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DEAD SEA RIFT |
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The Dead Sea, a unique geologic phenomenon is part of the Syrian-African Rift. The Dead Sea is the terminal lake of River Jordan System and known for being the lowest point (lake) in the world (-413 m; at present). The Dead Sea is a large strike ship basin (110km long and 16km wide) located within the Dead Sea transform between distinct higher in elevation. The Dead Sea comprises 2 basins; the northern basin is the deepest (-713 B.S.L) whereas the southern basin is very shallow. The Dead Sea Rift is part of the Syrian-African Rift extending from Turkey in the north to the eastern African rift in the south (Attalah, 1991). The extensive tectonic activity of the Dead Sea Rift in the southern Wadi Araba, since early Miocene (27 Ma years ago), resulted in a very clear landscape expressions; a rift valley bounded by distinct high mountains (Bassonetal, 1999). The Dead Sea occupies the lowest part of the Rift Valley (Horowitz, 1979) and located within the Dead Sea Transform. The Dead Sea Transform is a plate boundary separating the Arabian plate from the African plate and connects the divergent plate boundary in the Red Sea to the convergent plate boundary in the Red Sea to the convergent plate boundary in the Taurus mountains in southern Turkey (Larsen, et al., 1999). The bed rocks on either side of the Dead Sea Rift were connected prior to rifting. As aresult of rifting, the bed rocks on either side of the Dead Sea Rift were exposed; the eastern side the rift was uplifted more therefore the older rocks were exposed near the eastern shore. The eastern part of the rift is characterized by the present of intensive faults, volcanics and thermal springs. Origin of the Dead Sea Rift Barjous el al., (1990) stated that many hypotheses have been put forward to explain the Cenozoic structural development along the Dead Sea Rift. It has been described as a rift defined by 2 sets of normal faults (Blankenhorn, 1896; Picard, 1965 and Bender , 1974). According to Attallah, M. (1991) there are 2 theories explaining the origin of the Dead Sea. 1. The Graben Theory (Vertical Movement) The Dead Sea is a graben formed by vertical movement along parallel faults extending N-s and along flexture; each fault caused a small down thrown to the center of the graben forming step faulting (Fig.1). As a result of this movement the central part of the graben was lowered relative to its shoulders forming the Dead Sea, the Jordan valley and Wadi Araba. The formation of the Dead Sea basin is due to another type of faulting called transverse faults (Fig.2). 2. The Horizontal Movement Theory The Dead Sea Rift was formed mainly as a result of horizontal displacement a long normal faults. One of the models proposed by Quennell (1956) to explain the formation of the Dead Sea is shown in Fig. 3. In this model, 2 faults with horizontal left lateral displacement, overlapped in the present Dead Sea area. The northword horizontal movement of the Arabian plate relative to the Sinai plate resulted in a rhombus shaped structures in the area of overlap between the two faults forming the Dead Sea. Two phases of Neogene movement have been suggested (e.g Quennell, 1956; Freund et al., 1970). Geophysical studies also suggest 2 active periods in the Neogene 27-15 Ma, and a later one form 5 Ma-Present. The interval between these 2 periods is considered to have been a passive phase (Girdler et al., 1987). K-Ar ages for Neogene basalts in Jordan and Palestine indicate rate of movement to be 0.4 cm/yr for the second phase 5 Ma- present (Steinitz et al., 1978 and Barberi et al., 1980). Hatcher et al., (1981) and Kovach et al., (1986) interpreted aeromagnetic signature on either side of the transform as representing a sinistal movement of 107 km in the basement structures (Fig. 4). Phoenix Corp. (1980) have also effectively demonstrated about 110 km of offset in the aeromagnetic signatures. Sedimentation Indigenous sediments have been accumulated within the graben since early Miocene (Tchernov et al., 1987) and perhaps even since Oligocene when the trough began to subside tectonically (Neev and Emery, 1995). The Jordan valley has been occupied by successive lakes (Fig. 5) of various size and different salinities, since Pliocene, in which lacustrine sediments accumulated (Moumani, K., 1996). The most important lakes are: Lake Sedom Lake Sedom Formation, a late Miocene-Pliocene (7-3 Ma), is predominantly rock salt unit and comprises 1500-2000 m of the 2500m thick sedimentary sequence of Mount sedom (Zak, 1967). Lake Samra Lake Samra (350-63 Ka) is a fluvio-limnic lake extending 190 km. The sediments of this lake are 25-35m thick. Lake Lisan The Lake Lisan is extending 225km from the present-day Lake Tiberias (in the north) to 35km south of the Dead Sea (in the south). The sediments of Lake Lisan (60-18ka) are 40 m thick and consist of laminated lacustrine evaporites with various amounts of mudstone and sandstone. The Dead Sea The present-day shape of the Dead sea was formed, 12 ka ago, as a result of intensive evaporation and continuous subsidence of the Lake Lisan, which transformed into separted lakes, Tiberias, Beisan and Dead Sea (attallah, M., 1991). Dead Sea Levels According to Amos Frumkin (1997) 10 stages of the Dead Sea levels were recorded as follows:-
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