Origin and correlation of disconformity surfaces and marker beds, Nahr Umr Formation, northern Oman

During Aptian to Albian times a major influx of terrigenous material from the emerged Arabian Shield led to the deposition of the Nahr Umr Formation within the intracratonic Bab Basin. This argillaceous facies interfingers in northern Oman with sediments shed from reefal complexes. We studied a 100 km transect across the zone of facies intercalation extending from the margin of the NeoTethys (northern Jabal Akhdar) into the fringes of the Bab Basin in northern Oman (Foothills). The age of formation boundaries and key beds and surfaces in a reference section (Wadi Bani Kharus; I) was dated by use of the graphic correlation method. Graphic correlation indicates that the Nahr Umr Formation is of uppermost Aptian to Upper Albian age. Two types of stratigraphic markers were recognized: limestone marker beds, successions, and disconformity surfaces. Calcareous marker beds are probably related to increased carbonate production during sea -Ievel lowstands. lnvestigations of the geochemistry (stable isotopes, fluid inclusions) and sediment petrography of limestones beneath disconformities revealed that they are of combined submarine and subaerial origin. Evidence for a subaerial exposure stage is recognized along the basin margin (northern and southern Jabal Akhdar) but is found less frequently in the basinward settings of the Foothills. Marker-bed successions and disconformity surfaces are correlated throughout the sections and indicate coeval deposition of the Nahr Umr Formation in northern Oman.