Arab J Geosci (2017) 10:14 DOI 10.1007/s12517-016-2793-z

ARABGU2016

Rejuvenation of dry paleochannels in arid regions in NE Africa: a geological and geomorphological study

Bahay Issawi1 & Emad S. Sallam2

Received: 20 June 2016 /Accepted: 5 December 2016 # Saudi Society for Geosciences 2016

Abstract Although the River Basin receives annually ca. and west of . The nearly flat west of the Nile 1600 billion cubic meters of rainfall, yet some countries within Valley rises gradually westward until it reaches Gebel the Basin are suffering much from lack of water. The great Uweinat in the triple junction between , , and changes in the physiography of the Nile Basin are well . Gebel Uweinat has an elevation of 1900 m.a.s.l. sloping displayed on its many high mountains, mostly basement rocks northward towards the Gilf Kebir Plateau, which is that are overlain by clastic sediments and capped by volcanics 1100 m.a.s.l. The high mountains and plateaus in the southern in eastern and western Sudan. The central part of the Nile Basin and western Egypt slope gradually northward where the Qattara is nearly flat including volcanics in the Bayuda Mountains and is located near the Mediterranean coast. The depres- volcanic cones and plateaus in southwestern Egypt. The high sion is −134 m.b.s.l., which is the lowest natural point in Africa. mountains bordering the Nile Basin range in elevation from All these physiographic features in Sudan and Egypt are related 3300 to 4600 m.a.s.l. in the Ethiopian volcanic plateau in the to (i) the separation of South America from Africa, which east to ca. 3070 m.a.s.l. in the western Gebel Marra, and started in the Late and continued up to the 1310 m.a.s.l. in the Ennedi Mountains in northwestern Sudan. Cretaceous, giving rise to several generally E–W-oriented tec- In central Sudan, the Nile Valley rises approximately 200– tonic features inside Africa, (ii) the uplift of the 300 m.a.s.l. In Egypt, the River Nile is bounded by the Red Mountains and their continuation inside Africa resulted in the Sea Mountains in the east, assuming ca. 1000–2600 m.a.s.l., East African Rift System (EARS), (iii) the Guinea–Nubia mostly of basement rocks, which are covered to the north of Lineament crossing Africa from the Atlantic to the Red Sea Aswan by Phanerozoic sediments sloping to the west, passing where many havoc trends, mostly E–W-trending faults, and by the Nile Valley and continuing through the . uplifted basement features pierce the overlying sediments, (iv) The Phanerozoic cover on both sides of the Nile is known as the parallel and longitudinal structures associated with volcanic Eastern and Western Limestone Plateaus. These plateaus as- plateaus and cones extend from west Sudan (Gebel Marra) to sume elevations varying from 300 to 350 m.a.s.l. near the east- Ethiopian Plateau, passing by volcanics and plume features in ern bank of the Nile to 400–500 m.a.s.l. south Luxor at Esna between and the basins in east Africa were subjected to wrench related inversions, and (v) the Sudd linear E–W area stretching This article is part of the Topical Collection on Current Advances in more than 1000 km between Gebel Marra in the west, passing Geology of North Africa by South Sudan and reaching southwestern Ethiopia. Here, fluviatile and subsurface waters led to ponds, , and wet * Emad S. Sallam areas that are hard to exploit. The impact of these features led to [email protected] the present south to north River Nile, but passing by many Bahay Issawi changes in the direction of its many tributaries and slope rever- [email protected] sal of some of the major extinct rivers, either sectors of the main Nile or the rivers once flowed into the main river. The paleo- 1 Geological Survey of Egypt, Cairo, Egypt climatic changes during the Quaternary period: wet and dry 2 Department of Geology, Faculty of Science, Benha University, have a great effect on the physiographic features and slope Benha, Egypt reversal of the Nile Basin drainage system. 14 Page 2 of 20 Arab J Geosci (2017) 10:14

Keywords The Nile Basin . Geology . Stratigraphy . river channel and the desert beyond. This setting stimulated a Geomorphology . Hydrogeology . NE Africa close co-existence of people and aurochs to become accustomed to each other (Wendorf et al. 1987a, 1987b; Wendorf et al. 2001). The gradual spread of humans and animal domestication Introduction throughout the Nile Valley increased rapidly within an unbeliev- able high percentage. From 10,000 (Early Holocene) to From time immemorial, before the Nile reached Egypt at 600– 5000 years ago when Egypt became under Pharaonic rule, 700 ka ago, lived in NE Africa depending on rainfall Egyptians spread on almost every square meter of the Nile water (Wendorf and Schild 1980; Hassan 1981; Wendorf et al. Valley and an exponential increase in human population became 2001). Egypt then was not a desert area as it is now, but it was evident. Over time, the population of Egypt increased by an humid covered by different plants, fruitful trees, and many dif- unexpected rate reaching yearly by more than 2.5% (according ferent species of wild and tamed animals (Wendorf and Schild to the Egyptian Central Agency for Public Mobilization and 1976;Wendorfetal.1993). Rainfall decreases gradually since Statistics; August 2015). the , reaching 1500 mm/year (Simons 1972, 1987)to The many radar images reveal the occurrence of many old dry 1200 mm/year during the late (Pickford et al. 2008)to channels crossing African Sahara from the south to north and 600 mm/year in the early Quaternary (Williams 2009; Williams also rare channels from the north to south. In the work of Issawi et al. 2010). Rainfall built many pools, lakes, and local rivers et al. (2016), the central African waters (Congo River and White mostly trending E–W consequent to the uplift of the Red Sea Nile River) have shown to pass through old dry channels in the Mountains (Priabonian–Burdigalian). The main water stream Western Deserts of Sudan and Egypt. The present study confirms was the north–south Qena River, which drains the northern sector the importance of the two main drainage systems in the Eastern of the Red Sea Mountains. Southwards, the main river was the Desert (Wadi Gabgaba–Allaqi) and in the Western Desert (Wadi Gabgaba–Allaqi, trending north to northwest, draining northeast- Gilf). These two dry wadis were important drainage systems, ern Sudan and southeastern Egypt before joining the Qena River, carrying waters from rainy areas in Ethiopia through the Blue 120 km south of Aswan (Issawi and McCauley 1992, 1993). The Nile and from high mountains in Uweinat and Gilf Kebir. The plants and water were enough to keep a limited number of man- Gilf and Gabgaba–Allaqi are now dry channels since dry condi- kind and animals to live happily together though man avoided to tions dominated over the Gilf area and over all the Western live on the banks of the many rivers traversing old Egypt. The Desert of Egypt. On the other hand, the Gabgaba lost its connec- shrubs and pushes were a good hiding place for dangerous tion with the Blue Nile by the rising of the Bayuda volcanics, beasts. Gradually, over time, rainwater diminished; hence, man which blocked its connections with Ethiopian water. In the pres- had to go further south probably even to what is now Sudan, ent work, it is suggested that these two dry paleochannels can be where water was available. The Egyptian migration to the south rejuvenated, adding a good supply of water to the thirsty Egypt. continued until they encountered the Kush people in north Sudan. Thence, the Egyptians were compelled to dig water wells in the Nabta area west of Abu Simbel (Wendorf et al. 1985; Study area Wendorf et al. 1987a, 1987b; Wendorf and Close 1992; Wendorf et al. 2001) and in many other places in southern The River Nile Basin occupies an area of approximately three Egypt. The present was soft, muddy, and susceptible million square kilometers. The river generally trends S–Nfor for marine invasions during the Neogene and the Quaternary. about 6800 km, passing through tropical to Mediterranean In southern Egypt, the beginning of a permanent society climatic zones (Fig. 1). The Nile Basin displays a broad diver- started to develop, enhanced by the discovery of animal domes- sity in geology, physiography, climate, and fluvial tication (ca. 8000 BP) and probably with cultivation of some lands environments reflected in five discrete landscape sectors. around water wells a bit earlier (Wendorf et al. 1985; Wendorf These sectors have been adopted by Said (1981) and outlined and Close 1992; Wendorf et al. 2001). In the Nabta area, by Woodward et al. (2007)asfollows: archeologists discovered Late Neolithic Tumuli ceremonial com- plex, several megaliths, old houses, and a solar calendar 1. The densely forested equatorial region at the southern (Wendorf et al. 1985; Wendorf et al. 1987a,1987b;Wendorf headwaters of the White Nile, with tropical catchments and Close 1992; Wendorf et al. 2001). The close co-existence and perennial flow regimes. of cattle and humans in Nabta Valley was related to what was 2. The swampy areas of Sudd and central Sudan with low- then (during the Holocene) the floodplain of the Nile bordered by gradient floodplains, broad channel belts, and low- low and high deserts, lacking vegetation. On the other hand, high suspended sediment concentrations. floods in the lower Nile Valley around 12,500 BP, carried heavy loads of suspended sediment deposited on the floodplain, leading Fig. 1 Map of the Nile River Basin showing the drainage fluvial system,„ to a narrow unflooded margin of the valley located between the dams, and cataracts Arab J Geosci (2017) 10:14 Page 3 of 20 14 14 Page 4 of 20 Arab J Geosci (2017) 10:14

3. The Ethiopian highlands forming the headwaters of both Dams construction and problem of water supply the Blue Nile and Atbara River, both produce coarse boul- to Egypt der sediment loads. 4. The cataracts region of ephemeral tributary wadi systems Many important early engineering projects were implemented in arid areas extending from Khartoum in Sudan and to save Egypt’s land during flood times. The El-Kafara dam reach Cairo in northern Egypt. on the eastern side of the Nile near Helwan, 35 km south of 5. The Nile Delta of low-gradient floodplains, large distrib- Cairo, was built to prevent the flooding of the western part of utaries, and lagoons at the coastal zone of the the valley at BManf^ opposite Helwan, an important city dur- Mediterranean. ing Pharaonic time. The Faiyum depression was a drain area to protect the Lower Nile Valley against high Nile floods. The revival of some Nile tributaries to reach new areas away from The drainage of Africa since the Cretaceous has an intrigu- the main valley, as the Zeistorees canal connecting the Nile ing history involving shifts of their catchments and courses, with the extreme eastern part of the Delta is another example particularly since the splitting of Gondowana (Goudie 2005). of the importance of the Nile during Pharaonic time. The great These changes reflect the long and varied climates and tecton- and important engineering works on the River Nile and its ic history resulting in drastic changes in topography. Rifting, valley happened during Mohamed Ali Pasha, the Turkish ruler volcanic eruptions, doming, and swell formation are respon- of Egypt (1805–1840 AD). The control of water in the two sible for the development of river basins (Said 1981). The branches of the Nile on both sides of the Delta ( and many rivers in NE Africa have a long history in their flow Damietta) was done by building a huge barrage on the Nile at directions: El-Kanater El-Khairiya at the southern tip of the Nile Delta before the river’s branches. There, the dry paleochannels of 1. Echoing the uplift of the Red Sea Mountains during the the Nile in its Delta were flooded by water to gain new farm- Priabonian (Late Eocene) up to the Middle Miocene. ing areas. In Upper Egypt, a canal (El-Ibrahimia) connecting 2. The Miocene– East African Rift System. Assiut with Faiyum helped to widen the farming area of the 3. The Messinian crises in the Mediterranean changing the Nile Valley in west central Egypt. base level of the north flowing systems in northern Africa The British occupied Egypt in 1882 and in 1902 they built and southern Europe (Hsu et al. 1973). the carrying water to a level of 120 m.a.s.l. in 4. The tilting of the Ethiopian highlands during the Early front of the Dam. This expanded the Nile Valley on both sides Pleistocene. and new areas were added to the cultivated old areas, rising to 5. The drastic changes of the climate especially during the +120 m.a.s.l. Quaternary (Williams and Faure 1980; Woodward et al. In 1960–1968, the Egyptians built the High Dam, 8.0 km 2007). south of Aswan (Fig. 1 ); the Nile water in front of the Dam now rises to 180 m.a.s.l., thus higher areas in the Nile Valley The climate of the Nile Basin during the Pleistocene varied and the Delta were reclaimed which added more wealth and from wet to dry varying from wet to dry and vice versa with food for the increasing Egyptian population. increasing dry phases since the last 150,000 years. The advent Problems started to face the people living on the Nile Basin of dry conditions continued onward from 5000 years until especially in Egypt, where in Sudan the capacity of the today. This coincided with land degradation due to removal Roseires Reservoir (Fig. 1) on the Blue Nile had been reduced of plant coverage and also to human settlement on vegetated by almost 60% through silt accumulation, whereas at the areas. Dry phases alternated with wet conditions in the upper Khashm El-Gerba Reservoir on the Atbara River, another Nile Valley expressed by degradation and aggradation phases tributary of the Blue Nile further north of Khartoum, the ca- of alluvial plains in the lower Nile Valley. In the Faiyum- pacity is reduced by nearly 40% (Williams 2009). Both reser- locked depression, about 60 km to the southwest of Cairo, voirs were built to supply Egypt and Sudan with more water these phases are well expressed in sediments laid down or during dry phases of the Blue Nile. In Egypt, the High Dam eroded in the depression. There, 14 dry and wet phases were reservoir, i.e., Nasser Lake, silt is gradually accumulating in recorded in the depression from 35,000 years ago to the pres- the southern part near Halfa, and it has been estimated that in ent (Issawi et al. 2001), echoing low and high Nile water. This 500 years the reservoir area will be completely chocked by silt is revealed very well in the sediments of Lake Qurun in the (Shenouda 1984) unless engineering measures are taken. lower part of the depression ( 45 m.b.s.l.). The degradation At present, 300 million people depend on the Nile water for phases were tied with political and economic troubles, associ- their livelihood, but it has been estimated that by the year ated with famines and several social distresses enlarged, and 2220, the population will increase to probably more than dominated in all Egypt with time. On the other hand, Egypt 350 million; hence, a clear picture of the present Nile use became prosperous during aggradation phases. and Nile flood history is essential for future planning Arab J Geosci (2017) 10:14 Page 5 of 20 14

(Hassan 1981). However, we are entering uncertain times past. In the present study, we augment these settings into the where forecasting the impacts of future climate changes are Egyptian fluvial drainage system and the Sudan fluvial drain- not easy. It is hard to predict the climatic consequences of the age system. Albedo changes linked to the decrease in polar ice and release of greenhouse gases as permafrost melts since the responses may be non-linear. The core of the problem facing mankind The Egyptian fluvial drainage system living in the Nile Basin is a cancer-like growth of population, coupled by diminishing water resources; thus, a dark future is Recognition of large previously unknown, south, and west inevitable. Strange enough that the Nile Basin receives 1600 trending alluvial valleys in southwestern Egypt and Sudan billion cubic meters of rainwater, out of which the people by means of Shuttle imaging Radar has led to several living in the Basin (11 countries) use only 550 billion cubic reassessments of the history of the areas covered meters. The rest is lost in the ponds and marshes of South by Radar Images (McCauley et al. 1982, 1986; Mc Hugh Sudan or running to the Red Sea, along with evaporation, et al. 1988a,1988b). The images revealed what these authors transpiration, and seepage into the subsurface. The named Radar Rivers in southwestern Egypt and northwestern Ethiopians are building dams along the many branches of Sudan. Some of these are 25 km in width; others have the Blue Nile, causing a major conflict between this country channel-in-channel settings. Human artifacts were collected and Egypt. The Ethiopians are planning to completely dam the from the buried banks of some of these rivers revealed by Blue Nile for several years, preventing water from flowing digging in the channel course. These drainage systems are down to Sudan and Egypt. Through this daming process, the covered by an almost ubiquitous and complex thin to thick, Ethiopian reservoir can be filled making electrical generation >5 to >100 m Quaternary aeolian and fluvial veneer (Haynes possible. Through this policy, the Ethiopians are ignoring the 1982a,1982b; Maxwell and Haynes 1985; Breed et al. 1987). water needs of the other two countries. Egyptians depend The end result of Shuttle Radar Images studies since 1981 on mostly on the Ethiopian water; 85% of their water is coming Egypt’s desert surface is summarized by the discovery of two through the Blue Nile, only 15% from the White Nile. main former drainage systems; the Qena in the east of the Egyptians cannot wait for the Ethiopians to fill their reservoir. country running into N–SW direction since Priabonian time, The easiest solution is to let Egypt’s budgeted portion of the associated with the Red Sea Mountains uplift. The second is Blue Nile water seep through the constructed dam. Instead of the Gilf River in western Egypt flowing from south to north filling the reservoir in 4 years, it can be filled in 8 years or so, since post-Eocene time, following the retreat of the Tethys, without complicating Egyptians’ lives and Egypt’seconomy. which started gradually since the late Early Eocene The problem was not adequately considered by most (Ypresian). Egyptians except very late, when in 2014, the population reached 87 million (according to the Egyptian Central The Qena River Agency for Public Mobilization and Statistics 2015). All the solutions presented to overcome this problem are directed to Since the late , the slope of the Egyptian craton from increase the share of water coming from east Africa: Ethiopian south to north led to north–south transgressions of the Tethys water. However, the present Nile channel has a certain capac- over Egypt’s surface, followed by regressions during the Early ity and cannot carry more water even if the Ethiopians will Eocene and the following times in opposite direction (Issawi agree to supply Egypt with more than its share from the Blue et al. 2009). This palaeogeographic setting resulted in rivers Nile. If this happens, the added Nile water into Egypt will running S–N following the northward retreating shorelines, a flood the fields on the east and west banks of the Nile. The theme that was completely disrupted by the rise of the Red Sea Egyptians have to find other solutions for their problem dif- Mountains in eastern Egypt (Figs. 2 and 3). The uplift started ferent from adding more water to the already chocked river’s along the linear rift of the Red Sea during the Priabonian (Late course north of Aswan. Eocene) and continued until the final pulse at about 21 Ma, the So far, we have briefly reviewed the many hydrogeological boundary between the Aquitenian and the Burdigalian (Early systems, which dominated many parts in the east African Miocene) (Omar and Steckler 1995), as interpreted from fis- Sahara. This review clearly shows that what we see and call sion track analyses of zircon crystals in basement rocks. BSahara^ is only a recent landscape opposite to what was Contemporaneous with the uplift, another tectonic high dominated in the near past. Archeological findings in the pres- (swell) was formed in central Egypt known as the Galala ent vast and utterly dry desert (Wendorf et al. 1984, 1985, Bridge or High (Figs. 2 and 3), which became a water divide 1987a, 1987b, 1993; Wendorf and Schild 1976, 1980;Mc between short north flowing rivers into the Mediterranean and Hugh et al. 1988a, 1988b; Wendorf and Close 1992,and south flowing rivers which built the beginning of the Qena others) present further evidence for a totally different hydro- system. The effect of 14 million years of uplift resulted in a logical and paleoclimatological settings now and in the near 90° change in slope of Egypt’s surface, from south–north to 14 Page 6 of 20 Arab J Geosci (2017) 10:14

Fig. 2 The Egyptian drainage systems during the Late Eocene– Oligocene (after Issawi and Osman 2008)

east–west direction. Issawi (1983) noted that most of the ma- 1981). Also, associated with the Mid-Paleogene uplift are the jor wadis are oriented in that direction based on an analysis of many fractures and meridional faults parallel to the Red Sea Egypt’s map scale 1:2,000,000 (Geological Survey of Egypt trend. The most important Cenozoic drainage followed these,

Fig. 3 The Egyptian drainage systems during the Late Oligocene–Miocene (after Issawi and Osman 2008) Arab J Geosci (2017) 10:14 Page 7 of 20 14 many lineaments assuming an approximately N–Strend, unknown buried river channels lying below the sand. A which became the site of the Qena River system in central backhoe-excavated trench in the Shuttle swath revealed sedi- Egypt and the Gabgaba–Allaqi River system in the south ments and soils on the banks of the Radar Rivers under wind- (Fig. 3). These two main drainage systems marked the hinges blown sand. along which the Red Sea Mountains kept rising; possibly well Field investigations in the areas of the Radar Rivers (RR) before the Eocene (Osman et al. 2002) in the Allaqi case. have shown that at least the upper 40 m of these channels The two master rivers flowing in opposite directions: Qena (which are probably 100’s of meters deep) are now filled with to the south and Allaqi–Gabgaba to the north, met somewhere alluvium, mainly sands and fine gravels that were deposited south of what is now the city of Aswan (Fig. 3). Topographic by running water as late as the Late Pleistocene (Schaber et al. and sedimentary evidences suggest that the Qena system cap- 1994, 1997). Concurrent with and subsequent to the last stages tured the Allaqi stream, with the Qena River flowing to the of aggradation, these sediments were cemented by calcium south and southwest, disrupting the main Eocene Limestone carbonate deposited under fluctuating groundwater Plateau, sloping over the Red Sea Mountains to the west. conditions. The carbonates along the edges of the now Drainage and eventual incision first occurred at high altitudes aggraded paleovalleys in the course of the RR were dated by above 250 m, as evidenced by huge amounts of fluvial- Szabo et al. (1989, 1995) at 141 and 212 ka. Most of the transported Lower Eocene chert gravels present on top of the carbonates appear to have been precipitated from groundwater present Western Limestone Plateau (El Deftar et al. 1978;El and flushed from the carbonate scarps of the Western Hinnawi et al. 1978), in the Valley of the Kings west of Luxor Limestone Plateau, which overlooked the Qena River in be- (Issawi et al. 2009), and filling grabens in the Limestone tween Aswan and Qena. These episodes of deposition may be Plateau west of Minia (Mehanna 1979). related to Late Pleistocene humid climates that facilitated hu- During the Oligocene, Egypt’s climate was essentially that man occupation in this now hyper-arid region. Several wet of a rainforest, with precipitation estimated to be 1500 mm/ intervals during the Pleistocene together with a near surface year as evidenced by the rich vertebrate fauna and flora in the groundwater level dominated over the south Western Desert at Faiyum area (Beadnell 1905a, b; Simons 1972, 1987), gradu- >300,210,175,160,and140ka(Kropelin1993). These data ally reducing to ca. 1200 mm/year by the Late Miocene imply climatic conditions with annual rainfall approaching (Pickford et al. 2008). This amount of precipitation led to 400–600 mm/year (McHugh et al. 1988a, 1988b). Most dissolution and cave formation in the exposed limestone sur- workers in southwest Egypt agree on rain phases during the face beds midway between Bahariya and Farafra oases Middle to Late Pleistocene and the Holocene, though with (Pickford et al. 2008), and widening of fractures in the main different rates (Wendorf and Shield 1976, 1980;Haynes Limestone Plateau located in central Egypt, which later was 1980; McCauley et al. 1982, 1986; Kropelin and Pachur dissected into Eastern and Western Limestone Plateaus. The 1991;Kropelin1993; Wendorf et al. 1993, 2001). absence of gravels younger than Middle Miocene on the Western Limestone Plateau indicates the timing of rifting into two plateaus. In a major fracture in the main Limestone The Gilf River Plateau west of the Red Sea Mountains, the Qena River flowed southward, carving a wide floodplain on either side The uplift of the Egyptian craton started intermittently in the of its channel. Southwest of the present-day Aswan, the Paleozoic with the rise of many parts of southern Egypt, from Qena River flowed around the southeast corner of the Sinn Gebel Elba in the through the basement area El-Kaddab scarp at Gebel Kalabsha (latitude 23° 30′ N), east of the present Nile and further west to Gebel Uweinat and where the river lost its confined channel. Part of a possible the Gilf Kebir Plateau (Geological map of Egypt 1981; Fabre incised meander bend is present on the southeast edge of the 1988; Foucoult and Raoult 1995; Osman et al. 2002; Bumby plateau, although the present-day topographic gradients are and Guirad 2005;Issawietal.2009). The rise of the highly modified. Southwestward of Gebel Kalabsha, gravels basement rocks and the unconformably overly- atop outliers of the plateau indicate a less confined, braided ing Paleozoic sediments started earlier in the south than in channel pattern that predated the Kiseiba scarp at Darb El- north Egypt, resulting into a general slope to the northwest Arbain south of , and flowed to the southwest creating a depocenter, an embryonic stage of the major Siwa through what is now the Selima Sand Sheet (Maxwell and Basin (Fig. 3). The irregular-raised surface of southern Egypt Haynes 1985; Issawi and McCauley 1992, 1993). created a series of structurally controlled sub-basins: the Kom Although archeological investigations had identified lacus- Ombo sub-basin, the South Nile sub-basin, and the Dakhla trine and fluvial sediments in isolated sites in the Western sub-basin. Of more importance to the latter drainage, the Desert (Wendorf et al. 1984, 1993), it was the first flight of inter-basin tectonic highs became the sites of the many arches the Space Shuttle Imaging Radar (SIR-A) that put these sites that crossed Egypt from the southwest to northeast dividing into fluvial context. The images revealed a vast network of the surface into discrete drainage basins. 14 Page 8 of 20 Arab J Geosci (2017) 10:14

The Uweinat–Gilf High gave rise to centripetal drainage During its long course in Egypt, the Gilf River flowed over flowing to the north, east, and south in Egypt and Sudan and a Precambrian igneous and Paleozoic sandstone country in the to the west in Libya. The Gilf drainage system antedated the south between latitudes 22° N and 24° 30− N. Further north, Qena system, which evolved in response to the uplift of the the river system crossed Mesozoic and Cenozoic clastics and Precambrian basement of the Red Sea Hills. Before the Qena carbonates, with increasing carbonate north of latitude 26° N. system, the rivers flowing over east and central Egypt were During its course over the carbonate country, especially at the debouching their waters into the constantly retreating paleo- latitude of Farafra Oasis, (27° N), solution of carbonates has Tethys shores during the Paleozoic, Mesozoic, and Early been responsible for the development of the Farafra depres- Cenozoic. The earliest Qena system began with the initial sion and its surroundings. Karstic features are known from uplift of the Red Sea Hills, and may have been connected with Farafra–Ain Dalla (lat. 27° 08− N and long. 26° 5− E) stretch the Gilf River tributaries in the Dakhla Basin, then flowed where many caves in the Upper Cretaceous Khoman Chalk northward (Issawi and McCauley 1992, 1993). The arc-like and also in the Lower Eocene Farafra Limestone have become shape of the main Kharga and Dakhla Oases northern scarps a tourist attraction. may owe their initial development to the Qena–Gilf River at their base. The constant rising of the Uweinat–Bahariya arch led to the Stratigraphy of the Egyptian fluvial drainage system disruption of the two systems during the Miocene; hence, the Qena flowed southward into Sudan and probably through the With the northward retreat of the Tethys margin, three rivers Morhogoum Gap (lat. 19° 10− N, long. 23° E) and thence into were active for redistributing sediments eroded from the the Chad Basin (McCauley et al. 1986) before reaching the uplifted Egyptian craton, the Gilf River, the Bown and Atlantic Ocean in what these authors called the BTrans African Kraus River, and the Qena River (Fig. 3). The Gilf River, Drainage System^ (TADS). comprised a northward drainage from the Gilf Kebir Plateau, A corridor of linking many lakes in south was likely to be the oldest, since the plateau began to rise since Libya, Chad, and Sudan was proposed by Drake and the Late Paleozoic. In eastern Egypt, the northeastern Galala Bristow (2006) who also suggested a connection between High created a water divide between the S–SW flowing Qena the Sahabi River and the Niger River perhaps via Lake River and the northwest drainage namely the Bown and Kraus Chad. This Late Miocene water corridor was probably the River (Issawi et al. 1999). The Qena River carried chert route TADS used to reach the Atlantic. On the other hand, gravels from the Lower Eocene Thebes Formation, depositing Pias and Guichard (1957) suggested that Mega-lake Chad at them on the Western Limestone Plateau, whereas the second level 352 m.a.s.l. was no longer a closed lake but was drained Bown and Kraus River carried clastics from the Eastern with a substantial spillway, a former outlet to the Gulf of Desert high hills (Northern Galala Plateau and Ataqa Hills) Guinea via the Benue and Niger Rivers. to Faiyum area (Bown and Kraus 1988). These workers and others clearly point to a possible con- The sediments carried by the Qena River, south of the nection between the Egyptian fluvial system (Radar Rivers) Galala High, covered a good stretch of the present upper and the Atlantic Ocean. Paleontologic and seismic evidences Nile Valley as well as a thick gravel sheet on top of the now suggest that the Gilf River kept flowing northward to once-connected limestone plateau east and west of the present near the present site of in the Oligocene– Nile. These are known as the Katkut Gravels of Oligocene age Miocene, then turning eastward at the base of the arc like north (El Deftar et al. 1978; El Hinnawi et al. 1978). The gravel scarp of the Qattara Depression, and continued into the patches include reworked dark brown limestone and chert near the present site of Alexandria and angular to sub-rounded and disk-shaped rocks, bounded (Albritton et al. 1990) during the Late Miocene. Seismic re- by carbonate hash representing an aggradation of bed load flection profiles reveal a rough and gullied topography pro- sediments. At the end of the Miocene, the Mediterranean duced by the Messinian Rivers whose northern extremities lie was desiccated due to the closing of the Gibraltar straits and as much as 2.5 km below the present sea level. The Ras Alam separation of this sea from the Atlantic Ocean (Chumakov El-Rum Canyon trends north-northeast and by projection 1973a, 1973b; Hsu et al. 1973). The lowering of the would cross the present shoreline at about 31° 30− N and Mediterranean Sea level by 2–3 km led to the incision of 29° E heading towards the eastern end of the Qattara (Ryan channels by rivers flowing into the desiccating sea. In eastern and Cita 1978;Barber-Peter1981); a canyon used by the Gilf Egypt, the Galala Plateau continued into the Western Desert River. A feeder to the Gilf River might have come down from forming a water divide between north and south Egypt (Issawi Wadi El-Natrun (120 km northwest of Cairo) as evidenced by and Osman 2008). North of the divide, the rivers continued to a palatine fish indigenous to Chad and recorded by incise through headward erosion of north and south flowing Greenwood (1972) from the Miocene– sediments of rivers to reach the new base level—the desiccated Wadi El-Natrun. Mediterranean. South of Galala, the Qena system joined the Arab J Geosci (2017) 10:14 Page 9 of 20 14

Radar Rivers south of Aswan and continued its flow into plateau of Ethiopia. The main rivers flowing off this highlands central and west Africa through the Trans African Drainage westward include the Blue Nile (or the Abbai in the Amharic System (TADS) to the Atlantic Ocean (McCauley et al. 1982). Ethiopian language), the Atbara River, and some other smaller Communication was resumed between the Atlantic and the rivers all cut back deep canyons in the Ethiopian volcanic Mediterranean in the Early Pliocene through Gibraltar (Hsu plateau exposing in places the basement rocks of the Red et al. 1973), and saline water gushed into the empty channels Sea Mountains and the Mesozoic–Cenozoic sediments above north and south of the Mediterranean, rising about 110–120 m capped generally by flat horizontal basalt lava flows. These above the present sea level. Sediments of this time were re- flows give rise to sharp precipitous plateau margins affecting corded in Faiyum (Beadnell 1905a) and near the Sphinx in eastern Africa since the Early Tertiary. The volcanicity and the southern Giza (Said and Martin 1964; Issawi et al. 2005). The tectonic disturbances, which have fractured and deformed this rivers flowing north to the Mediterranean and the south run- ancient continent, have probably never breakdown this pla- ning system breached the Galala divide, and marine water teau apart. Southern Sudan and northern Uganda share high invaded the prior Qena drainage and its tributaries up to the ground rising to over 3000 m in the Imatong Mountains near level of 110 m.a.s.l. as far south as Aswan, where Early their borders. It consists of basement rocks, which crop out at Pliocene marine fauna was recorded in the boreholes drilled the central plateau of Karamja and west Nile in Uganda. The at the High Dam site (Chumakov 1973a,1973b). Sediments of high ground continues northwest along the Zaire and Central this time crop out west of El-Balliyna, 70 km south of Sohag African Republic border on the way towards Chad forming (Issawi et al. 2009), indicating a continuous marine sedimen- the Nile–Congo divide (Adamson and Williams 1980;Goudie tation along the Pliocene Gulf occupying the present Nile 2005)(Fig.4). Valley. The configuration of the area between South Sudan and When the seawater regressed during the Middle Pliocene, further northeast into the Ethiopian Plateau is governed to the empty gulf became a site for a stratigraphic inversion the east by the East African Rift System (EARS), which through erosion of the sediments and the Precambrian base- shows up at the surface, as a series of several thousand kilo- ment rocks from the high scarps on both sides of the valley. meters long aligned successions of adjacent individual tecton- The top unit in the scarps overlooking the gulf is the Eocene ic rift basins or grabens bounded by narrow but major faulted limestone, which gave rise to the calcareous Issawia zones. The grabens have an average width of 60–80 km for Formation (Said 1971)ortheMenuhaFormation(Issawi each, flanked by uplifted plateau of 1500 to >2000 m in ele- et al. 1978) units; both units belong to the Middle Pliocene. vation, filled with sediments and/or volcanics. The EARS in- Below the Eocene carbonates are the Cretaceous clastics, i.e., cludes two main lines: the eastern and western branches Dakhla and Nubia formations, which were re-deposited as the (Fig. 5) (Chorowicz 2005). Of importance to the present study Qena Sands of Late Pliocene–Early Pleistocene age, followed is the eastern branch, which runs over a distance of 2200 km, by the Kom Ombo gravels, which are mostly igneous, meta- from the Afar triangle in the north through the main Ethiopian morphic, and volcanic rocks released from the uplifted Rift to South Sudan and further south to the Kenyan Rift and Precambrian rocks of the Eastern Desert. In brief, most of continues to the Gregory Rift (Fig. 5). The structures in this the vertical sequence of Phanerozoic units was reversed dur- branch as in the other caused reversal in slopes of the affected ing the Pliocene and the Quaternary. It is clear that up to the rock formations lying along its course. The general structures Middle Pleistocene, no water entered Egypt from Ethiopia or of this system took place in two principle phases during the central African Lakes. The heavy mineral analyses of the Miocene and the Late Pliocene. The step faults along this above-mentioned sediments show nothing but Egyptian base- branch of the EARS are covered by Plio-Pleistocene volcanics ment rock-sourced minerals, i.e., opaque minerals, rich in zir- (Chorowicz 2005). con and epidote, and a high zircon--rutile (ZTR) The pre-Rift drainage pattern in East African rivers in value with lack of pyroxenes and amphiboles (Omar 1996), South Sudan Republic, flowed westwards across Uganda which are very common in the younger Ethiopian derived and the present positions of Lake Victoria and Lake Albert sediments (i.e., the Dandara Formation). into Zaire drainage system and ultimately into the Atlantic Ocean (Adamson and Williams 1980). The White Nile rises in Uganda (Victoria Lake) and flows as Sudan fluvial drainage system the Victorian Nile. Leaving Victoria Lake, it passes northward to Kioga Lake and continues westward where it meets the Albert Through the central plain area of Sudan, isolated mountains Nile at the most northerly part of its course where it crosses the break the monotony of the flat surface forming prominent Marchizone falls and continues further north towards Juba as it landmarks. These are invariably associated with rock types follows the dominant basement foliation for the next 1250 km, geologically different from the surrounding country. To the where at Khartoum, it joins the Blue Nile coming down the east in central Sudan, the interior plains give way to the high Ethiopian Plateau. For most of its course, the White Nile and its 14 Page 10 of 20 Arab J Geosci (2017) 10:14

Fig. 4 Drainage patterns in central and northeastern Africa showing the present and probable former limits of the Nile Basin (after Adamson and Williams 1980)

tributaries flow northward except for 200 km, between lakes Wo structural weakness, which crosses Africa from the Gulf of and Malakal where it turns sharply eastward. This stretch is par- Guinea (Vail 1972) and continues eastwards to the Bayuda allel or aligned with Bahr El-Arab, Khor Alat, and Lat River volcanics. The area between Gebel Marra and the main Nile tributaries and a system of E–W trending faults in Bahr El-Arab north of Khartoum is also traversed by numerous prominent province (Whiteman 1971;Vail1974). NE–ENE trending volcanic dykes and lineaments. This vol- Western is another area of high ground formed by canic belt was probably associated with the Ascension fault basement rocks with a relatively thin cover of Paleozoic– zone, which crossed the Mid-Atlantic Ridge and invaded Mesozoic sandstones. Only westward near the Chad border, a Africa in a northeast direction for 800 km, starting from the conspicuous volcanic building Gebel Marra is located. The Gulf of Guinea. It is interesting that this belt is parallel to the Gebel rises 3042 m around Deriba Crater, which represents the Sudd area in South Sudan as if Africa is divided into several highest ground in West Sudan. The Gebel is the center of Africa, tectonic ENE belts underlain by basement rocks at base, cov- betweentheMediterraneaninthenorthandCapeTowninthe ered by sandstone in the middle and volcanics on top. south, whereas it is centrally located in between the Atlantic and The great changes in the paleoclimates together with tectonics the Indian oceans (Brock 1972). Streams draining Gebel Marra had a great impact on these belts. The Guinea–Nubia Lineament flow southeast towards Bahr El-Arab and the White Nile, or (Guiraud et al. 1985) is another nearly E–W transform fault that is westwards by way of wadis Tawil, Azum, Kodja, and Chari crossing Africa from the Atlantic Ocean to the Red Sea (Fig. 6). Rivers flowing into Lake Chad. Another upstanding area is lo- The volcanic doming in Gebel Marra together with the many E– cated almost at central Sudan in the Nuba Mountain region of W (approximately) structures cause the Nile–Chad divide to southern Kordofan Province. Isolated and hills and curve sharply to the east, around the area in which the rivers have ridges rise about 600 m above the plain, the highest (1412 m) is recurved courses and in which the unconsolidated mantle occurs. Gebel Dair (Williams and Williams 1980). Prior to the eruption of Gebel Marra, Adamson and Williams The Gebel Marra and the Bayuda volcanic fields together (1980) suggested that the Nile–Chad watershed was almost with the Tagabo and Malaha volcanics lie on a major zone of 300 km to the west of its present position. According to this Arab J Geosci (2017) 10:14 Page 11 of 20 14

Fig. 5 East African Rift System (after Chorowicz 2005)

model, the present recurved upper reaches of Wadi Howar were tributary, draining parts of Gebel Marra and Ennedi massifs and part of Wadi El-Ku where its tributaries also originated from the assuming a length of 640 km and an average width of 11 km. The western side of the present Gebel Marra (Vail 1972). lower Wadi Howar was not an exotic river sustained by rainfall in In general, the drainage system in many parts of Sudan away the mountainous source area, but it was fed by substantially in- from the high plateaus in the southeast is now completely sand creased local rainfall supporting groundwater recharge during chocked, although extensive drainage features both in western phases in the Quaternary (Pachur and Kropelin 1987). Some and in northern Sudan and in southern Egypt testify for more evidences suggest that until the Late Miocene, the original direc- humid conditions in the early and middle Quaternary and even tion of flow was opposite to the present one and that Wadi Howar during most of the Cenozoic (Whiteman 1971;Williamsand had debouched its water in the Atlantic (Kropelin 1993), forming Adamson 1982; Williams et al. 2010). The Oligocene vertebrate a tributary of the Trans African Drainage System. remains in Faiyum (Simons 1962, 1965) and the galagid teeth remains in the Late Miocene sediments in between Bahariya and Wadi Gabgaba: a major source for more water supply Farafra oases (Pickford et al. 2008) are evidence of this fact. to Egypt During the late Quaternary, extensive parts of the Sahara were hydrologically linked to the Nile by way of many wadis in the Wadi Gabgaba (see Fig. 3) is a south–north river running east Sudan Western and Eastern deserts. Of importance are Wadi of the Nile, 350 km east of the Fourth Cataract. The wadi has a Howar and Wadi El-Melik in the west and Wadi Gabgaba in the length of 280 km before it crosses latitude 22° N and con- east. Wadi Howar (see Fig. 4) constitutes the Nile’s largest tinues into Egypt’s Eastern Desert assuming the same trend, 14 Page 12 of 20 Arab J Geosci (2017) 10:14

Fig. 6 Guinea–Nubia Lineament (after Guiraud et al. 1985). 1 Basement rocks. 2 Directional downthrown. 3 Lineament. 4 Basalts. 5 Sediments. 6 Epicenter of 22 Dec., 1983 earthquake in Aswan area. 7 Kalabsha fault for ca. 100 km before joining the northwest Wadi Allaqi com- is remarkable that in spite of two major fluviatile systems ing down the Precambrian Basement Complex of the Red Sea passing through Sudan (White and Blue Niles) yet most of Mountains. Wadi Allaqi runs for ca. 110 km before reaching Sudan is a dry country. The major problem in west Sudan, now Nasser Lake. It is said that the River Gabgaba Bcould Darfur, and Kordfan is the lack of water. This led to many easily usurp the course of the Nile^ since it was an easy pass wars between the farmers and animal herdsmen and between for this river to flow into Egypt instead of passing through the the Sudanese and the Chadians. Dongola long loop in Sudan and crossing five cataracts before To recapitulate, the Sudan area has a very different physi- reaching the First Cataract at Aswan. Apparently, the volcanic ography and climate in the near past, not to say in the old times eruptions near the headwaters of Gabgaba, i.e., the Bayuda of the Phanerozoic. These characteristics are recommended volcanics, forced the Gabgaba River away from joining the and should be well studied to win the shortest way to move present main Nile. water from Central and eastern Africa through the dry The Bayuda area within the Dongola loop of the Nile is a paleochannels in northeastern Africa. Precambrian surface dotted with ring complexes, volcanic flows and cones, some of which appear to be quite recent (Vail 1974). If it is possible to rejuvenate the Gabgaba– The Nile Basin drainage system along its long way Allaqi River course by Nile water from its Ethiopian source from central and East Africa to the Mediterranean through either the Blue Nile or the Atbara, it certainly would add much water and good farming lands in southeastern Egypt In general, all rivers in South Sudan Republic converge to and northeast Sudan (Fig. 7). form the White Nile. The main area of convergence is the The flat area in Sudan, south of latitude 22°N, at the foot Sudd area, which receives water from East African lakes via slopes of Gebel Kurga, Gebel Oda, and Gebel Iss, reaches Bahr El-Gebel, from the Nile–Congo divide via Bahr El-Arab 2 more or less 25,000 km ; this could be a good addition to and Bahr El-Ghazal, from the and also a the farming fields in northeast Sudan. The same setting is true negligible portion now (but might have been more in the past) north of latitude 22° N. The southern flat area bounded by the from the Nile–Chad watershed. The drainages from southwest Nile to the west and below the high scarps extending between Ethiopia and the border regions of Kenya reach the White Nile Gebel Aiynat and Gebel Umm Eltuor is a continuation of the via the Sobat River downstream of the Sudd area. The head- 2 Sudanese area. In Egypt, this area is roughly 12,000 km and waters of all these rivers traverse the basement area, which are can be cultivated by the suggested Gabgaba–Allaqi River. unconformably overlain in places, by volcanic rocks. The Both areas represent a former inland delta of the defunct many rivers in the White Nile domain incised their channels Gabgaba–Allaqi River and its tributaries during Pleistocene to varying depths and merge into the vast plains of South time when wet phases dominate the area. The Ethiopian new Sudan. Stream flow changes from confined to distributary built El Dam on the Blue Nile can be an excellent forms as they spread out across their fans, adding more sedi- source for water to rejuvenate the old Gabgaba River. ments and migrating laterally. The surface of most of the It is worth mentioning that south of Juba in South Sudan White Nile fluvial system is located in the Sudd area, which Republic, the White Nile water is lost within a swampy, bog- stretches about 1000 km in length southeast from Darfur in gy, and spongy very flat ground area. The water reaches Khartoum from the White Nile is most probably less than Fig. 7 Suggested connection (dotted red line inside circle) between the„ 10% of the main budget of this part of the Nile. Moreover, it White Nile and Gabgaba–Allaqi dry channel Arab J Geosci (2017) 10:14 Page 13 of 20 14 14 Page 14 of 20 Arab J Geosci (2017) 10:14 west Sudan towards Kenya and Uganda and assumes ca. 300 The East African Rift System (EARS) crossed this trough to 400 km in a NW–SE direction. This trough is covered by before joining the Gregory Rift; both rifts can be regarded as active or semi-stable alluvial fans, by swamps and sponges unique successions of graben basins linked by intracontinental formed by upward seepage of subsurface shallow water, by transforms and segmented by transfer and accommodation active distributary or confined streams, and by prior stream zones (Chorowicz 2005). The severe tectonics plus the con- channels, barely some have very inconspicuous gutters stant rainfall and discharge of (shallow) subsurface waters (Fig. 8). The thickness of sediments within the trough is esti- covering the thick sediments of this trough led to its very mated in the order of several thousand meters, as revealed by marshy characteristics. The area shows progressive incision seismic work of Chevron Oil Co. The sediments have been as if the sediments are constantly plowed by different tectonic ascribed to the Tertiary Um Rawaba Formation (Whiteman trends. Drainage diversion in Uganda from Miocene times 1971). onwards caused ponding of water and sediments in the

Fig. 8 Geomorphological map of the middle and lower reaches of the White Nile, the Blue Nile, and the Atbara River (after Williams and Adamson 1980) Arab J Geosci (2017) 10:14 Page 15 of 20 14

Albert Basin and overflow into South Sudan. The Quaternary and Hugues 1980). Through its long way to the Mediterranean history of the White Nile headwaters flows from Lakes Albert Sea, about 1620 km, the Nile flows in an utterly dry desert, and Victoria into the upper White Nile Basin forming the type never receiving any drop of water except in very rare cases and sequence of sediments in the Sudd area. where and when cloudbursts in Egypt’s Eastern Desert add a The White Nile and its tributaries dominate the drainage of negligible amount of water. most of central northeast Africa. The river started in Uganda and At Abu Hamed, 132 km north of the Fifth Cataract, the Nile flows as the Victoria Nile and Albert Nile along the East African bends southwest running for about 285 km before it assumes Rift System until it reaches the great Aswa shear zone. About its northern course at the delta of Wadi El-Melik coming from 65 km downstream, the river swings off to the north towards west Sudan desert after passing the Fourth Cataract in its Juba as it follows the dominant basement foliation (Williams course. From the delta of Wadi El-Melik, the river crosses et al. 1986; Williams et al. 2011). From here on for the next nearly the Third and Second Cataracts before reaching the Egyptian 1000 km, the river crosses unconsolidated Quaternary sands and border at latitude 22° N. In Egypt, the Nile has a general silts until it was joined by the main tributary of the Blue Nile. For north–south course ca. 1205 km, but bending few degrees to most of its course, the White Nile flows north, except for 200 km the west or east. The river passed the First Cataract at Aswan section, between Lakes No and Malakal where it turns sharply and two main loops: the first in Korosko, 180 km south of eastward (Vail 1974). A phase of high-energy flow in the White Aswan, covered now by Lake Nasser water, and another at Nilewasrecordedat27.8kyrfollowedbysomewhatreducedflow Qena midway between Aswan and Cairo. at 13.3, 10, and 4.8–4 kyr. The Holocene record of high Blue Nile At the Nile course in north Sudan, Whiteman (1971)sug- flood levels towards 13.9–13.2, 8.6, 7.7, and 6.3 ka were calcu- gested that ponding of the Nile occurred near its junction with lated by Williams (2009). The contrast between the two Niles the Atbara River. Most probably, more water was available (White and Blue) in the Holocene points to different climatic than could be carried by the shallow Nile channel. The conditions over both river basins (Williams and Adamson 1982). Dongola loop weakens and widens the rush of water in the Downstream from its junction with the Sobat River; the river course; hence, four cataracts are formed. This part of the White Nile flows northward in an almost horizontal gutter river is geomorphologically young, not yet graded by the wa- between the pediment of the Nuba Mountains south of ter passing through this region. The ponding plus the general Kordofan and the Ethiopian foot hills in the east. Basement flat deserts on both sides of the river are flanked by the Bayuda rocks crop out along the White Nile channel covered by the volcanic mountains on the east and sandstone high banks on Quaternary Um Rawaba and Gezira formations and in places the west. The accumulated water in north Sudan was enriched fill basin areas underlain by basement rocks. The sediments by waters from the ancestral Atbara, the Blue Nile, and the are mostly fluvial and partly lacustrine (Whiteman 1971). wadis in west Sudan. The lake formed by the excess of water TheBlueNilestartsfromLakeTanainEthiopia,at overflow to the north had been a closed basin until it was 1480 m.a.s.l., and drains a catchment area of about breached by the gushing of water when it reached a higher 200,000 km2. It is oriented about 150°–160° for about altitude than its northern side. The end result led to an exten- 150 km, matching the direction of the prominent lineaments sive lake south of Egypt’s border with Sudan. Blown sand in the Precambrian rocks. Thick deposits of pure volcanic glass enriched water storage in the lake by building a high section of fluvial derivation, point to Ethiopian volcanic eruptions, of chert (Hudi Chert) in the lake especially at the area of Batn which blanketed parts of the headwaters of the Nile system El-Hegar south of Halfa. The chert is believed to be Oligocene during 20,000 and 30,000 BP.(Adamsonetal.1979). The in age (Vail 1974), but it was hard to keep the water restricted Quaternary volcanic activity along ENE alignments of cones for a long time: Oligocene to Pleistocene, probably it was and craters together with volcanic ash covered parts of south- partly flowing westwards by the many wadis in western westEthiopianeartheOmoRiver(WilliamsandHugues1980). Sudan. The water in the lake kept rising up to +250 m.a.s.l., North of Khartoum, the main Nile is closely confined by when it spilled from the high lake in northern Sudan to a lower Precambrian basement rocks by Mesozoic sandstones and by surface in Egypt. The lake down in Egypt covered an exten- volcanic rocks. Near the Sixth Cataract of the Nile, the river sive part of the desert surface, reaching Bir Sahara and Bir cuts a deep, narrow gorge through the Sabeloka Ring Tarfawi ca. 250 km west of the Nile at Abu Simble. Similar Complex before exploiting major joints in the basement sur- seepage to the east covered wide areas, probably reached the face. The great bend north of the Fifth Cataract was a result of western side of Gabgaba River and penetrating many wadis updoming and volcanic eruption in the Bayuda area covered coming down Korosko High. by Precambrian surface dotted with ring complexes and vol- The new river entering into Egypt (the present Nile) most canic cones, some appear to be quiet recent (Vail 1974). probably during ca. +500 ka (Issawi and McCauley 1992, The last water the Nile gets from its east central Africa 1993) had a great effect on the Egyptian’shistorywhobuilt headwaters is from the Atbara River, associated with the one of the oldest civilizations in the world in the domains of Quaternary uplift of the western Ethiopian Plateau (Williams religion, art, and literature (Hume 1925). 14 Page 16 of 20 Arab J Geosci (2017) 10:14

The Nile in Egypt passed through a sandstone country at inland deltas for three major wadis, Kharit, Shait, and Natash, the Egypt–Sudan border, belonging to the Late Paleozoic are located. At Esna–Luxor, the Nile Valley widens in the west () near Abu Simbel, covered by clastics mostly and tightens in the east, 5 km to less than a kilometer, and of Cretaceous age. The Nile, in general, inherited courses of becomes narrower in the east at Sohag where the eastern scarp old rivers, some originally having opposite slopes, e.g., the nearly hugs the Nile. From Assuit to near Helwan, south of Nuba River in southern Egypt and the Qena River in central Cairo, the Nile Valley opens gradually westwards until it and southern Egypt, got their waters from Korosko Highland reaches nearly 35 km west of Minia and Beni Suef–Giza. in southern Egypt and from the Red Sea Mountains opposite On the east side, the Valley is narrow few tens of meters east Ras Gharib on the Red Sea coast, respectively. of Helwan–Beni Suef and Minia stretch to less than 2 km only Before the Nile, all the waters in the rivers of Egypt were east of Assuit. The scarps on both sides north of Qena contain supported purely by Egyptian precipitation no central or east younger Eocene limestones, Middle Eocene limestones at the African waters reached Egypt. The study of Nile sediments in latitude of Beni Suef, and Upper Eocene limestones and clays central and south Egypt proves the presence of two groups of near Cairo latitude. heavy minerals. The older sediments on the present Nile Basin Just north of Cairo, the Nile has two branches, Damietta in are known as the Qena Sands (Said et al. 1970). These are rich the east and Rosetta in the west embracing the Delta in-be- in zircon and epidote, a high zircon-tourmaline-rutile (ZTR) tween. The area of the Nile Delta is ca. 18,000 km2. value and opaque minerals. The other younger sediments of In general, the slope of the Nile in Egypt is 1 m each 14 km. the Dandara Formation (Said et al. 1970) are rich in pyroxenes In places, at Minia 250 km south of Cairo, the river has a (mainly augite), amphiboles strongly dwindled zircon, and shallow depth where the Middle Eocene limestones of the zircon-tourmaline-rutile (ZTR) value. The Qena Sands are old Galala Bridge can still be seen in the channel, hindering believed to be purely from an Egyptian source derived from sailing boats. the Red Sea Mountains, whereas the Dandara Formation is of Tectonics are very mild; with exception of the Kom Ombo Ethiopian derivation (Omar 1996). A well preserved calcare- and the Qena loop, almost none can be noticed in the course of ous root cast from the top third of the Dandara Formation was the river. In the surrounding scarps, many faults were mapped submitted to Barrey Szabo, U.S. Geol. Surv., Denver, CO, for from the Eastern and Western Limestone Plateaus especially uranium series dating; the result was 213 ± 14 ka (Szabo et al. in southeastern Kom Ombo, northern Qena, and south of 1989; Issawi and McCauley 1992). Thus, it is believed that the Cairo at the east–west Wadi Araba. The structures have a beginning of the Ethiopian water reaching Egypt via the Nile general Red Sea trend, reflecting the opening movements of was only slightly more than half million years ago. the Red Sea in post-Eocene times. When the Nile first entered Egypt, it had an elevation of The climate in Egypt is dry most of the year, except in the 250m.a.s.l.ormore.SeventeenNiloticfishremains,crocodiles, winter where rainfall is less than 20 mm/year, whereas it in- and other animal bones were discovered at Bir Sahara at creases to 70–100 mm/year near the Mediterranean coast. 247m.a.s.l.,anddated174ka(WendorfandSchild1980; Outbursts are not uncommon especially along the northern Gautier 1993; Van Neer 1993). The high elevation, i.e., coast and in Sinai. +247 m.a.s.l. where the Nilotic fossils were recorded at Bir Sahara proves that the level of the Nile water crossing Sudan border to Egypt was certainly higher than 247 m. This level was Discussion not known along the course of Qena River from its inland delta at Qena–Safaga road up to southwest Aswan where the Qena Study of the Nile Basin led to many facts, which might help River becomes a braided stream. This high water at the junction scientists to find a solution for the wasted water in the Basin between the Nile waters in Sudan and Egypt helped the Nile (Said 1993). Drainage of Africa has shown substantial chang- water to begin to flow opposite the course of the Nuba River, es after the Gondowana break up (Goudie 2005). Prior to which partly drained the Korosko High and the Qena River, rifting, drainage may have developed as a consequence of which drained the northern part of Egypt’s Eastern Desert. mantle plume, e.g., Mozambique—Red Sea, Ethiopian The Nile water at Bir Sahara apparently formed a large lake Plateau, and Eastern and Western Rifts inside Africa. The around this Bir. Issawi (1978) mapped a wide and great lake African rivers adapted to these tectonics, but the regression around the Bir, covered by Pleistocene sediments.Another lake of the Tethys off northern Africa in post-Early Eocene times; was discovered by Maxwell et al. (2010) at Selima Oasis in the Messinian Crisis in the Mediterranean and the changes in northwest Sudan, which extends inside Egypt until Bir climate during the Quaternary ice age led to many changes in Keisaba south of Darb El-Arbain, a distance of about 220 km. the trend of the southern African rivers. Many of the rivers The east and west sides of the Nile flood plain are narrow, have a range of intriguing characteristics that appear in slope only a few kilometers 1–2 km in the Aswan area, getting wider changes, e.g., Wadi Howar in Sudan, and Qena River in in west Kom Ombo, 10 km, and in east Kom Ombo where Egypt. The Mid-Atlantic Ridge development created several Arab J Geosci (2017) 10:14 Page 17 of 20 14 fault patterns inside Africa (Meyerhoff and Meyerhoff 1972; length of the continent, yet the geology of Sudan is Moody 1973). This pattern has a N 35° E orientation and meagerly studied. It is only recently with the introduc- invaded Africa for more than 800 km. On the other hand, tion of Radar studies that the fluvial systems in northern the Guinea–Nubia Lineament (Guiraud et al. 1985) is a major Africa including Sudan drive the attention of foreign W–E transform fault crossing Africa from the Gulf of Guinea scientists. The most important achievements resulting to the Red Sea. The eastern part of this fault mapped in Egypt out of these studies are evidence for the drastic changes (Issawi 1969)crossestheNileoppositeKalabsha(80km in climates and the changes in the topography of the south of Aswan) uplifted Precambrian came against present dry areas, e.g., Bir Sahara and Nabta areas. the surrounding Cretaceous sandstones. Moody (1973)ana- Apparently, the Sudan and Egyptian deserts areas were lyzed the fault pattern of the Gulf of Guinea and indicated that not very arid as it is clear today. This is evident by the it is of universal importance. Meyerhoff and Meyerhoff type of soils, the distribution of the prehistoric sites in (1972) named this fault zone Cameroun fracture zone striking many parts of the now barren desert areas, the many N 35° E, which extends 800 km inside Africa. This zone is an wide wadis in west Sudan (Howar, El-Melik, etc.), and offshoot of the Ascension fracture zone, which crosses the in other parts of the country, the closed topographic Mid-Atlantic Ridge. The faults of this zone dive beneath system in northern Sudan, south of Halfa, chocked the Archean rocks and assume different trends. This Nile flowing northward to Egypt. These resulted in the E–W trend of tectonics is very clear in the Sudd area in South formation of many fresh water lakes in extensive mud- Sudan. It stretches for almost 1000 km southeastwards from pans between latitudes 23° N and 19° N, in both Darfur towards Kenya and Uganda and assumes 300 to Eastern Desert (Gabgaba area) and Western Desert 400 km in a NW–SE direction. This linear stretch has very (Selima Oasis in Sudan and Bir Sahara in Egypt). swampy, spongy, semi-stable alluvial fans and braided These features give evidence for great changes in cli- streams with no obvious gutters. The area seems to be blun- mate and physiography. At places in Sudan, slope rever- dered and plowed by different tectonic trends leading to its sal was accomplished by the rise of groundwater levels, irregular bedding and soft, loose sediments. e.g., Wadi Howar, by volcanic eruptions, e.g., Gebel The E–W volcanics stretch almost >1000 km between Marra, and by flow of river waters in the direction of Gebel Marra in the west, Bayuda in the east passing by undercut sequence of a bed, e.g., tributaries of the Meiddob, and continuing to the Ethiopian volcanic plateau White Nile. is another linear stretch in north central Sudan. The E–W The play in the rivers’ courses is a reflection of tectonic faults of Bahr El-Arab and the other net of streams in the episodes that dominated over north Africa in general and in White Nile tributaries assuming the same trend (and/or per- Sudan especially during the Phanerozoic, being forceful dur- pendicular) are important structures in South Sudan. ing some times and relaxed in others. The structures are asso- In Egypt’s southern Western Desert, the sediments above ciated with volcanic eruptions, which form obstacles in the the Precambrian basement complex are generally thin unlike channel courses. For example, the Nile passed the hard and central and northern Egypt where thick sediments were pres- long way to reach Egypt instead of flowing through Wadi ent. This has a great impact on the type and magnitude of Gabgaba, which emanates east of Dongola loop; it goes structures revealed on the desert surface. In the south, many through a reversal course in the loop, and thence, northward E–W faults and uplift of basement rocks through the thin passing five cataracts before reaching the First Cataract at overlying sediments are very clear in the desert surface. In Aswan City. The course most probably, was controlled by the northern part of the country, the thick sediments act as the eruption of the Bayuda volcanics, which dams the easy shock absorber that subdued tectonic movements. Even geo- and short course through Wadi Gabgaba. physical work showed that the trends of deep structures differ It is now well known through heavy mineral studies that from surface ones. Still, the east–west structures are important the Ethiopian source minerals were found in the Nile sedi- in southern Egypt as in many areas in Sudan. ments only since >500 ka (Issawi and McCauley 1992; The N–S trending faults in NE Africa are echoes of the Issawi and Osman 2008). The Nile water apparently was major trend of the basement uplift along the Red Sea and the blocked in Sudan for a long time depositing the Umm East African Systems inside Africa. Beside changes in the Ruwaba, Gezria, El-Atshan, Tchad, and Hudi chert, mostly climate during the Late Cenozoic, the different slopes of the with the exception of the Hudi, all the other sediments are many rivers, their continuity to reach the sea or building in- Quaternary gravels, sands, conglomerates, clays, or lake de- land deltas, being braided or have obvious banks, and the posits. The Hudi chert is probably Oligocene in age. topography being high in times and low in others—all these Therefore, it means that for a long period of time, Oligocene and others led to diversified fluvial systems in NE Africa. (?) up to Quaternary, the Nile flows were chocked, and its Though the Nile samples, the geology of considerable waters stored in closed basins probably helped by volcanic portion of Africa as it flows northwards across half the eruptions damming its path to the north. In time, the change 14 Page 18 of 20 Arab J Geosci (2017) 10:14 in topography and shape plus huge water floods forced the the revival of Gabgaba–Allaqi River. Both areas, in Sudan entrapped waters to move north into Egypt. Discovery of the and Egypt represent former inland deltas of the Gabgaba– Nile fish remains in Bir Tarfawi–Bir Sahara area west of Abu Allaqi River and its tributaries during the Pleistocene Simbel in south Egypt at 247 m.a.s.l. reveals roughly the level when wet phases dominate the area. of water invading Egypt from Sudan, building the main river in Egypt; the Nile that flows miraculously through extremely dry deserts in northern Sudan and Egypt without receiving nearly a single drop of rain from wadis along its way to the In hindsight Mediterranean except in rare cases when heavy rains over the Eastern Desert added negligible amount of water into the Nile. The Egyptian population in 2016 reaches 91.5 million people, increasing annually by a rate of ca. 2.5% (according to the Egyptian Central Agency for Public Mobilization and Conclusions Statistics 2015). The Egyptian live on an area of ca. 40,000 km2 out of 1,000,000 km2; thus, the density of people 1. The history of the stratigraphic succession exposed on the in 1 km2 is 2250 persons. Their share in the Nile water and surface of the Nile Basin is greatly influenced by tectonic other waters (i.e., underground and recycling of drain water) features resulted from drifting of Gondowana since the reaches 60 billion cubic meters. Each has 600 m3/year. It is Paleozoic and continued up to the Cretaceous. General hard if impossible to put more water in the present Nile chan- – E W physiographic features characterize the Nile Basin. nel; otherwise, the water will cover the farming areas on both – The most important being the W EGuineaLineament, sides of the river. The only reasonable solution of this case is – the E W Sudd soft linear strip with many swamps and to rejuvenate the dry paleochannels in the Eastern and Western pogs, and the eruption of the many volcanics stretching deserts of Egypt and Sudan through connecting these dry – W E between Gebel Marra (ca. 3070 m.a.s.l.) in the west paleochannels with the rich rivers in southern and eastern – and the Ethiopian Plateau (3300 4600 m.a.s.l.) in the east. Africa. The dry Gilf River can be connected to the central The impact of all these features led to the present south to African water in South Sudan or Congo countries and the north Nile River, but passing by many changes in the dry Gabgaba–Allaqi River to the Blue Nile. The new rejuve- direction of the many Nile tributaries and slope reversal nated channels whether the Gilf or Gabgaba–Allaqi can add of some of the major extinct rivers, either sectors of the other two rivers into the Egyptian and Sudanese deserts. main Nile or the rivers once flowed into the River. 2. The paleoclimatic changes during the Quaternary, wet and dry, have a great effect on the physiographic features and Acknowledgements The authors are greatly indebted to Prof. Richard slope reversal of the Nile Basin drainage system. In the R. Parizek (Penn State University, USA) for his critical revision of the terminal Pleistocene, the climate over most of the Nile manuscript. Two anonymous reviewers are thanked for their revisions Valley was cool, dry, and windy. Increasing rainfall was and comments, which greatly improved this manuscript. Special thanks are extended to the AJGS’s Editor-in-Chief, Prof. Abdullah M. Al-Amri recorded in southern Egypt and in northern Sudan, and for his editorial support. more rainy in the Sudd area of South Sudan Republic during the Pleistocene and the Holocene. The drainage in parts of the Nile and other wadis inherited old courses References of probably Cretaceous–Tertiary rivers assuming opposite slopes than the present Nile drainage system. For instance, Adamson D, Williams F (1980) Structural geology, tectonics and control the Qena River in central Egypt had a N–S course, where- of drainage in the Nile Basin. In: Williams MAJ, Hugues F (eds) The as some of the now dry wadis were once flowing through Sahara and Nile. A.A. Balkema, Rotterdam, p. 607 Lake Chad to the Atlantic, e.g., Wadi Howar and Wadi El- Adamson D, Williams MAJ, Gillespie R (1979) Paleogeography of the Melik in Sudan. Gezira and the lower blue and White Nile valleys. In: Clark JD, 3. 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