Middle–Late Jurassic sedimentation and sea-level changes on the northeast African margin: A case study in the Khashm El-Galala area, NE Egypt

Abstract

The northeast African margin looks like a natural laboratory for studying mid-Jurassic sedimentation and sea-level changes on the southern periphery of the Tethyan oceans. A new, detailed investigation of two representative sections of the Bajocian–Oxfordian (Middle–Late Jurassic) strata has been undertaken in the Khashm El-Galala area in the Gulf of Suez region of Egypt. Facies and sequence stratigraphic architecture have been examined. 12 microfacies have been identified and grouped into 4 facies associations. The latter permit to establish fluvial, peritidal flat, restricted lagoonal/subtidal, and barrier shoal depositional environments. The fluvial, chiefly siliciclastic sedimentation took place in the Bajocian, and the marine, chiefly carbonate sedimentation took place in the Bathonian–Oxfordian. The stacking patterns of the recognized facies associations permit to classify the Bajocian–Oxfordian stratigraphical succession into the Bajocian lowstand systems tract, the Bathonian–early Callovian transgressive systems tract, and the late Callovian–Oxfordian highstand systems tract. This helps us to reconstruct the relative sea-level changes throughout the Bajocian–Oxfordian, in which the Bajocian lowstand was followed by the transgression that peaked in the early Callovian. Then, the sea level stabilized and started to fall gradually. This cycle corresponds well to the global long-term eustatic changes. If so, the eustatic control on the regional shoreline shifts was more important than the factors of local tectonic activity and sediment supply. Generally, the results of this study prove the importance of the northeast African margin for further justification of the Jurassic eustatic curve.