Rep,. ifl' eel j i'O ll l:
Sedimentary lIasins of the World, 3 (Series Editor: K.J. Hstil
• •
Edited by
R.C. Selley
DeparTment (~r Geology /11I/Jeria! Co f/ e~e of Scien ce . Technology and Medicine Royal Sd1001 (~f Mines London, Un ited Kin gdom
•
Sedimentary Basins of Egypt: An Overview of Dynamic Stratigraphy
AHMED S. EL HAWAT
ELSEVIER Amsterdam - Lausanne - New York - Oxford - Shannon - Tokyo 1997 Sedimentary Basins of Egypt: An Overview of Dynamic Stratigraphy
AHMED S. EL HAWAT
Initially, the quesliol1s lIIay be el e/llCllwl)' as 'WI/a/'?' and 'Where?' but soon the 'How,?' and 'When?' oj'proce.\",\', hislOty and geomell)' rake cellfer stage, ... one oflhe 1110.\'( rewording qiles l ion.~ thar Call be a~'ked is 'So what?' ... or 'Le i li S .w!e \Vlia! if mealls' R.N. Ginsburg ( 1982) - Seeking Answers
INTRO DUCTION in thi s paper to extend sy nthesis across into these areas when possible. Strati graphic subdivisions and lnfo rm ation and literatu re on the geology of nomenclature are often confusing and names are Egypt has been gathered and publi shed by Said therefore not the objecti ve in this paper. They are ( 1962, 197 1, 1990), summarized by EI-Shazly used here as a reference to other workers in Egypt. ( 1977) and an updated annotated geological bibl i Stratigraphic sequences are treated in stead in terms ography was published by EI-B az ( 1984). The latest of time, space, events, cycles and facies. volume on the Geology of Egypt edited by Said The first part of this paper deals with an overview ( 1990) is the most comprehensive reference on the of the Proterozoic evolu tion of the Afro-Nubi an cra subject to date. ton and the development of Phanerozoic sedimentary During the last few decades, exciting new re basins. The fo ll owing sections trace basinal develop search has been done by geoscienti sts fro m Egyptian ment through the Palaeozoic, Mesozoic and Tertiary and intern ati onal academic in stitutions, oil compa times. Each of these sections is concl uded with ni es. and government departments, such as the Ge a subsection hi ghl ighting the relatio nship between ological Survey of Egypt. These publicati ons have sedimentation and signi fica nt geologic events whi ch conrri buted a great deal towards our current under have taken place during thal particul ar time. The standing of the sedimentary basins of Egypt. In my last section is a su mmary and synthesis of common view, some of the most signi ficant contributions to themes of the geologic history of the deposi ti onal the geology of Egypt were based on the appli ca basins of Egypt. tion of the concepts of plate tectonics, global sea level changes, stratigraphy and sedimentology. The solution of the Nubian Sandstone problem in North SEDIMENTA RY BASINS Afri ca and the Middle East (Klitzsch et aI. , 1979; Kli tzsch, I 990a; Klitzsch and Squyres, 1990; Van The Afro-N ubian craton Houten, 1980; Van Houten et aI. , J 984, to menti on j ust a few) is a case of a poin t. The basement complex of Egypt is exposed north Because of th e vo lume and the detailed nature and west of the Red Sea and the Gul f of Suez, in of published material on the Egyptian geology, the the areas of Sinai and the Eastern Desert. It extends present work attempts to retrace basinal development south of latitude 24° north of Jabal Uweinat and in Egypt, and concisely present it in the li ght of Aswan. Basement exposures represelll about 10% dynami c regional and global events through time. of the total area of Egypt, the rest are covered by Since Libya and Tunisia were influenced by the Phanerozoic sediments whi ch increase progressively same events as Egypt a conscious attempt is made in thickness northwards fo ll owing the regional dip
Aji·icGI/ Basins. Sedimel1lary Basins of the World, 3 edited by R.C. Selley (Series Editor: KJ . Hsti). pp. 39-85. © 1997 Elsevier Science B.V., Amsterdam. All rights reserved. 40 A.S. EL HAWAT of African plate towards the Mediterranean Sea. and granodiorite plutonic bodies. These were later Irregul ar thickness distribution of the Phanerozoic partly metamorphosed into gneisses (890-876 Ma). sedimentary cover and basin development were in (3) Post-orogenic geosynclinal volcanic phase (665- flu enced by basement structures and tectonic hi story 654 Ma). (4) Development of post orogenic foreland since the Precambrian. basin s and molass sedimentation. (5) Late orogenic The basement complex of Egypt was recently re and post orogenic plutonic intru sions of granites and viewed by EI Gaby et al. ( 1990), Ri chter and Schan granodiorites (656-480 Ma). It was noted that in th e delm eier (1990) and Hassan and Hashad (1990). high mountai n areas, th e Nubian craton are formed In their study of th e structural development of the of orogenic granites and develop a 30 to 40 km thick basement complex of the northeast African plate, crust. Whereas the crust at the margin of the Red Schandelmeier et al. ( 1987) have subdivided the Sea trough is 20 km thick and consists of alkaline basement into two di stinctive parts, the pre-Pan metasomati c granites belonging to the latest plutonic African eastern Saharan craton and the Pan-African intrusions (EI-Shazly, 1977). The cru stal thickness Nubi an shield (Fig. I). of the east Saharan craton al so, exhibits similar or The eastern Saharan craton is located west of der of magnitude from Jabal Uweinat area to the the ri ver Nil e. The oldest of these pre-Pan-African Mediterranean coast. rocks are exposed in labal Uwainat which is located The Proterozoic Pan-A frican crustal accretion and southwest of Egypt and southeastern Libya. These subsequent continent to continent collision was as are dominated by granulite meramorphic rocks dated sociated with major development of transcontinental as Late Archean (2673 Ma) in age (Klerx, 1980). shear zones caused by strike-slip moti on parallel These rocks may represent a protocrust which was to the west African continental nu cleus (Morgan , developed as a result of compressive tectonics dur 1990, fi g. 7.4). Reactivation of these shear zones and in g continent to continent collision (Morgan, 1990). lineaments had a Significant influence on the devel Outwards from the Archean nucleus the craton con opment and evolution of sedimentary basins during sists of younger rocks that range from Early to Mid the Phanerozoic. dl e Proterozoic in age (Richter and Schandelmeier, In contrast to the spectacular Proterozoic events, 1990). These polymetamorphic and granitoid rocks tectoni cs and sedim entation during the Phanero are 2300 to 1800m years old and are arranged in zoic were relatively placid. During the Phanerozoic, a regional NW- SW, N-S, and E-W trending meta events were consistent with the cratonal evolutionary morphi c belt extending throughout northeast Afri ca process. Events were often initiated by uplifting of (Schandelmeier et aI., 1987). These authors rec cratonic areas due to the therma l expansion resulting ognized three stages of deformation that include: from the development of hot spot anomalies beneath ( I) initial folding (2 100 Ma), (2) development of the craton. Sedimentary basins were developed fol transcontinental shear zones and sigmoidal bend lowing crustal attenuation and fracturi ng of uplifted ing of metamorphic foliation (2000 Ma), and (3) areas and subsequent faulting and subsidence. Basi the development of l ebel Uweinat-lebel Kamil, 55' nal fillin g often produce symmetrical or asymmet dextral wrench faults, and 150' trending structural rical depositional cycles which usually startS with lineaments ( 1800 Ma). basal clastics followed by shall ow marine c lastics During Late Proterozoic, a second deformational and carbonate and, in some cases, evaporites. These event known as the Pan-African thermo-tectonic depositional cycles reflect stages of basinal subsi event took place. It resulted in thermal expansion dence and subsequent marine transgression. This is a and uplift of the basement, and in accretion of the common theme of tectonics and sedimentation in the oceanic cru st assemblage of the Nubian shield to Egyptian basins. Based on their individual tectonic the eastern margin of the Saharan craton. Extensive and depositional hi story a variation on the theme sllldies were published 0 11 the Nubian shield expo may occur. Sedimentary basins of Egypt are either sure in Sinai and the Eastern Desert east of the Nile intracratonic basins, pericratonic or ri fts bas ins. (EI Gaby et aI. , 1990; Morgan 1990). Five main evolutionary development stages rep Intracratonic basins resenting a complex hi story of crustal subduction of arc - trench system leading to accretion onto the east The Dakhla and Upper Ni le basins are broad African continental nucleus are recognized (EI Sha intracratonic depocentres which were developed in zly, 1977). These stages are : (J) Eugeosynclinal fly southern and central Egypt durin g th e Palaeozoi c sch sedimentation associated with island arc volcan and Mesozoic (Fig. 2) . They have evolved as a result ism and crustal subduction ( I 195- 856 Ma). These of structural differentiation and subsidence of the sediments and associated ophiolites were regionally rigid cratonic plate. Morgan (1990) suggested that metamorphosed and folded by later orogenic events. subsidence in Dakhla and the adjacent Kufra basin (2) Orogenic and syn-orogenic intru sion of granite in Libya was initi ated in response to cooling and SEDIMENTARY BASINS OF EGYPT: AN OVERVIEW OF DYNAMIC STRATIGRAPHY 4 1
°
hi E 01 T ERR A N E.• A:.:N:.. ___ • - I , " SEA ( - . '?, .11.x< md, \ \ [ I ,....., I Fagu:') TlBA {. "\ FAIYUM 1..1 S IWA , BASIN \ \ BA SIN ]... • .
~ ] ow ~~~~o~ ABU l ~"\ ~,; GHARAolG S INA I \: ,S: "l] Q.~f(..~~ I J '-'.... ~A'-, S.... ',N ...... I SIWA \ I OASIS "1 I I I I «I .. >-1" RED -<>'"1> -'I'" DE" SEA I FARAFRA oS E" Ii ~ I OASIS ' I I - I ,-, I I 26° 0 \ '",.1 - KHARGA%- '"'" ,- I OASIS \ I I -'" '"., I "'-0-' .> .... I \ I '" « I « ::E ..... __ --z. - I I I I I '" GIL F / //(})"xx' _- , - 24 I / ~ -- 24° { -- I I I I I - I I I - \ " - I - XI :--..-' '- \ I I I - ..:" I I x / \ I " <> ( I I X { ~ 5 I I \' x I I I I I i ~ '0 - I 22 ------1--____ +I ------EGYPT ------XXXX I I - SUDAN X X x I I
o 4 0 80 12:0kM.
LEGEND
x x x HIGHS x x EAST SAHARA CRATON X
NUBIAN SHIELD X TROUGHS
.-,..", ' BASINS FAULTS
Fig. I. Sketch teclonic map of Egypt showing basin configuration (compiled after Schurmann, 1971; EI Gesecry el al. . 1975; Klitzsch, 1986; Sch:l1ldelmeier el al. , 1987). thermal relaxation of the cru st at the closing stages The southern margin of these basins is marked of the Pan-African tectono-thermal event. Others by Precambrian crystalline basement high form ing a (Neev 1975, 1977; Keeley 1989) however, attribute line north of the Egyptian-Sudanese border (Fig. I). the ori gin of these basins to the major trans-Afri can Southwest of Dakhla basin, near the corner of the shear along the "Pelusiul11 Line". Egyptian-Sudanese-Libyan border point, the base- 42 A.S. EL HAWAT
MEDITERRANEAN SEA
N
0 100 2001 ~ r: ;" '" ., - ~ , ! • -1>..- .I:; / 0 • , ~ • " %- ~ / , ." "• • / • • • • -, I I' I .0 - I ,. 1- - I - I I ~ . - "- LEGEND • I I...... / • • • • Vii' • • • / / -.....;.~ - • .. . "- • • • ' . . Iv v": I EAST SAHARAN CRATON • • 'I ...... • • I I ... • • • • • - I '/ • • • I I - - I ,'/ I • • • -I \ :::.}- NUBIAN FIELD • / - I 'i • I - - .. 'i} \ I .. / / . .r.-.. • - - I I "It~ I ' . . · . ~ " '. . SHALLOW SEDIMENTARY • • • • • • ( . . . • .'. ., " / - . ; ,@. • • \ COVER • • • • • I • • . . . '. \ I " :,' 0 .... • , .' . . ,,-1000) ISOPACH CONTOURS . '...... ' · . . ,-'~ - Fig. 2. Teclonic map show ing inlracr:llonic basins of Egypl and Northern Sudan (After KliI7.sch, 1984). ment around Jabal Uweinat mountains consists of basin was separated from its western counterpart, Precambrian metam orphi c and igneous rocks and the Kufra basin of Libya, by NNW-SSE trending younger volcanics. They are partly covered by up to Uwei nate- Gardeba- Sirt hi gh. However, during the 600m of Palaeozoic clastics that extend north and Mesozoic thi s hi gh was cut by th e NW - SW trend· northeast to the Gilf Kebir area in Wadi Abel Malik ing fault system that joined the two basin s along a and Abu Ras Plateau (Klitzsch, 1986). To the south· common trough (Fig. 2). east of the upper Nile basin, and south of Aswan, Klitzsch (1986, 1990a) and Klitzsch and Squyres the Precambrian outcrops exhibit WSW-ENE ali gn (1990) recogni zed three major sedimentary cycles ment. Towards the east, it joi ns the NW- SE trendin g fi lling the intracratonic basin of Egypt and north Ray an swell that constitutes the Eastern Desert Pre ern Sudan (Fig. 2). These cycles correspond LO cambrian basement, and separate the Upper Nile recognizable tectonic events in the NE Afri can era· basin from the Red Sea graben. LO n. The basal cycle was devel oped during Early The Dakhla and Upper Nile basins are separated Palaeozoic and was terminated at the end of the from each other by the Kharga and Dakhla basement Vi sean. This cycle is dominated by clastic flu vial uplifts which are ali gned in N- S and WNW- ESE sediments, alternating with marine and margi nal ma directi ons respectively. During Late Cretaceous, the rine clasti cs associated with transgressive events. Dakhla and Upper Nile basins were joined as a re These transgressions took place during the Early sult of relief inversion and subsidence of the Kharga Cambrian, Earl y and/or Middle Ordovician, Early high. To the north , these in tracrato ni c basin s are sep Siluri an and Early Carboniferous. Uplifting of cen· arated from the northern pericraton ic margin al basin tral and southern Egypt durin g Late Carboniferous belt by the occurrence of the extension of Kartania to Early Jurassic led to erosion of Early Palaeozoic and Farafra high. These structures are recogni zed deposits. In the Upper Nile basin, Early Palaeo· in the subsurface from exploratory wells and geo zoic deposits were found onl y at the centre of the physical surveys. During the Palaeozoic, the Dakhla basin in the area between Wadi Qena and Wadi SEDIMENTARY BASIN S OF EGYPT: AN OVERVIEW OF DYNAMIC STRATIGRAPHY 43 Dakhla (Klitzsch, 1986, fi g. 4). Because of the struc tion encountered in Faghur #1 Well, in the vic ini ty tural set up, flu vial transport was directed mainly of Siwa oasis, is about 1700 m thick, but reaches southwards towards the Sudan. Together with the a th ickness of 2283 m in Gaghboub's Cori well Late Carboniferous glacial facies association found GI -83. A hiatus at the top of the Palaeozoic marks in southwest Egypt and northwest Sudan, they are the Hercynian tectonic movement. The Mesozoic assigned to the second depositional cycle referred section, on rhe other hand , is not significant in thick to as the Karoo cycle (Klitzsch, 1986). This cycle ness in comparison to that of the Pal aeozoic and was followed by a regressive phase inten'upted by Cenozoic. a si ngle tran sgressive event during the Aptian. In The Mauuh basin is located northwcst of the turn , thi s sequence is overlain by transgressive phase Western Desert and northeast of Siwa basin , it is which was interrupted by regressive events durin g bound to the south by the Qattarah ridge. The basin Turonian and Santonian times. These phases belong axis slopes to the northwest in the direction of the to the Early and Late Cretaceous respectively, which E- W trending Meditenanean offshore ridge (Fig. I). constituted the Nubian depositional cycle (Klitzsch, Like Al Jabal al Akhdar trough in Cyrenaica, subsi 1986; Klitzsch and Squyres, 1990). dence in Matruh basin seems to have started during the Jurass ic. During the Cretaceous, however, the Pericratonic basins basin was extended as far south as Qattarah depres sion and Jabal Agila as it was connected to rmbarka The pericraLOnic basins were deve loped on the subbasi n where 1830 m of sediments were accu northern continental margin of the Afro-Nubian cra mulated. To the north subsidence along the basin's ton foll ow ing the opening of the Tethys ocean during hinge belt accounts for the sudden increase of sed the Middle Jurass ic time. They occur on an attenu iment thickness which reaches 3445 m (EI Gazeery ated conlinenlal cru st consistin g of structural system et aI. , 1975). which run parallel to the nOltheast African coast of One of the major sedimentary basins in Egypt Egypt and northeast Libya (EI Hawat and Shelmani, that exhi bits a great hydrocarbon potential is Abu 1993). As a part of thi s system, these basins are Gharadig basin (Figs. 1 and 3). Currently, it pro bound to the north by a subsurface structural high duces 40,000 barrels of oil and 0.4 bel' of gas per trending parallel to the coastline in the Mediter day from Cretaceous reservoirs. The basin is located ranean offshore (Fig. I). They are also, separated in the central part of the Western Desert. The basin from the intracratoni c basins to the south by the was opened during the Early Cretaceous as a resul t subsurface Rayan-Nafsha and Farafra highs. of ri ght-lateral movement of E- W to ENE trend The pericralOnic sedimentary basins were gener ing normal fa ults, leading to the development of ally affected by th e same preva iling regional struc pull-apart grabens (Abdel Aal and Moustafa, 1988). tural and tectoni c conditions as the intracratoni c This basin is also considered to be an extension of basins. However, being located on the margin of the the E-W trending arm of the Sirt basin rift system craton, they were more susceptible to tectonic influ (Guiraud and Maurin, 1992). It has evolved as a ences induced by collision with the Eurasian plate result of the development of wrench faulting and than their southern counterparts on the stable craton. structural inversion related to the Late Cretaceous The subsurface basement highs and basins of the Syrian Arc fold system. The basin attains asymmet peri cratonic area were developed as a result of fold rical north-south cross-secti on with increased depth ing and associated faulting in two major directions. to the north. It is separated from the Matruh basin The older ESE- WNW trending Palaeozoic struc to the north by the Qattarah ridge, and from the tures are intersected by younger Mesozoic ENE Faiyum basin to the east and south by the Kat WSW trending set. These basins and highs exhibit taniya hi gh. The latter merges southwards into the considerab le changes in shape and size through time. Baharya basement platform. Abu Gharadig basin It should be noted that because of the changes of exhibits a general northeasterly trend with easterly centres of sedimentati on some authors used different tendency towards the centre (EI Gazeery and Taha, names for the same basi n at spec ifi c times (e.g. Kee 1971 ). ley, 1989). These basins include Siwa, Matruh, Abu The centre of the basin , whose depth is estimated Gharadig, Faiyum, lower Nil e or Gindy, and the Nile to be 12,200m (Awad, 1984), is filled by more than Delta (Fig. I). 1300 m of Palaeozoic sediments above the basement Siwa basin is one of the main Palaeozoic de complex. The basement is structurally higher at the pocentres in the Western Desert of Egypt. The basin southern border of the basin as it ri ses to a depth of is bound to the east by Mamura-Farafra ridge, and about 1265 m (Awad, 1984). Generally, the Palaeo extends westwards into Gaghboub basin across the zoic section decreases in thickne ss and pinches out border into Libya, where the basin attains greater south and east of the basin towards the Faiyum and depth (EI Gazeery et aI. , 1975). The Palaeozoic sec- Nile Delta basins due to the accun'ence of a Palaeo- 44 A.S. EL HAWAT TIME UNITS ROCK LITHO. UNITS LITHOLOGY a ENVIRONMENT • • • • • • • • • • MIOCENE MOGHRA =-' ....:.. . -'- -· . --,.- . . CONTINENTAL CLASTICS -0 >- • • • • • 0 I>: -- fLUVIOMARINE CLASTICS AND CJ) ISANTONIAN :I: => CJ) B-R. ~ 1>:0 0 UPPER CJ)- CJ) ALTERNATING CYCLES OF FLUVIAL AND • · • • • • DEVONIAN • - . • 0 ~ZALAT • • • - • : . 0 • • • • N S ILURIAN ACACUS • • • • • • FLUVIAL TO SHALLOW MARINE - . • 0 • • • • CLASTICS WITH IGNEOUS W • . -: • • ...J iOROOVICIAN • - . INTRUSIONS Fig. 3. A generalized stratigraphic col um n of Abu Gharadig and Faiyum basins (compiled after Awad, 1984; Bayoumi Cl a!. . 1987). zoic basement high (Fig. 5), and to truncation by the domin ated by continental clastic facies that changes Hercyni an unconformi ty. The sequence is followed into a thi ck sequence of marine carbonates to the by the Jurassic which develop a si ngle asymmetrical northeast (Bayoumi et aI. , 1997). depositional cycle consisting of a basal sandstone Sedimentation in Abu Gharadig basin during the facies grading upwards into carbonates, refl ecting Early Cretaceous was dominated by fluv iatile and progressive marine influence. Laterally however, the flu viomarine clastics. During the Late Cretaceous western and southwestern portions of the basin are transgression. however, the basin was enl arged and SEDIMENTARY BASINS OF EGYPT: AN OVERVIEW OF DYNAMIC STRATIGRAPHY 45 extended over an extensive area at the centre of the the west to its present day position (Salem, 1976). We stern Desert. Also, because of active basin subsi At mid-delta, the Late Cretaceous- Tertiary strata dence hi story, it has received the thickest Late Creta exhibit steep dips north of the hinge line. Younger ceous sequence throughout Egypt. The th ick organi c Neogene marine and deep water deposits, on the rich Senoni an-Turo ni an carbonates and shales were other hand. are cut by a series of normal rotational considered to be the main hydrocarbon source rocks fault system, laking a trend parallel to the Med iter in the basin. On the other hand , the Cenomani an ranean continental margin . Two major coarsening-up flu viatile and ftu viomarine sand s fo rm the princi depositional cycles belonging to the Miocene and ple reservoir (Awad, 1984; EI Gazeery and Taha, Plio-Pleistocene foll owed by the Holocene consti 1971 ). tute the Nile Delta sequence. Three major gas fie lds Bound by Abu Gharadig basin to the west and the were di scovered in the bas in , including El Wasta ni , Nile Delta basin to the east, EI Faiyum basin was Abu Madi and Abu Qir gas fi eld s. ln these fields devel oped durin g the Jurassic as a nOltherly sloping the orga ni c ri ch open marine and bas inal shales are basement. Like most pericratonic basins it was de recogni zed as the main hydrocarbon so urce rocks, veloped during the opening of the Tethys. Jurassic whereas the top part of the early cycle, and the basal and Cretaceous depocentres were located between tran sgress ive sands of the second cyc le are recog the Jabal Ri ss u- Katratani a and Mubaraka area at nized as forming th e main reservoir rocks (Marzouk, the centre of the basi n. However, this area was up 1974). lifted during the Late Cretaceous Syri an Arc tectonic acti vity. Consequentl y, the basin was effecti vely The Gulf of Suez rift basin subdi vided in to two major northern and southern Palaeocene- Eocene depocentres, which correspond Recent hydrocarbon explorati on activiti es and re to Tiba and Gindy (Lower Nil e) basins respecti vely search have led to extensive publications on the (EI Zarka, 1983). During the Palaeozoic, the NNW Gul f of Suez and the Red Sea rifts. These included SSE trending axis of the Lower Nile basin was lo comprehensive reviews, synthesis and origi nal data cated between the Gul f of Suez and the Nile River on the dynamic tectoni c evolu tion and sedimenta due to the occurrence of a major high to the west ti on in the ri ft system (Phillobos and Purser, 1993; (Fig. 6) that extended from Charge to Nafsha. The Bosworth, 1994; Patton et aI., 1994; Moustafa and Palaeozoic is represented by l520 m in Abu-Ham Khali l, 1995). The Gulf of Suez basin is a tensional mad we ll east of Cairo. Subsidence of the basin tecton ic rift that forms the northern ex tension of th e continued during the Jurassic, as a 2350 m thi ck Red Sea graben. The basin is 60 to 80 km wide and seq uence was deposited. During the Cretaceous the consists of two major tilted blocks found on each basinal axis was shi fted in a northwest-southeast side of the rift (Thiebaud and Robson, 1979). The directi on and the Lower Nil e basin was connected Gulf of Suez basin is separated from the Nile basin to Faiyum basin to the north. However, the deepest to the west by Urn EI Tenassib- Elba ridge of the area of sedimentation was established further south Nubian plate and is bounded to the east by the Si nai between Asyut and Minia. basin of the Arabian plate. Depositi on was main Foll owin g the Late Cretaceous Syrian Arc tec tai ned in the basin fo llowing the NNW- SSE trend of tonics, Faiyum basin was divided and the newly the basement structural lineaments since Palaeozoic developed Lower Nile (Gindy) basin and was sep (Said , 1962; Schandelmeier et aI. , 1987). aJ'ated from its northern co unterpart Tiba basin . As The ri ft, however, is considered to be a post the Lower Nil e basin was established as the major Eocene feature th at became a fully developed basin Palaeogene depocentre in Egypt, the Nile Delta is during the Miocene as it received more than 3700 recogni zed as the main Neogene depocentre in the 111 of sediments (Scott and Govean, 1985; Sell Pericratonic area of Egypt. wood and Netherwood, 1984; Schandelmeier et aI. , Due to its intermediate location, the Ni le Delta 1987). The Gulf of Suez basin contains several area constituted a part of the Lower Nile basin sedimentary units that are regarded as good so urce during Palaeozoic, part of the Faiyum basin during rock for oil. These include Kareem and Rudeis Jurassic and Cretaceous, and was part of the Tiba shales of the Gharandal Group, the Belayim shales basin during Palaeogene time. During the Neogene, of Ras Malaab evaporites, and Esna Shale of the the Nile delta basin was firm ly established as a result Palaeocene-Eocene sequence (Fig. 4). The Senon of the development of two hinge fau lts arranged ian and Eocene carbonates, however, are considered in a "V" shape with its head north of Cairo and to be the mai n hydrocarbon source rocks in the its base opened toward s the Mediterranean (Fig. I). Gul f of Suez basin. Oil was found in the Mi ocene, Subsi dence of the delta east-west trending hinge Cenomani an, Albian and Carboniferous sandstone belt started during the Middle Miocene due to sed reservoirs. Porous and fractured limestone and reefs iment loading fo ll owing the Palaeonile shift from of the Miocene, Eocene, and Late Cretaceous are 46 A.S. EL HAWAT TIME UNITS LITHO. LITHOLOGY a ENVIRONMENT • • • • • • • • • • • A • • • • • • • • • • W • • • • CLASTICS, EVAPORITES a CARBON t-z POST . L. II . C{)w • • • • • ATES . a.oOu ZEIT • • • • • CONTINENTAL TO SHALLOW MARINE -:::;; • • • • • WITH INDO- PACIFIC FAUNA. · :x::. .'. " . . • • • • • • • • • • RED BEDS a POST RIFT VOLCANICS PERMIAN- NUBIAN FLUVIAL AND MARINE CLASTICS. CARBONIF. C + 0 --"--'------Fig. 4. A generalized stratigraphic column of Gulf of Suez basin (after Chowdhary and Taha, 1987). also good reservoirs. The estimated oil reserves of the development of a gently inclined land surface the Gulf of Suez fields are amounted to 3800 million to the north and northwest. This surface formed a barrels. prominent unconformity over which the Palaeozoic clastic sequence was deposited. The unconformity surface exhibits strong erosional features, such as THE PALAEOZOIC kaolinitization and soil development. The Early Palaeozoic sequence consists of an al The Pan-African arc accretion and cratoni zation ternating siliciclastic-dominated succession of con of the Nubian shield was followed by a period tinental and marine stratigraphic units. The pat of extensive erosion and peneplanation resul tin g in tern of successive Palaeozoic marine incursions was SEDIMENTARY BASINS OF EGYPT, A N OVERVIEW OF DYNAMIC STRATIGRAPHY 47 • • • · . . • • • • • • • , • • • • • • • • • , • '. • . . . • • • • • .. ' . • . . . • • • • • • • • • • • • • Ca iro • • • · . - .'. . " '. • • · • • . • . . . . '.• . • • • • • • • • .' . . • • • • • • • • • • • • • • • • • • • • • • • • • • • • .' • . • . • . . ' . . . . • • • • • • • • • • • • • • • -'... :....;. . • · --:- ~~ .--' • • • .. • • • _. __ - · . . • -. • • • • • • • • • • · " • • • • • • • • · . I · '. . • • · . I . . . '. · . I . . . . . • • • • • • • • • • • · , . . • • • • · . I ' . . . . . •• •••••• · I ...... · I . " . . . • • • • • • • • • • • • • • • • • • • • • • · ·1 • • • • • · I . • • • • • • · I . . ct.:o . · . ' . ~----<, 22 ----- • • • ------'.• . • - ~ HIGHS rw'Lj SILURIAN OPEN MARINE • • • • • TROUGHS • • • • • SILURIAN NEAR SHORE- • • • . • • • • • • FLUVIAL TRANSITION LIMIT OF EARLY • - - -- CAMBRIAN TRANSGRESSION Fi g. 5. Palaeography of the Si luri an and approx imate limit of Lower Cambrian transgression. Map also shows Earl y Palaeozoic structural relief (compiled aftcr Kli llsch and Wyc isk, 1987; Sch:mdelmeicr CI al. , 1987). controll ed by the structural and palaeotopographic rine waters. However. the Dakhla basin to the south configuration of the craton which was inherited and Siwa and Abu Gharadig basins to the north from thc Pan-African event (Fig. 5). During the (Fig. 6) were the main foci of subsidence. Palaeo Pal aeozoic times marin e waters inundated Egypt in zoic sediment thi ckness in th ese depocentres reaches a southeasterly direction through the NNW-SSE up to 3000 metres. Thinner sediment acc ulllulations trending Kufra-Darfur and Dakhla-M isaha troughs. were fo und elsewhere in the cratonic and pericra These troughs we re the main passageways through tonic areas in the Nile basin. the Delta, Gu lf of Suez which the Early Palaeozoic seas extended as far basin and Sinai. The age of the Palaeozoic sequence south as northern Chad and the Sudan (Klitzsch, above rhe base men t unco nformity vari es in different 1986; Schandelmeier et aJ. , 1987). In the mean time, regions in Egypt, as elsewhere on the Nubian craton. flu vial and flu viogJac ial sed iments were transported This is attribu ted to marine tran sgression and conti from the hi gh areas from the south and east. The nental sedimenration over structurally controlled and distribution and accumulation of continental and ma irregu lar palaeogeography, as much as the subse rine sediments were controll ed by the positi on of the quent epeirogeni c movements of the craton. Also. Pan-African hi gh lands (Morgan, 1990). the paucity of time diagnostic fossils within the During the Palaeozoic tran sgression, the Egyptian siliciclastic-dominated sequence led to difficulty in craton was covered by a shallow to very shallow ma- age determination, stratigraphic subdivi sion and cor- 48 A.S. EL HAWAT 28 '" MEDITERANEAN SEA SEDIMENT THIC KNESS > 1.5 Km ////1 .:> :5. C Km Fig. 6. Pal aeozoic depoccillres in Nonhcrn Egypl (after EI Gezcery eLal.. 1972. 1975). relati on. Abdall ah et al. (1992) presented a review pass into micaceous shal es. Fossil s coll ected from and di sc uss ion of nomenclature of the Pal aeozoic cores of thi s well include lingul oid brachiopods stratigraphic units in the Eastern Desert of Egypt. and trilobites of Late Cambrian age (Dakkak, 1988; By the uplift of central and southern Egypt at the Khalil et aI. , 1983). end of the Vi sean during the Hercy nian tectonics, Elsewhere, the Cambrian (Araba Formation) was the earl y Palaeozoic depositi onal regime was ter described from Araba-Druba area of southwestern minaled. During thi s lime a great part of the earl y Sinai (Said, 197 1). It was later prove n that Araba Pal aeozoic sequence was eroded, and with the de Formation and its lateral equi valent s in the Eastern structi on of the old structural configuration, flu vial Desert to be Early Cambrian in age based on dat drainage was reversed to the south (Klitzsch, 1983, ing by trace fossil s (Seil acher, 1990). The sequence 1986, I 990a, b). is up to 120m thick and consists of basal lentic ular conglomerates containing angular vein quartz Cambrian and granitic pebbles, followed by a coarsening up cycle consisling of interbedded mi caceous sand The Early Cambrian marine transgression in stone and variegated red and green sandy mudstone Egypt extended to latitude 27°N (Fig. 5). Marine grading upwards inro red-brown arkosic sandstone Cambrian rocks found near Wadi Dakhla and Wadi unit. These units are intensively bioturbated with Qena areas consist of fluvial and shallow marine abundant Skolithos burrows and tri lobites traces of arkosic sandstone and sandy shale (Klitzsch, 1986; Cruziana (Said, 1971; Issawi and lux, 1982; Abdal fi g. 4). At the northern edge of Dakhla Basin the lah et aI., 1992). Cambrian is 457 m thick marine sa ndstone and shale On the eastern side of the Gulf the Cambrian found in the Bahariya well. These beds contain bra sequence is 100 metres thick. The lower part of chiopods and trilobites remains of Early Cambrian the sequence consists of I to 5 m thick coars age (Dakkak, 1988). ening-up cycles of soft red and green mudstone, Further north in Abu Gharadig basin, 443 metres grading upwards into red-brown arkosic bioturbated of Cambrian sediments are recognized. In Siwa sandstone. Thi s unit exhibit desicca tion cracks, wavy basin, the base of the Cambrian was reached in and lenticular bedding and low angle cross-lamina Fagur #1 Well. It consists of 851 metres thick tion. Ichnofau na is dominated by CruzianQ traces. sequence of quartz arenite and micaceous sandstone The upper part of the sequence contains 10- 15 m that grades upwards into shales. The top of the thick subunits of dark brown fi ssile, silty shale beds sequence is marked by a lithological break, where intercalated with coarse to very coarse often peb medium and fine sand stone with chert fragm ents bly sandstone units exhibitin g fining-up cycles with SEDIMENTARY BASINS OF EGY PT: AN OVERVIEW OF DYNAM IC STRATIGRAPHY 49 tabular, trough and herringbone cross-bedding show southwards into tillite consistin g of white sandstone ing ex tensive Skolithos and Bifimgites burrows and containing errati c quartz pebbl es sugges tin g ftu some Cruziana traces. This facies extends into the vioglacial origin (Beall and Squyres, 1980; Klitzsch, Eastern Desert and to Wadi Qena area in the Nile 1983). basin (Klitzsch, 1986). The coarsening-up cyclic In the Gulf of Suez area th e Ordovician- Silurian ity of sand-shale units suggest deposition of sand sequence, Naqus Formation (Said, 197 1), is up to bodi es in near shore area; and [he occurrence of 462 metres th ick. On the western side of the Gulf interlaminaled sands and shales indicate deposition the sequence overlies th e Cambro-Ordovician Araba in a shallow marine or protected lagoonal, tidal flat Formation with an apparent gradati onal boundary. It setting. The sequence may represent a prograding is also, unconformably overlain by the Earl y Car coasta l plain sequence foll owing the Early Cambrian boniferous Abu Thora Formation (Abdall ah et aI., an marine tran sgres sion (Bhattacharyya and Dunn, 1992). The sequence is unfossiliferous and consists 1986; Abdall ah et aI. , 1992). of finin g upwards to noncycli c, often cross-bed ded, well sorted coarse to medium grai ned, uniform Ordovician-Silurian feldspathic sandstone with few clay intervals. The sandstone contains occas ional scattered ve in-quartz Ordovician strata are relatively rare in Egypt. pebbles and cobbles up to 10 cm in diameter. These Ordovician outcrops, however, are found south west pebbles in the sandstone exhibit a general northward of the Dakhla basin in Jabal Uweinat area un con decrease in size, as feld spar grai ns in the sand fonnably underlain by cry stalline basement. They stone are kaolinitized giving the roc k a speckl ed co nsist of shallow marine sandstone beds containing appearance. Th e basal unit of th e sequence suggests abu ndant Cruziana rouaulti and Skolithos ichno emergence of the Cambrian marine sequence be low. fossil s of Earl y Ordovician age (Klitzsch, 1986; The top of the sequence, however, is marked by Klitzsch and Lejal-Nicol, 1984). development of prominent mottled and kaolinitized The Ordovician-Silurian deposits in the northern soil hori zon. The Ordovician- Silurian sand stone se basin s of the We stern Desert were undifferenti quence consists of low-an gle cross-bedded lenti cular ated and unrecogni zed from the Early Palaeozoic bodies whi ch were depos ited in northwesterly to seq uence beca use of th e paucity of index foss il s. north-northeasterly fiowing braided streams on a Therefore, so me authors use the stratigraphi c sub prograding alluvial fan settin g (Buh attacharyya and divi sion as those found in Ghadames and Murzuk Dunn, 1986). Issawi and J ux ( 1982) i Illerpreted this basins of Libya becau se of lithological similarities sequence as flu vio-glacial in origin. (Khalil et aI. , 1983). Recentl y, north of Siwa Oasis in the Wes tern Desert, the Silurian sequence was Devonian identi fied by means of palynomorphs in the sub surface of Basur # 1 and Kohla #1 wells (Keeley, Tn Siwa Basin of the Western Desert, the De 1989). The Silurian form s a coarsening up regressive vonian sequence was described from Zeitoun # 1 sequence bound by unconformities above and below. Well. It form s a sin gle, 288 metres thi ck, coarsen It consists of 626 metres of marine and marginal ing and shallowing up depositi onal cyc le bounded marine siltstone with minor amount of mudstone and by unconformities. The earl y part of the cycle con sand stone grading upward s into 400 to 700 metres tain s interbeds of skeletal limestone grading up into of braided stream and alluvial fan sandstone and pyritic claystone followed by sandstone and con conglomerate. In Foram # 1 Well to the west and glomerate at the top (McGarva, 1986). North of Sheiba # 1 Well east of Qaltarah Depression 200 Siwa Basin , a more complex 166 metres thick se to 300 metres of marine sa ndstone, siltstone and quence of the Late Devonian is reported. In thi s shale sequence was encountered. These rocks con area the sequence consists of basal sand ston e unit tain palynomorphs and ichnofossil Hariania dating overlain by two marginal marine and deltaic coars the sequence as Silurian (Klitzsch, 1990b). ening-up cycles. Each of these cycle consists of In the Gilf Kebir area of southwestern Egypt, argillite grading upwards into argi llaceou s sandstone the Silurian forms th e early 400 metres of the and arenaceous sandstone. The sequ ence is termi Palaeozoic sequence, where it rests unconformably nated by fossiliferous shallow marine limestone. over th e basement. The sequence consists of thi ck Late Devonian foss ils found in the seq uence include bedded ftuvio-deltaic and shallow marine sandstone Theodessia aff. hun8€1fordi, Produclella cf. hallina, interbedded with well bedded shale and siltstone. Leptostraphia magnifica, Platyracheela cf. mesaslri· These strata exhibit trace fossils of Cruziana, Ar ais and Feneslrillina aff. omaciOIO (Dakkak, 1988; Ih rophycus, and Skoiilhos burrows. This ichnofaunal fi g. 7). assemblage is similar to that found in the Sil The Devoni an is found in Jabal Uweinat and Abu urian sandstone of Libya. These deposits change Ras Plateau area on rhe southwest margin of Dakhla 50 A.S. EL HAWAT 26° 28° 30° 32° 34° MEDITERRANEAN SEA • • • • • • • • • I'E.Q • • • • • • SE.I' • • • • • • • • • • - • • • • • - • • • • • • • • •• • ..• · . :-...... '.'• • ';..Y' . '. . ',' . . '':' ... .: './ . : " .... ' .... '. /'...... '. '. ,' ...... :. :':'-./ // ., .' .. · .: ...... '... .. /.. · . . . '. . . . " .•• • .. /.• • •••• • .' • . • . .' .' · • . • • L __.:.:;I~O Km. . . • • ? • • . . . . • • • • • • ~----• • • • • ------ ------'. ". • • • • • '. . . . • • • • • 28° 30° -- LIMIT OF MARINE DEVONIAN ~OPEN TO SHALLOW MARINE WITH DELTAIC ~ AND FLUVIAL INTERCALATIONS ...... • : ALLUVIAL DEPOSITS • • , . .' " Fig. 7. Palaeogeography of the Early Carboniferous and the limit of Early Devonian transgression (after Klitsch and Wycisk, 1987). basin (Klitzsch, 1983). It forms a 70 m thick succes sists of basal clastic unit followed by a unit of mixed sion overlaying the Ordovician- Silurian sequence. It carbonate and clastics, and is overlain by a clastic consists of cross-bedded fluviatile sandstone which dominated unit at the top. These units are call ed Des corresponds to the Early-Middle Devonian Tadrart ouqy, Dhiffah and Safi formations respectively (Kee sequence of Libya. Elsewhere, in Wadi Abdal Malik ley, 1989). This cycle shows an increase in thickness the sequence is 10- 100 m thick shale and siltstone from east to west as it develops 670 to 950 metres containing plant detritus. It is overlain by fine to thick sequence towards Libya. The basal unit is 100- medium-grained, bioturbated sandstone with Bifun 300 metres thick. It consists of fining-up and deepen gites jezzanensis and Camerotoechia spp. trace fos ing-up sequence of kaolinitic fluvial sandstone grad sils. It also contains brachiopods and pelecypods that ing upwards into marginal marine, deltaic and pro indicate Devonian to Carboniferous age (Klitzsch, deltaic siltstone and mudstone. The middle part of the 1983). Carboniferous cycle is 300 to 450 metres thick, and consists of oolitic and bioclastic limestone interbed Carboniferous ded with mudstone and shale. As the carbonate facies decrease in thickness and abundance upwards, the se The Carboniferous sequence in the subsurface of quence grades into a third unit at the upper part of the Western Desert basins forms a symmetrical de the cycle. In Fagura #1 Well this unit forms a single positional cycle bounded by unconformities. It con- coarsening-up argillite and arenaceous sandstone se- 52 A.S. EL HAWAT • N s JURASSIC '00 SAND 6 SILT MESOZOIC ' 00 FLUVIO_ GLACIAL DEP OSITS ~ '0 CARBONIFEROUS A TO SHALLOW MARINE S. SILT a. SHALE 0 ' 0 20 30M . DEVONIAN 0 , , , , - m m CHANNEL FILLS COASTAL PLAIN 30 5° i~ BRAIDED STREAM GLACIAL LAKE MEANDERING STREAM D B m Fig . 9. North-soutb sketch prolHe of Carboniferous glacial facies (A) of SW Egypl and NW Sudan. Glacial till ite exposed north of Wadi Abdal Mali k (C). change south wards into glacial lacustrine deposils (D) in NW Sudan. Coastal nu vio-dehaic deposits (B) of Lower Carbon iferous Age are ex posed south of Wadi Abdal Malik (compiled after Klilzsch, 1983: Klitzsch :md Wycisk. 1987). glac io-lacustrine sedimentati on conditions (Figs. 8 The Early Carboniferous section in the Gulf of and 9), that are equi valent to Dwyka glaciation of Suez basin is 500 metres thick in the subsurface, south central Africa (Klitzsch, 1983; Klitzsch and and may reach a maximum of 80 metres in surfa ce Wycisk, 1987). sections. It is assigned to Umm Bogma Formation SEDIMENTARY BA SINS OF EG YPT: AN OVERVIEW OF DYNAM IC STRATIGRAPHY 53 (Kostandi , 1959; Soliman and EI Fetouh, 1970). Geologic events and sedimentation It form s a transgressive sandstone sequence with basal conglomerate of well rounded vein-guartz peb Morgan ( 1990) noted that the Palaeozoic se bles and well sorted, well rounded sand grading guence in North Africa and Egypt is characterized upwards into ferruginou s and magniferous claystone by the relative paucity of carbonate sediments in and shal e. The top shale unit forms a reg ional marker compari so n to siliciclastics when co mpared with horizon wi thin the basin . It grades into dolomitic other shelf areas of the wo rld . He suggested that unit contai nin g Early Carboni fe rous marine fauna. siliciclasti c dominance over carbonate sed imentation In turn, these carbonates grade laterall y into multi in Egypt is attribute to sustained erosion of the Pan coloured calcareous siltstone with poorl y preserved African mountains, epeirogeni c movements of the braclliopods, and bryozoan shoreface sandstone in craton and continental glaciation. Redi stribu tion and di cating lagoonal bay or open marine cond iti ons reworkin g of th ese sediments, on the other hand, was (B hartacharyya et aI. , 1983). attributed to th e hi gh eustati c sea level during the The Late Carboniferous Ataga Formation in the early Palaeozoic. Gulf area (Kostandy, 1959) consists of a single fin ing-up cycle of basal sand and shale facies. The lower Eustatic vs. tectonic control of sedimentation sand fac ies consists of a seri es of fining upward s len ti cular units with basal conglomerate and over Erosion, transportation , sedimentation and ma layin g clays. These sand s grade laterally northward s rine transgression during the Palaeozoic in Egypt into thin-bedded, rippled and bioturbated sand stone was controll ed by th e development of wi de grabens that interfi ngers with fossi li ferous marine shales. The and small er horsl blocks following the NNW-SSE sandstone, also, grades upward s into a coarsening-up trend (Schandelmeier et aI., 1987), and the occur seguence of interbedded sandstone and shale. These rence of major Pan-African mountains to the sou th . shales are either carbonaceous and contain plant re Several depocelllres were established due to post mains such as Lepidodendron and Sigillaria (Weiss Pan-African thennal relaxation and cooling and/or brod, 1969), or as in Umm Bogma area, it contains to shearing along major lineaments of the craton. bituminous coal seams. Elsewhere, the late uni t con The res ulting troughs were submerged und er marine sists of green clays with well preserved brachi opods conditi ons during the Ordovici an, Siluri an, Devo and bryozoa (Bhattacharyya et aI. , 1983). nian and Early Carbo ni ferou s transgress ions. Fluvial North of the Gulf of Suez area the cumulative sediments were carried in the opposite direction by thickness of the Early and Late Carboniferous se rivers after erosion from the Pan-Afri ca n highlands. quence may reach up to 600 m of carbon ates and The resulting depositional cycle attain an asy m marine shales. It is suggested that the Late Carbonif metri cal mOlif consisting of basa l fine-grained ma erous sequ ence was depos ited as a resu lt of rapid rine deposi ts grad ing upwards into coarse-grained prograd ation of fluviatile and fiuviomarine fac ies, progradational fluvial deposits. Otherwise, deposi followed by gradual marin e tran sgress ion lead in g to tional cyc les are symmetri cal , as in the Carboniferous the depos iti on of shallow marine and intertidal sands sequence in the peri crato ni c basin s. III these depoce n and shales. The top of thi s seg uence is marked by tres the Carboni fero us cycle begi ns and ends with a regress ive phase and the development of a so il coarse-grained continental clasti cs sand wiching a se hori zon (Bhattacharyya et aJ. , 1983). quence of mi xed siliciclastic-carbonate succession. These cycles are bounded by unconformities at the The Permian Ordovician- Si luri an, Siluri an-Devonian, Devonian Carboniferous and the end of the Permian . Because of the effect of the Hercyni an orogeny These eros ional boundari es were caused by eu and the uplift of southern and central parts of Egypt stati c low stands assoc iated with majortec toni c move (Klilzsch, 1983) there is no sedimentary record of ments of the craton. Bhattacharyya and Dunn (1986) the Permian in southern Egypt. However, north of demonstrated that marine transgress ion in the Gulf the Westem Desen in the Siwa Basin the Permi an is of Suez area during Cambrian and Early Carbonif represented in the subsurface by 70 m thick shall ow erous was interrupted by flu vial progradation dur water carbonates, sand stone and some shales. These in g Ordovician-Silurian (Nagus Formation) and early sediments contain Early Permian fossil s including Late Carboniferous (Ataga Formation) times. These Waagenocencha montepelierenses and Anisopyge cf. flu vial sandy progradation interrupted marine trans Prerassulata (Dakkak, 1988). In the Gulf of Suez gre ssions in different times and direc ti ons as a result basin the Permian and Triassic develop an undi f of verti cal block movement of the basement in the hin ferenti ated flu vial sandstone sequence assigned to terland, along the old tectonic lineaments (Fig. 10). Quseib Formation (Abdall ah et aI. , 1963). This sec At the end of the Vi sean and as a result of the tion is discussed in the Tria ss ic sequence. collision between Gondwana and the northern conti- 54 A.S. EL HAWAT Atoqo Safaga N , ..... : ... : .. , "C':': : .,' .. . '. ,'.' ... " . Upper :~ ~~:~ ~ '~d~ti ~~ ,: ',:, .. :':, :', : >~ <.:.< .... :.'...... ' _ J •• •• ' • ••- ..'. •• • • " • . . " . . Cretaceous .-. . - . .- .....'. . ... ' .. . .'-• '.• •••. . .: • . . . . • 'p'loin' 'Fci c i~ ~ ~.:-: : .:: .•.. , ':;':. S.:: ...... -:.::-::.. ... :'-.---, ... :...... : ...... , ...... :: ) .' ...... Jurassic " .. -' '. , .. ' ," • •• " . '. .:.' ..· . .- ...... " '.., " . . . · . '" . .'...... '. ." '.. ..' . · . . . . .' .. . · " . . .' .. . · .' '...... Carboniferous '. . . ' . ' .... ". . ':,'.;',- . '. ",' . , , , , ~ I , J , , , \ , I - I , / , , , I Basement / " • / / , , - / - , - I , , , -, ~ , , , , Pre-Cambrian -, , , I \ , , , , , , I • \ , , \ I , J - - - Fig. 10. Schematic profile ilIustraling the relationship between marine tran sgressions and wedges of claslic influxes induced by tcctonic movemenls of basement bl oc ks in NE Egypt (after Bhanacharyya and Dunn, 1986). nents during the Hercyni an orogeny, the NNW- SSE glaciall y polished surfaces and striations. In the ex structural elements that dominated Egypt during treme southwest of Egypt, in Iabal Uweinat area, the Early Palaeozoic were effectively deactivated (KI occurrence of U-shaped valleys and ro unded peaks itzsch and Wycisk, 1987). The upheaval has resulted in the crystalline basement are also, attributed to in the upli fting and erosion of southern and mid Early Palaeozoic glaciation sculpture (Bowen and dle Egypt (Fig. 8). The resulting east-west trending l ux, 1987). Uweinat-Aswan uplift was developed as a result of The Ordovician- Silurian glaciation in southwest magmatic upwelling from the mantel and was ac ern Egypt was also, confirmed by the di scovery companied by cru stal thinni ng and faulting. Some of of glacial tillite (Beall and Squyres, 1980). Sim the east- west trending faul ts in the region were lo ilar glacial deposits and cold water fauna were cally intruded by intermedi ate trachytic·phonolithic also reported from Libya. Fluvio-glacial sedimenta lavas of Permo-Triassic age (Schandelmeier et aI. , tion in the Gulf of Suez area is indicated by the 1987). One of the main resul ts of the Hercyni an mineralogical and textural immaturity and the oc orogeny was the reacti vati on of the ENE- WSW currence of erratic vein quartz pebbles and cabbies structural elements which became signi fi cant in the of Naqus Formation (Bowen and l ux, 1987). The development of sedimentary basins during the Meso ti ll ite deposits fo und in Wadi Abdul Mali k north zoic in Egypt (Kli tzsch, 1984). of Iabal Uweinat in southwestern Egypt, on the other hand, were deposited during the Carboniferous Palaeozoic glaciation glaciation (Figs. 8 and 9). Two hundred kilometres The second most important reason for the domi· to the southeast across the border in the Sudan, nance of siliciclastic sedimentation over carbonates these tillites change into several hundreds of me in the Palaeozoic sequence of North Africa and tres of glacial-lacustrine varve sequence whi ch are Egypt is conti nental glaciation. Smith et al. (1981) regarded by Klitzsch (1983) as equivalent to the suggested that during Late Ordovician-Earl y Si l· Dwyka glaciation of southern and central Africa, urian times th e south pole was located in the central where the pole was thought to be in the region of tbe Saharan region. The Pan-Afri can Hoggar mountains Transvaal. of Algeria and Tibesti and Jabal Uwein at moun tains of Libya and Egypt were some of the main glacial centres throughout the Pal aeozoic. Evidence MESOZOIC of glaciation found in southern Algeri a includes glacial morai nes, flu vio-glacial and glacial-lacus Tbe theme of tectonic and magmati c activities trine deposits as well as glacial landforms exhibiting of the Hercynian orogeny continued unabated from SEDIMENTARY BASINS OF EGYPT: AN OVERVIEW OF DYNAMIC STRATIGRAPHY 55 the late Palaeozoic to early Mesozoic, leading to the a I. , 1983). On the western side of th e Gulf of Suez breakup of the super continent of Pangea. During in EI -Galala EI-Bahariya Plateau, the Permo-Triassic the Mesozoic several events of global magnitude is 80 m thick (Abdallah et aI. , 1963). It consists have had a strong domino-effect tectonic influence of ferruginous sandstone, siltstone and shale with on sediment ary basins of North Afri ca and Egypt. minor gypsum and rock salt overlain by limestone These included the opening of the mid-Atlantic (lI1d marl. ocean during the Early Jurassic, the opening of the The flu vial-dominated sediments of southern Mediterranean Telhys during the Middle Jurassic; Sinai change northwards and upwards into a progres and the subsequent reversal of crustal movement sively mari ne siliciclastic and carbonate sequence of leading to subducti on of the Mediterranean oceanic Middle Triassic age. In tile subsurface (Halal # 1 crust due to colli sion between North Africa and Well ) of northeastern Si nai, th e southern lluvial Eurasia during the Late Cretaceous. These tecton dominated fac ies change into marginal marine and ics have led to movements of basement blocks in deltaic fac ies complex interbedded with carbonates th e cratoni c and peri cratoni c areas of Egypt, shi fts (Druckman, 1974). Southeast of thi s well in Arif and changes of depocclllres and inversion of sub EI Naga anticline, 200 metres of Mi dd le Trias siding basins into structural highs, or the reverse. sic sequence are exposed. The sequence exhibits The associated global eustati c events were also ef an upwards increase of marine influence, as the fec tive in influencing sedimelllati on in the North basal sandstone units grade upwards into carbonmcs Afri can and Egypti an basins. These include trans and evaporites interbedded with algal stromatoli tes gressions during the Middle Triassic, Middle and at the top. The lower unils of the sequence con Late Jurassic, Aptian and Cenomanian. As we shall sist of clean, multicoloured, coarse grained, trough see later, recognition of these events by utilizi ng cross-bedded sandstone containing vertebrate bone modern concepts of sedimentology and stratigraphy fragments, and vari egated shale and siltstone with was used with great effe ct in solving endemic geo plant remains. Palaeocun-ent analysis of the sand logical problems in North Afri ca and Egypt, such as stone fa cies suggest a domi nant north and northeast the Nubian Sandstone problem. transport di rection (Karcz and Zak, 1968). Up sec tion the cross-bedded sandstone units are overl ain by Triassic a succession of sandstone, shale, limestone and marl with Middle Triassic ammonite Ceraliles (Awad, The Late Carboni fe rous coll ision of Gond wana 1946). T he carbonates consist of skeletal wacke wi th th e northern continents resul ted in upl ifting of stone and grainstone gradi ng upwards into ooskeletal central and sOllthern Egypt and the development of packstone, mudstone and dolomites with algal stro an east- west trending basin to the north (Klitzsch, matolites. These in turn grade into dolomitic shal e 1984; Kli tzsch and Wyc isk, 1987). The occun-ence and anhydrite (Jenkins, 1990). of Tri assic deposits is restri cted to northern Egypt, The sandstones and shale were interpreted as be Sinai (Fig. 8), and northeast and northwest Libya in g deposited in a marginal marine estuarine-tidal (Shelmani et al. 1992, fi g. 3). [n these areas, de fl al- beach complex. T he limestone development in positi on of the Triassic seq uence was a result of the sequence suggest increased carbonale produc gradual transgressio n, where depositional facies di Li vity due to marine transgression and reducli on of achronollsly change both laterally northward and siliciclasti c influx into the basin. The occurrence of verticall y across the Permo-Triassic time line, from evaporites algal stromatolites, and dolomitic shale continental sandstone and shales to marine lime at the top of the sequence, on the other hand, sug stones and marl s. Most of the marine sediments were gest lermin al progradation of lagoonal and peritidal dated as Middle Triassic; th e Permian if present , is deposits over the hi gh energy, marginal marine car mostl y continental. bonate sand bodies. South of Sinai and along the Gulf of Suez the Permo-Triassic sequence constitutes a fluvial suc Jurassic cession. It consists of a fining-up cycles with basal lag of well-rounded ve in-quartz pebble conglomer The east-west trending Hercyni an upli ft ceased ate, overl ain by mid-channel trough cross-bedded, to dominate central and southern Egypt in Early and moderate ly well sorted sandstone and over-bank Middle Jurassic time (Kli tzsch, 1986; Schandelmeier mudstone. Some cycles may exhibit well developed et aI. , 1987). During Late Jurassic ( 145- 132 Ma) re soil hori zons at the (Op. Palaeocun-ent measure activation of the Palaeozoic NNW- SSE trending ments suggest NE and ENE fl ow directi on (Darwish, basement configuration took pl ace and dominated 1992). Locall y, greeni sh laminated kaolinite lenses sedimentation throughout the Mesozoic. These were up to 5 m thick occur within the sequence and are associated with continu ed extensional and strike interpreted as lacustrine deposits (Bhattacharyya et slip sini stral tectonics between Afri ca and Eurasia 56 A .S. EL HAWAT 28 J: (!) ::::J 24° J: 0 a: JABAL CI) f- UWEINAT ~ 22 S,O EROSION ~O 22° ~ OPEN MARINE --- JURASSIC SHORELINE SHALLOW TRANSGRESSION PALEOCURRENTS OF IN APTIAN TIMES EARLY CRETACEOUS REGRESSIVE OEPOSITS ALLUVIAL DEPOSITS EARLY CRETACEOUS Fig. II . Pal:lcogcography of Late Jurassic-Early Cretaceous and Aptian transgression (compiled aflcr Klit7..sch and Wyc isk, 1987: Van HOUien ct 31.. 1984). (Smi th , 197 1), in conjunction with alkaline magma stages of breakdown and coll apse of Sirt-Tibesti up tism in Egypt (Meneisy, 1990). li ft was taking place and leading to the development During the Mesozoic, the structural configura of Sirt rift system during Late Jurassic. ti on and physiographic features of th e basement The marine Jurass ic transgre ss ion in Egy pt of Egypt we re not pronounced, allowi ng success ive did not advance south further than latitude 29"N tran sgressions and regressions to take place over (Fig. II ). Jabal Maghara of northern Sinai offers th e wide areas (Schandel meier et aI. , 1987). These fea best Jurassic secti on in Egypt (AI Far, 1966). The tures extended westward s into Cyrenaica platform sequence has a maximum thi ckness of 1980 metres of northeastern Libya. North of this area , however, and consis ts of three major silic iclastic-carbonate cy Cyrenaica trough was subsiding at a faster rate in cles that extend from Earl y to Late Jurassic (Jenkins, response the extensional forces exerted during the 1990). The lower cycle is silicicl astic-dominated, opening of the Medi terranean Tethys. Sedimenta the remain ing cycles are arranged in an upwards tion in the trough was dominated by bathyal debris increasing th ickness and carbonate content. Each de now deposits and turbidites through out the Juras posi ti onal cycle consists of basal sandstone, shale sic and Early Cretaceous (Klitzsch, 1970; EI Hawat and occasional coal, overlain by limestone whi ch and Shelmani, 1993). Further to the west, the initial marks the climax of marine tra nsgressions during SEDI MENTARY BASINS OF EGYPT: AN OVERVIEW OF DYNAMIC STRATIG RAPHY 57 Early, Middle and Late Jurassic times respecti vely. during earl y Mesozoic continued to influence the These fac ies represent ftu via-deltaic, marsh and near North Afri can contin ental margin durin g Earl y e re· shore clasti c sedimentati on, fo ll owed by open ma taceous times. Sedimentary basin s of the south were rin e neriti c depos iti onal conditions associated with subjected to epeirogeni c movements of fa ult blocks max imum transgression. The upper part of the Late and main tained subs idence. These tectoni c activi Jurassic carbonate-dominated cycle (Masaj id Fo rma ties were responsible fo r sustainin g regressive fl uvial tion) consists of coralline and stromatoporoid patch siliciclastic sediment influ x in these basins. The bal reefs associated widl skeletal debris and oolitic shoal ance of this regressive depositional style was briefl y fac ies. Larerall y, however, the Jurassic sequence altered during a transgressive eustatic event during fo rms a series of parallel facies belts anoanged from the Aptian. These tectonic acti vities were also re south to north into siliciclasti c flu vial and margin al sponsible for the development of new depocentres marine fac ies, shall ow marine shelf carbonates and and maintaini ng subsidence al ong the old er ones on shelf margin reefs and ooids shoal complex. These the unstabl e peri cratoni c margin area of northern grade northwards in the MeditelTanean offshore into Sinai, the Western Desert and northeast Li bya. The deep marine carbonates (Jenkins, 1990, fi g 19.7). new depocentres include Matruh and Abu Gharadi g Regardless of the difference in nomenclature basins in Egypt (Fig. 12) and Sin rift basin in used, the Jurassic secti on in the subsurface of the Libya. Western Desel1 maintains the same lateral north south fac ies pattern and vertical cycli city as in Neocomian-Barremian. South of the Western Sinai. Hantar ( 1990), however, reported that th e Deselt, in the subsurface of the Dakhla basin , Early Jurassic cycle (Bahrei n Fm.) in the Western Wycisk (1987) recogni zed a 50-80 m secti on of Desert is dominated by continental clasti cs whi ch fl uvial deposits possibly of Neocomian age di passes laterall y and upwards into marginal marine rectly underl ain by Late Jurassic sand stones, and clastic (Khatatba Fm.) and foll owed by mixed clas is overl ain by flu vial sandstones sequence of pre ti c-carbonate facies (Wadi Atbrun Fm .) of Mi ddl e Apti an age. The Neocomi an- Barremi an sequence Jurassic cycle. These change northwards and up· was designated as Six Hill s Formation by Barthel ward s into the Late Jurassic carbonate-dominated and Bottcher (1 978) for expos ures on the southern cycle (Masajid and Sidi Barrani Fms.) . margins of Dakhla and tbe Upper Nile basins. In Elsewhere, in the Western Desert and west of the southwestern Egypt the sequence consists of 100 to Ni le Delta, the Faiuym Basin was the most promi 500 m thi ck sandstones, un conform abl y underl ain nent Jurassic basi n on the un stable pericratoni c area. by penepl aned crystalline Precambri an basement or In this basin Awad (1 984) reported the occurrence Palaeozoic rocks (Klitzsch et aI. , 1979). of 2290 metres of Jurassic secti on in the subs urface. The Six Hill s Formation forms a succession of The Early Jurassic sequence consists of 360 m thi ck finin g-up cycles of ill sorted, medium to coarse sandstone and shales of littoral affi li ation fo ll owed grained sandstone, grading upwards into white, mas by 1400 m thi ck shale sequence suggesting increased sive, mottled kaolinitic sandstone wi th well devel basinal subsidence during Middle Jurassic. The Late oped soi l hori zons showi ng root casts. The sandstone Jurassic, however, is charac teri zed by a 500 metres exhibits large scale tabular planar cross·bedding sets thick shall ow marine carbonate-dominated sequence. separated by conglomeratic layers of quartz pebbles. FUJ1her to the south on the stable craton, the Dip direction of cross-bed foresels suggest 1100th Earl y and Middle Jurassic sections are mi ssin g due east to nOlthwest dispersal pattern s. Fossils found to the residual effect of the Hercyni an structure and in these rocks are mainl y silicified wood fragments. erosion. The Late Jurassic sequence, however, was These fac ies were deposited in flu vial-dominated, fo und in a restri cted area in the sub surface of Dakhla fl ood-pl ain environment in sli ghtly sinuous channels Basi n (Wycisk, 1987). Thi s sequence consists of (Klitzsch et aI. , 1979; Hendriks et aI. , 1984). Further 200 m thick flu viatile sandstone that passes laterally to the south of Egypt, the base of the formati on to the north into an alternation of sandstone and consists of conglomerates that, also, indicate depo mudstone of shallow marine ori gin . The geographic sition under terrestrial conditions. Sediments at the di stribution of sequence suggests deposition in a top portion of the sequence are generally diffe rent. rapidl y subsiding embayment with opening to th e They fo rm a fi ning upwards sequence and exhibit north along AI Mesaha trough. a notable improvement of textural characteri sti cs. These features, together with the occurrence of oc Cretaceous casional burrows and Teredo borings in silicified wood, suggest marginal marine influence at the top Early C retaceous of the sequence (Kl itzsch et aI. , 1979; Hendriks The Tethyan extensional tectonics and associated et aI. , 1984). This fo rmation is equi valent to the sini stral strike-slip movements which were in itiated lower sandstone, flu vial-dominated, member of th e 58 A.S. EL HAWAT 32 MEDITERRANEAN SEA Bosin Sedimenf Thickness • -z > 1.5 km //111 > 2.0 km /lIlt RED SEA 26 Fig. 12. Eurly Cretaceous dcpoccntrcs in northern Egypl (after El Gczeery cl aI., 1972, 1975). tripartite subdivision of the Nubian (Sarir, Calanscio, an important reservoir in Al Alamain field and Faragh) sequence of southeast Sirt basin of Libya other oil fields in the Western Desert. It consists (EI Hawat, 1992; EI Hawat et aI., 1997). of lower limestone and upper dolomite units that In the subsurface north of the Western Desert the are skeletal, oolitic and contain orbitulines, Bryozoa, Early Cretaceous sequence is referred to as Burg echinoids and other fossils (Soliman and EI Badry, EI Arab Formation. The lower part of formation 1970). consists of sandstone (Alam EI Bueb) and shale Further south, these carbonates grade into the (Matruh) members of Neocomian-Aptian age (Han Aptian Abu Ballas Formation. This- formation is tar, 1990). The sandstone forms a coarsening-up clastic-dominated marine sequence which reaches a sequence as it grades up from shale units at the base. maximum thickness of 250 m at the centre of the It is overlain by limestone units at the top. These Dakhla Basin. On the periphery of the basin, the Abu marginal marine facies changes southwards into flu Ballas Formation is over 20 to 45 m thick and con vial-dominated deposits of the Six Hills Formation sists of five superimposed facies arranged in a sin and passes into carbonates to the north. The shale gle, coarsening-up, transgressive- regressive deposi member is dark, calcareous, pyritic and contain lig tional cycle (Hendriks and Kallenback, 1986). The nitic layers suggesting deposition in marginal marine basal facies of this sequence is multicoloured, lam marsh conditions. These shale facies are limited in inated, massive and bioturbated mudstone, rippled their distribution to Mersa Matruh area. siltstone and cross-laminated fine grained sandstone. It contains brachiopod (Ligula sp.), pelecepods gas Aptian. The Aptian was a time of transgres tropods, and Rhizocorallium sp. burrows. Reworked sion in Egypt (Fig. II) and Libya. The sequence mud conglomerate found in this facies suggests pe of AI Alamain Formation which was encountered riods of high energy storm activities. The basal in the subsurface of the northern Western Desert facies grades upwards into varicoloured siltstone and consists of two members. The lower clastic-dom fine-grained sandstone exhibiting cross-lamination, inated member develops a gradational relationship ripple laminations and herring-bone cross-bedding with the underlying Neocomian-Barremian clastics. in channels. Siltstone intercalations may contain It grades upwards into an upper, widespread car plant fossils and exhibit desiccation cracks. The bonate-dominated member (Abdin and Deibis, 1972; upper part of the sequence is coarsening-upwards EI-Zarka, 1983). Alamain Formation, however, does sandy units alternating with rippled and bioturbated not extend further south than latitude 29"N which siltstone. These facies were deposited in a beach marks the limit of carbonate sedimentation dur back shore environment which was possibly influ ing the Aptian transgression. This member forms enced by tidal and longshore currents (Hendriks and SEDIMENTARY BASINS OF EGYPT: AN OVERVIEW OF DYNAMIC STRATIGRAPHY 59 Kallenback, 1986). Abu Ballas Formation is discon 70 m of cross-bedded sandstone deposits of fluvial, formably overlain by fluviatile facies of th e Albian fluviomarine and coastal origin. These are laterally Cenomanian, Sabaya Fonnation. equivalent to Six Hills and Abu Ballas formations Abu Ballas Formation is also exposed in the up (Klitzsch and Wycisk, 1987). Abu Ballas Formation per Nile basin to the east (Hendriks et aI., 1984). is equivalent to the middle sandstone member and its The geographic distribution of the formation sug lateral variegates shale facies in the Nubian sequence gests, a shallow Aptian marine transgression cov of Sirt basin, Libya. The Aptian eustatic sea-level ering most of Egypt, except for the basement high rise led to reworking and sedimentation of the mid areas (Fig. II). Abu Ballas facies also suggests that dle sandstone member along E-W trending, fault the southern edge of the Tethys reached a maximum controlled inlets which were cutting ill NNW- SSE water depth of about 20 metres (Bottcher, 1982). trending basement hi ghs in the basin. The resulting In Gilf Kebir area, southwest of Dakhla basin, the lowering base level of equilibrium led to deposition Gilf Kebir Formation, which rests unconformably of the variegated shales in the marginal troughs of on the crystalline basement (Fig. 13), consists of the basin (EI Hawat, 1992; EI Hawat et aI., 1997). f me eor,g. f m e e ong. I I I A m I I I I I , B ««Zz ... --Zo 0« BRAIDED 0::- COASTAL PLAIN =>Z STREAMS en AND DELTA 1-8 => LOW SINUOSITY 0 Z t ILl CHANNELS 0 « « 0- I- « TIDAL FLAT ILl ESTUARY 0:: -Z 0 0 0 0:: I 100 ILl a. Z Z BRAIDED a. « e:( :::) -Z - STREAMS 0 al 0:: :::) --l l- ~ CERATODUS e:( >I!J ~ TIDAL FLAT LAGOON AND Z INOCERAMUS SHALLOW MARINE ~70 , ILIZ SAND BODIES I-e:( 'i!l FERR1GENOUS OOLITE NEAR SHORE If) => BARS - I 0 - - t!:!t Z ILl - - SPONGELIOMORPHA 0 W « « ~ - I- ILl I- " 0:: FLUVIAL LOW a. 0 SINUOSITY AND e:( 0:: Z TIDAL ILl PALEOSOLS e:( 10 .. CHANNELS - 0== al + --l --l BRAIDED e:( 0 STREAMS V A _ BASE ME Fig. 13. Lower-Upper Cretaceous sections in Gilf Kebir area SW Dakhla Basin (A) and the Upper Nile Basin south of Aswan (B) (compiled after Klitzsch and Wycisk, 1987; Van Houlen el al., 1975). 60 A.S. EL HAWAT Albian. Following the Aptian transgression , and and upper Nile (Van Houten et aI., 1984). The upper before rhe onset of the Early Cenomanian transgres sandstone member of the Nubian sequence of Sirt sion, continental sedimentation dominated the Al basin is also regressive. They are associated with bi an in Egypt. In the intracratonic basins of southern volcanic rocks and cun"ent transported pyroclastic Egypt. however, contin ental sedimentation was ex deposits (EI Hawat, 1992; EI Hawat et aI. , 1997). tended to Early Cenomanian, as the Late Cretaceous In the Gulf of Suez basin, the Early Cretaceous transgre ssion reached the Dalchla and upper Nile Malha Formation which is exposed on the west side basins duri ng the Late Cenomanian. Basaltic layers of the gulf is 50- 100 metres thi ck and consists of associated with these deposits give dates ranging continental to shallow marine sandstone and shale from 84 to 100 Ma (EI Shazly, 1977) and suggesting of Urgo-Aptian age (Abdall ah et aI., 1963; EI Sha that sedimentation during the Albian was associated zly, 1977). However, on the eastern side of the gulf with intense tectonic activities and rejuvenation of this formati on is thought to be of continental origin fau lt move ment. and of Albian age (Bhattacharyya and Dunn, 1986). The Albian sequence encountered in the sub In this area the Albian sequence consists of basal surface of the northern Western Desert develop a polymictic conglomerate containing angu lar to sub coarse ning upwards cycle of sedimentation overlay rounded chert, jasper, volcanic rock fragments and ing the Alamain carbonate unit. The cycle consists vein quartz pebbles, associated with poorly sorted of basal greeni sh gray shale, siltstone and sandstone kaoliniti c sandstone. It is thou ght that conglomerate interbeds (Dahab mem.). These grade upwards into clasts were derived from the nearby basement source (Kharita mem.) fine to coarse grained sandstone, as a result of uplift of the basement fault blocks (Van subordinate shale and carbonate interbeds that in Houten et aI., 1984). In the subsurface of central crease in thickness to the northwest (Hantar, 1990). Sinai the upper portion of 520 metres thick sequence To the south, on the eastern edge of the up of sandstone interbedded with shale has yielded per Nil e basin, the Albian- Cenomani an sequence corals and ammonites of Albian age (Jenkins, 1990). rests unconformably on deeply weathered Precam This sequence passes further to the north of Sinai brian clystalline basement. It consists of 30-100 m and the Mediterranean offshore into east-west trend thick, very coarse, pale yellowish to brownish gray, ing shelf margin carbonates consisting of oolitic and kaolinitic quartzose sand stone arranged in lent icu bioclastic limestone facies grading into deep marine lar fining up units with basal lag of angular quartz shale in the offshore area. pebbles (Ward and McDonald, 1979; Van HOUlen et aI., 1984). The sandstone often grades upwards Late Cretaceous into paleosols of mottl ed kaolinitic sandstone show The Late Cretaceous was a lime of a major ing vague roots and ferruginous nodules. Trough change in the depositional and tectonic hi story of the cross-bed sets indi cate westward flow direction from North African basins because of contemporaneous the basement highland of the present day Red Sea global tectonic and eustatic events. Basin develop (Fig. II ). Locally, however, cross-beds may indicate ment and sedimentation were influenced by three south to southwest flow directions due to the pres major factors, these are: (a) continued influence of ence of local highs. Elsewhere, in the upper Nile the NNW -SSE basement structural trends; (b) the and Dakhla basins palaeocurrents suggest northeast collision between the Afri ca and Eurasia; and (c) the and northwest flow directions away from basement global Late Cretaceous eustatic sea-level rise. hi ghs (Klitzsch et aI., 1979). These sediments were The NNW -SSE basement structural elements con deposited in low sinuosity braided stream systems tinued to control basin development as during the associated with abundant development of paleosols Early Cretaceous. These structural elements were en (Ward and McDonald, 1979; Klitzsch et aI., 1979; hanced by increased differential movements and in Van Houten et aI., 1984). creased basinal subsidence during Late Cretaceous Similar facies belonging to the Sabaya Forma (Klitzsch, 1986). Meanwhile, the extensional tecton tion was described from other parts of the upper ics and the associated sini stral strike-slip movement Nile (Hendriks et aI., 1984) and the Dalchla basins, which was associated with opening of the Mediter where it reaches a maximum thi ckness of 200 metres ranean Tethys during early Mesozoic was terminated. and rests di sconformably on the Aptian, Abu Bal These tectonic movements were reversed and re las Formation. All Authors emphasize the illsorted placed during the Late Cretaceous- Palaeocene time nature of the Albian-Early Cenomanian fluvial de by compressive and dextral shear movements con posi ts and the occurrence of paleosols in southern temporaneous with the opening of the north Atlantic Egypt. The diverse paleocurrents directions and the (Smith, 1971 ). In Egypt, these tectonic reversals were evidence of volcanic activities associated with thi s associated with magmatism which were dated from facies are indications of reactivation of basement the Albian to Campanian (I00-80 Ma) and peaked highs surrounding the intracratonic basins of Dakhla during the Turonian (90 Ma) (Meneisy, 1990). These SEDIMENTARY BASINS OF EGYPT: AN OVERVIEW OF DYNAMIC STRATIGRAPHY 6 1 26 28 32 ,. Mediterranean Sea '0 Abu Gharadig Bosin Sed iment Thickness > 1.5 km 1111 .-•- w-- 28 > 2.0 km ## z Red Sea Fig. 14 . Lale Cretaceous depoccnlres in northern Egypt (after EI GC7.cery Cl al., 1972. 1975). tectonic changes have led to the subducti on of the in northern Egypt during Early Cenomanian, and Tethys oceanic cru st and th e inversion of tile subsid reached the south during Late Cenomani an. The in g pericratoni c bas ins of Egypt into structural hi ghs Cenomanian sequence north of the Western Desert ex known as the Syri an Arc fold system. In Cyrenaica hibits a wide variation in thickness and lithology. Car it was responsibl e for the invers ion of the prev iou sly bonates were dominant in the northeast, but changed subsiding trough of AI Jabal al Akhdar into structural westward in to shale, and southward into sandy fac ies hi gh (EI Hawat and Shelmani , 1993). (Soliman and EI Badry, 1970). These deposits attain a These new tectonic condi tions have infl uenced maxi mum thi ckness in the subsurface in the depocen basin orientation throughout northern Egypt during tres of the Abu Gharadig (900 m), and Fai yum basins Late Cretaceous. The eastern basins in Sinai , the (J 154 m). Such thickness, however, decrease to 140 Gulf of Suez and the lower Nile (Gindy) basin were metres over structural hi ghs separating these basin s oriented in NNW- SSE direction foll owing the trend (EI Zarka, 1983; Awad, 1984). In surface exposures of the ri sing basement hi gh of the Red Sea. Basins of and subsurface sections the Cenomanian sequence the Western Desert such as Abu Gharadig, Faiyum form s a single clasti c-carbonate cycle th at suggests and other smaller basins were ori ented in NE-SW progressive increase of marine influence through direction (Fi g. 14). Also, tectonic reactivation of tim e. Th e basal tran sgressive sandstone is coarse faults, and the global marine transgressions were to fine grained calcareous and often glauconitic. In combined to produce a thick accumulation of Late places, it is variegated, friable. cross-bedded and may Cretaceous sediments in most of these basins. The contain foss il s of Exogyra, Os/rea as well as ve rte role of the Late Cretaceous eustatic sea-level ri se brate remains. It is often associated with carbona was not onl y important in covering the Afro-Nubian ceous, pyritic, fossiliferous shale. These sands and craton by marine water. It has also altered the sili shales were deposited in estuarine and shallow ma ciclastic depositional system which was domi nant rine environment (Allam, 1986). The clasti c sequence since the Palaeozoic, into carbonate-dominated sys grades up wards into oolitic, and bioclastic grain tem. The latter system lasted until the Oligocene stone and mudstone sequence whi ch is interbedded time when crustal tectoni cs reversed the depositional in places with anhydrite and chert (Soliman and EI regime through out North Afri ca to siliciclastic sedi Badry, 1970). These suggests deposition in a shall ow mentation yet again. marine, near shore intertidal and supratidal setting. The Cenomanian in the Gulf of Suez basin, forms Cenomanian, The Cenomanian in Egypt was a up to 300 m thick sequence at the centre of the time of major transgression (Fig. 5). Sedimentary present day Gulf, which coincides with a NW -SE records indicate that marine conditions has prevai led trending embayment (Kostandi, 1959). In central 62 A.S. EL HAWAT Sinai, the Cenomanian sequence consists of lagoonal ruginous nodules. The upper portion of the sequence to marginal marine shales and marls ri ch in oyster consists of a se ri es of coarsening-up cycles of lam banks, that grade nOithwards in the subsurface into inated claystone with plant remains, rippled silty 326 metres of interbedded carbonates and shales. clay and cross-bedded sandstone. Cycles are over Further to the north of Sinai the sequence is dom lain by bioturbated ferruginous sand stone or ool itic inated by dolomite and dolomjtic limestone which chamosite and haematite. Locally, phosphate pebble was deposited over a very broad shelf of restricted conglomerate and Late Cretaceous shells of Illoce circulation. These depositional areas change towards ramus are found. Van Houten and others (1984) the Mediterranean offshore into deep marine shale documented a reversal of palaeocurrent dispersal of Albian to Santonian age (JenlOns, 1990). The patterns in this palt of the sequence, to northeast and Cenomanian seq uences may exhibit a variable thick northwest (Fig. 13). They concluded that foll owin g nesses through ou t Sinai due to subsequent tectonic the initial transgression, marshes and coastal plain movements and erosion during the Turonian. depositional conditions had prevailed. These were To the south of Egypt in Dakhla and Up fo ll owed by progradation of ool itic ironstone-capped per Nile basins, the Late Cenomanian marine se sand bodies which were developed in the marine em quence (Maghrabi Formation) rests on the under bayment of Aswan during the peak of tran sgression lying Albian-Cenomanian (Sabaya Formation) with (Fig. 9). The Cenomani an fossils and sediments in an erosional surface marked by well developed pale dicate warm, humid to semi-humid climate, low tidal osol (Hendriks, 1986). In Dakhla basin the sequence range and weak wave energy. These conditi ons were consists of massive claystone, alternati ons of mud suitable for lateritic weathering and development of stone, siltstone an d fine-grained sandstone associated iron rich deposits (Hendriks, 1986). with occasional intraformational conglomerate, and cross-bedded sandstone filled channels. Sand, silt Thronian-Coniacian. The Turonian-Coniacian and shale are often arranged in fining-up, as well sequence in Egypt is represented by a regressive as, coarsening-up cycles. These exhibit bioturbation transgre ssive subcycle within the overwhelmi ng Late structures, and root casts, and are often associated Cretaceous transgression. The Turonian regression with coal beds, vertebrate remains and brachiopods was a resu lt of global tectonic events associated with (Lingula sp.). Sedimentary stru ctures of the sand volcanic activities and in trusions of alkaline vol stone filled channels indicate north to northeast canic rocks, the peak of which was centred at 90 sedim ent transport direct ion. The lateral and vertical Ma in Egypt (Meneisy, 1990). During tlUs time, Abu arrangements of these facies suggest a prograding Gharadig and Matruh basin s were the main centres supratidal, intertidal and subtidal facies areas asso of deposition in northern Egypt. These broad de ciated with an estuarine channel system (Hendriks, pocentres were oriented in NE-SW direction in re 1986). The sequence of Magharabi Formation also sponse to the progressive influence of the Laramide suggests that the Late Cenomanian transgression was orogeny and the development of the Syrian Arc fold foLlowed by progradation and regression in southern system (Fig. 16). Epeirogenic movements along NE Egypt, a possible prelude to the subsequent Turonian SW trending Kattanyia-Mubarak high, separated Abu regression. Elsewhere, on the southern margin of the Gharadig bas in from its eastern extension of Faiyum basin, tidal deposits are associated with small deltas, basin, where each of these basins received up to 1000 and muddy flood plains facies (Klitzsch, 1979). m and 880 m of Turonian-Coniacian sediments suc The Late Cretaceous transgression also reached cessively (Awad, 1984; EI Zarka, 1983). Sedimenta the Upper Nile basin during the Late Cenomanian. tion in these depocenrres was characterized by [he oc In the vicinity of the city of Aswan the sequence CUITence of repeated cycli c successjon of sandstone, is 30- 40 m thi ck (Fig. 13). [t pinches out towards carbonaceous shale, and fossiliferous carbonates. Re the basin margin (Fig. 15 ), as it grades into fluvial gionall y, northeastern Egypt including the Ni le Delta deposits in the direction of basement highs (Van region, ha s received a lesser amount of sediments Houten et aI., 1984; Ward and McDonald, 1979). in comparison to other depocentres. These relatively The lower palt of the sequence rests on the Al high palaeotopographic areas were si tes of extensive bian nonmarine sequence with a sharp to erosional carbonate accumulation including rudistid and coral basal contact, and forms succession of sand stone and reefs (Soliman and EI Badry; fig. 10). mudstone exhibiting an upwards decrease in grain The NW-SE trending embayment of the Gulf of size. The sandstone is coarse to medium grained, Suez basin, on the other hand, was maintained dur planar cross-bedded and is extensively bioturbated. in g the Turonian. The Early Turonian open marine Palaeocurrent measurements suggests southeast and section of (Abu Qada Formation) extended along the southwestern di spersal directions (Fig. 13B). The as same trend, but the Late Turonian (Wata Formation) sociated mudstone, on the other hand, is red to gray transgressed further south over an irregular topog coloured and forms mottled paleosols containing fer- raphy (El-Shinnawy and Sultan, 1972). [n Simu the SEDIM ENTARY BAS INS OF EGYPT: AN OVERVIEW OF DYNAMIC STRATIGRAPHY 63 MEDI T ERRANEAN SEA E Open to Shallow Oolitic F. Deposits Marine Marginal Morine E Erosion Coastal Pl ain Fluvial Palaeocu rrents lIillJ And Soil For mati on Fi g. ! 5. Palaeogeography during th e Cenomanian lran sgre ss ion (compiled after Van Houten ct aI., [984; Kli lzsch and Wyc isk. 1987). Turonian sequence consists of shale. marl and sand In the intracratonic basin s of southern Egypt, the stone changing into uniform wel l bedded limestone Turonian (Taref Formation) is 110 to 200 m thick and dolomite. These deposits represent inner shelf clasti c-dom in ated sequence . It ex hi bits an erosion and restri cted marine peritidal and sabkha sedimen basal contact showing deep scours cutting into the tation in central and northern Sinai. These deposits underlying Cenomanian (Klitzsch ot aI. , 1979; Ward change into deep marine fac ies in the offshore area and McDonald , 1979; Van Houten et aI. , 1984; (J enkins, 1990). The overl aying Coniacian depo Hendriks, 1986). Above the di sconformity, the basal sitional sequence, on the other hand, develop a unit of the sequence consists of conglomerati c, felds well defi ned facies belts because of the ascent of pathic sandstone W i~l qualtz pebbles and intraform a structurally controlled topographic features after the tional mud clasts and oolitic ironstone (Van Houten Turonian tectoni c events. The Coniacian sequence et aI. , 1984). The sequence is followed up by a consists of fluvi o-estuarine cross-bedded sandstone success ive series of fining-up, cro ss -bedded medium interbedded with variegated clays , and marls as soci to coarse-grained sandstone that ex hibit north and ated wi th oyster beds. These change northward into northwes t di spersal trend s (Fig. 16). The sa nd stone medi um to coarse grained glaucon itic and bioclas grades up iI1lo argi llaceo us sand stone exhibi tin g oc tic limestone grading into cro ss-bedded ooLi tic shoal casional paleosols or bioturbation. The upper part of compl ex in central Sinai (Lewy, 1975). Further to the sequence, however, consists of better sorted, finer the north these facies change into outer shelf, chalky grained sandstone, rippled siltstone and bioturbated li mestone and marl s. mudstone (Fig. 13B). The textural and mineralogical 64 A.S. EL HAWAT E ERO S ION E I$,tf! Open Marine E Erosion Of Uplifted Areas ~ Shallow Marine Alternating With Alluvial Deposits X Uplifted Folds /' Palaeocurrents, Alluvial Deposits Fig. 16. P:.llaeogcography of Coniacian to Campanian (compiled after Klitzsch :l11 d Wycisk, 1987; Van Houlen el al. , 1984). immaturity of the rocks at the base of the sequence onian. tectonics and sedimentation during the San suggest sudden influx of clasti c sediments as a re tonian was not associated with major magmat ism. sult of upli fting of source area (Van Houten et aI. , however, loca l volca ni c oli vine basalti c flo ws dated 1984). The upwards increase in textural maturity and as early Campanian (78- 84 Ma) were reported from decrease of grai n size suggest deposition of a pro Jabal Uweinat area (Menei sy, 1990). During this re grad in g all uvial plain, delta and tidal flat deposits, gressive phase the sea occupied onl y the deep basi which a resul ted from a progress ively waning clastic nal areas north of the Western Deserl. Depositi on in influx (Klitzsch et ai., 1979; Ward and McDonald, these basinal areas were dominated by fine-grained 1979; Van Houten et ai., 1984). The Turonian in the limestone, chalk and shale under restri cted euxinic intracratonic ba sin s is followed by a hiatus extending marine conditions. from the Coniacian to Early Campanian (Hermina, Because of the effect of the accelerated deve lop 1990, fi g. 14.3). It is attributed to the upliftin g of ment of the Syrian Arc fold belt, the NE- SW struc southern Egypt and development of the Syrian Arc tures in Bahari ya and Siwa oasis became pronounced. fold system further to the north. Near structural highs the Santoni an sequ ence is mi ss ing and the Campani an is often found unconformably Santonian. The Santoni an time was th e second overl ay ing the Cenomani an (Soliman and EI-Badry, phase of regressive events after the Turon ian wi thin 1970). On the Qattarah ridge nonh of Abu Gharadig the Late Cretaceous transgress ion. Unlike the Tur- basin , in the subsurface, the whole Mesozoic se- SEDIM ENTARY BASINS OF EGYPT: AN OVERVIEW OF DYNAMIC STRATIGRAPHY 65 quenec is mi ssing due La erosion and non depo The Late Campanian phosphatic sequence (Duwi sition , and the Cenozoic rocks rest unconformably Formation of Youssef, 1957; Rakhlyat Formation of on Ihe Palaeozoic (Awad. 1984). The Santoni an se Hendriks and Luger, 1987) of south Egypt are lo quence however, is fOlllld in nea rl y all orthe northern cated in a belt extend ing from the Red Sea to Oakhla basi 11 $ of the Western Desert. At the centre of the basin (Fig. 17). Phosphati c beds are associated wi th Abu Gharadig and Faiyu lll basin s, a thick accumula organic ri ch shal e and claystone that conta in variable tion of the Santonian deposi ts res ts conformab ly on amounts of di spersed phosphatic pe ll ets, nodules th e Turonian. These deposits consist of calcareous and fi sh remain s. Erosional scou rs and smail chan and carbonaceous pyritic shale thal grades upwards nels found in the shales are fi ll ed by glauconitic and towards the basin margin into chalk and organic sand stone and phosphate. These shal es al so co ntain carbon-ri ch limeston e. These facies suggest deposi lenticular, low-angle cross-bedded and rippled ph os tion in an outer neritic environment of restricted cir ph ate bodies, large sand bars and dunes. On the cu lation whi ch gave rise to euxinic co ndi tions. Ac Red Sea coast, where it was a palaeohigh, phosphate cording to Soliman and EI-Badry ( 1970, fig. 13), the bed s are assoc iated with oy ster reefal li mestone that area north of Dakhla and Upper Ni le basin s was the changes towards the centre of the Upper Nile basin main depocentre during the Santonian, where si lici in to organi c ri ch shale. I t is thought tha t phosphate clastics were dominant. M ea nwhile, carbonates dom nodul es and l:>e ll e(s were fi rst originated as a result inated deposition in higher areas of the Nile Delta of precipi tation of collophane from imerstiti al water area and northwestern Egypt. in mud wh ich was deposited in a quiet wa ter under ano xic condi ti ons. These pe ll ets were later reworked Campanian-Maastrichtian, During the Earl y and shaped into sand bodies by bottom currents and Campanian Egypt was still under the influence of the during storms, or durin g pe ri od of lowered sea leve l San toni an regre ss ive phase. Therefore, the Late Cre (Garrison et a I. , 1979; G lenn, 1979). taceou s transgression was not effectively resumed North of the Western Desert and locally in the until the Middle Campa ni an. Egypt was then cov sou thern basin s, the Late Campani an- Early Maas ered by an extensive shallow sea of partl y restri cted trichtian seq uence is marked by an unconformi ty circulation due to the occ urrence of a series of related to lCcto ni c ac ti vities. These we re assoc i islands to the north . T hese is land s constituted the ated with th e reac ti vation of the Syrian Arc tec NNE- SSW trending uplifted areas of the Syrian Arc tonic s, and the updom in g of the Red Sea high and fold system. Consequenliy, the prevailing oceano the accompanied rejuvenation of the Precambrian graphic condi tions led to the development of anoxic fault sys tem. Also, during thi s time, the co nnection geochemical environment ill which phosphatic sed i between the Upper Ni le and Dakhla basins was ments we re deposited during Late Campanian. establi shed as a result of tec tonic inversion and sub In Dakhla and Upper Nil e basins the Turonian sidence of Kharga Upli ft and marine tran sgression Coniacian is overlain unconformably by th e Middle (Schandelmeier et aI., 1987). These tectonic events Campanian (Quseir Formation or Mut Formation). were marked by the developm ent of syndeposi Thi s sequence form s a tran sgressive, fining-up depo tional mass fl ow depos its into the Upper Ni le basin. si tional cycle co nsisting of varicoloured claysLOnes, Subaqueous gravi ty inducing slumping, sli ding and siltsLones and occas ionall y conglomeratic very fine intraformational conglomerate are co mmonl y asso grai ned sand stone. Sandstones and mud stones are ciated wi th laminated gray calcareous silty claystone laminated, rippled, locally channell ed and exhibi t and thinly bedded clay siltstone showing small-scale trough and herrin gbone cross-bedded structure s. [ch fining-up and coarsening-up cyc les (Hend ri ks and nofossil s incl ude Dip/ocro/erion sp. and Tholossi Luger, 1987). l1oides. Fossil s include sili cifi ed wood, plant leafs, The Maastrichtian sequence (Dakhla Fm.) is 150 fi sh and other ve rteb rate remai ns that include di metres th ick seq uence of shale wh ich may extend nosa urs. These facies were depos ited in margin al in age to the Palaeocene. The Dakhla Fo rm at ion marine, tidal fl at and marsh conditions. These are consists of gray to white marls, lam inated clay overl ai n by bi olUrbated open marine, massive clay stone wi th silty intercalations. Shales may contai n stone, silty clay stone and glauconitic, phosph atic layers of intraformational conglomerate with phos sandstone of Late Campani an-Early Maastrichtian phatic nod ul es and verteb rate remains. Oysters and age (Hendriks et a I. , 1984; Hendriks and Luger, microfauna fou nd in th ese shal es indicate depositi on 1987). On the southern margin of the Upper Nil e in inner to middle shelf conditions. To the south and Dakhla basins the sequence consists of tidal nat of Dakhla and the Upper Nile basin, these shales deposits that grade iI1lo a success ion of flu viatile, change into deltaic and tidal flat estuarine clasti cs of flu viomarine, deltaic and open marine sand stone and Ki seiba Formation (Hendriks et aI., 1984, 1987). To shale fac ies of the lower part of Ki seiba Formation the north in the subsurface of the Western Desert, (Hendriks et aI. , 1984). these fa cies change into chalk and chalky limestone 66 A.S. EL HAWAT « o EROSION - /////1/ SHALLOW a OPENMARINE PHOSPHATE DEPOSITS @ UPLIFTED AREAS AND TEMPORARY EROSION Fig. 17. Palaeogeography of Maastricht ian \0 Lower Eocene (after Klilzsch and Wycisk, 1987). with abundant chert bands, and occasional shale beds Jurassic sequence is also transgressive in nature as (Khoman Fm.). The thickness of these chalks may it is c1 as ti c~ dol1l i na t e d at the base and is carbon vary fro m 1644 metres at basin centre to 20- 100 ate-dominated at the top. It refl ects the accelerated metres 0 11 structural hi ghs due to syndepositi onai rifting and drifting process leading to the opening tectonic movements of fa ulL blocks and active basi of the Teth ys. In northern Sinai and the Western nal subsidence (Hantar, 1990). These chalk fac ies Desert the Jurassic sequence is arranged in two extends eastwards into Si nai (Sudr Fm.). major depositional cycles exhibiting an increased marine influence th rough time. Each cycle ensues Geological events and sedimentation with deltaic and near shore clasti cs, and grades up into shale and shall ow marine limestones of Middl e The Mesozoic evolution and development of sedi and Late J urassie age. Evidence of the Jurassic trans mentary basins of North Afri ca and Egypt, fo llowing gression is not commonl y found in the cratonic areas the Hercyni an event, was a consequence of the break because of the residual effect of the Hercyni an uplift up of Pangea since the Triassic time. Cru stal move (Fig. 8) of central and southern Egypt. Late Jurassic ments associated with different phases of rifti ng and marine clastic sediments, however, were di scovered opening of the Atl antic ocean and the Tethys, and in the subsurface in the Dakhl a Basin restricted to eustatic sea-level changes have influenced tectoni cs Mesaha trough (Wycisk, 1987). and sedimentati on in the Egyptian basins. The Late Jurassic-Early Cretaceous (1 50-130 T he Tri assic is represented by a single transgres Ma) boundary in Egypt was associated wi th alka sive depositional cycle restricted in its di stribution to line volcani c acti vi ties th at coin cide with the initial northern Egypt due LO the residual influence of the opening of the Atl antic (Meneisy, 1990). T hi s time Hercynian uplift in southern Egypt. The foll owing was also associated with continued ri fting along the 68 A.S. EL HAWAT corresponds wi th the Cenomani an global sea level ment which led to the opening of the Tethys into rise (Va il et aI. , 1977). to compressional-dex tral shear tectonics resulted in Fac ies and events of the Early Cretaceous se the subduction of the Tethys oceani c cru st (S mi th, quence correlate well th roughout North Africa and 1971). In the intracratoni c basins of Egypt thi s event north of the Arabian shi eld (Va n Houten, 1980; Van led to a short epeirogeni c tectoni c ac ti vity on the Houten et ai., 1984). To the west of Egypt, in the craton and has led to reactivation of basement source southeast of Sirt basin of Libya, the fluvial-dom areas, causing clastic infl ux and creat ing a short in ated Early Cretaceous Sarir (Faragh, Calanscio) regressive pu lse. in otherwise, transgressive condi Sand stone sequence is intenupted by clean sand tions. The sequenti al wani ng of clas ti c influ x in stone uni ts. These sands exhibit sedimentological theses basins suggests resumption of ma rine trans and mineralogical attri butes consistent with marine gression duri ng the Conj acian time. The Turoni an and marg in al mari ne origin (EI-Hawat and EI Wor tectoni cs also was the cause for the development of fall i, 1990; EI Hawat, 1992; EI Hawat et aI. , 1997). the Syrian Arc system in the pericratonic area of The clean sand facies change laterally to the east northern Egypt and Sin ai. into Sh(lliow marine. lagoonal and lacustrine va ri e This tectonic event is also recognized through out gated shales of Aptian age (Viterbo, 1968). In the the North African basins. In offshore of Cyrenaica north west-southeast trending troughs forming the it was marked by a recognizabl e shall ow ing event in deep centre of Sirt basin , on the other hand , the the deep mari ne Late Cretaceous sequence (EI Hawat whole of the Early Cretaceous sequence changes and Shelmani, 1993). In Sirt rift basin of central into qu artzi ti c marin e sandstones rich in nan nofos Libya, the event is marked by restri cti on of marine sil s (Coccolith Fm. of Bonnefous, 1972). Whereas, condi tions in the margin al subbas in s and deposition these major troughs have acted as passageways for of a th ick evaporite sequence. Also, the Cenomania n the marine advance from the Tethys after the initial sequence in western Libya is terminated by a gypsif ri fting and coll apse of Sirt-Tibesti upli ft, sedimenta erous marl sequence representing a shall ow in g event tion in the marginal subbasin s was flu vial-dominated after the initi al transgression. Funher to the west, during the Neocomi an-Ban"emian and Albian tim es in Tunisia and in the offs hore area of Tripoli -Gabes respectively. During the Aptian eustatic sea-level bas in the Turon ian tectoni cs and associated changes rise, however, these subbas in s were flooded and in in sea-fl oor topograph y have led to the development fl uenced by marine water leadi ng to the deposition of anox ic co ndi tions and deposition of deep marin e of the middle sandstone and variegated shale un its carbonates wi th hi gh organi c carbon content. Thi s (EI Hawat, 1992; EI Hawat et aI. , 1997). Thi s trans anoxic fac ies are also reported to extend across the gression was often in terrupted by regressive events Medi terranean to Italy (Bishop, 1988). and sili cicl astic influ x generated from reactivation The second significant tectoni c event have taken of basement bl ocks of the young rift. In general, place duri ng the Santoni an. It was associated with depositional fac ies and events that resulted in the tri the openin g of the North Atl anti c and represents a partite subd ivision of the Earl y Cretaceous, Nubi an continuation to the Turonian event. In the so uthern sequence in Sirt basin are identical to those of th e basins of Egypt, the in tra-Senoni an unconformity Dakhl a basin . forms a hiatus extendin g fro m the end of the Turo nian to early Middl e Campania n. However, the San Late Cretaceous events toni an event was relati vely weaker than that of the [n contrast to the Earl y Cretaceous, the Late Turoni an as no significant magmati sm was reponed. Cretaceous sequence in Egypt was characteri zed by In north of the Western Desert bas ins the Santoni an an overall transgressive motif. Thi s transgression event was marked by a major regression, cau sed re was initi ated by the Cenomani an global eustatic activation of structural hi ghs of the Syri an Arc fold event, whi ch was continued at an accelerated pace system and res ulted in the deepening of depositional to peak during the Maas trichtian. However, thi s basins. In these bas in s marine conditions becam e transgression was significantly interru pted by two restricted and fin e grain limestone and chalks we re tectoni c events that left their record in the sequence. then deposited in anoxic organi c-m auer-ri ch condi These are the Turonian and the Santoni an tectoni c tions. North of Cyrenaica thi s event was associated events respectively. with shall owing, tectoni c inversion of Al labal al Meneisy (1 990) noted a general increase of al Akhdar trough and erosion . In AI Jabal al Akhdar kaline volcani c activity peaki ng during the Turonian a major unconfo rmity was developed, it extended (90 Ma). Thi s activity was proceeded by the opening westwards into Sirt basin and the Meditenanean of the south Atlantic (Morgan, 1990), and was as offshore (EI Hawat and Shelmani , 1993). sociated with a change in plate movement between By the beginning of the Middle Campani an trans Africa and Eurasia. Indeed, the Turoni an time marks gression Egypt was covered by a broad, shall ow and the change from extensional-sini stral plate move- semi-restri cted embayment whi ch was partly barred SEDIMENTARY BAS INS OF EGYPT: AN OVERV IE W OF DYNAMIC STRATIGRAPHY 69 32 ? ? • • • r" '.( • • II 30· o 50 100 150 200 250 KN . , I , I I ! • • • • • • • STRUCTURAL HIGH • • • • BASINAL MARL • • • ISLANDS rTiTiinl PLATFORM CARBONATES x x I!..11111J AND TIDAL FLATS x PELAGIC CHALK ~ CLASTIC WEDGES x x Fig. 19. Palaeogeography of Earl y Eocene time, northern EgypL(a ft er Salem, 1976). from [he Teth ys to the north by Syri an Arc islands. narrow, elongate and with irregular bottom topog Thi s embayment offered the most favorabl e anoxic raph y (S alem, 1976). These basins were shaped as conditions for precipitation of coll ophane and the relatively deep depocentres, surrounded by NE- SW accumulation of phosphates in southern Egypt. trending islands or submarine highs, where thinner Terti ary and th icker Mesozoic sequence are found (Figs. 19 and 20). TERTIARY During the late Palaeogene there was a chan ge in th e tectonic styl e and nature of magmatism in Egypt. Sedimentati on during the early Palaeogene co n The Syrian Arc compressive tectoni cs that dominated tinued to be influenced by co mpress ive tectonics and the Late Cretaceous-Earl y Terti ary was changed into dextral shear movements that dominated the Meso· extensional tectoni cs related to the opening of rhe zoic in North Afri ca. Sedimentary basins of Egypt Gulf of Suez-Red Sea rili during the Late Tertiary were subj ected to the accelerated influence of these (Morgan, 1990). The associ ated type of magmati sm forces which continued to reshape the Syri an Arc was al so changed from alkaline to tholeiiti c basalti c fold system and rejuvenate basement fault blocks. magma types respecti vely (Meneisy, 1990). This au· The earli er Campanian- Maastri chtian tran sgress ion thor (Meneisy, 1990) recognized three phases of mag· also, continued its inundati on of these basin s du rin g mati sm and corresponding tectoni cs in Egy pt. These th e Palaeocene, but began to lose pace gradually are Late Eocene- Early Oligocene phase (40 ± 10 Ma) lIntil the withdrawal of the Teth ys from so uthern related to the Pyrenean orogeny, Late Oli gocene Egypt at the end of the Earl y Eocene (Hendriks et Earl y Miocene phase (24 ± 2 Ma) re lated to th e ini tial aI. , 1987; Said, 1962). During this time, sedimentary rifting of the Red Sea and the Earl y- Middle Mi ocene basin s in the unstable peri craroni c margin became phase (20, 18 and 15 Ma). 70 A.S. EL HAWAT 32 32 MEDITERRANEAN SEA 30 Sediment Thickness > 1.0 km 11II > 2.0 km #IF Gi ndy eosin Fig. 20. Palaeocene-Eocene main depocentres in northern Egypt (after El Gezeery et al., 1972, 1975). At the end of the Eocene and during the Oligocene Egypt was not accompanied with intense tectonics. these global tectonic activities were culminated by The Dakhla Shale Formation found in these basins regression, siliciclastic sedimentation and volcanism appears to be lithologically continuous from the throughout North Africa. In fact, the extent of the late Late Cretaceous into the Palaeocene. However, the Palaeogene and early Neogene regression and silici Cretaceous- Tertiary boundary is marked within the clastic influx is not to be under estimated. During the sequence by a thin unit of intraformational conglom Late Oligocene and Early Miocene time the southern erate rich in reworked Cretaceous fauna (Hendriks et Mediterranean area of Egypt, Libya and Tunisia, as aI., 1987; Said, 1990). Away from the basin centre well as, the offshore areas of Tripoli-Gabes and Sirt the Cretaceous-Tertiary hiatus is followed by glau basins were transformed from carbonate-dominated conitic, conglomeratic material of Middle Danian to siliciclastic-dominated basins as the African shield age (Barthel and Hermann-Degen, 1981). began to rise (Benomran et aI., 1987). This was ac The Palaeocene sequence in the intracratonic companied by sinking of the Mediterranean and down basins forms a tripartite subdivision consisting of faulting all along the North African continental mar Danian shale unit (upper part of Dakhla Shale Fm.), gin in response to anticlockwise rotation of Arabia a middle limestone unit (Tarawan, Garra Fm. etc.) and the opening of the Red Sea and the Gulf of Suez followed by an upper shale sequence of Landanian (Sestini, 1984). age (Esna Shale Fm.). Like the Dakhla shale, the Esna shales consist of varicoloured, marine, often Palaeogene euxinic marl and shale sequence with carbonate in terbeds. The middle carbonate unit, on the other Palaeocene hand, consists of chalk, marly limestone. On the The Palaeocene sequence in the peri cratonic basinal margin, south and southeast of the Up basins of Egypt rests conformably on the Senon per Nile basin these middle and outer shelf facies ian carbonates but forms an unconformable relation change into claystone, siltstone and sandstone al ship with the Late Cretaceous on the surrounding ternating with coquinoid limestone and overlain by structural highs (EI Zarka and Radwan, 1986). At a sequence of massive, nodular fossiliferous lime the centre of Gindy basin, the Palaeocene sequence stone, claystone and marl. These facies successively reaches a maximum of 283 m in thickness. It con represent inner shelf, lagoonal and middle shelf sed sists of light coloured, fine grained lime mudstone imentation (Hendriks et aI., 1984). with chert nodules alternating with chalk and shale. The boundary of the middle limestone unit with Further to the south, the Late Cretaceous-Early the underlying Dakhla shale forms a significant re Tertiary boundary in the intracratonic basins of gional disconformity surface recognized through out SEDIMENTARY BASINS OF EGYPT: AN OVERVIEW OF DYNAMIC STRATIGRAPHY 71 southern and central Egypt and the Gulf of Suez boundary is located within Esna Shale Formation. and the Red Sea area. It corresponds with boundary These shales are overlain by the Thebes limestone between the planktonic foraminiferal zones P3 and which offers a recognizable physical stratigraphic P5, and is referred to as the "Velascoensis Event" Early Eocene boundary in the sequence. (Strougo, 1986). The limestone above the boundary In the Thebes Formation in Upper Nile basin forms is extensively bioturbated, develop nodular texture 300 metres thick shoaling-up cycle of rhythmically and contains phosphate nodules, vertebrate remains, bedded lime mudstone and chalk with occasional reworked coral heads and dwarfed fauna (Strougo, chert nodules, grading upwards into oyster reefs and 1986; Hermina, 1990). These features may suggest alviolinid rich sand shoals west of the basi n. To the slow rate of sedimentation, early lithification and east, in the proximity of the Red Sea hi gh, the se hardground development. In other places, the basal quence consists of limestone turbidites, intraforma PaJt of the middle limestone unit consists of periti tional conglomerates and rhythmically bedded cherty dal facies rich in sandy marls and vermetid debris limestones, suggesting unstable depositional condi (Barthel and Herrmann-Degen, 1981). In the Gulf of tions related to reactivation of the structures along the Suez-Red Sea area the middle unit consists of olis high. At the basin 's centre, the top of the Early Eocene tostromes of boulder size carbonate clasts floating sequence is marked by the development of nodular in marly matrix and associated with coarse grained chalk hardgrounds. In the region of the Red Sea high cross-bedded sandstone filled channels. Taken to this horizon is marked by subaerially exposed caliche gether these features points towards the occurrence and micro-karst surfaces (Snavely, 1979). of debris fl ow and mass movements. These were In the Gulf of Suez area, the Early Eocene fa developed in response to syndepositional tectonism cies are similar to those found in the Upper Nile associated with faulting and increased of deforma basin . However, the top of the sequence consists of ti on that preceded Red Sea rifting (Strougo, 1986). reworked phosphatic deposits, which is equivalent to the hard ground and karstified horizon of the Upper Eocene Nile basin. The Early Eocene facies were deposited The depositional sequence of the Eocene epoch in deeply submerged stable basins throughout Egypt in Egypt exhibits a general shallowing upward suc except in the vicinity of the structural highs. The cession of depositional units reflecting continuous extensive shallowing features at the top of the se and progressive uplift of the African craton as it was quence, on the other hand, are consistent with the responding to the compressive tectonics between global regression which resulted from lowering of Africa and Eurasia. The Eocene megacycle consists sea level at the end of the Early Eocene (Snavely, of three progressively shallowing-up depositional 1979; Abul Nasr and Thunell, 1987; Strougo et aI. , cycles each of which reflect phases of transgression 1990). The terminal Ypresian regression have also and sea level falls of global magnitude. resulted in the development of a pronounce discon In response to tectonics AI Faiyum basin was sub farmity surface within a deep marine sequence in divided by structural hi ghs into northern and south Al labal al Akhdar (EI Hawat, 1985); and it was ern depocemres during the Eocene time (EI Zarka, also associated with restriction of marine water cir 1983). The southern depocentre, Gindy basin, at culation and extensive evaporite precipitation in Sin tained a north-south orientation (Fig. 20), that forms basin in Libya. This disconformity extends further a transition between the NE-SW basinal trends of to the west in the offshore area of Tripoli-Gabes the Western Desert such as Abu Gharadig and the basin and the onshore of Tunisia. It marks the top of NNW- SSE trend of the Gulf of Suez and the Red the shoaling-up Ypresian nummulitic sequence and Sea high. West of the Western Desert, Siwa and contribute to the development of Metlaoui Group oil Matruh basins were also trending in NNW-SSE di reservoir (Bishop, 1988; Bernasconi et aI., 1991) rections in accordance to the structural trend of the The sea regression at the end of Early Eocene Sirt basin of Libya. from latitude 22° 30'N to latitude 27°N in Upper In the subsurface of the pericratonic basins Egypt, just south of the town of Asyut, led to the Early Eocene- Palaeocene attains a gradational the emergence of the cratonic areas of Dakhla and boundary with no clear break in sedimentation. In Upper Nile basins. During the Middle Eocene, the Gindy basin the Early Eocene sequence constitutes Lower Nile or Gindy basin was developed as the up to 930 metres of alternating lime mudstone, chalk main depoeentre between Asyut and Cairo. In Gindy and thin shale and marl interbeds. Locally, the lime Basin, the Middle Eocene forms a 717 m thick stone is glauconitic and dolomitic, and the shales are shoaling-up depositional cycle of bioclastic-algal pyritic and calcareous (EI Zarka and Radwan, 1986). limestone rich in large forms such as Nummulites In the intracratonic basins to the south, the Early gezahensis, alviolina, echinoids and oysters. This fa Eocene-Palaeocene boundary shows no physical cies association was deposited in tidal flat, bay, back stratigraphic manifestation as the palaeontological reef shoals and shelf edge environments (Philobbos 72 A.S. EL HAWAT and Keheila, 1979; Wahab and Khalifa, 1984). At bed (Abul Nasr and Thunell, 1987). The shallow the basin margin in Cairo area, the sequence is ing event of the Middle Eocene sequence which is 200 m thi ck and consists of yellowish white, hard, recogni zed in different areas of Egypt is consi stent poorly fossiliferous chalky limestone and dolomitic with the global eustatic lowerin g of the sea level limestone, overl ai n by white, hard chalky limestone whi ch marks the end of the Middle Eocene (Abul representing deposition in lagoonal. and shallow ner Nasr and Thunell , 1987; Strougo et aJ. , 1992). A itic conditions (S trougo et aJ., 1992). Further to the progradational , shoa ling-up numlTIulitic Luteti an se west and north of the Western Desert, the Middle quence overl ain by peritidal facies and followed by Eocene consists of a th in clastic-dom in ated sequence a di sconformity is exposed in Cyrenaica (EI Hawat, of sand, silt and shale which was derived from the 1986; EI Hawat and Shelmani, 1993). The Lutetian erosion of the Cretaceous structural hi ghs (EI Zarka sequence in the subsurface in Sirt basin consists and Radwan, 1986). of large-scale, progradational clinoform structures Simil ar fac ies changes are found in the Gu lf of recogni zed in seismic lines. Suez basin, where the Middle Eocene also, consti Continued lowering of the sea level during the tutes a shoa ling-up 1111llllTIulitic carbon ate seq uence . Late Eocene resulted in the progress ive emergence The sequence changes north of the basin into an and erosion of the structural hi ghs thm provided in creas ingly clastic-dominated succession of shales, clasti c sedimems to [he basin s of northern Egypt silts and in te rbedded limestones. The introduction (Fig. 21). The Late Eocene in the Western Desert of these clasti cs were also, attributed to the oc consists of a 220 m thick seq uence of sandy lime cu rrence of Late Cretaceous structural hi ghs source stone sandstone and shales associated locall y wi th north of Sin ai. T he Middle Eocene sequence in the oyster banks. These represent deposition in a shal area is capped by a second reworked phosphatic low, neriti c, lagoonal and deltaic condition s. In the ? • ?• 28° 2 30° 0, '", '00, '50, 2001(M., LAND //// STRUCTURAL HIGHS t /// 8ASINAL MUD ISLAND • • • • DELTAIC SEDIMENTS BASINAL MARL • • • • -r:t r• Fig. 2 1. Palaeogeography of Late Eocene time in nonbern Egypl (alkr Salem. 1976). SEDIM ENTARY BAS INS OF EGYPT: AN OVERVIEW OF DYNAM IC STRATIGRAPH Y 73 subsurface, the Late Eocene fac ies are often undi s (Fig. 24). Outcrops southwest of Cairo consist of 250 tin gui shed from the overl ying Oligocene deposits. m of sand ston e and grave l with local limestone and The Late Eocene si li ciclastic deposits generall y shale in te rbeds of ftu viomari ne ori gin (Said, 1962). thi cken northwards, but may also, thicken locall y These facies change westwards into flu vial sand s and toward basin centres as they prograde away from gravels, and grade northwards into deltaic siltstone, the surrounding structural hi ghs (EI Shazly, 1977; shale and glauconi tic sand stone. Locall y, conti nental Salem, 1976). Oli gocene facies are ove rl ain by basa lti c lava fl ows up to 250 m thi ck (EI Zarka and Radwan , 1986). Oligocene North of the Gulf of Suez basin, the Oli gocene The TCltiary marine regression and tectonic up consists of fossiliferous foramini feral marl s. These heaval conti nu ed in Egypt durin g the Oligocene as change south ward s in to red beds, consistin g of red the Arabian pl ate started to move in an an ti-clock di sh, clayey and pebbly calcareous sand stones, asso wise directi on around a pivotal point in the Jordan ciated locall y with post rifting basaltic nows (Salem, (Fig. 22). Th is movement was initi ated in response to 1976; Chowdhary and Taha, 1987). resistance to di fferential dri fting of the nOlthweSlern foreland of Africa in comparison to th e northeas t. Neogene Causin g the movement of Sin ai to the south west, and the sub sequ ent opening of the Gulf of Suez (Kl itzsch Miocene 1986; Schandelmeier et aI. , 1987). These movements The Earl y Mi ocene transgression was associated also led to the development of the NW- SE, ENE with depositi on of sili ciclasti cs (Moghra Formati on) WS W fa ult systems whi ch were associated with ex in the Western Deselt (Said, 1962). In the subsurface te nsive volcani ci ty throu ghout Egypt. These were the Mi ocene consists of 6 15 m thi ck coarsenin g-up combined to contri bute to the development and sub deltaic sequence of sandstone, shale and lim estone sidence of the Gulf of Suez and th e Nil e Delta basins intercalations. Th is sequence pinches out eastwards (EI Shazly, 1977; Ri zzini et aI. , 1978; Said, 1981). towards the Nile Delta in the region of Tiba basin , The Oli gocene in Egypt was a time of upli ft, re and chan ges north wards into pro-delta sills and gression, volca ni city and continental sedim entat ion marin e shal e (Fig. 25). Follow in g the ini tial Mi ocene PIVOTC!) / I S INA I MIC RO _ PL ATE I-EARLY TERTIARY JI: - OLIGOCENE - MIOCENE 1lI- LATE MIOCENE-PLIOCENE a QUATERNARY I) Arab ian Plate maves faster 4) An ti - clockwise movement than Nubian Plate . of Arabion Plate . 6) N . moveme nt of Arabian Plate 2 ) Deve lopment of NW-SE 5) Opening of Gulf of Suez . along Aqaba fault . R iede l shear. 7 ) Ope ni ng of Red Sea graben . 3) Deve lopment of NE - SW Syrian Arc folds. Fig. 22. Sketch diagr:ull of the structural development of Gul f of Suez- Red Sea- Gulf of Aqaba graben syslem (after Kli17"sch, 1986). EOCENE AF TER FAULTING L. EOCENE ked lower Eocene breccia , L Rewar looonoi depoa' s • d Conglomerate In LATE CRETA, , ------, / on . . '.• • '• . • ••• • - Mesozout • :.: .. : .',",' ------• • • • . .. .' - -- .' • .• - - - / ' . . . - " Paleozoic / ~ '/ • • '. '.' ..• •• . . I , , • • . . . '.• /" , , or, • '. . , , / , -- - -- • - • • • • • • • . '. • • • • /', ® END OF OLIGOCENE ' . Pre Mlocen. · . • • • · • . ., . . .' . • • • • I unconformity ( 00 , •• • • • • • • I / • • • • • • . : ... r '. . . . • • • • . . ' . . • • • • o I I I • • • • • • . , • J .' • • • • • • • I • • • • , / , • • • • - • • • • • , , , • • • . • • - • • • • / " • • • • • • • • • • • • , I - . • • • • , • • • - . • • • .. , , , ·, - , - • , , , , • - / _ Fan Conglomerate MIDDLE MIOCENE I - Middle ~,Hocen8 I , I I I / -, / , • /' , " ( • • / \ - ( -' / ) I - , - - , • , •» , - en Fig. 23. Rifl m"gin block (, ulling de velopmenl On Ihe we"em side o( Gul( o( Sucz (a flc, Klil7.,eh. 1986). SEDIM ENTARY BASINS OF EGYPT: AN OVERVIEW OF DYNAM IC STRATIGRAPHY 75 26' 28' 3 4' 32,~~~--~-----L----~--~----~--~~--~----~--~~~~ 32' Mediterranean Seo \ \ She lf " Carbonates? \ \ \ 30' 28' • Red SeQ 26' 28' 30' 34' SLOP E FAN . . . . <¥/ ~ PRODELTA D. . . . . SANDS -- MAR INE SHAL.E 1'11/ 1/ r V;; DE LTA D- -- LAND Fig. 24. PalacogcograpllY of (he Oli gocene, northern Egypt (after Salem , 1976). transgression in the Delta basin, the Aquitanian was Salem (1976) suggested that the Midd le Mi ocene a time of low sea level and uplift throughout the transgression was associated with the eastward s shift delta as indi cated by the low sed imentation rate of the Palaeonile from th e Western Desert to its of 60 to 70 m/Ma. East of the Delta a hi gher present day position (Figs. 25 and 26). The result sedimentation rate was estim ated (400-500 m/Ma) ing cessation of siliciclastic influx in to the We stern during the Burdigalian (Wray. 1985). Desert gave way to an increase in carbonate produc In the Gulf of Suez basin the Oligocene rifting ti vity and the deposition of Marmarica Formation was followed by Early Miocene marine transgression that extended into Cyrenaica. During the Middle over an ilTeguiar basin fl oor. The northern part of the Mi ocene (Langhi an), the Nil e Delta was affected by basin centre was fi ll ed by 2200 m thick Gl obi gerina tectonic in stability and gravi ty faulting. Thi s was marls that thins south wards to 200 m at the Gulf's fo ll owed during late Middle Miocene (M id and Late entrance (Salem, 1976). These marls change laterally Serravali an) by a pronounced sea level fall causin g an d upward s towards the rift's margin into calcareous a depositional hi atus that ranges from 6 to 2 Ma in sandstone , limestone and interbeds of marl s and gyp duration, and may extend to Early Tortonian (Wray, siferous sha les. The outer margin of the rift consists of 1985; Harms and Wray, 1990). The Mi dd le- Late crystalline basement half horsts and graben structures Mi ocene delta cycle is a coarsening-up depositional forming a seri es of platforms and basins. These are sequence that thins gradually southwards in the di covered by Early Miocene sediment apron of mi xed rection of Cairo (Fig. 28). The earl y part of the cycle allu vial grave ls conglomerate and sabkha evaporites consists of more than 700 metres of green, gray clay that grade basin wards into platform carbonates and stone interbedded wi th fossiliferous marls and rare basin rim reefs (EI Haddad et ai., 1984; Coniglio et quartzose sandstone interbeds. Following an uncon ai., 1988; James et ai. , 1988). It was noted that the formity, the second part is of Late Tortonian- Early Early Mi ocene sequence was interrupted by tectonic Messinian age. It consists of 1- 3 km thick, north movementsI causing reactivation of faults and ti lting west prograding c1inofonn sequence the deposition of fau lt blocks wi th in the basin (Fig. 23). These tec of whi ch was taking place in association with rapid tonics were associated with the development of an subsidence of the eastern P3lt of the delta, which was unconformity in the basinal sedi mentary sequence, influenced by an easterly longshore drift. During thi s and the development of karstification, subaerial dia phase the delta maintained a hi gh sedimentation rate genesis of platform carbonates and synsedimentary that reached 680 mil Ma (Wray, 1985). Sediments coll apse of basin rim reefs (James et ai., 1988). constituting this depositional phase consist of poorly 76 A.S. EL HAWAT • . . ~ . \ -y." . . . : \ · '. . H \ • \ · II' \ \ \ \ ,, r • I • I • ". 26° ~ .: ! LE GEND LAND PR ODELTA SEDIMENTS ~ CARB ONATE S - IV""""VVl DELTA - - MARINE SHALE ~ E VAPORITES ~-. . --. . . . ·x .'· CALCAREOUS SA NDSTONE : : . ' .'.'. ALLUVIAL FAN Fig. 25. Palaeogeography of Early Miocene lime. north ern Egypl (after Salem, 1976). sorted conglomeratic sands, clays and calcareous Mi ocene anh ydri te with minor interbeds of sand sandstone representing a prograding ft uvio-deltaic stone and shale (C howdhary and Taha, 1987). These and coastal de lta ic sedim entati on and associated evaporites attain a max imum thi ckn ess of 3540 me swamps and lagoons. Wray (1985) and Harms and tre s at the southern end of the basi n and decrease Wray (1990) poi nted out that during this phase of north wards to zero (Salem, 1976). Taken together the delta hi story, a major integration of the Nil e with thi ckness variation of the Earl y Mi ocene open drain age system has taken place for the first time. marine Globigerin a marl s, it was conclu ded that North of the delta region, th e Late Miocene cycle is these evaporites were deposited in a barred basin capped by 40 m th ick uni t of Late Messini an anhydrite whi ch was opened to the Tethys from the north in terbedded with thin clay layers (Fig. 27). In pl aces, (Said, 1962; Salem, 1976, fig. 16). On the basi the top pall of the delta sequence exhibits deepl y in nal margin, the Middle-Late Miocene sequence is cised channels and slump structures that produce an similar to that of the Earl y Mi ocene. It consists of angul ar unconfo rmabl e relationship with the overl ay peritidal carbonates associated wi th basin-rim reefs in g Pli ocene delta cycle (Ri zzini et aI. , 1978). In the and subtidal stromatolites on the gul f sid e. Away Weste rn Desert, the Tortonian- Mess in ian sequence from the basin centre th ese sedi ments change in to consists of 30-40 metres thick cross-bedded, well alluvial clasti cs near basement hi ghs. This deposi sorted, medium grained sands, clays and limestone, ti onal suite of carbonates and clasti cs were covered that grade up into gypsiferous clays and coarsely by Late Mi ocene evaporites and was foll owed by crystalline selenite (Omara and Sanad, 1975). The evapori te solution collapse breccia that resul ted from sequence exhibits a disconformable relationship with subaerial exposures and diagenesis (EI Haddad et aI. , the Early and Middle Miocene below, and the over 1984; Conigli o et aI. , 1988; James et aI., 1988). lay in g Pliocene carbonates. In the Gulf of Suez basin the Middle Mi ocene Pliocene consists of calcareous shale and marl in terbedded Following the Messinian lowering of sea level with anhydrite, and gradi ng upwards into mass ive durin g the Medi terranean salinity cri sis (HsU et anhydrite and rock salt and associated with gray aI. , 1973), and due to lowering of the base level shale interbeds. The sequence is overl ain by Late of erosion, the Ri ver Nil e drain age became deepl y SED IMENTARY BASINS OF EGYPT: AN OVERV IEW OF DYNAMIC STRATIGRAPHY 77 32 32 MED ITERRANEAN SEA , \ - , , o~s~f\' , ~~s,~f\" I, ~. EAS TERN I, C/.,f>. 28 0, 5,0 10,0 15,0 200, Km ~O'l' OESERT I, Delta fon ------Sha le Alluvial fall Calcareous 5 . 5 . Slope fan Carbonates Eva porites. L end Fig. 26. Pa laeogeography of M idd le M iocene lime, northern Egypt' (after Salem, 1976). entrenched as far south as the city of Aswan 1200 km extended up to the Quaternary (R izzin i et aI., 1978). inl and (Ryan, 1978). The occurrence of the Pliocene West of the delta in the Faiyum area, th e ( Pl aisancian) marine and estuarine clays and sand s Pli ocene consists of limestone, sa nd stone and bi o in the vicinity of Aswan (Chumakov, 1968) was clasti c shoreline facies. These may change laterall y attributed to the openi ng of the Atlantic fl oodgate in Wadi Natrull in to an association of clay, lim estone and refi ll in g of th e Mediterranean bas in durin g the and sand stone with vertebrate remain s ind icating flu Ea rl y Pli ocene transgression (Hsli et aI., 1973). The via-es tuarin e and marginal marin e condi tions. Fur Early Pliocene estuari ne deposits were foll owed by thcr to the west in the Western Desert and away from Late Plio-Pleistoce ne ftu vialile seq uence. the influence of the Nile, the Pli ocene sequence con In the Nile Delta basin, an Early Pliocene trans sists of 60 metres of pink ooLitic limestone whi ch is gressive sand unit (Abu Madi Form ation) forms unconformably underl ain by the Miocene (EI Shazly, the base of the Plio-Pleistocene Nile Delta cycle 1977). (Fig. 27). It consists of thi ck- bedded, rippled, cross In the Gulf of Suez basi n, the Late Mi ocene and pl ane-bedded, bioturbated sandstone, in terbed regression and eros ion was fo ll owed by subs idence ded with clay and occasional conglomera te at the associated with the opening of th e Red Sea to the base. The fo llowing delta cycle is 1500 m th ick Indi an Ocean. The post-Miocene seq uence in th e coarsening- up sequence that consists of deep shelf subsurface is up to 950 m thick, coarse to medium and slope clays with few quartzose sand interbeds. grained sandstone interbedded with red brown clay These sand beds increase in thickness and frequency stone and siltstone. These contain minor intercala upward s, as they grade into 300 m thick, large scale ti ons of limestone and anhydrite, associated with prograding fo resets of coarse- to medium -grained fauna of Indo-Paci fi c affiliation (Chowdhary and deltaic sand units. The foll owing 700 m of the se Taha, 1987). On the basin margin , acti ve extensional quence is thi ck-bedded, conglomerati c, coarse- to tectoni cs and the associated depos itional suites th at medium-grai ned quartzose sandstone wi th reworked began in Early Miocene ti me co nli nued unti l the chert, quartzite and dolomite pebbles. The top of present (Purser et aI. , 1987). It exhibits rapid lateral the sequence also contains coquina and peat deposits vari ati on of carbonates (reefs), evaporites and silici represeJ1lin g coastal and lagoonal sedimentati on that cl asti c sediments. Thi s is a typical facies associati on 78 A. S. EL HAWAT Middle Kafr w 01 z 1500 w Sheik u o -...J a.. Lower Abu Modi 300 Rosetta 50 • • • • • • • • • • • • • Messinian • • • --'• 700 w Qawasim z w u o- ::;: Tartonian Sidi Serravalian Salim Langhian Fi g. 27 . Stra tigraphic column of the Nile Delta (after Ri zzini et aI. , 1978). related to rift margi n depositi onal set up in arid lowed by a rapid return to a siliciclastic-Free, clear climatic conditions (Fig. 29). Under these conditions marine water leading to carbonate sedim entation and sporadic wet periods causing flash floods provided evaporite mineral precipitation ill areas of restricted coarse clasti cs from the hinterland. These were fo l- ci rculation (Purser et aI. , 1987). 80 A.S. EL HAWAT : : '.. . . ' . . . ',- . : .. :.' .,,', . . .' . . .' - . ,",---,-, L L..L..L..L..L-LL.. . .' .... " . • •••• • · .. ... " L..~L..L.. , -,-:::'. :.-..,. . " , ... · . . . . '. " . . " ' ...... L L L , , , '-:":"';""/ L..L.L..LL..LLL..L .;:.-: ... . •• • • • • • ' ...... • • • • • L..L..L..L L..L-L..L , " .' "" • • • .• .• "• • . .. · .. LLLLL..L..LLLLLLL.. " , ", ' -"""'" • • ••• • I ... . ' • • Ll...... LLLL • • , , t;CCc- L...LLL..LL .. , .... """" ...... , ... I '- " "'" , ,' .:, . ~ Basement Offshore Carbonates ~ (Mudstone ,wackestone) · • • • · • Alluvia fan grovel Conglomerate ·· • · • · a ·• • · • · · · · • •• •• [~[ Reef V:VN: Sabkha gypsiferou s sand ·-'. IIY . ..' Offshore shell bank Platform Carbonates Bosinal marl Lagoon carbonates ( mudstone) I' ! itr q Evaporites with minor carbonates Fig. 29. HYPolheLica l profile of Neogene- Qua ternary ri f! 1llurgin facies association from Gu lf of Suez-Red SC:.l graben (a fLer Purser et al.. 1987). from Sin ai and the delta, to the Western Desert of accumulati on of up to 3 km thick delta c1 inoform Egypt. In Libya, it resulted in the development of the sequence (Wray, 1985; Harms and Wray, 1990). Middle- Late Miocene olf-Iap relationshi p reported The sudden onset of the Mediterranean saJin from northern Cyrenaica and Sirt basin (El-Hawat ity crisi s during the Late Messinian was a result and Salem, 1985, 1987; EI-Hawat et aI. , 1985). The of the closure of its conn ec ti on with the Atlantic sa me unconformity was recognized fu rther south in Ocean (HsU et aI. , 1973, 1977). As a result, two Si rt basin , and was used as a correlati on datum types of faci es associations characteri ze the Late for the study of the Middle Miocene (Sell ey, 1968; Messini an sedimentation in North Africa. Their di s EI- Hawat, I 980a). tributi on was controlled by structures and geograph y. Although the earli er part of the Late Miocene was These are either evaporite--{;arbonare or evaporite a ti me of shoalin g of the Betic Strait that connected siliciclasti c associations. The fo rmer is fo und on the Mediterranean to the Atlanti c Ocean. Open ma platforms and structurally hi gh areas away from rine facies has prevailed in the Mediterranean during si liciclasti c sources; and the latter is found in the thi s time (HsU et aI., 1977). Stratigraphi c record in structura ll y low areas which we re influ enced by northeast Afri ca suggests th at the Late Tortonian river sources. in struc turall y high areas in Jaba l Naf Earl y Mess inian was a time of a limited tran sgres fusa of western Libya, Sirt basin , northern Cyrenai ca sion, whi ch did not alter the net off-lap relationship and the Western DeSeJ1 of Egypt the Late Messinian with the Middle Miocene sequence. However, ev consists of lenticul ar bodies of coarsely crystalline idence of this transgressive event is demonstrated gypsum and gypsarenite, associated with lim estone by the OCCUITence of local unconformable on-lap consisting of pell etal mud stone, alga l stro matolites relations found between the Late Miocene and old er and oncolites (EI-Hawat, 198Gb; Youssef, 1988). [n formations on the marginal hi ghs of western and the structurall y low areas of Sirt basin, and off the eastern Libya (EI-Hawat et aI., 1985) and the West Nil e Delta, evaporites are associated wi lh siliciclas ern Desert of Egypt (Omara and Sanad, 1975). In tics exhibiting evidence of subaerial exposure (De Libya, depositional facies were dominated by shal Heinzelin and EI-Arn auti , 1983; Ri zzi ni et aI. , 1978). low marine platform carbonates and reefs developed Due to con tinuous evaporati on and consequ ent over topographically hi gh areas. Topographi c lower fall of the Mediterranean sea level, during the Late areas of Sirt basin, on the other hand, were filled Messi nian the resulting lowering of the base level of by siliciclastics due to the innuence of rivers. East erosion caused deepening and lengthen in g of chan ward s in the Western Desert, the sequence consists nels located in the low areas of Sirt basi n and along of mixed siliciclastics and carbonates that grades the Palaeonil e. In Sirt basin, the entire Miocene further to the east into the clasti c facies of the delta. sequence was locally eroded by the post-Messini an In the latter, rapid subsidence rates and integrati on Sahabi Channel (Barr and Walker, 1972), which also of the PalaeoniJe drainage system has contri buted to extended nOJ1hward s in the Mediterranean offshore. SEDI MENTA RY BAS INS OF EGYPT: AN OVERV IEW OF DYNAM IC STR ATIGRAPHY 81 In the Nile Delta thi s event is marked by an uncon ates and/or evaporites. Depending 0 11 their location formity at the Mi ocene- Pliocene boundary (Harm s in the craton and their tectoni c hi story, the sedimen and Wray, 1990). Erosion in the Ri ver Nil e produced tary depocentres of Egypt are either intracraton ic, a deeply in cised canyon that reached 2,500 m be peri cratoni c, or ri ft basin s. low sea level north of Cairo, and - 200 m in the Sedimentati on and basin filling during Earl y area north of Aswan (Sa id, 198 1). With the opening Palaeozoic was influenced by the regional north wa rd of the Atl an ti c fl oodgate at Gi braltar (Hsu et aI. , tilt of the post-Pan-Afri can plate, and the occurrence 1977), the Early Pliocene transgression transformed of the NNW- SSE trending horst- graben basement the Sahabi Channel and the Nile into impressive in structures and mountains, continental glac iation land estu ari es. Earl y Pliocene (Pali sa ncian) estuarine and eustasy. These factors were combined to pro faun a wa s di scovered in an incised channel some duce siliciclastic-dominated depositional regimes. 1,250 km from the present coast (Chumakov, 1972). Whereas continental and fluvi al sed imentati on were The Sahab i Channel, set between the sea level and closely assoc iated with epeirogeni c tectoni c move - 400 m; was fi lied by calcareous sand stone, sands ments and eros ion of basement blocks. The Palaeo and shales, and contain s mi xed marine and conti zoic marine transgress ion during the Earl y Cam nental fauna of reworked Miocene and Pliocene age brian, Earl y Ordovician, Earl y Silurian and Earl y (De Hein zelin and El-A rn auti, 1983, 1987). On the Carboniferous led to the reworking and widespread higher ground, the Early Pli ocene cons ists of oolitic di stribution of silicicl asti c sedi ments over the cra and bioclastic limestone; that rests unconfo rm abl y ton. Dakhl a, Siwa and Abu Gharadi g basins were und erlain by Late Messini an evaporites. the main Palaeozoic depoce ntres in Egypt. Other depoce ntres have received a thinner sequ ence of Palaeozoic deposits. At the end of the Vi sean, Cen SU MMARY AND COMMON THEM ES tral and Uppe r Egypt was up li fted and erosion of the Earl y Palaeozoic took place. These tectoni c move The Afro-Nubi an craton consists of two parts sepa ments have resulted from the collision of Gond wa na rated by the River Nil e. The western and oldest part of with the nOlthern continents on one hand, and be the craton is Late Archean nu cleus surrounded by an cause of the deve lopment of thermal anomali es be Ea rl y to Middl e Proterozoic metamorphi c rocks. The neath the plate, along Jabal Uweinat-Aswa n trend on fonner constituted granuli te rocks of an earl y pro the other. These tec ton ic and palaeogeographi c con toc ruSl, and the latter co nsists of granitoi d and poly ditions have reversed the drainage fl ow di rec ti on of metamorphic rock ex tending throughout northeast rivers south wards and restricted the Permo-Triass ic Afri ca. East of the Nile, the Nubi an shield was devel sedimentati on [0 northern Egypl. oped as a result of crustal accreti on during Late Pro The inheri ted Permo-Triassic structural elements terozoic, Pan-Afri can thermo-tecto ni c events. Evolu were terminated during the M esozoi c by rej uvena tion of the Nubian shi eld involved an earl y fi ysch tion of old Palaeozoic NNW- SSE structural trends sedimentati on and cru sta l subducti on associated with and restoration of the northern tilt of the Afri can island arc vo lcani cs and ophi olites. A phase of oroge pl ate. Th ese were assoc iated with the opening of the nesis and plu tonic grani to id intrusions was followed central Atl anti c, ex tensional tectoni sm and sinistral by erosion and development of fo reland basins. Thi s strike-slip movement between Africa and Eurasia in turn was foll owed by a fin al phase of late Orogeni c and the opening of the Tethys. Like Earl y Palaeo event and post-Precam bri an penepl anation. zoic, the M esozoic sedimentary sequence consists of Ba sin development during the Ph anerozoic was a succe ssion of depositi onal cycles re fl ecting tecton influenced by the Proterozoic cru stal evoluti on and ics and eustasy. by the location of the North Afri can plate betwee n Becau se of the above indicated constrai nts the the relati vely more ri gid plates of northwest Africa Triass ic and the Jurass ic sequences were res tri cted in and Arab ia. Pos t-Pan -African crustal coo ling, dif aerial distri bution to northern Egypl. Sedimentati on ferential movements along old structural lineaments, during Earl y Cretaceous in Egypt was essentiall y driftin g and collision with the northern continents, regress ive in character due to the overwhelming and development of hot spot anomalies beneath the infl uence of basement tectonism. The Neocomi an craton were th e main causes of tectoni c movement, Barremi an and Albian sequences consist of fluvi al basin evolution and develop ment in Egypt. Basin fill and continental-dominated depos its, separated by ing was often initiated by therm al cru stal up-arching, the Apti an transgress ive ph ase that covered most of fracturin g and subsidence followed by mari ne trans southern Egypt. By contrast, the Late Cretaceous gress ion. These evolutionary stages were recorded was a time of overwhelming transgression, which in symmetri ca l or asymmetri cal depositional cycles was associated with increased carbonate producti vity consistin g of basal continental cl astics grading into and sedimentati on. It started with the Cenomanian marginal marine sediments and open marine carbon- global sea level ri se which reached its climax at the 82 A.S. EL HAWAT end of the Cretaceous and Early Tertiary. However, University, Cairo; Prof. William R. Dickinson for the Late Cretaceous sea level ri se was interrupted by merly of Stanford University, California; Dr. Graham two regressive phases associated with compressive Evans, Prof. Ri chard C. Selley and Prof. Douglas epeirogenic and shear tectonic movements during J. Shearman of Imperial College, London, whose the Turoni an and Santonian times. teaching and work was an inspiration to the author. I These tectoni c events were contemporaneous with am grateful to Dr. R. AI-Khazmi, of Garyounis Uni the opening of the north Atlantic and the switch in versity, Libya, for reading drafts of this paper and for the direction of plate movements along the Tethyan suggesting improvements to the text. Thanks are due realm. The Tethyan tectonics were transformed into to Ms. R. Banger of the University of Cambridge compressive and dextral shear movements leading to fo r her help during library research. The support subduction of the Mediterranean oceanic crust and provided by the Arabian Gulf Oil Co. (AGOCO) and eventual uplift of the African craton. These events GEOLIBYA, Benghazi , is greatly appreciated. This were associated with volcanic activities, develop paper is a contribution of the IGCP Project No. 369 ment of unconformities, siliciclastic influx and re on the Comparative Evolution of Peri Tethyan Rift stri ction of marine circul ati on in sedimentary basi ns Basins. leading to evaporites deposition or anoxic condi tions associated with precipitation of collophane. The most important tectonic feature in the pericra REFERENCES tonic area. however, was the inversion of subsiding basins and the development of the NE-SW to ENE Abdallah. A.M .. EI Adindani, A. and Fahmi, N .. 1963. Stratigra WSW trending Syrian Arc fold system. phy of lower Mesozoic rocks on western side of the Gulf of Suez, Egypt. Geo!. Survey. Min. Resour. Egy pt. 27, 23 pp. Transgression and the northwestern drift of Africa Abda llah, A.M., Darwish, M. , EI Aref M. and Helba. A.A. , continued to influence sedimentation and tectoni cs 1992 . 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