Phosphorite grains were authigenically precipitated within precursor marl and biosiliceous deposits during high water level and intense upwelling within the Tethys Ocean to the north of Jordan. With falling sea level, the oyster Lopha villei colonized bathymetric highs in the shallow shelfal environments in east-central Jordan during the uppermost Campanian-Lower Maastrichtian (Late Cretaceous). The oyster bioherms in the epeiric southern shelf of the Tethys formed small basins several hundreds of meters across and about 40-50 m deep. Under these lowstand conditions, oyster shells were shed off the bioherms and deposited as large cross-bedded units on the flanks of the basins. At the same time, precursor phosphatic sediments were reworked and winnowed to form high-grade phosphorite sand. More than 250 million metric tons (250X10 9 kilograms) of phosphorite sand were deposited basinward of the oyster beds. As sea level continued to fall, the oyster bioherms formed partially silled basins with low biological diversity in which marl and/or bituminous marl was deposited. The marls are overlain by the transgressive phosphatic marl and chalk of the Muwaggar Formation, which were deposited under open marine conditions.