Facies variation, depositional setting and hydrocarbon potential of the Upper Cretaceous rocks in the United Arab Emirates

Abstract

The Upper Cretaceous (Aruma Group) of the United Arab Emirates (UAE) was deposited over nearly 23 Ma. This was after a period of major erosional emergence in the Turonian. The variable thicknesses and lithofacies of the sediments of this group were controlled by regional subsidence induced by plate collision and partial subduction, eustatic sea-level fluctuations and differential sedimentation rates. The Upper Cretaceous in the southern UAE (Abu Dhabi region) consists of two major transgressive-regressive cycles involving the sediments of four formations, the Laffan, Halul, Fiqa and Simsima. In the central UAE (Dubai region) the group consists of the Laffan, Ilam, and Fiqa Formations, while in the northern UAE it consists of the Muti, Juweiza, Qahlah and Simsima Formations. The earliest Late Cretaceous sedimentation accompanied a marine transgression that probably began in the late Turonian, with the sea spreading to cover most of the UAE by Coniacian times. This marine event was marked by the deposition of basinal muds (not shales) and neritic marls. Later, during Santonian, neritic shelf carbonates were deposited. Subsequent subsidence in the early Campanian resulted in the accumulation of deep-water marls, argillaceous limestones and muds (shales). During the Maastrichtian, a widespread regression occurred, and neritic shelf bioclastic limestones and dolomites containing rudists and orbitoids were deposited on the shelf margin. Toward the centre of the basin, in the northern UAE, thicker, basinal, slope and shelf edge sediments were deposited resulting in a succession that consists mostly of marls, argillaceous limestones, cherts, conglomerates, sandstones and shales. Commercial hydrocarbons in the Upper Cretaceous are confined to the Simsima and Ilam Formations, which are the best potential exploration targets, particularly in the offshore of the northeastern Emirates in a belt parallel to the Oman Mountains. The basal part of the Upper Cretaceous is a major seal over middle Cretaceous reservoirs of the UAE.