bounded depression extending for a distance more than 650 kms between the uplifted Arabian and Nubian shields. Oceanic basaltic crusts that were erupted via two phases of sea floor spreading occupy the central portion of the Red Sea. The older spreading had occurred since 29-23 my, and the recent one started over the past 4.5 - 5.my. The spreading is believed to be at rate of 0.5 cm/y, but may increase to 0.6 cm/y or more in the extreme northern part of the Red Sea at the junction with the Gulf of Suez, where the Aqaba shear has been active since Late Miocene. The central spreading of the Red Sea is believed to be discontinuous duo to intersection of the Red Sea by six transform faults of NE- SW trend.

5- Gulf of Aqaba

Gulf of Aqaba separates Sinai from Saudi Arabia. It has a length of about 200 kms and a breadth of about 10-20 kms with water depth as Red Sea reaching to 2000m.

The Gulf of Aqaba trends due N30-25E and was opened at Late Miocene-Pliocene via sinistral movement along NE transform fault known as Aqaba-Dead Sea transform fault. The left lateral movement was related to NE differential movement of Arabia plate relative to Sinai plate.

6. Nile Delta Hinge Zone

This zone of normal faults extends parallel to the Mediterranean coast crossing approximately mid Delta Province. It is developed during the extensional regime that affected Egypt during Oligo-Miocene time. North of that zone the thickness of deposits especially Miocene-Pleistocene is much thicker than that in the south Delta. In the mean time there is a drastic facie change for the Miocene- Pleistocene deposits across the Hinge zone suggesting that its deposition was controlled by the activity of that zone of faulting.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3- STRATIGRAPHIC FRAMEWORK

3.1 Paleozoic rocks in Egypt

Introduction and Classification

The Paleozoic Era lasted about 325 my, started approximately from 570 my and ended at 245 my. It is subdivided into the following periods, from younger to older:

Permian

Late Paleozoic: Carboniferous

Devonian

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Silurian

Early Paleozoic: Ordovician

Cambrian

The Paleozoic rocks have yielded their secrets more readily than rocks of the Precambrian. They are more accessible, less altered and more fossiliferous. The Paleozoic Era was the Era of dismembering and rejoining of the Proterozoic Proto-Pangaea supercontinent.

With the beginning of the Paleozoic (during Cambrian), the "Proto-Pangaea" had begun to pull apart, and ocean tracts formed between the separating landmasses. "Lapetus Ocean" was the Cambrian Proto-Atlantic Ocean that was widening at the beginning of the Paleozoic.

Since Late Ordovician to the end of the Paleozoic, the drifted continents started and continued closing and gradual collision to each others forming several mountain ranges and, the consolidated supercontinent "Pangaea" was formed.

Precambrian cratonization and related megastuctures

With the end of Proterozoic, the basement rocks of the Arabo-Nubian Massif as portion of Africa, which was a plate of the Supercontinent "Protopangaea", were under cooling, consolidation and cratonization. Resulted from that cratonization is a group of mega-structures inherited within the Basement rocks of Egypt, Sudan, Chad, and Saudi Arabia. These Precambrian mega-structures include a major fold belt and three major shear zones, namely:

☻North Zalingei fold which is a regional fold belt with axes trending due N, NNE, NE, ENE, and E-W. This belt was formed during Early to Middle Proterozoic.

☻Transafrican lineament zone (Peluseim lineament zone), which extends from West Africa, crossing westcentral Egypt and continues in NE direction to east Mediterranean.

☻Central African lineament, which extends from southwest Africa crossing central Sudan and continues due NE direction

☻Najd Fault system, which dissects Saudi Arabia in NW direction

Beside these old four mega-structures other lineament trends cut NE Africa including 55°, 70°, 80°, 150°. These mega -structures and associated faults in the basement rocks controlled to large extent the creation and distribution of the intraplate basins of Egypt during the successive periods of the Phanerozoic eras.

Global geography and tectonic setting during Paleozoic Era

During the Paleozoic Era the supercontinent "Proto-Pangaea" that cratonized with the end of Proterozoic Era started drifting and fragmentation into Six separate continents during Cambrian – Silurian period. This drifting event was accompanied with extensional regime. From Devonian to Permian the drifted six continents recolloided with each others and accreted together another supercontinent "Pangaea" this event of collision was accompanied with a compression regime

Paleozoic Paleogeography in Egypt

Structural differentiation and related paleohighs and basins development in NE- Africa during Cambrian period was controlled by ENE-WSW oriented tensional forces. The major consequence of that extensional regime was the development of large NNW-SSE striking basins and horsts in western Egypt, eastern Libya and western Sudan (e.g. Kufra basin, Siwa basin, Khartoum basin and Uweinat Howar high). The rest of Egypt was a positive area except its northern stretch that was invaded by shallow Cambrian seas, received clastic sediments.

During the period interval Ordovician-Devonian, almost all-Egyptian territory was under compression regime and uplifting forming positive land under erosion except its southwestern corner that was invaded by a tongue of Silurian Shallow seas.

With the beginning of Carboniferous, paleo-Tethyes renewed invasion of the northern sectors of Egypt, and continued its deposition until Permian period when it started retreat again and consequent exposure of the Carboniferous and older deposits.

LOWER PALEOZOIC ROCKS IN EGYPT

The surface exposures of Paleozoic strata occupied small areas on the geological map of Egypt. These included the well known Carboniferous outcrops along the Gulf of Suez, Sinai and at Gabal Uweinat area.

The Lower Paleozoic (pre-Carboniferous) strata however were not clearly identified until relatively recent. The poor identification is due to insufficient stratigraphic evidences and nearly absence of index fossils.

A sequence of strata from Cambrian to Devonian outcrops only in the area between Gabal Uweinat and west El Gilf El Kebir Plateau. Such sequence of strata was also reported in the subsurface in the western part of north Western Desert. The lower Paleozoic strata (except Cambrian strata) are missing over most the remaining part of Egypt.

The following is a brief description of the Cambrian, Ordovician and Silurian succession in Egypt.

1. Cambrian rocks in Egypt

Surface occurrences: rocks of Early Cambrian age are exposed in:

West-central Sinai at Gabal Um Bogma

Southwest Sinai at Gabal Durba-Gabal Araba Stretch

North Wadi Qena

North Uweinat area

Subsurface occurrence: in deep wells drilled in the Gulf of Suez and north Western Desert.

Stratigraphic setting: the Cambrian deposits rest unconformably on an irregular surface of the Precambrian basement and lie unconformably below the Carboniferous rocks.

Facies and rock stratigraphic subdivision: the Cambrian succession in Egypt forms a regressive facies sequence. It starts with shallow marine clastic facies that grade upward to unfossiliferous fluvial sandstone facies. So the Cambrian succession can be divided into two facies types; lower shallow marine and upper fluvial deposits

The lower marine unit is distinguished by its overall pale red to dark chocolate brown colors. It begins with a basal conglomerate consisting of locally reworked boulders, cobbles and small gravels of igneous and metamorphic rock fragments mixed with quartz and quartzite grains being set in kaolinitic argillaceous sandy matrix. This basal conglomeratic unit is overlain by a series of alternating mudstone, sandstone and pebbly sandstone showing lenticular, falser and cross bedding with ripple marks and dissication cracks, and containing the trilobite's traces "Cruziana and Rusophycus". This Cruziana bearing unit is overlain by a thick unit of pale red to reddish white cross bedded sandstone, which is invariably penetrated by long tubes of Skolithos. Lithostratigraphically, this Cambrian marine rock unit is named by the formal name Araba Formation.

The upper fluviatile facies of the Cambrian succession is distinguished by its snow-white color. It consists entirely of sandstone with subordinate interbeds of conglomerate and kaolinitic mudstone. The sandstone shows a wide variety of grain sizes, and is almost cross-bedded with frequent synsedimentary deformation structures as recumbent and convolute lamination. The sandstone and mudstone interbeds display vertically an overall fining upward array. In some areas, this white sandstone unit is exploited for glass sands. Lithostratigraphically, the upper white sandstone unit of the Cambrian is termed by the formal name "Naqus Formation"

2. Ordovician rocks in Egypt

Distribution: Strata of Ordovician age have not been identified in north Egypt, neither at the surface nor in wells. The only location in southern Egypt where 0rdovician strata are identified was at Kurkur Talh in the northeastern part of G. Uweinat at the Egyptian- Sudanese boundary.

Facies and Stratigraphic nomenclature: At Kurkur Talh, the Ordovician deposits are tens of meters of fluvial and shallow marine sandstones containing trilobite’s tracks indicating Ordovician age. They overlie unconformably the Precambrian rocks and underlie the Silurian sediments. They are assigned by the formal name Kurkur Talh Formation.

3. Silurian rocks in Egypt

Distribution: as in Ordovician time, most Egypt was during the Silurian time as positive areas except its western margin forming the eastern margin of the Silurian-Ordovician seas that bordered Egypt from WNW. The Silurian is reported from the subsurface of the north Western Desert. Silurian rocks outcrops at large areas in SW Egypt.

Facies and Stratigraphic nomenclature: in SW Egypt, in the area between G. Uweinat and west of El Gilf El Kebir plateau, the Silurian sediments reach a thickness of approximately 400 m. They consist of fine to medium and partly coarse grained white sandstone of fluvial and deltaic origin, interbedded with nearshore, beach and shallow marine sand, silt and shale. Several beds of this succession contain Skolithos burrows and the Trilobites traces; Harlania harlania and Cruziana acacensis that suggest Silurian age. This Silurian succession is named by the formal name Umm Ras Formation.

UPPER PALEOZOIC ROCKS IN EGYPT

1- Lower Carboniferous Rocks

Distribution: of all the Paleozoic rocks of Egypt, strata of Carboniferous age were the first to be recognized and identified. The Lower Carboniferous rocks exist in:

West-central Sinai (e.g. G. Um Bogma)

South-west Sinai (e.g. G. Abu Durba)

Wadi El Dakhl, west side of the Gulf of Suez

SW Egypt in west of El Gilf El Kebir Plateau

Facies and Stratigraphic nomenclature: the Lower Carboniferous deposits show a wide variation in facies ranging from fully marine carbonates, shallow marine clastics, deltaic and continental sandstone to lacustrine and fluvioglacial deposits. So, the Lower Carboniferous deposits are treated under different formal rock units from place to another.

Lower Carboniferous rocks of west central Sinai

The Lower Carboniferous rocks of west-central Sinai are well exposed at G. Um Bogma. There, the succession is subdivided into two formal rock units being from older to younger:

Um Bogma Formation: it represents the oldest exposed Lower Carboniferous deposits in Egypt. It exists only in west central Sinai, and restricted in distribution to its type locality Um Bogma area. The Um Bogma Formation overlies unconformably the Cambrian Naqus Formation and rests below the Lower Carboniferous Abu Thora Formation. The formation consists essentially of fossiliferous dolostone and dolomitic limestone containing Spirefers and Productus. Its lower part in some local areas of Um Bogma area is formed of karstic paleosols of dissected shale capping discontinuous lenses of manganese ore.

Abu Thora Formation: this rock unit was previously called Ataqa Formation. It overlies the Um Bogma Formation and underlies the Perm-Triassic rocks of Qiseib Formation. At its type locality, Um Bogma area, the Abu Thora Formation consists of 100-200 m of interbedded pure quartos sandstone topped with siltstone and black shale with thin locally coal seams. The sandstone is very clean white, very rich in silica and is exploited as glass sand containing fossil plants of Lepidodendron and Sigillaria. The upper black shale yields molds and casts of brachiopods and various marine trace fossils.

Lower Carboniferous rocks of Wadi El Dakhl (west of GOS)

At Wadi El Dakhl, only Abu Thora Formation represents the Lower Carboniferous deposits. The Formation overlies unconformably the Cambrian Naqus Formation, and rests unconformably under the Lower Cretaceous Malha Formation. It consists essentially by thick bodies of giant cross-bedded pure sandstone, overlain by black fossiliferous shale. The pure sandstone bodies are extensively exploited for glass sand.

Lower Carboniferous rocks of southwest Sinai

At Gabal Abu Durba-Araba range, southwest Sinai, the Lower Carboniferous rocks are well exposed. They are represented by the Abu Thora Sandstone and Abu Durba Shale underlying unconformably the Permo-Triassic Qiseib Formation. The Abu Durba Shale consists of a succession of black fossiliferous shale, siltstone and sandstone containing different species of Productids, Spirifers and Rhynchonellids.

Lower Carboniferous rocks of southwestern Egypt

In Wadi Malik area; north of Gabal Uweinat, the Lower Carboniferous rocks consists of alternating silty shale, siltstone, fine to coarse grained sandstone and gravelly sandstone of fluvial, beach and shallow marine affinity. The lower part of the section contains rare imprints of brachiopods, some trace fossils and plant imprints of Early Carboniferous age. These Lower Carboniferous deposits are termed Wadi Malik Formation

2. Upper Carboniferous-Permian Rocks

During Late Carboniferous, in connection with the Hercynian tectonic event, large parts of central and south Egypt were uplifted, and the Carboniferous sea retreated due N According to the above mentioned paleogeography of Late Carboniferous, the marine sedimentary record of that period are restricted only in the northern part of Egypt in both surface and subsurface.

In surface the Permo-Carboniferous rocks outcrop only along the western side of the Gulf of Suez forming isolated occurrences at the footslope of Gabal El Galala El Bahariya and along Wadi Araba. Fluvioglacial Upper Carboniferous deposits expose also at the area north of Wadi Malik in SW of Egypt.

The Perm-Carboniferous rocks outcropping along the western side of the Gulf of Suez is formed essentially of green to gray shale, siltstone and fine to coarse grained sandstone and subordinate limestone interbeds that yield Upper Carboniferous brachiopods and crinoids. The shale, siltstone and sandstone interbeds display coarsening upward cycles indicating a deposition along shallow shelves to lower / middle shoreface environments. This fossiliferous marine succession was treated under three laterally equivalent formal rock units; namely from N to S: Aheimer Formation, Abu Darag Formation and Rod El Hamal Formation (Abdallah and Adindani, 1963).

In southwestern part of Egypt, the Upper Carboniferous deposits are formed of non-fossiliferous sandstone and conglomerate of fluvioglacial origin grading above to deltaic facies. These clastic sediments are described under the formal name North Wadi Malik Formation.

ECONOMIC POTENTIALITY OF PALEOZOIC ROCKS

The Paleozoic rocks in Egypt are mined and explored for:

Manganese deposits, from the Lower Carboniferous Um Bogma Dolostone at Gabal Um Bogma, west-central Sinai

Glass sand, from the Lower Carboniferous Abu Thora Formation and Cambrian Naqus Formation at Wadi El Dakhl

Source rocks for oil, from the Lower Carboniferous Nubia B (equivalent to Abu Thora and Durba formations) in the Gulf of Suez

Reservoir rocks (Carboniferous Nubia B and Cambrian Nubia A) for oil in the Gulf of Suez

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

III. STRATIGRAPHIC FRAMEWORK

III. 2. MESOZOIC ROCKS IN EGYPT

Introduction and classification

Mesozoic Era lasted about 159 -160 my; during which the super- continent Pangea, which had formed during the Paleozoic was dismembered. The process of drifting and fragmentation ultimately produced the present physical geography of the Earth Planet. During the Mesozoic two new vertebrate classes; the birds and mammals appeared. It is ended with biological crisis marked by the extinction of Dinosaurs and scores of other animals in both land and sea. It is divided into three periods being from younger to older:

☻Cretaceous 144-66 my

☻Jurassic 213 my

☻Triassic 248 my

1. TRIASSIC SYSTEM IN EGYPT (245-208 MY)

1.1. Global Geography and tectonic setting during Triassic

With the end of the Paleozoic era and during Early Triassic, the Earth was in the form of a single large continent called Pangaea in which Africa including Egypt were at south of the Equator. That supercontinent was formed via several collisions and joining between six smaller continents that were drifted from the older supercontinent Proto-Pangaea. From those collisions was that occurred between Gondwanaland and Laurasia during Late Paleozoic and Early Triassic and formation of Hercynian mountain in Europe.

1.2. Triassic paleogeography in Egypt

Resulted from that collision between Gondwanaland and Laurasia during Late Paleozoic and Early Triassic, an uplifting of central and southern Egypt as positive areas accompanied with retreat of the Lower Triassic Tethyes to the northeastern margin of Egypt. Consequently, the occurrence of marine deposits in Egypt must be restricted to NE corner of Egypt, while the rest of Egypt was positive land subjected to erosion and fluvial sedimentation.

1.3. Occurrence and distribution of Triassic rocks in Egypt

Surface occurrence: in Egypt, the marine deposits of Middle Triassic age outcrops only in the core of Gabal Aref El Naqa anticline in northeast Sinai, while southwards in central Sinai and Gulf of Suez, the exposures of the Triassic age are almost of fluvial origin.

Subsurface occurrence: a rather complete Triassic section of both marine and fluvial deposits is recorded in the subsurface well (Halal Well No. 1) drilled at Gabal Halal in north Sinai.

1.4. Triassic facies and rock stratigraphic classification in Egypt

From the above-mentioned paleogeography of Triassic, it can conclude that the Triassic deposits in Egypt comprises two main facies assemblages; marine and fluvial / fluviomarine.

1.4.1. Marine Triassic Deposits

These deposits outcrop only at the core of Gabal Aref El Naqa anticline, and were met with in the subsurface in Halal Well no. 1.

The exposed marine sedimentary succession in the core of Gabal Aref El Naqa belongs to Middle Triassic only, while the complete succession from Early to Late Triassic is preserved is reported in the subsurface Halal Well no. 1

The outcropping Middle Triassic marine deposits in the core of Aref El Naqa anticline were defined under the name Aref El Naqa Formation by Said (1971). In its type section, the formation rests below Jurassic rocks, while its base is unexposed.

The succession of Aref El Naqa Formation is subdivided into three informal members, being from base to top:

Member (A): it consists of plant bearing cross-bedded sandstone of Nubian facies that grade upward to alternating sandstone, clay and limestone carrying vertebrate remains and some bivalves.

Member (B) or Benekia bearing member: it is made up of limestone and shale carrying the ammonite Beneckia levntina

Member (C) or Ceratite- bearing member: it consists of fossiliferous limestone, marl and few beds of dolostone and evaporites. The limestone and marl of this member carry the ammonites Gevanites and Ceratites

In subsurface, the Middle Triassic Aref El Naqa Formation is reported from Halal Well no. 1. It is underlain by other two formations namely Zafir and Raaf formations of Early Triassic age.

The lowermost Zafir Formation consists mainly of brown to dark gray fissile shale grading above to fossiliferous sandstone, limestone and dolostone. The overlying Raaf Formation is formed mostly of fossiliferous shelf carbonate facies.

The Upper Triassic deposits which stratigraphically younger than the Aref El Naqa Formation is represented by Mohilla Formation. It is composed of dolostone, shale, algal stromatolites and evaporitic sabkha facies indicating a regressive episode with the end of Triassic period.

1.4.2. Fluvial / Fluviomarine Triassic Deposits

These Triassic facies outcrop in central and southern Sinai as well as in both sides of the Gulf of Suez. Dark red and chocolate brown colors distinguish these deposits. Its exposed successions are formed of alternating pale red channel gravelly sandstone and sandstone with flood plain brown / gray mudstone and mottled paleosols. These Triassic red deposits are defined by the name Qiseib Formation by Abdallah and Adindani (1963). At its type section; Wadi Qiseib, western side of the Gulf of Suez (10 km NE of Ras Abu Darag), the Triassic Qiseib Formation overlies the Permo-Carboniferous of either Rod El Hamal or Abu Darag or Aheimer formations.

According to Lejal-Nicol (1987), the lower part of the Qiseib Formation contains plant remains as Callipteris conferata, Astherotheca aff. Leeukuilensis, Thinnfeldia aff. decurrens, Triphyllopteris gothani, Ganganophyllum thonii var. minor, which assign Early Permian age. On the other hand Abdallah and Adindani (1963) recorded lamellibranchiads and gastropods in the upper part of the formation indicating Early Triassic Age. Accordingly the Qiseib Formation was dated to Permo- Triassic.

2. JURASSIC IN EGYPT (213-144 MY)

2.1. Global Geography and tectonic setting during Jurassic

During Jurassic Period the great continent Pangea started drifting and fragmentation with Atlantic Ocean began opening from south. Due to that opening from south, the African plate moved eastward relative to Eurasia. Such differential sinistral movement between Africa and Eurasia triggered and rejuvenated the movement and opening along the old E-W and ENE-WSW deep seated fractures inherited in the Basement shield of Egypt. Consequence to that rejuvenated movement on the old ENE lineaments, , partial melting of the lower crust and upper mantle occurred accompanied with gradual domal uplift in southern Egypt forming Oweinat- Aswan High and eruption of alkaline volcanics reflecting incipient rifting. In the mean time, isolated ENE trending basins opened in northern Egypt (e.g. El Maghara basin, Abu Gharadiq basin, and Obeiyed basin).

2.2 Jurassic paleogeography in Egypt

Consequence to the above-mentioned tectonic setting of Egypt during Jurassic, Jurassic shallow seas invaded and occupied only northern Egypt and filled the isolated basins. Its paleo-shorelines never extend far south of El Maghara-Wadi Araba- Abu Garadiq arbitrary line. On the other hand, southern and central Egypt was positive area subjected to erosion and fluvial sedimentation in isolated low-lying alluvial plains.

2.3 occurrence and distribution of Jurassic rocks in Egypt

i. Surface occurrences

Jurassic rocks are exposed in northern Sinai at G. El Maghara, G. Giddi, G. Minsherah and G. Aref El Naqa. In central Sinai, they share in forming the southern scarp of G. El Tih Plateau.

In the northern sector of the Gulf of Suez, isolated faulted blocks of Jurassic rocks outcrop in the western side of the Gulf (e.g. Khashm El Galala, Wadi Um Lug, Ras El Abd and Maa Sweilam.

In southern Egypt, the Jurassic deposits constitute a thick part of what is known Nubia Sandstone that outcrops in most southern terrain of the Western Desert.

ii. Subsurface occurrences

Thick Jurassic deposits bearing both source and reservoir rocks are met in most penetrating wells in many oil fields of north Western Desert (e.g. Obaiyed Field).

2.4 Jurassic facies in Egypt

The recorded Jurassic deposits in Egypt possess three main types of sedimentary facies, which include:

Proper marine shale and carbonate

Fluviomarine sand-shale and carbonate

Proper fluviatile sand and gravelly sands

The marine and fluviomarine facies are restricted to northern Egypt in both surface and subsurface occurrences, while the fluviatile facies is prevailed in central and southern Egypt.

2.5 Lithostratigraphy of the Jurassic rocks in Egypt

2.5.1 Jurassic rock units in north Sinai

The thickest Jurassic section exposed in north Sinai is that forms the core of G. El Maghara anticline. The latter is a large breached NE-trending anticline (of the Syrian arc system) with a gentle northern flank and steep often vertical to overturned and thrusted southern flank.

In the core of that anticline, the exposed Jurassic section attains about 1980 m, thick, and represents the type or reference section of the Jurassic rocks in Egypt.

The exposed Jurassic succession of El Maghara was studied by many authors of whom Al far (1966) subdivided it into six formal rock units (formations). These rock units represent alternation between proper marine and fluviomarine facies. They are, from older to younger:

Mashabba Formation (Early Jurassic)

Type section: Wadi Sadd El Mashabba, G. El Maghara

Thickness: 100m

Stratigraphic limit: base unexposed, and underlies the Rajabiah Formation

Lithology and facies: alternation between fluviomarine cross-bedded and rippled sandstone / mudstone, and shallow marine marly limestone. The sandstone contains drifted wood fragments while the marine marl yields corals, lamellibranchs and algae.

Rajabiah Formation (Early Jurassic)

Type section: Wadi Rajabiah, G. El Maghara

Thickness: 293 m

Stratigraphic limit: overlies the Mashabba Formation and underlies the Shusha Formation

Lithology and facies: proper marine carbonates represented by sandy oolitic fossiliferous limestone with calcareous shale interbeds. It yields Trigonia, Astarte, Nucula, Lopha, corals and algae

3. Shusha Formation (Early Jurassic)

Type section: around Shushet El Maghara, G. El Maghara

Thickness: 272 m

Stratigraphic limit: base unexposed, and underlies the Rajabiah Formation

Lithology and facies: Fluviomarine cross-bedded brown sandstone with minor coal bearing mudstone and several ironstone concretions

4- Bir Maghara Formation (Bajocian)

Type section: Bir Maghara, G. El Maghara

Thickness: 444m

Stratigraphic limit: it overlies Shusha Formation and underlies the Safa Formation

Lithology and facies: marine shelf deposits of hard dense coralline limestone and calcarenites, overlain by calcareous mudstone with ironstone concretions. It contains fossils of Ermocers, Thamboceras, Telermoceras, Trimargina as well as brachiopods, pelecypods and gastropods.

5. Safa Formation (Bathonian)

Type section: Wadi El Safa, G. El Maghara

Thickness: 215 m

Stratigraphic limit: it overlies Maghara Formation and underlies the Masajid Formation

Lithology and facies: deltaic cross-bedded sandstone and mudstone containing in its lower part economic coal seams. It contains fossils of Thambites, Haplophragmoides, Nodosaria dolioligera, Glomospra compacta, Quinqueloculina compressa

6. Masajid Formation (Bathonian- Callovian to Oxfordian

Type section: south of Wadi El Masajid, G. El Maghara

Thickness: 575 m

Stratigraphic limit: it overlies Safa Formation and underlies the Rizan Aneiza Formation of Early Cretaceous age.

Lithology and facies: marine shelf deposits of hard oolitic and oncolitic limestone with isolated patches of coral reef and mounds, and yields Ermoceras and Euaspidceras ammonites

2.5.2 Jurassic rock units in Gulf of Suez

The Jurassic rocks outcropping in the western side of the Gulf of Suez belong to Bajocian – Bathonian age. They occur in four isolated faulted blocks, namely from north to south; Khashm El Galala, Ras El Abd, Wadi Um Lug and Maa Sweilam.

The thickest section of those four blocks is that of Khashm El Galala. It attains a thickness of about 140 m starting with non-fossiliferous variegated cross-bedded sandstone overlain by interbedded fossiliferous limestone and shale with two horizons flooded with the brachiopods Rhynconella (Known as Rhynconella beds). The basal non-fossiliferous sandstone is believed to be of infra Liassic age. Similar succession of Middle Jurassic age occurs in the other three fault blocks but with reduced thickness (50-80m).

2.5.3 Jurassic rock units in south Western Desert

The basal part of the Nubian sandstone succession outcropping in south Western Desert, particularly south of Kharga and Dakhla depressions is dated to Jurassic-Early Cretaceous age. It is invariably fluviatile cross-bedded pebbly sandstone with subordinate mudstone and conglomerate interbeds containing abundant wood fragments, and is named Six Hills Formation.

2.5.4 Jurassic rock units in north Western Desert

Jurassic deposits are widely distributed and well developed in the subsurface of Western Desert. Its penetrated succession is divided into four formal formations being from bottom to top:

1- Bahrein Formation (Triassic-Early Jurassic)

Type Well: Betty 1

Thickness: 550 m

Stratigraphic setting: it overlies unconformably different Paleozoic rock units or locally the Precambrian Basement, and underlies either Khatatba or the Lower Cretaceous Alam El Buib Formation

Diagnostic facies: dark red to brown coarse to fine-grained sandstone with thin gravelly and mudstones layers. In Well Yakout 1, few anhydrite beds are present.

Depositional environment: fluvial to fluviomarine with local lagoons and sabkha

Geographic distribution: it occupies the central part of the north Western Desert except at the northeastern corner of the Qattara Depression (Sharib El Sheiba High). East-and northwards, the Bahrein Formation interfingures and changes to the marine Lower Jurassic Wadi El Natrun Formation

2- Wadi El Natrun Formation (Middle Jurassic)

Type Well: Well Wadi El Natrun 1

Thickness: 850 m

Stratigraphic setting: it overlies unconformably different Paleozoic rock units or locally the Precambrian Basement, and underlies Khatatba Formation

Diagnostic facies: marine carbonates mostly dolomitic

limestone interbedded with shale. Anhydrite is recorded locally

Depositional environment: shallow marine to Sabkha

Geographic distribution: it has limited distribution being restricted to the eastern sector of the north Western Desert. Due west the formation interfingures and changes to the fluvial Jurassic Bahrein Formation

Khatatba Formation (Middle Jurassic)

Type Well: Well Khatatba 1

Thickness: 1375 m

Stratigraphic setting: it overlies the Wadi El Natrun Formation in the eastern sector of the north Western Desert, while in the west it rests on the Lower Jurassic Bahrein Formation. The Khatatba Formation rests below the Middle/ Upper Jurassic Masajid Formation.

Diagnostic facies: fine to medium grained brown sandstone interbedded with brown shale and thin limestone near its top. Thin coal seams are present at different levels.

Depositional environment: marine to fluviomarine

Geographic distribution: it is widely distributed allover north Western Desert

4- Masajid Formation (Middle to Late Jurassic)

Type section: south of Wadi El Masajid, G. El Maghara

Thickness: 575m

Stratigraphic setting: it overlies Khatatba Formation and underlies the Lower Cretaceous Alam El Buib Formation

Diagnostic facies: marine oolitic and oncolitic limestone/ corraline limestone

Depositional environment: shallow marine

Geographic distribution: it is widely distributed allover north Western Desert

ECONOMIC POTENTIALITY OF JURASSIC ROCKS IN EGYPT

In El Maghara area, the Jurassic Safa Formation hosts the economic coal deposits of Egypt

The Jurassic marine deposits form a source rocks in many oil fields in both the Gulf of Suez and north Western Desert

The Jurassic clastics of El Khatatba Formation is one of the main reservoirs of gas in some hydrocarbon fields of north Western Desert

3. CRETACEOUS IN EGYPT (144-66 MY)

3.1. Global Geography and tectonic setting during Cretaceous

During Cretaceous Period the great continent Pangea continued drifting and fragmentation with Atlantic Ocean began opening from north. Due to that opening from north, the Eurasia plate moved eastward relative to African. Such differential dextral movement between Africa and Eurasia triggered and rejuvenated the movement and opening along the old E-W and ENE-WSW deep seated fractures inherited in the Basement shield of Egypt. Consequence to that rejuvenated movement on the old ENE lineaments, isolated ENE trending basins opened in northern Egypt (e.g. Abu Gharadiq basin and Shushan basin).

3.2 Cretaceous paleogeography in Egypt

Consequence to the above-mentioned tectonic setting of Egypt during Cretaceous, Cretaceous shallow seas invaded and occupied extensive areas of Egypt and filled the isolated basins. The most remarkable feature of the Cretaceous paleogeography in Egypt is the alternating transgressive-regressive states of the Cretaceous seas during the time interval Aptian-Albian. However, in general the overall Cretaceous facies succession of Egypt show a general facies change from proper marine facies in northern Egypt to marginal facies in central Egypt to fluvial facies at southern Egypt.

3.3 Cretaceous Classification

Maastrichtian (74-66 myr)

Campanian (84-74 myr)

Late Cretaceous Santonian (88-84 myr)

Coniacian (89-88 myr)

Turonian (92- 89 myr)

Cenomanian (96-92 myr)

Albian (108-96 myr)

Early Cretaceous Aptian (113- 108 myr)

Barremian (117-113 myr)

Hauterivian (121-117 myr)

Valanginian (144-121)

3.4 Lower Cretaceous deposits in Egypt

The lower cretaceous deposits belonging to the time interval Valanginian-Barremian couldn’t be defined and paleontologically documented. They are treated under the term undifferentiated lower Cretaceous rocks. On the other hand, the deposits belonging to Aptian and Albian are well differentiated by its faunal content. So the following paragraphs deal with the Aptian-Albian deposits of Egypt.

During Aptian age, a vast marine transgression invaded Egypt in the form of a large embayment that covered northern Egypt and almost all parts of Western Desert to approximately the Egyptian-Sudanese border. However, the central and southern Sinai, Gulf of Suez, all Eastern Desert as well as west Nile Valley areas were exposed areas subjected to erosion and local alluvial deposition.

With the beginning of Albian, a major retreat of the Cretaceous Sea had been occurred, and the Albian Sea occupied only north Sinai, north Gulf of Suez, Delta plain and north Western Desert, approximately at the southern border of El Qattara Depression. On the other hand, most of southern and central Egypt was positive areas subjected to erosion or fluvial deposition.

3.4.1 Aptian-Albian Stratigraphic Succession

Surface occurrences

The Aptian-Albian rocks of Egypt outcrop in:

a) Northern, central and southern Sinai

b) Gabal Shabraweet, North and South Galalas and along Wadi Qena

c) Southern sectors of the Western Desert

The Aptian-Albian rocks of Sinai

The exposed Aptian –Albian rock succession of Sinai shows a remarkable facies change from interbedded marine and fluviomarine in north to fluviatile facies in central and southern Sinai

In north Sinai, the Aptian-Albian marine/ fluviomarine deposits are best exposed at Gabal Rizan Aneiza, Gabal Lagama, Gabal Manzour, Gabal Halal, Gabal Yelleg and Gabal Maghara. In these localities, the Aptian –Albian succession starts generally of non-fossiliferous sandstone and mudstone, which grade upwards to fossiliferous sandy limestone, oolitic limestone and dolostone with several horizons of ooidal ironstone.

Lithostratigraphically, that succession is differentiated into two formal rock units, being from top to base:

2- Rizan Aneiza Formation

Author: Said (1971)

Type section: G. Lagama, north of G. Maghara

Lithology: basal cross-bedded pebbly to medium grained sandstone intercalates with plant-bearing gray shale. Oolitic fossiliferous limestone, rudist-bearing limestone, dolostone, marl and glauconitic calcareous sandstone overlie this clastic unit. The fossiliferous beds yield: Orbitolina lenticulata, O.concava, O. discoidea, O. trochus, Douvillecera mammilatun, Knemiceras sp, Pseudomesalia ssp, Diastoma oranta, Neithea sp, Trigonia sp, Venericardia deserti,

Stratigraphic contact: overlies either Jurassic Masajid Formation or Malha Formation and underlies the Cenomanian Halal Formation

Age: its dated to Aptian –Albian

1- Malha Formation:

Author: Abdallah and Adindani (1963)

Type section: Wadi Malha, southeastern corner of the northern Galala Plateau

Lithology: fluvial sandstone, kaolinitic, cross-bedded and intercalated with gravelly lenses and mudstone interbeds with several poorly developed paleosols. These fluvial clastics are getting shallow marine affinity towards the upper part and to the north of the type area. In the western side of the Gulf of Suez, Abdallah et al (1963) described the following fauna from the marine interbeds: Ostrea falco, O. baussignaulti, O. palaeomon, O. reneviericos and Aspidiscus sp

Thickness: highly variable from place to place it attains about 50 m at its type locality and increases northwards at the scarp of El Tih scarp to 300 m

Stratigraphic contact: overlies either Jurassic Formations or the Permotriassic Qiseib Formation or the Paleozoic Rod El Hamal / Naqus Formation and underlies the Cenomanian Halal or Galala or Raha Formations

Age: its dated to Aptian –Albian or even Jurassic in its basal part

In central and southern Sinai, the marine Rizan Aneiza Formation does not occur and the entire Aptian-Albian succession is completely represented by the fluvial facies of the Malha Formation, which attains a thickness ranging from 50- 300 m.

In both North Galala and South Galala plateaus and Wadi Qena, the entire Aptian-Albian succession is made up of fluvial sandstone and mudstone with subordinate gravel beds and upper coastal marine deposits representing the Malha formation of Abdallah and Adendani (1963). In Wadi Qena, these fluvial deposits are called Wadi Qena Formation b y Bandel et al (1992).

In south western Desert: the Aptian –Albian succession is formed of two units; lower marginal marine unit called Abu Ballas Formation, and upper fluvial deposits called Sabaya formation. Both units are well exposed and widely distributed along the floor anf footscarp of the Dakhla and Kharga depression

Abu Ballas Formation

Author: Barthel and Boettcher (1978)

Type section: Abu Ballas scarps in southwestern Egypt

Lithology and faunal content: the Abu Ballas formation is formed essentially of shale, silty shale and siltstone, being frequently ferruginous, gray, greenish gray, brown and red with thin intercalation of sandstone. The succession contains marine fossils of lamellibranchia, gastropods, echinoids, brachiopods and arthropods with abundant vertebrates and abundant plant remains

Thickness and stratigraphic limits:

The Abu Ballas formation attains about a thickness of about 44-m. it overlies the Jurassic Six Hills Formation and underlies the Sabaya Formation.

Age: based upon the collected fossils, the Abu Ballas Formation is assigned to Aptian age

Sabaya Formation

Author: Barthel and Boettcher (1978)

Type section: Qulu El Sabaya, south of the Abu Tartur Plateau, along the road between Dakhla and Kharga depression

Lithology and Faunal content:

The formation is made up of white, gray, yellowish brown and red fine to coarse-grained, occasionally conglomeratic sandstone, which is mainly cross- bedded. Several flood plain sandy mudstones with poorly developed paleosol intervals. The formation contains several intervals that carry very huge trunks of silicified wood trunks.

Stratigraphic limit and thickness:

The formation attains a maximum thickness of about 30-m, and it overlies the Abu Ballas Formation and underlies the Cenomanian Maghrabi Formation.

Age: the Sabaya Formation is assigned to Albian –Cenomanian age.

B) Subsurface Aptian-Albian deposits

Thick succession of Early Cretaceous age was penetrated in the subsurface of north western Desert. The succession encompasses several clastic and carbonate reservoirs in many fields of north western Desert. The succession is treated under the formal name Burg El Arab Formation, which is currently divided into four formal members, being from older to younger:

Alam El Buib Member

Lithology: sandstone; fine to coarse-grained, with thin shale and carbonate interbeds of shallow marine affinity. At Matruh basin, this member is changed to dark brown and dark gray pyritic shale with asphalt and carbonaceous layers. It is called Matruh Member

Thickness: 1800 m

Age: Barremian-Aptian

Alamein dolostone Formation

Lithology: Light brown hard crystalline dolostone exhibits karstic vuggy porosity and intercalates with few shale intervals of shallow marine environment

Thickness: 20-90 m

Age: Aptian-Albian

3- Dahab shale member

Lithology: gray to greenish gray shale of shallow marine origin

Thickness: 174 m

Age: Aptian-Albian

4- Kharita sandstone member

Lithology: it is one of the main oil reservoirs in many oil fields of north Western Desert. It is composed of fine to coarse-grained sandstone with subordinate shale interbeds. It is of fluvial origin with some intervals displays marine affinity especially in the northern fields.

Thickness: 1100 m

Age: Albian- Cenomanian

3.5 Upper Cretaceous Deposits in Egypt

3.5.1 Cenomanian Successions

☻Cenomanian paleogeography The Cenomanian stage is known to have witnessed a vast marine transgression both on a regional and global scales (Haq et al, ?). In Egypt, this transgressive stage lifts behind a widely distributed rock record with variable facies and thickness from north to south (Kerdany and Cherif, 1990).

☻Distribution of Cenomanian deposits

-Surface occurrences: the Cenomanian deposits outcrop in many sectors of Egypt including:

North Sinai (e.g. G. Halal), central Sinai (e.g. G. Raha) and southern Sinai (e.g. G. Nezzazat)

Western side of the Gulf of Suez (e.g. Northern Galala, Southern Galala and Wadi Qena)

Bahariya depression

Gabal Maghrabi; Dakhla Depression, south Western Desert

Subsurface occurrences: the Cenomanian deposits are widely distributed in the subsurface of north Western Desert (e.g. Abu Gharadiq basin).

☻Facies and rock straigraphic nomenclatures

In north Sinai, the exposed Cenomanian deposits are best developed and preserved in G. Halal, where they are formed essentially of fossiliferous carbonate facies with some shale intercalation, and are described under the formal name Halal Formation.

Halal Formation

Author: Said, 1971

Type section: G. Halal, north Sinai

Distinctive Lithology: according to Abdallah et al (1996), the Halal Formation is divisible into four units being from base to top:

Cross-bedded sandy limestone and calcareous sandstone unit with few dolostone interbeds and lagoonal shale at top (132 m, thick).

Fossiliferous oolitic limestone unit (117 m)

Shale and limestone unit (127 m)

Upper dolostone with algal rudist banks (77 m)

The Halal Formation is fossiliferous yielding: Nerinea gemmifera, Tylostoma, Pterodonta deffsi, Ceratostrea flabellata, Rhynchostron suborbiculatum, Exogyra olisiponensis, and Hemiaster cubicus

Stratigraphic Setting; the Halal Formation rests over the Lower Cretaceous Rizan Aneiza and underlies the Turonian marl

In central and southern Sinai

Southwards, from north Sinai, the Cenomanian carbonate facies of the Halal Formation changes gradually to be clastic- dominated with increasing the amount of shale, marl and sandstone intercalation. In central and southern Sinai, this clastic dominated Cenomanian succession is called Raha Formation

Raha Formation:

Author: Ghorab (1961)

Type locality: Raha scarp, Raha plateau, west-central Sinai

Distinctive Lithology: the Raha Formation starts with a thick section of highly fossiliferous olive green shale and marl grading up to very fossiliferous white to pale yellow limestone and marls forming the Abu had member. The top of the Raha Formation is formed of cross-laminated fine-grained sandstone with silty mudstone intercalation known as Mellaha sand member.

Stratigraphic setting: the Raha Formation overlies the Lower Cretaceous Malha Formation and underlies the Turonian Abu Qada Formation.

In North Galala, South Galala and Wadi Qena:

In these localities, the Cenomanian succession attains a thickness ranging between 250-70 m. it is nearly similar to that of the Raha Formation but being more glauconitic and more clastic with much sandstone intercalation in Wadi Qena. In these areas, Abdallah and Adindani (1963) described the clastic dominated Cenomanian succession under the formal name Galala Formation.

In El Bahariya Depression, Western Desert

The Cenomanian deposits represent the oldest exposed rocks in the Bahariya depression where they occupy its floor and share in building the surrounding scarps. Said (1962) after Stromer (1914) ranked these deposits as Bahariya Formation and assigned Gabal El Dist as its stratotype. Akkad and Issawi (1963) separated the uppermost dolostone and shale that belong to Late Cenomanian from the Bahariya Formation and defined them by the name Heiz Formation.

4.1- Bahariya Formation

Allover the Bahariya depression, the base of the Bahariya Formation is unexposed. In the exploratory well "Bahariya-1" and in most oil fields of north Western Desert, the Bahariya Formation rests above the Lower Cretaceous Kharita Formation being mostly of fluvial kaolinitic sandstone and mudstone. The upper boundary of this formation in the Bahariya region is a regional unconformity showing, from north to south, a remarkable reduction in the magnitude of time gab. In the northeastern sector of the depression including the overlooking northeastern plateau, the formation is overstepped by Lutetian carbonates (or equivalent ironstones) with a pronounced angular unconformity (pl.1a), while in the middle and southern sectors it underlies unconformably the Upper Cenomanian Heiz Formation.

In most oil fields of north Western Desert, the Bahariya Formation is currently divided into two informal members, namely: the "lower Bahariya" and "the upper Bahariya" members. The two members extend and are easily traced (with a little change) in the Bahariya depression. The lower Bahariya member builds up most of the isolated hills, buttes and ridges that litter the central belt of the depression floor. Most of these hills are capped by dark brown to black silicified ferricrete duricrusts that mask the outcrops with a dark tone and form what is known as "Black Desert". It consists almost entirely of very thick stacked bodies (5-15 m, thick for each) of sandstone with subordinate pebbly to granuley conglomerate. These sandstone bodies display generally a finning upward pattern in both grain size and bed thickness. Some bodies terminate with patchy colored and mottled paleosol intervals (0.5- 2 m, thick) composed of massive, poorly sorted and dissected sandy mudstone containing rootlets and scattered rhyzocretions. The sandstone is mostly yellowish white, weakly consolidated to friable and unfossiliferous except for few scattered ferruginized and silicified fragments of wood trunks. The sandstone possesses a wide spectrum of grain size ranging from fine- to very coarse sand with scattered pebbles and granules. However, medium to coarse sand size is the most pervasive.

The upper Bahariya member starts with deltaic sandstone and dark gray mudstone rich in coalified drifted stems. These deltaic clastics are followed by multicolored mudstone, sandy mudstone, fossiliferous marl and glauconitic sandstone of coastal to shallow marine origin. Dark brown ferruginous, glauconitic and fossiliferous sandstone and sandy mudstone that are commonly massive and concretionary are frequent throughout the succession. The member yields megafossil assemblage dominated with Exogyra columba, Ostrea africana, O. flabellata, O. isidis, O. rouvillei, O. mermeti, O. conica, Natica sp., Nicolia oweni, Neolobites fourtaui, Gigantichthys numidus, Ceratodus africanus, C. minimus. Some intervals rich in plant remains, and others contain vertebrates of turtles, plesiosaurs and crocodiles are reported.

4.2- Heiz Formation

Author: El Akkad and Issawi (1963)

Type section: El Heiz area, Bahariya depression

Distinctive Lithology: basal and upper units of reddish brown to egg yellow dolomitic sandstone and siliceous dolostone, enclosing a middle member of sandy clay and calcareous grits with ironstone concretions and flint.

Stratigraphic setting: it overlies the Bahariya Formation and underlies unconformably the Campanian Hefhuf Formation

Fossils and age: the formation contains badly preserved Hemiaster fournelli, Ostrea penensis, O flabellata, Neolobites and others suggesting Late Cenomanian age.

5- In South Western Desert

A clastic dominated Cenomanian section outcrop along the footslope of the Abu Tartur scarp, particularly at G. Maghrabi. It is described and defined under the name Maghrabi Formation

Maghrabi Formation

Author: Barthel and Herrmann-Degen (1981)

Stratigraphic setting: the formation overlies unconformably the Lower Cretaceous Sabaya Formation and underlies unconformably the Turonian Taref Fotmation

Distinctive Lithology: the formation consists essentially of massive gray mudstone interbedded with massive to cross-bedded bioturbated sandstone with subordinate conglomeratic beds. These deposits represent depositional facies of tidal flat, swamp and estuarine environments. The formation contains brachiopod and pelecypod molds as well as rare dinosaur bones, fish teeth and abundant microflora.

3.5.2 Turonian Successions

☻Turonian paleogeography: during Turonian, a major retreat of seas had occurred in Egypt with subsequent exposure of southern and central Egypt. The marine conditions are restricted only to the northern part of Egypt, while the rest areas are subjected to erosion and fluvial sedimentation.

☻Distribution of Turonian deposits

-Surface occurrences: the Turonian deposits outcrop in many sectors of Egypt including:

North Sinai, central Sinai (e.g. G. Raha) and southern Sinai (e.g. G. Nezzazat)

Western side of the Gulf of Suez (e.g. Northern Galala, Southern Galala and Wadi Qena)

Abu Roash anticline, Giza

Gabal Taref; Kharga Depression, south Western Desert

East Aswan area and south Eastern Desert

Subsurface occurrences: the Turonian deposits are widely distributed in the subsurface of north Western Desert (e.g. Abu Gharadiq basin).

☻Facies and rock straigraphic nomenclatures

The Turonian deposits show a drastic facies change from north to south, where it is carbonate dominated in north Egypt and clastic dominated in southern Egypt.

In Sinai and Two Galalas: in these areas, the Turonian succession is formed essentially of highly fossiliferous and ammonite bearing carbonates in the lower part and chertified limestone in the upper part. This carbonate-dominated section is treated under the formal name Wata Formation.

Wata Formation

Author: Ghorab (1963)

Type section: Wadi Wata, Raha Scarp, west central Sinai

Distinctive Lithology: the Wata Formation consists of three units; lower ammonite bearing limestone unit, middle clastic-dominated unit and upper chert bearing limestone unit. The lower and upper limestone units are thick to very thick-bedded, white to yellowish white, massive to nodular and fossiliferous. The middle clastic unit is formed of variegated mudstone with rippled and small-scale cross-laminated fine-grained sandstone with subordinate oolitic limestone and ironstone.

Stratigraphic sitting; the Wata Formation overlies the Cenomanian Raha or Galala Formation and underlies the Coniacian-Santonian Matulla Formation.

North Wadi Qena

In north Wadi Qena, the carbonate beds of the Wata formation, split and thin and intertongue with cross-bedded sandstone. The latter increases in abundance and thickness as going further southwards. There this Turonian Mixed carbonate clastic succession is treated under the name Umm Omeiyid Formation. This formation rests over the Cenomanian Galala Formation and underlies the Coniacian Santonian Hawashiya Formation. Further south at south Wadi Qena, the Turonian deposits are formed entirely of fluviatile deposits termed Taref Sandstone

In east Aswan area

In east Aswan area, the Turonian succession rests directly on the Precambrian basement rocks, and is formed almost entirely of fluvial cross-bedded sandstone with subordinate gravelly sandstone layers. These clastics are described under the formal name Abu Agag Formation.

in Abu Roash Anticline area

The Abu Roash area represents an inverted basin that was received thick pile of carbonates during Turonian. The preserved thick Turonian carbonate section outcropping in Abu Roash area is described under the formal name Abu Roash Formation. This formation is divided into five informal members assigned as "series", which are from older to younger:

Sandstone series: consisting essentially of glauconitic shale with isolated sand lenses, followed upwards by cross-bedded sandstone showing fishbone cross-bedding that is topped by interbedded calcareous shale, sandy limestone and subordinate sandstone. This upper interval is rich in small sized molluscan shells and echinoids.

Rudist series: consisting of alternating rudist bearing limestone bodies (2-4m) and calcareous shale and marl bodies (3-5 m).

Limestone series: consisting of well-bedded massive to bioturbated limestone beds with isolated nodules of chert

Acteonella-Nerinea series: consisting of basal shale with thin carbonate interbeds, followed above by several banks of the gastropod Acteonella salamonis and Nerinea. This bank unit is topped by mound like beds of large sized rudist Durania arnaudi

Flint series: consisting of thick to very thick bedded snow white chalk containing several levels of chert bands and nodules as well as abundant siliceous sponges and echinoids.

5- in South Western Desert

The Turonian deposits outcropping along the scarps of both Dakhla and Kharga depressions are represented entirely of stacked bodies of cross-bedded sandstone of medium to coarse grained with subordinate gravelly layers of braided steam origin. These fluvial clastics are termed Taref Sandstone. It overlies the Cenomanian Maghrabi Formation and underlies unconformably the Campanian Quseir Formation.

3.5.3 Coniacian- Santonian Successions

☻Coniacian-Santonian paleogeography: with the beginning of Coniacian time a renewed transgression had occurred with consequent submergence of northern and eastern part of Egypt. The marine invasion extends southwards to Aswan and south Eastern Desert. In the meantime the central and southern Western Desert was exposed as a positive area subjected to erosion. During Santonian, a renewed northward marine regression had occurred resulted to a restriction of marine setting to the northern part of Egypt with several isolated ENE trending submarine highs and island like folded blocks related to Syrian Arc deformation belt. In Egypt, it is difficult to separate the Coniacian depositional record from that of Santonian ones, so they are lumped together as one depositional sequence.

☻Distribution of Coniacian-Santonian deposits

-Surface occurrences: the Coniacian-Santonian sedimentary succession outcrop in many sectors of Egypt including:

North, central (e.g. Wadi Matulla) and southern Sinai (e.g. G. Nezzazat)

Western side of the Gulf of Suez (e.g. Northern Galala, Southern Galala and Wadi Qena)

Abu Roash anticline, Giza

East Aswan area and south Eastern Desert

Subsurface occurrences: the Coniacian-Santonian deposits are widely distributed in the subsurface of north Western Desert (e.g. Abu Gharadiq basin).

☻Facies and rock straigraphic nomenclatures

1- In Sinai and Two Galalas: in these areas, the Coniacian –Santonian succession is formed essentially of yellowish green to brown glauconitic shale, glauconitic sandstone and subordinate fossiliferous glauconitic limestone and several oyster banks, with phosphatic limestone top. This glauconitic clastic succession was defined under the formal name Matulla Formation

Matulla Formation

Author: Ghorab (1963)

Type section: Wadi Matulla, Abu Zenima Area, west central Sinai

Distinctive Lithology: the Matulla Formation consists of fluvial cross-bedded sandstone in the lower part. It is followed upward by shallow marine sequence of argillaceous limestone, marl and varicolored glauconitic shale, oyster banks and fossiliferous phosphatic chalky limestone at top.

Stratigraphic sitting; the Matulla Formation overlies the Turonian Wata Formation and underlies the Campanian Maastrichtian Sudr Formation.

North Wadi Qena

In north Wadi Qena, a similar sedimentary succession of the Matulla Formation exists with two to three horizons of ooidal ironstones. These Coniacian- Santonian deposits are described under the formal name Hawashiya Formation

In east Aswan area

In east Aswan area, the Coniacian-Santonian succession is represented by two distinctive rock units representing a deposition in deltaic to shallow marine environments and terminated with fluvial deposits. The two rock units are, from older to younger:

4.1-Timsah Formation

Author; El Naggar (1970)

Type section: G. Timsah, NE Aswan

Distinctive Lithology; nearshore marine to deltaic sequences of silt and fine-grained sandstone with thick shale intercalation. Two or three oolitic iron ore beds are widely distributed in many sectors of east Aswan.

Stratigraphic sitting: the formation overlies the Turonian Abu Agag Formation and underlies the Santonian Umm Barmil Formation

Fossils and Age: the formation contains ichnofossils like Thalassinoides, Skolithos, Tilaephyllum, Teichichnius and Diplocraterion as well as Inoceramus balli and Inoceramus cycloides suggesting Coniacian age

4.2 – Umm Barmil Formation

Author; El Naggar (1970)

Type section: G. Umm Barmil, NE Aswan

Distinctive Lithology; coarse to medium grained sandstone, large scale tabular and trough cross-bedded, originated from a low sinuosity fluvial environment.

Stratigraphic sitting: the formation overlies the Coniacian Santonian Timsah Formation and underlies the Campanian Quseir Formation.

In Abu Roash Anticline area

 

 

in Abu Roash area the Coniacian Santonian Deposits are represented by yellowish brown marl and glauconitic shale with fossiliferous and bioturbated limestone and oyster banks rich in Plicatula ferri. So it is described under the term Plicatula series

3.5.4 Companion –Maastrichtian successions

☻Campanian-Maastrichtian paleogeography: During Campanian-Maastrichtian time interval a renewed wide marine transgression had occurred with consequent submergence of northern, eastern and western parts of Egypt.

☻Distribution of Campanian-Maastrichtian deposits

-Surface occurrences: the Campanian -Maastrichtian sedimentary succession outcrop in many sectors of Egypt including:

North, central (e.g. Wadi Sudr) and southern Sinai (e.g. G. Nezzazat)

Western side of the Gulf of Suez (e.g. Northern Galala, Southern Galala and Wadi Qena)

Abu Roash anticline, Giza

Bahariya-Farafra depression

Dakhla-Kharga, Nile Valley and Quseir-Safaja district

Subsurface occurrences: the Campanian-Maastrichtian deposits are widely distributed in the subsurface of north Western Desert (e.g. Abu Gharadiq basin).

☻Facies and rock straigraphic nomenclatures

In Sinai and Two Galalas, Wadi Qena: in these areas, the Campanian-Maastrichtian succession is formed essentially of snow-white chalk and chalky limestone called Sudr Chalk

Sudr Chalk

Author: Ghorab (1963)

Type section: Wadi Sudr, , west central Sinai

Distinctive Lithology: the sudr Formation consists of two members; the lower one is formed of massive highly fractured chalk flooded with Pycnodonta vesiculare. The upper member is characterized by well-bedded chalk with melon-shaped chertified limestone concretions and subordinate shale beds.

Stratigraphic sitting; the Sudr Formation overlies the Coniacian -Santonian Matulla Formation and underlies the Maastrichtian-Paleocene Esna Formation.

2- in Abu Roash Area; the Campanian-Maastrichtian chalky facies is also developed and named Khoman Chalk

3- In Bahariya- Farafra district: in this district, the Campanian-Maastrichtian succession is made up essentially of chalky facies with clastics and phosphatic dolostone in its lower part. It is divided into two distinctive rock units being from base to top:

El Hefhuf Formation

Author: El Akkad and Issawi (1963)

Type section: Gabal El Hefhuf, Bahariya oasis

Distinctive Lithology: it starts with cross bedded ferruginous, siliceous and glauconitic gravelly sandstone grading up to interbedded fine grained sandstone and mudstone of paralic facies, and terminates up with fossiliferous phosphatic dolostone and limestone with chert nodules and concretions

Stratigraphic sitting: it overlies unconformably the Cenomanian Heiz Formation and underlies conformably the Maastrichtian khoman Formation

Fossils and Age; the formation yields Arca sp., Plicatula sp. Isocardia chargensis that assign Campanian age

2- Khoman Formation

Author: El Akkad and Issawi (1963)

Type section; Ain Khoman, Bahariya Depression

Distinctive Lithology: as Sudr Chalk

Age; Maastrichtian- Danian

3- in Dakhla-Kharga, Nile valley and Quseir-Safaga Districts (Red Sea area)

In these localities, the Campanian-Maastrichtian chalky facies dominating in north and central Egypt changed drastically to highly fossiliferous shallow to deep marine shale facies with subordinate carbonate interbeds and several oyster banks. This shale dominated succession, which forms transgressive sequence is divisible into three distinctive rock units being from older to younger:

Quseir variegated shale (Mut Formation)

Author: Youssef (1957)

Type section: G. Atshan, Quseir area, west Red Sea coast

Distinctive Lithology: The formation starts with varicolored claystone, siltstone and sandstone yielding plant remains fresh water gastropods, fresh water reptiles and dinosaur bones indicating a deposition in terrestrial to brackish environments (tidal flat / estuaries). This grades upward to shallow shelf facies of poorly fossiliferous varicolored mudstone and sandstone being in some intervals glauconitic and containing some marine gastropods and pelecypods.

Stratigraphic sitting: it overlies unconformably the Turonian Taref Sandstone and underlies the Campanian-Maastrichtian Duwi Formation.

Age: the Quseir Formation is assigned to Early to Middle Campanian.

Duwi Formation (Phosphate formation)

Author: Youssef (1957)

Type section; Gabal Duwi, Quseir area

Distinctive Lithology: shallow marine succession of alternating gray to green claystone, siltstone and glauconitic sandstone with several oyster banks and fossiliferous limestone as well as a number of phosphorite and phosphatic limestone interbeds. Some of these phosphatic beds have economic potentiality and are mined in Abu Tartur area and in Quseir-Safaga district.

Stratigraphic sitting: the formation overlies the Campanian Quseir Formation and underlies the Maastrichtian Dakhla Shale.

Fossils and age: the Duwi formation is fossiliferous with Inoceramus regularis, Neaera- Cardita subcomplanata, Bostrychoceras polyplocum indicating Campanian to Early Maastrichtian age

Dakhla Shale

Author: Said (1961)

Type section; scarp north of Mut, Dakhla oasis.

Distinctive Lithology; the Dakhla shale is divided into three distinctive members being from older to younger:

3.1 Mawhoob shale member. It consists of inner to middle shelf papery shale and marl of Early to Middle Maastrichtian age

3.2 Baris oyster member: it consists of shale and limestone interbeds crowded with Exogyra overwegi and Libycoceras ismaeli and dated to middle to Late Maastrichtian

3.3 Kharga shale member: it consists of dark green to gray shale with dwarfed fauna in its lower part grading in the upper part to fossiliferous marl and shale yielding fossils of Paleocene age. A thin horizon (0.5-2 m) of reworked phosphatic particles and reworked Maastrichtian fauna is recorded separating the Maastrichtian lower part of that member from its Paleocene upper part.

Stratigraphic sitting: the Dakhla shale overlies the Campanian- Maastrichtian Duwi Formation and underlies unconformably the Paleocene Tarawan Chalk.

Fossils and Age: the Dakhla formation if fossiliferous with Pycnodonta vesiculare, Exogyra overwegi, Pecten faraferensis, Isocardia chargensis, Crassatella zitterli, Cardita spp., Lybicoceras ismaeli. The formation is dated to Maastrichtian age in its lower part and Paleocene age in its upper part with the Cretaceous/ Tertiary unconformity boundary cuts through it.