Late Cretaceous and early Tertiary evolution of Jebel Ja’alan and adjacent areas, NE Oman

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Abstract
Jebel Ja’alan forms the northernmost extremity of the NNE-SSW trending Huqf-Haushi Uplift, a structural high which runs parallel to the SE continental margin of Oman. On Jebel Ja’alan Precambrian rocks, exposed in the core of this structural high, are overlain by a cover sequence of shallow water carbonate and clastic sediments of Maastrichtian to Eocene age. These cover sediments, and the structures which affect them, record a sequence of tectonic events leading to the uplift and inversion of Jebel Ja’alan in post middle Eocene times. In the Maastrichtian an extensional regime resulted in subsidence and the accumulation of fluvial clastic deposits, the Qahlah Formation, overlain by shallow marine limestones, the Simsima Formation, of Maastrichtian age. A post-Maastrichtian normal fault, the East Ja’alan Fault, downthrows Simsima Formation to the east against Precambrian basement to the west and controls the deposition of the Palaeocene/early Eocene Hasad Beds, which form debris fans distributed along the fault plane. The East Ja’alan Fault may have been linked to early extensional movement on the WNW-ESE trending North Ja’alan Fault which partly controlled deposition of the Eocene fluvial/marginal marine Rusayl Formation. A mid-Eocene transgression resulted in the deposition of the Seeb Formation shallow water limestones. All these sediments were deformed by a post middle Eocene compressional event which resulted in the formation of north-south trending asymmetric anticlines, forming a pop-up structure; the latter was controlled by a shallow level detachment dipping east which led to the detachment and removal of the Maastrichtian-Eocene sediments from Jebel Ja’alan. An associated deeper level basement ramp resulted in uplift and inversion of the Precambrian basement of Jebel Ja’alan. These compressional structures are displaced by later left-lateral strike-slip on the North Ja’alan Fault Zone.