CLAY MINERALOGY OF THE NUBIA FORMATION (EGYPT) 329
GEOLOGICA CARPATHICA, 54, 5, BRATISLAVA, OCTOBER 2003
329336
CLAY MINERALOGY OF THE NUBIA FORMATION,
WESTERN DESERT (EGYPT)
HASSAN MOHAMED BAIOUMY
1*
, ISMAEL SAYED ISMAEL
2
and IBRAHIM HASHEM ZIDAN
3
1
Central Metallurgical R & D Institute, 87 Helwan, Cairo, Egypt; *+: hassanbaioumy@hotmail.com
2
Faculty of Education, Suez Canal University, Suez, Egypt
3
Abu-Tartur Mining Project, El-Alphy Street, Cairo, Egypt
(Manuscript received July 11, 2002; accepted in revised form March 11, 2003)
Abstract: The term Nubia Formation has been used in a broad range of stratigraphic and sedimentological connotations
to designate terrestrial sandstone of Paleozoic to Mesozoic age in Egypt. The Nubia Formation is the oldest exposed rock
unit and forms the basal part of the scarp face and the floor of Kharga and Dakhla Depressions. It is overlain by the
Qusseir Shale Formation. The Nubia Formation in the studied locality is composed of very thick sandstone intervals
intercalated with several thin shale intervals. Bulk samples are composed of clay minerals and quartz with traces of
feldspars. Clay fractions separated from the different intervals of the Nubia Formation are dominated by kaolinite,
smectite, and illite. Kaolinite is the major constituent in all samples. Smectite represents a major constituent in the shale
intervals while it occurs as traces in the sandstone intervals. Illite occurs as traces in some samples. Clay minerals are
classified into three assemblages. Based on X-ray and Scanning Electron Microscope analyses, the studied kaolinite is
classified into two types. Authigenic kaolinite forms highly crystalline pore-filling books of stacked hexagonal flakes
and occurs between quartz grains in the sandstone intervals while detrital kaolinite of lower crystallinity associates
smectite and illite in the shale intervals. In the shale intervals occurrence of smectite as poorly crystalline flakes of
unclear outlines is suggestive of detrital origin. Authigenic kaolinite formed during diagenesis of the Nubia Sandstone as
a result of complete or partial dissolution or replacement of detrital feldspar grains. Abundance of detrital smectite in the
shales intervals suggests their formation under arid or semiarid climatic conditions.
Key words: Egypt, Nubia Formation, diagenesis, kaolinite, smectite, illite.
Introduction
The term Nubia Formation has been used in a broad range of
stratigraphic and sedimentological connotations to designate
terrestrial sandstone of Paleozoic to Mesozoic age in Egypt
(Snavely 1984). The Nubia Formation was first introduced to
the Egyptian stratigraphy by Russegger (1838 cited in Said
1962) to designate the brownish, highly dissected and almost
horizontal sandstone beds, which are widely distributed over
the southern parts of Egypt and Nubia in particular (Said
1962). Later, this term was used to designate any nonfossilif-
erous sandstone in the entire Paleozoic or Mesozoic succes-
sion. The Nubia Formation rests unconformably on the granit-
ic and metamorphic basement complex and is overlain by the
Qusseir Shale Formation.
Clay minerals formation results, either directly or indirectly,
from the hydrolytic decomposition of primary aluminosili-
cates. The rate of hydrolytic decomposition processes is
strongly affected by the rate of vertical water movement
through the medium, in other words, by leaching. Under oth-
erwise equal circumstances, higher leaching rates will pro-
duce more clay-sized material, and clay minerals belonging to
more advanced weathering stages (Jackson 1965). The princi-
pal factor determining leaching rate and clay mineral compo-
sition may be the intensity of rainfall (Singer 1984). Singer
(1980) found a strong negative correlation between montmo-
rillonite in the clay fractions of soils formed from Pleistocene
basalt and rate of rainfall. In the tropics, where leaching and
chemical weathering are intense, there is a conspicuous abun-
dance of the kaolinite group minerals and gibbsite near conti-
nental masses (Biscaye 1965; Zimmerman 1977).
The bulk of the geological literature on sandstones gives in-
dication of their content of authigenic clay minerals (Wilson
& Pittman 1977). Füchtbauer & Müller (1970) described se-
quences of diagenetic alterations, which affect sandstones of
various composition under differing geochemical conditions.
Clay neoformation and replacement of detrital grains are typi-
cal in many of these sequences. Millot (1970) claimed kaolin-
ite is a common diagenetic product in the sandstones. Exten-
sive referencing of the Russian literature by Sarkisyan (1972)
suggested that authigenic clays are common in many Mesozo-
ic and Paleozoic sandstones of various sedimentary basins in
Russia. Carrigy & Mellon (1964) and Carrigy (1971) conclud-
ed that authigenic kaolinite is abundant and widely distributed
in sandstones of divergent conditions and depositional envi-
ronments. Wilson & Pittman (1977) listed several criteria to
distinguish authigenic clays. These criteria include, the com-
position, morphology, distribution, and crystallinity of these
clays.
The use of clays in sediments to interpret climate change
was pioneered by Robert & Chamley (1987, 1991). More re-
cently, Robert & Kennett (1992) related the abundance of
330 BAIOUMY, ISMAEL and ZIDAN
smectite (70100 %) in the early Tertiary off Antarctica to in-
dicate arid and seasonal climates. In contrast, the occurrence
of kaolinite is interpreted by Robert & Kennett (1992) to indi-
cate high rainfall with warm temperature. In a subsequent pa-
per Robert & Kennett (1994) concentrated on the details of
δ
18
O changes and clay mineralogy. Kaolinite increased dra-
matically at the Paleocene-Eocene boundary, indicating a ma-
jor increase in temperature and/or precipitation (Robert &
Maillot 1990). Thiry (2000) pointed out that clay minerals in
sediments can be useful indicators of paleoclimatic condi-
tions.
The petroleum potential of the Nubia Beds is being investi-
gated actively at present (Klitsch et al. 1979). This interest, as
well as other research activity on the ground water, paleontol-
ogy, and sedimentology of Nubia (Klitsch 1978), has recently
led to a better grasp of the stratigraphy and depositional set-
ting. Our purpose in this paper is to shed light on the nature
and origin of the clay minerals separated from samples of the
Nubia Formation.
Location and geological setting
The Abu-Tartur plateau lies 600 km to the southwest of
Cairo, in the Western Desert. It is located between the Dakhla
Oasis to the west and Kharga Oasis to the east. The southern
Fig. 1. Geological map of Egypt with the localities of the studied area (modi-
fied from Spanderashvilli & Mansour 1979).
edge of the plateau overlooks the Nubia plain to the south,
whereas it gently tilts northward forming the general surface of
the north Western Desert. Elevations on the surface of the pla-
teau vary from 540 m to 570 m above sea level. In the northern
and western parts of the area, the plateau surface is covered by
limestone of the Eocene Garra Formation, which forms the
higher step making the main limestone plateau. Eastward and
southward, the plateau surface is highly dissected. The studied
section is located approximately 20 km to the north of the
Kharga-Dakhla route within the Abu-Tartur Mine (Fig. 1). The
Nubia Formation in the studied area is composed of thick
sandstone intervals separated by several thin shale intervals
(Fig. 2). It is overlain by varicoloured shales of the Qusseir
Formation. The basal part of the Nubia Formation is not ex-
posed.
Materials and methods
A total of 38 samples representing the different lithological
units of the Nubia Formation were collected in order to exam-
ine the possible variation in mineralogical composition espe-
cially clay minerals.
Separation of clay fraction (<2
µ
m) was carried out to exam-
ine the clay mineral composition of shales and their temporal
and spatial variations. Approximately ten grams of shale sam-
ples were transferred to a 600 ml beaker and treated
with dilute 1 N acetic acid to remove carbonates. Af-
ter no more effervescence with acid, the residue was
washed with distilled water and then treated with 30%
H
2
O
2
to remove organic matter. After the sample was
completely disaggregated, it was washed with dis-
tilled water several times in order to reach a complete
suspension. The suspended clay fraction (<2
µ
m) was
mounted on glass slides by dropper and left to dry.
For each sample, three oriented slides were prepared
by the same method and with the same thickness. One
is untreated, another is saturated with ethylene glycol
vapor at 60 °C for one hour, and the other is heated at
550 °C for three hours.
A Philips PW 1730 X-ray generator with Ni-filtered
Cu K
α
run at 40 kV and 25 mA was used to examine
both the bulk samples and clay fractions. Bulk sam-
ples were analysed by the X-ray technique after grind-
ing in an agate mortar and mounting in the sample
holder. The scans were limited to the 2
θ
2° to 80°
range. The clay fractions were analysed using the X-ray
technique. The scans were limited to the 2
θ
range
from 2° to 40°. Smectite was identified by the peak at
1.4 nm that is expanded to 1.7 nm after glycolation
and reduced to 1.0 nm by heating (Moore & Reynolds
1997). Kaolinite was identified by the peak at 0.7 nm,
which is not affected by glycolation, and disappeared
by heating at 550 °C for 3 hours (Moore & Reynolds
1997). Illite was identified by the peak at 1.0 nm,
which is not affected either by glycolation or by heat-
ing (Moore & Reynolds 1997). Clay minerals abun-
dance is estimated using the peak area of the first bas-
al reflections, without using any correction factor.
CLAY MINERALOGY OF THE NUBIA FORMATION (EGYPT) 331
Fig. 2. A detailed lithostratigraphic section of the Nubia Sandstone
Formation in the Abu-Tartur area, Western Desert, Egypt.
Five selected samples were observed on a fractured surface
under Scanning Electron Microscope (SEM) (Philips S-2400s)
at the Geological Survey of Egypt to examine the morphology
of clay minerals.
Results
Petrology and Petrography
The Nubia Formation in the studied area is classified into
several thick sandstone intervals separated by several thin
shale intervals (Fig. 2). The sandstone intervals are composed
of 40 to 20 m thick yellowish white, friable, medium- to fine-
grained, cross-bedded to cross-laminated sandstone. The shale
intervals are composed of 6 to 1.5 m thick of yellow, yellow-
ish grey, hard claystone.
Under the polarizing microscope, the Nubia sandstones are
composed entirely of white to pale grey, monocrystalline, sub-
rounded to subangular, and medium- to fine-grained quartz,
which are cemented by iron oxides and/or clay minerals
(Fig. 3). In some instance pyroxene and zircon crystals are de-
tected (Fig. 4 and Fig. 5 respectively). On the other hand, the
shales are composed entirely of brownish grey clay minerals
with some pale grey, monocrystalline, subrounded to suban-
gular, and medium- to fine-grained quartz (Fig. 6).
Mineralogy
Bulk samples are composed entirely of quartz with traces
of feldspars. The X-ray data for the clay fractions separated
from the different intervals of Nubia Formation are dominat-
ed by kaolinite, smectite, and illite. Kaolinite is the major
constituent in all samples and its contents range from 80 to
98 % of the clay minerals, while smectite occurs as traces
especially in the sandstone intervals ant its contents range
from 2 to 10 % of the clay minerals. In the shale interval on the
other hand it occurs as major constituent and its contents range
Fig. 4. A microscopic photograph of the Nubia Sandstone under the
polarizing microscope. It is composed entirely of monocrystalline,
subrounded, medium-grained detrital quartz cemented with clays and
iron oxides. In some instances it contains some pyroxene crystals (P).
Fig. 3. A microscopic photograph of the Nubia Sandstone under the
polarizing microscope. It is composed entirely of monocrystalline,
subrounded, medium-grained detrital quartz cemented with clays
and iron oxides.
332 BAIOUMY, ISMAEL and ZIDAN
from 20 to 30 % of the clay minerals. Illite occurs as traces in
all samples and its contents range from 1 to 7 % (see Fig. 10)
of the clay minerals. Other minerals present are quartz and
plagioclase. Representative X-ray diffraction patterns of the
oriented clay aggregate of <2 µm fraction of different inter-
vals are shown in Figures 810. The clay minerals are classi-
fied into three assemblages in descending order of abundance.
The kaolinite assemblage (Fig. 7) characterizes most of the
sandstone intervals, kaolinite-smectite assemblage (Fig. 8)
characterizes some of the sandstone intervals, and kaolinite-
smectite-illite assemblage (Fig. 9) characterizes the shale in-
terval. On the basis of the X-ray data, the kaolinite is classi-
fied into two genetic types according to its degree of
ordering. Well ordered authigenic kaolinite is very common
in the sandstone intervals (Figs. 78). Detrital kaolinite
characterized by a lower degree of ordering is very common
in the shale intervals (Fig. 9). Higher ordering is shown by
better separation of reflections in the range 2
θ
2° to 25°.
Fig. 7. X-ray diffraction pattern of the clay fraction separated
from the sandstone intervals. It is composed of kaolinite (K) with
some quartz (Q) and feldspar (F) and represents the kaolinite as-
semblage.
Fig. 6. A microscopic photograph of the shale interval under the po-
larizing microscope. It is composed entirely of clays with some de-
trital quartz grains (Q).
Fig. 5. A microscopic photograph of the Nubia Sandstone under the
polarizing microscope. It is composed entirely of monocrystalline,
subrounded, medium-grained detrital quartz cemented with clays and
iron oxides. In some instances it contains some zircon crystals (Z).
Semiquantitative analysis of clay minerals in the Nubia For-
mation is shown in Figure 10. Kaolinite contents range from
100 % to 65 % of the clay minerals. Smectite contents range
from 35 % to 5 % of the clay minerals. Illite represents 4 %
to 7 % of the clay minerals.
(On the term crystallinity see Report of the AIPEA No-
menclature Comm. For 2001: Guggenheim et al. 2002: Clays
Clay Min. 50, 3, 406409.)
SEM observations
SEM micrographs of the kaolinite separated from the sand-
stone interval consist of pore-filling books of stacked hexago-
nal flake filling the space between quartz grains (Fig. 11) or
coating the quartz grains (Fig. 12). Smectite occurs as flake
between quartz grains (Fig. 13). Crystals of kaolinite are more
or less similar to the well-formed, large crystals of clear out-
line of authigenic kaolinite reported by Wilson & Pittman
CLAY MINERALOGY OF THE NUBIA FORMATION (EGYPT) 333
(1977) and Keller (1978), while smectite is smaller and with a
less clearly defined outline compared with the well-formed,
large crystals of clear outline of authigenic smectite reported
by Keller (1978). Therefore the authors consider the studied
kaolinite to be authigenic kaolinite while smectite is consid-
ered to be detrital in which the size and outline of the crystals
are affected by transportation. This interpretation is also con-
firmed from the X-ray data.
Discussion
Conditions apparently conductive to forming kaolinite at
the earths surface are well summarized by Keller (1964). As a
weathering product, the presence of kaolinite implies (1) a
high Al:Si ratio, (2) an acid environment, and (3) Na, Ca, K,
Mg, and Fe absent or out of circulation. Dixon (1989) re-
viewed the origin and formation of kaolinite minerals and
showed that precipitation from solution of kaolinite required
acid conditions with moderate silica activity and small
amounts of base cations. The fact that kaolinite is formed by
aluminum silicate alteration in weathering and by diagenetic
environments is clear from geological relationships (Bucke &
Mankin 1971). Three major models of kaolinite formation
have been suggested by Degens (1960). The basic approach
involves interaction in solution between isolated species of
monomeric silica and alumina, with OH
and H
+
. A second
mechanism inserts an intermediate colloidal phase from which
crystallization proceeds. The third invokes structural arrange-
ment of alumina-silica residue left from selective leaching of
parent materials such as feldspars.
The occurrence of kaolinite in the sandstone intervals as
pore-filling books of stacked hexagonal flake between quartz
grains as observed under the SEM and its high degree of or-
dering as shown by the X-ray data, indicate that this kaolinite
is of authigenic origin. As far as kaolinite is the main weather-
Fig. 8. X-ray diffraction pattern of the clay fraction separated from
the sandstone intervals. It is composed of kaolinite (K) and smectite
(S) with some quartz (Q) and feldspar (F) and represents the kaolin-
ite-smectite assemblage.
Fig. 9. X-ray diffraction pattern of the clay fraction separated
from the shale interval. It is composed of kaolinite (K), smectite
(S), and illite (I) with some quartz (Q) and feldspar (F) and repre-
sents the kaolinite-smectite-illite assemblage.
334 BAIOUMY, ISMAEL and ZIDAN
Fig. 13. Scanning electron micrograph of shale sample from the
Nubia Formation. Smectite occurs as flakes of small and unde-
fined outline between quartz grains.
Fig. 10. Vertical distribution of clay minerals through the Nubia
Formation. The shale intervals have higher smectite contents com-
pared with sandstone intervals.
Fig. 12. Scanning electron micrograph of sandstone sample from
the Nubia Formation. Kaolinite (K) occurs as pore-filling books of
stacked hexagonal flakes between quartz grains (Q).
Fig. 11. Scanning electron micrograph of sandstone sample from
the Nubia Formation. Kaolinite (K) occurs as hexagonal crystals
of small and undefined outline between quartz grains (Q).
ing product of acidic and feldspar-rich rocks (Hay 1992 and
Parrish 1998), it is suggested that the kaolinite in the Nubia
Sandstone Formation was formed during diagenesis of the Nu-
bia Sandstone as a result of complete or partial dissolution or
replacement of the detrital feldspar grains which are recorded as
one of the constituents of the Nubia Sandstone Formation.
Early diagenetic kaolinite results from flushing sandstones
with meteoric water flow; thus maximum development of ka-
olinite is indicative of the proximity of shoreline, the continu-
ity of sandstone bed, and the sea level changes (rodoñ 1999).
In the absence of flushing, the kaolinite+feldspar assemblage
is stable until 120 °C, and then reacts forming illite. Experi-
ments of Huang et al. (1986) confirmed the role of fluid/rock
ratio in altering feldspar into kaolinite or illite. According to
Osborne et al. (1994), early diagenetic kaolinite crystallizes at
different temperatures with different habits: vermin-form be-
tween 25 and 50 °C and blocky between 50 and 80 °C. Late
diagenetic (telogenetic) kaolinite develops in sandstones
flushed by gravity-driven meteoric waters after the tectonic
inversion of a basin. Accordingly, and based on the morphol-
ogy of its grains, the kaolinite separated from the Nubia Sand-
stone Formation is considered as early diagenetic resulting
from flushing sandstones with meteoric water at temperatures
around 50 °C.
CLAY MINERALOGY OF THE NUBIA FORMATION (EGYPT) 335
The authigenic vs. detrital origin of smectite has been de-
bated vigorously (rodoñ 1999). On the basis of particle mor-
phology, detrital smectite can be distinguished from authigen-
ic smectite using morphology (Wilson & Pittman 1977). The
factors that strongly influence the origin and formation of
smectite as reviewed by Borchardt (1989), include low-lying
topography, poor drainage and base-rich parent material, lead-
ing to favourable chemical conditions characterized by high
pH, high silica activity and abundance of basic cations. Rob-
ert & Kennett (1992, 1994) related the abundance of smectite
(70100 %) in the early Tertiary off Antarctica to arid and
seasonal climates.
Occurrence of smectite as low crystalline flakes of unclear
outlines in the shales intervals is suggestive for detrital origin.
Its abundance indicates the prevalence of arid to semiarid cli-
mate during the deposition of this shale interval. This inter-
pretation is in agreement with the observation of Klitsch et al.
(1979) based on the identification and distribution of fossil
plants.
Conclusions
1. Clay fractions separated from the different intervals of
Nubia Formation are dominated by kaolinite, smectite, and il-
lite. Kaolinite is the major constituent in all samples while
smectite occurs as traces especially in the sandstone intervals.
In the shale intervals smectite occurs as a major constituent.
Illite occurs as traces in all samples.
2. Kaolinite is classified into two types. Authigenic kaolin-
ite forms highly crystalline pore-filling books of stacked hex-
agonal flake found between quartz grains in the sandstones in-
tervals and detrital kaolinite of low crystallinity associated
with smectite in the shale intervals.
3. Authigenic kaolinite formed during diagenesis of the Nu-
bia Sandstone as a result of complete or partial dissolution or
replacement of detrital feldspar grains.
4. Smectite is of detrital origin and its abundance in the
shale intervals suggests its formation under arid or semiarid
climatic conditions.
References
Biscaye B.E. 1965: Mineralogy and sedimentology of Recent deep
sea clay in the Atlantic Ocean and adjacent seas and oceans.
Geol. Soc. Amer. Bull. 76, 803832.
Borchardt G. 1989: Smectites. In: J.B. Dixon & S.B. Weed (Eds.):
Minerals in soil environments. Soil Sci. Soc. Amer. Madison,
Wisconsin, 657727.
Bucke P.D. Jr. & Mankin J.C. 1971: Clay-mineral diagenesis with
interlaminated shales and sandstones. J. Sed. Petrology 41, 4,
971981.
Carrigy M.A. 1971: Lithostratigraphy of the uppermost Creta-
ceous and Paleocene strata of the Alberta. Res. Council Al-
berta Bull. 27, 1153.
Carrigy M.A. & Mellon G.B. 1964: Authigenic clay mineral ce-
ments in Cretaceous and Tertiary sandstones of Alberta. J.
Sed. Petrology 34, 461472.
Dixon J.B. 1989: Kaoline and serpentine group minerals. In: J.B.
Dixon & S.B. Weed (Eds.): Minerals in soil environments.
Soil Sci. Soc. America Madison, Wisconsin, 467525.
Degens E.T. 1965: Geochemistry of sediments. Prentic-Hall, Inc.,
Eglewood Cliffs, N. J., 1 342.
Füchtbauer H. & Müller G. 1970: Sediment Petrologie. Teil II-
Sedimen und sedimentgestene. E. Schweizerbartsche Ver-
lagsbuchhandlung, Stuttgart, 1709.
Hay W.W. 1992: Erosion and weathering. Encyclopedia of Earth
System Science 2, 177185.
Huang W.L., Bishop A.M. & Brown R.W. 1986: The effect of flu-
id/rock ratio on feldspar dissolution and illite formation under
reservoir conditions. Clay Miner. 21, 585601.
Jackson M.L. 1965: Clay transformation in soil genesis during the
Quaternary. Soil Sci. 99, 1521.
Keller W.D. 1964: Processes of origin and alteration of clay min-
erals. In: Soil and clay mineralogy. Univ. of N. Car. Press,
Chapel Hill, 1122.
Keller W.D. 1978: Classification of kaolins exemplified by their
textures in scanning electron micrographs. Clays and Clay
Miner. 26, 120.
Klitsch E. 1978: Geologische Bearbeitung Südwest-Ägyptens.
Geol. Rdsch. 67, 509520.
Klitsch E., Harms J.C., Lejal-Nicol A. & List F.K. 1979: Major
subdivisions and depositional environments of Nubia strata
Southwestern Egypt. Amer. Assoc. Petrol. Geol. Bull. 63,
967974.
Millot G. 1970: Geology of clays (translated by Forrand W.R. &
Paquet H.). Springer-Verlag, New York, 1429.
Moore M.D. & Reynolds R.C. Jr. 1989: X-ray diffraction and the
identification and analysis of clay minerals. Oxford, New
York, 1332.
Osborne M., Haaszeldine R.S. & Fallick A.E. 1994: Variation in
kaolinite morphology with growth temperature in isotopically
mixed pore-fluids, Brent Group, UK North Sea. Clay Miner.
26, 591608.
Parrish J.T. 1998: Interpreting Pre-Quaternary climate from the
geologic record. Columbia University Press, New York
Chichester, West Sussex, 1327.
Robert C. & Chamley H. 1987: Cenozoic evaluation of continental
humidity and paleoenvironment, deduced from the kaolinite
content of oceanic sediments. Paleogeogr. Paleoclimatol. Pa-
leoceanog. 60, 17187.
Robert C. & Chamely H. 1991: Development of early Eocene
warm climates, as inferred from clay variations in oceanic
sediments. Paleogeogr. Paleoclimatol. Paleoceanog. (Global
and Planetary change) 89, 315331.
Robert C. & Kennett J.P. 1992: Paleocene and Eocene kaolinite
distribution in the South Atlantic and Southern Ocean: Ant-
arctic climatic and paleoceanographic implications. Mar.
Geol. 103, 99110.
Robert C. & Kennett J.P. 1994: Antarctic subtropical humid epi-
sode at the Paleocene-Eocene boundary: Clay-minerals evi-
dence. Geology 22, 211214.
Robert C. & Maillot 1990: Paleoenvironments in the Weddel Sea
area and Antarctic climates, as deduced from clay mineral as-
sociations and geochemical data, ODP Leg 113. In: P.F.
Barker & J.P. Kennett et al. (Eds): Proceeding of the Ocean
Drilling Program. Sci. Results Leg 113, 5170.
Said R. 1962: The geology of Egypt. Elsevier, AmsterdamOx-
fordNew York, 1337.
Sarkisyan S.G. 1972: Application of the scanning electron micro-
336 BAIOUMY, ISMAEL and ZIDAN
scope in the investigation of oil gas reservoir rocks. J. Sed.
Petrol. 41, 289292.
Singer A. 1980: The paleoclimatic interpretation of clay minerals
in soils and weathering profiles. Earth Sci. Rev. 15, 303327.
Singer A. 1984: The paleoclimatic interpretation of clay minerals
in sediments A review. Earth Sci. Rev. 21, 251293.
Snavely P.D. 1984: Depositional and diagenitic history of the
Thebes Formation (Lower Eocene), Egypt and implication for
early Red sea tectonism. Ph. D. Thesis. California Univ.,
U.S.A.
Spanderashvilli G.I. & Mansour M. 1970: The Egyptian phospho-
rites. In: O. Moharram et al. (Ed.): Studies on some mineral de-
posits of Egypt. UAR Geol. Surv. 89106.
rodoñ J. 1999: Use of clay minerals in reconstructing geological
processes: recent advances and some perspectives. Clay Miner.
34, 2737.
Thiry M. 2000: Paleoclimatic interpretation of clay minerals in ma-
rine deposits: an outlook from the continental origin. Earth Sci.
Rev. 49, 201221.
Wilson D. & Pittman E.D. 1977: Authigenic clays in sandstones:
Recognition and influence on reservoir properties and paleoen-
vironmental analysis. J. Sed. Petrol. 47, 1, 331.
Zimmerman H.B. 1977: Clay-mineral stratigraphy and distribution
in the South Atlantic Ocean. In: P.R. Supko & K. Perch-Niels-
en et al. (Eds.): Initial Reports DSDP, 39. U.S. Gov. Print. Off,
Washington, DC, 395405.