Geological and Tectonic Influences
Beginning in the Cretaceous Period (136-65 my) an area that encompassed the present plateau was both inundated by the ancient Tethys Ocean and undergoing lateral (strike-slip) displacement (Sneh, 1996). During the 60-80 my that followed, the bedrock profile that we see today evolved as several episodes of oceanic transgression and recession were depositing multiple layers of limestone. Today this limestone can be seen both on top and throughout the stratigraphic record exposed along the steep slopes of the major wadis.
During the Miocene (26-7 my), as the ocean waters receded for the last time (cf. Guiraud and Bosworth, 1999), tectonic activity began exerting a different force on the region. No longer moving laterally, the Sinai microplate and Arabian plate began to move towards each other. Today, we see this plate boundary (Garfunkel, et al.) along the western edge of the plateau in the Great Rift Valley that extends nearly 6,000 km from Turkey to East Africa.
The role of faults and fractures along plate boundaries as a major force in the development and location of river and stream channels has been identified in several studies (Potter, 1978; Cox, 1989; Burbank, et. al., 1996; and Miller, et. al., 1996). As a fundamental mechanism in bedrock weathering, fractures create conduits for surface and groundwater flow (Miller and Dunne, 1996; also cf. Oberlander, 1965; Aghassy, 1970; and Koons, 1994). The drainage network we see today, suggests that these processes began to work very early in the plateau’s tectonically active phase (cf. Ginat, et al., 1998; and Horowitz, 1987).
Wadi al-Karak and the associated Karak-Fayha
In response to the compression, which was taking place along the boundary between the plates, the plateau block began to be displaced vertically. This vertical displacement triggered the development of transverse faults at several points along the rift valley.
Though taking place approximately 20 million years BP, the scars of the faulting and fracturing are still clearly seen. In the following Landsat 7 image of Wadi al-Karak, the associated Karak-Fayha Fault (300 km in length) is easily recognized.
Though taking place approximately 20 million years BP, the scars of the faulting and fracturing are still clearly seen. In the following Landsat 7 image of Wadi al-Karak, the associated Karak-Fayha Fault (300 km in length) is easily recognized.
Wadi al-Mujib and the associated fault
In this image we see Wadi al-Mujib and the fractures and faults associated with it.
As streams began to develop along the course of the structurally unstable fault lines, fluvial erosion eventually incised the plateau surface, ushering in the early stages of the channel forming processes that would result in the formation of the canyons we see today. However, though geological and tectonic processes were the major forces defining the course of the plateau’s drainage network, the role of climate must not be overlooked for its contribution to the success of these processes.