R. E. Sheriff Lecture
The Geology of the Middle East

A. M. C. Sengör

The Middle East is that part of southwest Asia, which includes Anatolia, the trans-Caucasian lands, Iran and the Arabian Peninsula, plus Egypt. For the purpose of this lecture, the geology of the areas neighbouring the Middle East, especially that of the Mediterranean and Libya, is also considered.

Tectonically, the Middle East may be divided into three parts:

1. The Tethyside orogenic belt
2. The continental foreland (Afro-Arabia)
3. The oceanic foreland (Eastern Mediterranean)

The outstanding regional tectonic problems of the Middle East are the following:

1. Nature and evolution of the Precambrian basement
2. What happened during the Palaeozoic?
3. The relationship to the Palaeo-Tethyan ocean
4. What happened during the Aptian-Albian?
5. The nature and timing of the Syrian arcs orogeny
6. Timing of the collision of Arabia with Eurasia
7. The origin and evolution of the active tectonic regime

The answers to these questions given in this lecture are as follows:

1. The Precambrian basement of the Middle East is almost entirely a product of the Pan African orogeny, here extending from about 900 Ma ago to about 500 ma ago. An exception is the Istanbul Zone in NW Turkey that has a Cadomian basement. The Pan African evolution had the style of a Turkic type orogeny that ended with major strike-slip faulting and basin-and-range type extension that created the Hormuz Salt Basins.
2. The Palaeozoic witnessed the placement of an Andean-type continental margin along NE Gondwana-Land in the Middle East. Basin development in Arabia was largely a function of this compressional arc margin.
3. During the Permian, this arc turned extensional and parts of it began leaving Gondwana-Land as the Cimmerian Continent. Widespread basin evolution events in Turkey, Syria and along the Zagros margin were products of this series of events. The opening of the Eastern Mediterranean was also a part of this event. The Triassic rifting around the Eastern Mediterranean was not an aborted rifting.
4. In late Jurassic time rifting began affecting parts of Africa. These events heralded the mid-Cretaceous opening of the South Atlantic. After the Albian rifting ceased and a major unconformity developed along the southern margins of the Eastern Mediterranean and in the Arabian margins. The origin of the Marmarican taphrogen in NE Africa, together with that of the Sirt Basin in Libya, were products of this episode of rifting.
5. In late Cretaceous time Africa began approaching Eurasia almost head-on. This led to widespread ophiolite obduction events. These compressional events shortened the Marmarican rifts and gave rise to the Syrian Arcs orogeny beginning with the Santonian. The Jabal al-Akhdar orogeny in Cyrenaica is part of the same event.
6. In Eocene time the Bitlis digitation of the Apulian platform (here Menderes-Taurus block) collided with Arabia. This reshortened the Syrian arcs. When the Mus Suture north of Bitlis was finally closed in the late Oligocene, eastern Turkey began rising. By Burdigalian time land mammal exchange between Africa and Asia had become possible. Some 11 Ma ago (just before the opening of the Red Sea) the North Anatolian Shear zone formed and the expulsion of Turkey from the Middle East toward Europe began in a revolutionary fashion.