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

Abstract

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 thirdorder 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.