Download structure and tectonics of the southern gebel duwi area, eastern

STRUCTURE AND TECTONICS OF
THE SOUTHERN GEBEL DUWI AREA,
EASTERN DESERT OF EGYPT
BY MICHAEL J. VALENTINE
34°20'
26°15'
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26°10'
"QUSEIR
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26°05'
26°05'
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26°00'
34°00'
MILE S
Wis e, Greene, Volentine, Abu Zied B Trueblood, 1983
34° 10'
26000
34°20'
,
CONTRIBUTION N0.53
DEPARTMENT OF GEOLOGY 8 GEOGRAPHY
UNIVERS ITY OF MASSACHUSETTS
AMHERS~MASSACHUSETTS
STRUCTURE AND TECTONICS
OF THE
SOUTHERN GEBEL DUWI AREA
EASTERN DESERT OF EGYPT
By
Michael James Valentine
Contribution No. 53
Department of Geology and Geography
University of Massachusetts
Amherst, Massachusetts
April, 1985
Prepared in cooperation with the
Earth Sciences and Resources Institute
of the University of South Carolina
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ABSTRACT
This
study examines the Precambrian through.Tertiary
tectonic elements of an area of about 350 square km
the
Red
Sea
petrofabric
coast
work.
utilizing
older anisotropies.
Suez
and
largest
Tertiary
600
The study area,
Red
Sea,
contains
remnants of late Cretaceous
platform
sediments
are
to
These
preserved
as
Eastern
Fault trends are most prominent in the northwest-
trending,
be
the
early
coast.
outliers downfaulted along trends atypical of the
Desert.
test
500 km south of
cover along the Egyptian Red Sea
meter-thick
to
stress history, and the effects
10 km inland from the
preserved
and
mapping
The resulting data are used
ideas concerning faulting,
of
geologic
along
40 km long Gebel Duwi fault block and appear to
reactivated
Precambrian
Eocambrian
striking,
superimposed
upon
a
structures:
Najd
the
strike-slip
north-northwest
northwest-.
fault
Proterozoic
zone
fold
grain.
Red
in
Sea-related structures began to disrupt the area
Oligocene to early Miocene time;
conjugate
strike-slip
compression.
pattern
of
terminating
The
faults of that age
of
suggests
small
N25E
Tertiary faulting hierarchy involves a
northeast-tilted,
against
a pattern
northwest-trending
older north-south
iv
zones
with
blocks
some
suggestion
of en echelon patterns of the younger
blocks.
Typical throws on major faults are 500-800 meters.
Tilting was followed by an eastward shift of tectonic
activity
to form the main Red Sea basin.
regional
erosion
surface
developed
A
during
post-tilting
mid-Miocene
quiescence and has since suffered minor disruption.
Folding is minor except for drag folding along
major
fault zones and a 50 meter wavelength overturned fold atop
Gebel Duwi, which may be the result of gravity tectonics.
The
Sea:
1)
data suggest a multi-stage history for
the
post-early
by
Eocene
uplift accompanied
Red
N25E
compression; 2) Oligocene to early Miocene major faulting,
block tilting,
and subsequent erosion;
Miocene
activity
major
producing
erosion
the
main
surface
post-mid-Hiocene
to the east of
Red Sea trough
the
while
was enhanced along
final
3) early to
the
adjustments
mid-
study
the
area
regional
shoulders;
producing
4)
coast-
parallel horsts, with subdued tectonic activity continuing
through the present.
Results
evolution
and
developing
same
the
study
have
implications
style of deformation of the
ocean basins.
tilted
basement
of
for
shoulders
Possible continuations of
fault block structural style
controlled
the
of
the
by
grain along the zone of Najd trends should be of
interest for offshore petroleum exploration.
v
TABLE OF CONTENTS
Abstract
......................
iv
Chapter
I.
INTRODUCTION
.....
.....
Geographic Setting
• • • • • • • • • •
Regional Geologic Setting • • • • • • • • •
Previous and Current Work • • • • • • • • •
Geologic Nap and Gross Structural
Features • • . . . . . . . . . . . . .
Acknowledgements
• • • • • • • • • ••
II. PRECAMBRIAN BASEMENT STRUCTURE AND
ANISOTROPY • • • • • • • • • • • • • •
..
III. STRATIGRAPHY OF THE SEDIMENTARY COVER
....
....
.......
vi
3
3
8
12
15
20
Basement of the Study Area
••••••
Precambrian Tectonic Setting and Basement
Correlations • • • • • • • • • • • • •
Volcanic arc accretion model • • • • •
Volcanic-plutonic rocks • • •
Ophiolite melange • • • • • • • •
Gneisses and schists
••••••
Melange-type sediments
Summary of Arabian-Nubian Shield
development • • • . • • • • • • • • •
Regional Structural Grain • • • • • • • • •
North-south Hijaz-Asir grain •
Northwest Najd grain • • • • • • •
Folding • • • • • . . • • •
Bedding and volcanic layering
Foliations and cleavages
Lineations
Dikes and Sills • •
Quartz Veins
• • • • • • • • • • •
Cretaceous to Eocene Sediments
llubia Formation
Quseir Formation
Duwi Formation
Dakhla Formation
Tarawan Formation
1
20
24
26
28
29
29
31
31
33
37
37
38
41
43
46
48
51
55
55
55
59
61
63
64
...
Esna Formation
Thebes Formation
Topographic expression • • ••
Post-Lower Eocene to Pre-Middle
Miocene Deposits
• • • • • • • •
Nakheil Formation • • • • • •
Middle Miocene to Recent Deposits
Recent wadi alluvium
• • • •
....
....
....
IV. STRUCTURAL FABRIC • • • •
72
77
80
80
80
.......
84
V. MAJOR FAULT AND FOLD STRUCTURES
Zone
87
• • • • • • • • • • • • • • • • •
el Isewid Fault Zone . • • •
Nakheil Fault Zone • • •
Hammadat-Wadi Kareim Fault
•
•
•
•
•
•
•
68
68
71
71
72
Faults
Joints
Veins •
Lineaments
Basement lineaments
Cover lineaments • • •
Faul ts
•
Wadi
Wadi
Wadi
65
65
66
•
•
•
•
•
•
87
87
88
90
90
•
Bir Inglisi Fault Zone • • • • • •
Gebel Nasser-Gebel Ambagi Fault
Zone
Gebel Atshan Fault Zone
Folds • • • • • •
94
101
102
VI. REGIONAL TECTONICS
106
Tectonic History of the Study Area • • • •
Tectonic Heredity • • • • • • • • • • • • •
The Red Sea • • • • • • • • • • • • • • • •
The Falvey Model • • • • • • • • • • • • •
VII. SUMMARY AND CONCLUSIONS •
History of the Study Area • • • • •
Major Achievements of the Study
Future Work • • • • • • • • • • • •
vii
106
112
115
119
123
..
123
126
127
LIST OF TABLES
1. Said 1 s Cretaceous to Recent Stratigraphy
2. Akkad and Noweir's Basement Stratigraphy
3. Precambrian History • • • • • • • • • • • • •
4. Phanerozoic History • • • • • • • • • • •
ix
.
10
22 & 2.3
25
111
ILLUSTRATIONS
Plate
1 • Geologic Map of the Southern Gebel Duwi Area
2. Geologic Cross Sections
[Plates in back pocket]
Frontispiece--LANDSAT Return Beam Vidicon (RBV)
Image of the Gebel Duwi Area • • •
iii
Figure
1 • Index Geologic Nap of the Gebel Duwi Area
2
2. Topography of the Study Area • • • • • • • • •
4
3. Main Features of the Study Area
•••••••
5
6
4. Geologic Map of Egypt • • • • • • • • • • • •
5. Major Faults and Fault Blocks
••••••••
14
6. Structural Contour Map on Basement of
the Southern Gebel Duwi Area • •
16
7. Structural Contour Map on Basement of
the Quseir-Safaga Region • • • • • • • • • •
17
8. Ophiolite Belts of the Arabian-Nubian Shield •
30
9. The Alignment of Najd Trends in Egypt and
Saudi Arabia Prior to Red Sea Development
34
1 0 • Structural Grain of the Arabian Shield • • • •
36
40
11 • Basement Fold Data • • • • • • •
1 2 • Basement Planar Fabric Data
•••••
42
45
13. Three Phases of Basement Folding • •
1 4 . Basement Linear Fabric Data
47
50
1 5 • Basement Intrusions
1 6. Basement Quartz Veins
•.•••
52
1 7 • Stratigraphy of the Cretaceous to
Eocene Cover • • • • • • • • • •
56
1 8 • Fault Data • . • • • • • • • • • • • • •
73
76
1 9 . N20E Compression • • • •
78
20. Joint Data • • • • • • •
81
21 • Veins in the Sedimentary Cover • • • • • • • •
22. Basement Lineaments, Southern Gebel
Duvri Area
•..••••••••••••••
82
• • •
83
23. Basement Lineaments, Quseir-Safaga Area
24. Lineaments of the Sedimentary Cover • • • • • 86
25. Geology of the Gebel Nakheil Area • • • • 92 & 93
26. Geology of the Gebel Nasser Area • • • • • 96 & 97
27. Gebel Nasser Structure • • • • • • • • • • • • 98
28. Slip on Joints as a Mechanism of Folding • • • 100
.....
...
...
x
C H A P T E R
I
INTRODUCTION
Much
has
recent geologic interest in the Red Sea
region
centered on mechanisms of continental rifting,
small
ocean basin formation, and the relation of these processes
to
offshore petroleum exploration and developnent.
study
examines
the
mechanisms
influences
history,
of
of
tectonic
This
deformation,
heredity,
stress
and
the
interplay of these elements in an area adjacent to the Red
Sea.
The study area is near Quseir on the Red Sea coast of
Egypt
about
500
km
south
of Suez (Figure
chosen
for
its
blocks
and
their Cretaceous to
Duwi,
the
most
that
area,
is
excellent exposure
of
Tertiary
1) and
tilted
was
basement
Gebel
cover.
prominent of the tilted fault blocks
the
focus of the
study.
The
area
characterized by divergence of structural trends from
in
is
the
typical Red Sea-parallel trends present along the Egyptian
coast.
The
main
objective
of this study is
a
better
understanding of the interaction of Tertiary stresses with
pre-existing
anisotropies to produce the unusual
pattern
of Red Sea-related structures present in the Quseir area.
1
LEGEND
~Wadi Alluvium
[<~~-=;]Miocene-Recent
m
Ll
25°,
Sediments
Cretaceous- Eocene Sediments
Precambrian Basement
..,.- Normal Fault-ticks on down side
"
I
\. RICHARDSON ,
250
-:t~~~~~~~~-,~~~~~~J_~.:__,-~_:'._~~~~~~~~~:11.:50'
50
33
° 5 o'
34°20
1
Figure 1. Map of the Quseir-Safaga region of Egypt showing
location,
general
geology,
and study areas of recent
workers (geology after Said, 1962).
3
Geographic Setting
The 17 by 20 kilometer area considered in this
study
lies about 8 kilometers west of the coastal town of Quseir
along
the
Quseir-Qena
road and is centered
around
the
southeastern end of Gebel Duwi, the most conspicuous ridge
in
the Quseir area (Figure 1 ).
with
to
The terrain
is· rugged,
over 300 meters of total relief (Figure 2).
the
more
Quseir-Qena
maintained
remote areas can be gained
asphalt
by
Several gebels
and
road
via a series
from
of
the Quseir Phosphate Company
(mountains),
Access
the
dirt
raain
tracks
3).
(Figure
wadis (dry fluvial
valleys),
birs (brackish-water wells) will be used as landmarks
when discussing the geology.
Regional Geologic Setting
The Eastern Desert of Egypt includes the area between
the
Nile River and the Gulf of Suez/Red Sea
Its
most prominent feature is a north-northwest
4).
(Figure
trending
range of mountains that parallels the Red Sea coast.
This
Red Sea Range extends from Gebel Urn Tenassib (latitude 28°
30'N)
in
the north,
southeastward into Sudan forming
a
more-or-less linear series of mountain groups, rather than
a
true continuous chain.
Sedimentary plateaus occur
to
RED
SEA
.--- --:::--
~
26°10·
N
Main Rood
Wadi Course
Topogroph1c
Contour
Contour Interval
"50 merers
0
I
2
3
4
K M
\\
Figure 2.
"'
U
'\ 11
I
"\
\ \
r
J
26°
N
Topographic map of the southern Gebel Duwi area.
~
26° 10' N
0
D
Wadi ai\uVllUm
Dutt.to,"
'""¥
_,...,.,,_..road
---- Plrt tr.11.::.ll• •ucu1IJl'ic
~ '4· whe~ dnve
Y~hu.\c-. 1" frnnq,
lW
~~tc"'"e
• ,,..U.k ••h 1,,.-inr:i /wdl
26 001'NI
Figure
J.
LJ
~~~
<:=-
;f
q
"(,~
~- ""~
Yr<-~::::·.:.,-;,~
;.,,,~~
~.':'":-:.:
.::;;.
Hain fea~ures of the southern Gebel Duwi area.
l
V1
6
KM
30°
I
izeo
I
SAUDI
ARABIA
I
j 26°
I
E'J
Recent
Q
OliQoccnc-P1erstocene
~
Cr etoceo1.1s-Eoc.ene
•
Combrion-Tr1oss1c
124°
LJ Precomb11on
Figure
22°
4. Geologic map of Egypt (after Said, 1962).
7
the
north
and
coastal
plain
plateaus
are
west of these
lies
to
mountains,
the
east.
and
The
a
narrow
mountains
deeply dissected by a system of wadis
carries rare precipitation to the Nile,
and
that
the Gulf of Suez,
and the Red Sea.
The
Red
These
4).
sequence
of
late
Precambrian
rocks that underly the entire Eastern
crystalline
(Figure
Sea Range is made up
rocks
consist mainly of
volcanogenic 11etasediments intruded by granites
Sultan,
Sylvester,
et al.,
suggest
that
greenstono
accretion
unusual
This
this
1983).
belt
and
(Sturchio,
Engel et al.
resulted
of island arc systems in the late
(1980)
from
the
Proterozoic,
in that most greenstone belts are Archean in age.
Precambrian
Arabian-Nubian
tectonic
basement
fold
Greenwood
et
1980).
al.,
Eocambrian cratonization,
fabric
extension
activity
grain
a
(Engel
a pervasive
the
north-northwest
et
al.,
In the late stages
was superimposed on the
of
consolidated
craton and resulted in
trending
fault
layered
a
metavolcanics
greenschist-grade
of
Desert
1980;
of
this
northwest-trending
area,
a
probable
the left-lateral Najd fault system
of
the
Arabian Shield (Moore, 1979).
Following
Cretaceous
sediments
to
a
long
Eocene
were
period
platform
deposited
of
quiescence,
carbonates
unconformably
and
Upper
related
over
the
8
Precambrian
sediments
and
are
where
basement
of
the
Desert.
form the plateaus to the west of the
best exposed in the western part of
erosion
has produced a series of
down into the Nile Valley.
during
Eastern
These
mountains
the
scarps
desert
stepping
Uplift along the Red Sea Range
post-early Eocene time resulted in removal of
sedimentary
cover by erosion except in isolated
the
outliers
preserved by downfaulting associated with Red Sea rifting.
Much
of
this
study is concerned with a group
of
these
downfaulted sedimentary outliers in the Quseir area.
Middle
Miocene and younger Red Sea-related sediments
were deposited along the coastal plain unconformably
crystalline
sediments.
basement
rocks
and
Cretaceous
to
over
Eocene
These sediments are well preserved along most
of the Red Sea/Gulf of Suez coast from the southern end of
the Gulf of Suez to Ras Benas (23° 09 1 N).
Previous
Barron
Desert
phosphate
prompted
and Hume (1902)
of Egypt and
included
~
produce~
the Quseir area.
deposits
more
Current Work
studied the
central
Eastern
the first geologic map
that
interest in
the
of the Cretaceous Duwi Formation
has
Since then,
work in this area
of
the
desert.
Ball
9
(1913)
examined
north,
while
Safaga
district
and mapped the Um el Huetat area to
Hume
(1927) discussed the
with
respect to oil
entire
potential
the
Quseirof
the
sediments.
Beadnell
(1924)
produced a series of four
geologic
maps of the coastal area between Quseir and Wadi Ranga
a
scale of 1:100,000.
the
area
rocks
These were the first good maps of
produced at a useful
scale.
The
were separated into two groups;
Lower
Eocene
at
group
and
the
sedimentary
the Cretaceous
"Newer
to
Tertiaries
and
Pleistocene" group.
Youssef
(1949;
studied the Upper
1957)
Cretaceous
rocks in detail and divided them into four formations.
Said
split
(1962)
the
summarized the relevant literature
sedimentary
subdivisions.
Said's
rocks
of
the
area
stratigraphy (Table
and
into
1),
two
slightly
modified and refined, is still in use.
Several
studies in the Quseir area since
(El Akkad and Dardir,
Issawi
et
concerned
the
al.,
1969;
1966b;
Issawi et al.,
time
Abd el Razik, 1967;
1971)
have
been
with the stratigraphy and general structure
sedimentary
microfacies
Dardir,
1966a;
that
cover.
Nairn and Ismail
(1966)
did
study of the Nakheil Formation (El Akkad
1966b)
of
a
and
to determine the depositional environment
of this conglomerate-sandstone series.
10
Table 1
Said 1 s
(1962) sedimentary cover stratigraphy.
Pleistocene
Pliocene
Pliocene
Miocene
!Hoc ene
Terraces and Raised Beaches
Clypeaster-Laganum Series
Oyster and Cast Deds
Evaporite Series
Basal Lime-grits
Lower Eocene
Thebes Formation
Esna Shale
Chalk
Dakhla Shale
Duwi (Phosphate) Formation
Quseir Variegated Shales
Hubia Sandstone
Upper Cretaceous
11
Schurmann
work
(1966) combined over 50 years of
in Egypt with prior studies into
his
personal
comprehensive
text on the Precambrian of the northern Eastern Desert and
the
Sinai.
area
The stratigraphic sequence in that
basement
and other related questions are still being debated.
Data from recent studies (Akkad and Noweir,
1979;
Stern,
1980;
Dixon,
1979; Engel et al., 1980; Sturchio, Sultan,
Sylvester, et al., 1983) and better radiometric dating may
help to clarify the Precambrian history of the area.
the mid-1970 1 s,
Since
the
Earth
Sciences
University
of
supporting
to
larger areas.
are
South
Resources
Carolina
at
Much
of
Columbia
the work has
at
has
to
the
been
various
concentrated
has
involved
Of particular interest to the present work
Greene (1984) as well
preparation).
been
the west of the Quseir area or
studies of Trueblood (1981),
adjacent
Institute
studies in the Eastern Desert through
institutions.
farther
and
the Egyptian Studies Group of
All
Richardson (1982),
and
as work in progress by Abu Zied (in
these studies involve areas
that considered in this
study
directly
(Figure
1).
Prior to these investigations, only scanty structural data
were available for this part of the Eastern Desert.
Much work has also been done by the U.
Survey
in
concentrated
Saudi
Arabia.
Most
of
S. Geological
this
on the Precambrian basement of
work
the
has
Arabian
12
Shield (Greenwood et al.,
al.,
1979)
1980;
Moore,
1979; Schmidt et
with individual mapping of quadrangles
along
the Red Sea coast (Smith, 1979; Davies, 1980; 1981).
work
has
also
been done in the Arabian
Shield
Some
by
the
French Bureau de Recherche Geologiques et Minieres.
Numerous studies have also been done on the structure
and evolution of the Red Sea (e.g. Lowell and Genik, 1972;
Coleman,
1974;
Girdler and Styles, 1974; Cochran, 1983).
Several of these studies will be discussed in Chapter VII.
Geologic Hap and Gross Structural Features
IJo suitable base maps were available at the outset of
field
work.
available
a
However,
were
1 ).
Egyptian
series of high quality
photos at a 1 :40,000 scale.
are
the
government
made
black-and-white
air
These photos, taken in 1955,
ideal for location in the field and tracings of
them
used as a base for the resulting geologic map (Plate
The use of the air photos as a base resulted in
distortion around the edges of individual photos.
some
As the
photos were available only during my stay in Egypt, it was
necessary to construct a best-fit map in the field
1)
that
has been adjusted subsequently
using
imagery, but still contains minor distortions.
(Plate
satellite
13
Most
of
bounding
the
the northeast side of
Gebel Ambagi,
It
mapping northeast of the
Wadi
major
Nakheil,
fault
including
is from Trueblood (1981) and Greene (1984).
is included in Plate 1 for the purposes of
continuity
and completeness.
The
general structure of the map area
results
from
interplay of three major fault groups striking N60E,
N15W
to N15E,
and N50-60W,
The faults break the area into two
major blocks,
the Gebel Duwi block and the smaller
Atshan
block
(Figure
broken
into smaller blocks by subsequent
5).
These blocks
are,
Gebel
in
turn,
faulting.
The
"jagged" or "stepping" appearance of major N-S and N50-60W
faults
indicates
possible
reactivation of
older
fault
trends by later stresses.
The
Gebel
Duwi block terminates
against
the north-south Bir Inglisi,
Ambagi,
and
Gebel
to
the
Gebel
Atshan Fault Zones.
southeast
Nasser-Gebel
Another
tilted
block with a trend similar to that of the Duwi block
off
the
Sea
coast.
Eocene
southern end of the Atshan block toward the
This block is covered by the
Cretaceous
runs
Red
to
sediments of Gebel Hammadat (Figure 1).
Other
satellite
more-or-less north-south zones can be seen
imagery
Frontispiece).
to
These
disrupt
the
Duwi
block
on
(see
zones may also mark changes in the
orientation of the Gebel Duwi block from Red
Sea-parallel
14
-+~"'""'..,,.~~~-::-~""'r-~~~~~~~~.-~~~~~-;- 26°10'N
~
2
KM
J
FAULT BLOCK
~CONTACT
D
'
BEDROCK
r.:J WADI
8:.:.1 ALLUVIUM
34° 05' E
I
'S::d· .h lt;.K
1dz-. c=:: .. ·:.'b"'
I
26° 01' N
34°12'E
Figure 5. Major fault blocks and normal fault zones of the
study area.
15
to
a more westerly orientation.
Figures 6 and 7 show the
general fault block geometry of the Quseir-Safaga region.
The
major
surface.
faults generally dip 50° or more
Consistent
northeast
dips
of
the
at
platform
sediments suggest rotation of the tilted fault blocks
may
indicate
the
shallowing of listric fault dips at
and
depth.
This shallowing at depth is consistent with models for Red
Sea
extension.
displacement
where
the
is
Greater
than
600
meters
indicated on portions
of
of
vertical
these
faults
upper Thebes Formation is in contact with
the
basement (Plate 2).
Most large-scale folds in the cover of the area trend
parallel to, and are the result of, drag along post-Eocene
faults.
Examples of this style of deformation can be seen
in the broad folding of the cover of the Gebel Duwi
Block
and
fuajor
in
the open Gebel Nasser syncline.
The only
exception to this style of folding is the large fold
the
ridge of Gebel Duwi (Plate 2),
atop
which is discussed in
detail in Chapter V.
Acknowledgements
Dr. Donald U. Wise of the University of Massachusetts
acted
as
advisor
and provided much
assistance in all phases of the study.
needed
advice
and
Three-and-one-half
16
STRUCTURAL CONTOURS ON RECONSTRUCTED TOP OF BASEMENT
Quseir Area, Red Seo Coast of Egypt
34•to'
-
34•20'
2s•15'
- - Fault•
>
'00 tn tttrow
- - Faultl 200-~m rt1row
- - Fouttl < 200 m fhr'Ow
I
I
RED
I
·.J
I SE A
,f
§
I
26• 10'
26'10'
"OUSEIR
BASIN"
\
'.:i
\
\
\
2s·o5'
26'05'
"'-
0
0
2s·oo·
34'00
KM
MILES
~IN,
34•10'
Gfetnrt, iloliMttM, Abc.i l1" 8 Tr11tblood, r9!J
• ,
126 00
34•20'
Figure 6.
Structural contour map on reconstructed top of
basement
of the
Quseir-Gebel
Duwi area.
Contour
interval= 100 meters.
17
GENERALIZED STRUCTURAL CONTOURS ON RECONSTRUCTED TOP OF BASEMENT
Quself-Safaga Region, Red Sea Coast of Egypt
33°50'
34°00'
0
\~ ""'
34•10'
34°20'
~
F04J1f1 .> !500m tttrow
- - - Fou/11 200·500m tttrow
- - - F~lrt < 200m fhl'Ow
~ '"
\
26°40'
26°40'
"J"oo \
.,. ,) j
'f
} .y
R E D
RABAH
AREA
S E A
26°30'
26°30'
26°20'1---~
\
\
\
-~
--l 26°20'
\-~\
\
"\
\
_.a:P\
\
(
\
"QUSEIR
\ BASIN"\
\
\
26°t0'
1--
"<.
/';)[;~~
··--·
M/\W'UC'll I.,
\ . •\ :t.
·~c'C'1\ C'I
A•l"7
\
"'\
'--l 26°10'
\
'•~
'\
,_,
"
'\
26°26'
0
0
KM
10
MILES
26°00'
GEBEL
HAMMAOAT
AREA--10
a
W1u, Greene
Volentine, 1983
(GeoloQte boH after Akkad 6 Dardir, 1965)
33•50'
34•00'
34•10'
34•20'
Figure 7.
Structural contour map on reconstructed top of
basement
of
the Quseir-Safaga
region.
Contour
interval= 500 meters.
18
months of field work in the winter and spring of 1982 were
funded
Professors W. H. Kanas,
State Department.
and
U. · S.
by the National Science Foundation and the
Hobert Ressetar of the Earth Sciences
Steven Schamel,
and
Resources
Institute at the University of South Carolina administered
these funds and offered helpful advice.
Administrative
E.
provided by Dr.
of
l·i.
were
El Shazly, llr. Hafez Aziz, and all
the Egyptian staff connected with the Egyptian Studies
Group.
The Egyptian drivers Faried,
l:oustafa
The
and logistical support in Egypt
Kamal,
Ahmed,
somehow got me to the most inaccessible
staff
of
the guest house at
Company took care
the
Quseir
of meals and housekeeping,
and
places.
Phosphate
allowing me
to concentrate on ecology.
Professors
served
on
George E.
McGill and Charles
W.
my thesis committee and offered many
Pitrat
helpful
suggestions for the improvement of this manuscript.
David Greene and Hassan Abu Zied, fellow students and
workers
in
companionship
the
Quseir area,
geology
friendship
and
making the three-and-one-half months in the
desert much more comfortable.
the
provided
with David Greene
In addition, discussions of
greatly
facilitated
the
Laura Menahen helped with drafting and lettering
and
development of this thesis.
provided
encouragement
and moral support throughout
the
·q.~a~oJd
• S:llU"Bl{'.J.
Alli
s1qq. JO uo1q_uJnp
C H A P T E R
II
PRECAMBRIAN BASEMENT STRUCTURE AND ANISOTROPY
Some Tertiary structures were probably controlled, in
part, by basement anisotropy.
establish
This chapter is designed to
the nature of this anisotropy,
compositional.
Due
to
the
complexity
structural
of
and
basement
fracturing
patterns and their resemblance to those of the
Cretaceous
to
Eocene
cover,
a
fuller
discussion
of
basement fracturing will be included in Chapter IV.
Basement of the Study Area
The
Eastern
basement
Desert
of the study area,
basement,
like most
of
the
is dominated by a sequence
of
metavolcanics and volcanically derived metasediments.
The
volcanics
the
are aphanitic to porphyritic in character;
volcaniclastic metasediments are generally coarse grained,
commonly conglomeratic.
Both types are highly fractured.
The metavolcanics and metasediments correspond to the
upper
part
(Table 2).
south
and
of Akkad and Noweir 1 s
(1980) Abu Ziran
Group
A few small exposures of serpentinite present
southwest of Gebel Nasser may be part
Rubshi Group (Table 2).
20
of
the
21
It
at low,
resulted
will be shown that several periods of deformation
mainly greenschist,
grade metamorphic conditions
in a pervasive northwest
grain.
Compositional
layering is parallel to metamorphic foliation,
near-isoclinal
folding.
Dips
of
these
suggesting
features
are
dominantly to the southwest.
Pink
to
gray granites intrude the
sequences
of
the area.
examined
from
two
folded
Granite-country
rock
volcanic
contacts,
at about a dozen places in the study area,
quite sharp to gradational across a zone of
meters.
The
granites appear to have been
vary
one
to
emplaced
passively, possibly by processes akin to magmatic stoping,
as
large
xenoliths of green
around the edges of them.
layering,
and
significantly
other
are
description of the
Much
Further,
structures
deformed
characteristics
metavolcanics
in accord
Egypti~n
not
their
with
appear
to
be
These
margins.
Greenberg's
(1981)
Younger Granites.
of the basement west of Wadi Hammadat and south
of Gebel Nasser is underlain by granite.
the
present
volcanic
foliation,
do
around
are
southern
end
The granite
of the Gebel Nasser block
is
in
at
the
process of erosional unroofing.
Basement
observed
reflection
in
foliations
and
any of the granites.
of
crenulations
This
is
their emplacement late in the
were
probably
not
a
Precambrian
22
ROCK UNITS
SUPERGROUP
.t: GROUP
(and remarks)
MEMBER
FORMATION
Kab Ahsi Esscxite Gabbro
Kho" Volcanics
-(dislodging of contact between Nubia Sandstone and basement)
Nubia Sandstone
(regional unconformity)
Younger Granites
Phase /fl South Eraddia pluton
Phase II Gidami, Kab Amiri. Eraddia, Um Effein. Um Had, Um
Hombos and Sancyat plutons
Phase I Ahu Qarahish. Sodmein, Kab Absi. Atalla EJ Murr.
Atalla. Atalla gold mine, East Um Effein. Fawakhir
and Arak plutons
Post-Hammamat Felsites
Atalla. Rasafa-Shihimiya, Atshan, Qash, Mahdaf, Kohel, Arak
and Zeidun members
Qash Volcanics
~'
<
..,. - ->--=
•
<::: ~ =
::;
' -
f-
- -
.C:-
2. Shihimiya Formation
c.i
c. Um HaHa Greywacke Member
b. Um Had Conglomerate Member
-
-
:'i~ ~~
<
=
(local unconformity)
a. Rasafa Siltstone Mcmhcr
I lgla Formation
-
-
-
-
-
-
-
-
-
(regional unconformity)
0.>khan Volcanics
lunmetamorphoscd)
Older Granites
_ (transforming some Older Granite' into cataclastic-mylonitic gnci"e< of Shairian typ• or Shait Granites)
Um Shager. Abu Ziran and N & E Eraddia plutons
==·~.;
' Sid Metagabbros
Hammuda. Khors, Fannani. Sid. Fawakhir, Esh El-Zarga, Erad-
-'·- =~
::.:- :i
I. Barramia Scrpcntinites
Muweilih. Sancyat, Fannani, Alalla. Rubshi, Kab Amiri
·~
~~~2
dia. Saqia, Abu Diwan. Ruhshi and Abu ziran complexes
.t: Saqia
ranges
8. Abu Diwan Formation
7. Eraddia Formation
6 Sukkari Metabasalts
< Um Scleimat Formation
"'
4 Atalla Formation
::: c:
...
i~
':..; -=
J Atud Formation
z.E
<'V
- ...
""""
OI:
-
c:
~
=~
< u
::::>
'
-
-
-
-
-
-
-
-
- (local unconformity)
Muweilih Formation
I. Hammuda Formation
d. Absi Metamudslone Member
c. Khors Schist Member
b. Um Hombos Melapyroclaslic Lentil
a. Um Shager Metagrcywacke Memhcr
-\hu Fannani Schists
MEATIQ
GROUP
Table ,...
')
.
Thick succession of high grade siliceous gneisses and 'chists.
Subdivision inlo unils in progress.
Akkad
and
Noweirts
(1980)
stratigraphy
and
23
Stages o(
evolution
Aae
PRINCIPAL EVENTS
.. ~
1:
Lower
><
Cl) :c
c ,.. '...!.In
·;; ~ c 0 ·:;vu> 5
,.VlEu-
Cretaceous
l.LJ .J
g~~:::
t;;~
a..u
·;- ~'; .g ·c
'l.LJ
ZVl
Oa..
..... 't:I
9<
t;
.5-=
:;:;,;:E-;,.,
0;:: 0 c 'El
0 .J
E -l! Q.~
:l
62(}..5~
Ma
..c
E
'.:::!
~
- Intrusion of felsites as huge bodies. sheets and dykes along N W.-S.E. trends
~
- Earliest indication of N.W.-S.E. dJSlocauom controlling later emplacement of Post-
!!'
~.
Hammamat Felsites and Phase I of Younger Granite'
:; E
E "'
- Folding & faulting of Hammamal Group & older rock unit> - second phase folding
8a:
·-a
·c-=
- Deposition of dark greywackes
- Deposition of conglomerates derived from older units and reworked lgla Formallon
>
u ...
- Uplift in source area
- Deposition of grey siltstones. minor greywackes and conglomerates
Q.,
l.LJ
~·=
.9
.....
-a.~
..c
·- .
..
olj:::
-~~
""'cc
till ·::
~"';
660-700
i..§
::i ..
Ma
l.LJ
Cl)
<
:c
Ma
~
Q.,
:::; EE
c
.. 0 ::i
~ E Q.
!!'
·;:;
Group, heralding main phase of orogeny
'2
- Intrusion of diabases
- Eruption and intrusion of andesites. andesitic luffs and minor hasalts
"'u
,.,
l.LJ
:E
< ti
:i:
0>
Cl)
Q.,
.J
<
z
J
u
- Effusion of basalts and basaltic luffs
.
- Intrusion and eruption of basalts. minor andesiles .ind luffs
.!.!
siltstones and arkosic greywackes
- Deposition of alternating conglomerates and greywackes. minor siltstone, mudstone and
- Eruption of rhyolite, dacite, porphyries. acidic tuffs and minor interbcdded mudstones,
":
E
E"'
z 1! ~
>:§
0
Cl)
i
l.LJ
-l!.!.!
0
cj
intrusive andesites
- Deposition of siliceous tuffaceous mudstones and minor greywacke
- Deposition of alternating shales and calc-shales. minor siliceous limestone and car-
§j
bonaceous chert
- Eruption of lapilli-. lithic-. crys!al-tuffs merging into ep1clastic sediments
u ...
""'"
~~
>. 0
";' c
u·-
.&:. 0
-=-2
~
of
intraforrnational breccia
- Uplift in source area
- Effusion of pillowed spilites. diabase flows. spilitic crystal luffs. epiclastic adinole and
.2
"~
cu
u -
history
Subareal eruption of andesitic agglomerates and tuffs
affecting these and all older rock units
- Recurrent intrusion of concordanl ultramafic bodies at different horizons in lhe Abu Ziran
~
.&:.
Ma
conglomerates
- Rapid severe erosion and peneplanat1on
- Epcirogenic uplift accompanied by intrusion and eruption of andesiles and porphyries.
- Emplacement of basic plutonites during orogemc folding and regional metamorphism
.S
-c•·-·"'"'c
8
a: .2 e- .9
1300~~
- Deposition of primary red beds of purple s1ltstones. greywackes. minor arenole' and
- Regional fault and thrust movements
- Emplacement of tonalite, grandiorite & monzomte during waning phase of orogeny
.. u
U.!::
E c
.. "
tiG
·§~
z
l.LJ
- Eruption of tuffs & intrusion of subvolcanics into folded Hammamat Group
zl.LJ
t:ij
900-1000
- Emplacement of granite plu!Ons a> final epeirogemc mamfeslation. assoc1aled with and
- Elongate granodiorite plutons along N.W.-S.E. trends
:.;
:c
Q.,
- Uplift and main rejuvenation of old N.W.-S.E. faults
effecting pronounced contact metamorphism
u
<
- Prolonged quiescence, erosion and peneplanation
- Granite pluton cutting Phases I and II
- Adamellite plutons cutting Phase I. Hammamal Group, Posl-Hammamat Felsites and
.2
Cl)
- Rejuvenation o( old N.W.-S.E. faults
- Transgressive deposition o( quartz-aremles and shales on stable shelf
followed by various dykes
~
c
l.LJ
- Emplacement o( alkallne plutonites
- Explosive volcanism o( trachyte lavas. pyroclas11cs and associated dykes
- Deposition of allerna!ing greywacke. muds!one. minor conglomerate and pd1te
- Deposition of successive quartz-arenites, calc·pelite\ and greywack<,, 1ransotu1nal to
proper turbidi!e facies
- Extrusion of acidic tuffs and flow'
the Egyptian baseoent
through
the
lower Cretaceous.
21+
sequence
highly
of
foliated
as opposed to some
and
lineated granites
Quartz veins,
Desert.
dike
events,
were
of
the
of
older,
the
Eastern
felsite dikes, and a single mafic
observed to cut the granites.
Aplitic
dikes
were noted in the metavolcanics in close proximity to
large
and
the
granitic body in the southeastern part of the
will
be
Precambrian
discussed
history
further.
A
of the study area
summary
is
area
of
the
presented
in
Table 3.
Precambrian Tectonic Setting and Basement Correlations
The
serious
Precambrian
basement
of Egypt has
study since the establishment of
Survey of Egypt in 1896.
been
the
given
Geological
In 1911, the first geologic map
of Egypt was produced by the Survey with explanatory notes
by
Hume
(1912).
reconnaissance
The
map
was
based
largely
on
geology and about one-third of the country
remained ''terra incognito".
A revised edition of this map
was later published in the Atlas of Egypt (Little, 1928).
Hume
and
(1934),
Schurmann
Andrew (1938;
( 1 966)
1939),
developed
Neubauer (1962),
Egyptian
basement
stratigraphies without the benefit of adequate radiometric
dating.
As a result, much confusion remained as to ages,
25
MILLIO~S
2100
•AHCIEHT• GKEISSES AT GEBEL
OWEIKAT, W, DESERT, EGYPT [ 1]
1100
~
;z:
<
~
"';z:=>
;z:'
<
~
"'a::<
<
bOO
700
500
(J]
0
OLDEST DATED EGYPTIAN
OPHIOLITES [ 4]
"'
"'"'
800
0
(21
OLDEST DATED EGYPTIAN
METAYOLCANICS (41
0
...:I
900
0
OLDEST DATED ARABIAN
HIJAZ TEC70NIC CYCLE
0F YEARS BEFORE PRESENT
0
OLDEST DATED ARABIAN
OPHIOLITE [ 2]
METAYOLCA~ICS
1000
0
EGYPTIAN SINTECTOttIC
GRAllITES [ 5, 6 I
EMPLACEMENT AND METAMORPHISM
OF EGYPTIAN GNEISSES
AllD SCHIS7S (4]
DEYELOPMEllT OF
MEATIQ DOME [&]
..._..
BULK OF DATED EASTERN
DESERT METAYOLCANICS [a)
LATE TO POST-TECTONIC
EGYPTIAU GRANITES [6]
1-----t
POST-TECTONIC GRANITE~ IN
THE EASTERN DESERT [5]
1----4
ARABIAN POST-TECTONIC
GRANITES [7]
1----i
DOKHAN VOLCANICS [5]
1--1
DEPOSITION OF MOLASSETYPE SEDIMENTS (HAMMAHAT
Flo!. OF EGYPT) (J,51
1-----1
YOUNGEST PRECAMBRIAN ARABIAN
CALK-ALKALINE VOLCANICS [J)
0
NAJD FAULTING (J,7]
~
OLDER, SHAT7ERED
QUARTZ VEINS
FIRST PHASE FOLDING, HAIN FOLIA7ION,
LillEATIONS, HETAHORPHISH, OLDER
NORTHEAST QUARTZ VEINS
<
"'<
~
SECOND PHASE roLDillG, SECOND
FOLIATION/SCHISTOSITI
-i
? -i
0::
...
...
0
::i
"'
RED GRAKITES EHPLACED, YOUNGEST
QUARTZ VEINS, APLITE DIKES
,
.
CREllULATION CLEAVAGES
?-----·-:
HAFIC DIKES AND SILLS
BRIC~ RED-WEATHERING
FELS ITES
REFEREllCES1
(1] Schurcann,
2j
1974.
Flock ot al., 1980.
Greenwood et al., 1980.
(4] Hashad,
1980.
fJ
Table
____ ,
b
(5] Ries ot al., 198),
(6] Engel ot al., 1980.
[7) Schmidt et al., 1979.
(8] Sturchio, Sultan, 3ylve1ter, et al.,
1983
Summary of Prccar.ibrian history.
.
26
origins, and regional correlations of units.
El
Ramly
stratigraphy
(1972)
of
the
published
a
basement
central Eastern Desert
Western Desert of Egypt.
map
and
and
South-
Based on work since 1963
along
the Qift-Quseir Road in the Hammamat-Um Seleimat District,
Akkad and Noweir (1980) developed a basement stratigraphic
sequence
similar
El Ramly 1 s
to
(Table 2).
All
of
the
aforementioned authors placed the gneisses and schists
the
Meatiq Group at the base of the column,
the
oldest
exposed rocks in the Eastern Desert,
tentative age of about 1300 ~.y.
Basahel
attempted
with
making
(1980)
of
them
with
a
(Akkad and Noweir, 1980).
and Greenwood
et
al.
(1980)
have
to correlate the basement stratigraphy of Egypt
other
lithologic
parts
of
northeast
Africa.
Although
units of the Arabian-Nubian Shield
adequately described,
have
the
been
there is even now much disagreement
as to ages, origins, and regional correlations.
Volcanic Arc Accretion llodel
Until
northeast
relatively
Africa
ancient
sialic
Africa.
Many
the
northeast
recently,
it
was
thought
and Saudi Arabia were underlain
crust like that of western
and
that
by
an
southern
of the notions concerning the antiquity of
African
craton
were
based
on
the
now
27
outmoded
premise
metamorphosed
that
rocks are,
the more
highly
tectonized
the older they must
be.
With
little or no radiometric dating to constrain the ages,
was
and
it
assumed that the gneisses and schists of the basement
were Archean in age, and they were correlated with similar
rocks in other parts of Africa.
With
the
development
and
radiometric dating techniques,
rocks
for
became available.
of
various
absolute ages for basement
The only reported Archean dates
basement rocks of the Arabian-Nubian Shield are Rb-Sr
ages
on
Gebel
microcline and whole rock from the
Oweinat in the Western
Rogers et al.
evaluate
they
refinement
Desert
gneisses
(Schurmann,
1974).
(1978) state that data were unavailable
the validity of these dates,
do not accept them.
and
of
to
consequently,
If these dates are
eventually
borne out, these ancient rocks may represent a small block
of
been
sial "floating" in younger surrounding rocks.
It has
proposed that ancient sial is present under much
northeast Africa,
but it seems unlikely that it would
of
be
exposed only at Gebel Oweinat.
Many problems with the development of a model for the
evolution
of
the northeast African craton have
resulted
from the lack of agreement on a stratigraphic sequence for
the area.
this
Ries et al.
(1983) feel that they have solved
problem with a structural/tectonic sequence for
the
28
shield,
rather
contacts
central
They
than
they
see
a simple
stratigraphic
one.
between the major rock types
Eastern Desert of Egypt are dominantly
The
in
the
tectonic.
have therefore divided the basement rocks into
groups
baseu
on environment of development
as
four
outlined
below.
Volcanic-Plutonic Rocks. The bulk of the Saudi Arabian and
Egyptian basements consists of calcalkaline volcanics
volcanogenic
1979).
to
sediments intruded by granites
(Shackleton,
The volcanics and granites are chemically similar
igneous
products associated with
arcs (Greenwood et al.,
Dixon,
and
1979;
associated
Stern,
sediments
1980;
1979;
present-day
Gass,
Engel
1977;
et
island
1979;
al.,
1981;
1 980) ;
are very similar to those found
modern back-arc basins (Greenwood et al.,
the
in
1980;
Engel et
ages for the metavolcanics and
granites
al., 1980).
Radiometric
range from about 1000 M.y.
1980;
most
(Greenwood et al.,
Gass, 1979; Rashad, 1980; Roobol et al., 1983) with
Eastern Desert dates at 700-600 M.y.
1980; nies et al., 1983).
east
to 450 M.y.
across
(Engel et
al,
The rocks become younger to the
the Arabian Shield and exhibit
an
eastward
geochemical evolution suggestive of a maturing island
arc
(Fleck et al., 1980; Greenwood et al., 1980; Darbyshire et
al., 1983; Roobol et al., 1983).
29
Ophiolite
The existence of ophiolites
Melange.
in
Arabian-Nubian
Shield has been recognized
(Baker et al.,
1976; Gass, 1977; 1981; Dixon, 1979; Engel
et al., 1980; Shackleton et al, 1980).
sequences are rare,
common
in
sea
northwest
trending
Nubian
but partial sequences are
Shield
floor
are
located
8)
and
in
Radiometric dates of 825 M.y.
for Egyptian mafic volcanics
may
north-south
mark
and 860 H.y.
(Hashad,
relatively
These slivers
discontinuous belts in
(Figure
recently
Complete ophiolite
the Arabian-Nubian Shield.
abducted
only
the
of
and
the
Arabian-
old
sutures.
were obtained
1980) and a
single
date of 1165 tl.y. was obtained from Saudi Arabia (Fleck et
1980).
al.,
These
rocks
may
have
been
erroneously
classified as part of the Hubshi Group of mafic intrusives
by earlier workers.
Gneisses and Schists.
the
11
fundamental
11
These rocks were originally
gneisses and were thought to be part of
an ancient craton underlying northeast Africa.
now
been
and/or
identified as
sedimentary
metamorp~osed
rocks with dates of
They have
younger
1979;
al. '
1 983).
over
the
plutonic
emplacement
metamorphism ranging from 763 M.y. to 584 M.y.
al. ,
termed
and
(Schmidt et
Rashad, 1980; Sturchio, Sultan, Sylvester, et
volcanics have been thrust
In many places,
gneisses.
diapirically,
possibly
The
gneisses,
during
in
turn,
compressional
rose
episodes
30
~
, ..1.11114 "'"'""'" ,_, ..111
outtt.,11"4Katd 111 Mad
Ra• Su S.1t1r1. Alma '" "'""'
"*• fltltd dKkWtat
~ """'''*'·
1
tm
lly
[-]
.........
-~-.~~:!·
ti
C-'ttl clH•I
ClystathM l!Ht.aftt COYtftd "' ,_,
~f I 1<t11•y Vale"''" 11\d
.-CeflllOhhtd M,.llfl
Pt.tftfftretC H4tMtftl8fl Cl'llf
SOQUI
_,-
..... ~. ~~.;;. \ \
~ :o-· ......
...........·...•....... :-:::·'·..........
·.•.':···
'
~
" :•
'
~
~
'
;
~ ..·.:~ ~·~··
:-::~ ~
·.
·~
...~ ·:.:.•:H~:·...:.··~·.'·.
. ./·.···
-. ::• ~~: f..~:
'_f#"
Figure 8. Distribution
of mafic/ultramafic
zones in the
Eastern Desert of Egypt and western Saudi Arabia (Bakor
et al., 1976).
31
(Greenwood
et
complex tectonics
or
1980)
al.,
(Sturchio,
during
Sultan,
metamorphic
core
1983),
and Batiza,
and were later exposed by erosion as mantled gneiss domes.
Molasse-type
generally
Sediments.
the youngest rocks in
sequence.
the
these
are
structural/tectonic
They include the Hammamat Group of Egypt dated
at 616±9 M.y.
Murdarna
Stratigraphically,
to 590±11 H.y.
Group
of
Saudi
(Ries et al., 1983) and the
Arabia.
These
sediments
are
elastic-dominated and are interpreted as being orogenic in
origin (Greenwood et al., 1980; Schmidt et al., 1979; Ries
et al., 1983).
Summary of Arabian-Hubian Shield DevelopL1ent
The
chemistry,
Arabian-Nubian
ages,
Shield
and structure of rocks in the
suggest
that
the
craton
formed
through the accretion of island arc materials in the
Proterozoic. Single arc
al.,
1983)
and
1979)
Shackleton,
multiple-arc
positions.
trending
models
Collisions
lines
metamorphism,
(Greenwood et al., 1980; Roobol et
multiple
schemes,
late
arc
(Schmidt
have
been
ophiolite
along
produced
belts mark
north-south
mainly
1979;
al.,
proposed;
in
the
to
the
suture
northwest
greens chi st
the Hijaz tectonic grain,
northwest trending lineations,
et
grade
dominant west to
and west to northwest fold
32
vergence
formed
seen
in the shield.
The gneisses and
from sediments and/or plutons
metamorphism,
which
locally
during
reached
schists
collisional
amphibolite
grade
(Sturchio, Sultan, Sylvester, et al., 1983).
Uplift
and
deposition
time,
cut
resulting from the collisions caused
the
all
of molasse-type sediments.
last
the
pulses of
Volcanics of Eeypt
andesites
produce
(Mourad and Ressetar,
same
maematism
the
Dokhan
1980) and
minor
and rhyolites within the Murdama Group of Saudi
1980).
Arabia (Greenwood et al.,
with
At the
subduction-related
pre-existing rocks to
erosion
intrusion of the
These events overlapped
collision-generated
post-tectonic
granites that stabilized and ''cratonized" the new crust.
The
I.J. y • ago
Ilajd fault system developed between 520 and
( Greenwood et a 1 • , 1 9 8 0 ; Schmidt et a 1 • , 1 9 7 9 ) in
response
to
African
craton
the continuing collision of the
with the
continent (Greenwood et al.,
newly-created
Proterozoic
Arabian-Nubian
1930; Fleck et al., 1980) or
as the result of a collision with a continent to the
(Schmidt et al.,
that
of
During
late
1979).
east
A risid indenter model similar to
Molnar and Tapponier (1977) has been applied
both cases
the
590
(Schmidt et al., 1979; fleck et al.,
to
1980).
the hiatus in tectonic activity that followed
Precambrian
assembly
of
the
Arabian-Hubian
33
craton,
of
a
widespread erosion surface developed over much
the craton.
were
Cretaceous to Eocene platform
subsequently
extensive
Eastern
older
surface
is
on
this
surface.
preserved
in
This
the
western
Desert as a general concordance of basement
elevations
Within
deposited
sediments
where the sedimentary cover has been
the
basement
study area,
surface
along
it can be seen
as
a
the basal contact of
peak
removed.
weathered
the
Nubia
Formation.
Many details of this model need to be worked out, but
the general scheme is gaining wide acceptance.
The rapid
development of this area,
unusual mafic intrusions
by
unusually
Dixon
the
(1979),
greenstone
belt,
young
age
lack of arc-type blueschists,
of
and
extent of the Pan-African tectono-thermal event all
to anomalous mantle conditions beneath Africa in the
Precambrian.
This
may prove to be a fruitful field
noted
this
the
point
late
for
future investigation.
Regional Structural Grain
On
the scale of LANDSAT imagery
(Figure
9),
areas
bordering the edge of the Red Sea are seen to be dominated
by
more or less north-south braided structural trends and
northwest
structural
trends
(Greenwood
and
Anderson,
l
~
34
A
B
"'
Joo ~
-\!..,
'
oi.,
,.,(o
J;>
""'0
O'
0
<!
w
JVflJ//J. \1J;:_
(f)
0
w
• I
~
WI'\.,'
l<-">o
"'
~1
A\~
\
l<-">oA/
ex::
o'v
0)
I
J
<\10'1/
,.,ca"'
0
Figure 9. Palinspastic
reconstruction of the northern Red
Sea
prior
to Tertiary rifting
(after
Greenwood and
Anderson,
1977):
a)
line drawing of the northern Red
Sea
showing
lineaments
visible
on LANDSAT
images;
b)
reconstructed
Red
Sea margins prior
to
rifting.
Lines represent Hijaz- and Najd-parallel lineaments
in
Precambrian
terrains.
Note alignment of Gebel
DuwiGebel
Hammadat of Egypt and Wadi Azlam of Saudi Arabia
(both in heavy black) prior to rifting.
1
35
1977).
and
These can be associated with the Hijaz-Asir (N-S)
Najd
Arabian
(NW)
tectonic
Shield
provinces (Figure
(Greenwood
et
al.,
extensions into northeast Africa.
10)
1980)
of
and
the
their
A third trend parallels
the Red Sea and is associated with Tertiary rifting.
In
the
Arabian
mapping
has
been done,
dominant
al. ,
grain
1980;
published
somewhat
Shield,
where
extensive
structures paralleling
directions are well-known
1979;
Smith,
structural
sparse,
data
1980;
the
for the
north-south
Eastern
and northwest trends
1979;
~gypt
(El Shazly,
1976;
Abdel Khalek,
1979;
are
have
Engel et
Minor groups
of east-west and northeast trending faults have also
in
et
Although
Desert
Gass, 1981; Ries et al., 1983).
noted
two
(Greenwood
Davies, 1980; 1981).
been noted in the basement (Abdel Khalek,
al.,
basement
been
1964;
1977;
Garson and Krs,
Gass,
1981) and Saudi Arabia
(Garson and Krs, 1976; Davies, 1980; 1981 ).
Northwest-southeast lineations are present throuGhout
the
Precambrian
northwest
that
1983;
Sturchio,
mainly
have
Sturchio,
Sultan,
and Batiza,
1983).
These are
smearing
lineations
suggest northwestward tectonic transport.
lineations
are
1980;
Sultan, Sylvester, et al.,
stretched pebble and mineral
oriented
shallow
or southeast plunges (Shackleton et al.,
Ries et al.,
1983;
of the Eastern Desert and
present in
the
Saudi
Similarly
Arabian
36
39°
45°
42°
N
28°
·~~
24°
_.;;
r
z4°
RED
SEA
1
20°
j
.-l
[::::=.:):!Phanerozoic Cover
- - - Lineament
....... Fault
-
Approximate Province Boundary
39°
YEMEN
42°
45°
Figure 10. Structural grain of
the Arabian Shield
(after
Greenwood et al., 1980).
S= Shammar Province, N= Najd
Province, II= Hijaz-Asir Province.
37
basement (Greenwood et al.,
1980;
Smith,
1979;
Davies,
1980) •
North-South Hijaz-Asir Grain
The
braided
nature of the north-south
Hijaz
fault
grain (Figure 10) results from northwest, north-south, and
northeast trending individual faults,
folds, and plutonic
This pattern was produced by the complex tectonic
belts.
events of the late Precambrian (Greenwood et al., 1980).
Northwest Najd Grain
Nost
important
northwest
trending
to the present study are the
structures of
the
late
mostly
Precambrian
left-lateral llajd faulG system (Figure 10) of the ArabianNubian Shield (Greenwood et al., 1980; Moore,1979).
right~lateral,
faults,
which
complements
system
is
to
north
to northeast trending,
would
be
the
theoretical
the northwest set,
superimposed
on
and
are rare.
cuts
the
Najar
strike-slip
conjugate
The
older
Najd
Hijaz
structures.
Najd faults in Saudi Arabia form a braided system
the
surface with en echelon and curved faults
and
diverging
(Moore,
1979).
at
converging
The pattern of the
Najd
38
is
system
experiments
faulting
very
of
of
development
similar
Wilcox
rigid
of
compressional
to
that
et al.
blocks
primary
and
structures
(1973)
at
in
depth
in
which
resulted
secondary
an
in
developed
the
wrench
in
the
extensional
overlying,
less
and
rigid
medium.
The
across
Najd fault system extends over
the
Arabian
Shield.
Block
1100
motion
Phanerozoic cover southeast of the Arabian
the
extension
length
zone
of
the Najd zone,
approaching 2000 kilometers
narrows
kilometers
in
Shield,
may indicate
(Moore,
a
the
along
total
The
1979) •
to the northwest as it approaches
the
Red
Sea, where it is terminated and locally reactivated by Red
Sea rifting.
Possible extensions of the Najd zone can
be
found in similar trends on the western side of the Red Sea
(Figure
9).
Because some of the faults bordering
Duwi parallel Najd trends,
Gebel
it is this northwest extension
into the Eastern Desert of Egypt and possible later normal
reactivations
that
are
of particular interest
in
this
study.
Folding
There are
at least three,
perhaps four,
phases
of
folding that have affected the basement rocks of the study
39
area.
Only
quartz
veins
three
the granites,
felsite dikes,
show no evidence of
phases
being
of folding are coaxial,
and
youngest
affected.
producing
The
shallow
plunging, southeast-northwest to north-south trending fold
axes
(Figure 11a).
dominantly
Axial surfaces of the folds
northwest-southeast
strikes
with
exhibit
variable
southwest dips (Figure 11b).
The
study
Meatiq
area (Figure 1),
north-northwest
Sultan,
gently
notes
the
Dome,
about 10 kilometers
has an
trending
overall
anticlinal
west of
the
double-plunging,
form
(Sturchio,
and Batiza, 1983) and exhibits related N35W/S35E,
plunging
(1964)
also
northwest trendinc folds in Egyptian basement
near
Red Sea.
plunging,
minor folding.
Greene (1984) has mapped the
el Isewid
of Gobel Atshan,
El Shazly
synfor~
large,
S40E
in basement immediately
east
notinc rare coaxial outcrop-scale folds.
The large U60V trending ilamrawein Synclinorium lies in Abu
Zietl's
area (Figure 1) to the north (Wise et al.,
1983).
The map pattern of planar features in the casement of
the
area
any
of the present study (Plate 1) does not suegest
obvious major structures.
study
are
subparallel
Most minor folds noted in this
to
the axis
of
the
el
Isewid
synform, and lie on the flanks of this larger structure.
Sturchio, Sultan, Sylvester, et al.
two
late
(1983) have dated
Proterozoic compressional events that
affected
40
N
0
0
+
a
0
a
o
• First Phase
O Second Phase
•
NW Crenulat1on
0
NE Crenulat1an
0
Unknown Assoc1at1on
S 25 E
N
0
0
0
a
b
+
a
0
S 30 E
Figure 11. a)
Fold axes the in Precambrian basement of
the study area.
b) Poles to
axial planes of folds in the
Precambrian basement of the study area.
41
the Meatiq Dome.
up
to
The first event resulted in metamorphism
epidote-amphibolite grade and formed
ductile
zone up to 1800
shear
meters
northwest trending lineations.
dated
at 613±5 M.y.
thick
low-angle
containing
The end of this event
by U-Pb dating
syntectonic tonalite.
a
of
zircons
is
from
a
Similar structures elsewere in the
Eastern Desert suggest the regional nature of this event.
The
resulted
second
in
the
tectonic
event
was
deposition of the
the
uplift
Hammamat
sediments.
This Gave the Meatiq Dome its anticlinal structure and
dated
at around 600 M.y.
that
is
(Sturchio, Sultan, Sylvester, et
al., 1983).
Bedding and Volcanic Layering
Much
of the basement of the study area is faintly or
indistinctly bedded with monotonous units.
comaonly
broken
consistent
distances.
orientations
comparatively
Figure 12a
jumbled
to
such
bedding orientations are not
significant
layering
and
rare.
Therefore,
measured
in
Further, it is
1Ln
extent
that
maintained
over
bedding/volcanic
the
These orientations are
and on the geologic map (Plate 1).
dip moderately to the southwest.
field
plotted
are
in
Most beds
The remaining poles plot
as a diffuse northeast-southwest girdle suggesting a gross
42
N
N
+
... .
..' ' ...-:-.:.:. ....
.~.·..,_.._,:·~::,:.... :...
'
. ..
+
. ...
\.
. ..".
• '
. - ....
,/'
~I
•
,.
• •.:.•
(
.I\
V'
~.
•
.... .
·.
5 40E
a
b
N
N
..
+
c
..
..
+
d
Figure 12. Precambrian basement
fabric nets:
a) poles to
bedding/volcanic layering;
b) poles to main foliation;
c)
poles to second foliation/schistosity;
d) poles to
crenulation cleavaees.
43
south-southeast plunging fold system.
Foliations
and Cleavages.
area
study
Folds in the basement
associated
are
foliations.
The
produced
main basement foliation;
spaced
the
cleavage
first
recognized
feature
of
the basement and
northeast-southwest
Similar
been
girdle
folding
w~ll-developed
a
all
of
the
It is the most prominent
southwest at moderate to steep angles
poles.
of
which is present in almost
metavolcanics and metasediments.
fabric
phase
the
basement
several
with
of
dips
predominantly
(Figure 12b). A weak
is defined by
the
remaining
orientations of the main foliation
noted to the north of the study area (Ries
have
et
al.,
1983).
A
second
phase of folding affected bedding and
main foliation,
the
producing a second basement foliation.
It
appears as a weaker spaced cleavage in the volcanic layers
and
as
a schistosity in the fine-grained
volcanic
ash.
The
subparallel
to
developed,
may
foliation.
second
foliation
the main foliation
be
Northwest
and,
indistinguishable
strikes
and
sediments
is
moderate
southwest dips are characteristic of the second
(Figure 12c).
strongly
the
main
to
steep
foliation
Again, a weak northeast-southwest girdle is
defined by poles to this feature.
two
commonly
where
from
and
Ries et al.
(1983) note
cleavages with similar orientations in Wadi Um Esh to
44
the northwest of the study area.
Weak crenulation cleavage with a consistent northwest
strike
and
very steep dips
(Figure 12d) developed
result of a third phase of deformation.
present
only locally and,
poorly expressed.
as
a
This cleavage is
even where best developed,
is
This cleavage is seen to affect bedding
and the two older foliations.
All three phases of folding are evident in an outcrop
on
and
the north side of Wadi Hammadat (Figure
coaxial
features
for
13).
refoldinG of bedding and early axial
variable
represented
by
stereonets.
orientations
the
girdles that
of
these
their
planar
may
by subsequent deformational phases
the
Folding
account
features
poles
form
as
on
Tertiary faulting may also have affected the
orientations of Precambrian foliations.
A
second
crenulation cleavage,
which
result of a fourth phase of deformation,
stations
in
Hammadat.
N60-65E
The
the
was noted at two
basement between Wadi Kareim
strike
and a nearly vertical dip
and
Wadi
(Figure
crenulation must be younger than
the
12d).
second
as it affects schistosity, but its age relative to
the other crenulation is not known.
note
be
This cleavage is very strongly developed with a
second
phase,
the
may
that
Ries et
al.
(1983)
post-cleavage crenulations and kink b6nds
common northeast of the study area.
are
45
N
First Phase Fold•
0
Aids
&>
Q Aida I Plane
Second Phase Fold•
G Axis (Approximate)
0 Axial Plane
0
0
+
Crenulation•
&,Axis
6
Axial Plane
[>
Crenulat1on
~Bedding
Main
Fahat1on
0
5
L-1
CM
Second Phase
First Phase
Fold Axis
Fold
Axis
S07E,ll
S15E, 16
Figure 13.
Block diagram and
net showing three phases of
folding
of
Precambrian
basement as
noted
in
an
outcrop
along the central
southern edge of the Wadi
Inglisi
Horst Block.
The fold
affects
a
sandy· bed
within finer-grained metasediments.
46
Lineations.
planar
Lineations
features
basement
Intersections
formed
by the
are
intersections
of
of the main and second
various
'l'he s e
southeast
to south-southeast trends and
have
kinds.
foliations are most
common.
features
of
systematic
northwest-
shallow
plunges
(Figure 14a), paralleling fold axes.
Smeared
foliation
whereas
mineral lineations are found on first
surfaces,
within
volcanic
stretched pebbles are found within
layers.
These
features
northwest-southeast
plunges
generally
have
layers,
conglomeratic
fairly
consistent
to south-southeast trends and shallow
(Figure 14b).
southeast
also
phase
(1983) note northwest-
Ries et al.
stretching
lineations
with
very
similar
orientations in the plane of the nain foliation in Wadi Um
Esh (Ries et al.
1983,
Figure 7b).
They state that this
northwest-southeast orientation is noted everywhere,
where the stretching is weakly developed.
lineation
parallel
noted
several locations
at
Sultan,
Sylvester,
A
pencil-like
to the stretching lineation was
et
al.
in
their
(1983)
even
area.
also note
also
Sturchio,
similarly
oriented stretched pebble lineations at the 11eatiq Dome.
~ineral
and stretched pebble lineations are
parallel
to fold axes, yet appear to be, and have been proposed as,
indicators
of the direction of tectonic transport.
would require the rotation of early-formed fold axes
This
into
47
N
•
+
a
0
•
0
e
•
S.ddi~tCi.cnao•
Pr1rnory/S..c0f'\dor)' Fot1alt0tll------....---"rim.ory Fcl1Ql1on/ NW Cr•~IOl•Ol'I
Q
Pr1mar7 F!)looh(ll'l/N[ Crtcftulot1cn
G
StC.OtldQry
Fohat10f1INW Cr.-n~llotl
N
•
•
••
b
+
..
•
Fit;ure 14.
•
S1r11i:"-d~t
•
$m401'1d Jlll,11.,o•s
•
Precambrian
basement
lineations:
a) intersection lineations;
b) smeared mineral and stretched
pebble lineations.
48
parallelism
tectonic
with
"a"
the transport
direction,
lineations (Sander,
making
Ries
1930).
suggest that the lineations do indicate
(1983)
direction,
and
al.
transport
that folding occurred subsequent to
development,
et
them
lineation
that the existing lineations controlled
the orientations of the developing folds.
They see early,
open folds with axes paralleling these lineations and find
it
difficult to believe that these could
folds
be
sheath-like
formed during the rotation of fold axes.
The fact
that
the lineations consisGently lie in the plane of
the
main
foliation,
are
genetically
an indication that the two features
linked,
seems to contradict their
proposal.
It may be that these are tectonic "b" lineations
(Sander,
1930)
Clearly,
the
paralleling fold axes of the first phase.
solution
to this problem lies outside the
scope
of
this study.
Dikes and Sills
Three
types
of small-scale igneous intrusions
noted in the basement of the study area.
indicate
greatest
a
sigma
3 (direction of least
or
of
intrusion at the time of formation (Anderson,
1951).
The
consists
of
four
to
compression
plane
group
perpendicular
features
the
first
extension)
These
were
granitic
to
aplitic
49
intrusions
the
located around the borders of the granites
southeastern
portion
consistent
orientation
associated
with
The
(Figure
area.
15a)
They
and
the emplacement of the
of
intrusion
of the
these
small
have
in
no
are
probably
larger
plutons.
bodies
caused
minor
perturbations of the main foliation.
Two groups of mafic intrusions were identified: westnorthwest
to
horizontal
north-northwest striking dikes
sills
(Figure
15b).
They
are
rnetabasalts with the exception of a large,
north-south
and
nearly
fine-grained
coarse-grained,
striking dike which weathers to a dark
olive
green.
The
mafic sills were intruded parallel
layering,
by
the
to
volcanic
and their orientations were probably controlled
layerine;.
northeast
The
dikes are indicative
to east-northeast extension.
of
north-
At least one
is
youne;er than the granite w:1ich it cuts, but others exhibit
a
weak foliation indicating an earlier
origin.
Several
are cut by the youngest quartz veins.
North-northeast- to northwest-striking felsite
indicate
west-northwest--east-southeast
to
dikes
northeast-
southwest extension (Figure 15c). These dikes contain pink
phenocrysts
aphanitic
color
less
than four millimeters in length
groundmass.
makes
it
almost
Deep weathering
impossible to
to
a
obtain
in
an
brick-red
a
fresh
50
N
4
'l~
a
•
•
+
•
r,
b
•
•
+
•
•
•• •
•
J
~,I
~•
••
•
•
•
+
•
c
\
•
•
•
•
Figure 15. Poles
to
dikes
and
sills
in
Precambrian
basement: a) aplitic dikes; b) mafic dikes and sills;
c) felsite dikes.
51
Similar
sample.
immediately
to
dikes
were
noted
in
the east of the field
basement
the
area
(D.
Greene,
personal communication).
The
brick-red
basement
felsite
dikes are
relatively
young
features and are not nearly as shattered as
bulk of the basement.
shattered
quartz
FaultinG
the
They cut granites, rnafic dikes, and
veins;
none
was seen
did affect these features,
to
be
folded.
but the age
of
the
faults cutting them was not determined.
Quartz Veins
The orientations of 137 quartz veins were measured in
the
basement
concentrations
bodies
of
the
occur
field
area.
Especially
in areas adjacent to
the
high
granitic
in the southeastern section of the area (Plate 1 ).
The veins exhibit fairly consistent
northeast
(Figure
to
16).
north-northeast
orientations,
strikes
A small population of
and
having
steep
dips
northwest-striking,
steeply dipping veins is also present.
Quartz veins also are interpreted as having developed
under
the
influence
of
a stress
field
oriented
normal to
the plane of the
dominant
northeast
strike and steep dip indicate
horizontal
northwest-southeast
vein.
with
extension
sigma
Hence,
during
3
the
nearly
quartz
•
... .:.·'.'
•
••
•
ti
--:r--:
.-- ... .
-..
.
...
•
•
•
•
•
•
•
• ••
•
•
•
•• • ••
•
•
•
••
•
•
•
•
•
•
•
•• •
•
•
'
-
•
• •• •
'
•
•
•
• ••
• ••
L£1=U
N
53
vein
development.
developed
The northwest-striking veins may have
under local stress fields,
in part
associated
The granites may
with emplacement of the granites.
have provided a source for silica-rich solutions.
also
Five of
the northeast-striking veins with thicknesses greater than
20
centimeters
within them,
be
have zones of pink to deep
red
feldspar
giving them a granitic appearance.
This may
taken as a further indication that some quartz veining
was
associated with granite emplacement and with
stresses
in
the
Greenberg
(1981)
country
also
rock
roofing
associates
the
quartz
related
plutons.
veining
with
emplacement of the Younger Granites of Egypt.
The northeast-striking veins apparently belong to
least two major subsets;
older,
at
commonly shattered veins
and a younger group which is little affected by subsequent
deformation.
main
Some members of the older family exhibit the
foliation and are cut by felsite dikes
Only one was observed to be folded.
were not seen to be deformed,
no
evidence of foliation.
and
faults.
Younger quartz veins
except by faulting,
and show
None was seen to cut
felsite
dikes or siGnificant faults.
The
only
quartz-bearing structural features in
platform sediments are microjoint fillings.
a
pre-Mid-Cretaceous origin for all
quartz
the
This suggests
veins,
most
54
probably in the late Precambrian.
developed
prior to,
or during,
first phase of folding,
the early stages of
the
and their origin is unclear.
The
development of the younger,
tentatively
been
which
produced
also
Older, shattered veins
northeast striking veins
linked to the first phase
much
of the
of
metamorphism
has
folding,
of
the
basement (Sturchio, Sultan, Sylvester, et al., 1983).
The
veins
the
may have formed as A-C joints perpendicular to
regional sigma 3, with the metamorphism providing a source
of quartz.
were
Finally, quartz veins of various orientations
developed
granites.
in association with
emplacement
of
the
C H A P T E R
III
STRATIGRAPHY OF THE SEDIMENTARY COVER
Two
Egypt's
groups of Phanerozoic sedimentary rocks occur in
Eastern
consists
related
The older of
the
two
groups
of Cretaceous to Eocene platform carbonates
elastics
Eocambrian
basement
mostly
Desert.
that
basement.
and
were deposited
unconformably
Resting unconformably both on
the older sediments is
and
the
second
on
the
group:
littoral deposits associated with the formation of
the Red Sea.
Cretaceous to Eocene Sediments
There
area
are seven mappable formations
west of Quseir (Figure 17),
throughout
deposited during a late
Cretaceous through Early Tertiary southward
of
the
Nubia
transgression
Tethyan Sea.
Formation
The
(1837)
south
the
Nubia
to
Sandstone was a name applied by
sandstones cropping out along the
of Aswan.
Since then,
55
Russegar
Nile
several variations of
River
the
56
Hakheil Formation- thickness extremely variable;
chert nodule/pebble conglomerates1 sandatonee
and sandy ahalee;
commonly limey,
salty in
places
f:·.; :- '·
1fff!fi:1:\) POST-EOCENE
t::::l
0
Thebes Formation- limestone,
marl, and calcareoue
shale near the baee paeeing upward into chalky
and marly limestone near the top;
plentiful
black and brown chert nodules,
lenses,
and
banda increasing upward from the base
Cl
Ypresian
tr:l
z
t::::l
c
~~"'"'~~~~-0.. ~~~0"'~~0~:::::::::c~~~-=- ~ I
Esna
Formation- gray
to
gray-green
---
shales;
somewhat calcareous near baae
t=- ~
100
Dakhla
Formation- gray to green to red-brown
fissile ehalea; weather• to aal•on pink; •arly
near base and top;
high concentration of
fibrous gypou• vein• near baee
Cl)
a::
;::cl
------1
-
50
E-<
::£!
~
L...
0
---- --------- -------------
-
-
-
--
Landenian
Hontian
>
t""'
t::::l
0
Cl
t::::l
z
t::l
Dani an
Ha es-
----=--==- -
trichtian
Duvi For•ation- phosphoritea,
li•eatonea,
and
marls; highly foaailiferoua; economic phoaphate
beds
c::
--------------------------O::~::s:::::c:s:=:=C:=::m=-=-...:.ii:i
Quseir Formation- variegated shale and siltstone,
Campanian
some sandy;
blue-gray to yellow-brown to graygreen to red-brown; •anganeee concretion• and
staining com•on
-r-··~
-
i:-.--- · - ·
,..-.<;::
""
'"""" """"' ""
"""
r:::::.
Nubia Formation- clean terrigenoue
aandatoneo;
cream-colored, often kaolinitic basal layer;
trough and tabular croes-bedding common;
top
grades upward into Queeir Formation ohalee
~
'-<::-
~
""<:;:
""" ~
l
! . ....
J
J
,I
/
""""/
Basement- Eocambrian greenstonee, metavolcanice
and meteeedi•ente do•inate the atudy area
7
7
7
7
7
""
(/)
Santonian
:::0
t::l
z
0
z
H
>
0
:::0
t::l
>-3
>
0
tr:l
0
c::
C/l
-.;;:
J
7
7
,fl
~
'
1-tJ
1-tJ
t::l
z
~
F".
F.'
7
7
Conie.cian
.J
7
J(
PRECAMBRIAN
•
"
Figure 17. Stratigraphy
platform sediments.
1-tJ
of
the
)
Cretaceous
to
Eocene
57
name have been applied to sandstones and sandy shales over
most of northeast Africa,
stratigraphic position.
often without regard to age
Throughout this study, use of the
term Nubia Formation will conform to the usage of
(1957)
as
lying
Its
or
Youssef
applied to a predominantly nonmarine
sequence
unconformably on the Precambrian basement
complex.
upper
boundary is marked by a transition
to
poorly
consolidated, varicolored shales.
Based
on
sparse fossil evidence
within
the
Nubia
Formation and the overlying Quseir Formation, the Nubia in
this
region
is tentatively dated as Coniacian
Campanian in 1ge.
to
early
It has been considered by others to be
as old as Cenomanian (Ward and McDonald, 1979; Van Houten,
personal
communication)
Maestrichtian
and
as
Sandstone"
early
as
1972) in various parts of
(Issawi,
It should be noted that northward,
"Nubian
young
Egypt.
in the Sinai, an older
of Paleozoic age lies
beneath
units
correlative with the Cretaceous formation of the map area.
The
Desert
thickness of the Nubia Formation in the
is
highly
topographic highs.
variable,
thinning
over
Within the study area,
Eastern
basement
its thickness
varies from 70 to nearly 200 meters.
The
Nubia
can
be
divided
lithologic
units in the Qusoir
oldest
youngest,
to
into
area.
three
These
trough-cross-bedded
distinct
are,
from
conglomeratic
58
sandstone,
tabular-cross-bedded
laminated
siltstone
and
and
sandstone,
lenticular
ripple-
sandstone
units
as described by Ward and McDonald (1979).
The
lowermost
unconformably
trough-cross-bedded
on basement, which
along the contact.
Nubia
is
coarse
is
often
consistently marked by
sandstone
to
pebble
unbedded or poorly bedded.
a
attains
to
maximum
vicinity
of
southern
end
cream-colored
conglomerate
exhibiting
The basal zone
is
The remainder of the lowermost
trough-cross-bedded
a
kaolinitized
light
consists mainly of yellow-brown to
bedded
rest
Within the study area, the base of the
lavender and locally yellow staining.
unit
sandstones
sands.
red-brown,
non-
The
unit
basal
thickness of about 80 meters
in
the
Quseir and is 50 to 60 meters thick
at
the
of
Gebel
Great
Duwi.
variations are observed due to basement
characteristics
local
thickness
topography.
The
of the lowermost unit are consistent with
deposition on an alluvial plain (l!ard and
~cDonald,
1979).
The second unit within the Nubia Formation is made up
of
broad
lenses
tabular-cross-bedded
of
nonbedded
sands
and
sands that interfinger with
laminated fine sands to silts.
deposited
ripple-
Cross-bedded sands account
for more than half the thickness of this unit,
was
spectacular
on an alluvial plain (Ward
and
which also
MCdonald,
59
A
1 979).
reported
for
McDonald,
slightly
variable
thickness
of 50 to
140
meters
this unit in the Eastern Desert
1 979) •
At
Gebel
Duwi,
it has
greater than the underlying
(Ward
a
is
and
thickness
trough-cross-bedded
sands.
The third and uppermost lithologic subdivision of the
Nubia
Formation is dominated by dark brown to
brown
fine sandstones and sandy siltstones.
sands are trough-cross-bedded,
of
the unit.
dark
red-
Some of the
particularly near the base
An alluvial coastal
plain/shallow
marine
environment is postulated for the deposition of this unit.
The
unit grades upward into the variegated shales of
Quseir Formation.
the
Precise placeIT.ent of a contact between
the Nubia and Quseir Formations is difficult as there is a
transitional zone where sandy silts and variegated
are
interbedded.
the
where
shales
A fairly subjective boundary was drawn
variegated
shales
become
dominant.
The
thickness of the upper unit varies from about 20 meters at
Gebel Atshan to about 30 meters at Gebel Duwi.
Quseir
~
The
"
long
'!>
Formation
variegated shales of the Quseir
Formation
considered to be part of the upper Nubia
Youssef (1949) described them in detail,
were
Formation.
calling them the
60
"variegated
The name Kossier Variegated
clays".
was later applied to them by Youssef (1957),
(1956)
name,
the
Quseir
Formation,
Shales
but Ghorab's
has
gained
wider
acceptance.
The
Quseir
consolidated
from
Formation
shales,
gray-green
to
yellow-brown horizons.
consists
locally sandy,
blue-gray
to
mainly
bands
are
poorly
that vary in
red-brown
color
with
rare
Manganese staining and concretions
are common and some gypsum veining is evident.
phosphate
of
present in the upper
Local thin
part
of
the
formation.
Some workers
put
the
upper
lowermost
(Abd El Razik,
1967;
contact of the Quseir
phosphate
band.
However,
Trueblood,
formation
as
the
1981 )
at
the
lithology
continues to be dominated by variegated shales above these
isolated bands,
Youssef's (1957)
placement of the contact
at the base of a hard, brown, one meter phosphatic horizon
will
be
used.
horizon,
yields
Varicolored
but are secondary.
a
thickness
shales
exist
above
this
This placement of the contact
of 50 to 75 meters
for
the
Quseir
Formation in the study area.
Many of the early fossil-based age determinations for
the "Nubian Sandstones" were,
in fact,
from
A Senonian age is indicated
by
the variegated shales.
these fossils and agreed upon by most
based on evidence
authors
(Said,
~
i
-it
j
J
61
,'
;:.
~;
f\z-
~
'~
F
1962;
Issawi et al.,
In the Quseir area, a more
1969).
precise age determination of Campanian (Youssef,
1957; El
f--
r
f,t
Tarabili,
L
possibly Campanian to early Maestrichtian (Issawi et
~
1971 ;
'~'
r,
1966;
al.,
1972) has been made on the basis of fossil
Issawi,
gastropods
Abd El Razik, 1967; El Dawoody, 1970) or
and
pelycypods
from
the
Quseir
and
Duwi
f
Formations.
Fossils
found in the Quseir Formation are of
and fresh water origin (Newton,
1;_
J
fossil wood (Seward,
1909).
Plant remains and
Issawi et al., 1971) indicate
1935;
a marginal marine to estuarine environment of
The
Quseir
marine
deposition.
Formation marks an upward transition
continental environment to the shallow marine
from
a
environment
that produced the remainder of the platform sequence.
Duwi
Formation
Resting
Duwi
conformably
Formation.
on the Quseir Formation is
It was originally named
the
the
Phosphate
Formation by Youssef (1949), and that name continues to be
used
and
by many workers,
in
the Western Desert.
Formation,
Gebel
particularly along the Nile
given
Ghorab 1 s
(1956)
for its type locality in
Duwi area will be used here.
name,
the
River
Duwi
southern
This name is used by
62
most workers in the Eastern Desert.
The
formation
crystalline
marls,
or
consists
siliceous
mainly
of
limestones,
hard,
phosphatic
and shales and contains chert bands,
The
nodules.
marked
phosphatic beds are mined
Within
phosphate.
by
the study area,
a series of hard
phosphate
bands
beds,
lenses,
for
and
tricalcium
the lower contact is
porcellanite
interbedded
semi-
with
and
marls
siliceous
and
coquina
limestones.
The upper half of the formation is dominated by marls
and
oyster
Q~1r£~
coquinas.
Yi11~£,
with
a
ribbed,
triangular shell,
is the dominant fossil found throughout
the
A
formation.
phosphatic
the
~useir
bed marks
1972)
entire Duwi Formation,
(1957)
Campanian
three
soft,
meter,
top of the Duwi
workers (El Tarabili,
Issawi,
Youssef
~he
to
gray,
Formation.
In
area, this formation is 50 to 70 meters thick.
Various
1967;
one
1966;
Abd El
assign a Maestrichtian age
based on fossil dating.
Razik,
to
However,
dates the lower part of the formation
on the basis of fossil
ammonites,
the
as
gastropods,
and oysters.
Bays
connected to the open sea where strong currents
reworked
the
suggested
by
Formation.
bottom
sediments
are
the
environments
Said (1962) for the deposition of the
Duwi
Nairn (1978) notes that the fossil assemblages
..
~,
63
indicate
an open shelf environment and suggests that
phosphates
originated
shoals
bars,
or
in shallow coastal
with coarser
deposits
the
basins
behind
forming
during
storms.
Dakhla
Formation
Conformably
Dakhla
overlying
Formation,
which
the
Duwi
Formation
is composed mostly of
green to red-brown shales.
(1962)
these
gray
the
to
These weather to a salmon pink
color characteristic of the Dakhla slopes.
includes
is
rocks in the
Esna
Youssef (1957)
Formation,
but
Said
gives them separate formational status.
The
lower part of the Dakhla Formation is marly with
local limestone beds.
Immediately above the lower contact
are
of
several
abundant,
known
used
irregular,
dark
fibrous
gray-brown
shales
gypsum veins.
as
an
indication
bed of the Duwi Formation.
Formation
terminate
Formation.
of proximity
at
the
The
is dominated by
base
of
the
to
are
and
are
the
uppermost
The balance of the
fissile
chalk
with
These
as the "gypsy shales" by the local miners
phosphate
Dakhla
meters
of
shales, which
the
Tarawan
thickness of the Dakhla Formation ranges
between 145 and 170 meters.
64
Fossils
Maestrichtian
(Issawi
et
(Youssef,
upper
in
the
age
as
at
the base to early Landenian at the
top
al.,
1969;
1957;
Dakhla.
Dakhla
Said,
The
have
Issawi,
fixed
its
1972).
Other
authors
1962) assign a Danian age to
fossils are of shallow-water
the
marine
organisms indicating near-shore deposition.
Tarawan
Formation
The shales of the upper Dakhla
into
the
Formation.
1962)
or
Formation.
white
have
study area,
marls and marly chalks
of
grade upward
the
Tarawan
It is often called the Chalk Formation (Said,
lumped
together
with
the
overlying
Esna
Because these white, tan-weathering chalks are
lithologically
and
For~ation
distinct
from the shales above and
average thicknesses of 10 to 20 meters
below
in
the
they will be treated as a separate formation.
However, because the outcrop pattern at the 1 :40,000 scale
of the original geologic mapping is very narrow,
the unit
is combined with the Esna Formation on the map (Plate 1).
has
On the basis of fossil foraminifera,
a Landenian age
been
et
assigned
to this unit (Issawi
Issawi et al., 1971; Issawi, 1972).
shallow marine environment.
al.,
1969;
It was deposited in a
65
Esna Formation
The
chalks
Esna
Formation rests conformably on
In the Quseir
of the Tarawan.
the
area,
consists of 50 to 60 meters of gray to green,
this
with a few marly and silicic beds at the
brown
silicified
containing
unit
thin-bedded
shales
zone
white
top.
pelccypod
A
fragments
commonly forms the lowermost bed.
This
age
unit is dated as Landenian to early Ypresian in
on the basis of fossil foraminifera (Issawi
1971;
Issawi,
environment
following
1972).
and
the
It
al.,
was deposited in a near-shore
represents
somewhat
et
a
temporary
more distal
regression
deposition
of
the
Tara wan.
Thebes Formation
The
uppermost
unit
of
the
sequence is the Thebes Formation.
Cretaceous
In
the study area,
"lower Libyan",
(Sail, 1962).
the base of the Thebes Formation
is generally marked by hard limestone with chert
by
a
hard,
Turritella
----------
gray
casts.
to
Eocene
It is also known in the
literature as the "Operculina limestone",
and "limestone with flint"
to
brown-gray
limestone
overlain
containing
From the base to the top of the
main
66
ridge of the Thebes,
limestone
massive
the lithology is dominated by chalky
interbedded
gray
with thin
limestone,
crystalline
nodular,
conglomerate, marl, and some shale.
limestone,
recemented
limestone
Dark brown, gray, and
black chert is very common in the form of nodules,
and
lenses.
Above
the
main
ridge-forming
bands,
beds,
limestones tend to be more crystalline and thinly
the
bedded,
with chert slightly less common.
The
area
thickness of the Thebes Formation in
the
study
is everywhere greater than 160 meters and can exceed
200 1aeters.
The amount of erosion of the top of the unit
controls its thickness.
Fossil
formation
foraminifera indicate a Ypresian age for this
(Said,
1962;
El Tarabili,
1966; Issawi, 1972)
and its deposition marks a return to a more distal, deeper
water
environment.
the early Eocene,
Red
Sea
Uplift in the Eastern Desert
during
possibly related to the early stages of
development,
terminated
its
deposition
eventually brought the area above sea level,
and
resulting in
the subsequent erosion.
Topographic
The
Expression
units of the Cretaceous to Lower Eocene sequence
exhibit characteristic topographic expressions which
help
67
to
identify
profile
them in the field and on
air
photos.
The
of the stratigraphic column (Figure 17) indicates
each unit's relative resistance to erosion.
The
the
Nubia Formation can be distinguished easily from
underlying
basement
weathering pattern.
by
its
brown
color
and
its
The lower two subunits tend to
form
steep slopes, which are commonly covered with talus.
The
top
of the second subunit is commonly present as a
dip
slope with the less resistant upper subunit
minor
stepping
up to the overlying shales.
The
develops
Quseir Formation weathers relatively easily
gentle
slopes between the
units that bound it.
debris
two
more
and
resistant
It is commonly covered with its own
and that from the Duwi Formation.
This makes
it
difficult, in places, to determine whether the material is
in place or slumped.
The
Duwi
Formation,
limestones and coquinas,
identifie~
easily
especially
the
resistant
forms cliffs and ridGes that are
in the field and on air
photos.
uppermost coquina bed can be seen as a stripped dip
that
generally
Duwi-Dakhla
dips northeast in the
study
area.
contact is almost always covered with
The
slope
The
debris
from the overlying strata.
The
relatively
soft shales of the Dakhla
Formation
68
are
to
eroded back from the Duwi ridges and slope gently
the
The
more resistant chalks of the
slope
steepens
protected
by
Tarawan
near the top where
the chalk,
the
which forms a
up
Formation.
shales
narrow,
are
debris-
covered ledge.
The soft Esna Formation slopes moderately up to where
it,
in turn, is protected by the limestones of the Thebes
Formation.
The
limestones
forms
topographic
protective
ridges
that
cap
of
are
massive
the
features of the Quseir area.
most
Thebes
prominent
The main ridge
is formed at the boundary between the chalky lower half of
the
formation and the more crystalline limestones of
upper
Thebes.
A minor cliff is formed
the
approximately
a
third of the way up from tho base of the main ridge.
Post-Lower Eocene to Pre-Middle Miocene Deposits
Nakheil
Formation
Over
much
of
the
area,
the
Nakheil
Along
the
on basement.
The
unconformably overlies the platform sequence.
northeast side of Wadi Nakheil it rests
bulk
of
the
Nakheil deposits occur in
Formation
the
downfaulted
troughs northeast of Gebel Duwi and east of Gebel Atshan.
Youssef
(1949)
first described these rocks
as
the
69
and Sandstone Series" in the
"Conglomerate
The
sequence
consisting
is
extremely
variable
of chert nodule and
Quseir
lithologically,
limestone
conglomerates,
sandstones, sandy shales, and sandy limestones.
bed
of
area.
The basal
the unit is usually a chert and limestone
conglomerate.
instances
The
appears
formation
to
fine
distance from major faults.
in
similar
appearance
to
fines upward and
laterally
with
cobble
in
some
increasing
Several of its upper beds are
the
shales
of
the
Quseir
Formation and can be gypsiferous and/or salty.
Dy strict definition,
no
basement fragments
the Nakheil Formation contains
(Trueblood,
1981) suggesting
that
basement was not exposed at the time of deposition of this
unit.
However,
origin
were noted in the conglomerates in
As
some quartz pebbles of possible basement
Wadi
Nakheil.
basement is in contact with this unit in Wadi Nakheil,
these
pebbles
They
may
may have come directly from
also
have
come via
the
this
platform
source.
sediments,
however.
To date,
the Nakheil Formation has proved completely
unfossiliferous,
1966).
It
precise
age.
is
even
in thin section (Nairn and
therefore very difficult to assign
Said
Ismail,
it
a
(1962) proposes an early Eocene age,
while El Akkad and Dardir (1966b) and Issawi et al.
(1969)
70
assign it to the Oligocene,
it Middle Miocene.
occur
in
the
unconformity
(private
Similar conglomerates of Oligocene age
Gulf
of Suez
with
only
slight
with respect to the Thebes and
communication
Limestone
and Abd El Razik (1967) calls
older
from petroleum company
and chert conglomerates of
angular
units
sources).
pre-middle
Miocene
age are also exposed along the Gulf of Aqaba/Dead Sea rift
(Garfunkel et al., 1974).
The thickness of this formation is extremely variable
due
to its deposition as a tectonically controlled
Multiple
conglomeratic beds within the Nakheil
suggest
several
deposition.
whether
sediments
cannot
normal
prior to,
Nakheil Formation.
transport
would
in
be determined
faulting
during,
from
disrupted
this
the
study
platform
the
A much more detailed study of facies,
directions,
and
sources of
elastic
downwarps or in fault-bounded troughs.
(1966b),
its
or after deposition of
be necessary to determine whether it was
Dardir
Formation
periods of tectonic activity during
It
major
unit.
Issawi
et al.
(1971),
material
deposited
El Akkad
and
and
Richardson
(1982) favor the fault-bounded trough origin, perhaps in a
lacustrine environment.
However, as these studies provide
no concrete support for this preference,
the validity
of
their conclusions is uncertain.
The lower conglomeratic beds tend to form low ridges,
71
readily identifiable on the ground and on air photos.
Middle Miocene to Recent Deposits
A group of mostly littoral deposits of middle Miocene
to Recent age lies unconformably over the basement and the
aforementioned sediments.
the
most part,
This group is associated,
for
with Red Sea formation and deposition
the resulting basin.
in
These sediments crop out as a narrow
strip along the western coasts of the Gulf of Suez and Red
4).
Sea (Figure
In the Quseir area, the strip is 5 to 10
kilometers wide and consists of five distinct units.
the
exception of the recent alluvial deposits,
only
minor or no exposure in the mapped area
With
they have
(Plate
1).
For a more detailed description, see Greene (1984).
Recent
Wadi
The
Alluvium
present
wadi
system in the
Quseir
area
cuts
across all of the other units seen in the Eastern
Desert.
Wadi
elastic
floors
sediments
deposits
are
covered with a thin veneer
ranging in size from clay to
of
boulders.
cover large sections of the mapped area and
These
are
transported toward the Red Sea by catastrophic flooding of
wadis following rainstorms.
C H A P T E R IV
STRUCTURAL FABRIC
Faults,
were
As
folds,
joints
and a small number of
veins
noted in the Cretaceous-Tertiary platform sediments.
previously mentioned,
faults and joints
in
basement
also are discussed in this chapter.
Faults
Most
major
fault
eroded and buried
concerning
surfaces in the
under talus.
regional
fault
study
Cretaceous
Formation
to
of
of
motions are
190 faults were
based
sense
of
on
measured
the study area (Figure 18),
within
116
the
Nakheil
of
which
(Figure 18) and have an ascertainable
Few
motion.
minor
results.
Eocene platform sediments and the
exhibit slickensides
are
Consequently, inferences
faults, which yield reasonably consistent
Attitudes
area
of
the
fault
surfaces
show
significant mineralization; calcite mineralization is most
common, and some surfaces exhibit minor silicification.
single
fault surface has chert developed along it and
associated
with
~ineralization
is
a
set
of
chert-mineralized
probably the result
72
of
A
is
joints.
precipitation
.
N
..
ffi
iSen
:i
~
I>:
oo-r
!
n.~140
z
i...i
u
s
g
en
~
~
I>:
u
+
...
.
+
Fault;s
Oblique-slip Faults
n.=18
no=IB
·- ·.., . : .
0
0• 01•11•0•
0
o°: •• e -
.
,~ 0~..., .
. •o .;.•
..
.. . ... -
•.lo
N
0 O
o0
I•
e .,
00
0
Cl
'
\
Cj\
.
.... . ..
.......
+
0
0 ..
A~
Reverse Faults-----+---- Strike-slip Faults
n.•22
n.•3
N
N
n.z4
n,,•17
.·
..,-
A
A
#
••
'
''
0
'
Oa•IO
•o
0
.. ....
··.
..
A•·
\
..
"
N
no•73
u
i...i
..
A
'
1---...----- Normal
f5
..
'
~ "o"6
.. .
I>:
i:i..
Cl
/
N
N
N
n •12
no•ll
+
i+'
..\ I I
• •
..
'
+
.
oo!Jrf o
.<••
~··
•
..
I
• Pole to Fault
•Pole to Left-lateral Fault
O
O Slickenside
• Pole to Right-lateral Fault
6. Right-lateral Slickenside
Left-lateral Slickenside
Figure 20. Poles to joints in the study area.
.....J
\.tJ
74
from groundwater circulating through the cracks.
Attitudes
of
84
faults
in
basement
rocks
were
Minor chlorite was noted on a
measured (Figure 18).
few
of the surfaces and post-faulting silicification is fairly
common.
Thirty-seven
of
these fault
surfaces
exhibit
identifiable slickensides (Figure 18).
The
area
is dominated by west-northwest- to
northwest-striking,
faults
has
steeply to moderately dipping
(Figure 18),
time.
normal
as would be expected in an area that
undergone regional northeast-southwest
Tertiary
north-
These
faults
cut the
extension
entire
sequence as well as basement, indicating
in
platform
their post-early
Eocene age.
A
in
small number of northeast-striking reverse
basement
and
cover
northwest-southeast
of
number
Tertiary
sediments
southwest
compression.
northwest-striking
normal
to
(Figure
18)
suggests
possible
compression while a
northwest-striking
platform
parallel
(Figure
reverse
18)
larger
in
faults
faults are parallel
dipping,
or
bedding and are in close proximity to
faults.
These
reverse faults are
the
northeast-
suggests
Many of the moderately
reverse
faults
submajor
probably
the
result of flexural slip out of drag-folded synclines.
Steeply
faults
may
dipping,
northwest-striking
have formed as
minor
normal faults prior to
reverse
block
75
tilting.
A
conjugate
system
of
approximately
north-south-
striking right-lateral and northeast-striking left-lateral
faults
is
present
Eocene
(Figure
in all rocks
19).
from
basement
The development of this
through
conjugate
system is consistent with near-horizontal, north-northeast
compression.
Tertiary
H25E
Only
four of these strike-slip faults
sediments.
Therefore,
cut
a Tertiary age for
the
compression would be rather tenuous based solely
these
data.
oriented
However,
conjugate
Greene (1984) notes
Eocene strata directly to the
notes
that
.Miocene
of
east.
A
middle
tentative
Eocene
to
age
middle
cutting
Greene
similar structures were found
sediments.
compression
similarly
system of strike-slip faults
early
no
a
for
on
in
also
middle
the
112 5E
Miocene
has
therefore been assigned.
Similarly oriented strike-slip systems present in the
Gebel
Zeit area at the southern end of the Gulf
(Perry,
1982)
and
of
in the Azlam Graben of western
Suez
Saudi
Arabia (Davies, 1981) suggest the regional nature of these
stresses.
Eocene
Northwest trending folds in the Cretaceous
aged sediments of Gebel el Anz immediately to
northwest
(Trueblood,
compressional episode.
1981) may also be related to
to
the
this
76
Ltll·lol•rol
Riqhl·IOIUCI'
fo11Ul
Faul" and
Sl1clii•rit•••~
011•
N
a
Sl1c•tt1tide1
N
b
~·~~6
/4"-/
HS
/
...
:•: 4
-A>
4
4
',4 . .
4
4
4
hwlu
~
!<!!"
1
~,
/
/
Yi~
~·
_/
:i•q""o I
N
c
N
d
I
HZ>E
c~~u.ian
n•22
.,/'
+
y
..
I
Figure 19. Tertiary N20E compression:
a) and b) combined
strike-slip fault data;
c) calculated causal maximum
compressive stress orientations; d) N20E comression and
resultant strike-slip fault system.
77
Some
zones
segments of the major north-south normal
fault
may be reactivated right-lateral faults related
N25E
compression.
including
a
Four
section
of
the
right-lateral
of the northern end
of
to
faults,
the
Gebel
Atshan Fault Zone, have experienced both right-lateral and
younger normal motion.
strike-slip
faults
tentatively
Greene (1984) also notes numerous
reactivated
associates
this
as
normal
faults
and
with
the
reactivation
initiation of Red Sea rifting.
Joints
Attitudes
area;
117
(Figure
282 joints were measured in the
in basement and 165 in the platform
20).
joint
set
study
area
basement
of
Two
or three examples of
present at separate
were
and
measured to obtain
some scatter.
joints
are
steeply
present in both
sequences,
prominent
throughout
data.
the
Both
east-west- and
dipping major
Steeply dipping,
sediments
each
these
cover display approximately
north-south-striking,
with
stations
study
joint
sets
northeast-striking
but
are
better
developed in the cover.
A northwest-striking set with moderate to steep
is
better
developed
in cover.
Joints of this
basement have extremely variable dips,
set
dips
in
uhich may indicate
puo ·.,_i;'•J,,!i '%1
+
'®
SlNIOr 'M3AOJ
SlNIOr 1N3W3S\f8
N
N
,~
• •
••
• ••
••
•
•
•
• 0
.
•
·'·••
.
•
•
• •
+
••
.•
•
•
•
;f.o•l,IUJ)O ...
1u•ur
0
e
•
•••
•• ••
•
•
o.
•
•
·":.: ....
..,, ..•
••
0
•
.....
••
•
••
'·t• •
•
•
•
+
•••
••
••
,::• .: ••
••,,
0
••
•
••
• •
•
• •""
•
••
•• •
•
•
I .:'( ..
••
•
·'
1:91••
N
N
8l
79
that they are old and have been folded prior to deposition
of the platform sediments.
They also appear very
similar
to the main spaced cleavage in the basement; hence some of
these
"joints"
may
actually be
incorrectly
identified
cleavage surfaces.
The major north-south and east-west joint sets appear
to
bear little relation to any other observed
grains,
be
structural
although some of the older north-south joints may
related to east-southeast extension which
complemented
striking
N25E
compression.
would
Similarly,
have
northwest-
joints may be the result of northeast,
Red Sea-
related extension.
In
most
cases,
joints are undeformed and
othej' structural features,
the
Age
and between joint groups are complex and
contradictory.
all
indicating that they are among
youngest features in the study area.
within
cut
relations
commonly
At many locations, older, silicified sets
parallel fresher,
younger sets.
Much more detailed work specifically concentrating on
joints
these
is necessary to clearly understand the meaning
features.
orientations
However,
based
on
a
similarity
and character of basement and cover
of
of
joints,
it is proposed that most jointing is post-early Eocene.
80
Veins
Three northeast-striking, steeply dipping chert veins
were noted in the upper Thebes Formation atop Gebel Nasser
(Figure
21).
They
appear
sedimentary
deformation
related
an early
small
to
number
(Figure
21),
of
to have resulted
in the Early Eocene and
northwest-southeast
other veins were
but
from
noted
syn-
may
be
extension.
A
in
the
because of the small sample
cover
size,
no
useful information can be derived from them.
As
previously stated,
high concentrations of gypsum
veins are located in the lower Dakhla Formation.
Although
no examination of these features was undertaken,
they may
prove a fruitful subject for future study.
Linearaents
Basement
LANDSAT
Lineaments.
return
Basement lineaments were
beam vidicon (RBV) images at two
1 :208,000 and 1 :606,000.
includes
includes
images
whereas the 1:606,000 image
the entire
on
scales:
The 1 :208,000 image (Figure 22)
both Greene's (1984) area and the present
area (see Figure 1),
23)
drawn
Quseir-Safaga
show N30-70E trends of moderate
study
(Figure
district.
Both
intensity,
which
correspond to the major N60E faults of the study area.
81
a
II Black Chert
~§1 Limestone Conglomerate
0Marl
N
n=/2~
• •
••
b
•
•
A
Chert
Calcite
Quartz
I
•
I
+
\·
•
Figure 21 • a) Sketch of black chert dike in the upper
Thebes Formation of Gebel Nasser.
b) Poles to veins and dikes in the seJimentary
cover of the study area.
82
2b
0
20 IN
Rtu SU
~j
,\
'\
•
,
\
/
\,•'-:rr
'.~'-
•
,_
,,,
ft
; , ~/
::::f'
''Yf?_
/ ,·.,.,..~'·
-x~
\ ' /.
. ..---'/
. ' )(.......--,- ~........'
~II
'"j!:[R
,
x,'
/,
;~" /
,/ , ·I
'
x
-- )
)4
\'
--''
\<~/, :\\~
,,,.-"
,
2\olu'N
~'
,,_,.
..,
° uo IE
34°
i'
.
~U'E
'.
I
""·''\
*
·S
CJHCENTRA.T [UN fACTOil
9Y SUHBER
:uNCENT~ATIOM
FACTOR
BY i..t:Nl.ITH
~
,,"
."
t.:C.CEN7RAT[O!f
'°
~
r..,.,
~
w
r1:.:;cR
--·~,_,_
N
Figure 22. Lineaments in the basement of the study area.
TOP: Sketch map of the studied area
with
lineaments
superimposed.
CENTER: Rose diagram of lineament azimuths.
BOTTOM: Histogram of lineament azimuths by number.
Rose diagram and histogram are twice smoothed using
a ten degree running average calculated for every
degree.
83
26° 40'N
0
10
~
KM
25° 40'N-t--~~~~~~~~~~~-L
33° 30'E
34° 20'E
I
N
'---
/
CONCENTRATION FACTOR
BY NUMBER
'---
/
CONCENTRATION FACTOR
BY LENGTH
[ 5
"'""
U)
H
0
W
3:
=>
cc:
0
CONCENTRATION
U)
I
z
/~~
/
w
~
"---··/
FACTOR
/
E.
0
Figure 23. Lineaments in the basement of the Quseir-Safaga
area.
TOP: Sketch
maµ
of the studied area with
lineaments
superimposed.
CENT~R: Rose diagram of lineament azimuths.
BOTTOM: Histogram of lineament azimuths by number.
Rose diagram and histogram are twice smoothed using
a ten degree running average calculated for every
degree.
84
North-south
1:208,000 image,
This
trends
show
up
only
weakly
on
the
but are stronger on the 1 :606,000 image.
may be because they are overwhelmed on the 1:208,000
image
by
trends
parallel to the Red Sea that
are
very
prominent in the basement of the southern Gebel Duwi area.
Although
image,
the Red Sea trends are present on
they
are
not as strong,
the
regional
perhaps due to
greater
coverage of areas at increased distances from the Red Sea.
Although
northwest
clearly
the
trends,
present.
regional image exhibits
the
N60W Gebel Duwi (Najd)
Its
presence is also evident
1 :208,000 image as would be expected.
rose
more
diffuse
trend
on
is
the
The strength of the
diagram peaks representing the length and number
of
Duwi-parallel lines indicates that, although the number of
these
lines
parallel
does
lines,
not approach the number
of
Red
Sea-
the total length of lines for these
two
groups is nearly identical.
DiverGence of these results from data gathered in the
East-
field lies in the absence of east-west lineaments.
west
study
faults are relatively common in the basement of
area and have also been reported in the
(see Chapter II).
size
East-west faults may be of
in the Quseir-Safaga region,
the
literature
diminutive
being too small to
be
picked up on the RBV images.
Cover Lineaments.
Lineaments in the Cretaceous to
Eocene
85
cover were drawn on 1 :47,000 copies of the air photos used
during
field
(Najd)
trends,
north-south
work (Figure 24).
Northwest
and Red Sea trends
trends
show
trends,
weakly.
are best represented in the
Duwi
Minor
southern
end of Gebel Duwi and along the Bir Inglisi Fault Zone.
East-northeast
the
northeastern
and N20-30E trends are present
dip
slope
of
Gebel
along
Although
Duwi.
neither of these trends is particularly well-expressed
field
data
19),
for faultine
they
(Figure 17) or jointing
may be the result of
structurally
drainage down the dip slope of Gebel Duwi.
joints
paralleling
(Figure
controlled
Several large
wadis on the dip slope of Gebel
were
noted in the field,
were
located along the dip slope,
in
but as relatively few
Duwi
stations
these features may
be
underrepresented in the data.
With
of
the
present
same
the exception of the dip slope lineaments,
lineament
trends
have
in the ground data.
trends
Quseir area.
Sea-parallel
noted
corresponding
Generally,
these
by El Tarabili (1964;
1971)
all
fractures
are
the
in
the
llowever, his study showed much stronger Red
trends
based
on
ground
data.
Although
fractures parallel to the Red Sea dominate the sedimentary
cover (Figure 18),
they must be relatively diminutive
they do not appear as strongly on the air photos.
as
86
J4° 10'E
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fl s
CONCENTRATION
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•UMBER
B't LENGTH
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BT
i
i1
;:ii
COHCENTRATIOH FAC:'JR
CONCENTRATION FACTOR
I
:m
',
/\ f
FACTOR
Ea
Figure 24. Lineaments
in the sedimentary cover
of the
study area.
TOP: Sketch map of the studied area with lineaments
superimposed.
CENTER: Rose diagram of lineament azimuths.
BOTTOM: Histogram of lineament azimuths by number.
Rose diagram and histogram are twice smoothed using
a ten degree running average calculated for every
degree.
C H A P T E R
V
MAJOR FAULT AND FOLD STRUCTURES
Faults
Six major fault zones cut and bound the tilted blocks
of
the
Zone,
study area (Figure 7):
1) Wadi el
2) Wadi Nakheil Fault Zone,
Kareio
Fault Zone,
Isewid
3) Wadi Hammadat- Wadi
4) Bir Inglisi Fault Zone,
Nasser-Gebel Ambagi Fault Zone,
Fault
5)
Gebel
and 6) Gebel Atshan Fault
Zone.
Wadi el Isewid Fault
The
Wadi
el
~
Isewid Fault Zone forms
boundary of the Gebel Atshan Fault Block.
the
southern
The main fault
zone
is
exposed in outcrop between the southern
end
of
Wadi
Beda el Atshan and Wadi llammadat (Figure 3) where it
is a highly brecciated, quartz-cemented zone with evidence
of
normal
The fault zone marks
motion on it.
boundary between areas of moderate to extensive
of
a
sharp
unroofing
the granite to the south and only initial unroofing of
the granite to the north.
nature
The established north-side-down
of the fault motion can therefore be
87
inferred
to
88
offset
the
veining,
granite
in that
Youngest
fashion.
which cuts the granites,
may also have
quartz
figured
in the silicification of the breccia zone. Although Garson
and Krs
(1976) contend that U60E faults are the oldest
in
the basement, some normal motion occurred within tqe study
area
on
this fault subsequent to the emplacement of
Younger Granites (see Table
the
3).
In the study area, evidence for Tertiary reactivation
of this zone is lacking.
valleys,
small
Formation,
are
However, Greene's central Nubia
downfaulted
bounded
areas
on
their
of
preserved
southern
Hubia
ends
by
northeastward extensions of the Wadi el Isewid Fault Zone.
This
suggests
that at least those portions of
the
zone
were active in Tertiary time.
Wadi Nakheil Fault Zone
The Wadi Nakheil Fault Zone bounds the northeast side
of the Gebel Duwi Fault Dlock.
An extension of this zone
may also bound the northern end of the Gebel Atshan Block.
This
zone
degrees
Eocene
the
strikes approximately N55W and dips
to the southwest at the
surface.
platform sediments of Gebel Duwi,
Wadi
Nakheil Fault Zone,
about
50
Cretaceous
to
which parallels
are preserved
within
half-graben formed by normal motion on this zone.
the
89
A
minimum of 600 meters of post-early
places
and
Thebes limestones against Precambrian
tilted
throw
basement and cover to the
basemont
wadi
greater
than
600
northeast.
meter~
the
probably
the
Thebes-
Drag along
the
platform seuiments of this monocline
broad, open, synclinal form
At
as
Total
contact lies below an undetermined thickness
fill and Nakheil Formation.
folded
throw
greenstones
between Gebel Ambagi and Gebel Hakheil is
substantially
it
Eocene
Gebel Uakheil,
of
fault
into
a
(Plate 2).
the fault steps to the left where
is interrupted by and curves into a N60E fault segnent
that
transferred
normal motion from one section
fault zone to another.
of
the
Several such parasitic steps and
changes of orientation of the northwestern border fault of
the
Gebel
Duwi
Block can be seen
on
regional
LANDSAT
imagery (Frontispiece).
To
step
the southeast,
to
the
southwest
the Wadi Hakheil Fault
and continue
against the Gebel Atshan Fault Zone.
fault
to
a
Zone
may
termination
Alternatively,
between the northern end of Gebel Atshan and
the
Gebel
Ambagi may be an extension of the Gebel Atshan Fault Zone.
The
Thebes Formation at the northern end of Gebel
dip
under
the Precambrian
rocks
of
Atshan
appears
to
Gebel
Ambagi,
which has a total topographic relief in excess of
90
100 meters.
Therefore,
total normal offset on the short
northwest trending fault segment must exceed 700 meters.
Wadi Hammadat-Wadi Kareim Fault Zone
The southeastern end of the Gebel Duwi Fault Block is
bounded along its southwestern edge by the Wadi
Wadi
Kareim
southwest
Fault
Zone.
Faults
dip
llammadat-
northeast
and
on either side of the Wadi Inglisi Horst Block.
These faults terminate to the southeast against the
Gebel
Nasser-Gebel Ambagi Fault Zone.
Motions on these faults are less than those on faults
bounding
minor
the opposite side of the Gebel Duwi
offset of a north-northwest striking
(Plate
dipping
1)
felsite
indicates only slight motion on the
fault.
More
substantial
southwest dipping members.
of
Block.
Cretaceous
motion
The
body
northeast
occurred
Approximately 300-400
or later southwest-down throw is
on
meters
required
across the entire zone.
Bir Inglisi Fault Zone
The northwest trending Gebel Duwi Block is broken
transverse zones trending approximately north-south,
within
the study area and to the northwest.
The
by
both
north-
91
south
extending
ridges
southwestern
Gebel
between
the
Duwi and Gebel Hakheil
such a zone (Plate 1).
of
slope
dip
developed
These ridges consist of a
in
series
of
horst-and-graben-like structures that are less dropped
or
tilted to the northeast than the areas on either
side
of them.
Faulting imparted a gross anticlinal structure to the
north-south
The
ridees.
ridges
are bounded
by
hinge
faults that exhibit increasing throw northward along their
strikes.
Nowhere
is the throw on these
faults
than the thickness of the Thebes Formation.
greater
Displacements
become negligible to the south where the faults die out as
they
intersect
Gebel Duwi.
The faults may be
scissors
faults as a series of similar structures present south
the
of
main Gebel Duwi ridge exhibit increasing throw to the
south.
Gebel
Cretaceous
of
is
a
short
ridge
of
to Eocene sediments lying at the northern
end
the Bir Inglisi Fault Zone
ridges
located
the
Nakheil
(Figure 25) and,
like the
to the south, has an anticlinal structure.
It is
where the tladi tlakheil Zone steps to the left
intersection
platform
north-south
with the Bir Inglisi
Fault
Zone.
sediments of Gebel Nakheil dip east to the
of the step and west to the west of it.
at
The
east
92
Figure 25.
Geologic map of the Gebel Nakheil area.
PC=
Precambrian basement;
Kn= Nubia Fm.;
Kv= Quseir Fm. ;
Kd= Duwi Fm.;
Td= Dakhla Fm.;
Te= Tarawan and Esna
Fms.;
Tt= Thebes Fm.;
Tn= Nakheil Fm.;
Qa= wadi
alluvium.
93
I'
/
'/
'\
'
PC
'·
/
/
\
'-
,
26°10'
/
/
\'Strike and dip of
bedding
--
'0
KM
94
It may be that the series of anticlinal ridges in the
platform sediments result from drape folding over
basement
against
not
blocks.
The
north-south
zone
is
faulted
truncated
the step in the Wadi Nakheil Fault Zone and
appear
in the basement to the north
preparation).
(Abu
does
Zied,
in
However, exposures of the Bir Inglisi Fault
Zone south of Gebel Duwi suggest a structure of this kind.
There,
faults
upward
into the Nubia Formation,
and
Dakhla
(Plate
1).
in
basement
form a graben
extends
but the overlying
Formations are folded into a
A trend of N20W,
that
broad
Duwi
syncline
15NW was estimated for the
axis of this fold by constructing a best-fit beta
diagram
using bedding orientations measured around the fold.
The
Bir
the
south
Inglisi
Fault
Zone appears to be truncated
where it intersects the Wadi
Hammadat-Wadi
to
Kareim
and Gebel Nasser-Gebel Ambagi Fault Zones.
Gebel Nasser-Gebel Ambagi Fault
The
Gebel
southeastern
bounding
~
Nasser-Gebel Ambagi Fault Zone forms
the
termination of the Gebel Duwi Block and
its
faults,
and also bounds the western side of the
Gebel Atshan Block. The fault disappears under the Miocene
and younger sediments to the north and under wadi fill
to
the
el
south,
where
it may terminate against the
Wadi
95
Isewid Fault Zone.
An exposure at the southern end of Gebel Nasser shows
the
fault
Upper
zone dipping west-northwest at 45-50
Thebes
limestones are in fault contact
along
Formation
the
eastern
side
of
degrees.
with
Gebel
Duwi
Nassser
indicating a throw of over 300 meters at that location.
Topographically,
amphitheater
Gebel
with its broadly curved,
north-facing dip slope.
folding
Nasser
of
resembles
deeply
an
dissected,
This shape is the result of open
the platform sediments where they
have
been
dragged along the Gebel Nasser-Gebel Ambagi Fault Zone.
A
beta
orientations
IJasser's
diagram
constructed
using
bedding
measured around the "amphitheater" of
Thebes
approximately N10E,
plane
was
Formation.
20HE.
The
axis
is
Gebel
oriented
Approximately east-west bedding
slip noted in the Duwi Formation of southern
Gebel
Nasser is probably a result of this folding.
The eastern side of Gebel Nasser,
Atshan,
was
examined
in
some detail as it
involve numerous structural complexities
sliver
of
apparently
small,
along Wadi Beda el
appears
(Figure
26).
this southeastern end of tho Gebel Duwi
collapsed
graben-like
along the main fault
structure.
A
to.
sketch of
A
Block
create
the
to
a
ridge
(Figure 27) between stations 1253 and 1310 (see Fieure 26)
96
Figure 26.
Geologic map of the Gebel Nasser area.
PC=
Precambrian basement;
Kn= Nubia Fm.;
Kv= Quseir Fm.;
Kd= Duwi Fm.;
Td= Dakhla Fm.; Te= Tarawan and Esna
Fms.; Tt= Thebes Fm.; Qa= wadi alluvium.
26
05'
I]
_.....
............
•5
,.
Tt
Tt
/
10
---'-
••
/Nonnal fault, ticks on
/" downthrown side
;i'
Trend of gently plunging,
minor 1110nocl fne
Rotation sense fndicated
")""Strike and dip of beddfng
•0
'
"
Statfon location discussed
in text
0
KM
/
',, ,,
\
',.',....-'
34°
'°
-...J
98
NW
SE
1310
Talus
a
w
Wadi Seda
E
e I Atshan
b
[J Wadi Alluvium 1 / / '
Im Nakhei I Formation
~Platform Sediments
0 PC Basement
Figure 27. Gebel Nasser-Gebel Ambagi Fault Zone: a) sketch
of
view
of the ridge between stations 1310 and
1253
showing
style of deformation;
b) sketch cross-section
of
Gebel
Nasser
showing
faulting
and
extensional
collapse along Wadi Beda el Atshan.
99
and
a
27)
illustrate
(Figure
generalized cross-section of Gebel Nasser
the structural relations.
Many
of
the
"structural complexities" initially noted in this zone are
the result of extensional collapse of large blocks between
the two oppositely dipping normal faults.
Several minor southwest-down normal faults and
folds
are present in the Duwi Formation of southern Gebel Nasser
(Figure 26).
of
the
They are approximately parallel to the trend
Gebel
Therefore,
tilting
they
of
this
structures
llowever,
and
Block and the
bounding
it.
may be associated with the faultinG
and
block.
Age
north-south
these
l!asser-Gebel
basement
Duwi
features
Arnbai:;i
south
of
faults
relations
structures
between
are
these
uncertain.
do not extend across the
Fault
Zone
into
Gebel
Nasser;
Gebel
the
Precambrian
their
termination
suggests that the north-soutl1 zone may have existed
to the development of the
Other
northwest~trending
the
zone.
evidence suGgcsts a greater antiquity for
northwest-trending structures.
of
prior
Duwi
Formation
alon;
involves slip on joint surfaces.
the
One mechanism for folding
these
northwest
trends
Gentle warping resulting
from this mechanism was noted at station 1002 (see
Figure
26).
Joint surfaces at this location and slickensides on
them
are both perpendicular to now tilted bedding (Figure
28),
suggesting
that
motion
on
the
joints
predates
,,.
"
.
n\S
?\a\'0(\'11 se<l\\'lle
Figure 28. Slip on joints perpendicular to Duwi bedding as a mechanism
of folding at station 1002,
southeast Gebel Nasser.
Flexure zone
is approximately 3 meters across.
GN-GA= Gebel :iasser-Gebel Ambagi
Fault Zone.
0
0
101
tilting.
Gebel Atshan Fault
Gebel
Atshan
sediments
Quseir
~
along
is
the
through
an east-tilted block
eastern
edge of
of
the
study
Thebes Formations are exposed
west facing erosional scarp;
platform
the main ridge,
along
at
surface
Surfaces
bounds the Atshan
east.
within this zone near Wadi Ambagi exhibit
early
slickensides.
dropped
fault
slickensides
Gebel
and
to
younger
normal
The Thebes and overlying Nakheil Formations
into contact with the
indicating
Slivers
block
west
the
right-lateral
are
A north-
fault zone with a dip of 60-70 degrees to the
the
its
like Gebels
Duwi and Nasser, is capped by Thebes limestones.
south
area.
basement
along
more than 600 meters of normal
of the platform sediments are exposeu
this
motion.
along
the
Atshan Fault Zone as a result of drag on the fault.
Drag on a small,
fault
surface
Ambagi
westward-projecting irregularity in
about
resulted
(Plate 2).
in
one-half kilometer
a small-scale
south
anticlinal
of
tl1e
Wadi
upbulgine
The fault zone terminates to the south against
the Wadi el Isewid Fault Zone.
Its northward termination
is unclear.
An
elongate,
elevated
basin is formed between
the
102
main
ridge of Gebel Atshan and the basement highlands
the east.
An outlet of this basin into Wadi Hakheil cuts
Along
through the Thebes ridge at its northern end.
western
margin of this basin,
are
beds
nearly
degrees
upward
sands
largely
horizontal
'l' h e s e Ii a k h e i 1 d e p o s i t s
sandy
silts
underlies recent
with
a
few
Hakheil
alluvium,
f i ne
coarse
Formation,
approaches
the
of the basin are also nearly horizontal.
The
that
conglomerates
a
along
su~gests
geometry
and
attitude.
ed~e
eastern
Thebes
underlying
The uppermost part of the Nakheil
interbeds.
which
with
Dips of the two formations are within
of one another.
to
the
basal llakheil conglomerate
concordant
limestone bedding.
8
to
episodic
motion
and
tilting
continued during deposition of the Nakheil Formation.
Folds
A
small
number of folds were noted in the
llost are folds in the Thebes
sediments.
three
exceptions
folds
are
fold bods in the Duwi
1''orma ti on;
Therefore,
axial
north-south
planes
tend
to trend
paralleling
Tertiary
fault
the
l'orma ti on.
The
by
drat;
generally very open synclines formed
along normal fault surfaces.
southeast,
platform
their axes
to
and
northwest-
strikes.
Folds
1 03
range
in
size from regional features of
1-5
kilometers
wavelength to outcrop-scale structures \Iith wavelengths of
less
than
tens
of centimeters.
large
It
a meter and amplitudes on tlie order of
a
few
This relationship can be seen on a
scale in the broad,
open foldinc of Gebel
Nasser.
is also visible where the platforQ sediments of
Gebel
Duwi dip under the fill of Uadi Uakheil and reappear again
3
4
to
kilometers
boundine
to the
northeast
alone
the
fault
the northeast side of this valley (Plates 1
and
2).
A
large
main
major
exception to this style of folding
overturned
ridGe
of
fold in the Theb3s Foruation
Gebel
associated with jt.
amplitude
Duwi
(Plate
2)
axis,
d!pping
a
surface, and
sense.
structure
have
atop
the
minor
a nearly
northwest-southeast-trending
rotation
the
folds
The main fold has a wavelength and an
creater than 50 neters,
axial
and
is
Minor
gently
southwest
sou th we s t-over-:10rtheas t
folds
approximately
a
horizontal,
with
this
striking
axial
associated
eact-west
surfaces and enst-west trending, gently plunging axes.
evidence
was
seen to indicate that the strata below
Thebes
were folded.
The be f;
limestones,
occur1·ed
To accommodate this folding in
bedding-plane
faulting-
in the underlying shales of the Esna
No
the
the
probably
Formation.
As tho shales could only be examined with binoculars
from
104
the wadi floor below,
the existence of these faults could
not be confirmed.
Although
~hebes
to be folded,
enough
the
of
ifany
the
ci1e rty
in this
involved
laq~e
Formation as a whole was ductile
nunerous minor faults are
and
more
brittle
fold are broken.
line stone
the time of foldinc was probably less than 100
as
the
Formation.
have
the
involves
Thus,
overlain
deforr.1a ti on.
lower
half
of
meters
the
Thebes
only the upper part of the Thebes would
the observed folded strata at the time
1962),
no evidence of thicknesses greater than 200 meters
Quseir-Safa~a
the
of
Lower Eocene deposits can be several hundred
meters thicker in other parts of Egypt (Said,
in
beds
Depth of burial
at
fold
present.
deposits were present,
region.
Even
if
but
exists
these
thicker
maximum depth of burial should not
have exceeded 500 meters.
Two possible origins coce to mind for this structure.
it
First,
angle
have
could be due to regional compression at a high
to the fold axial trends.
produced folding in
thrusts
provides
This
cowpression
the limestone and bedding plane
in the underlying shales.
Strike-slip
evidence of late Eocene to early Miocene
northeast compression that could have caused the
A
second
could
possible mode of formation is
by
faulting
northfolding.
gravity
105
~ollowing
tectonics.
the tilting of the fault blocks, the
steepened Thebes Formation may have
11
slid downhill" to the
northeast on the underlying, less competent shales causing
folding and buckling.
parallel
to
The main fold trends approximately
bedding strikes in Gebel Duwi
and
has
the
fold root lies to the southwest of
the
proper transport sense for this mechanism.
Because
cliffs
the
of the Gobel Duwi ridgo and has beon eroded
away,
the choice between tho two possible modes of origin is not
clear-cut.
The fold was not followed out to its northwest
termination
accesn.
due to time constraints and
The
preferrod
as
difficulties
of
block tilting and gravity sliding origin is
it
seems
more
feasiblo.
The
lack
deformation of similar style in the area is the basis
this preference.
of
for
Nost of the significant deformation from
the
N25E
The
only other folds not directly attributable to drag on
fault
1 981 ) •
compression was apparently brittle
surfaces
However,
overturned
fold,
are
open,
gent~o
nature.
(Trueblood,
it must be borne in mind that the large
although a large and prominent feature,
had not been previously reported.
undiscovered.
warpings
in
Others may yet
remain
C H AP T E R
VI
REGIONAL TECTONICS
Phanerozoic History
Following
the
end
of
ih.2, Study Area
the cratonization of northeast
the
Proterozoic,
stable
tectonically
Paleozoic
and
Cretaceous
tl1rough
sediments
2f
much
was
and
of
of
a
Quseir
remained
the
so
became
During
a sequence of
as a result
shallow
area
at
the
throughout
Mesozoic.
Eocene time,
deposited
transgression
the
Africa
of
platform
the
epicontinental
Late
southward
over
sea
northeast Africa.
The
relative
disrupted
in
the
stability
of
the
middle Eocene by
which resulted in the cessation of
Quseir
epeirogenic
deposition.
area
was
uplift,
Regional
north-northeast compression in tho middle Eocene to middle
~iocene
of
res~lteJ
in the development of a conjugate system
strike-slip faults in the Quseir area (Figure
19)
as
well as in the Gulf of Suez region (Perry, 1982) and Saudi
Arabia
(Davies,
1981).
Schamel and Wise (1934) note
similarly oriented coupression of
the
~ocene
a
to Miocene age in
Sinai and tentatively relate it to the late stages of
development of Syrian Arc structures.
106
Further, they feel
1 07
that the system of conjugate strike-slip faults
under
the
influence of this compresional
controlled
the
faults
and
folding
Sea
northeast-striking
faults were produced in the Quseir
this compression.
in
later
North-northeast to north-northwest-
right-lateral
left-lateral
episode
orientations of the Gulf of Suez/Red
and the Gulf of Aden.
striking,
developed
area
by
N20E corapression also may have resulted
noted
by Trueblood (1981) and
in
downwarps
within which the llakheil Formation may have been deposited
(Gebel
Duwi,
Wadi Nakheil,
and Gebel Atshan
lows,
see
Figure 6).
During
stresses
Oligocene
chanced
to early
resulting
Miocene
in
time,
regional
northeast-southwest
extension related to the early development of the Red
rift.
A
faults
developed under these stresses,
oriented
conjugate
older
system of northwest-striking
faults
were
Sea
normal
and appropriately
reactivated.
This
normal
faultinb dropped and tilted blocks of Cretaceous to Eocene
platform
sediments
into
subsequently preserved as outliers.
may
have
been
deposited in
where
trOUGhS
these
they
were
The Hakheil Formation
downfaulted
troughs
rather than in earlier downwarps.
The style of Tertiary deformation is clearly shown on
structure
contour
maps
for
the
top
of
reconstructed
basement of the southern Gebel Duwi-Quseir area (Figure
6)
108
and the Quseir-Safaga region (Figure 7).
that
block
faulting
and
tilting
These maps show
toward
the
Red
Sea
This is noted in the field as a
dominate the study area.
northeast tilt of the Nubia-basement contact.
In many parts of the world,
reverse drag is commonly
present in areas dominated by block faulting along listric
normal
faults.
extensional
Nasser
It
seems
structure
along
Conversely,
unusual
that
this
is present only in
type
of
eastern
Gebel
Fault
Zone.
the Gebel Nasser-Gebel Ambagi
true drag can be seen alonJ most of the major
fault zones in the area.
Intersection relationships of most major faults could
not
be directly observed due to their burial beneath wadi
alluvium.
However, map patterns indicate that, generally,
northwest-striking
~orth-south
faults.
N60E
faults.
oldest
faults
in
This
the
faults terminate,
study area and
that
north-south
in turn,
suggests that il60E
faults are the youngest.
(Abu Ziad,
terminate against
faults
northwest
against
are
the
striking
Relations in areas to the north
in preparation) and to the east (Greene, 1984)
are somewhat more ambiguous.
Smaller-scale structures in
this study area also provide inconclusive evidence.
Eocene
to
early
Miocene
uplift
was
apparently
followed by a period of relative quiescence, with a middle
109
to
late Miocene erosion surface developing along the
1970; Schmidt
Sea coast of Egypt and Saudi Arabia (Brown,
1982; Greene, 1984).
et al.,
Red
The lack of major elevation
differences across normal fault zones in the study area is
Therefore, most of
a reflection of this erosion surface.
the
motion
on
experienced
substantial motion following the
~he
the nid-Tertiary erosion surface.
Gebel
el
erosion
Late
Miocene
Faults bounding Gebel Ambagi however, must have
surface.
of
these faults predated this
development
Miocene
basal
Rusas Formation deposited on a segment of
this
100
surface atop Gebel Ambagi now sits more than
meters above similar surfaces in the surrounding area.
regular
decrease
in
northeast
across
represent
the
basement
individual
slightly
peak
elevation
tilted
tilted
blocks
to
may
A
the
also
erosion
cid-Tertiary
suri'ace.
~rosion
faulting
resultinc from Eocene to Miocene uplift
removed tl1e bulk of the Cretaceous
to
and
Tertiary
cover during creation of the mid-Tertiary erosion surface.
The
iakheil
material
must
removed,
have
Johnson
deposited
Formation
been
(1977)
on
but
may well represent
part
an enormous quantity of
deposited in
the
proto-ned
Ghussun area of the Red Sea coast (near
the
sediment
Sea
notes Oligocene to Lower Miocene
Precambrian basement in the
of
rift.
redbeds
Ras
Benas-Abu
24°u).
Clastics
11 0
and
boulder beds of Oligocene to Miocene ace are found in
drill
cores offshore from Quocir and Safaga
1982).
Ayyad,
deposits
in
Miocene
(Tewfik
and Scarpa (1962) report similar
Carella
southern Egypt and
the
Sudan.
Pre-middle
redbeds and boulder conglomerates also
the Gulf of Suez region (Garfunkel and Bartov,
similar
and
exist
in
1977).
Ho
redbeds were noted in the study area or in
areas
to the east (Trueblood, 1981; Greene, 1984).
With
faults
(e.g.
the
that
exception
of generally
minor
disrupted the mid-Tertiary
motion
erosion
on
surface
the faults bordering Gebel Ambagi), the Quseir area
has remained relatively quiet for the past 10
~.
y.
Upper
Miocene evaporites along the Red Sea coast to the east
of
the
study area are cut by some minor faults,
but most of
the
deformation of these units is the result
of
and
tiltin~
in a zone of coastal flexure
Tilting of the
Red
Sea
Quaternary
~iocene
flowage
1984).
(Greene,
to Pleistocene sediments toward the
appears to have ended by the
beginning
of
the
as Pleistocene and lecent deposits have barely
noticeable dips.
Iience,
al though uplift has resulted in
the deep dissection of Upper Iiiocene and younger sediments
and the creation of several terrace levels along the coast
and
since
in wadis,
middle
little faulting has occurred in
~iocene
time.
Table
4
the
summarizes
area
the
111
Table
h
TIME
Phanerozoic history of the study area.
PERIOD
SUMMARY OF EVENTS AND INTERPRETATION
Cambrian to
Mid-Cretaceous
Tectonic stability.
Peneplanation of
Precambrian basement by erosion.
Mid-Cretaceous
to Middle
Eocene
Formation of large intracratonic basin
over much of northeast Africa.
Platform sediments deposited in this
basin. This may be a precursor to
Red Sea tectonics.
Middle Eocene
Uplift ends deposition of the platform
sediments.
Erosion creates an
unconformity atop the Thebes Formation.
Crustal doming is proceding prior to
rifting.
Late Eocene to
Early Miocene
1) il20S regional compression results in
the development of a conjugate system
of stri~e-slip faults: ililE to ilHW
trending right-lateral and UE trending
left-lateral faults.
This compression
may also have warped the platform
sediments.
fhis may be an early stage
of Rod Sea-related tectonics.
2) ilE-SW extenional stresses become
dominant resulting in new northwest
striking normal faults.
Horth to
northwest striking preexisting
structures are reactivated as normal
faults, emplacing outliers of
Cretaceous to Eocene sedi~cnts.
This phase is related to initiation
and widening of the Reri Sc~ rift.
Tho ~akheil For~ation
is
deposited during this time either in
downwarps created by ;i20E compression
or in fault-bounded troughs associate
with northeast extension.
~oto:
Early to
:.; i d d 1 e : \i o c e n e
Uplift and relative quiescence of the
study area results in the development
of the Mid-Tertiary erosion surface
adjacent to the Red Sea.
A few faults
experience substantial motion, but
major activity is centered closer to
the rift.
r;iddle lliocene
to present
1) Deposition of coastal sediments in
early Red Sea basin.
2) Slow, gentle uplift presaGes breakup and active sea-floor spreading in
the northern Red Sea.
This results in
the dissection of the Miocene erosion
surface and creation of raised beaches
and terraces along tho Red Sea.
11 2
Phanerozoic history of the study area.
Tectonic Heredity
Obvious deviations from Red Sea fault trends occur in
the Quseir-Safaga area.
controls
block.
The most prominent is that which
much of the orientation of the Gebel Duwi
Another
fault
dropped
and
tilted
fault
the
Gebel
Hammadat-Bahari block to the southeast (Figure 1).
be
Duwi
It can
seen on LANDSAT imagery (Frontispiece) that the
Gebel
Fault Zone jumps from Najd-parallel segments to
Sea-parallel
northeast
created
segments
side
Red
of
as does the
Gebel
fault
llammadat.
Sea-parallel
fault
Red
bordering
Tertiary
the
extension
segments
connecting
reactivated Najd segments.
Garson
Precambrian
and
rocks
Krs
(1976) note that several
along
the
Egyptian
Red
zones
in
coast
Sea
parallel the Gebel Duwi trend and claim evidence for leftla teral motion on many of these zones.
They feel that the
movement was a secondary feature of left-lateral,
strike-
slip motion on the Red Sea rift during Cretaceous to Early
Tertiary sea-floor spreading in the Gulf of Aden.
evidence
area
that
proposed
of
Cretaceous to Eocene stresses in
could have produced such motion,
Lacking
the
it
study
is
that any left-lateral motion on these faults
here
is
11 3
more
likely to be Precambrian in age and associated
with
Najd faulting.
Old
Najd fault trends exert much control over
orientations
As can
in this part of the Eastern Desert.
be seen in Figure 6,
fault
many of the faults which dropped and
tilted Cretaceous to Eocene sediments made use of both Red
Sea-parallel
are,
It
in
is
and Najd-parallel fractures.
turn,
possible
These
trends
commonly disrupted by north-south faults.
that
the
Red
Sea
faulting
may
have
reactivated more ancient north-south Hijaz grain, although
this
grain does not appear strongly in the bulk of
study
area basement.
The idea of the reactivation of Najd trends by
stresses is further supported by Greenwood and
(1977)
palinspastic reconstruction of the
Shield.
This
reconstruction (Figure
Anderson's
Arabian-Nubian
9) shows the
Azlam graben of Saudi Arabia aligned with the Gebel
Gebol Hammadat fault blocks prior to separation.
these
later
Wadi
Duwi-
Although
authors push the Red Sea back together farther than
may be warranted, this alignment of old llajd trends across
the Red Sea is not unrealistic.
Smith (1979) and
Davies
(1981) note reactivation of Najd trends to form the faults
that
bound
the
Azlam
basin,
and
Smith
(1979)
also
describes a Tertiary stratigraphy in the Wadi Azlam graben
114
of
sandstone,
gypsiferous,
multicolored
shales,
and
fossiliferous (abundant Q~1E~~) limestone very reminiscent
of
the
platform
similarities
suggest
a
of
sediments
in
the
Quseir
the Tertiary histories of
similar
origin and common
area.
these
control
The
basins
of
their
the northern end of the Gebel Atshan Fault
Zone,
orientations by Najd trends in the basement.
At
right-lateral
faults
associated
with
Tertiary
N25E
compression are connected by younger normal fault segments
with more northwest strikes.
reactivated
The later normal motion also
the right-lateral fault segments and resulted
in the jagged map pattern of the fault zone.
Typically,
normal
faults
developing
faulting
that
rift.
dip
Red
and
block
toward and
Sea-ward
rotation
step
dipping
down
adjacent
to the Gulf of Suez (Schamel
1984)
and
responsible
for
the
into
normal
appear
are
occur
a
faults
and
Wise,
preservation
sedimentary outliers north of Quseir (Figure?).
on
of
The dips
of major normal faults away from the Red Sea in the Quseir
area
and to the south as far as Mersa Alam (El Akkad
Dardir,
geometry
1966a) are unusual.
strike-slip
steeply
the strike-slip faults,
of regional extension.
Tertiary
It may be that this unusual
is related to the existence of
planes of weakness,
and
dipping
at the onset
Thus, both Najd faults and earlier
faults may have
exercised
control
11 5
over
not
only the strike of later normal
faulting,
but
also over dip directions of these faults.
The Red Sea
Several
and
evolution of the Red Sea.
question
has
models have been proposed for the
widely
is the extent to which true sea-floor
occurred
floored
The most
structure
and therefore,
debated
spreading
how much of the Red Sea
by true oceanic crust.
Two schools
of
is
thought
exist regarding this question: that the Red Sea is floored
entirely by oceanic crust (McKenzie et al.,
and
Styles,
1970; Girdler
1974) or that sea-floor spreading has
relatively recently and that only the axial trough of
southern
Red Sea is floored by oceanic crust
and Engels,
1972;
Tewfik
Ayyad,
and
contradictory
question
the
(Hutchinson
Lowell and Genik, 1972; Coleman, 1974;
1982;
Cochran,
1983).
Although
geological and geophysical data leave
unsettled
begun
at present,
the evidence favors
this
the
latter model.
Seismic
reflection
studies
are
inconclusive
as
basement is lost beneath thick, seismically opaque Miocene
to Recent evaporites and marine sediments that cover
of
the
main trough of the Red Sea.
Seismic
much
refraction
116
work is also inconclusive, but yields variable velocities,
most of which could be attributed to continental crust.
Evidence for an axial trough floored by oceanic crust
comes
from magnetic surveys.
exhibits
sharp,
symmetrical
crust
magnetic
smooth,
associated
Sea.
1974;
clearly
high-amplitude,
anomalies characteristic
low-amplitude
1976;
of
Roeser,
magnetic
and
Styles (1974)
ocean
1975).
anomalies
the main trough and shelves of
with
Girdler
trough
short-wavelength,
(Girdler and Styles,
Broad,
The axial
correlate
are
Red
the
these
broad
anomalies with the geomagnetic reversal scale of Heirtzler
et
this
al.
(1968) for the period 41-34 M.y.
correlation,
they
propose
a
ago.
Based on
two-stage
spreading
history for the Red Sea with spreading arrested between 34
and 5 M.y.
the
As
Kellogg
involving
results
relative
before present.
Sarat
Volcanics of
Recent paleomagnetic work in
southwest
Saudi
Arabia
and Reynolds (1983) places constraints on
two stages of Red Sea-floor
indicate
to
these rocks.
that
Africa
most
of
the
spreading.
motion
has occurred since the
of
models
Their
Arabia
eruption
The Oligocene to Miocene ages (29-24
by
of
M.y.)
of these volcanics would seem to preclude a major phase of
Eocene to Oligocene sea-floor spreading.
Geologic studies along the shores of the Red Sea give
no reason to believe that Red Sea-parallel normal faulting
117
and
block tilting does not continue out under the Red Sea
itself.
Hutchinson and Engels (1972) propose this type of
structure for the Danakil Depression.
(1972)
that
concur
Lowell
and
and show seismic and bathymetric
Genik
evidence
this structural style continues northward
to
19°N.
Frazier (1970) interprets the magnetic pattern of the main
trough
as
similar
resulting from tilted fault
to
addition,
(1974)
those
Hall
anomaly
block
along the coast of the
et al.
15
Red
(1977) show Girdler
(40 M.y.
isochron)
structures
Sea.
and
In
Styles'
continuing
over
Precambrian basement of the Buri Penninsula.
The
biggest problem with a model that proposes
that
only the axial trough is floored by true oceanic crust
the
A
is
amount of separation between Africa and Saudi Arabia.
substantial amount of separation between the
masses
is
required
to
account for the
more
two
land
than
100
kilometers of Cenozoic sinistral strike-slip motion on the
Gulf of Aqaba-Dead Sea rift (Freund et al.,
et al.,
1981).
separation
under
need
1968; Hatcher
Cochran (1983) shows however,
that
not be due to the creation of new
the Red Sea,
the
crust
but may be the result of crustal
and
lithospheric stretching and thinning due to block faulting
and dike injection.
faulting
Normal faults associated with
may be listric at depth as in the Bay of
block
Biscay
118
margin (de Charpal et al.,
rotation
1978), which would imply block
and allow for sufficient separation without sea-
floor spreading.
Cochran's
of
(1983) model calls for an extended
lithospheric
rifting and attenuation over
zone prior to small ocean basin formation.
period
a
diffuse
A broad
zone
of
crustal attenuation can account for the high heat flow
of
the entire Red Sea
region
(Girdler,
1970;
Coleman,
1974) as well as sea-floor spreading can.
~he
spreading
ridge
seems to be
northward from its present area of
active
spreading
21°N (Cochran,
extending
activity.
can be documented between
1983).
itself
Presently,
15°30 1 N
and
Between 21°N and 25°N, axial deeps
and hot brine pools suggest that a transition from crustal
attenuation
with
no
to
true sea-floor spreading is taking
continuous,
established.
The
organized
spreading
place
center
yet
northern Red Sea is still in the
pre-
spreading extension phase.
Crustal attenuation followed by eventual
rupture
and
geophysical
active
data
spreading fits
with
fewer
the
of
extension by block faulting
great,
it
is
not unreasonable for this
1979;
a
Red
and
Sea
Although the required
amount
Watts and Steckler,
geological
problems than
floored entirely by oceanic crust.
continental
and
rotation
mechanism
is
(see
Steckler and Watts, 1980; Keen
11 9
and Barrett,
1981;
Watts,
1981) and can account for the
Aqaba-Dead Sea fault motion.
The Falvey Model
Falvey (1974) proposed a model for the development of
ocean
basins and continental margins that explains nicely
much
of
what is seen in the study area and the
Red
region.
According
sign
regional
tectonic
large
to
this model,
activity
intracratonic
the
first
can be the development of
basin (or basins) 50 to
150
M.
Sea
of
a
y.
prior to continental break-up and the onset of actual seafloor
and
spreading.
This basin accumulates
shallow marine sediments.
fluvio-deltaic
The Cretaceous to
Eocene
platform sediments of Egypt represent deposition in such a
basin.
Maestrichtian to Paleocene shallow marine
along
the
1962)
and similar deposits of the Asfar Series
Jiddah,
Red
Saudi
Sea coast of Sudan (Carella
Arabia (Karpoff,
and
strata
Scarpa,
north
1957) indicate that
of
the
basin extended southward to at least 21°N.
A temperature anomaly in the asthenosphere results in
expansion and initial epeirogenic uplift about 50
thermal
M.
Y•
prior to break-up.
thinning,
and
the
The result is erosion, crustal
development
of
a
widespread
120
unconformity.
Swartz and Arden's (1960)
paleogeographic
reconstructions indicate that uplift began in the southern
Red
Sea
in
the mid-Cretaceous.
northward,
the
retreated.
Middle
Quseir
area
As
shallow seas of the
Eocene
doming
propagated
intracratonic
uplift and regression
basin
in
are marked by the Nakheil unconformity
the
atop
the platform sediments.
Falvey
resultant
predicts
density
of
volcanism.
by
to breakup.
axial
faulting
Continental
floor
graben
by
and
lithosphere
These changes result in
accompanied
with en echelon horsts
by
alkaline
characterized
and
grabens.
and deltaic sediments then begin to fill
valley basin.
outward
migrations
The rift valley thus formed is
block
rift
an
boundary
and volume changes in the
about 40 M. y. prior
collapse
phase
The rift valley continues
block collapse until the initiation
spreading.
It
to
the
widen
of
sea-
should be emphazised here that
in
this discussion, rift valley formation and widening, which
involve
confused
attenuation of continental crust,
with
later
continental
are not to
break-up/rupture
be
and
attendant sea-floor spreading.
The rift initiation and widening phase is represented
by
Oligocene to mid-Miocene faulting in the
northern Red Sea,
conglonerates
were
and Gulf of Suez.
study
area,
Redbeds and boulder
initially deposited in
the
widening
121
rift
These
valley.
evaporitic
were
followed
by
littoral
deposits resulting from episodic
invasion
and
of
the rift valley basin by waters from the Mediterranean Sea
to
the north.
Oligocene evaporites in the southern
Red
Sea (Hutchinson and Engels, 1972) indicate that rift basin
formation
was initiated to the south and spread northward
as northern Red Sea evaporites are Miocene in age
(Tewfik
and Ayyad, 1982).
Eocene
Yemen,
and
formation
Miocene
Saudi
to
Oligocene
and widening in the southern Red
Arabia
and
and Turayf,
basalts are present
Saudi Arabia
However,
Ressetar,
Nairn,
Middle
of
Jiddah,
between
(Coleman,
side of the Red Sea has few
Oligocene
Ethiopia,
Sea.
north
in a north-south band
Egyptian
Egypt
of
Saudi Arabia (Coleman, 1974) accompanied rift
alkaline
Jordan
plateau basalts
1974).
Neogene
in
the
Nile
The
volcanics.
and Monrad (1981) report some
to Miocene basalts along the Red Sea
and
Ammam,
Valley
that
they
coast
of
tentatively
associate with rift valley widening.
The
Red Sea Hills appear to be the maximum
extent
of
Egypt.
The relative quiescence following initial faulting
related
major
to
rift
Red Sea-related faulting or
westward
valley
widening
allowed
uplift
for
in
the
development of the mid-Tertiary erosion surface, which may
122
reflect
a
proposed
Once stresses
far
of
relieved
along
tectonic
activity was dominated by subsidence
the rift axis.
Red
Sea
edges
the
had
affected
been
area,
closer
to
This quiescence on the western side of the
is also evident in the sparsity of
magmatism
under
the
time lag.
noted
above.
the lithosphere,
As heat built
up
mid-Tertiary
sufficiently
areas further from the axis
again began to experience renewed,
but subdued,
once
tectonic
activity as indicated by minor fault motions and uplift.
Falvey proposes that rift valley development
through
major
and
actual continental break-up.
continental
new
crustal
(Hutchinson
Cochran,
between
1972;
in
the
Lowell
southern
and
time,
spreading
Red
Genik,
Sea
1972;
This resulted in a permanent connection
the Red Sea and the Indian Ocean through the Gulf
Of Aden.
not
and Engel,
198.3).
In Pliocene
rupture initiated sea-floor
generation
extends
As discussed previously, continental rupture has
yet occurred in the northern Red
Sea.
Post-Hiocene
uplift resulting in dissection of the mid-Tertiary erosion
surface
along
and
the
the series of terraces
northern
and
raised
Red Sea may be the result
beaches
of
slow,
gentle, regional uplift preceeding continental break-up.
C H A P T E R
VII
SUMMARY AND CONCLUSIONS
This
is
a
case study of the effect
continental-scale
rift
structure
of
opening
oblique
to
and
superimposed on a San Andreas-scale strike-slip zone:
Sea
tectonic
Precambrian
trends
(NJOW)
are
superimposed
Red
late
on
Najd (N60W) strike-slip structures.
a
In
the
Quseir region, the result is downfaulting and preservation
of
anomalously oriented fault blocks along master
that dip away from the Red Sea rift.
a
jagged,
faulting.
for
faults
The final product is
sawtooth pattern characteristic
of
parasitic
The results of this study may have implications
offshore
structures
under
the
Red
Sea
and
for
structure in similar settings elsewhere in the world.
History of
The
~
Study
~
Arabian-Nubian Shield was assembled through
consolidation
Precambrian.
of
island
arc
In the study area,
materials
and
N40W
the
N25-JOW fold
axial planar cleavages produced
123
late
this Proterozoic activity
resulted in three phases of coaxial folding.
axes
in
the
by
this
124
folding
area.
form
the dominant basement grain
Precambrian
N30E
quartz
veins
of
and
the
study
north-south
felsite dikes are also present in basement.
The
left-lateral
developed
across
Precambrian
result
through
of
strike-slip
Arabian-Nubian
fault
Shield
Early Cambrian time,
to
the east or
west.
Few
system
latest
in
possibly as
a collision of the young craton
continent
related
the
Najd
with
minor
a
another
structures
to this system were found in the study area,
but
Tertiary motion on the Wadi Nakheil and Wadi Hammadat-Wadi
Kareim
The
Fault Zones reactivated ancient
change
of
dominant
basement
Najd
structures.
erain
to
a
orientation north of the study area is related to the
U60W
old
Hajd grain (Abu Ziad, in preparation).
Quiescence
was
followed
related
the
Nakheil
by
elastics
Eocene.
of
in Cambrian through
mid-Cretaceous
deposition of platform
in the Late
carbonates
Cretaceous
through
time
and
early
Middle Eocene uplift resulted in the development
unconformity atop the
platform
sediments.
The
Formation may have been deposited in downwarps at
that time.
Post-middle
compression
caused
northeast-striking
system.
Eocene,
the
pre-middle
formation
strike-slip
of
faults
Miocene,
north-south
as
a
N25E
and
conjugate
This compression may be related to an early phase
125
of
Red Sea-related tectonic activity,
but its meaning is
unclear at present.
Following
southwest,
dropping
and
north-northeast
Red
Sea-related
compression,
extension
and tilting northwest trending
overlying
Formation
sediment to the
may
became
dominant,
basement
northeast.
also have been deposited in
troughs during this activity.
northeast-
The
blocks
Nakheil
fault-bounded
Four major tectonic trends
were active during that time:
1) N60E trends representing reactivated Precambrian
faults;
2) N50-60W
trends repesenting reactivated Najd
grain control the orientation of much of the
Gebel Duwi Block;
3) N-S trends
terminating
the southeast;
the Gebel Duwi Block to
4) N25-30W trends associated with Red Sea rifting.
The
north-south trend seems unusual in
anisotropies
do
that
Precambrian
not seem to account for it and
evidence
for Tertiary causal stresses are lacking.
Intersection relationships of Tertiary faults in
Cretaceous-Eocene
oldest,
that
followed by N50-60W,
order.
reflect
sediments suggest that N60E trends
older
anisotropies.
However,
basement
the
are
N-S, and N25-30W trends, in
these apparent age relations
age relations
or
dominance
may
of
126
Middle Miocene quiescence resulted in the creation of
a Mid-Tertiary erosion surface.
tectonic
activity
Renewed, but much subdued
has continued since the
late
Miocene
through the present.
A
second
related
phase
of motion on segments of
Red
master faults supports the notion of a
Red Sea history.
two-stage
This late motion may also have produced
a coastal horst in the area with the Gebel Duwi and
Hammadat
lows forming small coastal basins.
and-graben
Sea-
coastal
structure may be part
Gebel
This horstof
a
general
style of deformation along the Red Sea, but may be visible
only
where outliers of covering sediments are
Alternatively,
this
preserved.
may be a unique situation
from the interplay of Najd and Red Sea trends.
case,
the
implications
particular
existence
for
of
offshore
this
kind
of
structure,
resulting
In either
structure
which
may
has
have
importance to petroleum exploration efforts in
the Red Sea.
Ma.jar Achievements of the Study
Major
achievements
of
this
study
include
the
following:
1)
creation of a detailed geologic
southern Gebel Duwi area;
map
of
the
127
2) recognition of
anisotropies
and
structure;
major
Precambrian
their
control over
basement
Tertiary
3) filling
of a
gap in the
structural-tectonic
cross-section
of the Eastern Desert
at
the
latitude of Quseir, including the construction of a
structural contour map of the area;
4) definition
formation of
of the
geometry and mechanisms
Tertiary fault blocks;
of
5) provision of further evidence for Tertiary northnortheast
compression noted by Greene (1984)
and
Schamel and Wise (1984);
6) discovery of large overturned folds
in Thebes
the
only
limestones
atop
Gebel
Duwi,
structures of this sort reported in the CretaceousEocene sediments of the Eastern Desert;
7) tentative recognition of a class
graben coast-parallel structures.
Future
Several
areas
of
of
horst-and-
~
future
investigation
suggest
themselves as a result of this study.
1) Further work is needed on basement anisotropy and
how
it
controls
the
orientation of
Tertiary
faulting.
Of particular interest are variations in
the
orientation of the Wadi Nakheil Fault Zone
northeast of the
study area, controls on the northsouth trends, and the anomalous dips
of faults away
from the Red Sea.
2) Determination of the relationship between Gebel
Duwi and Gebel Hammadat would be helpful.
Are they
en echelon zones?
3) Determination of
the environment and timing of
deposition
of the
Nakheil Formation could
be
accomplished
through
provenance,
facies,
and
128
paleocurrent studies.
4) More
work on the
extent and age
of erosion
surfaces would be helpful in elucidation of Red Sea
history.
5) Determination of the areal extent of evidence for
N25E compression and its relation to early stages of
Red Sea tectonics would better the understanding of
Red Sea development.
Recognition of its presence or
absence in the Nakheil Formation would help to tie
down the timing of this compressional episode.
6) Location of more folds like that atop Gebel Duwi
might tell us more about the origin of the folding.
7) The
presence of a
coastal
horst-and-graben
structure elsewhere in basement of the Eastern
Desert could indicate a general deformational style
for the Red Sea and other developing ocean basins.
It
has been shown that the Hajd fault system affects
a zone greater than ten kilometers wide along the Egyptian
Red
Sea
coast,
deformation there.
highway
It
is
controlling
much
of
the
Tertiary
The affected area straddles the
across the Eastern Desert,
main
allowing easy access.
hoped that this study will serve as
a
guide
for
field trips and visitors interested in the geology of this
region.
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area:
34°
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