Sedimentological model, architecture, and evolution of a shallow-water Gilbert-type delta from the Lower Miocene, Red Sea Rift, Egypt

摘要

The lower Miocene Ranga Formation in the Wadi Gasus area (SE Egypt) represents deposits of turbidite-dominated Gilbert-type delta that prograded in a shallow shelf setting on the western margin of the Miocene Red Sea Rift Basin. Typical exposures are cliffs which enable investigation of vertical and lateral relationships among five facies associations (FA): delta topset, delta foreset, delta toeset-bottomset, prodelta, and shelf. The present study reports the first publicly available detailed sedimentological analysis and architecture of the Gilbert-type deltas in the Red Sea rift. The Ranga Formation is subdivided into the Aquitanian and Burdigalian syn-rift sequences. During rift climax of Aquitanian and Burdigalian sequences, tectonically influenced accommodation controlled the formation of shelf and prodelta systems. The rift sagging of these sequences were characterized by deposition of evaporite and Gasus Gilbert-type delta, respectively. The Gasus Gilbert-type delta represents deposition during the highstand systems tract of the Burdigalian sequence, being subdivided into four progradational deltaic parasequences that change from NNE to ENE progradation. The progradational pattern of the Gasus Gilbert-type delta was most likely driven by autocyclic switching of deltaic lobes, overprinted by allogenic controls. The Gasus delta represents an excellent surface analogue for Gilbert-type delta reservoirs due to high net-to-gross and wide lateral extent. The stratigraphic architecture and development of fluvial channels at the overfilling stage of the Gasus delta establishes their role as a conduit for coarse clastics to the deepwater blocks, which are main targets for future hydrocarbon exploration in the frontier Egyptian Red Sea Basin.