Subsidence in the gulf of suez: implications for rifting and plate kinematics

Abstract

The Gulf of Suez is a Neogene rift which has evolved as one arm of the Sinai triple junction together with the Gulf of Aqaba and the Red Sea. Backstripping of well data in the central and southern Gulf of Suez shows three distinct phases of tectonic subsidence. During the initial stage of opening of the rift, the rate of subsidence was very low. In the late Burdigalian (Rudeis fm.) there is a rapid increase in subsidence. By the Middle Miocene, the subsidence had slowed again. Extending the backstripping to a two-dimensional cross-section of the Gulf of Suez allows better quantitative estimates of extension. Correcting for the large regional uplift (~ 1100 m on the Egyptian side) is critical for obtaining accurate values for the extension. Uplift of the rift decreases the net tectonic subsidence by over one fourth, relative to that predicted by uniform extension. The total extension at the latitude of Gebel Zeit (28° N) is ~ 30 km, which corresponds to 32–36 km at the triple junction. Approximately 13 to12 of the extension occurred during the rapid subsidence of the second opening phase. Slower extension continued for the rest of the Miocene and throughout the Plio-Pleistocene. Stress directions calculated from microstructures exhibit several directional phases to the opening of the Gulf of Suez. These data, together with constraints from the other arms of the Sinai triple junction, can be combined into a scenario for the kinematic evolution of the region. At first, the Gulf of Suez is the northward continuation of the Red Sea, and both open at ≈ N30°. The first subsidence phase in the Gulf of Suez represents an initial startup of the rifting with very low amounts of extension. This geometry continued through the main phase of Suez extension. Subsequently, the Gulf of Aqaba formed as a strike-slip boundary. As the Arabia-Africa motion transferred to the Gulf of Aqaba, the direction of extension in the Gulf of Suez rotated clockwise towards perpendicular extension and slowed. The post-Miocene shift to oblique opening in the Gulf of Aqaba and the Dead Sea transform is the result of a minor change in the pole of opening. This change is below the current resolution of the data for the Gulf of Suez, which is probably opening at < 1 mm/yr.