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The southern margin of the Musandam Mountains (UAE and northern Oman) preserves a Late Permian to Late Cretaceous Neo-Tethyan platform margin sequence that provides important insights into the switch from deposition in shallow shelf to deeper-water margin slope environments. New biostratigraphic dating resolves ambiguities in previous works and better constrains the timing of the stages in the development of the south Musandam platform margin and their link to the wider Oman tectonic framework. The accumulation of Late Permian to Late Triassic mainly dolomitised shelf carbonates along this sector of the nascent Neo-Tethyan margin was ended by a phase of margin-edge collapse linked to the onset of a major phase of Neo-Tethyan rifting and extension, and deposition of a fore-reef talus assemblage. This is newly dated as also being Late Triassic (Norian-Rhaetian) and termed the Kharas Formation. Following non-deposition, or possible erosion of Early Jurassic deposits, differential subsidence in the Middle Jurassic led to deposition of on-lapping deeper-shelf/slope facies peri-platform lime mudstones, fine grained turbidites and minor, channelised coarser-grained graded conglomerates and packstones (Sumeini Group) along the southern side of the Musandam platform. In the west, oolitic peloidal packstone and grainstone shoals were deposited, here termed the Jarief Formation. Their Bathonian-Callovian age is coeval with the regional development of oolitic facies on the carbonate platform, linked to a mid-Jurassic sea-level highstand, and their redeposition into the adjacent Hawasina Basin as turbidites of the Guwayza Formation of the Hamrat Duru Group. Uplift and destabilisation of the margin of the carbonate platform throughout Oman in the Late Jurassic during a mild compressional regime cut off the coarser sediment supply to the Jarief Formation, which was superseded by deposition of Sumeini Group slope-facies lime mudstones with numerous intraformational truncation surfaces. Slope facies sedimentation then persisted along the length of the southern edge of the Musandam platform as the margin relaxed and subsided until the end of the Early Cretaceous. Uplift of the margin edge, related to changing regional compressive stresses as seafloor spreading increased in the South Atlantic and intra-oceanic subduction in Neo-Tethys initiated creation of the Semail Ophiolite, led first to collapse along the shelf edge, generating the thick and highly channelised post Aptian Ausaq Formation mega-breccias. This marked the end of the passive margin as a thick, Late Cretaceous predominantly shale and chert succession was deposited as the margin subsided with continent-ward migration of the foredeep that developed ahead of final emplacement of the Neo-Tethyan Hawasina Nappes and Semail Ophiolite during the Santonian. |
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