The stratigraphy and macrofauna of the Qahlah and Simsima Formations is described for 14 sections along the western margins of the North Oman Mountains between Al Ain and Al Dhaid. These are dated as latest Campanian to Maastrichtian in age. Deposition over a deeply weathered surface of ultrabasic rocks commenced with nearshore conglomerates, grits and cross-bedded sands which, in places, have an in situ bivalve fauna. Clastic input was abruptly terminated by a sea-level rise and repalced by ...