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ISSN 1661-5468
1
Department of Chemistry and Earth Sciences, College of Science, University of Qatar, P.O. Box 2713 Doha, Qatar,
hamadsaad@qu.edu.qa.
2
Department of Environmental Sciences, Faculty of Science, University of Alexandria, Moharam Bey 21511,
Alexandria, Egypt, mohamedibrahim59@hotmail.com.
Revue de Paléobiologie, Genève (juin 2005) 24 (1) : 225-241
Facies and palynofacies characteristics of the Upper Jurassic Arab D reservoir
in Qatar
Hamad AL-SAAD
1
& Mohamed I.A. IBRAHIM
2
Abstract
The oil producer Arab “D” unit in Qatar as well as in eastern Arabian Peninsula is composed of limestone and dolomitic limestone
assigned to the Kimmeridgian age. In Qatar, this member reveals the presence of six rhythmic microfacies of mudstone (micrite),
wackestone, dolomitic wackestone, packstone, grainstone and anhydrite. These sediments are believed to be deposited in numerous
short-term transgressive-regressive cycles, but generally the Arab D member represents a regressive cycle. The grainstone facies in the
middle part of the unit is rich in benthic foraminifera belonging to Kurnubia and Pfenderina.
Palynological analysis yielded ecologically and biostratigraphically significant dinoflagellate cyst species such as Cribroperidinium
globatum, C. longicorne, Dichadogonyaulax chondra, D. pannea, Epiploshaera bireticulata, Geochteodinia antennata, Systematophora
areolata and S. penicillata, giving evidence for a late Kimmeridgian age of the Arab D member. Amorphous organic matter is the
dominant element of the particulate organic matter. The Arab D member may have been deposited in shallow water of the middle
shelf depth (30-50 m) under arid to semiarid climatic conditions as deduced from the presence of Classopollis pollen and the capping
anhydrite.
Key words
Foraminifera, palynofacies, Jurassic, Qatar, Arab D.
1. INTRODUCTION
The Upper Jurassic sediments in the Arabian Peninsula
are typically composed of shallow-water limestones and
dolomites interbedded with restricted facies anhydrites.
This interval is considered the largest reservoirs in the
Middle East and the most important sequence for the oil
industry in the world since it contains about 50 % of the
oil and gas reservoirs of the world. In Qatar, no surface
Jurassic rocks are exposed. In this area, the distribution of
the subsurface Upper Jurassic sediments is controlled by
Qatar-Fars Arch, which is trending NNE-SSW (Fig. 1).
This was a positive structure during the Paleozoic and
gradually subsided during Jurassic times (Saint-Marc,
1987).
The present work is based on core and cutting samples
taken from three wells from onshore (Dukhan Field) and
offshore (Idd El-Shargi and Bul Hanine fields), Qatar
(Fig. 1). Fifty-seven samples were chosen from different
lithofacies to represent the Arab D reservoir. Thin sections,
crushed samples and SEM photographs were prepared
and have been used for the microfacies, microfaunal
and palynological analyse and the characterisation of
the total organic carbon content. It aims to document the
microfossil and palynofacies contents and delineate the
paleoenvironmental conditions that prevailed during the
deposition of these rocks in Qatar.
2. REGIONAL STRATIGRAPHY
The Upper Jurassic of the Arabian Peninsula is
subdivided from older to younger into the Hanifa,
Jubailah, Arab Formations and the Hith Anhydrite
(Table 1). The Hanifa and Jubailah Formations are
assigned to the Oxfordian/early Kimmeridgian stages.
While, the Arab Formation and the Hith Anhydrite are
assigned to the Kimmeridgian/Tithonian stages (POWERS,
1968). In this area, the Arab Formation comprises four
reservoir units (members) : Arab D, Arab C, Arab B and
Arab A in ascending stratigraphic order. These sediments
have been described by many workers such as (STEINEKE
et al., 1958 ; POWERS et al., 1966 ; POWERS, 1968 ; SUGDEN
& STANDRING, 1975 ; ALSHARHAN & KENDALL, 1986 ;
MOSHRIF, 1987 ; BEYDOUN, 1988 ; ALSHARHAN & NAIRN,
1994 ; AL-SILWADI et al., 1996 ; MEYER et al., 1996 ; AL-
HUSSEINI, 1997 ; AL-SAAD & SADOONI, 2001).
The Arab Formation obtained its name from the type
section in western Saudi Arabia. These units are
mainly formed by cycles of shallow-water carbonates
and evaporite facies. The Arab D reservoir is a well-
known unit throughout the eastern Arabian Peninsula
and has almost the same lithological features. Due to
the extensive dissolution of the anhydrite beds at the
outcrop, the type section (58.5 m) was defined in the
well Dammam-7 in eastern Saudi (POWERS et al., 1966).
It is composed of dolomitic limestones in the lower part,
limestones in the middle part and limestones with a thick
layer of anhydrite in the upper part. The main microfossil
content in this unit are of Clypeina jurassica, C. cf.
hanabatensis, Cylindroporella arabica, Kurnubia spp.
and Nautiloculina spp. Based on these fossils, the Arab
D was assigned an Early Kimmeridgian age (POWERS,
1968).
3. STRATIGRAPHIC NOMENCLATURE OF THE
ARAB D RESERVOIR IN QATAR
Scarce stratigraphic and biostratigraphic investigations
have been done on the Arab Formation of Qatar when
compared with the extensive work that was carried out in
Fig. 1 : Location map showing the studied sections.
MemberMemberMember
Arab B
Arab C
Lower
Upper
Arab D
Arab A
Lower
Jubailah
Arab D
Arab D
Arab C
Limestone 3
Arab BLimestone 2
Arab ALimestone 1
Fahahil
Fm.Fm.Fm.
HithHithHith
Sudgen & Standring
1975
Focke et al.
1986
Al-Saad & Sadooni
(2001)
&
Present Study
Age
Table 1 : Terminology and nomenclature of the Arab D member in Qatar.
226 H. AL-SAAD & M. I.A. IBRAHIM
Saudi Arabia, United Arab Emirates and Oman. In Qatar,
the stratigraphic nomenclature of the Arab Formation is
confused due to different lithostratigraphic schemes that
have been established by oil companies (Table 1). SUGDEN
(cited in SUGDEN & STANDRING) (1975) proposed the name
Fahahil Formation to encompass Arab “D” sediments in
Qatar. In the type locality at well Dukhan-66, the Fahahil
Formation (57 m) consists of dolomitic limestones in the
lower part, clean limestones in the middle, and dolomitic
limestone interbedded with thin horizons of anhydrite
above (Fig. 2). Because the sections studied here do not
represent a complete successive section at one locality,
the reference section designed by SUGDEN is used to show
the different lithofacies of the Arab D Member in Qatar.
In the present study, the Fahahil Formation is considered
as a synonym for the Arab D “member” because there
are no major lithologic or age differences that support
the introduction of a new terminology. Further, FOCKE
et al. (1985) applied the term “Arab D reservoir” to
encompass the upper part of the Jubailah Formation and
the overlying Arab D Member (the lowest member of the
Arab Formation). As a rock unit, the Arab D reservoir of
FOCKE et al. (1985) should be divided into two reservoir
units : the Arab D reservoir (member) and upper Jubailah
reservoir (Table 1).
The contacts of the Arab D Member with the underlying
and overlying units are conformable. The transition from
the compact mudstones of the Jubailah Formation to the
overlying dolomitic wackestone/packstone of the Arab
D Member seems to be gradual. While, the anhydritic
limestone of the Arab D Member is separated from the
overlaying dolomitic limestone of the Arab C Member
by a layer of anhydrite at the top of the Arab D Member.
In Qatar, the Arab D Member ranges in thickness
from 190 feet in onshore to about 800 feet in offshore
sections.
4. LITHOFACIES ANALYSIS
Petrographic analysis of the Arab D Member reveals the
presence of six major microfacies of which mudstone
and wackestone/packstone facies represents the thickest
one. The main microfacies are mudstones, wackestone,
packstone, dolomitic mudstone/wackestone, grainstone
and anhydrite. The typical sequences of associated
microfacies begin with mudstone at the base which
gradually change upwards into foraminiferal wackestone/
packstones with thin horizons of grainstones and end with
foraminiferal grainstones/packstones. Then, followed by
dolomitic wackestone and, they are finally capped by
anhydrite or anhydritic limestones. The classification
of the different microfacies is after DUNHAM (1962).
The identification of the foraminifera follows that of
(LOEBLICH & TAPPAN, 1988 ; BANNER et al., 1991).
4.1. Microfacies 1 : Mudstone
This microfacies represents the basal part of the Arab
D reservoir and consists of micritic limestones with
rare small benthic foraminifera (Textulariina) and shell
fragments (Pl. I, fig. 1). This sequence is gradually
upward change to wackestone facies. In the lower part of
the Arab D Member, the mudstone facies is interbedded
with thin layers of packstone and dolomitic mudstone/
wackestone facies. Some of this mudstone is barren
from microfauna and may indicate deposition in a saline,
shallow tidal flat, whereas others may indicate a lowstand,
probably starved conditions. The total thickness of this
unit is around 3 m at offshore Qatar, increasing to around
6 m at Dukhan Oil Field.
4.2. Microfacies 2 : Redmondoides wackestone
It is fossiliferous in parts with pelecypod fragments,
echinoderm debris, foraminifera and dasycladacean
algae. The foraminiferal content includes species of
Redmondoides and Pseudomarssonella while the main
algae are of Clypeina jurassica (Pl. III, fig. 1). This
microfacies is well developed in the middle part of the
member than the lower part. Very fine rhombic dolomite
and some argillaceous components were recognized
within this microfacies in offshore Qatar. This unit
is believed to be deposited in a quiet shallow lagoon
setting. It reaches a maximum thickness of around 7 m
offshore Qatar and 6.5 m at the Dukhan Oil Field.
4.3. Microfacies 3 : Pfenderina packstone
Microfacies 3 is observed in different stratigraphic levels
in the Arab D Member. This microfacies consists of
micritized medium to coarse-grained oolitic packstone.
It is very fossiliferous and includes representatives of
Pseudomarssonella maxima REDMOND, Nautiloculina
oolithica MOHLER, N. circularis (SAID & BARAKAT),
Pfenderina salernitana SARTONI & CRESCENTI, P.
butterlini BRUN, Redmondoides rotundatus (REDMOND)
and fragments of echinoderms and molluscs (Pl. III, figs
2 & 4). This unit is believed to be deposited in a vast
shallow lagoon environment deeper than the microfacies
2 setting. Its thickness is about 2 m at offshore Qatar and
1.5 m at the Dukhan Oil Field.
4.4. Microfacies 4 : Stromatolic dolomitic mudstone/
wackestone
It is mainly composed of thin beds of bioturbated,
stromatolitic, fine-medium grained rhombic dolomite
floating in a lime mud/wackestone matrix. This
microfacies scattered mainly at the middle and upper
Facies and palynofacies characteristics of the Upper Jurassic Arab D reservoir in Qatar 227
Fig. 2 : Gereralized composite stratigraphic section of the Kimmeridgian Arab D member in Qatar.
228 H. AL-SAAD & M. I.A. IBRAHIM
parts of the member. Most of these dolomites probably
occurred as replacement of the original texture (Pl. II,
fig. 3). This unit is believed to be deposited in a restricted
lagoon setting. It reaches a maximum thickness of around
3 m offshore Qatar and 2 m at the Dukhan Oil Field.
4.5. Microfacies 5 : Kurnubia oolitic-peloidal
grainstone
The grainstone microfacies are well-sorted and best
developed in the middle part of the Arab D Member.
Most grains in this unit are micritized and of different
sizes and shapes (oolitic and pellets). This microfacies
is very fossiliferous and includes abundant algae
(Dasicladacean), Kurnubia jurassica (HENSON), K.
palastiniensis HENSON, Pfenderina salernitana SARTONI
& CRESCENTI, Nautiloculina oolithica MOHLER, N.
circularis (SAID & BARAKAT), molluscan debris and
solitary corals (Pl. II, fig. 2). This unit is believed to be
deposited in quiet shallow lagoon setting. The thickness
is about 3.5 m offshore Qatar and 2.5 m at the Dukhan
Oil Field.
4.6. Microfacies 6 : Anhydrite
It occurs in the upper part of the reservoir and consists of
fine crystalline anhydrite and anhydritic limestones (0.1 to
0.3 m). This unit is believed to be deposited in a restricted
lagoon setting. The greatest sea-level fall occurred in the
upper Arab D Member, with an abrupt transition from an
offshore to lagoonal backshore environment (ALSHARHAN
& NAIRN, 1997).
5. FORAMINIFERA
The Arab D Member is moderately fossiliferous in
foraminifera. Some of the identified species are shown
in Plate IV. The identified elements are restricted to some
intervals and mainly, rare except in the wackestone,
packstone/grainstones facies in the lower and middle
parts of the member. In general, the dolomitic limestone
and anhydritic dolomitic limestone facies were found
barren from microfauna. Most of the identified species
such as Kurnubia and Pfenderina are well documented in
the Upper Jurassic sediments in the Middle East (POWERS
et al., 1966 ; POWERS, 1968 ; SUGDEN & STANDRING, 1975 ;
TOLAND et al., 1995 ; AL-SILWADI et al., 1996 ; HUGHES,
1996 ; SHARLAND et al., 2001).
The foraminiferal assemblage consists of fifteen
benthic species, in alphabetic order these are : Kurnubia
bramkampi REDMOND, K. jurassica (HENSON), K.
palestiniensis (HENSON), Nautiloculina circularis
(SAID & BARAKAT), N. oolithica MOHLER, Pfenderina
butterlini BRUN, P. salernitana SARTONI & CRESCENTI,
Pseudomarssonella bipartite REDMOND, P. maxima
REDMOND, P. plicata REDMOND, Redmondoides medius
(REDMOND), R. rotundatus (REDMOND), Trocholina
conica SCHUMBERGER, T. palestiniensis HENSON, and
Verneuilinoides maurittii TERQUEM.
6. PALYNOLOGY
Palynological investigation has yielded many significant
dinoflagellate cyst species within the Arab D Member.
Unfortunately, many samples from this member are
found palynologically barren. However, residues of
barren samples may contain other palynofacies types
such as amorphous organic matter (AOM), structured
organic matter (SOM), and opaque phytoclasts (Table
2, Fig. 3).
Table 2 : Percentage of palynofacies component in the
Arab D Member, well D-290 in Dukhan Oil
Field. AOM = amorphous organic matter, SOM
= structured organic matter, ô = absent, ò =
poor (<5 %), ¢ = frequent (10-30 %), p = rich
(>30 %).
The most abundant palynomorph element is the chitineous
microforaminiferal test linings, which constitutes about
30-55 % of the total palynomorphs. On the other hand
terrestrial miospores are rare and represented by species
of the spores Cyathidites spp., Deltoidospora spp., and
Dictyophyllidites harrisii whereas gymnosperm pollen
are represented by Araucariacites, Inaperturopollenites
and Classopollis pollen.
Seventeen dinoflagellate cyst species have been identi-
fied and recognized from the studied samples of the Arab
D Member. Generally, most cysts are not well preserved
and show biodegradation. These recognized cysts belong
to proximate species such as Cribroperidinium globatum,
Cribroperidinium granuligerum, Cribroperidinium ? lon-
gicorne, Ctenidodinium ?schizoblatum, Dichadogonyau-
Facies and palynofacies characteristics of the Upper Jurassic Arab D reservoir in Qatar 229
lax chondra, Dichadogonyaulax ? pannea, Gochteodinia
antennata, and Leptodinium spp., and chorate cysts such
as Epiplosphaera bireticulata, Hystrichosphaerina sar-
jeantii, Systematophora areolata, Systematophora orbi-
fera, Systematophora penicillata, and Tenua hystrix.
7. PALYNOFACIES, TOTAL ORGANIC CARBON
AND HYDROCARBON HABITAT
The Jurassic reservoirs in Qatar contain 98 % and
4.8 % of the ultimate recoverable oil and gas reserves,
respectively. The most prolific reservoirs of Qatar in
all the fields lie within the Arab Formation. These
reservoirs hold the largest oil accumulations in the world
(ALSHARHAN & NAIRN, 1997). Anhydrite layers between
the Arab members act as intraformational seals for oil
discovered in the Dukhan, Idd El-Shargi and Bul Hanine
fields. Previous studies demonstrate that the Upper
Jurassic oil of Qatar fields originated from the underlying
Hanifa and Jubailah source rocks. A comparison of the
gas chromatograms of the saturated hydrocarbons from
a typical Arab D oil, and extracts from the Hanifa and
lower Jubailah source rocks demonstrates their close
relationship (ALSHARHAN & NAIRN, 1997).
Fifteen samples representing the Arab D Member in
Dukhan (D-290 well, onshore) and Bul Hanine (BH-X
well, offshore) oil fields were analysed for their organic
carbon content (weight percentage). The results are
tabulated in Table 3 and illustrated in Figure 4.
Palynofacies can help not only for establishing the
depositional environment but also for the determination
of hydrocarbon source potential and assessment of
thermal maturity of the host sediments (BATTEN, 1981
& 1996 ; TYSON, 1995). The palynofacies composition
of the Arab D Member is illustrated from the absolute
abundance of the major particulate organic matter (Fig.
3).
Samples of the Arab D reservoir are characterized by
the abundance of AOM, which is generally produced
from the biodegradation of other palynofacies
elements (dinoflagellate cysts, microforaminiferal
linings, structured phytoclasts and miospores). Opaque
phytoclasts are common, while palynomorphs and
structured phytoclasts are subordinate (Fig. 3).
Kerogen of the Arab D member is dominated by AOM
ranging from 35 % up to 100 % especially in the basal
part of the member (mudstone microfacies). Thus, the
carbonates of the Arab D Member may have a type II to
type I kerogen composition as it contains dinoflagellate
cysts. Total organic carbon (TOC %) is generally high
between 0.43 and 8.55 %. The higher TOC percentages
are also belonging to the lower lime mudstone and
wackestone microfacies. Generally, these TOC
values indicate high source potential for hydrocarbon
generation. Accordingly, the Arab D Member is not only
the main reservoir rock in Qatar, but the basal part also
1
2
3
4
5
6
7
8
9
10
11
12
13
14
0
20
40
60
80
100
%
Sample
Percentage of Palynofacies Components
Palynomorph
SOM
Opaques
AOM
Fig. 3 : Percentage of particulate organic matter in well D-290,
Dukhan Oil Field.
Table 3 : Results of the total organic carbon analysis
(wt. %) of selected samples from Dukhan and
Bul Hanine oil fields.
Total organic carbon wt.%
0
1
2
3
4
5
6
7
8
9
Samples
Bull Hanine Dukhan
Fig. 4 : Total organic carbon content (TOC) of selected samples
from the Dukhan and Bul Hanine oil fields.
230 H. AL-SAAD & M. I.A. IBRAHIM
slows a source potential beside the main Hanifa and
Jubailah sources.
The thermal maturity of the organic matter in the
Arab D Member was determined using spore colours,
particularly those of psilate trilete spores as Cyathidites,
Deltoidospora, and Dictyophyllidites. It varies between
orange and pale brown, suggesting a thermal mature
facies.
8. AGE OF THE ARAB D MEMBER
In this study, the age determination of the Arab D reservoir
depends essentially on both benthic foraminifera and
dinoflagellate cyst species. The foraminifera species
such as Kurnubia and Pfenderina together with their
lateral equivalence in eastern Arabia are confirming a late
Kimmeridgian age for the Arab D reservoir (AL-SILWADI
et al., 1996).
On the other hand, each species of the recorded
dinoflagellate cysts range through the Kimmeridgian.
Nevertheless, the co-existence of these species in one
assemblage indicates a late Kimmeridgian age (Fig. 5).
Cribroperidinium ? longicorne has been reported
extensively from the early Kimmeridgian of France
(GITMEZ & SARJEANT, 1972) ; early-late Kimmeridgian
of southern England, Egypt and worldwide (RIDING &
THOMAS, 1988 ; IBRAHIM & SCHRANK, 1996 ; STOVER et
al., 1996).
Gochteodinia antennata is a marker Kimmeridgian
species recorded from England (GITMEZ & SARJEANT,
1972 ; RIDING & THOMAS, 1988) ; early Kimmeridgian
Fig. 5 : Stratigraphic ranges for the encountered dinoflagellate cyst species as reported from France, England, Denmark, Egypt and
worldwide (GITMEZ & SARJEANT, 1972 ; POULSEN, 1996 ; RIDING & THOMAS, 1988 ; THOMAS & COX, 1988 ; THUSU et al., 1988 ;
COURTINAT, 1989 ; STOVER et al., 1996 ; IBRAHIM & SCHRANK, 1996 ; IBRAHIM et al., 2002).
Facies and palynofacies characteristics of the Upper Jurassic Arab D reservoir in Qatar 231
of Denmark (POULSEN, 1996) ; and late Kimmeridgian of
Egypt (IBRAHIM et al., 2002).
Ctenidodinium ?schizoblatum occurs sporadically in
some intervals of the dolomitic lime mudstone and
wackstone. It was reported previousely from the late
Kimmeridgian/Portlandian of France (COURTINAT,
1989) ; and the late Kimmeridgian of Egypt (IBRAHIM et
al., 2002).
Most of the dinoflagellate cyst species recorded herein
have showed their top occurrence in late Kimmeridgian
elsewhere ; these are : Cibroperidinium globatum,
C. granuligerum, Dichadogonyaulax chondra,
Epiplosphaera bireticulata, Systematophora areolata, S.
orbifera, and S. penicillata (THUSU et al., 1988 ; RIDING
& THOMAS, 1988 ; THOMAS & COX, 1988 ; STOVER et al.,
1996 ; IBRAHIM et al., 2002).
According to the aforementioned discussion, a late
Kimmeridgian age is thus given to the Arab D Member
in Qatar as well as in eastern Arabia.
SHARLAND et al. (2001) emphasized that the Arab D
Member occurs between two maximum flooding surfaces
MFS J70 of the top part of the Jubailah Formation (late
Kimmeridgian, dated at 152.75 Ma) and MFS J80 of the
topmost Arab D Member (late Kimmeridgian, dated at
151.75 Ma). The Kurnubia jurassica foraminifera Zone
is recognized from this member in Abu Dhabi, indicating
a late Kimmeridgian age (AL-SILWADI et al., 1996). In
the United Arab Emirates, AZER & PEEBLES (1998) have
reported three strontium isotope values that indicate
middle to late Kimmeridgian age for the top of the Arab
D to the lower part of the Arab C Member.
9. PALEOENVIRONMENTAL INTERPRETATION
The litho- and biofacies content of sedimentary rocks is
made up of autochthonous and allochthonous components
derived from a variety of sources reflecting the original
depositional environment, the climate, and the character
and composition of the terrestrial vegetation. Therefore,
the foraminiferal and palynological content of a sample
can be used as a basis for paleoenvironmental and
paleoclimatic interpretations.
During the deposition of the Arab D Member carbonates,
arid condition dominated much of the eastern part of the
Arabian region that led to form interbedded sequence
of carbonates and evaporites (MURRIS, 1981 ; ALSHARHAN
& KENDALL, 1986). In Qatar, short-term transgressive-
regressive cycles are present in the Arab D reservoir
as indicated by the rhythmic sequences of wackestone/
packstone/grainstone microfacies. The anhydrite interval
that occurs at the top of the Arab D reservoir marks the
end of the Arab D regression cycle. The Arab D facies
in western Qatar seem to be deeper than in the eastern
area as inferred from the increase of amount of clean
limestone toward the western area of Qatar.
Marine microplankton dominates over terrestrial
sporomorphs. The highly-ornamented (long processes)
wall, chorate morphology of the majority of dinoflagellate
cyst species present within the lower Arab D reservoir
(lime mudstone and wackestone) is believed to be an
adaptation to open marine environments (DOWNIE et al.,
1971 ; HARKER et al., 1990). HARKER et al. (1990) showed
that fossil gonyaulacoid cysts, like Cribroperidinium,
and Hystrichosphaeridium, appear to be most common in
stable marine condition. In addition, the species richness
of dinoflagellate cysts throughout the Arab D reservoir
is low to moderate (1-10 species) which is interpreted as
reflecting relatively inshore to shallow-shelf conditions
(GOODMAN, 1979). However, the relative abundance of
gonyaulacacean over peridiniacean dinoflagellate cysts
typical of the basal Arab D samples is indicative of
slightly more offshore, possibly shelf conditions (G/P
ratio of HARLAND, 1973 ; LISTER & BATTEN, 1988 ; HARKER
et al., 1990). The common occurrence of foraminiferal
test linings in the present samples is indicative of normal
marine coastal and/or shallow environment (BATTEN,
1979 ; LISTER & BATTEN, 1988 ; TYSON, 1993 & 1995).
Accordingly, the carbonate sediments of the Arab D
reservoir may have been deposited in shallow water
of middle shelf depth (30-50 m) under arid to semiarid
climatic conditions as deduced from the presence of
Classopollis pollen and of course the deposition of
evaporites (anhydrite) capping the Arab D Member.
Plate I
Fig. 1 : Compact micritic limestone (mudstone) with ghost of agglutinated benthic foraminifera. Lower part of the Arab
D ; X25 ; Dukhan Field ; crossed nicols.
Fig. 2 : Wackestone with Pseudomarssonella maxima and shell fragments. Very fine rhombic dolomite are scattered in
this facies. Middle part of the Arab D Member ; X25 ; Idd El-Shargi Field ; crossed nicols.
Fig. 3 : Packstone with Pseudomarssonella bipartita and echinoderm debris. Middle part of the Arab D Member ; X25 ;
Dukhan Field ; crossed nicols.
Fig. 4 : Bioturbated argillaceous wackestone with shell fragments and very fine rhombic dolomite. Lower part of the Arab
D Member ; X25 ; Idd El-Shargi Field ; crossed nicols.
232 H. AL-SAAD & M. I.A. IBRAHIM
1
2
3
4
Plate I
10. CONCLUSION
Arab Formation is considered as one of the most prolific
oil reservoir of Qatar. The Arab D Member represented
a regressive phase from shallow open marine lime-/
mudstone and wackestone with occasional peloidal,
tidal-current, shoal grainstone and packstone in the
lower and middle parts through subtidal and intertidal,
well sorted, ooilitic, peloidal grainstone, packstone,
and anhydrite. The anhydrite represents the maximum
sea-level fall occurring in the Arab D Member as well
as in the Arab Formation. The deduced climate is arid to
semiarid. The grainstone facies in the upper part of the
unit is found rich in benthic foraminifera dominated by
Kurnubia and Pfenderina.
Palynomorphs are dominated by proximate and chorate
dinoflagellate cysts whereas amorphous organic matter
and opaques phytoclasts are high in abundance among
other palynofacies.
Age of the Arab D Member is late Kimmeridgian.
The main reservoir is the oolitic-peloida grainstones and
dolomitized limestones.
The basal organic-rich lime-/mudstone of the Arab D
Member in addition to the underlying Hanifa and Jubailah
formations are the main source for oil in the Upper
Jurassic Arab Formation in Qatar. Spore/pollen colours
demonstrate that the Arab D sediments are thermally
mature.
ACKNOWLEDGEMENTS
The authors would like to thank the management of
Qatar Petroleum for providing the samples necessary for
this study and the Scientific and Applied Research Center
(SARC), University of Qatar, for TOC analyses.
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lithologiques du Malm dans le Jura méridional.
Plate II
Fig. 1 : Pfenderina salernitana bearing compact packstone with Nautiloculina oolithica (middle of the picture). Middle
part of the Arab D Member ; X25 ; Dukhan Field ; crossed nicols.
Fig. 2 : Well-sorted oolitic grainstone with Kurnubia palastiniensis. Some grains are completely micritized. Middle part
of the Arab D Member ; X40 ; Dukhan Field ; crossed nicols.
Fig. 3 : Coral-algae bearing wackestone/packstone facies. Middle part of the Arab D Member ; X40 ; Dukhan Field ;
crossed nicols.
Fig. 4 : Medium grained rhombic dolomite crystals floating in a wackestone matrix. Most of these dolomites probably
occurred as replacement of the original texture. Upper part of the Arab D Member ; X25 ; Dukhan Field ; crossed
nicols.
234 H. AL-SAAD & M. I.A. IBRAHIM
Plate II
1
2
3
4
Systématique, biostratigraphie et éléments dʼinterprétation
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Plate III
Fig. 1 : Compact wackestone with Clypeina jurassica. Middle part of the Arab D Member ; X40 ; Dukhan Field ; crossed
nicols.
Fig. 2 : Pfenderina butterlini in packstone facies. The white is spar cement. Middle part of the Arab D Member ; X40 ;
Dukhan Field ; crossed nicols.
Fig. 3 : Redmondoides medius in micritized wackestone facies. Middle part of the Arab D Member ; X25 ; Idd El-Shargi
Field ; crossed nicols.
Fig. 4 : Pfenderina salernitana in argillaceous packstone with algal fragment (upper right of the picture). Middle part of
the Arab D Member ; X25 ; Dukhan Field ; crossed nicols.
236 H. AL-SAAD & M. I.A. IBRAHIM
Plate III
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3
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Accepté juillet 2004
Plate IV
Foraminifera from the middle part of the Arab D Member.
Fig. 1 : Nautiloculina circularis (SAID & BARAKAT) ; apertural view ; X 120.
Fig. 2 : Nautiloculina oolithica MOHLER ; apertural view ; X 120.
Fig. 3 : Verneuilinoides maurittii TERQUEM ; X 55.
Figs. 4, 5 : Kurnubia palestiniensis (HENSON) ; X 50.
Figs. 6, 7 : Kurnubia bramkampi REDMOND ; X 60.
Fig. 8 : Pseudomarssonella plicata REDMOND ; X 75.
Fig. 9 : Redmondoides royundatus (REDMOND) ; X 80.
Fig. 10 : Pseudomarssonella sp. X 100.
Fig. 11 : Redmondoides medius (REDMOND) ; X 60.
Fig. 12 : Trocholina palestiniensis HENSON ; X 115.
Fig. 13 : Trocholina conica SCHUMBERGER ; X 120.
238 H. AL-SAAD & M. I.A. IBRAHIM
Plate IV
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3
4
5 6 7 8
9
10 11
12
13
Appendix
Foraminifera
Pseudomarssonella plicata REDMOND.
Pseudomarssonella maxima REDMOND.
Pseudomarssonella bipartita REDMOND.
Pseudomarssonella sp.
Redmondoides royundatus (REDMOND).
Redmondoides medius (REDMOND).
Pfenderina salernitana SARTONI & CRESCENTI.
Pfenderina butterlini BRUN.
Nautiloculina oolithica MOHLER.
Nautiloculina circularis (SAID & BARAKAT).
Verneuilinoides maurittii TERQUEM.
Kurnubia palestiniensis (HENSON).
Kurnubia bramkampi REDMOND.
Trocholina palestiniensis HENSON.
Trocholina conica SCHUMBERGER.
Dinoflagellate cysts
Cribroperidinium globatum (GITMEZ & SARJEANT, 1972)
HELENES.
Cribroperidinium granuligerum (KLEMENT, 1960) STOVER
& EVITT.
Cribroperidinium ? longicorne (DOWNIE, 1957) LENTIN &
WILLIAMS.
Ctenidodinium ?schizoblatum (NORRIS, 1965) LENTIN &
WILLIAMS.
Cyclonephelium sp.
Dichadogonyaulax chondra (DRUGG, 1978) COURTINAT.
Dichadogonyaulax ? pannea (NORRIS, 1965) SARJEANT.
Dichadogonyaula sp.
Epiplosphaera bireticulata KLEMENT.
Gochteodinia antennata (GITMEZ & SARJEANT, 1972)
BELOW.
Hystrichosphaerina sarjeantii (GITMEZ, 1970) DUXBURY.
Leptodinium spp.
Lithodinia spp.
Systematophora areolata KLEMENT.
Systematophora orbifera KLEMENT.
Systematophora penicillata (EHRENBERG, 1843)
SARJEANT.
Tenua hystrix EISENACK.
Spores and pollen
Araucariacites spp.
Balmeiopsis limbatus (BALME, 1957) ARCHANGELSKY.
Classopollis torosus (REISSINGER, 1950) COUPER.
Cyathidites spp.
Deltoidospora spp.
Dictyophyllidites harrisii COUPER.
Inaperturopollenites spp.
Miscellaneous
Cuticle phytoclasts.
Microforaminiferal linings.
Plate V
Palynomorphs and phytoclasts from the Arab D Member. All magnifications X 600, except otherwise stated.
Fig. 1 : Dictyophyllidites harrisii COUPER, X 800.
Fig. 2 : Balmeiopsis limbatus (BALME, 1957) ARCHANGELSKY, X 800.
Fig. 3 : Classopollis torosus (REISSINGER, 1950) COUPER, X 800.
Fig. 4 : Lithodinia sp.
Fig. 5 : Dichadogonyaulax ? Pannea (NORRIS, 1965) SARJEANT.
Fig. 6 : Ctenidodinium ?schizoblatum (NORRIS, 1965) LENTIN & WILLIAMS.
Fig. 7 : Dichadogonyaulax sp.
Fig. 8 : Systematophora areolata KLEMENT.
Fig. 9 : Cribroperidinium globatum (GITMEZ & SARJEANT, 1972) HELENES, X 800.
Figs 10, 11 : Cribroperidinium ? longicorne (DOWNIE, 1957) LENTIN & WILLIAMS.
Fig. 12 : Systematophora orbifera KLEMENT.
Fig. 13 : Large fragment of cuticle phytoclast, X 400.
Fig. 14 : Gochteodinia antennata (GITMEZ & SARJEANT, 1972) BELOW.
Fig. 15 : Cribrperidinium granuligera (KLEMENT, 1960) BRENNER.
Fig. 16 : Cyclonephelium sp.
Fig. 17 : Microforaminiferal linings.
H. AL-SAAD & M. I.A. IBRAHIM240
Plate V
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3
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5
6
7
8
9
10
11
12
13
14
15 16
17
