SEDIMENTARY BASINS Red Sea Coast of Egypt. by Prof. Dr. Abbas Mansour

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1 SEDIMENTARY BASINS Red Sea Coast of Egypt by Prof. Dr. Abbas Mansour

2 Sedimentary basins Sedimentary basins are, in a very broad sense, all those areas in which sediments can accumulate to considerable thickness and be preserved for long geological time periods.

3 Sedimentary Basins Geophysics: 1 credit hour Summer Semester 2005 You can contact me: in my office, by phone ( ), or by (abbas_mansour@yahoo.com)

4 BASIC CONCEPTS AND TERMS A sedimentary basin is an area of the earth s crust that is underlain by a thick sequence of sedimentary rocks. Hydrocarbons commonly occur in sedimentary basins and are absent from intervening areas of igneous and metamorphic rocks (North, 1971). This fundamental truth is one of the cornerstones of the sedimentary-organic theory for the origin of hydrocarbons.

5 BASIC CONCEPTS AND TERMS A sedimentary basin is an area on the earth s surface where sediments have accumulated to a greater thickness than they have in adjacent areas. No clear boundary exists between the lower size limit of a basin and the upper limit of a syncline. Distinction between topographic and sedimentary basins Both types of basin have a.needs further elaboration Sedimentary basins may or may not.depressed basement.have been marked topographic basins during their history with continental and shallow infilled Many basins are.deposites sea-and totally lack deep,marine sediments

6 BASIC CONCEPTS AND TERMS Similarly, a distinction needs to be made between syndepositional and postdepositional basins. This simultaneous occurrence is shown by facies changes and paleocurrents that are concordant with structure. On the other hand, in some basins paleocurrent directions and facies are discordant with and clearly predate the present structure (Fig. 8.1). the distinction between these two types of basins is critically important in petroleum exploration because of the need for traps to have formed before hydrocarbon generation and migration.

7 BASIC CONCEPTS AND TERMS The term basin has two interpretations. In the broadest sense, as already defined, a sedimentary basin is an area of the earth s surface underlain by sediments. In a narrower sense basins may be subdivided into true basins; those that are subcircular in plan and those that are elongate (troughs). Embayments, lacking centripetal closure, are basins that open out into larger basins (Fig. 8.3).

8 MECHANISM OF BASIN FORMATION Sedimentary basins form part of the earth s crust, or lithosphere; they are generally distinguishable from granitic continental and basaltic oceanic crust by their lower densities and slower seismic velocities. Beneath these crustal elements is the more continuous subcrustal lithosphere. The crust is thin, dense, and topographically low across the ocean basins, but thick, of lower density, and, consequently, of higher elevation over the continents (Fig. 8.4). The lithosphere is made up of a series of rigid plates, which overline the denser, yet viscous, asthenosphere.

9 MECHANISM OF BASIN FORMATION Basins can form in four main ways (Fischer, 1975). Three of these processes are summarized in Fig One major group of basins, the rift basins, form as a direct result of crustal tension at the zones of sea florr spreading. A second major group of basins occurs as a result of crustal compression at convergent plate boundaries. Athird type of basin can form in response not to lateral forces but to vertical crustal movements. A fourth mechanism of basin formation is simple crustal loading due to sedimentation.

11 MECHANISM OF BASIN FORMATION Basins formed as a result of crustal thinning and rifting are of particular interest to the petroleum industry because they are an important habitat for petroleum. Many theories have been advanced to explain their formation. A useful review of these can be found in Allen and Allen (1990). Of the many models proposed, three are particularly significant: 1. Salveson (1976, 1979) proposed a model of passive crustal separation, in which the continental crust was deemed to deform by brittle failure, while the subcrustal lithosphere is thinned by ductile necking.

12 MECHANISM OF BASIN FORMATION 2. proposed a model that (1978)McKenzie subcrustal assumed that both the crust and.lithosphere deformed by brittle failure 3. proposed a model ( ) Wernicke in,for crustal thinning by means of simple shear which a low angle fault extends from the surface.lithospere right through the at 8.8.These three models are illustrated in Fig left The McKenzie model has received particular interest in the oil industry because it offers a means of predicting the history of heat flow in a.sedimentary basin

13 The main aim of this course This course is an attempt to summarize the more important aspects of the sedimentary evolution of the northern part of the Red Sea basin. Both qualitative and quantitative aspects of basin analysis identifying flux rates, tectonic activity and sedimentary geology have been addressed.

14 The main objectives of this course Stress the intimate relationship between the sedimentary and tectonic evolution of the NW Red Sea-Gulf of Suez rift. Understand NW Red Sea sedimentation and tectonics. Address the stratigraphic, sedimentary and tectonic evolution with special emphasis on the transition from rift to drift conditions. Provide the various controls on the sedimentological evolution of the Red Sea-Gulf of Aden rift system.

15 The main objectives of this course Compare betwenn the different stratigraphic and tectonic evolution of the eastern and western Red Sea margin during the rifting and drifting stages. Demonstrate the close relationship between rifting and the phases of continental and marine sedimentation. Discuss the marine terraces along the Red Sea coast and the Gulf of Aqaba. Address the stratigraphy and the regional structural setting of the Gulf of Suez. Present the Pleistocene and Recent sediments along the Red Sea coast of Egypt.

16 Coastal environments

EDIMENTARY BASINS. What is a Sedimentary Basin? by Prof. Dr. Abbas Mansour

EDIMENTARY BASINS. What is a Sedimentary Basin? by Prof. Dr. Abbas Mansour EDIMENTARY BASINS What is a Sedimentary Basin? by Prof. Dr. Abbas Mansour WHAT IS A SEDIMENTARY BASIN? A low area on the Earth s surface relative to surroundings e.g. deep ocean basin (5-10 km deep) e.g.