Structure and sequence of thrusting in deep-water sediments during ophiolite emplacement in the south-central Oman Mountains

Abstract

Sedimentological and stratigraphical investigations of the deep-water passive margin sediments of the Oman Neo-Tethys (the ‘Hawasina Ocean’), when allied with structural relationships between duplexes of these units emplaced on to the Oman margin during late Cretaceous ophiolite obduction, allow the reconstruction of sediment distribution in the Hawasina Ocean. From this starting point, and the observed stacking order of duplexes, the sequence of thrusting of the oceanic sediments can be deduced. Imbrication proceeded through foreland-propagating thrusts, whilst the assembled thrust stack was modified at a late stage of emplacement by out-of-sequence thrusting related to sequential locking of thrust planes towards the hinterland, and gravity sliding off the flanks of a major anticline that developed in the underlying autochthonous shelf and basement. Two main factors governed duplex and imbricate fan formation and distribution. Firstly, two contrasting sedimentary basins were present along the central Oman margin, the ‘Duru basin’ distal to the ‘Al Ayn basin’. Secondly, competent sedimentary successions were bulldozed ahead of the Semail Ophiolite, whilst less competent shale and chert units were overridden by the ophiolite or imbricated along its leading edge.