01-Mhasoub.indd


Mahsoub et al.: Bio- and Sequence Stratigraphy of Upper Cretaceous – Palaeogene rocks, East Bahariya Concession, Western Desert, Egypt
109

�
AB STRA CT
This work deals with the plankton stratigraphy of the subsurface Upper Cretaceous-Palaeogene succession of the 
East Bahariya Concession based on planktonic foraminifera and calcareous nannofossils. The examination of the 
cuttings from fi ve wells: AQSA-1X, KARMA-E-1X, KARMA-3X, KARMA-NW-1X and KARMA-NW-5X is bi-
ostratigraphically evaluated. It is possible to identify the planktonic foraminifera as well as the calcareous nannofos-
sil biozones. The analyses of calcareous nannofossils revealed the presence of several hiatuses. Information obtained 
from well data such as seismic facies analysis for the studied area has enabled classifi cation of the Upper Cretaceous-
Palaeogene succession into fi ve major 2nd order depositional sequences, separated by four major depositional sequence 
boundaries (SB1, SB2, SB3 and SB4). The Upper Cretaceous-Palaeogene succession in the East Bahariya is divided 
into 17 systems tracts. These systems tracts are: 7 System tracts of probable Cenomanian age, (the sequence strati-
graphic framework as well as the cycles and system tracts of the Cenomanian Bahariya Formation match well with 
those of CATUNEANU et al., 2006); 4 System tracts of Turonian age, 2 System tracts of Campanian-Maastrichtian 
age and 4 System tracts of Eocene age.

Keywords: Planktonic foraminifera, Calcareous nannofossil, Upper Cretaceous, Palaeogene, Seismic interpreta-
tion, Sequence stratigraphy, Bahariya, Egypt

Bio- and Sequence Stratigraphy of 
Upper Cretaceous – Palaeogene rocks, 

East Bahariya Concession, Western 
Desert, Egypt

�
Mohamed Mahsoub1, Radwan A.bul-Nasr1, Mohamed Boukhary2, 
Hamed Abd El Aal1 and Mahmoud Faris3

1 Faculty of Education, Ain Shams University, Cairo, Egypt; (mahsoub2005@hotmail.com; rabulnasr@
yahoo.com; mabdelaal81@yahoo.com)

2 Department of Geology Faculty of Science, Ain Shams University, Cairo, Egypt; (moboukhary@yahoo.com)
3 Department of Geology Faculty of Science, Tanta University, Tanta, Egypt; (mhmfaris@yahoo.com)

doi: 104154/gc.2012.09

Geologia Croatica 65/2 109–138 33 Figs. 1 Tab. Zagreb 2012

Geologia CroaticaGeologia Croatica

1. INTRODUCTION

The Western Desert of Egypt covers an area of approximately 
700, 000 km2, which represents two thirds of the total area 
of the country (EGPC, 1992).

The study area (Fig. 1) covers the Karama Field in the 
East Bahariya concession (EBC), located in the eastern mar-
gin of the Abu Gharadig Basin. The Karama Field was dis-
covered in January 2000 by Repsol and Apache, while drill-
ing the Karama 1-X well, which produced oil from the Abu 
Roash Member.

The Abu Gharadig Basin is located in the central north-
ern part of the Western Desert. Topographically the Abu 
Gharadig Basin can be subdivided into two main troughs, 
the western and eastern trough. This basin is recently con-
sidered to be the most promising of all as far as hydrocarbon 
potential is concerned since several oil and gas discoveries 
had been recorded within its thick marine Cretaceous se-
quence (AWAD, 1984).

The aim of the present work is the study of the plank-
tonic foraminiferal and calcareous nannoplankton biostratig-



Geologia Croatica 65/2Geologia Croatica
110

raphy of the Upper Cretaceous – Palaeogene rock units in 
the eastern part of the Bahariya concession and to integrate 
this data with that obtained from the seismic sections.

2. MATERIALS AND METHODS

Altogether 40 seismic sections were interpreted in order to 
illustrate the structural framework and depositional history 
of the study area. These seismic lines were supported by the 
composite, velocity and vertical seismic profi le (VSP) logs 
of eight selected wells (AQSA-1X, AQSA-2X, KARAMA-
E-1X, KARAMA-3X, KARAMA-SW-1X, KARAMA -SW-
10X, KARAMA-NW-1X and KARAMA-NW-X).

Cuttings from fi ve wells were selected for biostrati-
graphic studies that include several species of planktonic 
foraminifera and calcareous nannofossils.

Table 1: Shows the number and depth of the cuttings from the studied 
wells.

Wells Depth interval (m) No. of samples

AQSA-1X 338.4–2640 40

KARAMA-E-1X  365–2830 40

KARAMA-3X  365–2470 40

KARAMA-NW-1X  430–2600 40

KARAMA-NW-5X  450–2600 40

3. STRATIGRAPHY

The surface of the northern part of the Western Desert is cov-
ered by Miocene deposits, except for the Bahariya and Abu 
Roash areas that are covered with Upper Cretaceous and 
Eocene sediments (Fig. 2). In the Fayium area both Eocene 
and Oligocene limestones, clays and sandstones dominate 
the section. In the Bahariya and Fayium areas Oligocene 
volcanic basalt makes up a substantial part of the geological 
succession. The Miocene deposits are subdivided into the 
lower Miocene Moghra Formation and the Middle Miocene 
Marmarica Formation (SAID, 1962).

Based on the surface geological map of the Western 
Desert, the Miocene deposits are separated from the Eocene 
rocks in the south by a narrow band of Oligocene carbonates 
at Siwa (HARPE DE LA, 1883) while in Al Arag there is a 
gradual southerly change into a clastic succession at Baha-
riya and Fayium (OSMAN, 2003).

The Miocene surface usually doesn’t usually refl ect stru-
ctures at depth as an angular unconformity is observed at 
many places separating the Miocene and underlying Eocene 
deposits. The Upper Eocene deposits occupied mainly the 

Figure 1: Location map of the area under study (a, b).

Figure 2: Generalized lithostratigraphic column in the Abu Gharadig Basin.



Mahsoub et al.: Bio- and Sequence Stratigraphy of Upper Cretaceous – Palaeogene rocks, East Bahariya Concession, Western Desert, Egypt Geologia Croatica
111

central and the south eastern parts of the Western Desert. 
These marine deposits are mainly limestone represented by 
the Thebes and farafra Formations, the former representing 
an open marine facies while the latter is a shallow shelf litho-
facties (SAID, 1960). The Cretaceous deposits are mainly 
located at the southern part of the Western Desert and they 
consist mainly of the Nubia Formation.

3.1. Subsurface stratigraphy of the Western Desert

The subsurface lithostratigraphic column in the northern part 
of the Western Desert contains most of the sedimentary sec-
tion from Pre-Cambrian basement rocks to Recent deposits. 
The total thickness of the sedimentary section measures 
about 4270 m (YOUNES, 2003). Figure 2 summarizes the 
main stratigraphic units in the Abu Gharadig basin of the 
Western Desert.

3.1.1. Upper Cretaceous rocks

In Egypt, the Upper Cretaceous is marked by the beginning 
of a major marine transgression which resulted in the depo-
sition of a carbonate dominated section in the study area. 
According to ISSAWI et al. (1999), the Upper Cretaceous 
succession is subdivided into three lithostratigraphic units 
from the oldest Bahariya, to the Abu Roash and the Khoman 
Formations.

The sedimentary rocks of the Upper Cretaceous occur 
in three basins of the Western Desert; the Abu Gharadig, 
Shushan, and Alamin basins, which include the most impor-
tant hydrocarbon resources in the Western Desert. The for-
mations are discussed from oldest to youngest below.

3.1.1.1. Bahariya Formation
The type locality of this unit is located in the Gabel El Dist 
(Bahariya Oasis) where the base of the formation is not ex-
posed at the surface. The maximum thickness of this forma-
tion occurs in the Kattaniya-1 well (1143 m) (29° 49'N and 
30° 10'E). The name of this unit was proposed by SAID 
(1962), STROMER (1914a, b) and SMITH et al., 2006 based 
on dinosaurs remain for the lower Cenomanian fl uvio-marine 
(CATUNEANU, 2006) sediments which consist of argilla-
ceous sandstone with some carbonates.

3.1.1.2. Abu Roash Formation
The type locality of the Abu Roash Formation outcrops to 
the north of the Pyramids of Giza (30° 2' 44.59“N and 31°14' 
24.71“E). This unit is subdivided into seven lithostrati-
graphic members, termed from top to bottom as A, B, C, D, 
E, F, and G, which extend from the Santonian to the Upper 
Cenomanian. Most of the facies were deposited under neritic 
to open marine, basinal conditions. The Abu Roash repre-
sents the alternation of transgressive and regressive phases, 
characterized by:
1. Shallow to deeper marine carbonates on palaeohighs. The 

limestones-were dolomitized and have fracture porosity.
2. Shallow deposits, consisting of the alternation of shales 

and sandstones. During Turonian times, an evaporitic 
sequence was deposited in some areas.

Lithologically, this unit consists of white moderately 
hard fossiliferous, cherty, massively bedded, micro-to cryp-
tocrystalline chalky limestone. The shales are gray, dark 
brown and greenish in colour with moderate hardness, con-
taining some glauconite and pyrite. Dolomite is brownish in 
colour, buff, massive and moderate in hardness. This refl ects 
a nearshore or Sabkha type of depositional environment.

3.1.1.3. Khoman Formation
The type section of this unit is located at Ain Khoman, south-
west of the Bahariya Oasis. It represents an open marine 
facies which prevailed in the north Western Desert during 
the Campanian and Maastrichtian and it unconformably 
overlies the Abu-Roash Fm., particularly in the structurally 
highest area. Lithologically this formation consists of two 
main units: the lower unit is mostly limestone interbedded 
with shale, the limestone is massive, white dolomitic lime-
stone and the shale is brownish, gray with medium hardness 
while the upper, unit is of fi ne-grained white chalky massive 
limestone and massive dolomite and lacks of adequate res-
ervoir properties.

3.1.2. Cenozoic rocks

At the end of Cretaceous, sedimentation in the Western De-
sert was continuous in the structurally low and subsiding ar-
eas while some depositional gaps and erosional truncations 
were common on the pre-existing highs, which were reactiva-
ted, especially during the Palaeocene (SCHLUMBER GER, 
1984).

Palaeogene rocks include the Palaeocene to Middle 
Eocene Apollonia Fm. which consists mainly of shallow to 
open marine carbonates. The Upper Eocene to Oligocene 
Dabaa Fm. consists of shallow marine shales and the Mi-
ocene Moghra Fm. consists mainly of shallow to marginal 
marine sandstones with thin shale interbeds and a basalt ex-
trusion near its top. The basal part of the Moghra Fm. later-
ally changes to carbonates (Shoushan Formation) in the nor-
th west portion of the Western Desert. The Oligo-Miocene 
rocks are also overlain by the middle Miocene Marmarica 
Fm. to the northwest of the Western Desert, which consists 
of shallow marine carbonates (NORTON, 1967; ABDEL 
AAL & MOUSTAFA, 1988). Quaternary deposits uncon-
formably overlie the Miocene rocks and consist of Plio-Pleis-
tocene continental sands.

3.1.2.1. The Apollonia Formation
This is a widespread limestone with subordinate shale of 
Palaeocene to Eocene age. The type locality is located south 
of the village of Susa (32° 53' 48“N and 21° 57' 47“E) in 
Libya. The type section is 250 m thick and is made up of 
massive siliceous limestones with numerous chert bands.

The lithology is white, chalky limestone, in many places 
nummulitic, with some shaly zones, especially where the 
formation is thick. Glauconite and pyrite are common and 
widespread. Chert nodules occur, and are common in the 
lower part. The formation has been subdivided by several 
operators into units A to D where D is the oldest. Units B 
and D are thinner and dominanted by shale.



Geologia Croatica 65/2Geologia Croatica
112

3.1.2.2. The Dabaa Formation
The type section is the interval 579 to 1021 m interval of the 
Dabaa-1 well. Lithologically it is composed of gray and 
greenish-gray clay and claystone with subordinate thin beds 
of limestone, glauconite and pyrite minerals, of Upper Eo-
ce ne to Oligocene age.

The majority of the wells drilled in the study area re-
vealed the same stratigraphic column of the North-Western 
Desert with a few exceptions in the variations of thickness 
and the absence of some rock units.

4. BIOSTRATIGRAPHY

Cuttings from fi ve wells (AQSA-1X, KARAMA-E-1X, KA-
RAMA-3X, KARAMA-NW-1X and KARAMA-NW-5X) 
were selected for study and the identifi cation of microfos-
sils. Several species of planktonic foraminifera and calca re-
ous nannofossils have been identifi ed. Some stra ti grap hi cally 
important taxa are illustrated (Figs. 8–11 and Figs. 17–21).

Calcareous nannofossils were processed by the standard 
smear slide preparation from raw sediment samples as de-
scribed by Perch-Nielsen (1985). Smear slides were exam-

ined using a light photomicroscope with 1250x objective. A 
relative abundance of calcareous nannofossils was used as 
follows: A= abundant more than 5 specimens /fi eld of view 
(fov), C= common 1–5 specimens/fov, F= frequent one spec-
imen /2–5 fov, R= rare one specimen/6–10 fov and VR= very 
rare one specimen/more 10 fov.

4.1. Planktonic and benthic foraminifera

The planktonic foraminifera were used to date the different 
successions of the studied wells. Most successions range in 
age from the Cretaceous (Cenomanian) to the Oligocene. 
Planktonic and benthic foraminifera are encountered only in 
the marine upper half of the succession which is represented, 
in ascending order, by the Khoman Fm, the Apollonia Fm, 
and the Dabaa Fm.

4.1.1. Preparation technique

Samples were soaked in Hexametaphosphate solution and 
then washed through a 0.64 mm sieve. The operation was 
repeated until the residue became clean. Hard samples were 
then treated by ultrasonic cleaner. Foraminiferal specimens 
were picked and mounted on squared slides for identifi cation.

Figure 3: Distribution chart of the planktonic and benthic foraminifera of the Well Aqsa-1x.



Mahsoub et al.: Bio- and Sequence Stratigraphy of Upper Cretaceous – Palaeogene rocks, East Bahariya Concession, Western Desert, Egypt Geologia Croatica
113

4.1.2. The Khoman formation

The Khoman Formation contains planktonic and benthic fo-
raminiferal assemblages of Campanian – Maastrichtian age 
(Figs. 3 to 7).

The faunal assemblages of the Khoman Fm. belong to 
the following planktonic foraminiferal zones, from base to 
top, as follows: Globotruncana ventricosa Zone, G. aegy-
ptia ca Zone (CARON, 1985; CARON et al., 2006 and BER-
G GREN & PEARSON, 2006) and Gansserina gansseri 
Zone which are assigned to the Upper Campanian to Maas-
trichtian.

4.1.3. Apollonia Formation

The Apollonia Formation unconformably overlies the Kho-
man Formation. It consists mainly of limestone with occa-
sional argillaceous interbeds in some wells. It is relatively 
poor in foraminifera and almost barren at some levels. Ac-
cordingly, systematic biozonation is diffi cult and impractical 
to establish, especially due to the absence of some key spe-
cies (Figs. 3 and 7). However, some other species have hel-
ped in establishing different age divisions of the Apollonia 
Formation Figures 3 to 7 shows the distribution of planktonic 
foraminifera in the Apollonia Formation of the different 
wells. The Lower/Middle Eocene boundary has been drawn 
at the fi rst appearance of Middle Eocene species such as 

Acarinina bullbrooki especially when associated with Cata-
psydrax sp and Turborotalia cerroazulensis pomeroli. The 
Lower Eocene is estimated according to the occurrence of 
only lower Eocene species such as Morozovella formosa, 
Acarinina soldanii, & Acarinina pentacamerata. These three 
species together with Acarinina broedermanni represent the 
assemblage of the Lower Eocene (BOLLI, 1957; TOUMAR-
KINE & LUTERBACHER, 1985; BERGGREN & PEAR-
SON, 2006). They are usually followed by a barren interval 
before the inception of the Middle Eocene species. Accord-
ingly, the Lower/Middle Eocene boundary here is specula-
tive rather than factual.

The Middle Eocene part is the interval richest interval 
in foraminifera. All the species of the assemblage support 
this age determination based on comparison with those men-
tioned in the literature (BOLLI, 1957 & BLOW, 1979; TOU-
MARKINE & LUTERBACHER, 1985; BERGGREN & 
PEAR SON, 2006). It is worth mentioning, however, that ex-
cept for Acarinina and Truncorotaloides, the range of these 
species extends to the Upper Eocene. Yet, the index species 
of the Upper Eocene, Globigerinatheka semiinvoluta, is used 
to delineate the Upper Eocene upon its occurrence. This spe-
cies appears in some wells (Figs. 3 and 5) and is absent in 
others (Figs. 4, 6 and 7).

The latest Eocene fauna such as Cribrohantkenina, T.c. 
cocoaensis, T.c. cunialensis are absent from the material sug-

Figure 4: Distribution chart of the planktonic and benthic foraminifera of the Well Karama-3.



Geologia Croatica 65/2Geologia Croatica
114

gesting that the Upper Eocene when observed is incomplete. 
Accordingly, the boundary between the Apollonia Fm. and 
the underlying Khoman Fm. is represented by a hiatus span-
ning the whole Palaeocene and the basal part of the Eocene 
with some hiatuses within the formation. The recorded 
plank tonic foraminiferal zones: from the Morozovella arago-
nensis zone (P8, BOLLI, 1957 and TOUMARKINE & LU-
TERBACHER, 1985) to the Globigerinatheka semiinvoluta 
Zone (P15, Bolli, 1957) are delineated within the Apollonia 
Fm. With the pronounced unconformity with the overlying 
Dabaa Fm.

4.1.4. The Dabaa Formation

The Dabaa Fm. is devoid of identifi able planktonic fora-
minifera in spite of the sporadic occurrence of benthics spe-
cies. So, its Oligocene age, as estimated by sporadic fau na, 
is adopted here. The planktonic and benthic species are 
shown in Figures 8 to 11.

4.2. Nannoplankton biostratigraphy

The zonations of SISSINGH (1977) for the Upper Creta-
ceous and that of MARTINI (1971) and OKADA & BUKRY 
(1980) for the Lower Palaeogene were adopted here in the 

deep wells, contamination by caving is observed through 
examination of the cutting. In the study wells, nannofossils 
are frequent to rare and moderately to poorly preserve.

In the following, the recognized nannofossil biozones 
are discussed from, base to top. Abbreviations used are: FO 
= First occurrence, LO = Last occurrence. FO is used fol-
lowing the standard biostratigraphic scheme but taking into 
consideration that the samples are cuttings; the law of fi rst 
appearance is applied accordingly.

4.2.1. Upper Cretaceous calcareous nannofossil 
biostratigraphy

4.2.1.1. Quadrum trifi dium Zone (CC22)
Defi nition: It is defi ned as the interval from the FO of Quad-
rum trifi dium to the LO of Reinhardtites anthophorous.

Authors: BUKRY & BRAMLETTE (1970), emended 
by SISSINGH (1977)

Age: Late Campanian.
Occurrence: Aqsa-1x (1590–1800 m), Karama-3x 

(1500–1550 m), Karama-NW-1x(1450–1650 m) (in Khoman 
Formation).

Figure 5: Distribution chart of the planktonic and benthic foraminifera of the Well Karama-E-1x.



Mahsoub et al.: Bio- and Sequence Stratigraphy of Upper Cretaceous – Palaeogene rocks, East Bahariya Concession, Western Desert, Egypt Geologia Croatica
115

Figure 6: Distribution chart of the planktonic and benthic foraminifera of the Well Karama-NW-1x.

Figure 7: Distribution chart of the planktonic and benthic foraminifera of the Well Karama-NW-5x.



Geologia Croatica 65/2Geologia Croatica
116

Figure 8: Planktonic Eocene plate. 1 – Morzovella subbotinae MOROZOVA, 1929; 3690 ft, Karama-NW-1x. 2 – Globigerina eocaena GUEMBEL1966; 1650 ft, 
Aqsa-1x. 3 – Acarinina crassata CUSHMAN, 1962; 2430 ft, Aqsa-1x. 4 – Globigerina pseudoampliapertura (BOW, BANNER, 1962); 2130 ft, Karama- NW-1x. 
5–7 – Acarinina crassata, Toumarkine, BOLLI, (1970); 1800 ft, Aqsa-1x. 8 – Turborotalia cerroazulensis possagnoensis, Toumarkine, BOLLI, (1970); 2430 ft, 
Karama-3x. 9–11 – Turborotalia cerroazulensis pomeroli, Toumarkine, BOLLI, (1970); 1890 ft, Karama-3x. 12 – Turborotalia cerroazulensis BOLLI, (1970); 1830 
ft, Karama-E-1x. 13 – Globigerinatheka index (fi naly, 1939); 1770 ft, Karama- E-1x. 14,15 – Globigerinatheka tropicalis (BLOW, BANNER, 1962); 2130 ft, Ka-
rama- NW-1x. 16 – Globigerinatheka semiinvoluta (KEIJZER, 1945); 1830 ft, Karama- E-1x.

Remarks: In addition to the zonal marker, the nanno-
fossil assemblage includes: Watznaueria barnesae, Cycla-
gelosphaera reinhardtii, Lucianorhabdus. cayeuxii, Cribro-
sphaerella ehrenbergii, Aspidolithus parcus, Eiffellithus 
eximius.

4.2.1.2. Tranolithus phacelosus Zone (CC23)
Defi nition: It is defi ned from the LO of Reinhardtites antho-
phorus to the LO of Tranolithus phacelosus.

Authors: SISSINGH (1977)
Age: Late Campanian to Early Maastrichtian.
Occurrence: Karama-3x (1370–1435 m), Karama-NW-

1x (1150–1420 m) (in Khoman Formation).
Remarks: In addition to the zonal markers, the nanno-

fossil assemblage includes the large sized forms of Eiffell-
ithus turiseffelii and Arkhangleskiella cymbiformis.

4.2.1.3. Arkhangleskiella cymbiformis Zone (CC25)
Defi nition: It is defi ned from the LO of Reinhardtites levis 
to the FO of Nephrolithus frequens.

Authors: PERCH – NIELSEN (1972), emended by SIS-
SINGH (1977)

Age: Late Maastrichtian.
Occurrence: Aqsa-1x (1400–1540 m), Karama-NW-5x 

(1700–1400 m) (in Khoman Formation).
Remarks: The CC25 Zone is unconformably overlain by 

zone NP12 (Early Eocene), with a marked hiatus spanning 
the uppermost Maastrichtian, as well as the entire Palaeocene 
and the lower part of the lower Eocene.

4.2.2. Lower Palaeogene calcareous nannoplankton 
biostratigraphy

4.2.2.1. Tribrachiatus orthostylus Zone (NP12)
Defi nition: The Base is defi ned by the fi rst occurrence (FO) 
of Discoaster lodoensis and the top by the last occurrence 
of Tribrachiatus orthostylus.

Authors: BRÖNNIMANN & STRADNER (1960)
Age: Early Eocene (Ypresian).



Mahsoub et al.: Bio- and Sequence Stratigraphy of Upper Cretaceous – Palaeogene rocks, East Bahariya Concession, Western Desert, Egypt Geologia Croatica
117

Figure 9: Planktonic Cretaceous plate. 1 – Heterohelix navarroensis (LOEBLICH, 1951); 4320 ft, Karama-3x. 2,3 – Heterohelix globulosa (EHRENBERG, 
1840); 3630 ft, Karama-NW-5x. 4 – Heterohelix sp. 3810 ft, Karama-NW-5x. 5,6 – Rugoglobigerina macrocephala BRONNIMANN, 1952; 4320 ft, Karama-
NW-1x. 7 – Rugoglobigerina scotti (BRONNIMANN, 1952); 4530 ft, Karama-NW-1x. 8 – Rugoglobigerina sp. 4770 ft, Karama-3x. 9 – Rugoglobigerina rugosa 
(PLUMMER, 1926); 3930 ft, Karama-3x. 10 – Globotruncanella sp. 3810 ft, Karama-NW-5x. 11 – Globotruncanella petaloidea (GANDOLFI, 1955); 4620 ft, 
Karama-E-1x. 12–14 – Globotruncana linneiana (D,ORBIGNY, 1839) ); 4710 ft, Karama-3x. 15,16 – Globotruncana cf. falsostuarti SIGAL, 1952; 5520 ft, Kar-
ama-E-1x. 17,18 – Globotruncana sp. 4830 ft, Aqsa-1x. 19 – Globotruncanita stuarti (DE LAPPARENT, 1918); 4710 ft, Karama-3x. 20,21 – Globotruncanita 
cf. stuartiformis (DALBIEZ, 1955); 4770 ft, Karama-NW-5x. 22,23 – Hedbergella cf. holdelensis OLSSON, 1964; 4110 ft, Karama-3x. 24 – Hedbergella delrioen-
sis (CARSEY, 1926); 4620 ft, Karama-3x. 25 – Globotruncana cf. aegyptiaca NAKKADY, 1950; 3930 ft, Karama-NW-X. 26 – Rosita (contusotruncana) fornicata 
(PLUMMER, 1931); 5940 ft, Aqsa-1x. 27 – Rosita (contusotruncana) contusa (CUSHMAN, 1926); 3780 ft, Karama-NW-1x.

Occurrence: Karama-E-1x (600–700 m), Karama-NW-
1x (600–700 m), Karama-NW-5x (650–660 m) (in Apollonia 
Formation).

Remarks: In addition to the zonal markers, the nanno-
fossil assemblage includes in the investigated wells the FO 
of both Scyphosphaera magna and Ericsonia formosa which 
defi ne the base of NP12.

4.2.2.2. Discoaster lodoensis Zone (NP13)
Defi nition: LO of Tribrachiatus orthostylus or FO of To-
weius crassus to the FO of D. sublodoensis.

Assemblage: The characteristic assemblage in clu des: 
Coccolithus pelagicus, Ericsonia formosa, Helicos phae ra 
lophota, Pontosphaera multipora, Sphenolithus moriformis, 
Pontosphaera multipora, Chiasmolithus solitus, Discoaster 



Geologia Croatica 65/2Geologia Croatica
118

barbadiensis, Reticulofenestra dictyoda, Helicosphaera lo-
phota, and Neococcolithes dubius.

Authors: BRÖNNIMANN & STRADNER (1960) and 
BUKRY (1973)

Age: Early Eocene (Ypresian).
Occurrence: Karama-3x (800–1180 m)
Remarks: In addition to the zonal marker, the nanno-

fossil assemblage includes (in the base of the zone) the FO 
of Reticulofenestra dictyoda and Helicosphaera lophota. Its 

top cannot be defi ned due to the marked hiatus which in-
cludes zones NP14 through NP17 in Karama-NW-5x.

4.2.2.3. Discoaster tani nodifer Zone (NP16)

Defi nition: This zone includes the stratigraphic interval from 
the LO of Rhabdosphaera gladius to the LO of Chiasmo-
lithus solitus.

Assemblage: Besides the nominated species, Zone 
NP16 includes: Ericsonia formosa, Helicosphaera lophota, 

Figure 10: Benthic Cretaceous plate. 1 – Gyroidinoides depressus (HAGENOW); 3930 ft, Karama-NW-1x. 2,3 – Gavelinella monterelensis 4140 ft, Karama-
NW-1x. 4 – Stensioeina pommerana BROTZEN; 4380 ft, Aqsa-1x. 5 – Coryphostoma cf. gemma CUSHMAN 1927; 4380 ft, Aqsa-1x. 6 – Corphostoma crassum 
VASILENKO, MYATLYUK 1947; 7–9 – Globorotalites conicus CARSEY 1926; 3780 ft, Karama-NW-1x. 10,11 – Cibicidoides sp.; 4470 ft, Karama-E-1x. 12 – Gy-
roidina sp.; 3990 ft, Karama-NW-5x. 13 – Gavelinella sp.; 3810 ft, Karama-NW-5x. 14,15 – Arenobulimina sp.; 4380 ft, Aqsa-1x. 16 – Dorothia retusa KAMIM-
SKI et al. 1988; 4710 ft, Karama-3x. 17 – Bolivinoides draco (MARSSON, 1878). 18 – Cibicides sp. 19 – Laevidentalina cf. catenula CUSHMAN &JARVIS 1932. 
20,21 – Anomalinoides sp.; 4620 ft, Aqsa-1x. 22 – Gaudryina Laevigata FRANK 1914; 3990 ft, Karama-NW-5x.



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Pontosphaera multipora, Sphenolithus moriformis, Pont-
osphaera multipora, Chiasmolithus solitus, Discoaster bar-
badiensis, Reticulofene stradictyoda, Neococcolithes dubius, 
Reticulofenestra hampdenensis, Cribrocentrum reticulatum, 
Sphenolithus moriformis, and Reticulofenestra umbilica.

Authors: HAY et al. (1967), emend MARTINI (1970)
Age: Middle Eocene
Occurrence: Karama-NW-1x (705–760 m), Aqsa-1x 

(805–1080 m), Karama-3x (810– 1180 m) (in the Apollonia 
Formation).

Remarks: The base of the zone is placed at the level of 
the fi rst appearance of Reticulofenestra umbilica in the stud-
ied wells. Rhabdosphaera gladius, the marker of the base 
of the zone is often of little use for zonation (PERCH-

NIELSEN, 1985, p. 439). It is well known that Reticulo-
fenestra umbilica has its FO at the base of the middle Eo-
cene zone NP16 (MARTINI, 1971) and CP14 (OKADA & 
BUKRY, 1980).

In the study wells, a large scale hiatus is recorded below 
and above the sediments of Zone NP16, and thus the top and 
ba se of Zone NP16 cannot be accurately detected in such 
wells.

4.2.2.4. Chiasmolithus oamaruensis Zone (NP18)
Defi nition: This zone is defi ned as the interval from the FO 
of Chiasmolithus oamaruensis to the FO of Isthmolithus re-
curvus.

Assemblage: The zone includes the following nanno-
fossil taxa:,Pemma basquensis, Discoaster tanii, Pemma pa-

Figure 11: Benthic Eocene plate. 1 – Cancris auriculus FITCHTEL, MOLL, 1798; 1890 ft, Karama-NW-1x. 2 – Hanzawaina sp. 2100 ft, Aqsa-1x. 3 – Cibicidoides 
ungerianus 2130 ft, Karama-NW-5x. 4 – Cibicidoides kullenbergi PARKER, 1953; 2160 ft, Karama-3x. 5 – Nonnion scaphum FITCHTEL, MOLL, 1798; 1950 ft, 
Karama-3x. 6 – Lenticulina sp.1530 ft, Karama-3x. 7 – Planulina sp. 1800 ft, Aqsa-1x. 8 – Uvigerina eocaena GUMBEL, 1868; 1650 ft, Aqsa-1x. 9 – Bulimina 
jacksonensis CUSHMAN, 1925; 1800 ft, Aqsa-1x. 10 – Bulimina alazanensis CUSHMAN, 1927; 1890 ft, Karama-NW-1x. 11 – Nodosaria sp. 1890 ft, Karama-
3x. 12,13 – Uvigerina tempoalae BOERSMA, 1984; 1740 ft, Karama-NW-1x. 14,15 – Eponides ellisoare SEGUENZA, EMEND, 1968; 1830 ft, Karama-E-1x. 16 
– Quinqueloculina seminula LINNE, 1958; 1620 ft, Karama-E-1x. 17 – Baggina sp. 2430 ft, Karama-E-1x.



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pillatum, Reticulofenestra hillae, Cribrocentrum reticula-
tum, Reticulofenestra umbilica, Helicosphaera compacta, 
Discoaster tanii,Discoaster tanii nodifer, Ericsonia formosa, 
Reticulofenestra dictyoda, Reticulofenestra hampdenensis, 
Reticulofenestra hillae and Chiasmolithus oamaruensis.

Authors: MARTINI (1970)
Age: Middle to Late Eocene.
Occurrence: Karama-NW-5x, Aqsa-1x (560–1400 m), 

Karama-3x (660–740 m), Karama-E-1x (795–1250 m) (in 
Apollonia Formation).

Remarks: The base and top of Zone NP18 are well de-
fi ned in Karama-3x, Karama-E-1x and Karama-NW-5x.

4.2.2.5. Isthmolithus recurvus Zone (NP19/20)
Defi nition: The interval from the fi rst occurrence of Isthmo-
lithus recurvus to the last occurrence of Discoaster sai pa-
nensis,and /or Discoaster barbadiensis.

Assemblage: Zone NP19-20 includes Isthmolithus re-
curvus, Pemma basquensis, Reticulofenestra dictyoda, Dis-
coaster tanii, Reticulofenestra hampdenensis, Reticulofe-
nestra hillae,Cribrocentrum reticulatum, Sphenolithus 
mo ri formis, and Reticulofenestra umbilica.

Authors: HAY, MOHLER & WADE (1966), EMEN-
DED MARTINI (1970).

Age: Late Eocene.
Occurrence: Karama-3x (570–595 m), Karama-E-1x 

(630–700 m), Karama-NW-1x (620–705 m), Karama-NW-
5x (650–680 m) (in Apollonia Formation).

Remarks: The fi rst occurrence of Isthmolithus recurvus 
marks the base of the combined zone NP19/20. MARTINI 
(1971) used the lowest occurrence of Sphenolithus pseudo-
radians to defi ne the base of zone NP20, but subsequent 
work (MARTINI, 1976) has shown that S. pseudoradians 
occurs much earlier and that the two zones cannot be differ-
entiated. Therefore, zones NP19 and NP20 are also combined 
here, and Zone NP19/20 is defi ned as the interval between 
the fi rst occurrences of I. recurvus and the last occurrence of 
Discoaster saipanensis and D. barbadiensis.

Figures 12 to 16 show the distribution of the nanno-
plankton in the different wells and some stratigraphically 
important taxa are represented in Figures 17 and 18 which 
are identifi ed from the Aqsa-1x, Karama-3x, Karama-E-1x, 
Karama-NW-1x and Karama-NW-5x wells respectively.

Figure 12: Distribution chart of the nannofossils of the Well Aqsa-1x.



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Figure 13: Distribution chart of the nannofossils of the Well Karama-3x.

5. SEQUENCE STRATIGRAPHY

The target of seismic stratigraphic analysis is to divide the 
seismic sections of the East Bahariya Concession into dis-
tinct depositional sequences that make up the investigated 
Late Cretaceous-Eocene succession in the study area. These 
sequences are bounded from above and below by marked 
sequence boundaries (EMERY & MYERS, 1996). The fol-
lowing steps were followed to achieve the aim of this study: 
A) Reorganization of the time-depositional units depending 
on the detected unconformities or changes in seismic pat-
terns. B) Following these recognized unconformities in the 
different investigated seismic sections, it was important to 
defi ne the major sequence boundaries. C) Seismic facies 
analysis, interpreting depositional environments from seis-
mic refl ection characteristics. D) Sequence stratigraphic 
analysis of the different formations using the available bios-
tratigraphic data and lithological composition.

5.1. Detailed sequence stratigraphic analysis

Analysis of the sequence stratigraphy in the studied area is 
based mainly on the interpretation of various key surfaces 
(sequence boundaries (SB), transgressive surfaces (TS), trans-
gressive surfaces of erosion (TSE) and maximum fl ooding 
surfaces (MFS)) and system tracts (lowstand systems tracts 
(LST), transgressive systems tracts (TST), highstand systems 
tracts (HST)) well logs (natural, radioactivity, receptivity and 
density logs) and foraminiferal content. These factors detect 
the depth and the environmental conditions during deposition 
in the seven investigated wells (AQSA-1X, AQSA-2x, KA-
RAMA-3X, KARAMA-E-X, KARAMA-NW-1X, KAR-
AMA-NW-5X, KARAMA-SW-1X and KARAMA-SW-10X) 
located in the studied East Bahariya concession (Figure 1).

The studied Upper Cretaceous-Eocene succession in the 
East Bahariya concession at the Western Desert is subdivided 
into fi ve major 2nd order depositional sequences (UCS1, 



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Figure 14: Distribution chart of the nannofossils of the Well Karama-E-1X.

UCS2, UCS3, ES and ORS). These are separated by four 
major depositional sequence boundaries (SB1, SB2, SB3 and 
SB4) as shown in (Figs. 19 and 20).

5.1.1. Upper Cretaceous sequence 1 (UCS1) 
(Cenomanian)

The fi rst sequence (UCS1) is represented by the Upper Cre-
taceous rocks including the Upper Bahariya Fm. (Fig. 19). 
The top of this sequence is bounded by the depositional se-
quence boundary SB1 which represents the boundary be-
tween the Abu Roash-G Member and the underlying Baha-
riya Fm. It is the deepest identifi ed and selected surface in 
the study area, which regionally, extends along the East Ba-
hariya Concession, indicating a regional unconformity be-
tween the Abu Roash Formation and the underlying Bahariya 
Formation and the second order depositional sequence bou-
n dary (EL BASSYOUNY, 1970, CATUNEANU et al., 2006).

The base of this sequence can not be followed on the 
seismic sections because these are badly processed (Fig. 21), 

while the upper part of the Bahariya Fm. displays discon-
tinuous, moderate to low amplitude refl ectors. Internal con-
fi gurations including onlap, toplap, downlap and parallel re-
fl ectors were recognized.

The external form of this sedimentary body appears ei-
ther as sheet-like or wedge-shaped units. The principal in-
ternal confi gurations appear to be parallel to subparallel.

Interpretation
Clear differences between the high and low to moderate am-
plitude refl ectors in this formation testify to the existence of 
at least two different lithological units. One has high ampli-
tude and displays parallel to divergent refl ector terminations. 
These units are interpreted as shale to siltstone beds. The 
other lithological units which have a low to moderate ampli-
tude and are characterized by disconnected refl ectors are in-
terpreted as sandstone beds. According to Darwish et al., 
(1994) and ISMAIL et al. (1989) the Bahariya Formation 
lithologically is subdivided into the lower Bahariya and up-
per Bahariya units.



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Figure 15: Distribution chart of the nannofossils of the Well Karama-NW-1X.

The Lower Bahariya Formation is composed of a rela-
tively sand rich succession of fi ne to medium grained sand-
stone and shale while the Upper Bahariya Formation is com-
posed mainly of very fi ne-grained sandstone with shale 
intercalated with limestone beds. Pyrite and glauconite min-
erals are common, which were deposited in a shallow marine 
to fl uvio-marine environment with alternating high and low 
energy.

Based on the results of the analyzed seismic lines, this 
subdivision of the Bahariya Fm. into two units has been iden-
tifi ed in the all investigated seismic lines thus confi rming the 
interpretation of the seismic facies.

5.1.2. Upper Cretaceous sequence 2 (UCS2) 
(Cenomanian–Turonian)

5.1.2.1. Abu Roash-G Member (Cenomanian)
Based on the interpretation of the seismic lines, the Abu 
Roash-G Member can be subdivided into two main parts. 

The lower part is characterized by low amplitude and mo de-
ra te continuity refl ectors. Their refl ection geometry at the sequ-
en ce boundaries is considered as erosional truncation (Fig. 23).

From the studied seismic lines the refl ection geometry 
at the sequence boundaries are considered concordant with 
lower and upper sequence boundaries of this formation. The 
seismic facies of the lower part of the Abu Roash-G Mem-
ber appears as low to moderate amplitude and moderate con-
tinuous refl ectors in the internal confi guration as parallel re-
fl ectors, which in the external outline seems to represent 
elongated wedge-shaped beds.

The seismic facies of the upper part of the Abu Roash-
G Member is characterized by high amplitude and very con-
tinuous refl ectors. The internal refl ection geometry at the 
upper sequence boundary is considered concordant and runs 
parallel to the sequence boundary (Figs. 21 and 23).

Interpretation
The characteristic confi guration of the seismic facies in the 
lower part of the Abu Roash-G Member is interpreted as sand 



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Figure 16: Distribution chart of the nannofossils of the Well Karama-NW-5x.

Figure 17: Nannofossils Cretaceous plate. 1 – Eiff ellithus turriseiff elii (DE-
FLANDRE in DEFLANDRE & FERT, 1954) REINHARDT (1965) K-NW-1x; 2,3 
– Lu cianorhabdus cayeuxii DELANDRE (1959), depth (5040-5070) Aqsa-1x; 
4,5 – Calculites obscurus (DEFLANDRE, 1959), depth (4470-4500) K-3X; 6 
– Reinhardtites anthophorus (DEFLANDRE, 1959), depth (5640-5670) K-E-
1X; 7 – Cribrosphaerella ehrenbergii (ARKHANGELSKY, 1912), depth (5100-
5130) K-NW-1X; 8 – Eiff ellithus eximius (STOVER, 1966) depth (5850– 5880) 
K-E-1X; 9,10 – Micula murus MARTINI (1961), depth (4470–4500) K-3X; 
11,12 – Watznaueria barnesae (BLACK in BLACK & BARNES, 1959), depth 
(5935–5940) Aqsa-1x.

bars (Fig. 23). The low amplitude and discontinuity of the 
seismic refl ectors support this interpretation. These sand beds 
may represent deposits of a prograding delta system, with 
offshore (pro-delta) silty mudstones at the base overlain by 
(in ascending order) lower, middle and upper shoreface sand-
stone, distributary-mouth bar sandstone.

The internal confi guration as parallel refl ectors of the 
upper part is interpreted as homogenous sediments, which 
are arranged in parallel thin beds. These features exhibit cy-
cles of mudstone, glauconitic siltstone, limestone, and sand-
stone deposits.

Based on the depositional environment of the Abu 
Roash-G Member (MARK et al., 2009) which is conside red 



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Figure 18: Nannofossils Paleogen plate. 1 – Reticulofenestra hillae BUKRY 
& PERCIVAL (1971) Aqsa-1x; 2 – Ismolithus recurvus DEFLANDRE (1959), 
depth (1920–1950) K-3x; 3 – Pemma basquensis (MARTINI, 1959c) BALDI-
BEKE (1971) K-NW-1x; 4 – Reticulofenestra umbilica (LEVIN, 1965), depth 
(2400–2430) Aqsa-1x; 5 – Pontosphaera multipora (KAMPTNER, 1948) 
ROTH (1970) K-NW-1x; 6 –BIsmolithus recurvus DEFLANDRE 1959 K-E-1x; 
7 – Braarudosphaera bigelowii (GRAN & BRAARUD, 1935), depth (2130–
2160) K-3x; 8 – Dictyococcites bisectus (HAY, MOHLER, WADE, 1966), depth 
(1920–1950) K-3x; 9 – Ismolithus recurvus DEFLANDRE (1959), depth 
(1920–1950) K-3x; 10 – Ericsonia formosa (KAMPTNER, 1963), depth 
(2400–2430) K-NW-5x; 11 – Zygrhablithus bijugatus (DEFLANDRE in DEF-
LANDRE & FERT, 1954), depth (2640–2670) K-3x; 12 – Chiasmolithus 
oamarunsis (DELLANDRE, 1959), depth (2400–2430) K-3x; 13 – Mi c-
rantholithus bramlettei (BRONNIMANN & STRADNER, 1960), depth (3390–
3420) K-3x; 14 – Sphenolithus radians DEFLANDRE in GRASSE (1952), 
depth (3390–3420) K-3x; 15,16 – Pontosphaera multipora (KAMPTNER, 
1948), depth (2400–2430) K-3x.

Figure 19: An interpretation of seismic section 5455.

to be delta to shallow marine environment, our interpretation 
agrees with the statements and characteristic features such 
as sandstones bodies and shale beds that were re cog nized in 
the interpreted seismic lines (Figs. 21, 23 and 24).

5.1.3. Abu Roash A, B, C, D, E and F members 
(Turonian)
The Abu Roash Fm. is generally characterized by several 
strong correlated internal refl ectors representing the contacts 
between its members. The parallel refl ectors alternate with 
weak to moderate internal refl ectors, which show chaotic to 
hummocky internal confi gurations (Fig. 24). The external 
forms of these members (A, B, C, D, E and F) display dif-
ferent geometries such as sheet-like and wedge-shaped 
forms, which can be indicated by parallel to divergent inter-
nal refl ection confi guration.

Based on Biostratigraphy BARAKAT et al. (1987), these 
facies features exhibit cycles of shallow marine limestone, 
sandy limestone and shale of the Abu Roash A, shallow of 
the Abu Roash B Member, relatively restricted deep marine 
shale, sandstone and limestone of the Abu Roash C Member, 
the limestone and shale of Abu Roash D, shallow marine 

Figure 20: An interpretation of seismic section 1417.

sand and shale of the Abu Roash E Member, and the deep 
marine limestone and shale of the Abu Roash F Member 
(Figs. 23 and 25).

Interpretation

The alternation between weak –moderate and high amplitude 
internal refl ectors suggests at least two different lithological 
units. The obvious parallel refl ectors are interpreted as shale 
beds. The low amplitude refl ectors have a chaotic to hum-
mocky internal confi gurations, which indicate impure lime-



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stone or highly bioturbated sandstone beds. The Abu Roash 
Fm. of Turonian age consists of limestone with shales and 
sandstone intercalations providing a good source reservoir 
and cap rocks for hydrocarbons (BAYOUMI et al., 1987).

According to BARAKAT (1987) the habitats of the fau-
nal assemblage together with the occurrence of detrital 
quartz grains in the Abu Roash F-A Members suggest a shal-
low marine environment of the neritic zone. Furthermore the 
Abu Roash Fm. was deposited in shallow-shelf to open-ma-
rine conditions (BARAKAT et al., 1987; BAYOUMI et al., 
1994, 1996).

5.1.4. Upper Cretaceous Sequence 3 (UCS3) 
(Campanian-Maastrichtian)
The Khoman Fm. is equivalent to sequence (UCS3). This 
sequence is bounded by SB2 below and the above. SB2 is at 
the end of the Turonian. Detailed analysis of SB2 reveals 
that it is of the type 2 boundary of VAN WAGONER et al. 
(1988). It is characterized by partial erosion of the Coniacian 
and Santonian between the Khoman and the top of the Abu 
Roash Formation, as shown by truncation of the top Abu 
Roash especially in structurally uplifted places (BAYOUMI 
& LOTFY, 1989). It is an important disconformity recorded 
in all the Cretaceous-Tertiary successions of Egypt (HE-
WAIDY et al., 2006).

The seismic facies of the lower part of the Khoman Fm. 
is moderate to low in the continuity and amplitude repre-
sented by disconnected refractors. These refl ectors exhibit 
several characteristic terminations such as onlap, truncations 
and complicated sigmoidal confi gurations. A group of paral-
lel irregular refl ectors is characteristic for this lower part of 
the Khoman Fm.

Figure 21: Lithologic section of the Upper Cretaceous-Eocene Succession correlated with seismic profi le 1219.

The seismic facies of the middle part of the Khoman Fm. 
is entirely different in character which is dominated by very 
weak continuity and amplitude with prevailing chaotic seis-
mic confi gurations (Fig. 26). The external geometry of this 
part represents an inhomogeneous lithological character, 
which appears to be similar to reef or salt dome geometry 
(Fig. 26).

The internal configuration of the upper part of the 
Khoman Formation is characterized by very high continuity 
and amplitude with parallel refl ectors. These refl ectors ex-
tend concordantly with the upper boundary of this sequence 
and display onlap and oblique parallel confi gurations. The 
external geometry in the upper part occurs as sheet like units 
to platform geometry especially to the north of the study area 
(Fig. 26).

Interpretation

Based on the fossil content and the description of the seismic 
facies with respect to characteristics of these seismic refl ec-
tors, one could conclude that the logical interpretation of the 
seismic confi guration, such as very closed and parallel refl ec-
tors, indicate a well bedded and homogenous lithology, which 
can be shale beds intercalated with limestone or chalk.

Parallel, irregular refl ectors groups are interpreted as 
isoclinals small folds within the lower part of the Khoman 
Fm. Fold structures can be attributed to compressional stress 
in the study area during the Late Cretaceous.

The poorly and weak amplitude refl ectors in the middle 
part indicate massive chalk limestone. The moderate to low 
continuity and amplitude signify limestone with a high 
number content of chert nodules. This interpretation agrees 
with the lithology of the Khoman Fm. which consists mainly 



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127

Figure 22: Shows the lower part of seismic line 
5667(middle of the study area), (b): The interpreted 
seismic line 5667 displaying the main internal con-
fi gurations which characterized the seismic facies of 
Upper Cretaceous Sequence 1 (UCS1).

Figure 23: Shows the lower part of seismic line 
5727(middle of the study area), (b): The interpreted 
seismic line 5775 illustrates the internal confi gura-
tions of sandstone in the lower part of Abu Roash-G 
Member as a part of Upper Cretaceous Sequence 2 
(UCS2).

Figure 24: Showing the lower part of seismic line 
5930 (east of the study area), (b): The interpreted 
seismic line 5930 illustrates the internal confi gura-
tions of sandstone in the lower part of Abu Roash-G 
Member as a part of Upper Cretaceous Sequence 2 
(UCS2).



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Figure 25: Relative sea level fl uctuations in the Upper Cretaceous, Western 
Desert. 

Figure 26: Showing one of the internal con-
fi guration which distinguish the seismic facies 
of Upper Cretaceous Sequence 3 (UCS3) (up-
per part of line 5667).

of chalky limestone with pyritic, cherty strata in the lower 
part and interbeds of shale in the upper part (BARAKAT et 
al., 1984, ABDEL HAMID, 1985 & GHANEM, 1985).

Facies characteristics, faunal content and planktonic ra-
tio indicate an upward shallowing in the depositional regime 
from a deep middle/outer to shallow inner shelf during dep-
osition of the Khoman Formation (HEWAIDY et al., 2006).

5.1.5. Eocene sequence 4 (ES)

The fourth sequence is represented by Eocene sediments 
(ES), which comprise the Apollonia Formation (Figs. 19, 
20). This sequence is bounded by SB3 in the lower part and 
by SB4 at the upper part Figs. 19 & 20, show the SB3 which 
appears at the end of the Upper Cretaceous (Campanian – 
Maastrichtian) and separates between the Eocene sequence 
(ES) and Upper Cretaceous sequence (UCS3) sequences. 
The SB3 has moderate to high amplitude refl ectors and is 
also marked by the radioactivity increase in the gamma ray 
logs (Fig. 27).

Based on the fossil content, the available data and for-
mer geological studies, the lower part of this sequence 
boundary is affected by submarine erosion causing the ero-
sion causing the removal of the uppermost part of the Maas-
trichtian and all of the Palaeocene (BAYOUMI et al., 1987).

Seismic facies of this sequence which is represented by 
sediments of the Apollonia Formation have three main fea-
tures which are also very clear in the gamma logs.

The seismic facies of the lower part of the Apollonia Fm. 
is moderate to low both in continuity and amplitude, while 
to the north of the area; refl ectors are moderate to high am-
plitude and continuity. The internal confi gurations appear to 
be parallel to divergent (Fig. 28). This part shows the in-
crease in gamma rays (more than the upper part of the 
Khoman Formation). In general the refl ection geometry at 
the lower sequence boundary of the Apollonia sequence is 
considered concordant and exhibits even onlap near to cen-
tral part of the study area (Fig. 28)

The seismic facies of the middle part of the Apollonia 
Formation is distinguished by high continuity and amplitude. 
Also the principal internal confi gurations appear to be paral-
lel to the divergent refl ectors. The external form of these 
sediments is considered to be a wedge like geometry with 
local irregular bedding features. These structures occur as 
small isolated and relative high amplitude refl ectors of small 
domal structures.

The seismic facies of the upper part of the Apollonia 
Formation is characterized by low to moderate continuity 
and amplitude. The principal internal confi gurations appear 
to be parallel to divergent. The external form of these sedi-
ments is sheet-like and wedge shaped units.

The foraminiferal assemblage recorded from the upper 
part of this sequence suggests the end of the restricted envi-
ronment that prevailed during deposition of the underlying 
Eocene sediments.

Interpretation

Based on the seismic facies confi gurations the parallel high 
amplitude refl ectors display a carbonate ramp geometry, 
which has a very slight dip and occurs as an elongated 
wedge. The local irregular bedding structures are interpreted 
as convolute bedding which may be related to slumping.

This carbonate ramp extends from north to the south 
(Fig. 28). It is worth mentioning, that the thicknesses of this 



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129

Figure 27: System tracts, logs, fauna and depositional environment of Well K-NW-1X.

carbonate ramp decreases laterally to the south. The low am-
plitude refl ectors in the lower part indicate a heterogeneous 
lithology, which may be related to mixed pure carbonate 
sediments contaminated with cherty nodules and lenses par-
allel to bedding.

The lithological composition and the characteristics of 
the seismic refl ectors of this sequence suggest that its depo-

sitional conditions range the inner shelf at the base to the 
outer shelf at the top of this sequence.

5.1.6. Oligocene to recent sequence 5 (ORS)

The Oligocene to recent facies in the study area are repre-
sented by the sediments of the Dabaa Fm. in the lower part 
and the Moghra Fm (Miocene) at the top of the investigated 



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seismic lines. Both formations build up a complete sequence 
the lower boundary of which is represented by the sequence 
boundary (SB4), whereas the upper boundary represents the 
top of all interpreted seismic lines in the study area. The se-
quence boundary represents the unconformity surface due 
to erosion of sandstone and siltstone from type section de-
fi ned in the Dabaa-1 well (TAWADROS, 2001).

Based on the analyzed lines, the seismic facies of the 
Upper top facies are characterized by: Internal confi guration 
of the lower part gradually increasing in both the continuity 
and frequency of seismic refl ectors upward showing several 
seismic terminations such as toplap with parallel to sigmoi-
dal confi gurations. These refl ectors run parallel to each other 
and display a high amplitude and frequency in the middle 
part of this sequence. The external form of this unit resem-
bles sheet-like units.

The upper part of the sequence is characterized by cha-
otic, discontinuous, high frequency and low amplitude re-
fl ectors (Fig. 29). The internal confi guration of the seismic 
facies is characterized by seismic termination features: on-
lap, toplap and erosion truncations. The external form is of 
the sheet-like and wedge shaped units with observable chan-
nel-like geometry.

Interpretation

A gradually increase in both the continuity and frequency of 
the seismic refl ectors in the lower part of this sequence in-
dicates changes in the lithology. Hence the lower part of this 
sequence is interpreted as shale beds of the Dabaa Forma-
tion intercalated with evaporites concentrated in the lower 

part of the sequence and characterized by low amplitude re-
fl ectors and very chaotic seismic confi guration (Fig. 29).

The upper part of this sequence is interpreted as sand-
stone beds of the Moghra Formation because of the relatively 
low seismic refl ectors, in addition to the occurrence of typi-
cal sandstone features such as channel fi ll structures.

These characterize the Upper top facies of the Dabaa 
and Moghra Formations suggesting a change from shallow 
marine inner shelf environment at the base to fl uvial facies 
at the top. This assumption agrees in some points with the 
interpretation of the seismic lines.

5.2. Gamma ray response

The change in the gamma ray responses in the various units 
can be recognized. The boundary between units UCS1 and 
UCS2 is marked by a decrease in the gamma ray values (Fig. 
30).

The presence of sandstone and shale intercalations in 
many parts of the UCS1 unit causes oscillation of the gamma 
ray curve (Figs. 29, 30). The contact between the units UCS2 
and UCS3 can be detected by a decrease in the gamma ray 
values (Figs.20, 29) accompanied with the change from shale 
to limestone lithofacies.

The boundary between the unit UCS3 and the ES is 
marked by a slight increase in the gamma ray values. UCS3 
shows no change in gamma ray values because it is com-
posed only of chalk limestone. The ES unit shows some high 
values in the gamma ray log which are ascribed to the shale 
intercalations in this unit (Fig. 29).

Figure 28: Showing the lower part of seismic 
line 5630 (middle of the study area), (b): The 
interpreted seismic line 5630 illustrating the 
internal confi gurations of Eocen Sequence.



Mahsoub et al.: Bio- and Sequence Stratigraphy of Upper Cretaceous – Palaeogene rocks, East Bahariya Concession, Western Desert, Egypt Geologia Croatica
131

The upper part of the ORS unit is characterized by a 
marked decrease in the gamma ray values with respect to the 
underlying unit ES.

6. DISCUSSION OF THE SYSTEMS TRACTS

The Upper Cretaceous – Palaeogene succession in the East 
Bahariya concession is divided into 17 systems tracts. These 
systems tracts are outlined below:

6.1. System tracts of Cenomanian age

6.1.1. Lowstand systems tract (LST1)

This systems tract represents the fi rst one studied in this 
work. It comprises the upper part of the first sequence 
(UCS1), which represents the upper part of the Bahariya 
Formation. The lower boundary of this tract is not traceable 
on seismic profi les. This lowstand system is characterized 
by low GR and relatively high resistivity (Fig. 30).

Sediments of the LST1 are mainly sandstones with silt-
stone interbeds. These deposits are overlain by the clastic 
and non-clastics deposits of shale and limestones, which be-
long to the lower part of the Abu Roash-G Member (Fig. 31).

The available data indicate that this interval represents 
the maximum drop in sea level. This drop started with the 
deposition of the coarse clastics (sandstone) of the Bahariya 
Formation and continued and increased with deposition of 
more clastics and evaporites. This systems tract is widely 
recognized across the Western Desert.

The TST is missing, due to either non-deposition or sub-
sequent erosion. The HST of this sequence is also missing, 
most likely due to subaerial erosion (fl uvial incision) where 
the upper (LST1) is directly overlain by the 2nd order depo-
sitional sequence of the Abu Roash Formation, being trun-
cated at the top by the sequence boundary (subaerial uncon-
formity).

The age of this lowstand system is Early Cenomanian. 
The LST1 deposits are limited by the fi rst sequence bound-
ary (SB1), which delineates the end of the 1st sequence and 
the beginning of the second.

6.1.2. Highstand systems tract 1 (HST1)

Based on the available data and their resulting interpretations 
LST and TST system tracts in the investigated well sections 
are entirely missing. The absence of these may be attributed 
to the erosion cycle, which is indicated by truncation at the 
top by the sequence boundary due to subaerial unconformity.

This highstand system tract occurs in the Lower part of 
the Abu Roash-G Member, and represents the maximum 
phase of transgression after deposition of the Bahariya For-
mation (Fig.32).

The progradational HST1 sediments are characterized 
by an upward increase in GR and moderate to low resistiv-
ity. Lithofacies of the HST1 sediments are entirely different 
from those of the LST1 sediments (Fig. 31), and includes 
mainly shales and limestones. The limestone is laterally var-
iable in thickness whereas the shale is concentrated mainly 

Figure 29: Showing the upper part of 
seismic line 5455 (west of the study area), 
(b): The interpreted seismic line 5455 dis-
playing the main internal confi gurations 
which characterized the seismic facies of 
Upper Eocene to Recent Sequence (UERS).



Geologia Croatica 65/2Geologia Croatica
132

in the central part of the studied area. The total thickness of 
this high system tract reach a maximum (30 m) in the Karma-
SW 1x well and is minimal (18 m) in the in Karama-NW 5x 
well (Fig. 31).

6.1.3. Lowstand system tract (LST2)

This systems tract represents the second studied low system. 
It consists of a small part of the Abu Roash-G Member. The 
progradational LST2 sediments are characterized by low GR 
and relatively high resistivity.

Sediments of the LST2 are present all over the study area. 
The lithological composition of these deposits is mainly sand-
stone, mudstone and siltstone. The thickness of the LST2 
sediments is quite small and uniform (about 10 m) (Fig. 31).

Seismic facies analysis and Gamma ray log confi rm that 
the sandstone sediments indicate that, the prevalent environ-
ments of depositions during deposition of this system tract 
were estuaries or shorelines.

The sandstone units were most likely deposited as bay-
head deltas, tidal channels and barrier beaches because they 

Figure 30: System tracts, logs and depositional environment of Turonian, Campanian–Maastrichtian, Eocene and Recent Sequences of Well Aqsa-1X.



Mahsoub et al.: Bio- and Sequence Stratigraphy of Upper Cretaceous – Palaeogene rocks, East Bahariya Concession, Western Desert, Egypt Geologia Croatica
133

display the characteristic features of tidal environments with 
a high dynamic regime of and wave infl uence.

6.1.4. Transgressive systems tract (TST1)

The retrogradational deposits of TST1 are marked by high 
GR and represents the onset of transgression and sea-level 
rise (NUMMEDAL & SWIFT, 1987). It overlies the trans-
gressive surface (TS1), which tops the lowstand systems tract 
(LST1) (Fig. 31). The TST1 sediments are composed of shale 
and limestone deposits in most of the area and mainly shale 
with a few limestone interbeds in the West of the study area.

The maximum fl ooding surface (MFS1) separates the 
deposits of the retrograding interval of the TST1 below from 
the prograding deposits of the HST1 above (Fig. 31). This 
surface, together with the TST1 sediments, is associated with 
high peaks in the GR logs (SCHAFFER 1987; ARMEN-
TROUT & CLEMENT, 1990).

The thickness of this system tract shows an increase in 
the middle part of the investigated area and decrease later-
ally in both sides (Fig. 31). Interpretation of seismic facies 
and Gamma ray log indicate that open marine conditions 
prevailing during the deposition of this system tract.

6.1.5. Highstand systems tract 2 (HST2)

This highstand system tract overlies the sediments of the 
transgressive systems tract TST1. Lithofacies of the HST2 
sediments are clearly different to those of the HST1 sedi-
ments. HST2 sediments contain more shale in comparison 
with the HST1 (Fig. 31). The thickness of the HST2 sedi-
ments is quite variable. The maximum thickness (about 10 
m) is detected at Aqsa-1X and K-SW-1X wells, while the 

minimum thickness (4 m) in K-NW-1X well (Fig. 31). From 
GR and lithology the prevailing environmental conditions 
during deposition of this system tract are deep marine con-
ditions.

6.1.6. Lowstand system tract 3 (LST3)

The aggradational LST3 sediments have quite a similar well 
log response to those of the LST2 sediments (Fig. 31). The 
lithology of these deposits is mainly pro-delta silty-mud-
stone, lower, middle and upper shoreface sandstone, distrib-
utary-mouth bar sandstone, and distributary-channel sand-
stone, silty-muddy interdistributary or coastal plain deposits. 
The thickness of these deposits is quite variable with maxi-
mum thickness (about 12 m) drilled in K SW-1X and K SW-
10X wells and minimum thickness (about 5 m) in K-NW-1X 
well. The log shape and the lithofacies characteristics of 
these sediments indicate that the LST3 sediments are depos-
ited in similar conditions to those of the LST1.

6.1.7. Transgressive system tract 2 (TST2)

The retrogradational TST2 sediments have a quite different 
lithological composition and log response characteristics to 
those of the TST1. These sediments include the upper parts 
of the Abu Roach-G Member, composed of shale, limestones 
and sandstone respectively.

The upper boundary of the TST2 sediments is marked 
by an abrupt increase in the GR where the lower part shows 
low to moderate GR values. The increase of GR values in 
the upper part is due to an increase in the shale ratio within 
this system tract. The high shale content is attributed to the 
fact that, the Early Turonian started with the great transgres-

Figure 31: Schematic diagram for W-E correlation of the system tracks in the Abu Roash-G Member.



Geologia Croatica 65/2Geologia Croatica
134

sion of the Late Cretaceous, which was recorded as the max-
imum fl ooding surface in the Western Desert (MFS2) (BAR-
AKAT, 1987). The thickness of these deposits is quite va riable 
with the maximum thickness of 60 m in well K-SW-1X.

6.2. Systems tracts of Turonian age

6.2.1. Highstand systems tract 3 (HST3)
This highstand system tract comprises the Abu Roash F, E 
and D Members. With the advent of the Turonian, the max-
imum fl ooding surface (MFS2) covered the northern part of 
the Western Desert (BARAKAT, 1987). This system tract 
tops the transgressive systems tract TST2 and represents the 
upper part of the Abu Roash-G Member.

Lithofacies of the HST3 sediments are similar to the 
HST1 sediments, composed mainly of shale and limestone 
(Figs. 26 and 29) where the Abu Roash members E, F and 
G are the most prolifi c and outstanding source rocks in the 
Western Desert (Lüning, 2004).

6.2.2. Lowstand systems tract 4 (LST4)
This lowstand systems tract is relatively thin representing 
part of the Abu Roash Fm. In the Turonian time (Figs. 26 
and 29). It overlies the high stand system tract (HST3). The 

intervals of LST4 are characterized by a relatively decrease 
in gamma ray values.

This systems tract is part of the Abu Roash-C Member, 
composed of shale, sandstone and limestone indicating a 
shallow shelf marine (sublittoral) environment (ABDEL 
KHALEK, 1989).

6.2.3. Transgressive system tract 3 (TST3)

TST3 sediments have quite similar lithological well log char-
acteristics to those of TST1, which is exclusively composed 
of shale and limestone sediments.

The upper boundary of the TST3 deposits is marked by 
moderate GR values. The second maximum fl ooding surface 
(MFS3) in Turonian time in the Western Desert is encoun-
tered directly above this system tract (Figs. 27 and 30).

This system tract is apart of the Abu Roash-D Member, 
which consists of limestone alternating with thin fl int bands 
refl ecting a shallow shelf marine environment (ABDEL 
KHALEK, 1989).

6.2.4. Highstand systems tract 4 (HST4)

This highstand systems tract occupies the top of the upper 
part of the Abu Roash Fm. and consists mainly of shale, lime-
stone and sandstone intercalations and its deposits display 
moderate to high GR values, because the main lithological 
component is shale.

HST4 overlies the transgressive surface (MFS3), which 
tops the second transgressive systems tract of Turonian age. 
The predominant environmental conditions of deposition we-
re those of shallow marine shelf (ABDEL KHALEK, 1989).

6.3. System tracts of Campanian–Maastrichtian 
age

6.3.1. Transgressive system tract 4 (TST4)

This transgressive systems tract represents the beginning of 
the sequence boundary (UCS3), which covers the high stand 
system tract sediments (HST4) high stand system tract sed-
iments whereas the LST was truncated during the Coniacian 
and Santonian at the top of Khoman Formation due to sub-
aerial exposure represented by an unconformity.

Lithofacies of the LST4 sediments are composed of sed-
iments of limestones intercalated with shale which denotes 
the lower part of the Khoman Fm. (Figs. 27 and 30). The 
relatively deep sea conditions that prevailed by the offset of 
the Early Cenomanian persisted during the Late Cenoma-
nian, Turonian and attained their peak in the Maastrichtian 
(BARAKAT, 1987) as refl ected by the interpreted MFS4 sur-
face. The TST4 is characterized by a strong increase in the 
gamma ray, which indicates an increase in sea level in the 
Western Desert (MFS4).

6.3.2. Highstand systems tract 5 (HST5)

This highstand systems tract represents the upper part of the 
Khoman Fm. and consists of open-marine white chalky lime-
stone with chert bands.

Figure 32: Formations, Sequences, Systems tracts and sea-level changes 
of the Upper Cretaceous-Eocene age of the subsurface East Bahariya suc-
cession.



Mahsoub et al.: Bio- and Sequence Stratigraphy of Upper Cretaceous – Palaeogene rocks, East Bahariya Concession, Western Desert, Egypt Geologia Croatica
135

It overlies the transgressive surface (MFS4), which tops 
the transgressive systems tract of Campanian-Maastrichtian 
age.

Data such as GR and fossil content indicate that the en-
vironmental conditions, which were prevailing during the 
deposition of the system tract, were indicative of a shallow 
inner shelf of marine environment.

6.4. Systems tracts of Eocene age

6.4.1. Lowstand systems tract 5 (LST5)

This lowstand system tract represents the lower part of the 
Apollonia Fm. (Figs. 27 and 30) wich overlies the sequence 
boundary (SB3), where It is tops the high stand systems tract 
(HST5).

The fossil content and available composite logs indicate 
that, this lowstand systems tract is composed of shallow ma-
rine limestone with numerous chert intervals. The cherty in-
tervals of LST5 are characterized by a relative increase in 
gamma ray values. The high values are attributed to the con-
centration of organic matter within the chert beds.

The lithological, foraminiferal data and characteristics 
of the seismic refl ectors of this sequence suggest that the 
depositional conditions in this systems tract range from outer 
shelf to inner shelf at the base of the Eocene period.

6.4.2. Transgressive systems tract 5 (TST5)

This transgressive systems tract includes the middle part of 
the Apollonia Formation. It overlies lowstand systems tract 
sediments (LST5) of the Eocene Sequence (ES). The MFS5 
surface delineates the upper boundary of the retrograding 

sequence of the TST5 sediments. This surface is marked by 
the maximum GR response and the foraminiferal content 
(Figs. 27 & 30). The MFS5 is overlain by the prograding se-
quence of HST6 sediments.

This systems tract represents the maximum transgres-
sion recorded in the Western Desert area during the Middle-
Late Eocene. Based on various types of available data the 
environmental conditions prevailing during the deposition 
of the system tract are outer shelf to inner shelf.

6.4.3. Highstand systems tract 6 (HST6)

This highstand systems tract consists of the upper part of the 
Eocene Sequence (ES) and represents the upper part of the 
Apollonia Fm. It is characterized by the abrupt increase of 
the Gamma ray values (Figs. 28 & 31). This increase in 
Gamma values is due to the high mud and silts fractions.

Highstand systems tract (HST6) overlies the maximum 
fl ooding surface MFS5, which tops the transgressive systems 
tract of Eocene age, where it includes limestone with shale 
interbeds. Limestone beds are rich in foraminifera which 
may indicate a deeper water habitat.

6.4.4. Transgressive systems tract 6 (TST6)

This transgressive systems tract includes the Dabaa Fm. It 
overlies the highstand systems tract (HST6) of the Eocene 
Sequence (ES). Transgressive system tract 6 (TST6) is char-
acterized by an increase of gamma values with oscillation, 
but in the upper part gamma values suffer a moderate de-
crease compared to the lower part of this transgressive sys-
tem tract (TST6).

Figure 33: Illustrates the major stru-
ctural trends in the Western Desert 
(after EGPC, 1992).



Geologia Croatica 65/2Geologia Croatica
136

The available data suggest that the LST was removed 
due to marine erosion (TAWADROS, 2001). The environ-
mental conditions, which were predominant during the dep-
osition of this transgressive systems tract, were marine outer 
shelf to deep marine environments.

The aforementioned interpreted palaeo-environments of 
the study area exhibited echoes of the tectonic events affect-
ing the southern margin of the Tethys Ocean. The study area, 
however, is located 80 Km offshore southern Tethys Ocean 
in the Abu Gharadig Basin, which is situated on the North 
African Plate. This basin developed in conjunction with a 
complex series of E-W and Northeast-Southwest oriented 
normal and wrench faults (Fig. 33) that formed during the 
Late Jurassic rifting and continued into, or were rejuvenated 
during the Early Cretaceous along the east Mediterranean 
margin resulting in the oceanization of the eastern Mediter-
ranean basin. Rifting resulted from the initiation of the clo-
sure of the Tethys (GUIRAUD, 1998).

7. SUMMARY AND CONCLUSIONS

The calcareous nannofossils identifi ed belong to CC22, 
CC23, CC25 of the Campanian – Maastrichtian age and 
zones NP12, NP13 of Early Eocene age and NP16 of Mid-
dle Eocene age and NP18 and NP19/20 of Late Eocene age. 
The ages of the different rock units were identifi ed by means 
of planktonic foraminifera as well as calcareous nannofos-
sils and some hiatuses were detected within the studied wells 
as follows:
1. The latest Cretaceous and the all of the Palaeocene are 

probably missing in the whole area, resulting in a major 
unconformity which may suggest tectonic instability due 
to pulses of epeirogenic movements affecting the area.

2. The boundary between the Apollonia Fm. and the over-
lying Dabaa Fm. is represented by an unconformity with 
corresponding hiatuses of different time spans. While 
the latest Eocene planktonic foraminifera such as Cri-
brohantkenina, Turborotalia cerroazulensis cocoaensis, 
Turborotalia cerroazulensis cunialensis are absent, it is 
possible to identify the Upper Eocene by means of the 
index calcareous nannofossils. The Apollonia Fm. (Cam-
pa nian-Maastrichtian) rests unconformably on the Kho-
man Fm. (Eocene) in the study wells. The upper part of 
the Maastrichtian, as well as the entire Palaeocene, the 
basal part of the Eocene, and the upper part of the Mid-
dle Eocene are missing. The Eocene/Oligocene bound-
ary could not be delineated due to the absence of nan-
nofossil assemblages in the Dabaa Fm.

3. The Upper Cretaceous-Palaeogene succession for the 
studied area allows classifi cation into fi ve major 2nd or-
der depositional sequences, separated by four major dep-
ositional sequence boundaries (SB1, SB2, SB3 and 
SB4). The Upper Cretaceous–Palaeogene succession in 
the East Bahariya is divided into 17 systems tracts. 
The se systems tracts include: 7 System tracts of Ceno-
manian age; 4 System tracts of Turonian age, 2 System 
tracts of Campanian – Maastrichtian age and 4 System 
tracts of Eocene age.

ACKNOWLEDGEMENT

*The authors wish to express their deep gratitude to the 
Egyptian General Petroleum Corporation (EGPC) for releas-
ing the seismic sections, composite logs, e-logs, cuttings on 
which the biostratigraphy is based and for providing the of-
fi cial permission to publish this work. The authors are deeply 
indebted to Professor Dr. Christian BETZLER, Geoscience 
Department, Hamburg University for his co-supervision 
through a Channel System of the Egyptian Mission Depart-
ment. The Mission Department as well as Ain Shams Uni-
versity are greatly thanked. The authors thank Professor 
Dr.sc. Bruno SAFTIĆ, Faculty of Mining, Geology and Pe-
troleum Engineering, University of Zagreb and the anony-
mous reviewer for reviewing the manuscript, their comments 
enhanced the quality of the manuscript. These thanks are ex-
tended to the Associate Editor, Professor Vlasta ĆOSOVIĆ, 
particularly Mme Alisa MARTEK and all the staff of GEO-
LOGIA CROATICA for their efforts.

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Manuscript received March 3, 2011
Revised manuscript accepted March 04, 2012

Available online June 29, 2012