The Eastern Mountains. The Cretaceous sea - 70 million years ago

In the Hajar Mountains the uplift, caused by colliding continents during the Cretaceous, produced a chain of islands formed of ophiolite (the Semail ophiolite), now an unfossiliferous, reddish-black rock exposed on some jebels in the eastern mountains and especially well-exposed in Wadi Ham, Emirate of Fujairah. A broad shallow and warm sea lapped against the Hajar islands and its limestones are now called the Simsima Formation. Knowledge of the palaeontology and stratigraphy of these carbonate sediments is of particular interest to ADCO, for they comprise the primary oil-bearing rocks in the Shah field, south of Liwa. The best exposures of the Simsima Formation are found at Jebel Huwayyah - known as Fossil Valley, Jebel Rawdah, Jebel Buhays and Qarn Murrah.

Around the ophiolite islands, coarse beach conglomerates and beach sands were deposited. In exposed environments with high wave activity, the pounding of the waves eroded the beach rocks to form large beds of boulders which had little in the way of marine life. In more protected bays, reefs and thickets of corals and rudist bivalves lived close to the shore while sandy bays had their own fauna of burrowing bivalves and marine snails.