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El Amal Project Field Trip Cairo – Ain Soukhna Road

Bill Bosworth November 21

st, 2015

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El Amal Project Field Trip

Cairo – Ain Soukhna Road

November 21st, 2015

Field Trip Leaders: Dr. Bill Bosworth, Apache Egypt Companies

Sponsored by: Apache Egypt Companies

Overview

Northeastern Egypt underwent a complex

and interesting Phanerozoic geological his-

tory. In the area east of the city of Cairo

and reaching nearly to the Gulf of Suez,

most of the surface outcrops are comprised

of Eocene and younger strata. Field trips in

this region must therefore focus on late

Cenozoic sedimentation and deformation.

Some of the exposures are incredibly ro-

bust, and the area is crossed by paved

roads that make access very easy. Many

visitors would be amazed by how diverse

this geologic setting is, and by how much

can be learned about the greater context of

the geology of Egypt.

This field trip will stop at six very im-

portant outcrops along parts of both the

new and original Cairo – Ain Soukhna

road. We will examine the large-scale

structural setting, which was dominated by

compressional tectonics in the Late Eocene

(late Syrian Arc deformation) and then ex-

tensional tectonics in the Miocene (Gulf of

Suez rifting). This will bring us to out-

crops of the Middle and Late Eocene Ob-

servatory and Maadi Formations, overlain

by the Oligocene Gebel el Ahmar For-

mation and an unnamed but very important

Early Miocene section. We will observe

beautiful examples of siliciclastic fluvial

sandstones and conglomerates, large-scale

cross-bedding in carbonate platform strata,

basalt flows, major unconformities, minor

and major faulting, effects of diagenetic

silicification, and some very incredible

fossils.

Of utmost importance during the trip is

safety around the highways. We will be

stopping in locations where the buses can

be parked far removed from traffic lanes.

However, everyone must be extremely

careful any time they are walking to out-

crops any place near these roadways.

Please remain in the areas indicated by the

field trip leaders, and do not use mobile

phones while at the outcrop. The use of

phones will distract attention from presen-

tations and is unsafe while scrambling on

rocky surfaces. No hammers are necessary

and please do not try to remove the well-

preserved fossils we will see from the out-

crops.

This trip has been kindly sponsored by

Apache Egypt Companies which have a

long-standing commitment to supporting

students, educational institutions, and

training programs for young graduates

here in the host country of Egypt.

Stratigraphy

The stratigraphic column along the Cairo-

Ain Soukhna Road includes a thick section

of Eocene age shallow marine platform

carbonates deposited in an epeiric conti-

nental sea, overlain by Oligocene cross-

bedded and channelized fluvial sandstones

and conglomerates. These are then covered

locally by sub-alkaline basalt flows that

were erupted from fissures during the ini-

tiation of Miocene Gulf of Suez rifting.

The following brief description of these

stratigraphic units (Figure 1) is taken from

Klitzsch et al. (1987), Abd-Allah (1993),

and other references given at the end of

this field guide.

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Figure 1. Tectonostratigraphy of the field trip area. Sources of terminology are given in

the text. Absolute time scale is from Gradstein et al., 2012 (rounded to nearest Ma).

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Mokattam Formation (Group)

The Mokattam Formation was introduced

by Said (1962) from Gebel Mokattam,

near Cairo. Klitzsch et al. (1987) consider

the Mokattam to be of group status. It is

made up of white to yellow, nummulitic

limestones, dolomitic limestones, and

marls. The Mokattam Formation was con-

sidered Late Middle Eocene (Late Lute-

tian) by Cuvillier (1930b). The recent stud-

ies of Strougo (1979, 1985) indicate that it

is of Early to Middle Lutetian age.

The Mokattam Formation includes bio-

stromal limestone beds that are highly en-

riched in Nummulites gizehensis and

Nummulites midawarensis as well as Luci-

na mokattamensis, Wakullina (Huyella)

lefevrei, and corals. The thickness of this

formation as measured by Abd-Allah

(1993) is about 137 m.

Observatory Formation

The Observatory Formation was described

by Farag and Ismail (1959) from the ob-

servatory plateau, east of Helwan. This

formation consists of while to golden-tan

marly limestones with nodular limestones

at its top. Its age is Lutetian (Farag and

Ismail, 1959; Said, 1962; Strougo, 1985).

The Observatory Formation designates a

sequence of biogenic and bioclastic, fre-

quently cross-bedded, white limestones

and chalky limestones with some dolomit-

ic ledges in the middle and upper parts.

According to Abd-Allah (1993) it under-

lies the Qurn Formation and overlies the

Mokattam Formation.

The faunal content of the Observatory

Formation is characterized by the great

abundance of large miliolids, Febulerie

and Idalina, and imperforate conical

forams, Dictyoconus (Abd-Allah, 1993).

Other associated fossils include: Vulsella

crispata, Spondylus aegyptiacus, Wakulli-

na (Huyella) lefevrei, Lucina metableta,

Pterolucina monosulcata, Fimbria lamel-

losa, Fimbria kaitbeyensis, Anodontia in-

juriata, Barbatia (Rostarca) russeggeri,

Nucula (Lamellinucula) eymari, Mac-

rosolen uniradiatus, Fibularia luciani,

Echinocyamus blanckenhorni, Echino-

lampas africana, Echinolampas perrieri,

Orbitolites sp., corals and bryozoa.

The maximum thickness of the Observato-

ry Formation measured by Abd-Allah

(1993) at Gebel Akheider is about 203 m.

In general, the cross-bedding, corals, and

larger foraminifera belonging to the genera

Fabularia, Idalina and Dictyoconus in-

crease eastward, while the genus Nummu-

lites dominates in the west.

When bicycling or trekking through the

Wadi Digla Preserve the wadi floor and all

the massive cliff-forming section belong to

the Observatory Formation.

Maadi Formation

Klitzsch et al. (1987) refer to the Late Eo-

cene strata east of Cairo as the Maadi

Formation, first introduced by Said (1962).

The unit consists of grayish-green, highly

calcareous shale/mudstone and typically

dark-brown, highly argillaceous and are-

naceous limestone. The thickness of the

formation is about 70 m.

Abd-Allah (1993) divides these rocks into

three formations: Qurn, Wadi Garawi, and

Wadi Hof Formations. Strictly speaking, it

is probably not possible to map these for-

mations throughout the area and hence we

prefer the more general term Maadi For-

mation for our purposes.

Typical fossils of the Maadi Formation

include Nummulites contortus-striatus,

Nummulites fabiani, Nummulites incras-

satus, and Carolia placunoides. Numerous

other fossils are also listed by Abd-Allah

(1993). For the field geologist, one of the

most diagnostic features of the Maadi

Formation is the presence of extensive

oyster beds (e.g., ostrea clotbeyi, Ostrea

(Turkostrea) multicostata strictiplicata,

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Ostrea (Turkostrea) bogharensis) and the

general high abundance of fossil remains.

Gebel el Ahmar Formation

An unconformity separates the Upper Eo-

cene rocks from the Oligocene sediments

which were deposited in a fluviatile envi-

ronment (Said, 1962). The Oligocene

rocks often occur within fault-bounded

graben, or infill topography that existed at

the end of the Eocene. The unit consists of

varicolored, often unstratified, typically

cross-bedded and channelized sands, grav-

els, and chert-cobble conglomerates. Shuk-

ri (1954) called this the Gebel el Ahmar

Formation after exposures on the east side

of Cairo, many of which are now gone due

to extensive urban development. The

thickness is about 50 m but is extremely

variable.

The main fossils present in the Oligocene

strata are fossilized tree trunks which can

be up to 10 m in length. Fresh water snails

are also present.

Miocene Formations

The start of the Miocene Epoch is marked

by patchy eruptions of sub-alkaline basalts

and associated syn-depositional extension-

al faulting. These basalts have traditionally

been referred to as “Oligo-Miocene” in

age, based on general stratigraphic posi-

tion and K-Ar age dating (the K-Ar age

dates ranged from about 28 to 20 Ma

throughout the greater Cairo-Suez region).

New Ar40

/Ar39

dates, which are much

more reliable, show that all these basalts

(extrusive flows and dikes alike) were

produced at ~23 Ma – the Oligocene-

Miocene boundary – and within a very

short time period (Bosworth et al., 2015).

So any strata overlying the basalts, or con-

taining basalt detritus, are of Miocene age

(this would include the “upper Oligocene

unit” of Abd-Allah, 1993).

The rocks immediately overlying the bas-

alts, or laterally interfingering with them,

are basalt cobble conglomerates and highly

silicified sands. The basalt cobbles are

highly weathered, gray, and very friable.

They are not recycled through subsequent

erosion events.

In the eastern part of the Cairo-Ain Sou-

khna district most of the lower part of the

Miocene section consists of marine biotur-

bated marl, shale, sandstone and marly

limestone (Abd-Allah, 1993). The most

prominent fossils of this unit are bivalves

(Anadara diluvii, Glycymeris nummaria,

G. deshayesi, Spondylus cressicosta, Amu-

sium geneffensis, Chlamys holqeri, C.

submalvinae, Pecten ziziniae, P. cristato-

costatus, Hyotissa virleti, Crassostrea

gryphoides, Ostrea digitalina, Codakia

mediolaevis, Linga (Linga) columbella)

and echinoids (Psammechinus dubtus ,

Scutella zitieli , clypeaster istnmicus, En-

cope sp., Echinolampas amplus).

Abd-Allah (1993) assigned the age of this

assemblage, based chiefly on the pectinids

and the oysters, to the latest Early Miocene

(uppermost Burdigalian) to the Middle

Miocene (Langhian-Serravalian), which

agrees with the view of Sadek (1926).

Topping the marine strata is a non-marine

Miocene unit composed of massive chalky

sandstones and sandstones with gravel

bands. Sadek (1926) assigned this unit to

the Late Miocene. It is about 25 m thick.

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References

Abd-Allah, A.M.A. (1993) Structural ge-

ology of the area between El Galala El

Bahariya and Gebel Okheider. Ph.D.

Thesis, Ain Shams University, Cairo,

Egypt.

Bosworth, W., Stockli, D.F., and Helge-

son, D.E. (2015) Integrated outcrop,

3D seismic, and geochronologic inter-

pretation of Red Sea dike-related de-

formation in the Western Desert, Egypt

– the role of the 23 Ma Cairo “mini-

plume”. Journal of African Earth Sci-

ences, 109, 107-119.

Cuvillier, J. (1924) Contribution à l’étude

géologique du Mokattam. Bull Inst.

Egypte, 6, 93-102.

Cuvillier, J. (1930) Révision du nummuli-

tique Egyptien. Mem. Inst. Egypte, 16,

371 p.

Farag, I.A.M. and Ismail, M.M. (1959)

Contribution to the stratigraphy of the

Wadi Hof area (north-east of Helwan.

Bull. Fac. Sci., Cairo Univ., 34, 147-

168.

Gradstein, F.M., Ogg, J.G., and Hilgen,

F.J. (2012) On the geologic time scale.

Newsletters on Stratigraphy, 45, 171-

188.

Hermina, M., Klitzsch, E. and List, F.K.

(1989) Stratigraphic Lexicon and Ex-

planatory Notes to the Geological Map

of Egypt, 1:500,000 scale, Conoco

Inc., Cairo, Egypt, 263 p.

Klitzsch, E., List, F.K., Pöhlmann, G.

(1987) Geological Map of Egypt,

1:500,000 scale, Institut für An-

gewandte Geodäsie, Berlin, 20 sheets.

Moustafa, A.R. and Abd-Allah, A.M.

(1992) Transfer zones with en echelon

faulting a the northern end of the Suez

Rift. Tectonics, 11, 499-506.

Sadek, A. (1968) Stratigraphical and struc-

tural studies on the Cairo-Suez district.

Ph.D. Thesis, Cairo Univ., 275 p.

Sadek, H. (1926) The geography and geol-

ogy of the district between Gebel

Ataqa and El Galala El Bahariya (Gulf

of Suez). Geological Survey of Egypt,

120 p.

Said, R. (1962) The Geology of Egypt.

Elsevier, Amsterdam, 377 .

Shukri, N.M. (1954) On cylindrical struc-

tures and colouration of Gebel Ahmar

near Cairo, Egypt. Bull. Fac. Sci., Cai-

ro, Univ., 32, 1-23.

Strougo, A. (1979) The Middle Eocene –

Upper Eocene boundary in Egypt.

Ann. Geol. Survey Egypt, 9, 454-470.

Strougo, A. (1985) Eocene stratigraphy of

the eastern greater Cairo (Gebel Mo-

kattam-Helwan) area. Middle East Re-

search Center, Ain Shams University,

Sci. Res. Series, 5, 1-39.

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Field Stops

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Figure 2. Location map for field trip stops.

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Figure 3. View of Middle Eocene roll into fault zone at Gebel Akheider (Stop 1).

Stop 1: Overview of Gebel Akheider looking west from turn-off on the Ain Soukhna Road

(Figure 3). Southward dip/roll into a fault zone is due to late Syrian Arc compression during

the Late Eocene.

Figure 4. Panorama of the Oligocene Gebel el Ahmar Formation roadcut (Stop 2).

Stop 2: Gebel el Ahmar Formation fluvial sandstone section (Figure 4). Well-developed cut

and fill structures, cross- and convolute bedding, small-scale sandstone deformation bands.

Group will sketch this outcrop.

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Figure 5. Blank sketch page for Stop 2.

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Figure 6. Cross-bedded Observatory Formation nummulitic limestones (Stop 3).

Stop 3: Observatory Formation cross-bedded and channelized platform carbonates (Figure 6).

Some beds contain abundant nummulites (large benthic foraminifera) and if re-worked can

form exploration targets in the subsurface.

Figure 7. Fault Zone Panorama in Maadi Formation (Stop 4).

Stop 4: Approximately east-west striking fault zone in Maadi Formation of complex litholog-

ic associations (Figure 7). Abundant fossils – please do not damage! Group will sketch this

outcrop.

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Figure 8. Blank sketch page for Stop 4.

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Figure 9. Google Earth satellite image of the NW-SE trending graben at Stop 5 and 6.

The light gray areas are mostly Middle Eocene Observatory Formation to the northeast

of the graben and Late Eocene Maadi Formation to the southwest of the graben. Si-

liciclastics are Gebel el Ahmar Formation except locally where they sit above the 23 Ma

basalts. Mapping is only preliminary and many of the smaller Oligocene exposures are

not indicated.

Stop 5: 23 ± 0.5 Ma basalt plug/flow within NW-SE trending graben (Figure 9). Dated by

Ar40

/Ar39

technique (Bosworth et al., 2015).

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Figure 10. Complexly faulted basalt-cobble conglomerate overlying Gebel el Ahmar

sandstone (Stop 6).

Stop 6: Complex faulting at the unconformity between the Oligocene Gebel el Ahmar se-

quence and the unnamed basalt cobble conglomerate above (Figure 10). Location is shown in

Figure 9.