Tectono-stratigraphic development of the Qamar basin, eastern Yemen

Abstract

The Qamar Basin is a polyphase rift basin located in eastern Yemen, adjacent to the Indian Ocean. It probably originated as part of an extensive rift system which developed during the Late Jurassic to Early Cretaceous and led to the break-up of Gondwanaland. Rift reactivation during the mid Cretaceous affected limited areas including the Qamar Basin. A third episode of rifting occurred during the Oligo-Miocene prior to sea floor spreading in the Gulf of Aden. Since spreading in the Gulf began in the Middle Miocene, the offshore Qamar Basin has been thermally subsiding. In contrast, the onshore part of the basin has been elevated by over 1 km. The nature of the pre mid-Cretaceous basin fill is unknown. During Santonian to Early Campanian times thick fluvio-deltaic clastics accumulated in a rapidly subsiding depocentre. Marked deepening during the Early Campanian led to deposition of deep water limestones. During the Late Campanian prograding deep marine clastics infilled the basin. Minor transgression during the Maastrichtian caused a resumption of marine carbonate deposition. Sedimentation was interrupted during the Early Palaeocene, following which shallow marine carbonates were deposited over a large area of the Arabian Peninsula. After a hiatus spanning the Late Eocene to Late Oligocene, carbonate sedimentation resumed offshore in an active rift basin. Deep water carbonates and carbonate turbidites accumulated in lows whilst reefs developed on footwall highs. From the late Miocene onwards the reefs have been gradually drowned by rapidly accumulating clastics. Onshore the Tertiary rift episode was associated with major uplift and only a thin veneer of recent wadi deposits overlies the rift topography. The superposition of Jurassic, Cretaceous and Tertiary rifts, which has not been described elsewhere in the region, is tentatively related to the evolution of the Indian Ocean.