Tectonic Evolution and Structural Setting of the Suez Rift
Published:January 01, 1994
Six distinctive tectonic episodes punctuate the stratigraphic record of the Gulf of Suez area. These episodes include the Pan-African event (late Proterozoic), which resulted in the development of the continental lithosphere of the area, a Cambrian extensional event, the Hercynian event (late Paleozoic), the Neo-Tethyan rift event (Jurassic), the Syrian Arc event (Late Cretaceous-early Tertiary) and the Gulf of Suez rift event (Oligocene[?]-Miocene). The structural fabrics imparted to the continental crust during the late Proterozoic and Cambrian appear to have played an important role in controlling the subsequent structural development of the Gulf of Suez area.
The first evidence of Tertiary rifting that led to the present-day expression of the Gulf of Suez is manifest by Oligocene-Miocene basaltic volcanism and in poorly age-constrained, continental to shallow-marine clastics of the Abu Zenima and Nukhul formations. The Nukhul Formation was deposited over much of the present-day extent of the rift basin, suggesting that subsequent extension experienced by the crust was constrained to the initial area of deformation. Subsidence during the initial phase of extension was slow.
Accelerated subsidence and extension is recorded in the deep-marine lithologies of the Rudeis Formation. This subsidence was disrupted midway through the deposition of the Rudeis Formation by the "mid-Rudeis" event, which resulted in the structural reorganization of the rift. This event correlates roughly in time with the onset of significant motion on the Dead Sea wrench system and marks the progressive abandonment of the Gulf of Suez as a site of active extension. After the mid-Rudeis event, variable and reduced tectonic subsidence rates prevailed in the gulf. The onset of significant evaporite deposition is recorded in the Belayim Formation, and evaporites subsequently become the major lithology of the South Gharib and Zeit formations as tectonic subsidence diminishes and basin restriction increases. Open-marine conditions and a change from dominantly Mediterranean to Indo-Pacific fauna took place in the Pliocene as a link was established to the Indian Ocean through continued extension in the Red Sea.
Four distinct fault populations are documented in the rift and show varying amounts of both strike-slip and dip-slip motion, depending on their orientation relative to the principal direction of extension. The major faults establish domains in their dip direction, subdividing the Gulf of Suez rift into three major structural subbasins with alternating structural asymmetry along the axis of the rift. Extension increases along the axis of the rift from northwest to southeast. Associated with this increase are increases in fault-block dip, the number of faults with large throw, and geothermal gradient. Fault-block size decreases with increasing extension to the south along the rift axis.
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Interior Rift Basins
Not only are rift basins the foundation for much of the geologic history of the earth, but they also are very attractive areas for hydrocarbon accumulations. Klemme stated that this geographic area has provided significant hydrocarbon reserves: "By area, these basins represent slightly over 5% of the world's basins (50% productive). However, high recovery has resulted, as they contain 10% of the world's present reserves (12% of the oil reserves and 4% of the gas reserves)." The rift basins discussed in this volume are only a few of the productive and, more importantly, potentially productive rift basins in the world. The term "rift" was coined by Gregory (1896) for the graben that now bears his name in the Kenyan portion of the East African rift system. The study of geology of rift basins began in the Rhine graben. The discovery of hydrocarbons in rift basins about the turn of the century provided new motivation for understanding these basins. This publication was initiated by the AAPG Publications Committee in 1985 and contributors were invited to write. AAPG designed their "World Petroleum Basins" series and sought to publish the definitive volume on each of several basin types. In this volume, "Interior Rift Basins," a detailed, 3-paper overview was written about the Suez Rift basin as representative of interior rift basins. The key papers were followed by less detailed reviews of three other selected interior basins: Pripyat and Dnieper-Donets Basins; Reconcavo Basin, Brazil; Albuquerque Basin Segment of the Rio Grande Rift.