Sequence architecture of a Jurassic ramp succession from Gebel Maghara (North Sinai, Egypt): Implications for eustasy

The Jurassic succession at Gebel Maghara, North Sinai, Egypt, represents a mixed carbonate-siliciclastic sequence. Combining information from both fossils and rocks allowed a plausible reconstruction of the depositional environments and of the basin evolution. The Jurassic succession of Gebel Maghara was deposited on a ramp, and the architecture of the ramp facies was strongly controlled not only by sea-level changes but also by extensional tectonics in connection with rifting of the Tethys, North Gondwana. Seven tectonically modified third-order sequences (DS 1-DS 7) have been recognized. The first three sequences (DS 1-DS 3), ranging from the Toarcian to the Bajocian, record sea invasion (intertidal to shallow subtidal conditions) across an intracratonic area as a result of eustatic sea-level changes during a quiescent rift stage. The remaining sequences (DS 4-DS 7) reflect open marine mid to outer ramp settings. Non-marine conditions around the Bajocian-Bathonian boundary, documented by caliche, represent the maximum regression of the sea. During an active extensional stage, horsts, which formerly acted as barriers separating the Maghara sub-basin from the main ocean, subsided. Subsequent rejuvenation and reactivation of faults shifted the homoclinal physiography of the ramp to a distally steepened ramp during the early Bathonian, creating a 200-m-thick deltaic wedge. Similar processes during the early Kimmeridgian created a calcirudite-calcarenite succession of slope origin. The diversity and the epifaunal/infaunal percentage of the macrofauna display a cyclic pattern which coincides more or less with the sequence stratigraphic architecture.