Tectonics of Africa; Earth sciences; Vol.:6; 1971 - unesdoc - Unesco

Western desert
The Western Desert (Fig. 9), and especially its northein part,
has been thoroughly explored during the last twenty-five
years, mainly by the American oil companies Oasis and Phillips.
Fifteen deep wells have been drilled; five of them reached
the Pre-Cambrian and the rest gave valuable information on
the Tertiary, Mesozoic and Palaeozoic sections.
In the southernmost part of the Western Desert Pre-
Cambrian outcrops between the southern political boundary
and the latitude of Aswan. In the extreme south-west Pre-
Cambrian is known from the Uweinat mountains (comer
point of Egypt, Sudan and Libya). It is partly covered by
Palaeozoic sediments and young volcanics. In the central
Western Desert no information on Pre-Cambrian has as yet
been obtained, but probably it wil be shallower than in the
northernmost part. South of the Aswan latitude the Pre-
Cambrian outcrops show a WSW.-ENE. alignment. North
of the line of outcropping Pre-Cambrian the pronounced
north-south trending Kharga Uplift contains some Pre-Cambrian
outcrops. At 160 km to the west of the north-south
trending Kharga Uplift another horst (the Dakhla Uplift)
is known which-contrary to that of Kharga-has a nearly
perpendicular strike, i.e. WNW.-ESE.
North of latitude 27" the major structurai lines change
their trend to the NW.-SE., i.e. Rayan swell, mainly on the
eastern shore of the river Nile, and further to the west a graben
and another fault north-east of Baharia Oasis, where a
more ENE.-WSW. trending domal structure has been observed.
Between the Kharga horst and the River Nile a depression
has been assumed running in a NNW.-SSE. direction
over a distanceof about 400 km; it passes the Nile downstream
of Qena and ends at the Rayan swell. North of the
Rayan swell more east-westerly trends occur in the Fayum
and near Beni Suef, the latter being a high observed on both
sides of the river Nile, north-west of the Wadi Araba structure
with NE.-SW. strike and known for its Carboniferous
outcrops. Another low possesses a pronounced east-west
trend. These northern trends therefore have great variations
in strike, probably due to differences of age. They are adjacent
to the northern and best-known part of the Western
Desert.
The southernmost deep well drilled in this northern area
of the Western Desert is well Baharia No. 1, about 250 km
WSW. of Cairo and about 200 km SSW. from Alexandria.
At 1,829 m depth Pre-Cambrian was penetrated in this well.
A second deep test was drilled in Al Nafsha about 100 km
SSW. from Fayum. At 750 m depth the Pre-Cambrian was
reached, i.e. several hundred metres higher than in the Baha-
ria well. The Umbarka well indicates a rising of the Pre-
Cambrian surface towards north-west. Table 2 shows the
deep wells drilled and formations encountered. Figure 9 gives
an interpretation of these data.
From south-east to north-west there is a regional in-
crease in the depth of the Pre-Cambrian surface (below sea
level). The highest level is the line Baharia-Abu Rawash
including Khatatba (250 km). This is followed northward by
a band 100 km wide, in which the Pre-Cambrian surface is
about 4,000 m sub-sea. Further towards the coast of the
TABLE 2. Exploration deep tests in the Western Desert
(incomplete)
Well Depth in metres Bottom formation
Alam al Buaib
Al Alamein
Al Nafsha
Abu Rawash
Baharia
Khatatba
Burg ai Arab
Al Dabba
Betty
Faghur
Ghazalat
Eib Afia
Mamour
Mersa Matruh
Wadi Natrun
Umbarka
4 725
4 390
750
1 900
1 829
1884
4 063
1864
4 463
3 330
3 073
3 068
3 733
4 571
4 054
3 669
Lower Cretaceous
Lower Cretaceous
Carboniferous (?)
Pre-Cambrian
Pre-Cambrian
Pre-Cambrian
Pre-Cambrian
Lower Cretaceous
Nubian Sandstone
Cambrian
Old Palaeozoiss
Cambrian
Cambrian
Palaeozoics
Lower Cretaceous
Pre-Cambrian
Pre-Cambrian
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