DEFINITION OF STRATIGRAPHY

The stratigraphy of the northern Sinai consists of three major

divisions: the Lower Clastic (Pre-Cenomanian) Division, the

Middle Calcareous (Cenomanian-Eocene) Division, and the

Upper Clastic (Oligocene-Miocene to Recent) Division.

Paleozoic rocks of the Sinai are generally thin, (approximately

2,215 feet [675 m] total thickness), sparsely fossiliferous,

and predominantly continental (fluvial and paralic),

except for a lower Carboniferous marine sequence (Um

Bogma formation). The exposures of the Paleozoic sequence

are limited to the southern part of central Sinai, near Abu-

Zenima and Um Bogma.

The Triassic (245–208 million years ago [Ma]) is

exposed as a 656-foot (200-m) thick section at Gebel Arief

El-Naqa. Elsewhere, the unit has been penetrated in at least

two wells. At Gebel El-Halal, in a petroleum exploratory

well, a thickness of 2,200 feet (671 m) was penetrated, and at

Abu Hamth, only 92 feet (28 m) of Triassic is known. The

Triassic sequence changes from continental sandstones, siltstones,

and shales overlain by a marine transgressive

sequence (argillaceous micrites, biomicrites, and sparites)

exposed in the south at Arief El-Naqa to a transgressive

sequence of shallow marine carbonate deposits, with the top

of the section at 3,640 feet (1,109 m) at El-Halal.

Jurassic (208–144 Ma) deposits conformably overlie

the Triassic and continue the trend of continental sedimentation

in the southern parts of the peninsula and gradually

deepening marine conditions to the north. The most significant

outcrop area is at the core of Gebel Maghara, where

over 6,651 feet (2,000 m) of Jurassic is exposed, while at

the El-Halal well, 10,610 feet (3,234 m) of Jurassic are

known. At Gebel Maghara, the sequence records a relatively

stable shelf, which deepened to the north. High-energy reefs

gave way southward to low-energy lagoons that interfingered

with continental-fluvial environments. The exposures

at Gebel Maghara record a mid-Jurassic marine regression,

followed by the worldwide mid-Mesozoic transgression.

The regressive sediments include erosional products derived

from the southern mountainous province. These were

logged in the Abu Hamth well (near Nakhl) as an approximately

3,280-foot (1,000-m) thick deposit of interbedded

sand and shale.

The Cretaceous system (144–66 Ma) in the Sinai is typically

separated into two principal divisions: the lower Cretaceous

Malhah formation is closely related to other

terrigenous sandstones found widely distributed in northern

Africa (the “Nubian Sandstone”), while the upper Cretaceous

(herein belonging to the Middle Calcareous Division) represents

a change to marine conditions, which overspread the

Sinai in the Cenomanian.

The lower Cretaceous (pre-Cenomanian) (144–98 Ma) is

widely referred to as “Nubian-type Sandstone” in the Sinai.

This nomenclature commonly refers to sandy facies of the

entire Lower Clastic Division, especially in the central portions

of the peninsula. In the fold belt, the unit is exposed in the central

part of the larger anticlines, and in the south, in escarpments

and tectonic depressions separating El Tih plateau from

the southern mountains and from El Egma plateau. The lower

Cretaceous attains a thickness of around 1,640 feet (500 m) in

the southern exposures, dipping 120° to the northeast. At the

Abu Hamth well in central Sinai near Nakhl, the unit is

around 770 feet (235 m) thick and occurs at 2,395 feet (730

m) below land surface. The northern exposures range between

164 and 1,706 feet (50 and 520 m) in thickness, and in the

deep well at El Khabra, the lower Cretaceous is 3,202 feet

(976 m) thick. The lower Cretaceous trends toward finer grain

sizes and decreasing age to the north. The basal beds are conglomeratic

and were deposited after the uplift that produced

the Jurassic/Cretaceous unconformity. In the lower part of the

section, the dominant lithology is ferruginous sandstones,

interbedded with shales. These were deposited in northerly

flowing streams that were debauching onto a shallow carbonate

platform. In the upper part of the lower Cretaceous

(Aptian-Albian; 119–98 Ma), the sandstones give way to

shales and sandy limestones, marking the marine transgression

that continued throughout the remainder of the Mesozoic.

The Middle Calcareous (Cenomanian-Eocene) Division

is comprised of predominantly carbonate rocks and includes

a thin, but important shale unit (Paleocene Esna formation).

There are three upper Cretaceous sub-units (Cenomanian,

Turonian-Santonian, and Senonian; 98–75 Ma), along with

the Paleocene and the Eocene systems (66–36 Ma). In most

well logs made public by the oil industry, however, the upper

Cretaceous is undifferentiated.

The Cenomanian (98–91 Ma) Halal formation follows

the familiar pattern of clastics (marls and shales) to the south

and carbonates (dolomites grading into deep marine deposits)

to the north. At about the latitude of Nakhl (29°57’ N), these

are interbedded, indicating the position of the transition

between a marine environment to the north and a terrigenous

environment in the south.

The Turonian (91–89 Ma) Wata formation is conformable

with the Cenomanian and is distinguished based on

the appearance of the “Ora”; interbedded shales, marls, limestones,

and sandstones. The limestone content increases

toward the top of the section, until it becomes a pure, massive

limestone that forms the tops of cuestas, such as those of

the El Tih plateau. This indicates a continuation of the environments

of the Cenomanian and has led to problems separating

the units. The Coniacian (88–87 Ma) Matallah

formation marks the beginning of widespread deposition of

chalky limestones, a trend which continued throughout the

remainder of the Cretaceous. The remaining Cretaceous units

(Santonian-Campanian [Duwwi Formation] and Maastrichtian

[Sudr formation]; 88–66 Ma) are characterized by

increasing chalk content and a southerly transgression of

chalk-bearing deposits.

The upper Cretaceous units attain substantial thicknesses,

exceeding 1,968 feet (600 m), and are widespread

throughout north and central Sinai. They form many of the

side slopes of the anticlinal hills. The Paleocene (66–58 Ma)

is represented by the Esna formation, a gray-green shale

deposit that is widespread and thin (maximum 213 feet; 65

m) at Gebel Minshera, averaging around 98–115 feet (30–35

m). The shales are usually grouped with the Maastrichtian

(75–66 Ma), as they were both deposited in similar environments

between structural highs.

The Eocene (58–36 Ma) is characterized by bedded and

massive chalky limestones with flint bands interspersed

throughout the lower part (the Egma formation). The upper

Eocene (43–66 Ma) (Minya Formation) contains more clastics

(marls, green-brown shales, and gypsiferous shales) and

represents a regression of upper Eocene age. In northeastern

Sinai, the Eocene is known as the Plateau Limestone and

forms the tablelands of the El Egma plateau and the Khorasha

plateau. The Eocene also occurs near the surface in the

synclines within the fold belt.

The Oligocene (36–24 Ma) was a time of uplift in Sinai

that resulted in the northward retreat of the sea and the

deposition of regressive sediments (prograding deltas and

submarine fans). These deposits are seen only in boreholes

but attain great thicknesses, exceeding 5,900 feet (1,800 m)

offshore. Onshore, the Oligocene is the age of basaltic intrusions,

which occur as northwest-southeast olivine-bearing

dikes. The dikes outcrop on the southern side of Gebel El

Maghara and in the El Hasana area. The Early Miocene

(24–17 Ma) is exposed south of El Arish as a thin (49 feet; 15

m) sequence of marl, marly limestone, and shale. Elsewhere

in northeast Sinai, Miocene rocks are found in boreholes,

reaching a maximum thickness of greater than 770 feet (235

m). Thicknesses of greater than 3,281 feet (1,000 m) have

been reported in offshore exploratory wells.

Late Tertiary and Quaternary (Pliocene-Pleistocene-

Holocene) (5.3 Ma–present) deposits are widespread

throughout the Sinai and vary widely in depositional environment.

The late Tertiary includes a conglomerate bed of

Pliocene age (Al Hajj Formation) (5.3–1.6 Ma); and the Quaternary

(1.6 Ma–present) includes the lower Pleistocene El

Fagra calcareous sandstone (kunkur); coastal plain deposits

of the Sudr and El Qaa plains; deltaic deposits, such as at

Nuweiba on the Gulf of Aqaba; alluvial and pluvial terraces

along the major wadis; wadi fill deposits, including colluvium

in the upper reaches of Wadi El Arish and its tributaries; lake

deposits, such as in Lake Bardawil and the Bitter Lakes, and

those of Wadi Feiran; and eolian deposits that are widespread

throughout the northern Sinai and scattered elsewhere.

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