Activity 6/ Write 5
GY 402 Sedimentary Petrology (W)
Paper Critical Review 2
Introduction: Time for another critical paper review, this one dealing with a more complex
sedimentological study. The subject for today is provenance; the origin of sediment and what it
can tell you about paleotectonic setting(s). Enjoy!
1) Discussion component (Activity 6): As we did for the previous critical review exercise, I
want you to actively participate in an open discussion concerning the merits of the attached
paper. I will expect you to be able to identify the purpose of the paper, the quality of the data
presented, the limitations of the author(s)'s interpretations and the quality of their writing. I am
also interested in how you feel this paper relates to GY 402 AND whether or not you learned
something from reading it. Did you like the paper or did it really suck? Why?
At the start of the activity session, I would first like you to get into your groups and to spend the
first 10 minutes coming up with a "collective opinion" about the paper you all read. After that,
well it will be a free for all discussion about the journal article, beaches in general and if you so
desire, life the universe and everything. The activity grade that you will receive will be based on
your group's efforts (i.e., you will receive a single group grade for the activity). Sink or swim
together!
2) Writing Component (Write 5): Unlike Activity 4 which required a review after the
discussion session, this time I want your 1 page written critical review before the discussion. Use
the same format that you did for the midterm question. This writing exercise is due at 12:00
noon Thursday (right after the end of the discussion) as it will also be used for a peer review
exercise (Peer 2), that is due the next day.
Journal of African Earth Sciences 85 (2013) 31–52
Contents lists available at SciVerse ScienceDirect
Journal of African Earth Sciences
journal homepage: www.elsevier.com/locate/jafrearsci
Provenance, diagenesis, tectonic setting and reservoir quality
of the sandstones of the Kareem Formation, Gulf of Suez, Egypt
Samir M. Zaid
Geology Department, Faculty of Sciences, Zagazig University, 44511 Zagazig, Egypt
a r t i c l e
i n f o
Article history:
Received 20 November 2011
Received in revised form 6 April 2013
Accepted 26 April 2013
Available online 11 May 2013
Keywords:
Provenance
Diagenesis
Reservoir quality
Kareem sandstones
Gulf of Suez
a b s t r a c t
The Middle Miocene Kareem sandstones are important oil reservoirs in the southwestern part of the Gulf
of Suez basin, Egypt. However, their diagenesis and provenance and their impact on reservoir quality, are
virtually unknown. Samples from the Zeit Bay Oil Field, and the East Zeit Oil Field represent the Lower
Kareem (Rahmi Member) and the Upper Kareem (Shagar Member), were studied using a combination
of petrographic, mineralogical and geochemical techniques. The Lower Rahmi sandstones have an average framework composition of Q95F3.4R1.6, and 90% of the quartz grains are monocrystalline. By contrast,
the Upper Shagar sandstones are only slightly less quartzose with an average framework composition of
Q76F21R3 and 82% of the quartz grains are monocrystalline. The Kareem sandstones are mostly quartzarenite with subordinate subarkose and arkose. Petrographical and geochemical data of sandstones indicate
that they were derived from granitic and metamorphic terrains as the main source rock with a subordinate quartzose recycled sedimentary rocks and deposited in a passive continental margin of a syn rift
basin. The sandstones of the Kareem Formation show upward decrease in maturity. Petrographic study
revealed that dolomite is the dominant cement and generally occurs as fine to medium rhombs pore
occluding phase and locally as a grain replacive phase. Authigenic quartz occurs as small euhedral
crystals, locally as large pyramidal crystals in the primary pores. Authigenic anhydrites typically occur
as poikilotopic rhombs or elongate laths infilling pores but also as vein filling cement. The kaolinite is
a by-product of feldspar leaching in the presence of acidic fluid produced during the maturation of
organic matter in the adjacent Miocene rocks.
Diagenetic features include compaction; dolomite, silica and anhydrite cementation with minor ironoxide, illite, kaolinite and pyrite cements; dissolution of feldspars, rock fragments. Silica dissolution, grain
replacement and carbonate dissolution greatly enhance the petrophysical properties of many sandstone
samples.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
The Middle Miocene Kareem Formation is an important hydrocarbon bearing-reservoirs in the southwestern part of the Gulf of
Suez including Zeit Bay Oil Field and East Zeit Oil Field (Hilaly
and Darwish, 1986; Saudi, 1992; Darwish and El-Araby, 1993;
Alsharhan and Salah, 1995; Zahran, 2005; Fig. 1). The Middle
Miocene Kareem sandstones served as one of the primary source
of oil and gas, while the Middle Miocene evaporites (Belayim Formation) represent the excellent capping rocks for these reservoirs.
Almost 23% of the oil is produced from the sandstones of the
Kareem Formation (Alsharhan and Salah, 1997). In the Gulf of Suez
area, the Miocene rocks have wide geographic distribution, either
exposed or subsurface.
Provenance studies of clastic sedimentary rocks often aim to
reveal the composition and geological evolution of the sediment
E-mail address: samir_zaid75@yahoo.com
1464-343X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.jafrearsci.2013.04.010
source areas and to constrain the tectonic setting of the depositional basin. Previous works have revealed that the chemical
composition of clastic sediments is a function of a complex interplay of several variables, including the source rock composition,
the extent of weathering, transportation and diagenesis (Taylor
and McLennan, 1985; Bhatia and Crook, 1986). However, the
tectonic setting of the sedimentary basin may play a predominant
part over other factors, because different tectonic settings can
provide different kinds of source materials with variable chemical
signatures (Pettijohn et al., 1987; Bhatia, 1983; Chamley, 1990;
Armstrong-Altrin and Verma, 2005). Many attempts have been
made to refine provenance models using the framework composition (Suttner et al., 1981; Dickinson et al., 1983; Weltje et al., 1998)
and geochemical features (Bhatia, 1983; Suttner and Dutta, 1986;
Roser and Korsch, 1986, 1988; Armstrong-Altrin et al., 2004).
Significant contributions have been made by several studies in
relation to the regional geology, petroleum prospects, sedimentology and tectonic evolution of the Kareem Formation including the
32
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
Fig. 1. Location map of studied wells, Gulf of Suez, Egypt.
EGPC Stratigraphic Committee (1964), Hilaly and Darwish (1986),
Darwish and El-Araby (1993), Salah (1994), Alsharhan and Salah
(1994, 1995) and Salem et al. (2000). However, very few studies
have ever been related to reservoir properties, diagenesis and its
implications for reservoir quality except Alsharhan and Salah
(1997) and Zahran (2005).
In this regard, there still exists a gab between the understanding the reservoir properties and factors controlling the reservoir
quality of Kareem sandstones. With the main of helping to close
the gab, this paper gives an account of the petrophysical properties
of reservoir rock to characterize the reservoir and also describes
how the diagenetic aspects, petrophysical parameters and detrital
composition influence the reservoir quality.
The stratigraphic columns of Zeit Bay Oil Field and East Zeit Oil
Field include the rock units from Paleozoic to Post Miocene normally encountered in the Gulf of Suez (Fig. 2). The Miocene sequences were previously subdivided by the EGPC Stratigraphic
Committee and Subcommittee (of 1964 and 1974, respectively)
into two main groups, the Gharandal and Ras Malaab. The term
‘‘Gharandal’’ was introduced by Said (1962) to describe the strata
that lie beneath the Miocene evaporites on the Sinai side of the
Gulf of Suez. The rocks were divided into two formations: the
Nukhul and the Rudies. The term ‘‘Ras Malaab’’ was first introduced to describe surface exposures at the entrance to Wadi
Gharandal. As the name ‘‘Gharandal’’ was already reserved for
the underlying clastic group, the closest geographic name, ‘‘Ras
Malaab,’’ was chosen for this group (EGPC, 1964). This group was
redefined and subdivided by the EGPC (1974) into the Zeit, South
Gharib, Belayim, and Kareem formations, in descending order.
The Kareem Formation disconformably overlies the Rudies
Formation and unconformably overlies by the Belayim Formation.
The average thickness of the Kareem Formation is around 165 m.
The Kareem Formation is composed mainly of interbedded
sandstones, shales and carbonates with minor anhydrites in its
lower parts. The sandstones of the Kareem Formation is medium
to dark greenish grey, brownish grey, argillaceous and fossiliferous.
The siliciclastics were deposited in alluvial and submarine fans
building out from the rift shoulder, while the carbonates and anhydrites were precipitated in local lagoons as a result of sea level fluctuations. The formation is divided into the Rahmi and overlying
Shagar members, and is Langhian to Serravalian in age (Alsharhan
and Salah, 1997).
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
33
Fig. 2. Stratigraphic succession of the Gulf of Suez with correlated lithostratigraphic columns of East Zeit and Zeit Bay wells (Darwish and El-Araby (1993) and Zahran (2005)
after modifications and additions).
Rahmi Member consists of interbedded shales, sandstones and
four beds of anhydrite with very thin beds of carbonate. The sandstones are yellow to yellowish-white in color. Rahmi Member is
also referred to informally in the oil industry as the ‘‘Markha Member’’. Shagar Member consists mainly of interbedded shales and
carbonates with thin laminae of sandstone and siltstone (Tewfik
et al., 1992). The member unconformably overlies the Rahmi Member, and lies below the evaporites of the Belayim Formation (Youssef, 1986).
2. Geological setting
The study area is located within the main structural units in the
Gulf of Suez region (Fig. 1). The Gulf of Suez is a rift graben formed
as a result of tectonic movements initiated in the Oligocene which
continued with intensity until Post-Miocene times. Tensional
faults of considerable displacements determine the configuration
of the graben and its boundaries. According to Said (1990), the Gulf
of Suez is divided into three uplifted belts separated by two structural lows (Fig. 1). The highs and lows are of Gulf parallel trend and
dissected by NE–SW Aqaba trending faults. Five major tectonic episodes have been recorded in the Gulf of Suez. These, from base to
top, the pan-African event, the Hercynian event, the Neo-Tethyan
event, the Syrian Arc event and the Gulf of Suez event.
The stratigraphic sequence in the Gulf of Suez (Fig. 2) comprises
three stages; pre-rift, syn-rift and post rift stratigraphy. During the
post rift stage, a rapid subsidence from the early Miocene to the
Recent within the central depression of the rift has allowed for
accumulation of up to 5 km of continental and marine sediments.
Sedimentation is primarily governed by block structures with a
thick series of clastics and evaporites in the grabens and erosion
or carbonate buildup on the crests of the titled blocks.
At the end of the Aquitanian there was renewed tectonic activity in the Gulf of Suez which included uplift of the rift shoulders
and rapid subsidence of central trough (Zahran, 2005). The major
structural blocks of the Gulf of the Suez region were delineated
and tilted at that time leading to the erosion of Nukhul sediments
of the structure highs. This subsidence and fragmentation of a rift
during the Burdigalian resulted in increased clastic influx to the basin (Rudies Formation).
There was a general marine transgression within the rift and
deeper parts of the basin accumulated a thick sequence of shales
and carbonates. Rapid subsidence, accompanied by the deposition
of mixed carbonates, clastics and evaporites (Kareem Formation)
continued through the Serravalian. The Kareem Formation consists
mainly of the Rahmi lagoonal facies overlain by the Shagar
Member generally along the shores of the present Gulf, the distribution of the anhydrites follows the Kareem shoreline (Tewfik
et al., 1992). The sediment thickness within the Kareem Formation
ranges from 400 to 1400 feet. The predominantly marine Rudies
and Kareem formations together with the Nukhul Formation make
up the Gharandal Group which is sometimes given a name of
‘‘Globigerina Marls’’.
From Mid Serravalian to the Latest Messinian, the Gulf of Suez
and Red Sea rift was restricted from the open ocean and underwent
almost continuous evaporite deposition in the subsiding basin,
resulting in the accumulation of up to 3 km of shallow, subaqueous, marine evaporitive carbonates, anhydrite, clastics and halite
which forming Belayim, South Gharib and Zeit formations. This entire sequence forms the Ras Malaab Group.
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
SR–R
P
SR–R
P
SA–R
P
SR–WR
P
SA–R
P
SA–R
P
SA–R
P
SA–R
P
SA–R
P
SA–SR
P
SA–SR
F>P
SR–R
P
SR–R
P
SR–R
P
SR–R
P
SA–SR
P
SA–SR
P
SA–SR
P
Grain roundness
Grain contact
2809
SR–WR
P
R–WR
P
SR–R
P
SR–WR
F>P
EZ20
9
M–C
Ms
2805
2784
EZ19
8
F–M
Ms
EZ18
8
F–M
Ms
2782
2780
EZ17
8
F–M
Ps
Ms
SR–WR
P
EZ16
7
F–M
Ps
Ms
SA–R
P>C
2779
2760
EZ15
7
F–M
Ms
EZ14
6
M–VC
M–Ps
2756
2744
EZ13
6
M–VC
M–Ps
EZ12
5
M–C
Ms
2741
2734
EZ11
5
M–C
Ps
EZ10
4
M–C
Ps
2733
Lower Kareem (Rahmi Member) at East Zeit Bay Field
EZ9
4
F–C
Ps
ZB17
9
M–C
Ps
ZB16
8
M–C
Ps
ZB15
8
M–C
M–Ps
ZB14
7
M–C
Ms
ZB13
7
F–M
Ms
ZB12
6
F–M
Ms
ZB11
6
F–M
Ms
ZB10
5
F–M
Ms
ZB9
5
F–M
Ms
ZB8
4
F–M
M–Ps
ZB7
4
M–C
M–Ps
1565
1561
1550
1547
1533
Lower Kareem (Rahmi Member) at Zeit Bay Field
Textural data/depth
Table 1
Textural data of the Lower Kareem Rahmi Member.
1577
1578
1580
4.1. Sandstone petrofacies and texture
The Kareem Formation is composed of sandstones and less
common shales and carbonates. The study deals with the petrographic characteristics of sandstones, and their diagenetic influences on reservoir quality. As the carbonates in the Kareem
Formation do not constitute potential reservoirs in the southern
Gulf of Suez, they have not been included in this study (Evans,
1990; Alsharhan and Salah, 1997). The analyzed sandstone samples of the Lower and Upper Kareem Formation are fine to coarse
grained, subrounded to well rounded and moderate to poorly
sorted (Tables 1 and 2). All types of major grain contact, including
point, long, and concave–convex are present. However, an abundance of point contact was noted. The framework grains of the
sandstones are composed of monocrystalline quartz (Qm), polycrystalline quartz (Qp), K-feldspar (K), plagioclase (Pl), and lithic
fragments (LF). Quartz dominates over feldspar and lithic fragments (Tables 3 and 4). Sandstone classification was made using
Dott–McBride scheme (Fig. 3). The sandstones of the Kareem Formation are mostly quartzarenite with subordinate subfeldspathic
arenites (subarkoses) and feldspathic arenites (arkoses). Quartzarenites present in the Lower Kareem (Rahmi Member) where
the subarkoses and arkoses recorded only in the Upper Kareem
(Shagar Member).
The Lower Kareem (Rahmi) sandstones have an average framework composition of Q95F3.4R1.6, Framework constituents comprise 80% of the rock, and the matrix and cement constitute
about 20%. Matrix partly consists of clay minerals and detrital
constituents. The observed type of cement includes ferroan and
nonferroan dolomite and calcite, silica and anhydrite (Fig. 4).
Average existing pore space constitutes 14% of the rock (Table 3,
1591
1582
4. Results
Sample no.
Core no.
Av. grain size
Grain sorting
In this study we examined 152 m of 9 cores taken from a well
in Zeit Bay Oil Field (depths of 1452–1604 m) and 188 m of 10
cores taken from a well in East Zeit Oil Field (depths of 2653–
2841 m), representing the Lower Kareem sandstones (Rahmi
Member) and the Upper Kareem sandstones (Shagar Member).
Thin sections prepared from 76 blue epoxy-impregnated samples
were examined under the binocular microscope. The amounts of
detrital components, as well as the textural modal grain size
and sorting parameters, were determined by counting 300 points
in each of 38 selected representative thin sections. Sorting was
estimated by comparison with the standard charts of Beard and
Weyl (1973). Carbonate cements were stained for identification
with an acid solution of alizarin red and potassium ferrocyanide
(Dickson, 1965).
The morphology and the textural relationships between minerals were examined in 8 gold-coated samples by scanning electron microscope (SEM) equipped with energy-dispersive
spectrometer (EDS), using an accelerating voltage of 10 kV. In order to identify the clay minerals present in the sandstones, X-ray
diffraction analyses of the <2 lm fraction were performed for
studied samples. Major element concentrations for fifteen selected samples were determined by X-ray Fluorescence (XRF)
Spectrometry technique on fused beads (Rollinson, 1993). X-ray
Fluorescence Spectrometry technique and SEM analyses were
performed at the laboratory of the National Research Center of
Egypt. Analytical precision is better than 3% for the major oxides.
Loss on ignition (LOI) was estimated by firing the dried sample at
1000 °C for two hours. Moreover, the total iron is expressed as
Fe2O3.
EZ21
10
M–C
Ms
2835
3. Sampling and methods
1531
34
35
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
Table 2
Textural data of the Upper Kareem Shagar Member.
Textural data/depth
Sample no.
Core no.
Av. Grain size
Grain sorting
Grain roundness
Grain contact
Upper Kareem (Shagar Member) at Zeit Bay Field
Upper Kareem (Shagar Member) at East Zeit Bay Field
1463
1465
1470
1474
1520
1523
2666
2668
2678
2679
2680
2720
2722
2723
ZB1
1
F–C
M–Ps
SA–SR
P
ZB2
1
F–C
Ps
SA–SR
P
ZB3
2
M–C
M–Ps
SA–SR
P
ZB4
2
F–C
Ms
SR–R
P
ZB5
3
F–M
Ms
SR–R
F>P
ZB6
3
M–C
Ms
SR–R
F
EZ1
1
F–C
Ps
SA–SR
P>F
EZ2
1
F–C
M–Ps
SA–SR
P>F
EZ3
2
VF–C
M–Ps
SA–SR
P
EZ4
2
VF–C
M–Ps
SA–R
P
EZ5
2
VF–C
M–Ps
SA–R
P
EZ6
3
VF–C
M–Ps
SR–R
P
EZ7
3
M–C
Ms
SR–WR
P
EZ8
3
M–C
Ms
SR–WR
P
Abbreviations: VF–C = very fine to coarse grained; F–C = fine to coarse; F–M = fine to medium; M–C = medium to coarse; M–VC = medium to very coarse; M–Ps = moderate to
poorly sorted; Ms = moderately sorted; Ps = poorly sorted; SR–R = Subrounded to rounded; SA–SR = Subangular to subrounded; SA–R = Subangular to rounded; SR–
WR = Subrounded to well rounded; R–WR = Rounded to well rounded; P = Point contact; P > C = Point contact > concave convex contact; P > F = Point contact > float contact;
F > P = Float contact > Point contact.
Fig. 4a). Quartz is mainly monocrystalline type with undulatory
extinction (Fig. 4a and e). Few quartz grains are of polycrystalline
type. Some of quartz grains contain inclusions of rutile, zircon
and tourmaline (Fig. 4e). Long, point, and concavo-convex contacts
are common (Fig. 4e) and are caused by pressure solution and compaction. Some quartz grains display syntaxial overgrowths
(Fig. 4d), and some others are corroded at their margins (Fig. 4b
and c). Heavy minerals, mica flakes, clay minerals (especially kaolinite) and bioclastic shell fragments are also existed (Fig. 4f). Mica
and heavy minerals (rutile, zircon and tourmaline) appear in accessory quantities (<1.0%, Table 3).
The Upper Kareem (Shagar) sandstones have an average detrital
framework composition of Q81.3F14.6R4.1. Framework constituents
comprise 73% of the rock, and the matrix and cement constitute
about 27%. The framework is cemented with dolomite, anhydrite,
calcite and silica (Fig. 5). Average existing pore space constitutes
9.7% of the rock. The quartz grains are of undulose and plutonic
types. They are dominantly monocrystalline (Fig. 5c and d) and
rarely polycrystalline. Some grains are corroded and partially replaced by dolomite and/or anhydrite cement in part (Fig. 5c and
d). Many of quartz and feldspar grains have a secondary overgrowth (Fig. 5b–d). Feldspars include K-feldspars, and plagioclase,
which is partially altered to sericite. Perthite, orthoclase and
microcline fragments are also present. The lithic fragments are
mainly of granitic, volcanic or carbonate composition. Glauconite
pellets, algal fragments and planktonic foraminiferal tests are also
recorded (Darwish and El-Araby, 1993). Some bioclasts (Foraminifera) are selectively leached and partially occluded a secondary
intraparticle and moldic porosity. Most of pore filling dolomite cement is corroded (Fig. 5e and f) and partially occluded vuggy
porosity (Fig. 5a and c).
The important constituent framework grains of the sandstones of the Kareem Formation are quartz including both monocrystalline and polycrystalline type. Monocrystalline quartz
grains are generally stretched and show undulatory extinction.
Polycrystalline quartz grains represent weakly foliated grains of
equant and prolate shapes. Sedimentary lithics include fragments
of quartzose siltstone, siliceous and non-siliceous shale fragments and carbonate rock fragments. The siliceous materials
usually have fine-grained texture and commonly contain a siliceous matrix. The carbonate grains commonly represent coarsely
crystalline limestone grains generally coated with iron oxide. In
addition to the main framework constituents, a suite of heavy
minerals including opaques are observed in the studied sandstones. These mineral grains include hematite, rutile, tourmaline,
zircon, and muscovite.
The sandstones of the Kareem Formation are loosely indurated
to hard. The mean grain size ranges from fine to coarse-grained. A
major portion of the framework grains is rounded to subrounded
and unimodal. These sandstones are (76%) moderately well sorted,
followed by (14%) well sorted, and (10%) moderately sorted.
4.2. Clay mineralogy
The clay minerals identified in sandstones are kaolinite, illite and
smectite. Kaolinite dominated in Upper Shagar sandstones, while
both illite and smectite are recorded with kaolinite in the Lower
Rahmi sandstones (Fig. 6). These variations may be related to relative changes in the climatic conditions in the source area. The moderate crystallinity exhibited by the clay minerals indicates their
detrital origin from weathering horizons and soils developed on silicic rocks, and transportation in a fluvial environment (Keller, 1956;
Abu-Zeid et al., 1989, 1991). Source area weathering is confirmed by
the low percentage of smectite and absence of chlorite (Fig. 6).
The predominance of kaolinite with little or without illite, especially at the Upper Member, indicates their sedimentary origin under continental conditions (Lonnie, 1982; Tsuzuki and Kawabe,
1983; Amer et al., 1989).
4.3. Diagenetic minerals
The most common diagenetic constituents of the sandstones of
the Kareem Formation in studied wells are dolomite, calcite, anhydrite, quartz, and kaolinite:
(1) Authigenic quartz is present in all samples under investigation. It was better developed in large intergranular pore networks and the pores are often occluded by large quartz
overgrowths (Fig. 4b). It ranges between 0.3% and 2.5% with
an average of 0.5%. Quartz cement mainly occurs as syntaxial
overgrowths (Fig. 4d). Also, it occurs as syntaxial outgrowths
in clay-coat-rich sandstones (Fig. 4b and c). Thus, quartz
overgrowth is recorded as second cement in this unit after
iron oxide. The pore waters required for the precipitation
of these overgrowths would have been acidic or slightly
alkaline, in an environment containing sufficient dissolved
silica to allow quartz overgrowths formation.
During diagenesis sediments were subjected to different conditions, which might activate sources of silica for quartz cementation, such as dissolution of feldspar (Hawkins, 1978), pressure
solution (Bjørlykke et al., 1986; Houseknecht, 1988; Dutton and
Diggs, 1990; Bjørlykke and Egeberg, 1993; Dutton, 1993; Walderhaug, 1994), replacement of quartz and feldspar by calcite (Burley
and Kantorowicz, 1986) and transformation of clay (Hower et al.,
1976; Boles and Franks, 1979; Rodrigo and Luiz, 2002). The
dissolved silica of the sandstones of the Kareem Formation was
probably derived from the extensive dissolution of feldspar and
36
Table 3
Detrital grains modes and the derived QFL indices of the Lower Kareem Rahmi Member.
S. no.
Core no.
Depth
Qm
Qp
KF
Pl
Lp
Lv
Ls
M
Op
Hm
Gl
Bio
Clays
QFL%
Qt
Zeit Bay Field
L
Qm
Cement and/or matrix
F
P.C.P
Lt
ZB7
4
1531
90.8
2.2
2.5
0.1
0.3
0
0.7
0.1
0.2
Tr
0
Tr
3
96.2
2.7
1.1
93.9
2.7
3.3
11.7
16
ZB8
ZB9
4
5
1533
1547
91.5
89.5
2.6
2.3
2.5
2
0.2
0.4
0.2
0.5
0
0
1.3
1.5
0.2
1
Tr
Tr
Tr
Tr
0
Tr
Tr
Tr
1.5
2.8
95.7
95.4
2.7
2.5
1.5
2.1
93.1
93.0
2.7
2.5
4.1
4.4
12.9
11.5
17
16
ZB10
ZB11
5
6
1550
1561
84.5
85.5
2.8
2.6
3.5
2.5
1.2
0.5
0
0.2
0
0
1.5
1
Tr
0
Tr
0.6
Tr
Tr
Tr
Tr
Tr
Tr
6.5
7.1
93.4
95.4
5.0
3.3
1.6
1.3
90.4
92.6
5.0
3.3
4.4
3.9
15.5
15.7
14.5
14.2
ZB12
ZB13
6
7
1565
1577
88
87
2.8
3
2.9
4
0.5
0.2
0.2
0.1
0
0
1
0.3
Tr
0.3
Tr
Tr
Tr
Tr
Tr
Tr
Tr
Tr
4.6
5.1
95.2
95.1
3.6
4.4
1.3
0.4
92.2
92.0
3.6
4.4
4.1
3.4
16.2
15.7
13.8
12.5
ZB14
ZB15
7
8
1578
1580
89
87
2.5
3
3.4
3.5
0.5
0.6
0
0
0
0
2
0.8
Tr
0.3
0.7
0.7
Tr
Tr
0
0
0.5
0.3
1.4
3.7
93.9
94.7
4.0
4.3
2.1
0.9
91.4
91.6
4.0
4.3
4.6
3.9
16.8
14.1
13
12.5
ZB16
ZB17
8
9
1582
1591
88
83
2
2
5.4
5
0.2
0.2
0
0.1
0
0
0
1.6
1.4
3.2
Tr
Tr
Tr
Tr
0
Tr
Tr
Tr
3
5
94.0
92.5
5.9
5.7
0.1
1.8
92.1
90.3
5.9
5.7
2.1
3.8
14.5
15.3
13.5
13
EZ9
4
2733
85.5
2
6.6
0.6
0
0
1.6
0.5
Tr
Tr
Tr
0
3.3
90.9
7.5
1.7
88.8
7.5
3.7
17.4
11.5
EZ10
EZ11
4
5
2734
2741
86
84.5
2.1
2.6
5.8
4.7
0.9
0.8
0
0.1
0
0
0.4
1.5
0.5
0.5
Tr
Tr
Tr
Tr
Tr
Tr
0
0
4.3
5.5
92.5
92.4
7.0
5.8
0.4
1.8
90.3
89.6
7.0
5.8
2.5
4.4
15.5
14.6
12.5
14.5
EZ12
EZ13
5
6
2744
2756
88
89
2
3
3.3
3.9
0.3
0.3
0
0
0
0
1.8
2.1
0.4
0.4
Tr
Tr
Tr
Tr
Tr
0
Tr
Tr
4.2
1.3
94.3
93.6
3.8
4.3
1.9
2.1
92.2
90.5
3.8
4.3
3.9
5.1
13.1
11.9
15.5
16
EZ14
6
2760
88.5
2
2.7
0.6
0.4
0
2.1
Tr
Tr
Tr
Tr
Tr
3.7
94.0
3.4
2.6
91.9
3.4
4.6
12.7
15
EZ15
EZ16
7
7
2779
2780
87
89
2.3
2.3
3.6
3.5
0.2
0.3
0.5
0
0
0
1.5
2.5
Tr
Tr
Tr
1.1
Tr
Tr
Tr
Tr
0.3
0.7
4.5
1.7
93.8
93.5
4.0
3.9
2.2
2.6
91.4
91.2
4.0
3.9
4.5
4.9
11.9
15.9
16.5
13.5
EZ17
EZ18
8
8
2782
2784
88.5
87
2
3
3
3.7
0.3
0.6
0
0
0
0
1
0.3
0.7
0.7
Tr
Tr
Tr
Tr
Tr
Tr
0
0
3.5
4.7
95.5
95.1
3.5
4.5
1.1
0.3
93.4
92.0
3.5
4.5
3.1
3.3
15.5
16.6
13
12.2
EZ19
EZ20
9
9
2805
2809
90
89
2.1
2.1
4.5
5
0.6
1.3
0.4
0
0
0
0.3
0.3
0.2
Tr
Tr
Tr
Tr
Tr
0
0
0
0
1.9
2.3
94.1
93.2
5.2
6.4
0.7
0.3
91.9
91.1
5.2
6.4
2.8
2.4
15.8
16.3
13.8
12.5
EZ21
10
2835
91.6
3
2
1
0
0
0.3
0.2
Tr
Tr
0
0
1.9
96.6
3.1
0.3
93.6
3.1
3.3
14.3
13.0
83–91.5
87.8
2.0–3.0
2.4
2.0–6.6
3.7
0.1–1.3
0.5
0–0.5
0.13
0–0
0
0.3–2.5
1.14
0–3.2
0.6
0–0.7
0.7
0–Tr
0
0–Tr
0
0–0.7
0.2
1.3–6.5
3.6
92.4–96.6
94.2
2.5–7.5
4.4
0.1–2.6
1.3
88.8–93.9
91.7
2.5–7.5
4.4
2.1–5.1
3.8
11.5–17.4
14.6
11.5–17.0
14.0
Range
Average
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
East Zeit Oil Field
QmFLt%
F
Average
3
Abbreviations: Monocrystalline quartz (Qm); Polycrystalline quartz (Qp); K-feldspar (K); Plagioclase (Pl); Plutonic lithic fragment (Lp); Volcanic lithic fragment (Lv); Sedimentary lithic fragment (Ls); Mica (M); Opaque (Op);
Hematite (Hm); Glauconite (Gl); Bioclasts (Bio); Q = Quartz; F = Feldspar; Fr = Fracture; D = Dolomite; I = Iron oxide; QO = Quartz overgrowth; PC = Point contact; LC = Line contact; CXC = Concave convex contact; Dd = Dolomite
dissolution; P = pores; Qc = Quartz corrosion; FO = Feldspar overgrowth; Il = Illite; Py = Pyrite; K = Kaolinite; An = Anhydrite. Qt = Qm + Qp, F = Pl + KF, L = Lp + Lv + Ls, Lt = L + Qp, Q = total quartzose grains, F = total feldspar,
Pl = plagioclase, KF = K-feldspar, L = unstable lithic fragments, Lt = lithic + polycrystalline quartz grains and P.C.P = pointe counted porosity.
9.7
14.8
1.2
0.0
21.1
1.8
70.0
0.8
0.2
0.0
3.1
0.0
1.7
0.5
1.3
74.1
22.5
3.4
72.3
22.5
5.2
9.6
5.7–
12.4
17.4
6.2–21.3
0.5–
11.5
4.8
30.5
11.9–
30.6
64.2–
83.2
64.7
2.3
0.5–
8.5
11.9–
30.6
30.5
67.2
67.2–
90.9
Tr
0–
5.8
0.0
0–
6.2
Tr
Tr–
1.5
Tr
0–
Tr
1.7
Tr–
2.7
0–
0.3
0.0
1.6
0.5–
8.3
0–
0
0.0
0.7
0–
0.7
62–
83
0.5
29.8
5.2–
29.8
2.5
0–
2.7
64.2
0–
1.5
7.8
10.5
18.7
14.1
EZ8
2723
Range
5.7
12.4
21.3
6.2
5.1
3.3
30.6
28.2
20.4
27.0
73.6
67.0
64.2
68.4
2.1
1.3
3.9
3.0
20.4
27.0
67.3
70.4
0.7
Tr
0.0
0.7
Tr
0.3
Tr
Tr
Tr
Tr
Tr
Tr
2.7
1.3
0.3
0.0
0.0
0.0
1.5
1.3
3.7
3.0
0.0
0.0
0.0
0.0
0.5
0.0
0.0
0.0
28.1
27.0
1.5
0.6
17.8
26.3
3.0
2.0
62.0
66.8
3
3
EZ6
EZ7
2720
2722
2
2
EZ4
EZ5
2679
2680
69.8
66.5
2.0
3.0
1.5
0.5
Tr
1.3
0.7
75.7
70.0
0.7
Tr
2.9
0.0
30.6
28.2
5.9
6.0
12
7.8
8.3
15.0
19.2
18.6
11.5
9.4
3.1
21.1
16.9
14.3
71.5
76.2
75.8
2.1
8.5
6.9
16.9
14.3
21.1
76.8
74.5
78.8
Tr
0.0
0.7
2.0
0.0
Tr
0.3
0.7
Tr
0.0
0.0
2.3
2.3
1.5
0.0
0.0
0.0
2.0
8.3
6.7
0.0
0.0
0.0
0.0
0.0
0.0
11.6
12.3
0.6
0.0
1.5
19.6
16.5
12.4
1.0
3.0
2.5
69.6
74.0
72.5
2666
1
1
2
EZ1
East Zeit Bay Field
EZ2
EZ3
2668
2678
7.8
10.5
6.7
5.0
1.7
0.5
20.7
10.9
13.3
28.0
27.9
30.3
70.4
69.2
78.2
68.7
5.6
2.8
1.7
0.5
27.9
30.3
13.3
28.0
0.2
Tr
81.1
69.2
Tr
0.0
0.0
0.0
0.0
0.0
0.3
0.3
Tr
Tr
0.0
0.0
Tr
Tr
5.3
2.3
1.7
0.5
0.0
0.0
0.0
0.0
0.0
0.5
0.0
0.5
27.8
29.7
0.6
1.0
12.0
26.7
0.0
0.0
74.0
68.0
3
3
ZB5
ZB6
1520
1523
2
2
ZB3
ZB4
1470
1474
70.0
69.0
2.7
0.5
0.0
0.0
Tr
Tr
1.7
Tr
1.5
0.3
2.2
0.7
70.4
69.2
8.3
3.3
11
8.5
15.7
18.1
5.0
4.8
11.9
13.9
81.0
83.2
4.2
2.7
13.9
11.9
83.9
83.5
5.8
Tr
1.7
6.2
Tr
Tr
Tr
Tr
Tr
Tr
0.0
0.0
2.0
3.4
0.0
0.0
0.5
0.5
1.0
0.8
10.0
12.2
0.6
2.3
76.0
77.0
1463
1
1
ZB1
Zeit Bay Field
ZB2
1465
P.C.P
QmFLt%
Qm
Clays
Hm
Ls
Lv
Lp
Pl
KF
Qp
Qm
Depth
Core no.
S. no.
Table 4
Detrital grains modes and the derived QFL indices of the Upper Kareem Shagar Member.
M
Op
Gl
Bio
F
L
QFL%
Qt
F
Lt
Cement and/or matrix
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
37
volcanic lithic fragments, kaolinitization and chemical compaction (Zhang et al., 2008; Umar et al., 2011).
(2) Carbonate cement is the second cement in the studied
sandstones. It ranges from 4.5% to 20.1% with an average of
2.8%. The carbonate cement contains ferroan and nonferroan calcite and dolomite.
Generally, dolomite cement is more common than calcite cement phase (Figs. 4, 5 and 7). In some cases, dolomite occurs as
coarsely crystalline cement (Figs. 4b and 7a and b). Ferroan
dolomite occurs mainly as fine and medium rhombs pore
occluding phase (Figs. 4c, 5d and 7f) and locally as a grain
replacive phase (Fig. 7a).
The source of magnesium is those released through the
washing of clay minerals. On the other hand, wide spread ferroan carbonate cementation is thought to have occurred under
reducing alkaline pore water conditions (Morad, 1998; El-ghali
et al., 2009). The ions required for cement formation were
probably derived from alumino-silicate grain dissolutions, and
clay mineral transformations.
Weakly ferroan calcite is the minor carbonate cement phase
in the sandstones of the Kareem Formation. It commonly occurs
in association with detrital carbonate components suggesting
that these acted as nuclei for cement formation. The ferroan
calcite cement has survived dolomitization most probably due
to poor permeability for the circulation of Mg-rich fluids
(Fig. 7a and b).
(3) Authigenic feldspars are less abundant in the sandstones of
the Kareem Formation. They are most frequent as an early diagenetic mineral and predate any tectonic deformation (Kastner,
1971). They are formed almost exclusively as overgrowths on
detrital feldspar grains in sandstones.
In the studied samples, feldspar overgrowths are ubiquitous,
usually as incipient overgrowths (Fig. 5b), and sometimes intergrown with authigenic clay phase.
Feldspar overgrowths in sandstones have presumably resulted
from the dissolution and kaolinitization of silicate grains, particularly feldspars and micas, which can be accomplished by meteoric
waters (Morad et al., 2000; El-ghali et al., 2009). Meteoric water
influx into the sandstones is attributed to relative sea-level fall
and basin ward shift of the shore line. This would be a form of
‘‘distillation’’ of an impure to pure feldspar and would explain
the general dependence on the presence of detrital feldspars in
most of the studied samples of the Upper Kareem (Shagar)
sandstones.
(4) Authigenic anhydrite typically occurs as poikilotopic rhombs or elongate laths infilling pores but also as vein filling cement
(Figs. 4a and e and 5a and d). The anhydrite was precipitated after
the quartz, calcite and dolomite (Fig. 5a and d). The sulfate for
anhydrite precipitation could have been derived from the dissolution and reprecipitation of early gypsum cementation as gypcrete,
since it is highly soluble and remobilization of anhydrite is common during diagenesis (Schmid et al., 2004). Sullivan et al. (1990)
suggested that sulfate for anhydrite precipitation may be supplied
by fluids expelled from surrounding evaporites.
(5) The authigenic kaolinite that is so common in some sandstone has the appearance of a well crystallized, pure pore filling
that was precipitated from a solution and shows no evidence of
alteration from a precursor clay mineral (Pettijohn et al., 1973).
38
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
Fig. 3. QFL triangular diagram shows the classification of reservoir sandstones of the Kareem Formation (modified from Dott (1964) and McBride (1963).
PC
Q
PR
a
QO
D
Q
Vu
100 µm
b
I
QS
d
DC
D
FC
QC
QO
D
QO
D
An
D
I
I
QC
Fr
100 µm
FC
c
Sh fr
PR
LC
100 µm
D
An
Q
Fr
F
D
VU
MO
Qin
100 µm
e
VXC
100 µm
f
Ca
100 µm
Fig. 4. Photomicrographs of quartzarenites showing: (a) Laths of authigenic anhydrite (An) vein filling cement (Note: reduction in primary porosity (PR)). (b) Dust line of iron
oxide cement (I) separating detrital quartz (Q) from authigenic silica (QO). Quartz grains are fractured (Fr) and corroded at their margins (QC) and primary pores are occluded
by large quartz overgrowth (QO). (c) Quartz cement occurs as syntaxial outgrowths (QO) in clay-coat-rich sandstones (Note: fine to medium dolomite rhombs (D) pore
occluding phase). (d) Some quartz syntaxial overgrowths (QS) post date iron oxide (I) (hematite) and pre-dated dolomite cement (D). (e) Closely packed, long (LC), point and
concave–convex contact (VXC) of quartz, chert, and highly altered feldspar. Note: quartz inclusions (Qin), pore filling authigenic anhydrite (An) and reduction in primary
porosity (PR). (f) Compaction and dissolution of bioclastic shell fragments (ShFr) with oversized pore left (Note: vuggy (Vu) and moldic (Mo) pores).
The kaolinite is determined in the sandstones of the Kareem
Formation as booklets and vermicular aggregates in mud intraclast,
mud matrix, pseudo matrix and detrital grains, as pore filling cement (Fig. 7e), and as grain coating on detrital grains (Fig. 7c). Also,
the late phase kaolinite is precipitated on early phase quartz overgrowth (Fig. 7d).
The kaolinite formation is dependent on: (a) sufficient porosity
and permeability to allow migration of interstitial pore waters and
to provide growth space, (b) the presence of K-feldspar and/or
muscovite as a source of Al and Si, and (c) pore waters of an acidic pH.
The presence of illite is visible as fibrous illite, mat like and
lath like crystals within kaolinite, mud matrix, and mud intraclast. It is oriented perpendicular to grain surfaces. Additionally,
illite seems as platelets occur arranged on the framework grain
surfaces and as high birefringence patches. So, illite cover kaolinite and quartz grain edge (Fig. 7d). Illite, which typically forms
during progressive burial under elevated temperature (90–
130 °C; Morad et al., 2000) required high K-pore water to
achieve illitization in the sandstone.
On the other hand, the occurrence of mixed layer illite/smectite
is less common in the sandstones of the Kareem Formation. The
honeycomb like texture of grain coating clays is mixed layer illite/smectite. Mixed clay occurs as a minor pore lining to locally
pore-filling clay with ragged-platy morphology. SEM analysis indicates that illite/smectite post-dates the quartz cementation
(Fig. 7c).
39
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
D
Ca
An
FO
D
F
DC
VU QC
QO
VU
a
b
D
An
c
QO
D
DC
An
100 µm
DL
Py
D
QC
d
100 µm
QO
e
f
Fig. 5. SEM images and photomicrographs of subarkose and arkose showing: (a) Pore filling authigenic anhydrite cement (An) after calcite (Ca) and dolomite (D). (b) Feldspar
overgrowth (FO) and corroded dolomite (DC) overgrown by anhydrite cement. (c) Monocrystalline quartz grains (Q) and authigenic silica (QO) are corroded (QC) and partially
replaced by dolomite cement (D). (d) Pore filling dolomite (D) partially replaced by authigenic anhydrite cement. (An) Note: authigenic anhydrite after quartz overgrowth
(QO) and dolomite cement (D). (e) Quartz overgrowth (QO) is partially replaced by later dolomite cement (D), thus predate dolomite. Note: leaching and corrosion of dolomite
cement (DC). (f) Framboidal pyrite (Py) crystallites locally replace dolomite cement. Note: dolomite cement is partially leached (DL) and corroded.
Fig. 6. Lithologic logs, clay content %, Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW) and Maturity Index (MI) of the Middle Miocene Kareem
sandstones at studied wells.
(6) Pyrite is known as a diagenetic mineral in sandstones and
implies reducing conditions, presumably reflecting a deoxygenated environment of deposition. Pyrite cement is
recorded as partial cement at certain levels within sandstones. Pyrite cement is also present in trace amounts as
framboids located within dissolved grains and dolomite
matrix (Fig. 5f). Pyrite cementation continued at a later stage
of diagenesis, locally occluding the pores.
4.4. Geochemistry
The geochemical classification diagrams of Pettijohn et al.
(1972) and Herron (1988) for the sandstones of the Kareem Formation (Fig. 8a and b) provide the same petrographic results. The
major element contents of the sandstones of the Kareem Formation
are given in Table 5 with their ratios between elements. These elements are compared in Table 6 with the average composition of
40
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
Il/sm
D
D
Il/sm
D
VU
D
QO
100 µm
a
I
P
VU
K
K
D
c
QO
D
QO
100 µm
b
Fr
QC
D
Il
d
QC
f
e
100 µm
Fig. 7. SEM images and photomicrographs of arenites and subarkoses showing: (a) Dolomite (D) after a shell fragment with dissolved margins. Dolomite is coarsely
crystalline and locally present as a grain replacive phase. (b) Recrystallization of microcrystalline dolomite cements (D) forming coarsely crystalline dolomite that enhanced
intercrystalline porosity. (c) Quartz overgrowths (QO) engulfed by dolomite (D) and coated by illite/smectite (il/Sm) thus predate illite/smectite and dolomite. (d) Iron oxide
(I) coating around detrital quartz, thus predate silica (QO) and dolomite cements (D). Note: kaolinite (K) coating on quartz grains; while illite (Il) cover kaolinite and quartz
grain edges. (e) Pore filling authigenic kaolinite (K) engulfs, thus post-dates quartz overgrowth (QO). (f) Fine to medium dolomite rhombs (D) present as pore occluding phase
and locally as a grain replacive phase. Note: quartz grains are fractured (Fr) and replaced by dolomite cement.
Fig. 8. Chemical classification of sandstone samples from the Middle Miocene
Kareem Formation based on (log (SiO2/Al2O3) versus log (Na2O/K2O) diagram of
Pettijohn et al. (1972), and (b) the log (SiO2/Al2O3) versus log (Fe2O3/K2O) diagram of
Herron (1988).
passive margin sandstones (Bhatia, 1983), Amazon big river sands
(Potter, 1978) and average arkosic sandstones (Pettijohn, 1963) to
be used later for investigating provenance and tectonic setting.
Table 5 shows that, most of sandstone samples are rich in SiO2
(69.9–94.2%). The source of silica is mainly quartz, chert, quartzite,
feldspars and clay minerals. Sandstones have a wide range of Al2O3
(0.97–11.78%), MgO (0.07–6.6%), K2O (0.12–6.0%) and Fe2O3
(0.03–4.5%). Al2O3 and K2O content may relate to the presence of
K-feldspars (orthoclase and microcline), illite and mica, while
MgO content may relate to the abundance of dolomite cement
and Fe2O3 content may relate to the abundance of iron oxide heavy
minerals and partly to Fe-containing clay minerals. In contrast, the
sandstones of the Kareem Formation possess low average contents
of Na2O, TiO2, MgO, and CaO. The source of Na2O is principally
related to plagioclase feldspar. Ti-opaque minerals and rutile are
the main holders of TiO2. MgO content is related mostly to the
presence of dolomitic materials as fragments or cement. Carbonate
cement and rock fragments and diagenesis of plagioclase are the
main source for CaO.
Kareem sandstones are highly depleted in most of the major
elements except SiO2 (due to enrichment in quartz) suggesting
an intense degree of weathering and reworking that removed
ferromagnesian minerals and feldspars.
Generally, most major elements show positive correlations with
Al2O3 (Fig. 9). However, these elements show marked negative correlations with SiO2, confirming that much of SiO2 is present as
quartz grains (Akarish and El-Gohary, 2008). The high K2O/Na2O
ratios (av. 8.27%, Table 5) are attributed to the common presence
of K-bearing minerals such as K-feldspar, mica, illite, muscovite
and biotite (McLennan et al., 1983; Nath et al., 2000; Zhang,
2004; Osae et al., 2006). A positive correlation between K2O and
Al2O3 (r = 0.92) implies that the concentrations of the K-bearing
minerals have significant influence on Al distribution and suggests
that the abundance of these elements is primarily controlled by the
content of clay minerals (McLennan et al., 1983; Jin et al., 2006;
Akarish and El-Gohary, 2008).
Alteration of rocks during weathering results in depletion of
alkalis (Na2O, K2O) and preferential enrichment of Al2O3 in sediments (Cingolani et al., 2003). Therefore, weathering effects can
be evaluated in terms of the molecular percentage of the oxide
components, using the formulae of Chemical Index of Weathering
(CIW = [Al2O3/(Al2O3 + CaO + Na2O] 100; Harnois, 1988) and
Chemical Index of Alteration (CIA = [Al2O3/(Al2O3 + CaO + Na2O + K2O] 100); Nesbitt and Young, 1982).
5. Discussion
Based on the petrographic study, the sandstones of the Kareem
Formation are classified as quartzarenites, subarkoses and arkoses.
Quartzarenites present in Lower Kareem, where the subarkoses
and arkoses recorded only in Upper Kareem. The average contents
of different quartz grains in these sandstones show granitic and/or
41
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
Table 5
Chemical composition of the Middle Miocene Kareem sandstones.
Depth
S. no.
SiO2
Al2O3
TiO2
CaO
MgO
Na2O
K2O
Fe2O3
MnO
P2O5
LOI
Sum
SiO2/Al2O3
K2O/Al2O3
K2O/Na2O
TiO2/Al2O3
Fe2O3/Al2O3
log SiO2/Al2O3
log Fe2O3/K2O
CIW
CIA
Lower Kareem (Rahmi Member)
Upper Kareem (Shagar Member)
1531
1550
1577
1582
2734
2760
2784
2835
1463
1470
1520
2668
2679
2720
2723
ZB7
93.10
1.20
0.07
0.05
1.27
0.03
0.13
1.10
0.03
0.00
2.82
99.80
77.58
0.11
3.82
0.06
0.92
1.89
0.93
93.46
84.87
ZB10
87.50
1.12
0.09
0.13
6.60
0.17
0.77
1.13
0.03
0.06
2.38
99.98
78.13
0.69
4.53
0.08
1.01
1.89
0.17
78.87
51.14
ZB13
90.30
0.97
0.06
0.14
5.08
0.06
0.12
1.05
0.01
0.00
2.49
100.28
93.09
0.12
2.00
0.06
1.08
1.97
0.94
82.91
75.19
ZB16
90.10
0.97
0.06
0.14
5.30
0.06
0.12
1.08
0.01
0.00
2.49
100.33
92.89
0.12
2.00
0.06
1.11
1.97
0.95
82.91
75.19
EZ10
88.30
1.12
0.09
0.13
5.80
0.17
0.77
1.13
0.03
0.06
2.38
99.98
78.84
0.69
4.53
0.08
1.01
1.90
0.17
78.87
51.14
EZ14
90.60
1.09
0.06
0.09
3.20
0.06
0.12
1.50
0.01
0.07
3.22
100.02
83.12
0.11
2.00
0.06
1.38
1.92
1.10
87.90
80.15
EZ18
90.10
1.16
0.06
0.11
3.90
0.14
0.82
1.00
0.01
0.01
3.28
100.59
77.67
0.71
5.86
0.05
0.86
1.89
0.09
82.27
52.02
EZ21
94.20
1.20
0.20
0.00
0.20
0.14
0.81
1.03
0.02
0.01
3.23
101.04
78.50
0.68
5.79
0.17
0.86
1.89
0.10
89.55
55.81
ZB1
90.30
5.90
0.21
0.01
0.07
0.19
1.10
1.13
0.01
0.03
2.06
101.01
15.31
0.19
5.79
0.04
0.19
1.18
0.01
96.72
81.94
ZB3
90.00
6.02
0.22
0.15
0.80
0.19
1.13
1.15
0.05
0.03
1.35
101.09
14.95
0.19
5.95
0.04
0.19
1.17
0.01
94.65
80.37
ZB5
69.90
11.78
0.69
0.20
1.10
0.30
6.00
4.50
0.12
0.03
4.60
99.22
5.93
0.51
20.00
0.06
0.38
0.77
0.12
95.93
64.44
EZ2
90.10
4.21
0.12
0.07
3.06
0.20
0.86
1.09
0.02
0.00
1.32
101.05
21.40
0.20
4.30
0.03
0.26
1.33
0.10
93.97
78.84
EZ4
90.50
4.33
0.12
0.12
1.10
0.39
1.20
1.20
0.02
0.00
2.02
101.00
20.90
0.28
3.08
0.03
0.28
1.32
0.00
89.46
71.69
EZ6
79.60
8.49
0.30
0.20
0.40
0.20
5.20
2.00
0.04
0.03
1.70
98.16
9.38
0.61
26.00
0.04
0.24
0.97
0.41
95.50
60.26
EZ8
75.96
9.57
0.50
0.14
0.18
0.17
4.82
2.90
0.01
0.06
5.77
100.08
7.94
0.50
28.35
0.05
0.30
0.90
0.22
96.86
65.10
gneissic source. These have been confirmed by overall variation in
the relative abundance of different types of quartz grains (monocrystalline and polycrystalline). The narrow grain-size range suggests either more or less uniform size of the sediments supplied
to the basin or the uniform hydrodynamic conditions prevailing
during deposition of these sandstone units (Ahmad and Bhat,
2006). The greater abundance of alkali feldspar than plagioclase
further supports for granitic and/or gneissic source. The dominance
of moderately well sorted either reflects the change in water turbulence during deposition or pulses of sediment supply during episodes of rifting and uplift. The overall sorting indicates alluvial and
marine fan-delta settings (Folk, 1980; Alsharhan and Salah, 1997).
5.1. Tectonic setting
Dickinson and Suczek (1979) and Dickinson et al. (1983), have
related detrital sandstone compositions to major provenance types
such as stable cratons, basement uplifts, magmatic arcs and recycled orogens. To interpret the tectonic discrimination source fields,
the Lower and the Upper Kareem sandstones were plotted on QtFL
and QmFLt ternary diagrams of Dickinson et al. (1983). The Lower
Kareem sandstones fall in the craton interior, whereas the Upper
Kareem sandstones fall in the transitional continental, craton interior and partly in recycled orogenic fields (Fig. 10a and b).
Fig. 10a and b shows that the Lower Kareem sandstones are
mature and derived from relatively low lying granitoid and gneissic sources. The low percentage of unstable grain (feldspar and
other rock fragments) <6%, the dominance of monocrystalline
quartz, and alteration of feldspar grains, indicate that Lower Kareem sandstones were transported from the far along the rift. However, the Upper Kareem sandstones are derived from craton
interior, transitional continental and recycled orogenic setting.
The high percentage of unstable grain >15%, indicate that the
Upper Kareem sandstones show short transport distance and
quick burial. This means that the Upper Kareem sandstones are
typically rift sandstone and their deposition constrained the
beginning of the faulting in studied area (Zaid, 2012). This result
supports and gives a great evidence for the unconformable relationship between the Lower Kareem (Rahmi Member and the
overlying Upper Kareem (Shagar Member) (Youssef, 1986; Tewfik
et al., 1992).
The percentages of major elements (Table 5) were used to discriminate the tectonic setting of sandstones (Schwab, 1975; Bhatia,
1983; Roser and Korsch, 1986, 1988; Armstrong-Altrin et al., 2004).
The discriminate function diagrams were used to understand the
provenance for the Lower and Upper Kareem sandstone terrain.
The discriminate function diagram of Roser and Korsch (1988) suggests that both Lower Rahmi and Upper Shagar sandstones may be
derived from mature polycyclic continental sedimentary rocks
Table 6
Comparison of the average chemical compositions of the studied Middle Miocene sandstones and other different sandstones.
SiO2
Al2O3
TiO2
Fe2O3
MnO
CaO
MgO
Na2O
K2O
P2O5
K2O/Na2O
Fe2O3/MgO
Al2O3/SiO2
Modern Big Rivers (Amazon) (Potter, 1978)
Arkose (Pettijohn, 1963)
Passive Margin (Bhatia, 1983)
Present work
85.32
7.47
0.78
2.76
0.05
1.12
1.02
0.23
1.14
0.02
5.00
3.78
0.09
80.18
9.04
0.31
2.37
0.28
2.81
0.52
1.56
2.91
0.10
1.86
2.89
0.11
81.95
8.41
0.49
3.28
0.05
1.89
1.39
1.07
1.71
0.12
1.60
2.89
0.10
87.3
3.94
0.19
1.53
0.03
0.11
2.54
0.16
1.6
0.03
8.27
4.05
0.05
42
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
r = 0.91
0.8
0.7
100
SiO2%
TiO2%
r = 0.85
0.6
0.5
0.4
0.3
0.2
0.1
0.0
60
0
2
4
6
8
10
12
14
0
2
4
Al2O3%
8
10
12
14
0.14
5
r = 0.82
r = 0.66
0.12
4
0.10
MnO%
Fe2O3%
6
Al2O3%
3
0.08
0.06
0.04
2
0.02
1
0.00
0
2
4
6
8
10
12
14
0
2
4
Al2O3%
6
8
10
12
14
Al2O3%
0.25
7.00
r = 0.5
0.20
r = 0.65
6.00
MgO%
CaO%
5.00
0.15
0.10
4.00
3.00
2.00
0.05
1.00
0.00
0.00
0
2
4
6
8
10
12
14
0
2
4
Al2O3%
8
10
8
0.50
12
14
r = 0.92
r = 0.6
0.40
6
K2O%
Na2O%
6
Al2O3%
0.30
0.20
4
2
0.10
0.00
0
2
4
6
8
10
12
14
Al2O3%
0
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
Al2O3%
Fig. 9. Co-variation of major elements versus Al2O3 for the Middle Miocene Kareem sandstones. Notice the positive correlation of Al2O3 with the major elements, SiO2 and
MgO show negative correlation.
(Fig. 11a). The discriminate degrees of Bhatia (1983) favor a passive
margin setting for Lower Kareem sandstone and active continental
margin setting for Upper Kareem sandstone (Fig. 11b). The plotting
of samples in the active continental margin field is not consistent
with the petrography and the chemical composition. According to
Bhatia (1983), Potter (1986) and Roser and Korsch (1988), passive
margin sandstones exhibit variable composition. Their characteristics may overlap those of active continental margin sandstones,
but they can be distinguished by their higher K2O/Na2O ratio and
depletion in Al2O3, CaO, Na2O and TiO2 with respect to those from
other settings, features reflecting their recycling and matured nature. Moreover, Bhatia classification gives poor results for fine siliciclastic sediments, which may be misclassified (Roser and Korsch,
1985, 1988). Tectonic discrimination diagrams of Roser and Korsch
(1986), and Bhatia (1983) suggest that both lower and upper
sandstone falls in the field of passive tectonic margin (Fig. 11c).
In silica-rich sands (SiO2 > 70%), with a K2O/Na2O ratio more
than unity (Bhatia, 1983) and a FeO + MgO content less than 5%
(Taylor and McLennan, 1985), the correlation with a passive margin setting is distinct. The sandstones of the Kareem Formation
match all these parameters (Table 5). The uniform chemical characteristics of the sandstones of the Kareem Formation (e.g., high
SiO2/Al2O3, K2O/Na2O; Table 5), strongly suggest that the Kareem
sandstones derived from recycled older rocks and also from stable
continental areas away from the rift area and deposited in a passive margin of a syn rift basin.
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
43
Fig. 10. (a) QtFL and (b) QmFLt ternary diagrams for the sandstones of the Kareem Formation, after Dickinson et al. (1983).
5.2. Source area weathering
Chemical data from the Lower and the Upper Kareem sandstones were plotted according to the formula of Nesbitt and Young
(1982) and Harnois (1988). The average CIW value of the Lower
and Upper Kareem sandstones is 84.6% and 94.7% respectively,
which indicates a high weathering (recycling) for both Lower and
Upper Kareem sandstones. These CIW values (n = 15, mean = 89.3,
s = 6.6; median = 89.5), in general, can be due to either absence of
intense recycling in a humid climate or intense recycling in an arid/
semiarid climate (Osae et al., 2006; Wanas and Abdel-Maguid,
2006).
The average CIA value of the Lower and Upper Kareem sandstones is 65.6% and 71.8% respectively, which indicates a moderate
degree of weathering in the source region for the Lower Kareem,
and a higher degree of chemical alteration for the Upper Kareem
44
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
Fig. 11. The tectonic discriminate function diagrams for the sandstones of the Kareem Formation of (a) Roser and Korsch (1988), (b) Bhatia (1983) and (c) Roser and Korsch
(1986) A: Oceanic island Arc, B: continental island Arc, C: active continental margin, D: passive margin.
sandstones. The low CIA values of the Lower Kareem sandstones
are due to the direct input of immature continent detrital minerals
into the depositional system (Bakkiaraj et al., 2010).
The variation in CIA values (n = 15, mean = 68.5, s = 12.1; median = 71.7), may reflect changes in the proportion of feldspars
and the various clay minerals in the analyzed samples. Size sorting
during transportation and deposition generally results in some degree of mineral differentiation which may modify the CIA (Pettijohn, 1975; Nesbitt and Young, 1982).
The sandstones of the Kareem Formation show upward decrease in maturity. The Lower Member of the Kareem Formation
shows a higher degree of alteration (CIA and CIW) than the Upper
Member. This may imply that the Upper Member of Kareem sandstones is geochemically moderately immature. Their source areas
possibly suffered from weathering, but this was not intense. The
Climate
precipitation
Semi-quantitative
weathering index
High
mountain
0
Relief
Moderate
hills
1
Low
plains
2
Semi arid and
Mediterranean
Temperate
subhumid
0
0
0
0
1
0
1
2
Tropical
humid
2
0
2
4
Fig. 12. Log-ratio plot after Weltje et al. (1998). Q: quartz, F: feldspar, RF: rock
fragments. Fields 1–4 refer to the semi-quantitative weathering indices defined on
the basis of relief and climate as indicated in the table.
presence of relatively high proportions of equant subangular to
subrounded feldspars, poor to moderate sorting, open matrix-supported texture and partly sutured quartz grains, point to short
transportation from a source area with a mix of weathering products from older bed rock (Pettijohn, 1975). In contrast, the Lower
Rahmi Member has higher alteration values characteristic of sediments derived from an extensively weathered, chemically mature,
source terrain.
On the other hand, the mineralogical Maturity Index (MI = [quartz/(quartz + feldspar + rock fragments]); Bhatia and Crook,
1986; Mansour et al., 1999), ranges from 0.64 to 0.94 (Fig. 6), suggesting moderate to relatively high mineralogical maturity. Also,
MI decreased from 0.94 at the Lower Member to 0.64 near the
top. These relationships may reflect that the chemical composition
may be correlated, to a great extent, with the petrographic modal
data.
Petrographic evidence such as heterogeneous roundness for different grains (coarser ones are rounded and finer ones are angular)
implies the importance of mechanical effects for grain shape configuration. Coarse-grained feldspars are related to a low degree of
chemical weathering. Moreover, the rounded quartz overgrowths
indicate recycling, which, in turn, can modify the compositional
data towards the quartz-rich sandstones. The point count data
for the sandstones of the Kareem Formation samples on Weltje
et al. (1998) diagram, shows that the Lower Kareem sandstones
plot in the field number 4, suggesting the sedimentation in a
Fig. 13. The effect of source rock on the composition of the sandstones of the
Kareem Formation using Suttner et al. (1981) diagram.
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
45
Fig. 14. (a) The ratio SiO2/Al2O3 and Q/(F + RF) in the different types of Kareem sandstones. (b) Chemical maturity of the sandstones of the Kareem Formation expressed by
bivariant plot SiO2 versus Al2O3 + K2O + Na2O, Fields after Suttner and Dutta (1986).
low-relief and tropical, humid climatic conditions, whereas the
Upper Kareem sandstone samples plot in the field number 2, indicating either deposition on a low-relief with a temperate and subhumid climate or on tropical, humid conditions within an area
with a moderate relief (Fig. 12). Many of the sandstone samples
plot in plutonic field, indicating a plutonic source (Fig. 12). The sedimentary environment of the Kareem Formation is probably one of
a linear fault controlled the coastline adjacent to a relatively low
relief hinterland with small scale alluvial drainage systems. Despite the subtropical to tropical sea conditions, carbonate production was inhibited due to siliciclastic input (Zahran, 2005).
QFRF ternary diagram of Suttner et al. (1981), indicate a metamorphic source rock in a humid climate for the Lower Kareem
sandstones and a plutonic source rock in a humid climate for the
Upper Kareem sandstones (Fig. 13). However, this particular diagram can discriminate only sources of metamorphic and plutonic
rocks (humid or arid conditions) and does not discriminate between different tectonic settings. The diagrams (Figs. 12 and 13)
are defined for first-cycle sediments and the effect of recycling
and long distance transportation can shift the data on these diagrams toward the humid conditions (Jafarzadeh and Hosseini-Barzi, 2008). These considerations probably imply that new diagrams
should be proposed such as those suggested in the field of sedimentary rock geochemistry (Armstrong-Altrin and Verma, 2005)
and already proposed in the area of igneous rock geochemistry
(e.g., Agrawal et al., 2004; Verma et al., 2006).
To make use of the chemical parameters, the ratio of SiO2/Al2O3
against that of quartz, quartzite and chert/(feldspar + rock fragments), (Q/F + RF) was plotted (Fig. 14a) which is interpreted to reflect the maturity of sandstones (Pettijohn, 1975). Higher SiO2 ratio
coincides with higher silica phases of quartz, quartzite and chert
which in turn reflect that such sandstones are mature. Fig. 14a
indicated that the sandstone maturity decreased from the Lower
to the Upper Kareem. A bivariant plot of SiO2 against total Al2O3 + K2O + Na2O proposed by Suttner and Dutta, 1986) was used in order to identify the maturity of the sandstones of the Kareem
Formation as a function of climate (Fig. 14b). This plot revealed
the semi-humid to humid climatic conditions of the samples
investigated.
Paleoweathering conditions can also be detected using the
Al2O3–CaO + Na2O–K2O (A–CN–K) ternary diagram of Nesbitt and
Young (1984) (Fig. 15), where unweathered rocks are clustered
along the left-hand side of the K-feldspar-plagioclase join (Nesbitt
and Young, 1984; Holail and Moghazi, 1998). All the samples ana-
Fig. 15. A–CN–K ternary diagram of molecular proportions of Al2O3–(CaO + Na2O)–
K2O for the Middle Miocene Kareem sandstones (after Nesbitt and Young (1984)).
Also plotted is the average upper continental crust (Taylor and McLennan, 1985), as
well as some rock forming minerals important in silicate rock weathering; shown at
the side is the CIA scale. Arrows 1–3 represent the weathering trends of
granodiorite, adamellite and granite, respectively (Nesbitt and Young, 1984). The
sandstones of the Kareem Formation fall closer to moderately to highly weathered
minerals.
lyzed here plot parallel to the Al2O3–K2O edge, supporting the conclusion that the sandstones of the Kareem Formation were derived
from a granite source terrain. The plotting of the samples away
from the weathering trend, along the A–K edge toward the K apex,
shows the samples are enriched in K and depleted in Ca and Na.
The high K2O contents of the sandstones can be explained in various ways. It may be due to post-depositional changes, probably
late diagenetic reactions occurring during and following burial
through the reaction of basin waters, trapped seawater or brines
with minerals of profiles, i.e. K-metasomatism, (Nesbitt and Young,
1989; Fedo et al., 1995). This process can occur through two different paths, representing the conversion of kaolinite (as a matrix) to
illite and/or conversion of plagioclase to K-feldspar (Fedo et al.,
1995). Another possibility is that the K is primarily related to the
presence of detrital K-bearing minerals (McLennan et al., 1983;
Nath et al., 2000; Zhang, 2004).
46
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
The sandstone samples of the Kareem Formation plot close to
Al2O3–K2O boundary, indicating moderate to intense weathering
conditions in the source area. Obviously the highest degree of
alteration (in terms of CIA) is compatible with the sediments having maximum kaolinite and less feldspar content. CIA values correlated well with kaolinite content (Fig. 6). They decrease upwards
with a decrease in kaolinite and increase in feldspar.
5.3. Provenance
A high percentage of quartz (92.2–96.6%) and textural features
such as medium to fine grains, moderately sorting and the subangular to subrounded shape and low-percentage of feldspar (2.5–
7.5%) and other rock fragments (0.1–2.6%); (Table 3), show transportation from distant/remote sources or extensive reworking of
the sediments and indicates a cratonic or a recycled source for
the Lower Kareem Rahmi Member (Al-Habri and Khan, 2008).
Whereas, the textural features such as medium to coarse grains,
poorly sorting and the subangular to subrounded shape and
high-percentage of unstable grain: feldspar (11.9–30.6%) and other
rock fragments (0.5–8.5%); (Table 4), indicate that the Upper Kareem Shagar sandstones show short transport distance and quick
burial.
The Kareem sandstones deposited in the craton interior to transitional continental (Fig. 10), derive from the exposed basement
shield area, probably platform or uplifted basement rocks. They
might be derived mainly from weathered and low-lying crystalline
basement rocks or from recycled sediments. The presence of mixed
altered and fresh feldspars may reflect immature sediments interfingered with more mature phases. This would favor a weathered
crystalline granitic source terrain (Pettijohn, 1975; Roser et al.,
1996; Akarish and El-Gohary, 2008).
Relatively unstrained monocrystalline quartz grains that contain common inclusions are present in all samples, suggesting a
plutonic origin (Basu et al., 1975; Potter, 1978; Hindrix, 2000).
The polycrystalline quartz grains composed of three or more crystals with straight to slightly curved intercrystalline boundaries
indicate that the sandstones of the Kareem Formation were derived
from plutonic igneous rocks (Folk, 1974; Blatt et al., 1980). The low
percentage of feldspar and rock fragments or their absence in many
samples especially from the Lower Kareem Rahmi Member favors a
cratonic source, mature transport regime and long moderate
chemical weathering in a warm dry climate (Amireh, 1991; AlHabri and Khan, 2008).
The quantitative petrography provides important information
on the nature of the source area. The high proportion of quartz,
as well as the dominance of K-feldspar over the more chemically
unstable plagioclase in the sandstones of the Kareem Formation
suggests that the source was exposed to prolonged weathering
and that the sediment is at least partly multicyclic (Osae et al.,
2006). This mineralogy is consistent with their derivation from
plutonic rocks. However, the presence of rare rounded detrital
quartz grains, sedimentary lithic fragments, and rounded grains
of zircon and tourmaline, suggest that a component of the provenance is older (pre-existing) sedimentary rocks.
Moreover, the presence of greater than 70% SiO2 implies the
sandstones are rich in quartz from quartz-rich crystalline provenance. K2O/Na2O ratio can be considered as a simplified chemical
provenance indicator (Potter, 1978). Higher values of this ratio reflect derivation from granites rather than from basic rocks. This is
also confirmed by the clay mineral content, as an illite and kaolinite were considered to be inherited from weathering horizons and
soils developed on silicic (granitic) rocks. In addition, the low percentage of smectite (9%) and the absence of chlorite clay minerals
also preclude mafic source rocks.
In the rift basins, arkoses are common and sandstones have low
mineralogical maturity because the sediment may have been derived from uplifted horsts along the rift where erosion pierced
the sedimentary cover and cut into the crystalline basement, as
is also the case with the sandstones of the Kareem Formation.
The coexistence of arkosic and subarkosic sandstones with subordinate quartzarenites was interpreted as an interplay of pulses
of rapid uplift of the source area and quick subsidence of the basin,
followed by a period of quiescence within an overall transgressive–
regressive cycle in a rift tectonic regime.
During quiescence, the first-cycle quartz sand may have been
supplied from a nearby quartz-rich source area. A unique combination of tropical climate, low relief, low rate of sedimentation and
long residence on the beach formed the mature, first-cycle quartzarenite (Suttner et al., 1981). However, the imprint of climate,
although preserved for the first 75 km of transportation in high
gradient streams, is rapidly destroyed as soon as a high-energy
marine environment (beach) is reached (Suttner et al., 1981). The
relative proportion of quartz (87.7%) to feldspars (9.9%) and lithic
fragments (2.4%) in the present study sediments is dependent
not only on the source rock and climate, but also to some extent
on the degree of stability of the basin of deposition (Dickinson
and Suczek, 1979). During basin instability, sediments supplied
from the source area were quickly buried and more or less retained
the original composition, except for the modification of unstable
constituents (lithic fragments and feldspars) induced by chemical
weathering, which has a greater capacity to alter sandstone composition (Basu, 1976; James et al., 1981; Franzinelli and Potter,
1983; Suttner and Dutta, 1986; Dutta, 1987).
The above-mentioned observations reveal that the sediments of
the sandstones of the Kareem Formation may have been derived
from a variety of source rocks (mixed provenance). This interpretation is also supported by the presence of abundant opaque mineral
grains including iron oxides (hematite), which reflect derivation
from metamorphic and igneous rocks. The presence of alkali feldspars indicates their source as plutonic and metamorphic rocks
(Trevena and Nash, 1981). The suite of heavy minerals including
zircon, rutile, and tourmaline indicates an acid igneous source for
these sandstones. While the presence of rounded grains of rutile
and zircon, is an indication of the reworked source for these
sandstones.
5.4. Diagenetic sequence
The role of diagenesis of the sandstones of the Kareem Formation was interpreted on the basis of pore geometry, size and filling
material. The depositional environment, composition, textures,
pore-fluid composition and migration and burial history are the
main factors which affect the Kareem Formation diagenesis
(Metwalli et al., 1987; Alsharhan and Salah, 1997). The main physical and chemical diagenetic processes have been identified as the
following:
Deposition of the Kareem Formation sands took place through
rapid influxes of terrigenous material that was deposited on the
neritic zone of the continental shelf. The sands were mildly compacted so that a fair proportion of the primary intergranular porosity was preserved, and some ductile components were slightly
compressed. Compaction led to partial leaching of detrital grains.
Sandstones are subjected to mechanical and chemical compactions during its progressive burial as evidenced from close packing
of detrital framework which has caused a reduction in primary
porosity of the sandstones (Fig. 4a and e). This compaction is also
evidenced by concave–convex, sutured contacts of neighboring
clastic grains (Fig. 4e) and a certain degree of stylolitization. The
occurrence of chemical compaction is clear along detrital quartz
grains. The presence of quartz fracturing (Figs. 4b and c and 7f)
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
and deformation of mud intraclasts provides evidence of mechanical compaction (Fig. 4f). The sandstones of the Kareem Formation
were subjected to some mechanical compaction till carbonate
cementation occurred which ceased the effect of mechanical compaction. However, mechanical compaction continued in sandstones with little or rare dolomite as indicated by their sutured
and long grain contacts (Umar et al., 2011).
Chemical compaction occurred by pressure dissolution both
along intergranular contacts and fractures (Zhang et al., 2008).
Feldspar dissolution is well recorded in some sandstone samples. This dissolution is due to relatively acidic conditions, in which
the stability of feldspars is reduced. Dissolution appears to postdate compaction (Fig. 5c). This process caused a local increase in
porosity.
Iron-oxide cement occurs as a coating around detrital grains
(Figs. 4b and c and 7d) and/or patches filling pore spaces in the
sandstones of the Kareem Formation. It predates other diagenetic
events, such as early silica and dolomite cement (Fig. 7d). The absence or weak coating at grain contacts suggests that the ironoxide mineral is of diagenetic origin, not an oxidized rim of detrital
grains. It appears that, the hematite cement in the sandstones of
the Kareem Formation may be derived in solution from iron rich
minerals such as hornblende, pyroxene, olivine, magnetite, biotite
and chlorite, which release their iron in sediments, under oxidizing
diagenetic environment, the iron was precipitated as hematite or
as goethitic precursor oxide and subsequently converted to hematite (Darwish and El-Araby, 1993).
Authigenic silica is common in sandstones that lack early calcite
and dolomite cements (Umar, 2007). The detrital core may be
clearly outlined by dust rims. Quartz overgrowths engulf, and thus
post-date, hematite (Figs. 4b and c and 7d), but are, in some cases,
engulfed by, and thus predate, anhydrite and/or dolomite (Figs.
4b–d, 5d and e and 7c). The presence of authigenic clays modified
the overgrowth habit of quartz (Rossi et al., 2002; Umar et al.,
2011). Quartz overgrowth is partially replaced by later dolomite
cement (Figs. 5e and 7c and f).
The kaolinite exists as pore filling aggregates (Fig. 7e) postdates the quartz overgrowth phase (Umar et al., 2011). SEM analysis indicates that mixed layer clays (illite–smectite) post-date
the quartz cementation (Fig. 7c).
The precipitation of secondary silica was accompanied, and
most probably succeeded by partial or complete dissolution of
the carbonate fragments (Fig. 4f). The presence of silica overgrowths maintained the framework, so that the oversize pores left
after the dissolution of the carbonate fragments were preserved
(Fig. 4f).
Carbonate cementation is represented by calcite and/or dolomite cements recorded in the quartzarenites, subarkose and arkose
47
of the Kareem Formation reflecting an increase in pH and/or temperature in the pore waters. The carbonate cements and pore-fills
are mainly dolomitic (Figs. 4b–d, 5c and d and 7f). The ions required for ferroan dolomite cement formation were probably derived from alumino-silicate grain dissolution, and clay mineral
transformation (Tucker and Wright, 1990). Cementation particularly by quartz and by dolomite prevented further significant compaction. Dolomite rhombs that found between the quartz grains
cause close-packed textures (Figs. 5d and 7f) of crystal mosaics
or isolated rhombs. The aggrading recrystallization of the primary
dolomite is recorded in the studied sandstone types (Fig. 7a and b).
Illite occurs as grain coating of detrital grains or pore filling cement (Fig. 7d). It is found mostly within the matrix and partly in
pore spaces, and therefore the textural relationship with other
authigenic mineral is not clear. For this reason, it is difficult to
determine the relative time of illite authigenesis.
Silica dissolution and replacement of quartz grains by calcareous cement was recorded in some samples (Fig. 5d). Silica dissolution and replacement by carbonate cements are controlled by
changes in pH, partial pressure of CO, and temperature; they typically occur when the pore waters are under saturated with respect
to carbonate (Pettijohn et al., 1987). This process leads to a decrease in sandstone porosity.
The chemistry of the interstitial fluid grows strongly alkaline
and unsaturated with silica; so the major parts of the silica overgrowths, and to a lesser extent, parts of the detrital quartz grains
were dissolved. This process causes a local increase in porosity.
Carbonate cements are partially leached (Fig. 5f) as the fresh
water influx and the pore fluids were rendered acidic.
As a result of dolomitization and expelling the excess calcium, a
rise in the Ca/Mg ratio of the interstitial fluid happened and led to
the precipitation of anhydrite both as pore filling (Fig. 4a and e)
and as a replacement of dolomite (Fig. 5d). It is probable that a
mixing with fresh water occurred at this phase supplying the sulfate ions (Tucker and Wright, 1990). Recrystallization of some
anhydrite clasts took place most probably at this stage.
Pyrite occurs in some sandstone samples and display typical
euhedral shapes (Fig. 5f). Pyrite replaced other diagenetic minerals,
indicating that it is the last diagenetic phase.
5.5. Paragenetic sequence
The inferred paragenetic sequence of the sandstones of the
Kareem Formation is shown in Fig. 16. The sandstones have undergone intense and complex episodes of diagenesis, including early
and late diagenesis due to the influence of depositional environment, deep burial and uplift. The paragenetic sequence is inferred
with respect to time by SEM, XRD and thin section study.
Fig. 16. Paragenetic sequence of the sandstones of the Kareem Formation, Gulf of Suez.
48
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
During early diagenesis, minor amounts of pore-filling and
replacement calcite and quartz overgrowths occurred. During burial, mechanical compaction started to reduce pore spaces. Compaction is documented by a tight grain supported fabric of sandstones.
The compaction continued in all sandstones till the precipitation of
massive carbonate (especially calcite) in some sandstones ceased
further compaction and continued up to a late stage in sandstones
with little carbonate cement. Mechanical compaction continued
from early to late diagenetic stages. Mechanical compaction can
be observed by a physical breakdown of feldspar grains (Fig. 5c).
The dissolution and alteration of unstable grains such as feldspar and granitic rock fragments to kaolinite (Fig. 7e) was the second important diagenetic event in terms of relative timings. Partial
kaolinitization of feldspar took place. The iron oxides were precipitated at the second diagenetic stage (Fig. 4b). Sources for iron
oxide (hematite) cements might be the libration of iron by alteration of iron rich minerals such as hornblende, pyroxene, olivine,
magnetite, biotite and chlorite. Chemical compaction was activated at this stage allowing pressure solution to provide the silica
for quartz cementation. Quartz cement had started to precipitate in
open pores before carbonate cementation. This is evidenced by the
presence of well developed quartz overgrowths engulfed and corroded by dolomite cement (Figs. 4b and c, 5d and 7c). Quartz overgrowth is well developed and continued to late diagenetic stage in
samples with little/or rare carbonate cement. The presence and
growth of illite on kaolinite indicates its later origin than kaolinite
(Fig. 7d). Also, rarely of mixed layer clays (illite–smectite) partially
embedded and grown on authigenic silica indicates its later origin
than quartz cementation.
The precipitation of authigenic silica was predated partial or
complete dissolution of the carbonate fragments as indicated by
well preserved oversize (moldic and vuggy) pores left after the dissolution of the carbonate fragments (Fig. 4f).
The carbonate cementation started slightly later than quartz
cementation as indicated by euhedral quartz overgrowths which
are embedded and partially replaced by dolomite (Fig. 4d). During
the alteration and the dissolution of bioclastic shell fragments, Mg
ions were librated and reacted to precipitate dolomite overgrowth
on calcite cement (Fig. 4f).
Illite may be formed diagenetically by a number of processes.
The most important processes include replacement of feldspar
and volcanic fragments particularly along thin cleavage planes
and illitization of kaolinite (Fig. 7d).
The late diagenetic events started by the dissolution and
replacement of silica by carbonate cements (Figs. 4c and 5d). This
process typically occurs when the pore waters are under saturated
with respect to carbonate (i.e., the interstitial fluid is strongly alkaline) so the major part of the silica overgrowths, and to a lesser extent, parts of the detrital quartz grains were dissolved. Partial
leaching of the carbonate cement occurred when the pore fluids
were rendered acidic.
Authigenic anhydrite typically occurs as pore filling and partially replaces dolomite cement (Fig. 5d). This indicates their later
origin after dolomitization. Octahedral pyrite crystallites locally replace dolomite cement (Fig. 5f) and authigenic clays, indicating
that it is the last diagenetic phase. It is probably formed during
the sulfate reduction phase.
The relative importance of compaction and cementation to
destruction of porosity of sandstone, within the Kareem Formation
is illustrated in Fig. 17, a Houseknecht plot (Houseknecht, 1987).
The data shows a two-fold distribution. The majority of points plot
in the cementation field, whereas a small clustered subpopulation
apparently lost porosity by compaction. Much of the porosity within the clustered subpopulation is locally to severely enhanced by
secondary dissolution. Alsharhan and Salah (1997) who studied
the Kareem Formation, indicated the same causes of porosity
reduction. They pointed out that primary porosity was originally
much higher but has been greatly reduced by successive phases
of cementation and mechanical compaction during diagenesis,
and that porosity reduction continued due to mechanical compaction in sandstones with little or rare carbonate cement.
The petrographic analyses reveal a number of controls on
porosity development, which include the depositional controls
(grain size, sorting, roundness, grain contact and grain density)
and the diagenetic controls (cementation and compaction). The
main controls on reservoir quality are carbonate and silica cement
and total clay contents (Fig. 18).
Petrographic examination of grain size, grain sorting and roundness against point counted porosity show positive correlations (Tables 1–4; Figs. 4b and c and 5c and d). However, these positive
relations reveal that the overall porosity development is probably
controlled by the interplay of cementation and secondary porosity
creation.
The study reveals that the porosity increases with samples of
floating to point contacts (Fig. 4b and c) and decreasing with long,
concave–convex and sutured contacts as shown in (Fig. 4e). A scatter plot of helium porosity and horizontal permeability against
point counted porosity show a positive degree of association
(Fig. 18a and b).
Type and nature of cement and pore-occluding cement control
on porosity development. A scatter plot of detrital and authigenic
clay, authigenic quartz overgrowth; carbonate cement, anhydrite
and other cement against point counted porosity show a poor degree of association (Fig. 18d–h).
Dolomite cement is the strong control on porosity. Dolomite cement, especially the non-ferroan poikilotopic type, tend to sit in
pores, blocking pores throats and so reduce permeability more
than grain coating cements such as quartz. In the sandstones of
the Kareem Formation, only samples with low dolomite cement
contents have very high permeability values. Samples of less than
Fig. 17. Houseknecht plot compaction and cementation versus porosity destruction
of Kareem sandstones, Gulf of Suez.
49
B
25
r = 0.63
20
15
10
5
0
0
10
20
Pointed counted porosity (%)
A
Point counted porosity (%)
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
25
r = 0.49
20
15
10
5
0
30
0
500
25
D
r = 0.5
20
15
10
5
0
2.6
2.65
2.7
2.75
2.8
r = 0.6
20
15
10
5
0
0
20
15
10
5
0
0.5
Point counted porosity (%)
Point counted porosity (%)
F
r = 0.56
10
5
0
1.6
2
Other cement (%)
point counted porosity (%)
Point counted porosity (%)
H
15
1.2
8
10
12
15
10
5
0
20
40
60
80
100
Total carbonate (%)
20
0.8
6
r = 0.55
0
r = 0.5
0.4
4
20
1
25
0
2
25
Quartz and feldspars overgrowth (%)
G
2000
Detrital and authigenic clays (%)
25
0
1500
25
Grain density (gm/cm3)
E
1000
Horizontal permeability (m.d)
Point counted Porosity (%)
C
Pointed counted porosity (%)
Helium Porosity (%)
25
r = 0.7
20
15
10
5
0
0
10
20
30
Anhydrite (%)
Fig. 18. Relationships of helium porosity, horizontal permeability, grain density and different rock cements versus visual point counted porosity, Kareem sandstones, Gulf of
Suez.
20% total carbonate generally have porosities greater than 12%,
while samples possessing greater than 12% total carbonate have
less than 10% porosity.
The helium porosity values of cored intervals range between 6%
and 30%, indicated poor to very good quality, while the horizontal
permeability values of most samples range between 200 m.d and
2090 m.d, indicated good to excellent quality.
The pore type and the main total porosity have been determined from petrographic and SEM studies in conjunction with conventional core analysis data. Three main pore types have been
recognized in the core samples: (a) primary intergranular macropores, (b) secondary intragranular mesopores, and (c) insignificant
intraparticle and intracrystalline micropores. Local occurrences of
moldic, fractured and vuggy porosity greatly enhance the petrophysical properties of most samples.
Pore interconnection is typically poor to good and may vary locally to be very good. Pores generally display irregular pore walls,
as a result of common dissolution enlargement of pores. Occasional
planar pore walls are associated with well developed quartz
overgrowths.
50
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
6. Conclusions
The Middle Miocene Kareem sandstones served as one of the
primary source of oil and gas in the southwestern part of the Gulf
of Suez including Zeit Bay Oil Field and East Zeit Oil Field. The Kareem Formation disconformably overlies the Rudies Formation and
unconformably overlies by the Belayim Formation. The sandstones
of the Kareem Formation are mostly quartzarenites with subordinate subarkoses and arkoses. Quartzarenites present in the Lower
Kareem Rahmi Member where the subarkoses and arkoses
recorded only in the Upper Kareem Shagar Member. Dolomite,
calcite, anhydrite and pyrite are important accessory authigenic
and detrital components.
In The Lower Kareem, sandstones are mature and derived from
craton interior to transitional continental setting (i.e., sandstones
were transported from the far along the rift). This indicated by
the low percentage of unstable grain such as feldspar <4% and other
rock fragments <2%, the dominance of monocrystalline quartz, and
most of feldspar grains altered. However, the Upper Kareem sandstones are derived from craton interior, transitional continental
and recycled orogenic setting. The high percentage of unstable
grain >15%, indicate that the Upper Kareem sandstones show short
transport distance and quick burial. This means that the Upper
Kareem sandstones are typically rift sandstone and their deposition
constrained the beginning of the faulting in the studied area.
The sandstones of the Kareem Formation show upward decrease in alteration (CIA and CIW) and also show upward decrease
in maturity (MI). These relationships may reflect that the chemical
composition may be correlated, to a great extent, with the petrographic modal data.
Petrographic analyses reveal a number of controls on porosity
development, which include both textural and mineralogical factors. Grain size, grain sorting and roundness against point counted
porosity show positive correlations. However, these positive relations reveal that the overall porosity development is probably controlled by the interplay of cementation and secondary porosity
creation. The study also reveals that the point counted porosity is
directly proportional to helium porosity, horizontal permeability
and connectivity, but it inversely proportional to grain density.
Sandstone reservoir quality is largely determined by diagenetic
processes that either reduce or enhance porosity. The most important diagenetic processes in the sandstones of the Kareem Formation are compaction, cementation by dolomite, calcite, quartz,
anhydrite, clays, and iron oxide. Compaction, both mechanical
and chemical, has a large influence on the intergranular volume.
The intergranular volume is partly correlated to the amount of diagenetic carbonates, indicating that porosity reduction continued in
sandstones with little or no carbonate cement, whereas massive
cementation by dolomite prevented later compaction and preserved a larger intergranular volume. Mechanical compaction and
authigenic cements reduce the porosity and permeability, whereas
dissolution of unstable clastic grains and soluble cements increase
porosity in sandstone. The present porosity of sandstone varies
from 6% to 30% with an average of 18%. The primary porosity of
the sandstones is reduced due to intense mechanical compaction
and due to filling of early authigenic cements such as carbonate,
quartz, clay minerals and iron oxides.
The successive burial was responsible for the reduction in
porosity due to compaction as indicated by long and sutured contact between neighboring clastic grains. In some samples, the early
carbonate cement reduced or prevented further compaction and
the resulting close packing of clastic grains. Authigenic kaolinite
and iron oxide also played an important role in the preservation
of porosity. Kaolinite and mixed layer clays have reduced the
permeability but preserve porosity as intercrystalline porosity.
Grain-coating rims of iron oxide in some cases prevented the formation of quartz overgrowths and thus preserved porosity.
The dissolution of unstable clastic grains began in the early
stages of diagenesis which produced an empty pore volume for
secondary cementation. Some pores were protected by clay and/
or iron oxide coats and remained open. Another episode of dissolution occurred in the late stages and dissolved authigenic minerals,
mainly carbonates, thus producing secondary porosity.
Dolomite and ferroan dolomite cements are the strong control
on porosity. Samples of less than 20% total carbonate generally
have porosities greater than 12%, while samples possessing greater
than 12% total carbonate have less than 10% porosity.
Petrophysically, the reservoir quality of the Kareem Formation
is locally moderate- to good. Porosity types are dominated by primary interparticle forms and secondary intragranular and insignificant intraparticle and intracrystalline micropores. A local
occurrence of mm-sized vuggy and moldic pores following carbonate dissolution greatly enhances the petrophysical properties of
many arenites.
Acknowledgments
The author is especially grateful to the Suez oil company
‘‘SUCO’’ for providing the available data needed to complete this
work. The author acknowledges the journal reviewer for his very
constructive and helpful comments as well as for editorial comments by P. Eriksson, which helped to improve the manuscript.
References
Abu-Zeid, M.M., Amer, K.M., El-Mohammady, R.A., 1989. Petrology, Mineralogy and
Provenance of Sandstones of ‘‘Nubia’’ Facies in West Central Sinai. Earth Sci.
Ser., 3. Middle East Research Centre, Ain Shams University. pp. 20–34.
Abu-Zeid, M.M., Amer, K.M., Yanni, N.N., El-Wekeil, S.S., 1991. Petrology, mineralogy
and sedimentation of the Paleozoic sequence of Gabal Qattar, Wadi Feiran,
Sinai, Egypt. Journal Geology 34, 145–169.
Agrawal, S., Guevara, M., Verma, S.P., 2004. Discriminant analysis applied to
establish major element field boundaries for tectonic varieties of basic rocks.
International Geology Review 46 (7), 575–594.
Ahmad, A.H., Bhat, G.M., 2006. Petrofacies, provenance and diagenesis of the dhosa
sandstone member (Chari Formation) at Ler, Kachchh sub-basin, Western India.
Journal of Asian Earth Sciences 27, 857–872.
Akarish, A.I.M., El-Gohary, A.M., 2008. Petrography and geochemistry of lower
Paleozoic sandstones, East Sinai, Egypt: implications for provenance and
tectonic setting. Journal of African Earth Sciences 52, 43–54.
Al-Habri, O.A., Khan, M.M., 2008. Provenance, diagenesis, tectonic setting and
geochemistry of Tawil sandstone (Lower Devonian) in central Saudi Arabia.
Journal of Asian Earth Sciences Bulletin 33, 278–287.
Alsharhan, A.S., Salah, M.G., 1994. Geology and hydrocarbon habitat in rift setting:
southern Gulf of Suez, Egypt. Canadian Journal of Petroleum Geology Bulletin
42, 312–331.
Alsharhan, A.S., Salah, M.G., 1995. Geology and Hydrocarbon Habitat in a rift
setting: northern and central Gulf of Suez, Egypt. Canadian Journal of Petroleum
Geology Bulletin 43, 156–176.
Alsharhan, A.S., Salah, M.G., 1997. The Miocene Kareem formation in the southern
Gulf of Suez, Egypt: a review on stratigraphy and petroleum geology. Canadian
Journal of Petroleum Geology Bulletin 20, 327–346.
Amer, K.M., Abu-Zeid, M.M., El- Mohammady, R.A., 1989. Particle-Size Distribution
and Depositional Environment of the Sandstones of ‘‘Nubia’’ Facies in West
Central Sinai. Earth Sci. Ser., 3. Middle East Research Centre, Ain Shams
University, pp. 146–160.
Amireh, B.S., 1991. Mineral composition of the Cambrian–Cretaceous Nubian series
of Jordon: provenance, tectonic setting and climatological implication.
Sedimentary Geology 71, 99–119.
Armstrong-Altrin, J.S., Verma, S.P., 2005. Critical evaluation of six tectonic setting
discrimination diagrams using geochemical data of Neogene sediments from
known tectonic settings. Sedimentary Geology 177 (1–2), 115–129.
Armstrong-Altrin, J.S., Lee, Y.I., Verma, S.P., Ramasamy, S., 2004. Geochemistry of
sandstones from the Upper Miocene Kudankulam Formation, southern India:
implication for provenance, weathering and tectonic setting. Journal of
Sedimentary Research 74 (2), 285–297.
Bakkiaraj, R.Nagendra., Nagarajan, R., Armstrong-Altrin, J.S., 2010. Geochemistry of
sandstones from the Upper Cretaceous Sillakkudi Formation, Cauvery basin,
southern India: implication for provenance. Journal of Geologic, Society, India
76, 453–467.
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
Basu, A., 1976. Petrology of Holocene fluvial sand derived from plutonic source
rocks: implications to palaeoclimatic interpretation. Journal of Sedimentary
Petrology 46, 694–709.
Basu, A., Young, S., Suttner, L.J., James, W.C., Mack, C.H., 1975. Re-evaluation of the
use of Undulatory extinction and polycrystallinity in detrital quartz for
provenance interpretation. Journal of Sedimentary Petrology 45, 873–882.
Beard, D.C., Weyl, P.K., 1973. Influence of texture on porosity and permeability of
unconsolidated sand. American Association of Petroleum Geologists Bulletin 57,
349–369.
Bhatia, M.R., 1983. Plate tectonics and geochemical composition of sandstones.
Journal of Geology 91, 611–627.
Bhatia, M.R., Crook, K.A.W., 1986. Trace element characteristics of greywackes and
tectonic setting discrimination of sedimentary basins. Contributions to
Mineralogy and Petrology 92, 181–193.
Bjørlykke, K., Egeberg, P.K., 1993. Quartz cementation in sedimentary basins.
American Association of Petroleum Geologists Bulletin 77, 1538–1548.
Bjørlykke, K., Aagaard, P., Dypvik, H., Hastings, A.S., Harper, D.S., 1986. Diagenesis
and reservoir properties of Jurassic sandstones from the Haltenbanken area,
offshore mid-Norway. In: Spencer, A.M., Holter, E., Cambell, C.J., Hanslien,
P.H.H., Nysæther, E., Ormaasen, E.G. (Eds.), Habitate of Hydrocarbons of the
Norwegian Continental Shelf. Graham and Trotman, London, pp. 275–276.
Blatt, H., Middleton, G., Murray, R., 1980. Origin of Sedimentary Rocks. PrenticeHall, New Jersey.
Boles, J.R., Franks, S.G., 1979. Clay diagenesis in Wilcox sandstones of southwest
Texas: implications of smectite diagenesis on sandstone cementation. Journal of
Sedimentary Petrology 49, 55–70.
Burley, S.D., Kantorowicz, J.D., 1986. Thin section and SEM textural criteria for the
recognition of cement-dissolution porosity in sandstones. Sedimentology 33,
587–604.
Chamley, H., 1990. Clay Sedimentology. Springer-Verlag, Berlin.
Cingolani, C.A., Manassero, M., Abre, P., 2003. Composition, provenance, and
tectonic setting of Ordovician siliciclastic rocks in the San Rafael block:
southern extension of the Precordillera crustal fragment, Argentina. Journal of
South American Earth Sciences 16 (1), 91–106.
Darwish, M., El-Araby, A.M., 1993. Petrography and diagenetic aspects of some
siliciclastic hydrocarbon reservoirs in relation to the rifting of the Gulf of Suez.
Egyptian Journal of Geology 3, 1–25.
Dickinson, W.R., Suczek, C.A., 1979. Plate tectonics and sandstone compositions.
American Association of Petroleum Geologists Bulletin 63, 2164–2182.
Dickinson, W.R., Beard, L.S., Brakenridge, G.R., Erjavec, J.L., Ferguson, R.C., Inman,
K.F., Knepp, R.A., Lindberg, F.A., Ryberg, P.T., 1983. Provenance of North
American Phanerozoic sandstones in relation to tectonic setting. Geological
Society of America Bulletin 94, 222–235.
Dickson, J.A.D., 1965. A modified staining technique for carbonates in thin section.
Nature 205, 587.
Dott, R.H., 1964. Wackes, greywacke and matrix: what approach to immature
sandstone classification. Journal of Sedimentary Petrology 34, 625–632.
Dutta, P.K., 1987. Origin of rarity of first cycle quartzarenite (abs). American
Association of Petroleum Geologists Bulletin 71, 551p.
Dutton, S.P., 1993. Influence of provenance and burial history on diagenesis of
Lower Cretaceous Frontier Formation sandstones, Green River Basin, Wyoming.
Journal of Sedimentary Petrology 63, 665–667.
Dutton, S.P., Diggs, T.N., 1990. History of quartz cementation in the Lower
Cretaceous Travis Peak Formation, East Texas. Journal of Sedimentary
Petrology 60, 191–202.
EGPC Stratigraphic Committee, 1964. Oligocene and Miocene rock Stratigraphy of
the Gulf of Suez Region, Egypt, Report, 142 P.
EGPC Stratigraphic COMMITTEE, 1974. Miocene rock stratigraphy of Egypt. Journal
of Egyptian Geological Society 18, 1–59.
El-ghali, M.A., Morad, S., Mansburg, H., Miguel, A.C., Sirat, M., Ogle, 2009. Diagenetic
alterations to marine transgression and regression in fluvial and shallow marine
sandstones of the Triassic Buntsandstein and keuper sequence, the Paris basin,
France. Marine and Petroleum Geology 26, 289–309.
Evans, A.L., 1990. Miocene sandstone provenance relations in the Gulf of Suez;
insights into synrift unroofing and uplift history. American Association of
Petroleum Geologists Bulletin 74, 1386–1400.
Fedo, C.M., Nesbitt, H.W., Young, G.M., 1995. Unraveling the effects of potassium
metasomatism in sedimentary rocksand paleosols, with implications for
paleoweathering conditions and provenance. Geology 23, 921–924.
Folk, R.L., 1974. Petrology of Sedimentary Rocks. Hemphill Publication Co., Austin,
Texas.
Folk, R.L., 1980. Petrology of Sedimentary Rocks. Hemphill, Austin, Texas, 182 p.
Franzinelli, E., Potter, P.E., 1983. Petrology, chemistry and texture of modern river
sands, Amazon River System. Journal of Geology 91, 23–39.
Harnois, L., 1988. The CIW index: a new chemical index of weathering. Sedimentary
Geology 55, 319–322.
Hawkins, P.J., 1978. Relationship between diagenesis, porosity reduction and oil
replacement in Late Carboniferous sandstone reservoirs, Bothamsall oil field, E.
Midlands. Journal of Geological Society of London 135, 7–24.
Herron, M.M., 1988. Geochemical classification of terrigenous sands and shales
from core or log data. Journal of Sedimentary Petrology 58, 820–829.
Hilaly, H., Darwish, M., 1986. Petrographic, diagenesis and sedimentological history
of the pre Belayim sedimentary sequence and their reservoir characteristics,
Zeit Bay Oil Field, Gulf of Suez, Egypt. 8th EGPC Exploration Seminar, Cairo 1, pp.
406–429.
51
Hindrix, M.S., 2000. Evaluation of Mesozoic sandstone composition, southern
Junggar, northern Tarim and western Turran basins, northwest China: a detrital
record of the ancestral Tian Shan. Journal of Sedimentary Research 70, 520–532.
Holail, H.M., Moghazi, A.M., 1998. Provenance, tectonic setting and geochemistry of
graywackes and siltstones of the Late Precambrian Hammamat Group, Egypt.
Sedimentary Geology 116, 227–250.
Houseknecht, D.W., 1987. Assessing the relative importance of compaction
processes and cementation to reduction of porosity in sandstone. American
Association of Petroleum Geologists Bulletin 71, 637–642.
Houseknecht, D.W., 1988. Intergranular pressure solution in four quartzose
sandstones. Journal of Sedimentary Petrology 58, 228–246.
Hower, J., Eslinger, E.V., Hower, M.E., Perry, E.A., 1976. Mechanism of burial
metamorphism of argillaceous sediments, 1-mineralogical and chemical
evidence. American Association of Petroleum Geologists Bulletin 87, 725–737.
Jafarzadeh, M., Hosseini-Barzi, M., 2008. Petrography and geochemistry of Ahwaz
Sandstone Member of Asmari Formation, Zagros, Iran: implications on
provenance and tectonic setting. Revista Mexicana de Ciencias Geológicas 25
(2), 247–260.
James, W.C., Mack, G.H., Suttner, L.J., 1981. Relative alteration of microcline and
sodic plagioclase in semiarid and humid climates. Journal of Sedimentary
Petrology 51, 151–164.
Jin, Z., Li, F., Cao, J., Wang, S., Yu, J., 2006. Geochemistry of Daihai Lake sediments,
Inner Mongolia, north China: implications for provenance, sedimentary sorting
and catchment weathering. Geomorphology 80, 147–163.
Kastner, M., 1971. Authigenic feldspars in carbonate rocks. American Mineralogist
56, 1403–1442.
Keller, W.D., 1956. Clay minerals as influenced by environments of their formation.
American Association of Petroleum Geologists Bulletin 40, 2689–2710.
Lonnie, T.P., 1982. Mineralogic and chemical composition of marine and nonmarine
transitional clay beds on south shore of Long Island, New York. Journal of
Sedimentary Petrology 52, 529–536.
Mansour, A.M., Kurzweil, H., Osman, M.R., 1999. Sedimentary nature of Nile
sediments in Upper Egypt: relationships and implications to weathering,
climate of provenance. Sedimentology (Egypt) 7, 37–54.
McBride, E.F., 1963. A classification of common sandstones. Journal of Sedimentary
Petrology 33, 664–669.
McLennan, S.M., Taylor, S.R., Eriksson, K.A., 1983. Geochemistry of Archean shales
from the Pilbara Supergroup, Western Australia. Geochimica et Cosmochimica
Acta 47, 1211–1222.
Metwalli, M.H., Wali, A.M., Abd El-Shafy, A., 1987. Cretaceous petroleum-bearing
rock types-their diagenesis and significance in the Gulf of Suez area, Egypt.
Sedimentary Geology 53, 269–304.
Morad, S., 1998. Carbonate cementation in sandstones; distribution patterns and
geochemical evolution. In: Morad, S. (Ed.), Carbonate Cementation in
Sandstones, vol. 26. International Association of Sedimentologists, pp. 1–26
(Special Publication).
Morad, S., Ketzer, J.M., De Ros, F., 2000. Spatial and temporal distribution of
diagenetic alterations in siliciclastic rocks: implications for mass transfer in
sedimentary basins. Sedimentology 47 (Suppl. 1), 5–120.
Nath, B.N., Kunzendorf, H., Pluger, W.L., 2000. Influence of provenance, weathering
and sedimentary processes on the elemental ratio of the fine-grained fraction of
the bed load sediments from the Vembanad Lake and the adjoining continental
shelf, southwest Coast of India. Journal of Sedimentary Research 70, 1081–1094.
Nesbitt, H.W., Young, G.M., 1982. Early Proterozoic climates and plate motions
inferred from major element chemistry of lutites. Nature 299, 715–717.
Nesbitt, H.W., Young, G.M., 1984. Prediction of some weathering trends of plutonic
and volcanic rocks based on thermodynamic and kinetic considerations.
Geochimica et Cosmochimica Acta 48, 1523–1534.
Nesbitt, H.W., Young, G.M., 1989. Formation and diagenesis of weathering profiles.
Journal of Geology 79, 129–147.
Osae, S., Asiedu, D.K., Banoeng-Yakubo, B., Koeberl, C., Dampare, S.B., 2006.
Provenance and tectonic setting of Late Proterozoic Buem sandstones of
southeastern Ghana: evidence from geochemistry and detrital modes. Journal
of Asian Earth Sciences 44, 85–96.
Pettijohn, F.J., 1963. Chemical composition of sandstones-excluding carbonate and
volcanic sands. In: Data of Geochemistry, sixth ed., US Geol. Surv. Prof. Paper
440-S, 19 p.
Pettijohn, F.J., 1975. Sedimentary Rocks, third ed. Harper and Row, New York, 628 p.
Pettijohn, F.J., Potter, P.E., Siever, R., 1972. Sand and Sandstones. Springer-Verlag,
New York.
Pettijohn, F.G., Potter, P.E., Siever, R., 1973. Sand and Sandstone. Springer-Verlag,
618 p.
Pettijohn, F.G., Potter, P.E., Siever, R., 1987. Sand and Sandstone. Springer, New York,
553 p.
Potter, P.E., 1978. Petrology and chemistry of modern Big River sands. Journal of
Geology 86, 423–449.
Potter, P.E., 1986. South America and a few grains of sand: Part 1– beach sands.
Journal of Geology 94, 301–319.
Rodrigo, D.L., Luiz, F.D.R., 2002. The role of depositional setting and diagenesis on
the reservoir quality of Devonian sandstones from the Solimones Basin,
Brazilian Amazonia. Marine and Petroleum Geology 19, 1047–1071.
Rollinson, H.R., 1993. Using Geochemical Data: Evaluation, Presentation,
Interpretation. Longman, United Kingdom, 352p.
Roser, B.P., Korsch, R.J., 1985. Plate tectonics and geochemical composition of
sandstones: a discussion. Journal of Geology 93, 81–84.
52
S.M. Zaid / Journal of African Earth Sciences 85 (2013) 31–52
Roser, B.P., Korsch, R.J., 1986. Determination of tectonic setting of sand-stone–
mudstone suites using SiO2 content and K2O/Na2O ratio. Journal of Geology 94,
635–650.
Roser, B.P., Korsch, R.J., 1988. Provenance signatures of sandstone–mud-stone suites
determined using discriminant function analysis of major-element data.
Chemical Geology 67, 119–139.
Roser, B.P., Cooper, R.A., Nathan, S., Tulloch, A.J., 1996. Reconnaissance sandstone
geochemistry, provenance, and tectonic setting of the lower Paleozoic terraines
of the West Coast and Nelson, New Zealand. New Zealand Journal of Geology
and Geophysics 39, 1–16.
Rossi, C., Kalin, O., Arribas, J., Tortosa, A., 2002. Diagenesis, provenance and reservoir
quality of Triassic TAGI sandstones from Ourhoud field, Berkine (Ghadames)
Basin, Algeria. Marine and Petroleum Geology 19, 117–142.
Said, R., 1962. The Geology of Egypt. Elsevier, Amsterdam, New York, 317p.
Said, R., 1990. The Geology of Egypt. A.A. Balkema Publishers, Rotterdam,
Netherlands, 734p.
Salah, M.G., 1994. Geology of the Northwestern Red Sea with Special Emphasis on
the Petrology, Sedimentology and Hydrocarbon Potential of the Miocene
Kareem Formation. Unpublished PhD. Thesis, Cairo Univ. 166p.
Salem, A.M., Morad, S., Luiz, F., Mato, I.S., Al-Aasm, 2000. Diagenesis and reservoirquality evolution of fluvial sandstones during progressive burial and uplift:
evidence from the Upper Jurassic Boipeba Member, Reconcavo basin, northern
Brazil. American Association of Petroleum Geologists Bulletin 84, 1015–1040.
Saudi, A.M., 1992. Subsurface Geology of Kareem Formation, Southern Gulf of Suez,
Egypt. M.Sc. Thesis, Al Azhar University, 264 p.
Schmid, S., Worden, R.H., Fisher, Q.J., 2004. Diagenesis and reservoir quality of the
Sherwood sandstone (Triassic) corrib field, slyne basin, west of Ireland. Marine
and Petroleum Geology 21, 299–315.
Schwab, F.L., 1975. Framework mineralogy and chemical composition of continental
margin-type sandstone. Geology, Bulletin 3, 487–490.
Sullivan, M.D., Haszeldine, R.S., Fallick, A.E., 1990. Linear coupling of carbon and
strontium isotopes in Rotliegend sandstone, North Sea: evidence for cross
formational flow. Geology, Bulletin 18, 1215–1218.
Suttner, L.J., Dutta, P.K., 1986. Alluvial sandstone composition and palaeoclimate:
framework mineralogy. Journal of Sedimentary Petrology 56, 329–345.
Suttner, L.J., Basu, A., Mack, G.M., 1981. Climate and the origin of quartzarenites.
Journal of Sedimentary Petrology 51, 1235–1246.
Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: Its Composition and
Evolution. Blackwell Science Publisher, 312 p.
Tewfik, N., Harwood, C., Deighton, I., 1992. The Miocene Rudies and Kareem
formations in the Gulf of Suez: Aspects of sedimentology and geohistory. 11th
EGPC. Exploration Seminar, vol. 1, Cairo, pp. 84–113.
Trevena, A.S., Nash, W.P., 1981. An electron microprobe study of detrital feldspar.
Journal of Sedimentary Petrology 51, 137–150.
Tsuzuki, Y., Kawabe, I., 1983. Polymorphic transformations of kaolin minerals in
aqueous solutions. Geochimica et Cosmochimica Acta 47, 59–66.
Tucker, M.E., Wright, V.T., 1990. Carbonate Sedimentology. Blackwell, 482p.
Umar, M., 2007. Facies Distribution, Depositional Environment, Provenance and
Reservoir Characters of Upper Cretaceous Succession, Kirthar Fold Belt Pakistan.
Ph.D. Thesis, Centre of Excellence in Mineralogy, University of Baluchistan,
Pakistan, 191p.
Umar, M., Friis, H., Khan, A., Kassi, A.M., Kasi, A.K., 2011. The effects of diagenesis on
the reservoir characters in sandstones of the Late Cretaceous Pab Formation,
Kirthar Fold Belt, southern Pakistan. Journal of Asian Earth Sciences 40 (2), 622–
635.
Verma, S.P., Guevara, M., Agrawal, S., 2006. Discriminating four tectonic settings:
five new geochemical diagrams for basic and ultrabasic volcanic rocks based on
log-ratio transformation of major-element data. Journal of Earth System Science
115 (5), 485–528.
Walderhaug, O., 1994. Temperatures of quartz cementation in Jurassic sandstones
from Norwegian continental shelf-evidence from fluid inclusion. Journal of
Sedimentary Research 64, 311–324.
Wanas, H.A., Abdel-Maguid, N.M., 2006. Petrography and geochemistry of the
Cambro-Ordovician Wajid Sandstone, southwest Saudi Arabia: implications for
provenance and tectonic setting. Journal of Asian Earth Sciences 27, 416–429.
Weltje, G.J., Meijer, X.D., De Boer, P.L., 1998. Stratigraphic inversion of siliciclastic
basin fills: a note on the distinction between supply signals resulting from
tectonic and climatic forcing. Basin Research 10, 129–153.
Youssef, A., 1986. Coastal to shallow marine Miocene facies in Zeit Bay area, Gulf of
Suez, 8th EGPC. Exploration Seminar, vol. 1, Cairo, pp. 344–359.
Zahran, I.M., 2005. Petrology and Lithostratigraphy of the Miocene Rocks, Amal
Field, Gulf of Suez, Egypt and its Hydrocarbon Potentiality. Unpublished PhD.
Thesis, Zagazig University, 261p.
Zaid, S.M., 2012. Provenance, diagenesis, tectonic setting and geochemistry of
Rudies sandstone (Lower Miocene), Warda Field, Gulf of Suez, Egypt. Journal of
African Earth Sciences 66–67, 56–71.
Zhang, K.L., 2004. Secular geochemical variations of the Lower Cretaceous
siliciclastic from central Tibet (China) indicate a tectonic transition from
continental collision to back-arc rifting. Earth and Planetary Science Letters 229,
73–89.
Zhang, J., Qin, L., Zhongjie, Z., 2008. Depositional facies, diagenesis and their impact
on the reservoir quality of Silurian sandstones from Tazhong area in central
Tarim basin, western China. Journal of Asian Earth Sciences Bulletin 33, 42–60.