An important feature of the middle Cretaceous Arabian continental margin was the regional upwarping in the foreland of the northern Oman Mountains. We interpret this upwarp as an early expression of a cratonward-migrating peripheral swell associated with the emplacement of the Semail Ophiolite onto the margin. Subsurface stratigraphic data indicate that the swell was expressed during the Cenomanian and attained its maximum relief during the Turonian. By the Santonian, further downflexure of the margin took place around an axis west of the study area, burying the then-inactive Turonian swell beneath the deposits of the westward-expanding foreland basin. We suggest that establishment of the later, more cratonward flexural regime took place abruptly rather than as a continuo sly migrating wave.

The middle Cretaceous swell axis paralleled the present-day axis of the Oman Mountains. The upwarp was slightly asymmetric to the east, and loosely constrained estimates of its width and height are 150 km and 244 (93 mi and 800 ft), respectively. The dimensions suggest an anomalously low flexural rigidity (10²² N m) for the middle Cretaceous continental lithosphere. We attribute this low apparent rigidity to the combined effects of remnant thermal and mechanical processes of an earlier rifting event and compression of the margin during the Cretaceous emplacement of the Semail Ophiolite.

The small dimensions of the middle Cretaceous swell suggest that other continental margins with similar geologic histories may also have narrow extinct swells buried beneath foreland deposits. Such swells may have significant impact on the entrapment of hydrocarbons, as we propose for the Sajaa-Margham trend.