CRETACEOUS SEDIMENTARY-ROCKS ON THE MASIRAH OPHIOLITE (SULTANATE OF OMAN) - EVIDENCE FOR AN UNUSUAL BATHYMETRIC HISTORY

Autochthonous sedimentary rocks on the Masirah Ophiolite preserve a re cord of vertical movements of their oceanic basement. The Masirah Ophi olite was formed in the uppermost Jurassic and subsequently underwent thermal subsidence for about 20 Ma as documented by pelagic sediments. Submarine alkali-basaltic volcanism in the lower Barremian marks the onset of rapid basement uplift to or above sea-level. Carbonate platfo rms grew in Barremian/mid-Aptian time on highs of oceanic basement. Th e uplift is interpreted as the result of transpressive tectonism along a large oceanic fracture zone. The platforms submerged in the mid-Apt ian and reached the CCD in the Albian. Ribbon cherts were deposited du ring the Albian to Santonian time. The first influx of siliciclastic d etritus, shed from the Arabian craton, is recorded in Coniacian sandst ones. Ophiolitic conglomerates interfinger in the Campanian to mid-Maa strichtian with continent-derived sandstones, reflecting regional comp ressive tectonism. Crystalline exotics, deposited in the late Maastric htian, are derived most likely from the Precambrian basement of Arabia , whilst the origin of the sedimentary exotics, dated Triassic to Cret aceous, remains unclear. The Masirah Ophiolite was overthrust at the C retaceous-Tertiary boundary by an upper ophiolite nappe and emplaced o nto the margin of southeast Oman.