Assiut university researches
Sedimentological and Stratigraphical Studies
on the Area South West of West of Gebel
Ataqa, Gulf of Suez, Egypt
Hassan Soltan Hassan Mihamed
‫ح سن س لطان ح سن محمد‬
Ahmed Reda M.El-Younsy, Mohamed Khalil, Mohamed Ahmed Essa
‫ محمد أحمد ع ي سى‬،‫ محمد خ ل يل‬،‫أحمد ر ضا ال يون سى‬
Abstract:
Previous studies on the calcareous rocks of the north-eastern
desert showed the need for further sedimentological studies
of the Middle Eocene rocks, especially after the growing
interest by the state to search for the necessary raw materials
for cement industry. The study area extends on shore of the
Western side of Gulf of Suez between Latitudes 29° 40’ and
30° 00 N, and Longitude 32° 00’ and 32° 30’ E, covering an
area of about 800 sq km. forming a part of the great Eocene
plateau of the Northern Eastern Desert of Egypt. It consists of
a series of elongated and widely- spaced North-West and
East-West trending topographic highs and lows, which are
mainly structurally controlled. The topographic highs, are also
structural highs and mostly made up of hard Middle Eocene
limestone beds, while the topographic lows, are also of
structural origin and are occupied by soft rocks ranging in age
from Late Eocene to Recent. Both the pre-rift sediments
(represented by the Tertiary rock units of Middle and Late
Eocene) and syn-rift sediments (represented by the
Oligocene and Miocene deposits) are occurred in the study
area. The current study is interested in the stratigraphy of the
Middle Eocene rocks, as well as the depositional
environments that prevailed during their deposition in the
study area. Also, thin study throws light on the validity of
these raw materials for cement industry. To achieve this
purpose, two major stratigraphic columnar sections were
measured and sampled in detail to clarify the facies
characteristics, cyclic pattern of sedimentation and
depositional changes of the studied sequence. About 170
samples were collected in order to cover most of the middle
Eocene carbonate varieties encountered in the investigate
area at SUMMRY AND CONCLUSION 83 both Gabel Kahylia
along the western bank of wadi Hagul Gabel Okheider along
Cairo-Sukhna road. Lithostratigraphicaly; the Middle Eocene
limestone (of Lutetian age) exposures in the study area are
subdivided into two rock units from base to top are: 1- Minia
Formation: It is recorded only in the southwestern part of the
studied area at Gabel Okheider (about 40m. thick), and
unconformable overlain by Mokattam Formation. It is
composed of grayish white, bedded to massive limestone and
marly limestone, with thin intercalations of dolomitic and
sandy limestone intercalations. Planner cross bedded
limestone is also recorded in the middle parts of this
formation. Very dense bioturbation horizons are also present.
In the investigated area, the Minia Formation is of Middle
Eocene (Lutetian) age. 2- Mokattam Formation: It is widely
distributed in the study area at both Gabel Okheider (reaches
65m.), and Gabel Kahylia (about 120m. thick). In the study
area, it is mainly composed of yellowish with, thinly to thick
bedded, hard limestone rich in fossils (mostly nummulitic).
Thin beds of dolomitic limestone, marly limestone and
bioturbated horizons are also present. In the investigated
area, the Mokattam Formation is of Middle Eocene (Late
Lutetian) age. Relationships between the studied rock units
are noticed and the contact between them is recognized. For
detailed sedimentological investigation, about 107
microscopic thin sections representing the studied Middle
Eocene sequence are described and an adequate
petrographic classifications is given using Dunham
classification (1962), which is modified by Embery and
Klovan’s (1971). SUMMRY AND CONCLUSION 84 Careful
analyses of the studied microfacies lead to the delineation of
six main type of limestone depositional facies comprising 16
microfacies types. They are: Packstone - to gainstone (30%),
grainstone (28%), packstone (22.4%), wackestone- to
packstone (15%), wackestone (2.8%) and lime -mud to
wackestone (1.8%). According to the diversity ratio of the
allochems components existing in each facies together with
field studies, the studied Middle Eocene carbonate sequence
of the Minia Formation and the overlying Mokattam Formation
have been deposited on an isolated shallow marine platform
carbonate bank, with high carbonate productivity. This is
evidenced by the abundance and diversity of shallow marine
fauna, frequent benthic with total absence of palntics;
extensive and diverse of carbonate facies types; dominant of
high -energy fabric and well developed large -scale tangential
cross-bedding. Three main carbonate facies reflecting
sedimentary environments have been recognized:
Nummulites bank facies, carbonate bar facies and restricted
lagoon facies are proposed. 1- Nummulites bank facies. This
facies constitutes the main part of the Mokattam Formation
succession at both the Kahylia and Okheider sections. In the
northeastern part of the studied area, at Kahylia section, it
forms a pronounced shallowing upward cycles with a
noticeable variation in thickness (10- 27m thick) and
alternated vertically with carbonate bar facies. It is of minor
importance in the Minia Formation succession at Okheider
section, where it collectively measures 7m thick. SUMMRY
AND CONCLUSION 85 It is composed of moderately hard
bedded, massive nummulitic limestone with benthic
foraminiferal shells. Also it includes several microfacies
associations such as, nummulitic bioclastic wackestone to
packstone, mollusca bioclastic packstone, echinodermal
bioclastic packstone, benthonic foraminiferal grainstone and
peloidal packstone to grainstone. The effect of bioturbation
must also be considered. This facies has been developed in
well-aerated shallow water, where swells represented
submerged paleohigh initiated on the Middle Eocene
nummulites banks. 2- Carbonate bar facies. This facies is
common in the Mokattam Formation succession, which was
exposed in the northeastern part of the study area at Kahylia
section and alternated with the nummulites bank facies. It is
represented by several successive horizons, with marked
variation in thickness (2 - 12m. thick). It is also recorded in
the Minia Formation sequence exposed in the southwestern
part of the area at Okheider section and is alternated with
lagoon facies and is represented by few horizons (8 - 12m
thick). It is composed of thick bedded limestone, generally of
medium to coarse - skeletal packstone and grainstone
texture. It includes several microfacies associations such as
echinodermal bioclastic grainstone and foraminiferal
bioclastic packstone to grainstone. It is characterized by well
rounded allochems and crudely large-scale cross-bedding of
tangential and trough types. The cross-bedded packstone
normally flanks and caps of the small patch reefs.
Occasionally it terminates with slightly dolomitize horizons
and rare bioturbation effect. The densely fossiliferous
tangential cross-bedded packstone to grainstone designate
large - scale tidal bars (tide - dominated carbonate bars) that
formed in the upper shallow subtidal regime. SUMMRY AND
CONCLUSION 86 3- Restricted lagoon facies. The lagoon
facies represent the main lithologic character of the Minia
Formation succession in the southwestern part of the area at
Okheider section, where it collectively measures 54m thick
and is alternated vertically with the carbonate bar facies. It is
of minor importance in the Mokattam Formation succession in
each of the Okheider (about 20m thick) and the Kahylia
(about 4m thick) sections. It is composed of dark grey to
grayish white thick bedded, hard fossiliferous limestone,
mostly crowded with mollusca, miliolids, echinodermal
fragments, peloids and benthonic foraminifera and displays
slight to moderate bioturbation. It includes a wide variety of
microfacies, which is represented by, echinodermal bioclastic
packstone, peloidal bioclastic packstone – to grainstone,
mollusca lime - mud to wackestone, foraminiferal packstone
microfacies. The lithologic and textural characters of this
facies suggest sedimentation on marine carbonate platform
with a slightly protected lagoon located behind the bank
margin in tropical, warm and shallow subtidal setting. The
depositional nature of the studied sedimentary facies of the
both Minia and Mokattam Formations developed during the
Middle Eocene at both the Kahylia and Okheider sections
points to slight change in the bathymetry of the sea due to
sea – level oscillations during deposition related to marine
sea – level changes of the Tethyan Sea. Evidence of these
fluctuations is indicated by the cyclic nature of these facies
and their geographic migration at the northeastern (Kahylia)
and southwestern (Okheider), parts of the study area. In the
present work, an attempt is made to throw light on the
common diagenetic phenomena and their paragenesis. The
diagenetic history of the studied Middle Eocene carbonate
sequence is discussed with special SUMMRY AND
CONCLUSION 87 reference to compaction, cementation,
recrystalization, silicification, ferrugination and dolomitization.
There is growing interest in searching for raw materials, which
are necessary for cement industry, especially after the
construction of many factories along Cairo -Suez and Cairo Ain Sukhna roads. A Preliminary study to determine the
suitability of limestone as an industrial stone in the study area
has been carried out. Samples were collected from the
chosen exposures of the limestone sequence representing
the apparent variations covering the exposed Middle Eocene
limestone raw materials in the study area. It approximately
measures 109 meters thick at the eastern scarp of Gabal
Kahylia and reaches about 134 meters thick at Gabal
Okheider along Cairo -Sukhna road. These samples were
subjected to complete chemical analysis using X-ray
fluorescence technique at Lafarge Cement Company, Egypt.
The chemical analysis results of all samples at both Kahylia
and Okheider sections have been discussed in some detail.
The average chemical analysis of the limestone raw materials
was input into the mix- design software program of Lafarge
cement, Egypt, company, using the results of previously
analyses of clays by Lafarge Cement Company to obtain the
ideal cement quality parameters. The average percentages of
the most objectionable components such as MgO are slightly
higher (2.12%) in Okheider samples than Kahylia samples
(0.99%). Also, the average percentages of the undesirable
elements in cement industry such as SO3 and CL are slightly
higher in Okheider samples (SO3 is 0.11%) and (CL is
0.26%) than Kahylia samples (SO3 is 0.01%), and (CL is
0.10). Also, petrographic studies SUMMRY AND
CONCLUSION 88 revealed that the Okheider limestone is
highly dolomitized than the Kahylia limestone. Accordingly,
the Kahylia limestone is more suitable for cement industry
than those of Okheider. Also it lies few kilometers north of the
Lafarge cement Egypt factory. Thus, the cost of
transportation of the main raw materials (limestone), will be
lower (22.9 EP/Ton, obtained mix design program), than
those of Okheider limestone.