A longitudinal carbonate fan from the Jurassic of the Oman Mountains: the Guweyza limestone formation of the Hamrat ad Duru

Abstract

When sedimentological, stratigraphical and structural data are considered, the continental rise sediments of Oman Neo-Tethys (the Hamrat Duru Group) can be restored to their original basin configuration, prior to their southwest-directed emplacement with the Semail ophiolite onto the Oman continental margin during the Late Cretaceous. The Hamrat Duru Group sediments are preserved in well-exposed imbricate fans, the largest of which forms the Hamrat ad Duru range in the south-central Oman Mountains. In the south-central Hamrat ad Duru, middle and upper Jurassic ooid-rich carbonate sediment was transported from the adjacent Oman carbonate platform during periods of tectonic instability into the Oman Neo-Tethys (Hawasina basin) by high- and low-density turbidity currents to form sediment sheets with a margin-parallel axis of deposition. Palaeocurrents are northwest-directed (parallel to the Oman margin) along the southwest of the Hamrat ad Duru and northeast-directed (away from the margin) in structurally higher, more distal imbricates of the northeastern Hamrat ad Duru. This implies sediment input at the southern end of the Hamrat ad Duru. These trends are reflected in the distribution of sedimentary facies, with most proximal facies developed in the southern Hamrat ad Duru, passing into progressively more distal facies to the northwest and northeast. Sediment thinning and fining is more accentuated away from the margin towards the northeast and sedimentation was concentrated parallel to the Oman margin. The Hamrat ad Duru represents a longitudinal fan that was at least 120 km long and extended at least 60 km away from the margin.