DEFINITION OF SYRIAN ARC FOLD BELT

The term Syrian arc fold belt is used

to denote the broad S-shaped belt of deformed Paleozoic,

Mesozoic, and Cenozoic rocks that sweep across a region of

complex convergent, transform, and divergent plate boundaries

from North Africa, through the Sinai peninsula, into the

Levant and as far as the Euphrates Valley. The Syrian arc

includes several individual components with distinct geological

histories such as Palmyra fold belt, Levantine fold belt,

and the Cairo-Sinai fold belt, but there are enough broadscale

similarities between them to warrant a general grouping.

The main active tectonic elements surrounding the Syrian

arc are the Red Sea, North African and Levantine continental

margins, the Bitlis suture, and the Dead Sea transform.

About 65–68 miles (105–110 km) of sinistral displacements

have accumulated along the Dead Sea transform, with 37–40

miles (60–65 km) of translation in pre-Miocene times, and

25–28 miles (40–45 km) from the Miocene to present. Displacement

along the Dead Sea transform diminishes northward

to about 12–18 miles (20–30 km) before it merges with

the Bitlis suture and East Anatolian fault. The displacement

not accommodated in this northern segment of the Dead Sea

transform may have been taken up in the Palmyride section

of the Syrian arc fold belt.

The northern part of the Syrian arc lies about 155 miles

(250 km) south of the Bitlis suture, with the area between

the two occupied by the Tauride foreland basin and fold and

thrust belt, which continues eastward into the Zagros. Considerable

controversy surrounds the origin of the northern

part of the Syrian arc: (1) contractional deformation associated

with transpressional strains along the Dead Sea transform,

with the fold belts representing a series of en echelon

fold belts associated with northward diminution of displacements

on the Dead Sea transform; (2) far-field effects of contraction

across the Bitlis/Zagros suture; (3) reorganization of

plate motions between the North Atlantic–Eurasian and

African plates in the Santonian; or (4) combination of the

different models.

The Syrian arc fold belt continues southward through

the Levantine fold belt into the North Sinai fold belt and then

continues with diminished intensity toward the southwest

past Cairo. The numerous rugged isolated hills of the Syrian

arc in northern Sinai are distinct from the other physiographic

provinces of the Sinai Peninsula, which is divided into

three physiographic provinces. Precambrian magmatic and

metamorphic rocks of the Arabian-Nubian Shield form high,

rugged mountains in the south with drainages flowing to the

east and west. This basement terrane is overlain by a dissected

homoclinal limestone plateau consisting of a Mesozoic

and early Cenozoic continental margin sequence in the central

part of the peninsula, with drainages flowing north. A

sandy plain parallels the coastline in the north.

The northern part of the limestone plateau is deformed

by a series of east-northeast trending folds and faults of the

Syrian arc. The hills, including Gebels Maghara, Halal, and

Yelleg, are the expression of doubly plunging anticlines, with

axial surfaces striking northeast-southwest. These folds affect

Jurassic through Cretaceous carbonates, deposited on a shallow

platform that deepened toward an open basin (Tethys

Sea) to the north. The rocks are exposed in breached southward-

vergent anticlines with shallow fold limbs on the north

side and steep to overturned southern limbs. Thrust faults

pass through the southern limbs of some of the folds, and

there may be east-northeast striking strike-slip faults at depth

reflecting formation of the fold belt in a zone of transpression.

Contractional deformation in the northern part of the

Syrian arc, and in northern Sinai, began with minor uplifts

in the Late Cretaceous prior to opening of the Red Sea, followed

by tectonic quiescence through the Paleogene and

interrupted by minor Middle Eocene uplift. The major phase

of uplift in the northern part of the Syrian arc began in the

Late Oligocene to Early Miocene, concomitant with rifting

of the Red Sea basin and motion along the Dead Sea transform.

Recent seismicity is consistent with transpressional

deformation. Thus, deformation in this part of the Syrian arc

appears to be related to both far-field stresses transmitted

from contraction across the Bitlis suture in the Late Cretaceous,

transpressional deformation associated with Red Sea

rifting and motion along the Dead Sea transform in Miocene

to Recent times.

Tectonism in the north Sinai-Cairo region began in the

Late Cretaceous and mostly ended by the Eocene. However,

less intense deformation and uplift probably continues

through the present day, as demonstrated by historical earth-

quakes and recent seismicity, uplifted Holocene beach terraces

in the area between Bardawil Lagoon and Gebel Maghara,

and fault scarps cutting recent alluvium. The North Sinai-

Cairo-Faiyum area has a well-documented historical earthquake

record that demonstrates ongoing activity in the fault

and fold belt. On August 7, 1847, a large earthquake with an

estimated magnitude of 5.5–5.9 shook the Faiyum-Cairo

region. Hundreds of people were killed and injured, and thousands

of structures were destroyed. The earthquake was felt in

much of north Africa and across Egypt, with heavy damage

reported south of Cairo as far as Assuit. A magnitude 4.8

earthquake shook the area again on January 10, 1920. On

October 12, 1992, another magnitude 5.9 earthquake shook

the Dahshur area, northeast of the Faiyum region, along the

same belt that extends into northern Sinai. Heavy damage was

reported in the region including Cairo, and hundreds of people

were injured and thousands of houses were damaged in

the rest of Egypt. Most recent seismicity in the Sinai Peninsula

is related to rifting and strike-slip faulting along the Red Sea

and Gulfs of Suez and Aqaba, although faulting related to

movements along the Faiyum–northern Sinai trend is possible.

Most of the Syrian arc fold belt appears to be developed

over areas that have a thicker-than-average section of Late

Paleozoic–Mesozoic rocks, suggesting that the fold belt developed

over a zone of older rifting. In the Palmyride fold belt,

this Mesozoic rift takes the form of an aulacogen developed

over an older possibly Proterozoic age suture. Further south

the increased thickness of Mesozoic sediments formed along

the rifted Levant–North Africa margin. The fold belt extends

southwest through a fault-bounded depositional trough

including the Faiyum depression that may also follow an

older rift structure. The Syrian arc thus appears to mark a

zone of long-standing crustal weakness. Much of the Cretaceous

deformation may be due to the fact that this weak zone

was the first to fail when far-field stresses were imposed by

collisional events across the Bitlis/Zagros suture. Younger

transpressional deformation along the Dead Sea transform

related to the opening of the Red Sea and the rotation of Arabia

away from Africa are also recorded.

See also CONVERGENT PLATE MARGIN PROCESSES; SINAI

PENINSULA.

Taconic Mountains, Taconic Orogeny See APPALACHIANS.

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